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AWD COMPONENT ANALYSIS Project Report, May 31, 2016

Gunter Niederbacher Pilot Systems International

Contract T8080-150132

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Contents

1 Abstract.................................................................................................................................... 6

2 Executive Summary ................................................................................................................. 7

3 Introduction ........................................................................................................................... 10

3.1 Background ..................................................................................................................... 10

3.2 Purpose........................................................................................................................... 11

3.3 Data Sources ................................................................................................................... 11

1 AWD/4WD Systems and Components .................................................................................. 12

1.1 AWD Systems Classification ........................................................................................... 12

1.1.1 Definitions ............................................................................................................... 12

1.1.2 AWD Component Nomenclature ............................................................................ 15

1.1.3 AWD Systems Classification .................................................................................... 15

1.2 Current and Future AWD Systems ................................................................................. 17

1.2.1 System Architecture ................................................................................................ 17

1.2.2 Components / Function .......................................................................................... 22

1.2.3 System Function & Operating Modes ..................................................................... 37

1.3 Comparative Assessment of Positives and Negatives .................................................... 40

1.3.1 Vehicle Architecture ............................................................................................... 40

1.3.2 Disconnect Systems ................................................................................................ 40

1.3.3 Secondary Driveline Torque Limitation & Duty Cycle Management ...................... 41

1.3.4 Full Time vs. On-Demand Systems .......................................................................... 41

1.3.5 Rear Axle Architecture ............................................................................................ 42

2 AWD Vehicles by Make & Model ........................................................................................... 43

2.1 The North American AWD Vehicle Market - Overview .................................................. 43

2.1.1 Fuel Consumption and Vehicle Mass Data ............................................................. 43

2.2 AWD Vehicles by Make & Model ................................................................................... 47

2.2.1 Audi ......................................................................................................................... 48

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2.2.2 BMW ....................................................................................................................... 52

2.2.3 Daimler Benz ........................................................................................................... 58

2.2.4 Fiat Chrysler (FCA) ................................................................................................... 64

2.2.5 Ford ......................................................................................................................... 74

2.2.6 General Motors (GM) .............................................................................................. 76

2.2.7 Honda ...................................................................................................................... 80

2.2.8 Hyundai (Kia) ........................................................................................................... 82

2.2.9 Jaguar Land Rover (JLR - Tata) ................................................................................ 85

2.2.10 Mazda ...................................................................................................................... 88

2.2.11 Mitsubishi ................................................................................................................ 89

2.2.12 Nissan (Infiniti) ........................................................................................................ 92

2.2.13 Subaru ..................................................................................................................... 94

2.2.14 Tesla ........................................................................................................................ 97

2.2.15 Toyota .................................................................................................................... 98

2.2.16 Volkswagen ........................................................................................................ 101

2.2.17 Volvo ................................................................................................................... 103

3 AWD Efficiency Improvement Potentials ............................................................................ 106

3.1 Definitions .................................................................................................................... 106

3.2 System Level ................................................................................................................. 106

3.2.1 Architecture .......................................................................................................... 106

3.2.2 Disconnect System ................................................................................................ 107

3.2.3 Downsizing ............................................................................................................ 107

3.2.4 Electric Rear Axle Drive (eRAD) ............................................................................. 108

3.3 Component Level ......................................................................................................... 109

3.3.1 Fuel Efficient (FE) Bearings ................................................................................... 109

3.3.2 Low Drag Seals ...................................................................................................... 111

3.3.3 Lubrication Strategies ........................................................................................... 111

3.3.4 Advanced CV Joints ............................................................................................... 113

3.3.5 Dry Clutch Systems ............................................................................................... 113

3.4 Design ........................................................................................................................... 113

3.4.1 Hypoid Offset Optimization .................................................................................. 113

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3.4.2 Non Serviceable Components ............................................................................... 114

3.4.3 Bearing Preload Optimization ............................................................................... 114

3.4.4 Single Shaft Power Transfer Units ........................................................................ 115

3.4.5 Propshaft Gear Ratio ............................................................................................. 115

3.5 Materials ...................................................................................................................... 116

3.5.1 Magnesium Housings ............................................................................................ 116

3.5.2 High Efficiency Lubricants ..................................................................................... 117

3.6 Manufacturing Process ................................................................................................ 117

3.6.1 Vacuum Die Casting .............................................................................................. 117

3.6.2 Hypoid Manufacturing .......................................................................................... 118

3.7 Advanced Engineering / Development Process ........................................................... 119

3.7.1 AWD Duty Cycle Management ............................................................................. 119

3.7.2 Performance Adaptation to Vehicle Variants ....................................................... 119

3.8 Advanced Operating and Control Strategies................................................................ 119

3.8.1 Disconnect strategies ............................................................................................ 119

3.9 Summary of Efficiency Improvement Potentials ......................................................... 120

4 Trend Analysis ...................................................................................................................... 122

4.1 The Baseline ................................................................................................................. 122

4.1.1 Global Vehicle Production .................................................................................... 122

4.1.2 Fuel Consumption ................................................................................................. 123

4.2 Technical Trend Analysis in AWD Research and Development ................................... 126

1.1.1 Technical Trend Analysis in AWD Research and Development ............................. 126

4.3 AWD Market Trend Analysis ........................................................................................ 127

5 AWD System Teardown Analysis ......................................................................................... 130

5.1 Ford Fusion ................................................................................................................... 133

5.1.1 AWD Technology ................................................................................................... 133

5.1.2 Power Transfer Unit .............................................................................................. 136

5.1.3 Propshaft, Axles .................................................................................................... 141

5.1.4 Rear Drive Module ................................................................................................ 142

5.1.5 Mass & Rotational inertia Analysis ....................................................................... 152

5.1.6 Design Analysis ...................................................................................................... 154

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5.2 Jeep Cherokee .............................................................................................................. 158

5.2.1 AWD Technology ................................................................................................... 158

5.2.2 Power Transfer Unit (PTU) .................................................................................... 161

5.2.3 Propshaft & Axles .................................................................................................. 167

5.2.4 Rear Drive Module (RDM) ..................................................................................... 168


5.2.6 Design Analysis ...................................................................................................... 181

5.3 Volkswagen Tiguan ....................................................................................................... 185

5.3.1 AWD Technology ................................................................................................... 185


5.3.3 Propshaft & Axles .................................................................................................. 191



5.3.6 Design Analysis ...................................................................................................... 203

6 Disconnect System Cost Analysis......................................................................................... 207

6.1 Jeep Cherokee .............................................................................................................. 208



6.2 Alternative Disconnect Systems ................................................................................... 212

6.2.1 Side Shaft Disconnect ........................................................................................... 212

6.2.2 Front Axle Center Disconnect ............................................................................... 213

6.2.3 Others ................................................................................................................... 214

7 Summary and Conclusions .................................................................................................. 215

7.1 AWD/4WD Systems and Components ......................................................................... 215

7.1.1 Current and Future AWD Systems ........................................................................ 215

7.1.2 Component and System Function ......................................................................... 217

1.1.2 Comparative Assessment of Positives and Negatives ........................................... 219

7.2 AWD Vehicles by Make & Model ................................................................................. 221

7.2.1 The North American AWD Vehicle Market – Overview ........................................ 221

7.2.2 Fuel Consumption and Vehicle Mass Data ........................................................... 223

7.3 AWD Efficiency Improvement Potentials ..................................................................... 224

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7.3.1 System Level ......................................................................................................... 224

7.3.2 Component Level and Design ............................................................................... 225

7.3.3 Materials ............................................................................................................... 226

7.3.4 Manufacturing Process ......................................................................................... 226

7.3.5 Summary of Efficiency Improvement Potentials .................................................. 227

7.4 Trend Analysis .............................................................................................................. 228

7.4.1 Technical Trend Analysis in AWD Research and Development ............................ 228

7.4.2 AWD Market Trend Analysis ................................................................................. 228

7.5 AWD System Teardown Analysis.................................................................................. 230

7.5.1 Component Data Comparison .............................................................................. 231

7.5.2 Mass & Rotational Inertias.................................................................................... 233

7.6 AWD Disconnect System Cost Assessment .................................................................. 235

8 Appendix A: List of Tables and Figures ................................................................................ 236

9 Appendix B: Major North American AWD System Suppliers .............................................. 244

10 Appendix C: Vehicle Data .................................................................................................... 249

11 Appendix D: Equivalent Mass Definition ............................................................................. 250

11.1 Equivalent Mass ........................................................................................................... 250

11.2 Relative Effects of Rotational inertia on Vehicle Dynamics ......................................... 251

12 Appendix E: Evaluation of Rotational Inertia and Equivalent Mass .................................... 253

13 Appendix F: List of Terms and Acronyms ............................................................................ 255

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1 Abstract

All Wheel Drive (AWD) vehicles have become increasingly popular in North America.

Canada and the northern regions of the USA are seeing increasing demand for vehicles

with AWD.

This report addresses various aspects of AWD in conjunction with mass reduction and

fuel efficiency.

In the first section AWD systems and components currently on the market are

categorized. Vehicle architecture, design aspects and component function are

explained. Operating modes and AWD controls are explained and individual systems

advantages and disadvantages are discussed. Specific enablers for efficiency

improvements (e.g. AWD disconnect systems) are listed and their direct and indirect

effects are discussed.

The second section contains a list of vehicles currently on the market by make and

model broken down into vehicle platforms and AWD system architecture. Basic vehicle

data is given and design specifics on component level are discussed. Special emphasis is

put on added mass and fuel consumption for a selected list of vehicles.

In the third section AWD efficiency improvement potentials are discussed on a

qualitative level. The section is broken down into system, component and parts level

and includes design, materials and manufacturing process aspects.

A general trend analysis for AWD technology is included in the fourth section Market

data and historic trends are discussed.

Section five covers the teardown of three popular AWD vehicles: Ford Fusion, Jeep

Cherokee and Volkswagen Tiguan. Driveline components were completely

disassembled. Mass and rotational inertia data is listed for each individual part. A photo

documentation of the assemblies and major parts and a presentation of special design

features is included.

In section six a high level cost analysis for AWD disconnect systems is documented.

Section seven finalizes the report with a summary and the conclusions from the above

analyses.

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2 Executive Summary

Transport Canada (TC) contracted Pilot Systems International to perform a study

concerning the North American passenger car and light duty truck All Wheel Drive

(AWD) market at its current status and future trends.

In a first section current and future AWD systems are analyzed and AWD technology is

explained. The second section contains an overview of the AWD vehicles currently on

the market. An efficiency improvement potential analysis was performed in the third

section, followed by a general trend analysis in section four. Section five contains a

teardown analysis of the main AWD components of three selected vehicles. A high level

cost analysis of AWD disconnect systems was performed in section six. The study

concludes with a summary and conclusions in the seventh section.

AWD systems are classified in SAE Standard J1952 into

Part Time Systems

Full Time Systems

On-Demand Systems

In a part time system driver intervention is required to rigidly engage AWD. Part time

systems have been traditionally mechanical systems with no electronic controls. Driver

activated AWD systems with an electronically controlled clutch, as currently used in light

trucks, are considered on-demand systems.

Full time AWD systems feature a center differential to distribute torque between the

front and rear axle permanently with a preset torque bias. An active or passive locking

device may be added to improve the traction potential of the system. Full time systems

take advantage of sophisticated Brake Traction Control (BTC) systems. BTC offers a very

cost effective way of maintaining traction in adverse conditions by using the brake

system and specific control logics to keep wheel slip within dynamic limits.

On-demand systems are by far the most prevalent AWD systems on the market today.

The core of the system is a Torque Transfer Device (TTD), typically contained in a Rear

Drive Module (RDM). Most vehicles have active systems which electronically control

torque distribution between the front and rear axle.

With the addition of a mechanical driveline disconnect device part of an on-demand

AWD driveline can be brought to a complete standstill while the vehicle is in motion.

Driveline parts that are not rotating do not generate parasitic losses.

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AWD systems add mass to a vehicle and generate additional driveline losses with the

result of increased fuel consumption.

Figure A: Fuel Consumption Increase (L/100km) over Added Mass in AWD Vehicles – City and Highway Cycles (Red dots indicate vehicles with AWD disconnect systems)

Figure A shows the increase of fuel consumption over added mass for a selected list of

AWD vehicles. Data is based on fuel efficiency estimates published annually by the US

Environmental Protection Agency (EPA).

Several areas of potential improvement have been identified:

A highly integrated vehicle architecture allows AWD components to be as compact and

lightweight as possible. A single shaft Power Transfer Unit (PTU) can save up to 10kg in

component mass compared to a more complex two shaft unit.

AWD disconnect systems have the ability to lower fuel consumption between 2 and 7%

compared to a non-disconnect AWD system.

Downsizing the AWD drivelines is a very effective way of taking mass out of AWD

components. For passenger cars and small SUVs the axle torque level required to

provide sufficient traction in adverse conditions is relatively small and can be

transferred in a smaller package.

Magnesium has been used for a long time to reduce transfer case and axle housing

mass. The 30% mass reduction compared to aluminum can take as much as 8% out of

the total mass of an RDM.

Small improvements on driveline parts (e.g. bearings, seals etc.) and refined

manufacturing processes (e.g. ground hypoid gears) add up to considerable gains in

efficiency.

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On the high end, hybrid and electric systems can provide a breakthrough in overall

system efficiency. Vehicle pricing has so far proven prohibitive and widespread use of

this type of vehicles is dependent on cost reductions and changes in the economic

environment.

Three main technological trends have been identified:

Actively controlled Multi-Plate Clutches, (MPC)

Active Disconnect Systems, (ADS)

Electric Rear Axle Drives, (eRAD)

Controlled MPC in on-demand systems are the dominating technology in AWD

drivetrains. ADS are a more recent trend to reduce real world fuel consumption in AWD

vehicles. eRAD is the latest emerging technology to dramatically improve fuel economy.

Volvo was the most recent entry into the market with the XC90 Hybrid SUV.

The popularity of CUV/SUV in North America is driving an increase in the adaption of

AWD/4WD systems. About one third of all vehicles sold in North America in 2015 were

AWD. The AWD take rate varies dramatically between vehicle segments and equipment

levels. Sedans throughout the segments are the least likely to be sold with an AWD

system. In the SUV and pick-up segments AWD outnumber 2WD drivelines, with the

luxury vehicles having the highest take rate in their respective segments.

Regional differences in the USA are also very distinctive, with northern and rural states

having the largest percentage of AWD vehicles. This fact suggests similar Canadian

trends.

In a teardown analysis, three PTUs and

RDMs were disassembled and analyzed

with respect to mass, rotational inertias

and design features. Figure B shows the

contribution of individual AWD driveline

components to the added mass.

Rotational inertias add very little

equivalent mass and have therefore been

found negligible with respect to fuel

consumption. Figure B: AWD Component Mass Comparison

A high level cost analysis of AWD disconnect devices shows the system incremental

price to be in the range of $90 – $100 US, including the mechanical disconnect device

and modifications necessary to the TTD. Jeep Cherokee is an exception since the system

was designed to accommodate a planetary low gear, which adds mass and cost not

related to AWD disconnect.

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3 Introduction1

Transport Canada’s (TC) ecoTECHNOLOGY for Vehicles Program (eTV)

Transport Canada’s ecoTECHNOLOGY for Vehicles Program (eTV) www.tc.gc.ca/eTV is a

horizontal initiative of the Clean Air Agenda, which forms part of the Government of

Canada’s broader efforts to address the challenges of climate change and air pollution.

eTV’s mandate is to carry out proactive work to assess the safety and environmental

performance of emerging advanced on-road vehicle technologies. The program tests,

evaluates and provides expert technical information on light-duty vehicle (LDV) and

heavy-duty vehicle (HDV) technologies that are expected to enter the Canadian market

over the next 10-15 years.

Environment Canada

EC’s mandate is to protect the environment, conserve the country's natural heritage,

and provide weather and meteorological information to keep Canadians informed and

safe. Environment Canada is building on its accomplishments with the environment

through credible science, effective regulations and legislation, successful partnerships,

and high-quality service delivery to Canadians.

U.S. Environmental Protection Agency (EPA) Assessment and Standards Division,

National Vehicle and Fuel Emissions Laboratory, Office of Transportation and Air

Quality

The U.S. Environmental Protection Agency’s (EPA) Assessment and Standards Division

identifies and develops future emission control strategies (such as new vehicle, engine,

and fuel quality standards) and national policy on mobile source emission control. The

division develops regulations and policies, determines the contribution of mobile

sources to pollutant emission inventories, and assesses the feasibility, cost, and in-use

effectiveness of emission control technologies.

3.1 Background

In the U.S. North East, Upper Midwest and in Canada, All Wheel Drive (AWD) can

represent up to 70% of sales volume depending on vehicle model. The additional mass

associated with AWD systems is typically about 90 kg, or roughly 4% to 10% of total

vehicle mass. Because of this increased system mass, as well as added drivetrain

parasitic losses, AWD typically increases fuel consumption and CO2 emissions by

between 2% and 8%. As GHG emissions regulations become more stringent

1 Request for Proposal T8080-150132- All Wheel Drive Component Analysis, Transport Canada

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manufacturers continue to seek opportunities to reduce the added mass, friction, and

drag associated with All Wheel Drive (AWD) systems, using a variety of methods and

technologies.

3.2 Purpose

AWD vehicles are increasingly popular in Canada, due in part to their performance in

challenging winter driving conditions. However, the inclusion of AWD systems can result

in reductions in overall vehicle fuel efficiency and increases in GHG emissions due to

added vehicle mass and drivetrain parasitic losses.

3.3 Data Sources

The following data sources were used to compile this report, in dropping order of

magnitude:

Pilot Systems International team non-confidential experience/knowledge

OEM, Tier 1&2 and dealer websites

Publications in technical papers, brochures

OEM and supplier publications

OEM and supplier interviews

Research groups

Academia

Customer advocate groups (e.g. Consumers Report)

Sources are referenced in footnotes. Non-referenced tables, figures and

diagrams have been developed by Pilot Systems and associates for non-

exclusive use in this report. Vehicle images in section 2 are for illustration

purposes only and have been downloaded from OEM and dealer websites.

All trademarks, logos and company or product names used in this report are

property of the individual vehicle or parts manufacturer.

This project will characterize how current and future advances in AWD

systems can potentially reduce these losses, in addition to comparing existing

2WD and AWD vehicles, in terms of GHG emission and fuel consumption

performance.

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1 AWD/4WD Systems and Components

1.1 AWD Systems Classification

This chapter follows the SAE J19522 standard in its October 2013 revision. System

descriptions, nomenclature and classification have been edited to reflect latest

developments in the area of AWD system development.

1.1.1 Definitions

A conventional All Wheel Drive (AWD) system consists of a means to distribute torque

to all wheels of a vehicle. The term ‘AWD’ stands for all systems that drive all wheels of

a vehicle regardless of the number of axles or the mechanics or controls involved. Based

on desired performance, traction and handling characteristics, there are different types

of systems to achieve these ends. These AWD systems include 4X43 and other

configurations. There are three basic types of systems and a combination of those

defined below:

Part-Time

Full-Time

On-Demand

Combinations of the above

AWD systems may have an additional, selectable reduction gear to provide two speeds -

one for normal driving (High-range) and one for improved ground speed control and

increased tractive force (Low-range).

PART-TIME AWD (4WD) SYSTEM

In a part-time AWD system (sometimes also simply called 4WD system) driver

intervention is required to rigidly couple and decouple primary and secondary axles.

When a part-time system is engaged the primary and secondary axles become rigidly

connected through the torque distribution device (i.e., Power Transfer Unit (PTU),

transfer case). The primary axle is normally connected unless in neutral mode. The

secondary axle(s) is/are engaged in AWD and disengaged in two-wheel drive. The torque

distribution device is commonly referred to as a transfer case (or T-case) in primary rear

2 SAE J1952 All Wheel Drive Systems Classification (Oct 2013) 3 Indicates the total number of wheels (4) and the number of wheels driven (4) – not part of the official nomenclature, although OEMs are using this term for marketing (decals, etc.)

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wheel drive based AWD vehicles. In a primary front wheel drive based vehicle the

torque distribution functions are typically managed in the PTU, transaxle, or secondary

axle(s).

This basic type of system requires the driver to select between two-wheel drive and

AWD commonly using either a switch or lever. Part-time systems may allow the driver to

shift between two-wheel drive and AWD while the vehicle is in motion.

Although part-time AWD achieves maximum traction under certain conditions it should

be limited to off-pavement usage or on-pavement usage in low traction scenarios.

Torque "wind up" is experienced during on-road dry pavement usage when making

moderate to tight low speed turns. This "wind up" (also referred to as crow hop or

binding) is due to the fact the front and rear axles are rigidly connected (no center

differential) and rotating at the same speed but traveling different distances.

FULL-TIME AWD SYSTEM

In a full-time AWD system front and rear axles are driven at all times through a center

differential.

Unlike a part-time system, the full-time system employs a center (inter-axle) differential

that allows the front and rear axles to turn at different speeds on any surface.

Depending upon the design of the differential, the input torque can be nominally split to

the front and rear axles in a fixed ratio. As an example, a 35:65 split means that 35% of

the torque is directed to the front axle and 65% to the rear axle.

For maintaining traction in adverse conditions torque through the center differential

must be modulated to distribute power to the axles with the greatest traction. Torque

modulation can be done passively, actively, with a torque biasing device, or with brake

based traction control systems.

This type of system can be used on any surface at any speed.

ON-DEMAND AWD SYSTEM

In an on-demand all-wheel drive system, the secondary drive axle may be driven by an

active or passive coupling device, or by an independently powered drive system. A

secondary drive axle, which is driven by an independently powered drive system, may

also provide the primary vehicle propulsion.

In a typical on-demand AWD system, the vehicle operates in 2WD (either front or rear

depending upon the basic vehicle architecture) until AWD is required, such as during

primary axle slip, yaw correction, or by other control strategies. In the case of secondary

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axles driven by an active or passive coupling device, torque transfer from the primary to

the secondary axle(s) can be modulated, dependent on driving conditions. Most systems

are typically relative speed control devices and activate when there is a speed difference

between the primary and secondary axle(s) due to slippage; however, pre-emptive slip

or other control strategies are common.

On-demand systems may have a disconnect device that allows the vehicle to be driven

in the more fuel efficient 2WD mode under normal driving conditions. The engagement

of AWD can be driver controlled or automatic, with sophisticated engagement

algorithms in place.

This type of system can be used on any surface at any speed.

COMBINATION SYSTEMS

Some of the AWD systems currently on the market offer selectable features that would

place them in the Part-time, Full-time or On-demand category, depending on what

mode the driver has selected. These vehicles are typically rear wheel drive based SUVs

or trucks, with a highly flexible transfer case providing multiple driving modes. Most

systems offer a combination of Part-time and On-demand systems, many times paired

with a selectable low gear to provide enhanced speed control and tractive force in off-

road conditions.

For classification purposes, the highest level mode (Part-time -> Full time -> On-demand

low to high) will be used as the main category for the vehicle. However, part-time or

full-time capabilities need to be noted to assure the full spectrum of vehicle

performance is understood.

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1.1.2 AWD Component Nomenclature

Figure 1-1: AWD Nomenclature

1.1.3 AWD Systems Classification4

This high level classification concentrates on functional attributes and does not include

architecture, vehicle class or information about the type of controls.

An attempt has been made to include hybrid drives but the large variety of driveline

architectures and component combinations would make it difficult to keep up with the

fast pace of development in the field of hybridization and electrification.

4 SAE J1952 All Wheel Drive Systems Classification (Oct 2013)

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Table 1-1: AWD Systems Classification

Type Synchronization

capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation

No No indeterminate n/a PT non-synchro

Yes No indeterminate n/a PT synchro

fixed n/a FT fixed torque

passive FT variable torque passive

active FT variable torque active

passive OD synchro variable torque passive

active OD synchro variable torque active

n/a yes indeterminate activeOD independently powered

variable torque activeSAE J1952 (Oct 2013)

Synchronisation capable: capable of synchronizing front and rear axle during AWD engagement while vehicle is in motion;

Synchronizer clutch or AWD coupler are the classic components to provide that capability

Longitudinal speed differentiation: front and rear axle can be at different speed (e.g. cornering) w/o torque wind-up

Typically enabled by either a center differential or an AWD coupler

Longitudinal torque distribution mode: type of torque transfer between front and rear

Part Time

(PT)

Full Time

(FT)

On-Demand

(OD)

n/a Yesvariable

yes yes variable

Passive: non controlled torque transfer determined by external feedback (typically wheel speed difference)

Torque modulation: torque transfer device type

Fixed: torque bias fixed by design (e.g. open diff)

Variable: torque bias variable by design (e.g. passive/active torque transfer device or active locking diff etc.;

hybrids with independently driven electric rear axle fall also into this category)

Indeterminate: torque bias determined by input torque, wheel speed and tractive conditions

Typical for part time systems

Active: electronically controlled torque transfer

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1.2 Current and Future AWD Systems

1.2.1 System Architecture

1.2.1.1 Front wheel drive (FWD) based system architecture

Upgrading FWD vehicles to AWD is relatively simple. Most AWD systems are so called

hang-on systems with passive or active on-demand torque transfer devices (AWD

couplers). Very few vehicle manufacturers offer permanent AWD via center differential,

which requires additional measures to assure traction is maintained if one wheel loses

grip entirely (see also next chapter: ‘RWD based system architecture’).

Added components

Power Transfer Unit Rear axle shafts

Propshaft Electronic control unit

Rear Drive Module Rear axle subframe and suspension modifications

Figure 1-2: FWD Based AWD System Architecture

The base FWD driveline architecture offers a line of advantages over RWD:

Underbody packaging becomes easier

Overall driveline mass is reduced

No NVH (Noise, Vibration & Harshness) problems with a propshaft at high

speed

Driveline efficiency is better because of the lack of hypoid gear sets

Traction is typically better because of more mass on the drive axle

Vehicle dynamics are more docile, understeer is more manageable for the

average driver

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Reduced cost

Sales of FWD vehicles have outnumbered RWD vehicles for many years and continue to

gain market share. However, some of the obvious advantages of FWD need to be

sacrificed when converting to AWD for improved traction and vehicle dynamics in

adverse conditions.

1.2.1.2 Rear wheel drive (RWD) based system architecture

RWD vehicles are typically sold in the upper and luxury segments, in the light truck and

SUV segment and as a niche product or sports cars. The base RWD architecture offers

some advantages over FWD:

Front end packaging allows for larger engines and transmissions with better

performance

RWD drivelines typically can manage higher torque output

Sports car drivers typically prefer moderate oversteer characteristics

Most framed vehicles (e.g. light trucks) have simple rear axle layouts for

heavy loads

Added components

Transfer case Rear propshaft (modified)

Front propshaft Electronic control unit

Front axle Figure 1-3: RWD Based AWD System Architecture

The centerpiece of the RWD based AWD architecture is the transfer case (T-case) which

splits up torque between the axles. Many T-cases in today’s vehicles incorporate an

AWD coupler and have on-demand characteristics. However, the center differential (CD)

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can still be found in many upper class vehicles. Torque bias between front and rear axle

is typically between 50/50 and 40/60.

Open CD equipped vehicles need some means of torque management to overcome the

disadvantage of losing traction if only one wheel loses grip (note: now you have four

wheels hunting for that slick spot so an open CD can be worse than 2WD). Mechanical

locking devices, torque sensing limited slip differentials or active/passive couplers are

some of the ways to improve traction in adverse conditions. An elegant and very

popular way is to use the brake system to slow down a slipping wheel. So called ‘Brake

Traction Control’ is known from 2WD vehicles and works very well for AWD vehicles.

A special version of this architecture is the ‘Symmetrical AWD’ from Subaru. This

purpose built AWD architecture tries to minimize the number of gears involved in

transferring torque from the transmission to the wheels. Audi is using a similar layout in

some of their quattro™ systems. The main difference from conventional T-case layouts

is that the front propshaft is integrated in the transmission. In this case, the

transmission becomes dedicated to AWD rather than a modular component that can be

used for RWD and AWD with minimal modifications. Applications are therefore limited

to vehicle lines purpose built for AWD.

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1.2.1.3 Front wheel drive based hybrid AWD architecture

Added components

Rear axle electric drive Control unit

Battery Optional: engine/transmission driven generator Power electronics

Figure 1-4: FWD Based ‘Through the Road’ Hybrid AWD

One way of dramatically improving Fuel Efficiency (FE) and simultaneously providing

AWD to a FWD based vehicle is adding an electric drive axle to the rear. This type of

architecture is typically used as a Plug in Hybrid Electric Vehicle (PHEV) with battery

sizes that allow driving some distance in pure electric mode.

The FE penalty associated with the added mass of approximately 250 - 350 kg5

(depending on the battery size) in pure gasoline powered mode can be compensated by

the ability to recuperate brake energy and the use of electric power assistance or pure

electric drive for short distance driving. The results are highly dependent on the mission

profile and the size of the battery.

An optional generator driven by the primary powertrain adds flexibility to this concept.

5 Compare to 50 – 150 kg of added mass for a mechanical AWD system, see Figure 2-3

21

1.2.1.4 Electric Drive

Figure 1-5: Electric AWD

Added components

Front & rear axle electric drive Control unit

Battery

Power electronics

Deleted Components

Internal combustion engine

Transmission & driveline components

Gasoline fuel system

22

1.2.2 Components / Function

1.2.2.1 Power Transfer Unit (PTU)

The PTU is an integral part of a typical FWD based AWD driveline. It is directly bolted to

the transmission and picks up torque from the front differential located in the final drive

section of the transmission (Figure 1-6).

Figure 1-6: Power Transfer Unit6

The main function of a PTU, besides picking up torque from the front axle, is to provide

a 90° angular drive (typically a hypoid drive) to transfer torque to the rear axle via the

propshaft.

The PTU may contain a disconnect device, usually a shift sleeve or a dog clutch, to

improve fuel efficiency by disconnecting the rear driveline (see chapter 1.2.2.4).

6 http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems

23

There are various types of PTUs: the simplest version is a single shaft PTU as shown in

Figure 1-6. The single stage PTU is the most cost effective and most efficient solution.

However, packaging constraints may require a two shaft or even a three shaft (with an

idler gear, see Figure 1-7) PTU to enable repositioning the output shaft in the usually

very complicated underbody environment. This adds cost, mass and creates additional

losses in the drivetrain. Newer vehicle designs try to incorporate AWD options from the

beginning and provide necessary space for the best solution.

Figure 1-7: PTU Architecture; Single Shaft (center), Two Shaft (left) and Three Shaft (right)

24

Figure 1-8: Power Flow in a PTU (2015 VW Tiguan)7

The power flow in a single shaft PTU is shown in Figure 1-8. The final drive and the

differential are part of the transmission. The hollow shaft connects to the differential

cage via spline and picks up power directly from the final drive. The ring and pinion

(hypoid set) redirect power by 90°, with the pinion driving the propshaft to the rear.

1.2.2.2 Rear Drive Module (RDM)

The RDM is driven by the propshaft and provides a 90° angle to drive the rear wheels via

drive shafts. It also houses the rear axle differential.

In FWD based AWD systems the RDM typically contains an integrated Torque Transfer

Device (TTD) that actively or passively controls torque delivered to the rear axle. Current

AWD systems typically rely on the active TTD to improve tractive force and vehicle

dynamics with a minimum of compromise.

The TTD is the corresponding part in a modern ‘disconnect system’, besides the PTU

disconnect clutch.

There are various options for the location of the TTD within the RDM. The conventional

solution was in-line, directly at the input, as shown in Figure 1-9. More sophisticated

RDMs with disconnect function require a more complex solution as described in the

next chapter.

7 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf

25

Figure 1-9: RDM with integrated Torque Transfer Device 8

1.2.2.3 Torque Transfer Device (TTD)

The TTD, or more commonly called the ‘AWD coupler’, modulates drive torque to the

rear axle either passively (e.g. viscous couplers, progressive hydraulic units etc.) or

actively. The main components are the Multi Plate Clutch pack (MPC, see Figure 1-10)

and a subsystem to compress the clutch pack to transfer torque from the input shaft to

the output. Today’s AWD systems are predominantly active type systems to provide

flexible torque control with integrated Electronic Control Units (ECU).

Active units can be of 4 different types with similar functionality:

hydraulic

electro-hydraulic

electro-mechanic

electro-magnetic

Hydraulic types generate pressure with a pump that acts on speed difference between

input and output shaft. The electro-hydraulic type uses an electric motor driven pump

independently from coupler speed and provides better response. Most hydraulic

8 http://www.kfztech.de/kfztechnik/triebwerk/allrad/haldex.htm

26

systems fall into this category. The system architecture is highly flexible and is preferred

for high end systems.

Electro-mechanic actuators use gear or cam driven ball ramps to pressurize the clutch

pack. Performance is equal to the electro-hydraulic systems. However, packaging

constraints may prove challenging.

Electro-magnetic actuators (Figure 1-10) use a magnetic field to pressurize a small pilot

clutch. The pressure generated by the magnetic field results in a small torque in the pilot

clutch which is augmented in the main clutch pack via ball ramp mechanism.

Active couplers are controlled by an Electronic Control Unit (ECU) and are capable of

adjusting torque based on various sensor inputs and therefore can respond to varying

driving conditions within milliseconds. Vehicle dynamics, safety and performance can be

significantly enhanced. Control algorithms interact with other vehicle control systems

such as ABS or vehicle stability control to optimize vehicle performance.

The core of the TTD is typically a wet clutch pack compressed by a piston to modulate

torque. (Figure 1-10) The clutch pack needs to be designed to carry the required

maximum torque without slipping or overheating. Electronic protection algorithms are

typically utilized.

Figure 1-10: Electro-magnetically actuated AWD coupler 9

The TTD is also a key element in AWD disconnect systems. If properly designed it

provides minimal drag in the open position to allow the AWD drivetrain to come to a

complete standstill while driving the vehicle at any speed. This is usually accomplished

by establishing a large gap between the clutch plates, sometimes supported by wave

springs to establish even separation throughout the clutch pack. If AWD is required

9 Source: www.borgwarner.com

27

either by driver intervention or by vehicle dynamic controls the TTD synchronizes the

standing drivetrain to allow the front dog clutch to engage. The process takes longer

than the typical AWD drive response time, approximately 200 – 400 milliseconds vs. 100

ms, to allow the piston to travel the increased distance due to the gaps. It should be

without any negative feedback to the driver. Once engaged the coupler response is back

to less than 100 ms for torque modulation.

The location of the AWD coupler within the RDM is critical to its function. Figure 1-11

shows four different arrangements for the AWD coupler:

• In-line represents the conventional layout for FWD based AWD systems. The

coupler is directly driven by the propshaft and runs at the lower propshaft

torque and higher speed.

• The parallel arrangement is required if the AWD coupler needs to act as the rear

disconnect and synchronization device. This way the hypoid set, which is a main

contributor to parasitic losses, comes to a standstill when disconnected

• Half shaft disconnect is an alternative to parallel. However, the differential gears

are spinning inside the differential housing and can create additional losses.

Torque is modulated by the coupler and balanced across the differential.

• The dual clutch system provides a way of eliminating the axle differential

entirely. Two individually controlled couplers are required. The advantages are

the functionality of a limited slip differential and, within limitations, the

possibility of torque vectoring.

Figure 1-11: Rear Drive Module Architecture Variants

28

AWD couplers are using a specially formulated lubricant to provide optimum friction

behavior in terms of noise, vibration and harshness, thermal stability, lowest possible

viscosity to support responsiveness of the hydraulic system and low drag characteristics

in open mode. Hypoid sets on the other hand are requiring higher viscosity fluids to

maintain lubrication in the sliding contact areas of hypoid gears up to maximum

operating temperature. RDMs therefore have separated lubrication systems for the

AWD coupler and the gear sets.

1.2.2.4 Torque Vectoring

Torque vectoring is a feature that allows the drivetrain to transfer more torque to the

outside wheels during cornering, thus making even a heavy vehicle more ‘nimble’.

Figure 1-12 illustrates that effect, with significantly higher tractive force on the outside

wheels, shown in green, than on the inside wheels, shown in red. This can be achieved

by two completely different methods:

1. Brake Traction Control induced torque vectoring

2. Clutch controlled torque vectoring

1) Braking the inside wheels slightly during cornering induces positive yaw10 which

helps the vehicle to turn faster. This method does not require any mechanical

devices and simply uses the brake system, with special algorithms included in the

electronic control unit to address vehicle dynamics inputs and driver request

through the steering wheel. It also works during acceleration and braking. The

system could be considered an extension of Vehicle Dynamic Control since it uses

the same mechanical components.

The downside of this method is that the brake force used to generate positive yaw is

converted into heat and therefore lost. It can also be a challenge to the brake

system.

10 Yaw is the movement of a vehicle about its vertical axis. Positive yaw is the movement towards the inside of the path (oversteer), negative yaw is the movement towards the outside of the path (understeer)

29

______ Figure 1-12: Torque Vectoring11

2) Clutch controlled torque vectoring (Figure 1-13) requires an array of mechanical

components to allow the generation of positive yaw: The rear drive module has two

wet clutches and a pair of overdrive gears as opposed to only one AWD coupler in

conventional systems.

Since the outside wheels during cornering travel a longer path, they are turning

faster, with the differential balancing torque and speed. However, torque can only

be transferred from a faster turning part to a slower turning part. In order to direct

drive torque to the faster turning (outside) wheel, torque vectoring systems feature

a pair of overdrive gear sets that rise the ring gear speed to a higher level. The clutch

picks up that higher speed and can now actively control torque flow to the

respective wheel.

This method does not waste any driveline torque but rather transfers the available

tractive force to the outside wheel to generate positive yaw. Cost, complexity and

mass penalties are on the negative side.

11 https://www.audiusa.com/technology/performance/quattro

30

______ Figure 1-13: Audi Sport Differential12

1.2.2.5 Disconnect Systems

Most OEMs have disconnect systems on the market or are developing them for their

next generation AWD vehicles. Light trucks and SUVs were leading the way more than a

decade ago not only for fuel efficiency improvements but also for better Noise,

Vibration and Harshness (NVH) performance.

Today, the development focuses on FWD based AWD systems where additional cost and

complexity are accepted in order to improve fuel efficiency. The improvement potential

lies somewhere in the range of 2 – 4 % depending on the test cycles used for

comparison13. These numbers are valid only for comparison between 2WD and AWD

modes and will be reduced in real life conditions where engagement algorithms

determine the actual time driven in the more efficient 2WD mode. (see also 3.2). The

goal is to eliminate parasitic losses and rotational inertias in the secondary driveline

12 http://www.audiworld.com/articles/the-audi-s4-quattro-drive-and-sport-differential/ 13 SAE 2015-01-1099 ‘Beyond Driveline Disconnect’

31

when traction is sufficient for safe driving. The additional mass of an AWD system

remains in place.

The FWD based disconnect system consists of three main components:

The front end disconnect, typically a dog clutch

The rear end disconnect, typically provided by a specially designed and located

AWD coupler

A control system that, preferably without driver intervention,

activates/deactivates AWD based on driving conditions.

Figure 1-14 shows the front end of an AWD drivetrain for a vehicle with FWD based

architecture. A shift sleeve or dog clutch (shown in two positions) engages/disengages

the front ring gear, typically actuated by an electric linear actuator.

Figure 1-14: Front Axle Disconnect System, Integrated in the PTU

32

Figure 1-15 shows the counterpart on the rear axle. The AWD coupler has been moved

from the input shaft downstream between the rear ring gear and the differential.

Special care needs to be taken in the design of the coupler: In a conventional open

clutch the residual oil film causes drag that can be large enough to cause significant

losses. The coupler therefore allows for larger spacing of the clutch plates to overcome

that negative effect although at the expense of increased reaction time for engagement.

Figure 1-15: Rear axle disconnect via AWD coupler

Figure 1-16 shows a comparison between active AWD and 2WD mode. In the right hand

schematic the AWD system is disengaged. The green parts of the driveline are at a

complete standstill although the vehicle is driving at normal speed. The components not

rotating include the hypoid sets which are a main contributing factor for parasitic losses.

Rotational motion is in the front between the hollow shaft carrying the ring gear and the

PTU input shaft. In the rear speed difference is between the clutch plates in the AWD

coupler.

33

Figure 1-16: AWD System Status Before (left) and after (right) Disconnect – FWD based vehicles

Engagements and disengagements require precise sequencing: During disengagement

the AWD coupler needs to unload the secondary driveline first to allow the front dog

clutch to freely disengage subsequently. On reconnect, the AWD coupler needs to

synchronize the secondary driveline first. The dog clutch in the front connects the two

parts then at (or close to) the same speed.

While variations of disconnect systems in the market or under development do exist, their

functionality does not vary dramatically. What may vary is the location of the disconnect

device.

Besides the system described above front end disconnects can be located at the front

wheel hubs, thus stopping even the front differential and drive shafts, or in one of the

drive shafts, stopping only the hypoid set but allowing the differential gears and the

drive shafts to spin. A balance of cost, complexity and efficiency gains must be found.

The rear end disconnect couplers may also be located on one or, in so called ‘Twin

Systems’, in both outputs of the axle, with the same effect as described above.

RWD based disconnect systems for on-demand and 4WD drivetrains are actually

somewhat simpler and therefore cheaper to implement. The transfer case architecture

need not be changed since either a mechanical clutch (4WD) or an AWD coupler will already

exist. Originally this type of system was used on trucks and SUVs with a driver actuated

system. New developments (Chrysler 300) show fully automated systems as well.

34

Figure 1-17: AWD System Status Before and After Disconnect – RWD based vehicles

The front axle disconnect is typically a shift sleeve or a dog clutch, very similar to the

components used in FWD based disconnect systems.

Figure 1-17 shows the system status before and after disconnect. In a typical application

(Chevrolet Silverado, Ram 1500, Chrysler LX), the chain drive in the transfer case and the

front hypoid set are at a standstill, while the front differential is spinning. The main

contributors to driveline losses are here non-rotating.

Figure 1-18: Front Wheel Hub Disconnect

Further improvements can be achieved by disconnecting the front driveline directly at

the wheel hubs, as shown in Figure 1-18. The complete front axle including the

35

differential and drive shafts, are non-rotating when disconnected. However, this comes

with significantly increased complexity and associated cost, with relatively minor gains

in efficiency.

1.2.2.6 Transfer case

Transfer cases (also known as T-cases) are typically found in light trucks and SUVs with

RWD base architecture. The transfer case is commonly bolted directly to the rear end of

the longitudinal transmission and splits torque between the front and the rear axle.

There are several types of T-cases available today:

4WD manually activated or electrically shifted – creates a positive lock between

front and rear axles and is typically used for rugged off-road driving

Center differential AWD – typically comes with an active or passive locking

device for the CD to provide traction in difficult terrain

Active transfer cases – an electronically controlled torque transfer device

typically directs torque to the front axle when needed. This type of transfer case

is often combined with a front axle disconnect device that improves fuel

efficiency. Multiple modes of activation are provided, ranging from full lock (off-

road) to full control. A driver interface allows different modes to be selected.

Figure 1-19 shows an active 2-speed transfer case as used in light trucks and SUVs. The

driver selectable low gear option allows for greater speed control when driven in

challenging off-road situations, and provides extra torque for the tough jobs.

Most transfer cases are single-offset in which the front propshaft is driven by a gear set

or a chain drive off center, whereas the rear output which drives the rear propshaft is in

line with the input.

Double-offset T-cases have front and rear output in line, offset from the input. They are

mostly used in heavy trucks and equipment.

The so-called symmetrical AWD (Subaru) architecture is a minimal offset version, where

the input and rear output are in line and the front propshaft is integrated in the

transmission.

36

______ Figure 1-19: Active 2-speed transfer case14

Figure 1-20: Torque Flow in an On-demand Transfer case

14 http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems

37

Figure 1-20 shows the torque flow in an active on-demand T-case. The rear axle is

directly driven by the engine and transmission, the front axle is connected via active

coupler and the front axle torque is modulated by the AWD coupler.

As an alternative to chain drive as shown above, a conventional gear drive has been

used. This design is not as cost efficient as the chain drive and is not the first choice for

light duty vehicles, but in the underbody environment of sedans and SUVs it might help

with packaging issues.

Gear drive becomes a necessity when torque requirements exceed the capacity of chain

drives. Gear drives are used in medium to heavy truck applications and in very few truck

based and off-road oriented SUVs (e.g. Mercedes G-Wagon).

1.2.3 System Function & Operating Modes

AWD disconnect system control

To maximize fuel efficiency, AWD vehicles equipped with automatic AWD disconnect

devices should be driven in the more efficient 2WD status as much as possible, with

AWD mode employed only when required. Sophisticated engagement/disengagement

algorithms are put in place to make sure the driver has the best possible experience

under all circumstances. Figure 1-21 shows a high level approach to maximize efficiency

and make good use of the AWD system when required.

38

______ Figure 1-21: High Level AWD System Disconnect Algorithm15

The shift logics use an array of sensors, many of them already available in the vehicle

(e.g. ambient temperature, windshield wipers, wheel speed sensors, accelerometers,

etc.) to decide on a strategy to react to any environmental changes as required.

At low vehicle speed (1st, sometimes 2nd gear) the AWD system is very often engaged to

avoid wheel spin at high torque. At this speed, adverse effects on efficiency are

negligible. However, this may significantly increase the disconnect shift frequency and

may be a challenge regarding durability and driving comfort.

In automatic mode the driver has no direct control over the disconnect system. Based on

sensor input algorithms determine when to engage or disengage the AWD system.

However, many systems provide an override option for the driver to have AWD

permanently engaged. This obviously eliminates the system advantages.

15 U.S. Patent 8,164,767

39

Secondary driveline torque limitation (‘Downsizing’)

The amount of additional torque needed to propel the vehicle through adverse

conditions is relatively small and usually does not have to exceed a level that exploits

the tractive potential of the secondary axle to the maximum. That opens up the

possibility to limit torque in the secondary driveline, with downsized components saving

cost, mass and fuel. In most driving conditions, the effect of torque limitation is hardly

noticeable to the driver and does not negatively affect performance.

Duty cycle management

An advanced method to allow for downsizing the AWD driveline is active duty cycle

management. In addition to torque limitation, control algorithms minimize the work the

AWD system has to go through, thus enhancing component durability and allowing for

downsized parts in the system.

40

1.3 Comparative Assessment of Positives and Negatives

This chapter provides a snapshot of positive and negative effects of vehicle architecture

and features added to the AWD system to improve efficiency and performance.

The facts & features are color coded for positive or negative effects as follows;

Quantitative effects are typically system related and cannot be given in a simplified way.

Vehicle simulation with accurate driveline component models would allow an in depth

analysis of quantitative and qualitative effects on fuel efficiency. Additional information

and an attempt to quantify gains and losses can be found in chapter 3.9.

1.3.1 Vehicle Architecture

FWD based AWD

RWD based AWD

Very efficient base architecture due to lack of hypoid gears

Not as efficient base architecture as FWD

Secondary drivetrain is very inefficient due to two hypoid sets, high use of AWD drives total efficiency down significantly

Front drivetrain has nearly the same efficiency as rear, permanent use has little negative effect on efficiency

Packaging allows for hybridization by adding an independent electric rear axle

Typically offers more torque capacity

Active coupler technology enables driveline downsizing by limiting peak torque and managing duty cycles in the secondary driveline

Table 1-2: FWD/RWD Architecture Positives and Negatives

1.3.2 Disconnect Systems

FWD based AWD

RWD based AWD

Significant efficiency improvements, more so for FWD based systems, if in 2WD mode most of the time

Added complexity and cost

Compromise between AWD availability for vehicle dynamics events and efficiency improvements

AWD coupler needs to move from in-line to parallel arrangement with added complexity

AWD coupler in the transfer case is already located ideally

Table 1-3: Disconnect Systems Positives and Negatives

41

1.3.3 Secondary Driveline Torque Limitation & Duty Cycle Management

Significant mass and some rotational inertia savings possible

Extreme off-road performance compromised

Compromise between AWD availability for vehicle dynamics events and mass savings

Table 1-4: Torque Limitation Positives and Negatives

1.3.4 Full Time vs. On-Demand Systems

Full Time

On-Demand

Superior vehicle handling potential Handling compromise at low speed if RWD based (torque oversteer)

No torque management devices necessary if used with Brake Traction Control (BTC)

AWD coupler (passive or active) required to manage torque transfer

Proven mechanical torque biasing devices work well with BTC

Electronic Limited Slip Differentials (eLSD) provide additional flexibility

Always transfers torque across at least one less efficient hypoid set

Primary driveline is highly efficient (FWD based vehicles)

Always transfers torque across a less efficient hypoid set (RWD based vehicle)

No downsizing because of permanent torque transfer; driveline sizing needs to account for biasing devices

Active coupler technology enables driveline downsizing by limiting peak torque and managing duty cycles in the secondary driveline Driveline sizing based on torque split if

used with BTC only

2WD vehicle dynamics characteristics can be preserved (understeer for FWD, oversteer for RWD)

Table 1-5: Full Time vs. On-Demand AWD Positives and Negatives

42

1.3.5 Rear Axle Architecture

This table illustrates Positives and Negatives for rear drive module (RDM) architecture

variants per Figure 1-11 in FWD based AWD vehicles.

In-Line Parallel Half-shaft Dual clutch

Torque level required + o o o

Rotational inertia - o o o

Packaging + - + -

Disconnect compatibility no yes yes yes

Complexity + - + -

Cost + - o - Table 1-6: RDM Architecture Positives and Negatives

43

2 AWD Vehicles by Make & Model

In the past years almost every OEM in the North American automobile market

developed and offered AWD versions of part of their vehicle lineup. Originally a

stronghold of off-road vehicles and trucks, AWD technology advanced significantly and

found its way into virtually all vehicle segments typically used in every day, on-road

driving. This has led to a vast array of AWD systems on the market. Many of them are

similar or identical in architecture, component design and mode of operation. Rather

than repeating design details on every make and model, identical systems are cross-

referenced in this chapter. Unique details relevant to fuel efficiency will be outlined for

every model.

This chapter covers the most popular vehicles on the market. It also tries to cover the

most influential or promising AWD systems in terms of mass reduction, component

efficiency improvements and control strategies aimed at enhancing fuel efficiency

regardless of their sales numbers. Exotic systems with low annual sales or AWD

technology from older vehicles (4WD systems) not relevant to fuel efficiency

improvements are not covered.

System classification follows SAE standards as described in 1.1.3. For standard size

trucks and SUVs with multiple operating modes the highest level mode was used for

classification.

2.1 The North American AWD Vehicle Market - Overview

The following chapters show some more detailed information about some of the most

popular or, from a system standpoint, most interesting AWD vehicles on the North

American market. The number of platforms listed for the larger OEMs gives an

impression of the variety of systems on the market. However, many of these platforms

share the same system architecture and functional features with only design variations

for packaging reasons and torque level.

A comparison will be given between 2WD and AWD versions to understand mass and

fuel efficiency penalties that come with added components and complexity. Numerical

values can be found in Appendix C.

2.1.1 Fuel Consumption and Vehicle Mass Data

The following charts show the difference in fuel consumption between 2WD and AWD

for selected vehicles (Figure 2-1 and Figure 2-2). The numbers reflect EPA estimates.

Fuel consumption increase for AWD vehicles is typically in the range of 5 – 10%. Added

mass and driveline losses contribute to this effect.

44

Mass data is shown in Figure 5-3. Vehicles with the largest mass increase include the Jeep

Cherokee (135 kg increase partially due to the disconnect system) and the Acura MDX

(‘Super Handling AWD’ mostly due to complexity).

______ Figure 2-1: Fuel Consumption Comparison between 2WD and AWD, MY 201516

16 Source: http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf; dealer websites, data tables see chapter 10

(No 2WD versions)

AWD Disconnect

AWD Disconnect

http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf

45

______ Figure 2-2: Fuel Consumption Comparison between 2WD and AWD, MY 2015 (continued)17

17 Source: http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf; dealer websites, data tables see chapter10

(No 2WD versions)

AWD Disconnect

AWD Disconnect

46

______ Figure 2-3: Vehicle Mass Comparison between 2WD and AWD versions, MY 201518

18 Source: Dealer websites, data tables see chapter10

(No 2WD versions)

AWD Disconnect

AWD Disconnect

47

2.2 AWD Vehicles by Make & Model

The following table is used to explain the AWD architecture of individual vehicle

platforms with color coding providing a quick overview of a manufacturer’s vehicle line

up with respect to AWD systems. A more detailed description can be found in section

1.1.3.

Table 2-1: AWD System Classification (SAE J1952, Oct 2013)

Synchronization capable: capable of synchronizing front and rear axle during AWD engagement while

vehicle is in motion; Synchronizer clutch or AWD coupler are the classic components to provide that

capability"

Longitudinal speed differentiation: front and rear axle can be at different speed (e.g. cornering) w/o

torque wind-up; typically enabled by either a center differential or an AWD coupler"

Longitudinal torque distribution mode: type of torque transfer between front and rear

Fixed: torque bias fixed by design (e.g. open differential)

Variable: torque bias variable by design (e.g. passive/active torque transfer device or active

locking differential etc. Hybrids with independently driven electric rear axle fall also into this

category)"

Indeterminate: torque bias determined by input torque, wheel speed and tractive conditions.

Typical for part time systems

Torque modulation: torque transfer device type

Active: electronically controlled torque transfer

Passive: non controlled torque transfer determined by external feedback (typically wheel speed

difference)


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation









variable torque active

Part Time

(PT)

Full Time

(FT)

On-Demand

(OD)

n/a Yesvariable

yes yes variable

48

2.2.1 Audi

Table 2-2: Audi Platforms and Models

SAE AWD Classification

Table 2-3: Audi AWD Classification

Audi is selling their AWD system under the quattro™ brand. The systems have evolved

from the original Audi quattro™ to currently three different systems. The entry level

models A3, Q3 and TT are based on the Volkswagen MQB platform and use the Haldex

on-demand system similar to VW.

The larger sedans have permanent AWD with a Torsen™ center differential in

combination with automatic transmissions (NA market), and a ‘crown gear’ differential

with rear axle bias with their dual clutch transmission (not sold in NA).

The large SUVs use a transfer case with Torsen ™ center differential.

19 Phased out in 2016


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Part Time

(PT)

Full Time

(FT)

On-Demand

(OD)

n/a Yesvariable

yes yes variable

Audi

Platform Nameplate

MLB B/C A4/A5/A6/A7/Q5

MLB D A8/Q7

MQB A/B A3/TT

PQ35 Q3

PL71-7219 Q7

49

Audi has just announced their latest development in AWD technology: the ‘Audi

quattro™ with ultra technology’ features an electro-mechanically actuated AWD coupler

in place of the Torsen™ center differential and a mechanical rear axle disconnect

device20. That makes the driveline an on-demand system with disconnect capability. This

system will ultimately replace the permanent system in the larger sedans.

20 http://jalopnik.com/audis-high-tech-new-quattro-is-about-to-piss-off-its-bi-1760502139

50

A6

Table 2-4: Audi A6 Basic Information

The A6 driveline is based on a longitudinal FWD architecture and features full-time AWD

with a Torsen® center differential (CD). The Torsen® CD provides a mechanical torque

sensing locking effect, the overall system performance is enhanced by brake traction

control. For classification purposes, this defines the A6 as a full-time variable torque

passive system. Figure 2-4 shows the 8-speed automatic transmission with Torsen®

center differential.

Powertrain

Engine Longitudinal 4, 6 or 8 cyl

Transmission 8-speed longitudinal automatic

Driveline

Architecture FWD based

T-case Type Integrated Torsen® center differential

Source ZF Mass n/a

Features none

RDM Type Open rear differential

Actuation n/a Source n/a

Mass n/a Torque transfer n/a

Features Optional dual clutch torque vectoring

AWD Controls

Passive AWD torque modulation

Brake traction control assist

Brake assisted torque vectoring

Optional: Active torque vectoring

51

The engine is entirely located in front of the front axle with the front axle differential

nested between the engine and the transmission and driven by an integrated front

propshaft. Subaru is using a similar architecture.

______ Figure 2-4: Audi 8-Speed Automatic Transmission with Integrated Torsen Differential21

21 http://www.audi-technology-portal.de/en/drivetrain/transmission-technologies/tiptronic_en

52

2.2.2 BMW

Table 2-5: BMW Platforms and Models


Table 2-6: BMW AWD Classification

BMW is marketing their AWD vehicles under the ‘x-Drive’ name and is well known for

their RWD platforms. All vehicles starting with the 2-series sedan and the X1 series SUV

up have a RWD based architecture, with a transfer case with an active coupler driving

the front axle. Smaller vehicles like the Minis and the Active Tourer are based on the

new UKL FWD platform. Some others will follow. All systems are active on-demand.

BMW

Platform Nameplate

L2 X1

L3 Mini

L7 X3, X4, 2/3/4-Series

L4 X5, X6

LG X7

L6 5/6-Series

LG 7-Series

UKL X1, 2-series Active Tourer, Countryman, Paceman


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Part Time

(PT)

Full Time

(FT)

On-Demand

(OD)

n/a Yesvariable

yes yes variable

53

BMW Active Tourer

Table 2-7: BMW Active Tourer Basic Information

Powertrain

Engine Transversal 4-cyl

Transmission 9-speed automatic

Driveline


PTU Type 2- shaft

Source GKN Mass n/a

Features none

RDM Type In-line AWD coupler; active on-demand

Actuation Electro – hydraulic Source BorgWarner

Mass n/a Torque transfer Multi plate clutch

Features None

AWD Controls

Active AWD torque control


54

BMW 3/4/5/6/7 Series with xDrive

Table 2-8: BMW 3/4/5/6/7 Series Basic Information

Powertrain

Engine Longitudinal 4, 6 or 8-cyl


Driveline

Architecture RWD based

RDM Type Open differential

Source n/a Mass n/a

Features none

T-Case

Type Single speed, active on demand Geared drive, LH drop

Actuation Electro-mechanical Source Magna Powertrain

Mass n/a Torque transfer AWD coupler to front axle

AWD Controls



55

Figure 2-5: BMW 3/4/5/6/7 Series Transfer Case with Geared Drive22

XDrive for BMW sedans features a geared transfer case, as shown in Figure 2-5). The

reason for using geared drive in this type of vehicle is underbody packaging. It carries

some cost and mass penalties over the more prevalent chain drive, with no efficiency or

performance advantages (see also section 1.2.2.6).

The function of the active torque control is identical to chain drive T-cases used in the

cross over models (X3 – X6, see Figure 2-6).

22 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems

56

BMW X3/X4/X5/X6 with xDrive

Table 2-9: BMW X3/4/5/6 Basic Information

Powertrain



Driveline


T-Case

Type Single – speed, active on-demand, Chain drive, LH drop

Actuation Electro-mechanical Source Magna Powertrain

Mass n/a Torque transfer AWD coupler

Front Axle Type Open differential

RDM Type Open differential

AWD Controls



57

Figure 2-6: BMW X3 / X4 / X5 / X6 Single Speed Active On-demand Transfer Case with Chain Drive23


58

2.2.3 Daimler Benz

Table 2-10: Daimler Benz Platforms and Models


Table 2-11: Daimler Benz AWD Classification

Mercedes uses the 4MATIC™ designation for their lineup of AWD vehicles. Entry level

vehicles are built on the FWD based MFA platform and have an electro-hydraulically

actuated AWD coupler in the RDM, which classifies them as on-demand AWD systems.

All upper level vehicles are RWD based and have a transfer case with center differential.

On sedans traction is enhanced by brake traction control only. SUVs have optional

passive limited slip devices.


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










On-Demand

(OD)

yes yes variable

Part Time

(PT)

Full Time

(FT)n/a Yes

variable

Daimler Benz

Platform Nameplate

MFA A-Class, B-Class, CLA, GLA

MRA MID-SIZE C-Class, GLC

W212 CLS, E-Class

W204 GLK, C-Class Coupe

W164 GL-Class/GLS, R-Class, ML-Class/GLE

W222 S-Class

W461 G-Wagen

59

The G-Wagen is an extreme off-road capable vehicle and has a unique drivetrain. It has a

frame mounted geared 2-speed transfer case with center differential. All three

differentials have driver activated mechanical full locks.

60

Mercedes Benz CLA/GLA 4-Matic

Table 2-12: Mercedes CLA/GLA Basic Information

Powertrain

Engine Transversal 4 or 6-cyl

Transmission 7-speed DCT

Driveline


PTU Type Single shaft

Source GKN Mass 8.5 kg

Features none


Actuation Electro – hydraulic Source Magna Powertrain


Features None

AWD Controls



61

Figure 2-7: Mercedes CLA/GLA 4-Matic Power Transfer Unit24

The GLA has a very highly integrated PTU as shown in Figure 2-7. The input shaft picks

up torque right from the transmission final drive, which from a design and cost

standpoint is about as efficient as it can possibly be. From a gear efficiency standpoint it

is equivalent to a two shaft PTU.

Figure 2-8: Mercedes CLA/GLA Rear Drive Module25

24 25 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems http://www.automobilismo.it/tecnica-la-trazione-integrale-4matic-mercedes-per-classe-a-classe-b-e-cla-auto-20265

http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems

62

Mercedes Benz C, E & S-class 4-Matic

Table 2-13: Mercedes C, E and S-Class Basic Information

Powertrain



Driveline


T-Case

Type

Integrated open center differential, 50/50 torque split Single stage beveled gear drive, RH drop

Actuation n/a Source Mercedes Benz

Mass n/a Torque transfer n/a

Front Axle Type open

RDM Type open

AWD Controls


63

______ Figure 2-9: Mercedes C, E and S-Class 4-Matic Powertrain

The longitudinal 4-Matic drivetrain used by Mercedes in the C, E and S-Class vehicles has

a planetary center differential with a 50/50 torque split between front and rear axles.

One notable feature (similar to Porsche’s Panamera and the MLB platform from Audi) is

a slightly beveled gear set to drive the front axle. Packaging reasons were the main

driver behind this technology. The T-case does not have an idler gear or a chain drive

and packages much closer to the main driveline. Taking one gear set out of the driveline

also increases efficiency.

The AWD system is assisted by Brake Traction Control, a feature common in AWD and

2WD vehicles.

64

2.2.4 Fiat Chrysler (FCA)

Table 2-14: FCA Platforms and Models


Table 2-15: FCA AWD Classification

Fiat Chrysler

Platform Nameplate

C-EVO/CUSW 200, Cherokee

LX 300, Charger

WK Grand Cherokee, Durango

WK Grand Cherokee, Durango

JK Wrangler

MK Compass, Patriot

BU (Small Wide) Renegade

DS/DJ 1500 Pickup

DS/DJ 1500 Pickup

C/D Journey


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Part Time

(PT)

Full Time

(FT)

On-Demand

(OD)

n/a Yesvariable

yes yes variable

65

Jeep is marketing their AWD systems under a variety of names. Basic on-demand

systems on FWD based vehicle platforms start with an AWD coupler in the RDM, options

include locking devices on both axles depending on model.

Cherokee and Renegade are equipped with an AWD disconnect system with a low gear

option in their Trailhawk versions.

RWD based models (Grand Cherokee, Dodge Durango) may have full time AWD in their

base version, and on-demand transfer cases in the premium versions, with optional axle

locking devices.

A complete lineup of Jeep AWD systems and nomenclature can be found on the Jeep

website under http://www.jeep.com/en/4x4/#FreedomDrive2.

http://www.jeep.com/en/4x4/#FreedomDrive2

66

Jeep Cherokee

Table 2-16: Jeep Cherokee Basic Information

Powertrain



Driveline


PTU Type 2- shaft with integrated disconnect

Source AAM Mass 22.6 kg

Features none

RDM Type Parallel AWD coupler; active on-demand

Actuation Electro – hydraulic Source AAM

Mass 33.1 kg Torque transfer Multi plate clutch

Features AWD coupler acts as rear disconnect

AWD Controls



Secondary axle disconnect

67

Versions

Trailhawk

Trail Rated® version of the Jeep Cherokee

Table 2-17: Jeep Cherokee Trailhawk Basic Information

AWD Systems:

ACTIVE DRIVE I: Base system with active coupler on the rear and brake traction control;

selectable driving mode for Auto / Snow / Sport / Sand and Mud.

ACTIVE DRIVE II: Low gear with 56:1 crawl ratio is added to the base system

ACTIVE DRIVE LOCK: Mechanical rear axle lock is added

Technical information and AWD component breakdown for the standard version of Jeep

Cherokee is provided in section 5.2.

Driveline

PTU Features 2-speed PTU, planetary low gear

RDM

Features 2-speed Mechanical differential locker

Vehicle

More ground clearance with 1” suspension lift and larger tires

Better break-over and approach/departure angles

68

Jeep Grand Cherokee

Table 2-18: Jeep Grand Cherokee Basic Information

Powertrain

Engine Longitudinal 6 and 8-cyl


Driveline


T-Case

Type

Chain drive, LH drop Base version: Single speed, Permanent AWD, Center differential with 50/50 split Premium(P): 2-speed electric shift

Actuation (P): electro-mechanical Source Magna Powertrain

Mass n/a Torque transfer AWD coupler


RDM Type open

AWD Controls



69

Figure 2-10: Jeep Grand Cherokee Single Speed (left) and 2-speed (right) Transfer Cases26

Jeep Grand Cherokee offers a base version with an open center differential and 50/50

torque split in single speed and with a 2-speed option, and a premium version with a 2-

speed electric shift and active on-demand AWD coupler. Figure 2-10 shows the

difference in complexity between the two versions.

AWD systems:

QUADRA-TRAC I®: Full Time AWD with single speed transfer case and 50/50 center

differential

QUADRA-TRAC II®: 2-speed active on-demand transfer case

QUADRA-DRIVE® II: eLSD added to the rear axle

QUADRA-TRAC® SRT®: Single speed on-demand Transfer case and rear axle eLSD,

upgraded in strength for SRT®

Jeep Grand Cherokee is sharing its QUADRA-TRAC® I and II AWD systems with Dodge

Durango.


70

Jeep Wrangler

Table 2-19: Jeep Wrangler Basic Information

Powertrain

Engine Longitudinal V6

Transmission 6-speed manual, optional 5-speed automatic

Driveline


T-Case

Type Chain drive, LH drop 2-speed, part time

Actuation Electric shift, driver actuated Source Magna Powertrain

Mass n/a

Front Axle Type Open differential

Rear Axle

Type Open differential, optional limited slip (‘Trac Loc™)

AWD Controls


71

Versions

Rubicon

Extreme off-road version of the Wrangler

Table 2-20: Jeep Wrangler Rubicon Basic Information

AWD Systems:

COMMAND-TRAC®: 2-speed part time transfer case (2.72:1) with open axle differentials

ROCK-TRAC®: 2-speed part time transfer case with 4:1 low gear, electric axle locks front

and rear, electronic front sway bar disconnect

Driveline

Transfer Case Features 2-speed part time, 4:1 low ratio

Axles Features Mechanical 100% differential locks, driver actuated

Vehicle

More ground clearance with larger tires

Electric sway bar disconnect

72

Chrysler 300

Table 2-21: Chrysler 300 Basic Information

Powertrain

Engine Longitudinal 6 or 8-cyl


Driveline


T-Case

Type Single speed active on—demand Chain drive, RH drop

Actuation Electro-magnetic Source BorgWarner

Mass n/a Torque transfer AWD Coupler


Source Magna Powertrain (axle) and Warn Industries (Disconnect)

Mass n/a

Features AWD disconnect, electro-mechanically actuated

RDM Type open

AWD Controls



Front axle automatic disconnect

73

Figure 2-11: Chrysler 300 Axle Disconnect Unit (left) and Front Axle (right)27

The Chrysler 300 front axle is directly bolted to the right hand side of the structural

engine oil pan, with the cross shaft shown in Figure 2-11 going right through the oil pan.

The disconnect system is bolted to the opposite side and provides an electro-

mechanically activated disconnect to the front left half shaft.

The transfer case is a conventional chain driven unit with integrated, electro-

magnetically actuated AWD coupler.

27 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems and Warn Industries


74

2.2.5 Ford

Table 2-22: Ford Platforms and Models


Table 2-23: Ford AWD Classification

Ford is offering AWD on their based platforms with an electro-magnetically activated

AWD coupler in the rear axle.

The full size SUVs and F150 trucks feature on-demand transfer cases. Some basic

versions of F150 have a part time transfer case.


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Full Time

(FT)n/a Yes

variable

On-Demand

(OD)

yes yes variable

Part Time

(PT)

Ford

Platform Nameplate

CD4 Edge, Fusion, S-Max, MKX/MKZ

C1 Escape, Focus, MKC

PN96/T1 Expedition, Navigator

D3/D4 Explorer, Flex, Taurus, MKS/MKT

T3 F150

F150

75

Ford Fusion

Table 2-24: Ford Fusion Basic Information

Technical information and AWD component breakdown is provided in section 5.1.

Powertrain



Driveline




Features none


Actuation Electro – magnetic Source Sterling Axle (Ford)


Features None

AWD Controls



76

2.2.6 General Motors (GM)

Table 2-25: General Motors Platforms and Models


Table 2-26: General Motors AWD Classification

GM FWD platforms feature on-demand AWD systems with an active coupler in the

RDM.

Full size trucks and SUVs are equipped with 2-speed transfer cases with an active

coupler driving the front axle. The systems have front axle disconnect devices that are


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Part Time

(PT)

Full Time

(FT)n/a Yes

variable

On-Demand

(OD)

yes yes variable

General Motors

Platform Nameplate

31XX Canyon/Colorado

ALPHA ATS/CTS

EPSILON XTS, Regal/LaCrosse

GAMMA Trax/Encore/Mokka

LAMBDA Acadia/Traverse

THETA ANTARA/Captiva/Equinox/SRX/Terrain

K2XX Silverado/Escalade/Sierra/Suburban/Tahoe/Yukon

K2XX Silverado, Sierra

77

driver activated. Small trucks and entry level full size trucks (work trucks) have a part

time transfer case.

Chevrolet Equinox

Table 2-27: Chevrolet Equinox Basic Information

Powertrain


Transmission Transversal 6-speed

Driveline


PTU Type 2- shaft


Features none


Actuation n/a Source n/a


Features None

AWD Controls



78

Chevrolet Silverado / GMC Sierra

Table 2-28: Chevrolet Silverado / GMC Sierra Basic Information

Powertrain

Engine Longitudinal 6 and 8-cyl


Driveline


T-Case Base Model

Type 2 Speed Manual Shift Chain drive, LH-Drop

Actuation Manual-Mechanical or optional electric shift Source Magna Powertrain

Mass n/a Torque transfer Cone Synchronizer w Dog Clutch

T-case Premium

Type

2-speed electric shift Active on-demand Multi plate Clutch

Source Magna Powertrain

Front Axle

Type Frame mounted, open diff

Source AAM

Mass n/a

Features Center disconnect , electro-mechanically actuated shift sleeve

Rear Axle

Type Open,

Source AAM

Mass n/a

Features optional mechanical locker (G80)

AWD Controls

Active AWD torque control (premium only)


79

Figure 2-12: Chevrolet Silverado / GMC Sierra Transfer Cases: 4WD Base Model (left) and AWD Premium Model (right)28

The Chevrolet/GMC line-up of full size trucks is a typical example of an AWD

architecture developed for full frame vehicles. The transfer case comes in 3 different

types: The base model is 2-speed part time 4WD with the option of manual or electrical

shift, and is mostly used for work trucks. Figure 2-12 shows the difference in complexity.

The premium model with 2 speeds has four driver selected modes:

2Hi is the most fuel efficient mode and provides torque to the rear wheels only.

The front axle is disconnected and not rotating.

AUTO is the preferred AWD mode when driving in inclement weather or

moderate off-road. An electromechanically controlled multi plate clutch

modulates torque as required.

4Hi has the AWD coupler locked at full torque capacity and provides extra

traction in off-road conditions

4Lo engages the reduction planetary gear set to provide better speed control

and higher tractive force in harsh off-road conditions.

The front axle disconnect system is driver controlled and does not have an automatic

mode.


80

2.2.7 Honda

Table 2-29: Honda Platforms and Models


Table 2-30: Honda AWD Classification

Honda AWD vehicles are active on-demand. The top-of-the-line vehicles offer ‘Super

Handling AWD’ (SH-AWD), which is the Honda version of torque vectoring (compare to

Audi, BMW and Mitsubishi)


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










On-Demand

(OD)

yes yes variable

Part Time

(PT)

Full Time

(FT)n/a Yes

variable

Honda

Platform Nameplate

2SL/2SF Pilot/MDX

C-5 CR-V, RDX

D-5 RLX, Odyssey, Crosstour, TLX

GSP(2) HRV/Fit

81

CR-V

Table 2-31: Honda CR-V Basic Information

Powertrain


Transmission CVT with sport mode

Driveline



Source Honda Mass 8.9 kg

Features none


Actuation Electro – hydraulic Source Honda – Tochigi


Features none

AWD Controls



82

2.2.8 Hyundai (Kia)

Table 2-32: Hyundai Platforms and Models


Table 2-33: Hyundai AWD Classification


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










On-Demand

(OD)

yes yes variable

Part Time

(PT)

Full Time

(FT)n/a Yes

variable

Hyundai / Kia

Platform Nameplate

HD Ix35, Sportage, Tucson

NF/CM Santa Fe, Sorento, Maxcruz, Veracruz

83

SantaFe

Table 2-34: Hyundai SantaFe Basic Information

Powertrain



Driveline



Source Hyundai-Wia Mass n/a

Features none


Actuation Electro – hydraulic Source Magna Powertrain (Axle from Hyundai-Wia)


Features None

AWD Controls



84

Figure 2-13: Magna Dynamax AWD Coupler29

Figure 2-13 shows one of the most compact AWD couplers on the market. The unit consists of an electro-hydraulic actuator and a multi plate clutch. The coupler bolts directly to the rear axle in an in-line configuration and is optimized in terms of torque level and AWD control system response.


85

2.2.9 Jaguar Land Rover (JLR - Tata)

Table 2-35: Jaguar Land Rover Platforms and Models


Table 2-36: Jaguar Land Rover AWD Classification


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Part Time

(PT)

Full Time

(FT)

On-Demand

(OD)

n/a Yesvariable

yes yes variable

Jaguar Land Rover

Platform Nameplate

PLA-D6a F-Type, XJ

PLA-D7a XE, XF,

D8 Discovery, Evoque

DEFENDER Defender

PLA-D7u Range Rover

86

Range Rover Evoque

Table 2-37: Range Rover Evoque Basic Information

Powertrain



Driveline



Source GKN Mass n/a

Features Electro-mechanically actuated disconnect

RDM Type Dual clutch AWD coupler; active on-demand

Actuation Electro – hydraulic Source GKN


Features disconnect

AWD Controls



Automatic disconnect

87

Figure 2-14: Evoque Rear Drive Module and RDM Architecture (insert)30

The Evoque RDM features a unique twin coupler (or dual clutch) system which

eliminates the need for a differential (Figure 2-14, see also Figure 1-11). The rear axle

system has limited slip characteristics and, within limitations, torque vectoring

capabilities. The RDM also acts as a disconnect device in conjunction with the PTU.

30 http://www.automobilrevue.ch/artikel/a/auf-die-sparsame-tour.html

88

2.2.10 Mazda

Table 2-38: Mazda Platforms and Models


Table 2-39: Mazda AWD Classification

Mazda AWD vehicles use an electro-magnetic AWD coupler similar to the Ford Fusion.


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










On-Demand

(OD)

yes yes variable

Part Time

(PT)

Full Time

(FT)n/a Yes

variable

Mitsubishi

Platform Nameplate

SKYACTIV B CX-3

SKYACTIV C CX-5

SKYACTIV D CX-9

89

2.2.11 Mitsubishi

Table 2-40: Mitsubishi Platforms and Models


Table 2-41: Mitsubishi AWD Classification

Mitsubishi AWD Technology

Mitsubishi offers two different AWD systems under the name ‘Super All Wheel Control’.

The Outlander features the baseline system with an electro-magnetically actuated AWD

coupler very similar to the Ford Fusion (see also section 1.2.2.4). In addition to the in-

line AWD coupler Outlander also features an Active Front axle Differential (AFD) which

controls wheel slip across the front axle by means of an electronically controlled coupler

(a.k.a. eLSD or electronically controlled Limited Slip Differential). Figure 2-15 shows a

schematic of the Outlander system. Traction is further enhanced by Brake Traction

control.


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










On-Demand

(OD)

yes yes variable

Part Time

(PT)

Full Time

(FT)n/a Yes

variable

Mitsubishi

Platform Nameplate

GS Outlander, Lancer

90

Figure 2-15: Mitsubishi S-AWC (‘Super – All Wheel Control’)31

The top-of-the-line system is Mitsubishi’s Active Yaw Control (AYC) system. It is available

in the GSR version of the Lancer. The system was the first in the North American market

to provide full torque vectoring capabilities (see also section 1.2.2.4). Audi, BMW and

Honda followed much later with similar systems. However, cost, complexity and mass

penalties have kept torque vectoring systems in a market niche.

31 http://www.mitsubishi-motors.com/en/spirit/technology/library/s-awc.html

91

Figure 2-16: Lancer Evolution Rear Drive Module with Active Yaw Control (AYC) 32

32 http://www.mitsubishi-motors.com/en/spirit/technology/library/s-awc.html

92

2.2.12 Nissan (Infiniti)

Table 2-42: Nissan Platforms and Models


Table 2-43: Nissan AWD Classification


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










On-Demand

(OD)

yes yes variable

Part Time

(PT)

Full Time

(FT)n/a Yes

variable

Nissan

Platform Nameplate

B Juke

B0 Terrano

D Murano, Pathfinder, QX60

X61B Frontier, Titan, Armada, Xterra, QX80

CMF-C/D Rogue

FR-L Q50, Q60, Q70, QX50, QX70,

93

Nissan Rogue

Table 2-44: Nissan Rogue Basic Information

Powertrain


Transmission CVT

Driveline



Source Univance Mass n/a

Features none


Actuation Electro – magnetic Source Nissan / GKN


Features None

AWD Controls



94

2.2.13 Subaru

Table 2-45: Subaru Platforms and Models


Table 2-46: Subaru AWD Classification

Entry models sold in North America feature manual transmissions and permanent AWD

with a rear axle biased center differential – the original ‘Symmetric All Wheel Drive’.

Premium models are equipped with the Lineartronic™ CVT with an on-demand AWD

system (Figure 2-17).

The Subaru Lineartronic ™ is a Continuously Variable Transmission (CVT). The transfer

case, front axle drive and rear axle drive are completely integrated. The transmission is

purpose built for AWD and Subaru does not offer a 2WD version. Torque transfer to the

rear axle is managed in the transmission via AWD coupler33.

33 http://www.subaru-global.com/tec_awd.html

Subaru

Platform Nameplate

SI(2) Legacy, Impreza, Forester, WRX, Outback, Crosstrek

SI(2) Impreza, Forester, WRX, Crosstrek


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










On-Demand

(OD)

yes yes variable

Part Time

(PT)

Full Time

(FT)n/a Yes

variable

95

Figure 2-17: Subaru AWD CVT Transmission34

34 http://www.subaruforester.org/vbulletin/f155/subaru-lineartronic-cvt-cutaway-102264/

96

Outback

Table 2-47: Subaru Outback Basic Information

Powertrain


Transmission Lineartronic ™ CVT

Driveline

Architecture AWD dedicated

Transfer Case Type Integrated AWD with coupler driving rear axle

Source n/a Mass n/a

Features none

Axles Type open

Features None

AWD Controls



97

2.2.14 Tesla

Model S

Table 2-48: Tesla Model S Basic Information

Powertrain

Engine 2 electric

Transmission Single speed e-drive

Driveline

Architecture Permanent AWD

AWD Controls

Electric motor control units

98

2.2.15 Toyota

Table 2-49: Toyota Platforms and Models


Table 2-50: Toyota AWD Classification

Toyota (Lexus)

Platform Nameplate

F1 Land Cruiser 200, LX, Sequoia, Tundra

F2 Tacoma

GS GS, IS

LS LS

MC-M RAV-4, Highlander, Sienna, Venza

99

Rav4

Table 2-51: Toyota Rav4 Basic Information

Powertrain



Driveline



Source Toyota Mass 11.7 kg

Features none


Actuation Electro – magnetic Source Toyota

Mass 17 kg Torque transfer Multi plate clutch

Features None

AWD Controls



100

Highlander

Table 2-52: Toyota Highlander Basic Information

The Highlander is based on the same platform as RAV4 and the AWD system

architecture is identical.

Highlander offers a full hybrid version with electric rear axle drive (eRAD). This AWD

system is not a classic eRAD system as described in section 1.2.1.3 but a full hybrid with

an additional electric rear axle drive. It does not have plug-in capabilities (PHEV).

Powertrain

Engine Transversal 4/6-cyl


Driveline


PTU Type n/a

Source Toyota Mass n/a

Features none


Actuation Electro – magnetic Source Toyota


Features None

AWD Controls



101

2.2.16 Volkswagen

Table 2-53: Volkswagen Platforms and Models


Table 2-54: Volkswagen AWD Classification


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Part Time

(PT)

Full Time

(FT)

On-Demand

(OD)

n/a Yesvariable

yes yes variable

Volkswagen

Platform Nameplate

MQB A/B Passat, Golf,

PL71-72 Touareg

PQ35 Tiguan

102

Tiguan

Table 2-55: Volkswagen Tiguan Basic Information

Technical information and AWD component breakdown is provided in section 5.3.

Powertrain


Transmission 7-speed DCT

Driveline



Source Magna Powertrain Mass 17.2

Features none


Actuation Electro – hydraulic

Source Magna powertrain, AWD coupler BorgWarner Haldex Gen IV

Mass 35.3 Torque transfer Multi plate clutch

Features None

AWD Controls



103

2.2.17 Volvo

Table 2-56: Volvo Platforms and Models


Table 2-57: Volvo AWD Classification

Volvo AWD systems are based on the Haldex AWD coupler and are exclusively on-

demand. All systems are Haldex Gen V, except for XC90 which kept Gen IV35.

Volvo also offers a hybrid version of the XC90, with a ‘through the road’ AWD

architecture. The vehicle is not yet available on the North American market, and critical

data have not yet been officially released.

35 The Haldex system is explained in detail in section 5.3.1 (VW Tiguan)


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Part Time

(PT)

Full Time

(FT)n/a Yes

variable

On-Demand

(OD)

yes yes variable

Volvo

Platform Nameplate

C1 V40

CD-EU S60, S80, V60, V70, XC70, XC60,

SPA XC90

104

XC90

Table 2-58: Volvo XC 90 Basic Information

Powertrain

Engine Transversal 4 cyl supercharged

Transmission 8-speed Automatic (Aisin)

Driveline


PTU Type n/a

Source n/a Mass n/a

Features none


Actuation Electro – hydraulic Source Haldex


Features None

AWD Controls



105

XC90 T8 PHEV

Table 2-59: Volvo XC90 T8 PHEV Basic Information

Powertrain

Engine Transversal 4 cyl supercharged Electric Motor (eRAD)

Transmission 8-speed Automatic (Aisin)

Driveline

Architecture FWD based, AWD only, eRAD

Front Axle Drive

Internal Combustion Engine, with Starter Generator

Rear Axle Drive Electric Rear Axle Drive (eRAD)

AWD Controls


106

3 AWD Efficiency Improvement Potentials

The following section explains design features, materials and processes that may offer

improvements to driveline efficiency or component mass reductions. The numbers

referenced are mostly from supplier publications and may reflect special circumstances

on a particular component. These numbers cannot be applied to other similar

components. Actual improvements in fuel economy need to be evaluated, preferably by

method of vehicle simulation.

3.1 Definitions

There are two basic types of losses in a drivetrain:

Torque transfer losses

Parasitic losses

Torque transfer losses are generated whenever the driveline transfers any level of

torque. They include gear friction losses, bearing losses due to reaction forces and losses

in driveline joints.

Parasitic losses occur in any component that moves relative to another contacting

surface or medium independently from the actual torque transferred. They include seal

drag, bearing preload losses, churning losses from gears submerged in the lubricant,

pumping losses from bearings or idling lubricant pumps and drag in a multi plate clutch.

Both types of losses are dependent on the operating temperature of the driveline

component. As the temperature rises to a typical operating temperature of 70 to 120°C

the losses drop significantly. However, driving statistics indicate that short distance

driving during which operating temperatures do not stabilize is the most frequent mode

of operation in urban environments. Special care needs to be taken therefore to

optimize component efficiency in all temperature ranges.

3.2 System Level

3.2.1 Architecture

AWD systems have traditionally been seen as add-ons to existing platforms. Many times

the original design did not possess provisions to easily accommodate the AWD

components. As an example, power transfer units (PTUs) in FWD based vehicles have

107

been difficult to package in the tight space between the engine, transmission and body

structure.

More recent vehicles have been designed with the AWD option in mind from the

beginning, and take advantage of simpler, light mass and more efficient components like

a single shaft PTU (see also 3.4.4)

The rear drive module in AWD vehicles is typically mounted in a subframe to isolate

reaction forces and noise paths. Optimized structures can save mass within the rear

suspension module.

3.2.2 Disconnect System

Axle disconnect systems are available for FWD and RWD based vehicle architectures

(see also chapter 1.2.2.4). They are most effective on FWD architectures because they

take out two hypoid sets that are main contributors to parasitic losses. The secondary

driveline also has a dramatically lower overall torque transfer efficiency, again, because

the hypoid sets typically run with 3 – 5% losses each under load. This is addressed by

optimizing AWD engagement strategies and torque levels.

In addition, disconnecting the secondary driveline also eliminates the rotational inertia

effects since the driveline components do not have to be accelerated/decelerated with

the varying vehicle speed. The effects can be described by calculating the ‘Equivalent

Mass’ (see Appendix D). The translational kinetic energy is still there, but the rotational

kinetic energy becomes zero. The vehicle performs as if the equivalent mass would have

been taken out.

Disconnect systems can save up to 4% - 7% in fuel consumption36 /37, depending on

vehicle application and driving conditions. Some lower percentages were given at the

2015 SAE World Congress: 2.4 – 3.3 %38 depending on driving conditions. However, a

sophisticated, fully automated disconnect strategy is required to balance fuel efficiency

with vehicle dynamics, traction and safety requirements in real-life driving. Driver

override options (‘Sport’, Off-road, etc.) can further reduce the actual effectiveness of

disconnect systems.

3.2.3 Downsizing

The torque capacity of secondary drivetrains in FWD based AWD vehicles is a major

factor for increased mass and decreased efficiency. The relative amount of torque

required to drive on snowy surfaces is far lower than that typically provided by the AWD

36 http://articles.sae.org/13610/ 37 http://articles.sae.org/13615/ 38 http://papers.sae.org/2015-01-1099/

108

system. Downsizing therefore provides a high potential for improvements with minimal

impact on overall vehicle performance. Downsizing also reduces cost of the drivetrain

and, with proper algorithms to manage the duty cycle of the secondary drivetrain, has

no negative effect on strength and durability.

3.2.4 Electric Rear Axle Drive (eRAD)

Hybrids are generally known to substantially improve vehicle efficiency, sometimes

doubling the mpg compared to their conventional base vehicles. The eRAD architecture

is actually a simple FWD based vehicle with an added electric drive on the rear axle. It is

perfectly suited for hybridization of vehicles with a FWD architecture, since the electric

part of the drivetrain is independent from the conventional drive in the front (see also

section 1.2.1.3).

Besides providing additional power to overcome added mass, the eRAD is capable of

recuperating brake energy to feed back into the battery and such improve efficiency.

Figure 3-1: Volvo XC90 T8 Hybrid39

39 http://www.volvocars.com/us/cars/new-models/xc90-t8-twin-engine

109

3.3 Component Level

3.3.1 Fuel Efficient (FE) Bearings

Tapered roller bearings (TRB) used in axle drives to support hypoid gear sets are

typically assembled with substantial preload to cope with driveline forces and thermal

expansion. This inevitably leads to significant parasitic losses. Bearing suppliers have

recently addressed this problem by developing technology that greatly improves rolling

resistance and therefore bearing efficiency. One way is to use ball bearings instead of

tapered rollers, in particular angular contact double row ball bearings with different

diameters and ball sizes between the rows to create the tapered effect (Figure 3-2).

Figure 3-2: Angular Contact Double Row Ball Bearing (left) as a Replacement for Tapered Roller Bearings40, Power Loss Comparison (Under Lab Conditions, right)41

The manufacturer claims an improvement of up to 50% in internal friction and up to

1.5% savings in fuel consumption42 when combined with other axle improvements. This

technology comes at a price and has not been implemented throughout the vehicle

lines.

Other bearing manufacturers were able to improve conventional tapered roller bearings

to a point close to the above mentioned, with less cost penalty.

40 http://articles.sae.org/11380/ 41 http://www.schaeffler.com/remotemedien/media/_shared_media/08_media_library/01_publications/schaeffler_2/symposia_1/downloads_11/Schaeffler_Kolloquium_2010_28_en.pdf 42 Schaeffler Group, http://articles.sae.org/11380/

110

Figure 3-3: Substitution of Tapered Roller Bearings (red) with Angular Contact Ball Bearings (blue)43

Figure 3-3 shows an example for the application of FE bearings in a rear axle. Ring &

pinion bearing design calls for pairs of bearings capable of taking high axial and radial

forces in all directions. Significant axial preload needs to be established to keep the

axle’s performance within specifications. In the above illustration pinion bearings show

the innovative tandem design (blue) that can take the high reaction loads, whereas the

ring gear bearings can be angular contact ball bearings (blue) with lower load capacity.

The red bearings show the conventional solution. The required sizes between TRBs and

FE bearings are very similar so the upgrades do not create significant design challenges.

Figure 3-4: Power Loss Distribution between Gears, Bearings and Oil Splash in a Single Stage Axle under Load44

43 http://www.powertransmission.com/issues/0810/pte0810.pdf 44

111

3.3.2 Low Drag Seals

Shaft seals are subject to friction forces between surfaces rotating at different speeds

(or rotating/non rotating surfaces). The ‘tightness’ of a seal is required to provide

sufficient performance through the vehicle life. By optimizing the seal specifications

parasitic losses can be minimized.

Figure 3-5: Low Drag Seal45; Conventional Seal with Garter Spring on the Right Hand Side for Comparison46

Manufacturers may use different design options to design efficient seals. Figure 3-5 shows

a radial shaft seal ring with no garter spring to increase radial seal forces. A 70%

reduction (35W vs. 110W) is claimed in a specific application47 with the same durability

and functionality. For comparison, a conventional seal with garter spring is shown on

the right hand side.

Another way of improving friction performance is to coat the seal lips with a low friction

compound.

3.3.3 Lubrication Strategies

Axles with hypoid sets require special lubricant formulations to provide constant

performance over the lifetime of a vehicle. Axles are typically filled for life48 and do not

require oil changes for a long time.

The viscosity of axle fluids is typically higher than transmission fluids and creates

therefore more parasitic losses. The lubricant level and distribution within the axle is

one specific area where improvements can be made. Lubricant additives to enhance

performance are being developed.

45 http://articles.sae.org/7639/ 46 http://supersprings.biz/garter-springs 47 Freudenberg-NOK; http://articles.sae.org/7639/ 48 ‘Life’ is typically considered to be up to 150,000 miles

112

Recent developments in lubrication strategies have included dry sump systems to

minimize shear losses from driveline parts rotating partially submerged in the oil sump.

A dedicated scavenger pump moves oil from the sump to a separate reservoir and

provides on-demand lubrication for driveline components engaged during AWD

operation.

Figure 3-6 shows a comparison of a standard AWD system and a disconnect system with

a controlled dry sump lubrication system. Significant power savings can be achieved at

vehicle speeds above 40 mph (64 kph).

Figure 3-6: Spin Loss Comparison between Standard and Disconnect AWD Systems49

Chassis dynamometer tests conducted with a baseline AWD driveline and a disconnect

system showed a 3.3% improvement in fuel efficiency in the FTP75 cycle and 2.4% in the

highway cycle due to improvements in windage losses.49

49 SAE 2015-01-1099 ‘Beyond Driveline Disconnect’

113

3.3.4 Advanced CV Joints

Constant Velocity (CV) joints as shown in Figure 3-7 are used in propshafts and half

shafts. CV joints have increased torque losses at the extreme angles experienced during

suspension articulation or, as front axle joints, due to steering. New joint geometry has

been shown to improve the overall performance of the drive shafts. Significantly

improved efficiency comes also with increased strength or reduced packaging size and

mass.

Figure 3-7: Advanced Driveshaft Joint for Reduced Friction and Mass50

3.3.5 Dry Clutch Systems

Dry clutches do not have any drag losses while in the open position, and have been used

in transmissions in many applications. There are no known AWD system applications as

of today.

3.4 Design

3.4.1 Hypoid Offset Optimization

Hypoid gears are designed with an offset between input shaft and output shaft to

balance strength and durability between pinion and ring gear. This offset creates

additional sliding motion between the engaged gear tooth surfaces and thus increased

system friction. Hypoid gear losses under torque can be in the range of 3 – 5% and are

one of the biggest contributing factors to overall driveline efficiency.

50 http://media-centre.gkndriveline.com/drivelinecms/opencms/en/media-centre/news/gkn-news/article_0132.html

114

Figure 3-8: Hypoid Offset

By reducing this offset a compromise needs to be found between efficiency and

strength. Bevel gears with no offset (spiral gears) offer the best efficiency but are not as

strong as hypoids and need to be sized accordingly, giving up some of the advantages by

increasing mass. The need for an offset is reduced as gear ratios get lower (see also

3.4.5).

3.4.2 Non Serviceable Components

Axles and power transfer units are relatively simple and reliable components. This fact

allows for design solutions that eliminate access/assembly covers and bolts by simply

welding the housing parts. The unit becomes non-serviceable, but mass reductions and

a fully automated assembly/welding process justify the move to this technology. One of

the methods used is fully automated friction stir welding.

3.4.3 Bearing Preload Optimization

Tapered bearing preload is a necessity for hypoid assemblies and contributes

significantly to parasitic losses. By carefully designing the components to minimize this

preload in axles and PTUs some efficiency improvements can be achieved. Special care

needs to be given to assemblies with different materials since the thermal expansion

coefficients may be different, such as aluminum housings and steel shafts. The overall

performance of a component becomes highly temperature dependent.

115

3.4.4 Single Shaft Power Transfer Units

Figure 3-9: PTU Architecture; Single Shaft (center), Two Shaft (left) and Three Shaft (right)

The PTU is typically located in an area that does not provide much extra space. Older

AWD vehicles were mostly converted from FWD base vehicles and required

complicated, multi-shaft PTUs to find a way from the front axle to the rear.

As AWD vehicles become more popular, the AWD option has been designed into the

base vehicle already, allowing for a more direct way to transfer torque to the rear axle

via single shaft PTU (Figure 3-9 center). Eliminating additional gears in a PTU saves cost,

mass and improves efficiency.

3.4.5 Propshaft Gear Ratio

Decreasing the propshaft gear ratio allows for better balanced hypoid sets with less

offset and therefore improves efficiency. However, the increased propshaft torque level

requires a heavier propshaft.

Typical axle ratios are between 2.5 and 3 to reduce propshaft torque and mass.

Applications are known to go as low as 1.05 (non-matching numbers of teeth to

minimize noise problems)

116

3.5 Materials

3.5.1 Magnesium Housings

The material of choice for AWD component housings today is aluminum. As an

alternative, magnesium alloys have been proven to provide significant mass savings on

housings when properly designed.51

Magnesium is approximately 30% lighter than aluminum with similar material

properties. The magnesium casting process allows for very thin walled parts in areas

where stresses are low, which opens up design opportunities to save additional mass

and cost without compromising structural integrity.

The surface quality of magnesium parts is superior to aluminum die cast which enables

the use of net formed parts with minimal machining in some applications.

Higher material prices and a more complicated manufacturing process52 have so far

slowed down the more widespread use of magnesium. However, under pressure from

fuel efficiency regulations, several initiatives are under way to promote the use of

magnesium in structural driveline component applications.

A current application for magnesium is housings for transfer cases currently being equipped on

light trucks. The location of the transfer case provides sufficient cooling for operating

temperatures well within the material specifications of magnesium. PTUs and RDMs are typically

designed with very small oil volume and high power density. The consequential elevated

operating temperatures and limited cooling make it difficult to use magnesium in these

applications

51 The old Volkswagen Beetle from the 50’s era had an engine block and a transmission housing made from magnesium 52 Magnesium and especially Mg chips are flammable and need special precautions during machining

117

3.5.2 High Efficiency Lubricants

Small improvements to the efficiency of gear trains can be made by changing the

chemistry of the lubricants with additives aimed at specific problem areas. Better heat

resistance allows for lower base viscosity lubricants.

Figure 3-10: Influence of Lubricants and Temperature on Driveline Torque Losses53

Figure 3-10 shows Torque losses for different lubricants at various temperatures and the

corresponding viscosity. Note that differences in lubricants become very small at the

typical operating temperature of 90˚C and above.

3.6 Manufacturing Process

3.6.1 Vacuum Die Casting

AWD component housing design addresses the need for strength and durability.

However, some areas of a housing are not under stress and do not require increased

wall thickness.

53 http://www.geartechnology.com/issues/0912x/gt0912.pdf

118

Vacuum high pressure die casting processes require a minimum wall thickness to make

sure the dies can be filled properly. New technology in the casting process allows to

reduce the minimum wall thickness and eliminates redundant housing material54.

3.6.2 Hypoid Manufacturing

The gear manufacturing process defines some characteristics of the finished gears. The

typical process used today is hobbing/lapping. The gears are cut and in a finishing

process ‘broken in’ with abrasive lapping paste providing the final surface quality. The

final step is heat treating. Hobbing and lapping is the mainstream manufacturing

process in North America today.

As a newer alternative, gears can be cut, then heat treated and finally precision ground.

This method provides better control over the final surface geometry and can improve

efficiency and NVH performance. European OEMs seem to be more likely to use this

process.

Figure 3-11: Influence of Micro Finishing and Coating on the Friction Coefficient in Gears55

Micro finishing or coating gear sets has been introduced recently as a further

improvement to surface quality and performance, as shown in Figure 3-11. The

coefficient of friction can be lowered significantly with both methods. Differences may

show over the lifetime of the gears as gear surfaces ‘wear in’ and coatings can ‘wear off’

over time.

54 http://articles.sae.org/13615/ 55 http://www.geartechnology.com/issues/0912x/gt0912.pdf

119

3.7 Advanced Engineering / Development Process

3.7.1 AWD Duty Cycle Management

Many AWD systems used in current on-road vehicles are typically dormant until a

traction event or a vehicle dynamic situation requires them to jump into action. The

secondary drivetrain therefore does not have the same requirements in terms of

strength and durability as the main drive does.

AWD control algorithms are capable of limiting the maximum torque and the time of

exposure to the minimum required for proper function and performance. This allows for

light mass secondary drive lines without sacrificing base performance.

3.7.2 Performance Adaptation to Vehicle Variants

AWD systems can be easily designed and tuned to different torque and performance

levels, even within the same family of vehicles. By carefully adapting the system to

vehicle requirements mass and cost savings can be achieved.

3.8 Advanced Operating and Control Strategies

3.8.1 Disconnect strategies

Disconnect strategies contribute significantly to efficiency gains in FWD based AWD

vehicles. More details are given in chapter 1.2.3.

120

3.9 Summary of Efficiency Improvement Potentials

Table 3-1 and Table 3-2 show a summary of the above listed potentials for fuel

efficiency improvements with their direct effects in different areas. The tables are an

estimate generated in peer discussions and should be used to gain an understanding of

the direction each measure is aiming and a rough quantity of gains, losses and

compromises. Fuel efficiency and mass savings were the decisive factors for the

do/don’t columns.

It seems evident that the most effective area of improvements is on the systems level.

Some of the most promising measures are also coming at significant cost and will have

to be looked at from an amortization standpoint as well as efficiency.

Table 3-1: Summary of Efficiency Improvement Potentials

Cost [$] > 100 10 - 100 < 10 < 10 10 - 100 >100

Weight [kg] >2.5 .5 - 2.5 < .5 < .5 .5 - 2.5 >2.5

Fuel Consumption [%] > 2 .5 - 2 < .5 < .5 .5 - 2 >2

Performance [%] > 10 1 - 10 < 1 < 1 1 - 10 > 10

Packaging difficult improved

cost / deterioration savings / improvements

easy

Co

st

We

igh

t

Fue

l Efi

cie

ncy

Pe

rfo

rman

ce

Pac

kagi

ng

Do

it

~ Do

n’t

Disconnect system FWD

Disconnect system RWD

downsizing

eRAD (Hybrid)

FE bearings

Low drag seals

Actuator technology

Lubrication strategies

Advanced CV-joints

Dry clutch systems

Component Level

System Level

121

Many of the listed items contribute only marginally to fuel efficiency. However, if looked

at from a cost per gain perspective, they all add up to some considerable improvements.

OEMs constantly assess the effectiveness of new technology but tend to implement it only

on a step by step basis.

Table 3-2: Summary of Efficiency Improvement Potentials (continued)56

56 * Magnesium housings recommended for transfer cases, more difficult for PTUs and RDMs

Co

st

We

igh

t

Fue

l Efi

cie

ncy

Pe

rfo

rman

ce

Pac

kagi

ng

Do

it

~ Do

n’t

Hypoid offset reduction

Lube level

Friction welded housings

Bearing preload optimization

single shaft PTU

Propshaft gear ratio

Subframe / integrated mount system

MaterialsMagnesium housings *

High efficiency lube

Thin Wall Vacuum Die Casting

Microfinished hypoid gear sets

AWD duty cycle management

Performance adaptation to vehicle variants

Disconnect strategy

Advanced Engineering / Development Process

Advanced Operating and Control Strategies

Design

Manufacturing Process

122

4 Trend Analysis

4.1 The Baseline

4.1.1 Global Vehicle Production

Vehicle production numbers have been in a steady growth in the past years. IHS data

suggests that this trend will last past 2021 in an almost linear fashion, as shown in Figure

4-1. The largest markets, China, Europe and North America are showing solid growth

rates, with China clearly in the lead (Figure 4-2). The most aggressive growth rates can be

found in the South Asia and Africa regions but these regions comprise much smaller

volumes.

Figure 4-1: Global Light Vehicle Production Forecast by Region, total numbers57

57 Source: IHS Data, 2015

123

Figure 4-2: Global Light Vehicle Production Growth between 2014 and 202158

4.1.2 Fuel Consumption

After a long period of stagnation, fuel efficiency as defined by CAFE rules has been

improving dramatically in the last ten years (Figure 4-3). This is true for passenger cars

as well as light trucks. This trend can be expected to keep its momentum, with the

automotive industry successfully taking on the challenge to improve even further.

Figure 4-4 shows the adjusted fuel efficiency for the period between 1975 and 2015.

Adjusted fuel efficiency reflects real world driving and is not comparable to automaker

CAFE standards compliance testing. It is typically about 20% lower than standard values

(‘Window sticker’). However, the same tendency as shown in Figure 4-3 can be seen

here.

AWD vehicles are typically rated about 3 – 7% below the average of all vehicles due to

increased mass and driveline losses, depending on base vehicle architecture and

technology level.

58 Source: IHS Data, 2015

124

Figure 4-3: Average Fuel Efficiency of U.S. Light Duty Vehicles (CAFE)59

Figure 4-4: Adjusted CO2 Emissions (left) and Adjusted Fuel Economy (right) for MY 1975-201560

59 U.S. Department of Transportation, National Highway Traffic Safety Administration, Summary of Fuel Economy Performance (Washington, DC: Annual Issues), available at http://www.nhtsa.gov/fuel-economy as of Mar. 12, 2014. 60 http://www3.epa.gov/otaq/fetrends.htm

mpg

125

One interesting trend is shown in Figure 4-5: Although vehicle mass and horsepower have increased substantially between 1980 and 2015, the adjusted fuel economy has, after a light setback up to 2005, actually got much better in the last decade. This indicates that the automotive industry has been able to overcompensate the generally negative effects of mass and horsepower increase on fuel economy. The turning points came in the mid-eighties when horsepower became decoupled from fuel efficiency, and around 2005 when the prospect of stricter CAFE regulations put in place by legislation (and technology that became available in the last decade) helped increase fuel efficiency without sacrificing performance and driving comfort.

Figure 4-5: Fuel Economy, Horsepower and Mass Changes between 1975 and 201561

AWD technology is following this trend by applying new technology (e.g. driveline

disconnect devices), optimizing components (e.g. bearing technology, mass reduction,

mass optimization) and applying sophisticated control algorithms (e.g. torque limitation,

duty cycle management, aggressive disconnect algorithms).

61 http://www3.epa.gov/otaq/fetrends.htm

126

4.2 Technical Trend Analysis in AWD Research and Development

1.1.1 Technical Trend Analysis in AWD Research and Development

Three major technology trends can be identified:



Electric Rear Axle Drives, (eRAD)

Actively controlled MPC are the dominant technology in AWD driveline systems. Every OEM in

the North American market offers at least one vehicle platform equipped with this technology.

This type of AWD offers great flexibility in terms of torque bias, vehicle dynamics, peak and duty

cycle torque management, vehicle integration (packaging, electronic control system etc.) and

cost control. The system is flexible enough to use a single system design across multiple vehicles

or platforms. It also provides driver selectable automatic modes for different road or

environmental conditions (e.g. sand, rock, snow, etc.) or driving dynamics (e.g. economy, sport,

etc.) within the same software package.

Active AWD disconnect systems are a more recent trend in AWD systems. Driver activated

center axle disconnect devices have been in use in pick-up trucks and full size SUVs for a long

time, preceded by manual locking hubs and similar devices. The current trend favors fully

automated, electronically controlled devices. Their main operating mode is without driver

intervention, although an override option usually exists. The majority of disconnect systems

uses an actively controlled MPC to synchronize the driveline components during engagement

while the vehicle is in motion.

Electric Rear Axle Drives are the latest emerging technology to dramatically improve fuel

economy. This technology is focused on the FWD based vehicle architecture with a transverse

powertrain. Volvo was the most recent entry into the market with the XC90 Hybrid SUV. The

electric rear axle is completely independent from the conventionally powered front axle

(‘through the road hybrid’), and adds additional power and the ability to recuperate energy

during braking. A front end starter/generator enhances front axle drive efficiency. System cost is

currently limiting this application to luxury vehicles and first adopters as customers.

In addition to the three main trends driveline component manufacturers around the

world are honing the performance of their product by applying the latest technologies

to reduce mass and internal friction. Although savings on the individual parts (e.g.

bearings, seals etc.) may seem very small, they all add up to considerable improvements

in fuel efficiency. These items may be considered ‘low hanging fruit’ since they are not

very cost intensive and can in many cases be ‘dropped in’ to existing designs.

127

4.3 AWD Market Trend Analysis

The popularity of CUV/SUV in North America is driving an increase in the adaption of

AWD/4WD systems. Recent data reported by WardsAuto showed a 55.4% of all light

trucks, CUV and SUV were built with AWD or 4WD in 2014, an increase of 8.2% from

2009. As North America is the largest Market for AWD/4WD now and into the future,

forecasts by IHS Automotive predicts a 21% increase in AWD/4WD by 2020, a CAGR of

6.3% from 2014 to 2021.

Figure 4-6: MY 2015 Driveline Architecture Distribution in NA, All Segments62

However, demand is impacted by other regional and economic factors which are shown

in the following charts. As seen in the charts in Figure 4-7 AWD/4WD demand rate are

highest in the Luxury and Utility (Pickup) market segments. Non-CUV and passenger

vehicles have the lowest usage.

62 Pilot Systems, March 2014 CAR & DRIVER, based on IHS data

128

Figure 4-7: AWD Take Rate by Vehicle Segment in MY 201563

Northern and agricultural US regions tend to have the largest adaption rates per capita. The five states with the greatest market share of four-wheel-drive vehicles are also the five with the lowest population densities:

FOUR-WHEEL-DRIVE SALES (%)/POPULATION-DENSITY RANKING:

Alaska: 78/50

Wyoming: 76/49

North Dakota: 76/47

Montana: 72/48

South Dakota: 67/46


129

Figure 4-8: AWD Take Rate [%] by US State, Sorted by Regions, MY 201564

Figure 4-9: AWD Take Rate [%] by State, Sorted by High (AK) to Low (FL) AWD Content64


130

5 AWD System Teardown Analysis

Three vehicles were selected for AWD component teardown analysis:

Ford Fusion

Jeep Cherokee

Volkswagen Tiguan

All three vehicles have a FWD based AWD system architecture with the AWD coupler

incorporated in the rear drive module as shown in Figure 5-1. One of the vehicles, Jeep

Cherokee, includes an AWD disconnect system.

Figure 5-1: AWD System Architecture

The scope of work in this section is to provide the total mass of AWD components,

subsystems and parts and an estimate for the associated rotational inertias for rotating

parts. Total component masses are shown relative to the total vehicle mass. Rotational

inertias are broken down into an equivalent mass to demonstrate the effects of

rotational inertia on vehicle dynamics. Rotational inertias for parts less than 50 grams

are not reported.

Technical aspects of the AWD systems are discussed. In the design analysis section

special enablers for fuel efficiency improvements, mass reductions, packaging

advantages and cost reductions applied in the components are outlined.

Power Transfer Units (PTU) and Rear drive Modules (RDM) were purchased and

disassembled to a level that did not require destructive methods. As a result, some

parts were not separated (e.g. pressed in bearing cups and shims from housings or

131

shafts, vent tubes, etc.). Although the Bill of Materials (BoM) may list these parts they

have no mass associated since it is included in the main part they are attached to.

Actuators and some coupler parts were not completely disassembled and are listed with

their subsystem mass and rotational inertia. Total mass and rotational inertia values are

not compromised by this method.

Lubricants were drained and measured at room temperature. However, not all of the

lubricant can be expected to drain in a teardown operation. The draining process was

considered complete when dripping stopped.

Mass are shown as measured. Small discrepancies between parts mass and the initial

total mass of the AWD components as delivered due to residual lubricant in the coupler

sections, main component sections and measurement rounding errors have been

corrected based on service manual information and estimates.

Unless specifically denoted

Displacements were measured using hand tools (electronic vernier caliper, ruler

etc.) to an accuracy of 0.1 mm

Masses up to 5.7 kg were measured with a Dymo M25-US scale to an accuracy of

+- 5.7 grams (all individual parts after disassembly); Components as received

were measured with a Rubbermaid Model 4010 with an accuracy of +- 1%

Volumes were measured with domestic, kitchen style measuring jugs to an

accuracy of 0.01 L

Rotational inertias are calculated based on measurements made with the

accuracies above

and estimates for complex structures; they are accurate to +- 5%

Equivalent masses are calculated based on measurements made with the

accuracies above

All measurements in SI units unless otherwise indicated

Total incremental mass between 2WD and AWD as listed in the vehicle data also

includes modifications to the vehicle body or subframe, which can be significantly

different from the 2WD version. An example is shown in Figure 5-2. The difference

between the measured AWD components and listed vehicle mass is categorized as

‘Others’ in the mass analysis sections.

132

Figure 5-2: Chassis Integration of an RDM (Ford Fusion)65

The following information is provided:

AWD technology overview

Components o Power Transfer Unit o Propshaft66 o Rear Drive Module o Axle shaftsError!

ookmark not defined.

General component data o Technical data o Rotational inertia o Equivalent mass of

rotating parts

Bill of Materials (BoM) including

o Component o Materials67 o Mass o Rotational inertias

Main parts picture documentation

Design review o Masses & rotational

inertias o Notable design

features

65 Source: Ford Motor Company / Dealerships 66 Propshafts and axle shafts: general data only 67 High level material specs, no detailed analysis performed, only non-ferrous components indicated

133

5.1 Ford Fusion

5.1.1 AWD Technology

The Ford Fusion AWD system is a front wheel drive based on-demand system with an

active in-line AWD coupler in the Rear Drive Module (RDM). The coupler is electro-

magnetically activated and controlled via remote AWD Electronic Control Unit (ECU). It

does not have a driveline disconnect system.

5.1.1.1 AWD Coupler

The internals of the AWD coupler are shown in Figure 5-3. There are six main

components:

Electro-magnetic coil

Electro-magnetic control clutch

Cam mechanism to augment the control torque

Main clutch transferring the rear drive torque

Input case connecting to the propshaft

Output shaft connecting to the rear differential

Figure 5-3: Ford Fusion AWD Coupler68/69

68 http://eb-cat.ds-navi.co.jp/enu/jtekt/tech/eb/catalog/img/pdf/catd1002ex.pdf 69 Not an exact cross section of the Ford fusion AWD coupler, balloons refer to coupler BoM in Table 5-6

134

The electro-magnetic coil is stationary; the other five components rotate at propshaft

speed.

Figure 5-4 shows the operating principle of the clutch. In the left image the current is off

and the clutch plates are separated, not transferring torque. In the right image coil

current creates magnetic flux which pulls the armature and compresses the control clutch.

The torque generated in the control clutch activates the cam mechanism and creates

the compression force for the main clutch. The drive torque to the rear wheels is

transferred through the main clutch. The amount of torque is determined by the current

in the magnetic coil and can be controlled between zero (open clutch) and maximum

torque per AWD algorithms in the ECU.

Figure 5-4: Electro-magnetic Clutch - Operating Principle70

5.1.1.2 AWD Control Logic

A high level look at the control logic is given in Figure 5-5. The basic control module

consists of six main parts:

Road surface condition judgment is based on wheel speed sensors, accelerometer

inputs and yaw sensors. This is the main module that controls slip between front

and rear wheels.

Drivetrain system input torque control translates the torque request from the

control module into the corresponding electric current in the coil.

70 http://eb-cat.ds-navi.co.jp/enu/jtekt/tech/eb/catalog/img/pdf/catd1002ex.pdf

135

Driveline vibration / noise reduction provides a compromise between vehicle

dynamics, traction and noise/vibration in the driveline by selecting optimal

operating points in the system

Highly accurate control is required to have quick system response and accurate

torque bias between front and rear wheels according to the driving situation.

Driving mode judgment decides whether to run in automatic mode or respond to

the driver selected override mode.

Coordinate with other electronically controlled devices: ABS and vehicle dynamic

control are higher in the vehicle control system hierarchy. The AWD control

system needs to work with the boundary conditions given by those systems and

create an integrated torque transfer strategy.

Overheat protection (detail): AWD couplers have limited heat capacity. If worked

hard the temperature limits may be reached. First line of defense is to go to

maximum torque, if driving situation allows, to limit heat generation in the

slipping clutch. If that does not work or is not applicable due to vehicle driving

situations the system reverts into 2WD mode. A cool-off period is required before

going back into full AWD mode.

This high level description of an AWD control logic is valid for most on-demand AWD

systems controls and, with some variations, has been adopted by most OEMs.

Figure 5-5: Ford Fusion AWD Basic Control Logic71

71 http://eb-cat.ds-navi.co.jp/enu/jtekt/tech/eb/catalog/img/pdf/catd1002ex.pdf

136

5.1.2 Power Transfer Unit

Mass72 [kg] 12.2

BoM mass summation (% difference) [kg] 12.1 (1%)

Lubricant73 [L] 0.450

Gear tooth count (ring/pinion) 31/11

Gear ratio 2.818

Gear manufacturing process Hobbed/lapped

Mass of rotating parts [kg] 7.287

Total rotational inertia input shaft [kg.m2] 9.041e-03

Total rotational inertia output shaft [kg.m2] 3.48e-03

Dynamic tire radius [m] 0.334

Equivalent mass of rotational inertias [kg] 0.329

Equivalent mass factor74 1.027 Table 5-1: Ford Fusion Power Transfer Unit – Technical Data

72 As received, Includes lubricant 73 Nominal, per service information 74 See section 11 Appendix D

137

Figure 5-6: Ford Fusion Power Transfer Unit75

Ford Fusion Power Transfer Unit - Bill of Materials

Name Material76 Qty Mass Rotational inertia

[kg] [kg.m2]

1 Output flange nut 1 0.064 25e-05

2 Output flange 1 0.852 1.38e-03

3 Deflector Syn 1 0.010

4 Transfer case rear seal Syn/Mix 1 0.044

5 Outer output shaft tapered roller bearing 1 0.233 2.59e-04

6 Outer output shaft shim 1 0.006

7 Input Shaft Seal LH Syn/Mix 1 0.020

8 Transfer case vent77 1

9 PTU housing Al 1 3.240

10 Input shaft 1 3.632 8.30e-03

11 Input shaft bushing Syn 1 0.006

12 Input shaft outer bearing 1 0.198 3.22e-03

13 Input shaft outer bearing shim 1

14 O-ring cover seal Syn 1 0.006

15 PTU cover Al 1 0.882

16 PTU cover bolts (.010 ea) 9 0.090

17 Intermediate shaft seal Syn/Mix 1 0.056

18 PTU fill plug 1 0.018

19 Input shaft seal RH Syn/Mix 1 0.030

20 Output shaft 1 1.735 1.16e-03

21 Inner output shaft tapered roller bearingError! Bookmark not defined. bearingError! Bookmark not defined.

1 0.397 6.53e-04

22 Inner output shaft shim 1

23 PTU drain plug 1 0.028

24 Face seal Syn/Mix 1 0.004

25 Input shaft inner bearing 1 0.176 4.19e-04

26 Input shaft inner bearing shim 1

27 Lubricant (415 ml) Lub. 0.354

Table 5-2: Ford Fusion Power Transfer Unit, Bill of Material rotating parts [input]/[output]

75 Source: Ford Motor Company / Dealerships 76 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub. – lubricant, no indication - steel 77 Unspecified masses included in housings

138

Figure 5-7: Ford Fusion Power Transfer Unit - Parts

139

Figure 5-8: Ford Fusion PTU, Top View

Figure 5-9: Ford Fusion PTU Input Shaft Figure 5-10: Ford Fusion PTU Output Shaft

140

Figure 5-11: Ford Fusion PTU, Output Shaft with Pinion in Main Housing

141

5.1.3 Propshaft, Axles78

Propshaft

Mass [kg] 9.5

Total rotational inertia [kg.m2] 7.556e-03

Equivalent mass [kg] 0.537

Equivalent mass factor 1.057

Left Axle Shaft

Mass [kg] 6.0




Right Axle Shaft

Mass [kg] 6.0



Equivalent mass factor 1.008 Table 5-3: Ford Fusion Propshaft/Axle Technical Data79

78 Inertias and equivalent mass are estimates based on mass and design features 79 Masses are from similar Escape AWD system

142

5.1.4 Rear Drive Module

Mass80 [kg] 26.1

BoM mass summation (% difference) [kg] 25.8 (1.2%)

Lubricant main81 [L] 1.15

Lubricant Coupler [L] 0.28


Gear ratio 2.818







Equivalent mass factor 1.040 Table 5-4: Ford Fusion Rear Drive Module – Technical Data

Figure 5-12: Ford Fusion Rear Drive Module82

80 As received, Includes lubricant 81 Nominal, per service information 82 Source: Ford Motor Company / Dealerships

143

Ford Fusion Rear Drive Module - Bill of Materials

ID Part Name Mat’l83 Qty Mass Rotational

inertia

kg Kg.m2

1 RDM housing Al 4.096

2 drain plug 0.018

3 fill plug 0.016

4 companion flange bolt 0.034

5 companion flange 1.180 1.26E-03

6 companion flange washer 0.082 3.28E-05

7 rock shield Syn 0.012

8 seal, AWD coupler cover Syn 0.040

9 retaining clip, AWD coupler cover 0.014

10 outer bearing, AWD coupler cover 0.280 1.12E-04

11 shim, outer bearing AWD coupler cover 0.004

12 button screw, torx for AWD coupler cover (0.018 ea.) 4 0.072

13 AWD coupler cover Al 1.064

14 AWD coupler stub shaft 0.980 1.01E-03

15 oval head countersunk screw, torx for stub shaft (0.02 ea.) 4 0.080

16 AWD coupler assembly Steel/Mix 5.014 9.77E-03

17 race bearing, AWD coupler output 0.094 6.19E-05

18 AWD coupler coil Syn/Mix 0.272

19 AWD coupler yoke 0.392

20 AWD coupler snap ring 0.004

21 button screw, torx for AWD coupler yoke (0.004 ea.) 3 0.012

22 pinion gear 1.656 6.28E-04

23 seal, for pinion gear Syn 0.072

24 nut, for pinion gear 0.050

25 inner ball bearing for pinion gear 0.204 5.18E-05

26 outer ball bearing for pinion gear 0.234 5.94E-05

27 crush sleeve 0.046 1.50E-05

28 cover, for differential housing Al 1.888

29 Large hexagon flange screw for cover (0.074 ea.) 4 0.296

30 small hexagon flange screw for cover (0.002 ea.) 5 0.100

31 drain plug for cover 0.026

32 ring gear 1.840 6.79E-03

33 hexagon flange screw, for ring gear (0.022 ea.) 10 0.220 9.50E-04

34 differential case 3.134 5.05E-03

35 tapered bearing v2 side of differential case 0.230 1.06E-04

83 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub. – lubricant, no indication - steel

144

36 tapered bearing v4 side of differential case 0.230 1.06E-04

37 shim side gear V2 side 0.012

38 side gear 0.228 8.57E-05

39 shim side gear V4 side 0.012

40 side gear 0.228 8.57E-05

41 shim pinion gear V1 side 0.004

42 pinion gear 0.114 6.57E-05

43 shim pinion gear V3 side 0.004

44 pinion gear 0.114 6.57E-05

45 differential pinion gear cross shaft 0.140 1.03E-04

46 Half shaft seal, V2 side 0.094

47 inner half shaft race cup V2 side 0.126

48 shim for inner half shaft race cup V2 side 0.078

49 Half shaft seal, V4 side 0.096

50 inner half shaft race cup V4 side 0.126

51 shim for inner half shaft race cup V4 side 0.074

52 Lubricant, main case (440 ml) Lub. 0.366 Table 5-5: Ford Fusion Rear Drive Module, Bill of Material rotating parts [input]/[output]

145

Figure 5-13: Ford Fusion Rear Drive Module - Parts

146

Figure 5-14: Ford Fusion Rear Drive Module

Figure 5-15: Ford Fusion Rear Axle Differential Assembly

147

Figure 5-16: Ford Fusion Rear Axle Assembly: Pinion in the Center Part [1] of the 3-piece Housing

Figure 5-17: Ford Fusion AWD Coupler Assembly

148

5.1.4.1 Ford Fusion AWD Coupler

Ford Fusion AWD Coupler – Bill of Materials

ID Part Name Material84 Qty Mass

kg

1 Input case Al 0.978

2 Rear housing 1.410

3 O-ring cover Syn 0.002

4 retainer clip for inside parts 0.010

5 output shaft 0.670

6 retainer clip for race bearing bottom 0.002

7 race bearing for bottom of shaft 0.106

8 shim for top race bearing 0.008

9 race bearing for top 0.016

10 control cam 0.074

11 cam balls (0.002 ea.) 6 0.012

12 control clutch reaction plates (0.026 ea.) 2 0.052

13 control clutch friction plate 0.022

14 Armature 0.160

15 Main cam 0.282

16 Friction plates (0.038 ea.) 12 0.456

17 Reaction plates (0.046 ea.) 12 0.552

18 Lubricant, coupler (170 ml) Lub. 0.124 Table 5-6: Ford Fusion AWD Coupler, Bill of Materials85 rotating parts [input]/[output]

84 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel 85 Inertias included in RDM BoM

149

Figure 5-18: Ford Fusion AWD Coupler, Control Clutch and Ball Ramp Mechanism

Figure 5-19: Ford Fusion AWD Coupler, Input Case

150

Figure 5-20: Ford Fusion AWD Coupler Control Clutch Plates

Figure 5-21: Ford Fusion Main Clutch Plates

151

Figure 5-22: Ford Fusion AWD Coupler - Parts

152

5.1.5 Mass & Rotational inertia Analysis

Figure 5-23: Ford Fusion AWD Mass Analysis86/87

Ford Fusion AWD adds 72 kg or 4.5% to the 2WD base vehicle. Figure 5-23 on the right

hand side indicates contribution of the added parts. Equivalent mass based on

rotational inertias and gear ratios is shown in Figure 5-24 below.

Figure 5-24: Ford Fusion Equivalent Mass Analysis

86 Source: Vehicle mass: Dealer website, AWD components measured 87 The category ‘other’ includes any parts not directly related to driveline components (e.g. body structure reinforcements etc.)

153

Table 5-7: Ford Fusion Mass Distribution Analysis

The front axle carries 12.55 kg more mass on top of the added AWD components

(category ‘other’), most likely due to variations in driveline components (Transmission

and front drive shafts).

Most of the AWD rear axle mass increase over FWD is due to the added AWD

components

88 Reported mass of TC FWD/AWD model variants 89 AWD components measurements 90 Split 50/50 between front and rear 91 The category ‘other’ represents the difference in mass between the FWD model plus added AWD parts and the AWD model

Mass [kg]

Total front rear

FWD88 1612 956 656

AW

D

add

ed

par

ts8

9 PTU 12.2 12.2

Propshaft90 8.5 4.25 4.25

RDM 26.1 26.1

Halfshafts 12.0 12.0

Other91 13.2 12.55 0.65

AWD110 1684 985 699

154

5.1.6 Design Analysis

5.1.6.1 Power Transfer Unit (PTU)

The vehicle has a very compact and lightweight single shaft PTU. The ring gear on the

input shaft is laser welded as shown in the pictures below. This design feature saves

more than 1 kg in structural mass compared to a bolt-on solution.

Figure 5-25: Ford Fusion PTU Laser Welded Ring Gear

155

5.1.6.2 Rear Drive Module (RDM)

The RDM has a three piece housing with a rarely seen axial split line as shown in Figure

5-26.

The picture also shows the ring gear that is bolted to the differential case. This design is

heavier than laser welded solutions and requires a more complex assembly process. The

unit shown below carries the same torque as the one in Figure 5-25. More material is

required on the back side of the ring gear to provide sufficient thread depth for the ring

gear bolts.

The differential bearings are conventional tapered roller bearings.

Figure 5-26: Ford Fusion Rear Axle Differential

156

Figure 5-27 shows the rear axle pinion. The pinion bearings are a pair of high efficiency

tandem ball bearings (only one shown here). Preload is determined by the size of the

crush sleeve between the bearings, which is a more cost efficient and robust design

compared to shimming.

Figure 5-27: Ford Fusion Rear Axle Pinion with High Efficiency Tandem Ball Bearings

5.1.6.3 AWD Coupler

The Ford Fusion AWD coupler is a cost effective, completely sealed unit with very little

lubricant content and limited external cooling. The advantage of compact size may be

offset by making thermal management difficult because of lack of heat sink capacity and

cooling circuit.

The unit input case that holds the outer multi plate clutch elements (Figure 5-28 is made

from aluminum for mass saving, with a steel flange bolted to it on the input side to

provide the necessary torque capacity. The rear housing is threaded and permanently

secured by pins. The advantage of the electro-magnetic actuator is that there is no active

mechanical element outside the coupler housing.

157

Figure 5-28: Ford Fusion AWD coupler - Input Case Detail

158

5.2 Jeep Cherokee


The Jeep Cherokee AWD system is a front wheel drive based on-demand system with an

active parallel AWD coupler in the Rear Drive Module (RDM). The coupler is electro-

hydraulically activated and controlled via remote AWD Electronic Control Unit (ECU). It

also features a driveline disconnect system.

5.2.1.1 AWD Coupler

Figure 5-29 shows the hydraulic system schematics: An electro-hydraulic actuator

(basically a hydraulic pump driven by an electric motor) pressurizes the high pressure

circuit and activates the piston in the hydraulic module.

Figure 5-29: Jeep Cherokee AWD Hydraulic System

159

The Cherokee coupler is completely integrated in the RDM as a result of the unique

architecture. Lubrication circuits are separated by a sealed hydraulic system body and

cover on the right hand side of the RDM (see Figure 5-30). The parallel arrangement

requires the AWD coupler to carry full axle torque, which subsequently increases the

size of the multi plate clutch.

The AWD coupler acts also as the rear disconnect device and is responsible for

synchronizing the driveline during the AWD reengagement process.

Torque is transferred through the transfer shaft into the differential cage and is split

between left and right in the differential.

Figure 5-30: Jeep Cherokee AWD Coupler92

92 ‘AAM EcoTrac™ Disconnecting AWD’, CTi USA 2013

160

5.2.1.2 Disconnect System

The system consists of the electro-mechanically activated PTU disconnect (see also

Figure 5-35) and the electro-hydraulically activated AWD coupler in the RDM. In 2WD

mode the entire rear driveline between the two hypoid sets, including the hypoids, is at

standstill.

Engagement/disengagement is controlled by the electronic control unit (ECU). ECU

algorithms are networking with vehicle sensors and controls (e.g. ABS, brake traction

control or vehicle dynamic controls).

At low speeds AWD is always engaged to be ready for high acceleration in 1st gear. The

disengagement sequence proceeds as follows:

1) Disengage AWD coupler to relieve driveline torque

2) Disengage shift sleeve in the PTU

3) AWD coupler goes into low drag mode to allow the driveline to come to a

complete standstill

In case the control system senses the need to reengage, the order of actions is reversed:

1) The AWD coupler engages very dynamically to synchronize the driveline to

match speed on both sides of the shift clutch in the PTU

2) As soon as synchronization speed is established the shift sleeve is activated

and connects the input shaft with the primary shaft (Figure 5-31). Small

speed differences at the shift sleeve can be tolerated without creating noise

or structural problems. The reconnect process takes normally about 300

milliseconds.

Figure 5-31: Jeep Cherokee PTU Disconnect Cross-section, Shift Fork Actuator Module on the Right

161

The added mass for the Jeep Cherokee disconnect system is 0.6 kg in the PTU and 8.6

kg93 for the RDM. However, the RDM includes mass to accommodate a potential low

gear option. Disconnect without that option could be achieved at much lower mass.

Basic AWD torque control follows the example shown in section 5.1.1 for the Ford

system.

5.2.2 Power Transfer Unit (PTU)

Mass94 [kg] 22.6



Gear tooth count (helical1/helical2, ring/pinion) 38/33 29/13

Gear ratio (helical1/helical2, ring/pinion, total) 1.152 / 2.231 /2.570




Total rotational inertia secondary shaft [kg.m2] 6.42e-03




Equivalent mass factor 1.006 Table 5-8: Jeep Cherokee Power Transfer Unit – Technical Data

93 ‘AAM EcoTrac™ Disconnecting AWD’, CTi USA 2013 94 As received, includes lubricant 95 Nominal, per service information

162

Figure 5-32: Jeep Cherokee Power Transfer Unit96

Figure 5-32 shows a cross section of the single speed PTU for the standard version,

viewed from the front. The input from the transmission is via the hollow input shaft that

carries the front axle disconnect shift sleeve. A helical gear set drives the secondary

shaft that carries the hypoid ring gear. The hypoid pinion gear drives the propshaft to

the rear axle.

Note: The front axle intermediate shaft connects the front differential side gear (not

shown) to the right hand front wheel and is not part of the AWD system.

Jeep Cherokee Power Transfer Unit – Bill of Materials

ID Part Name Mat'l97 Qty Mass Rotational

inertia

kg Kg.m2

1 PTU Body; with inner & outer race cups for output Al 4.890

2 screw, short 6 point with shoulder 0.004

2 screw, long 6 point with shoulder (0.008 ea.) 3 0.024

3 shift module Steel/Mix 0.930

4 c-clip, output pinion V3 side 0.002

5 deflector , output V3 0.092 0.00E+00

96 AAM EcoTrac™ Disconnecting AWD’, CTi USA 2013 97 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel

163

5 seal, output V3 Syn/Mix 0.054

6 O-ring, output V3 0.000

7 cover, V4 side Al 2.348

8 fill plug 0.044

9 flat ring seal Syn/Mix 0.010

10 seal, in cover Syn/Mix 0.014

11 screw, 6 point flange & washer for cover (0.016 ea.) 12 0.192

12 pinion gear with portion of tapered race bearing 1.736 5.35E-04

13 inner tapered race bearing pieces for pinion98 0.142 7.04E-05

14 outer race bearing for pinion 0.230 8.54E-05

15 sleeve shim for pinion 0.032

16 nut to pinion 0.640 2.51E-05

17 intermediate shaft99 1.714 2.50E-04

18 retaining clip V2 side drive 0.002

19 1st retaining clip v4 side drive 0.016

20 2nd retaining clip v4 side drive 0.004

21 Intermediate shaft output bearing (sealed)99 0.180 9.87E-05

22 ring gear assembly with pinion intermediate gear 3.778 6.18E-03

23 shim v2 side ring gear 0.006

24 race cup v2 side ring gear 0.064

25 tapered race bearing v2 side ring gear 0.128 7.20E-05

26 shim v4 side ring gear 0.008

27 race cup v4 side ring gear 0.108

28 tapered race bearing v4 side ring gear 0.260 1.66E-04

29 Primary shaft 2.698 3.28E-03

30 race cup v2 side shift intermediate gear 0.112

31 tapered race bearing v2 side shift intermediate gear 0.190 1.69E-04

32 shim for cup v4 side shift intermediate gear 0.010

33 race cup v4 side shift intermediate gear 0.108

34 tapered race bearing v4 side shift intermediate gear 0.262 1.66E-04

35 shift gear 0.624 3.56E-04

36 shift gear sleeve 0.240 3.45E-04

37 shift gear race bearing 0.080 4.00E-05

38 shift gear seal Syn/Mix 0.018

39 Lubricant (540 ml) Lub. 0.430 Table 5-9: Jeep Cherokee Power Transfer Unit, Bill of Material rotating parts [input]/intermediate/[output]

98 All tapered roller bearings w/o cup 99 Not part of AWD driveline

164

Figure 5-33: Jeep Cherokee Power Transfer Unit - Parts

165

Figure 5-34: Jeep Cherokee PTU Assembly, Shift Actuator (black)

Figure 5-35: Jeep Cherokee PTU, View of Input Shaft and Primary Shaft (w/ Shift Sleeve, Actuator Removed)

166

Figure 5-36: Jeep Cherokee PTU, View of Helical Gear Stage, Primary Shaft (large) and Secondary Shaft (small)

Figure 5-37: Jeep Cherokee PTU, Primary Shaft (left) and Secondary Shaft (right)

167

Figure 5-38: Jeep Cherokee PTU, Pinion

5.2.3 Propshaft & Axles100

Propshaft

Mass [kg] 13.1




Left Axle Shaft

Mass [kg] 8.3




Right Axle Shaft

Mass [kg] 8.5


Equivalent mass [kg] .055

Equivalent mass factor 1.007 Table 5-10: Jeep Cherokee Propshaft/Axle Technical Data

100 Inertias and equivalent mass are estimates based on mass and design features

168

5.2.4 Rear Drive Module (RDM)

Mass101 [kg] 33.1


Lubricant, main case102 [L] 0.8

Lubricant, AWD coupler [L] 0.4


Gear ratio 2.733







Equivalent mass factor 1.012 Table 5-11: Jeep Cherokee Rear Drive Module – Technical Data

Figure 5-39: Jeep Cherokee Rear Drive Module

101 As received, Includes lubricant 102 Nominal, per service information

169

Figure 5-39 shows a cross section of the single speed RDM. The pinion drives the hypoid

ring gear, and via a spline connection the inner friction plate carrier of the TTD. The

actuator provides hydraulic pressure to modulate torque transfer in the TTD. The outer

friction plate carrier is driving the rear axle differential via hollow shaft.

The TTD acts as the rear axle disconnect. By opening the gaps between the friction

plates wide enough it reduces drag in the clutch pack and allows the secondary driveline

to come to a complete standstill while the vehicle is driving at speed.

Jeep Cherokee Rear Drive Module – Bill of Materials

ID Part Name Mat'l103 Qty Mass

Rotational inertia

kg Kg.m2


2 housing fill plug 0.046

3 input flange 1.028 1.18E-03

4 input coupler nut 0.052 1.70E-05

5 input coupler washer 0.018 0.00E+00

5 input flinger 0.090 1.08E-04

6 seal, input coupler Syn/Mix 0.042

7 cap screw, Allen for oil reservoir cover (0.003 ea.) 4 0.012

8 oil reservoir cover Syn/Mix 0.202

9 oil reservoir gasket Syn 0.020

10 cap screw, Allen for pump assembly 0.018

11 actuator assembly Steel/Mix 1.200

12 pinion 1.420 4.28E-04

13 shim for inner bearing pinion gear 0.004

14 Inner tapered roller bearing for pinion104 0.232 7.31E-05

15 Outer tapered roller bearing for pinion 0.208 6.55E-05

16 crush sleeve 0.092 3.12E-05

17 clutch cover Al 1.522

18 hexagon flange screw for cover (0.005 ea.) 9 0.450

19 hexagon flange screw for cover (o.032 ea.) 2 0.640

20 output flinger 0.060 1.08E-04

21 seal V4 output Syn/Mix 0.040

103 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel 104 All tapered roller bearings w/o cup

170

22 V4 output O-ring Syn 0.000

23 V4 output shaft c-clip 0.002

24 Hydraulic system body Al 2.970

25 oil pressure sensor 0.020

26 oil pressure port plug, torx #30 0.004

27 drain plug under pump 0.014

28 drain plug above pump 0.014

29 shim, for clutch body race cup 0.010

330 race cup, for clutch body 0.112

31 Tapered roller bearing, for ring gear 0.190 1.75E-04

32 hexagon flange screw, for clutch body (0.032 ea.) 4 0.128

33 seal , flat ring ; between housing and clutch housing Syn/Mix 0.012

34 output shaft, V4 1.940 2.43E-04

35 transfer shaft 1.222 4.82E-04

36 ball bearing, for transfer shaft 0.248 1.09E-04

37 clutch thrust bearing 0.172 6.91E-04

38 clutch thrust bearing 0.172 6.91E-04

39 clutch assembly

39.1 Clutch Cage 1.708 8.10E-03

39.2 Clutch plates 1.610 8.18E-03

39.3 Hub 0.760 1.56E-03

39.4 Retaining ring105 0.00E00

39.5 Springs106 3 0.00E00

40 ring gear 4.128 1.18E-02

41 V4 output shaft c-clip, inside 0.002

42 inside c-clip, v2 shaft 0.002

43 outside c-clip, v2 shaft 0.002

44 O-ring V2 side Syn 0.000

45 v2 output shaft 0.850 1.26E-04

46 Housing insert Al 0.312

47 shim, inside plate 0.008

48 race cup, inside plate 0.112

49 tapered roller bearing, ring gear 0.188 1.75E-04

50 retainer clip output V2 side 0.002

51 seal, output V2 side 0.040

52 output flinger 0.060 1.08E-04

53 retainer clip for differential bearing V2 side 0.004

54 race bearing for differential V2 side 0.106 3.00E-05

105 Included in clutch pack 106 Included in cage

171

55 differential case 1.812 2.10E-03

56 shim side gear V2 side 0.006 0.00E+00

57 side gear 0.220 1.23E-04

58 shim side gear V4 side 0.006 0.00E+00

59 side gear 0.218 1.23E-04

60 shim pinion gear V1 side 0.004 0.00E+00

61 differential pinion 0.106 5.07E-04

62 shim pinion gear V3 side 0.004 0.00E+00


64 differential small gear pin & c-clip 0.162 1.28E-04

65 Lubricant, main case (400 ml) Lub. 0.314

66 Lubricant, AWD coupler (140 ml) Lub. 0.102

Table 5-12: Jeep Cherokee Rear Drive Module, Bill of Materials rotating parts [input]/[output]

172

Figure 5-40: Jeep Cherokee Rear Drive Module - Parts

173

Figure 5-41: Jeep Cherokee RDM, Top View with Actuator and Oil Reservoir Cover

Figure 5-42: Jeep Cherokee RDM, Hydraulic System Body with Ring Gear and Clutch Pack

174

Figure 5-43: Jeep Cherokee RDM, Pinion with inner TRB and Crush Sleeve

Figure 5-44: Jeep Cherokee RDM, Ring Gear

175

Figure 5-45: Transfer Shaft with Ball Bearing

Figure 5-46: Jeep Cherokee RDM, Differential

176

5.2.4.1 Jeep Cherokee AWD Coupler

Figure 5-47: Jeep Cherokee AWD Coupler107 - Parts

107 Parts list included in main BoM

177

Figure 5-48: Jeep Cherokee Clutch Assembly, Hydraulic System Body, and Transfer Shaft Ball Bearing

Figure 5-49: Jeep Cherokee AWD Coupler, Outer (left) and Inner (right) Plate, Reaction Side

178

Figure 5-50: Jeep Cherokee RDM, Outer (left) and Inner (right) Plate, Friction Side

179


Figure 5-51: Jeep Cherokee Mass Analysis108/109

Jeep Cherokee AWD adds 135 kg or 8.1% to the 2WD base vehicle. Figure 5-51 on the right hand side indicates the contribution of the added parts. Equivalent mass based on rotational inertias and gear ratios is shown in Figure 5-52.

Figure 5-52: Jeep Cherokee Equivalent Mass Analysis

108 Source: Vehicle mass: Dealer website, AWD components measured 109 The category ‘other’ includes any parts not directly related to driveline components (e.g. body structure reinforcements, etc.)

180

Table 5-13: Jeep Cherokee Mass Distribution Analysis

Table 5-13 shows a comparison of FWD and AWD vehicle mass distribution between

front and rear.

The negative value in the category ‘other’ for the front axle load represents FWD parts

taken off and replaced by AWD parts (transmission cover, intermediate shaft etc.) and

minor design changes to the front structure.

The AWD rear axle carries 56.6 kg more structural mass than FWD (category ‘other’),

representing rear axle subframe and suspension changes and structural reinforcements

to the body.


Mass [kg]

Total front rear

FWD110 1677 998 679

AW

D

add

ed

par

ts1

11 PTU 22.6 22.6

Propshaft112 13.1 6.55 6.55

RDM 33.1 33.1


Other113 49.4 -7.15 56.55

AWD110 1812 1020 792

181


5.2.6.1 Power Transfer Unit

The PTU is a two shaft design, most likely driven by packaging constraints, that adds

mass to the overall drivetrain.

The ring gear on the secondary shaft is laser welded, as shown in Figure 5-53.

Figure 5-53: Jeep Cherokee PTU, Laser Welded Ring Gear

182

5.2.6.2 Rear drive Module

The RDM features a laser welded ring gear with the weld seam very close to the outside

diameter of the ring gear, which is beneficial from a structural perspective (Figure 5-54).

Figure 5-54: Jeep Cherokee RDM Ring Gear Laser Weld

The hydraulic system body has a built-in strainer that eliminates the need for an

external oil filter, as shown in Figure 5-55.

Figure 5-55: Jeep Cherokee Hydraulic System Body with Integrated Strainer

183

5.2.6.3 AWD Coupler

The AWD coupler is very efficiently designed as a module, with a pre-assembled multi

plate clutch assembly that plugs right into the hydraulic body (Figure 5-56).

Figure 5-56: Jeep Cherokee AWD Clutch Assembly

The Jeep Cherokee coupler features a unique clutch plate design with every plate

carrying friction material on one side and acting as a smooth reaction plate on the other

side, as shown in Figure 5-57. This design may improve the performance of the multi

plate clutch pack as a heat sink and help with peak temperature management.

The clutch plates also have an approximately 50% larger diameter, compared to Ford

Fusion and VW Tiguan, to carry the design axle torque and allow for geometrical

integration.

184

Figure 5-57: Jeep Cherokee AWD Inner and Outer Clutch Plates, Friction Side on the left, Reaction side on the right

185

5.3 Volkswagen Tiguan


The Volkswagen Tiguan AWD system is a front wheel drive based on-demand system

with an active in-line AWD coupler in the Rear Drive Module (RDM). The coupler is

electro-hydraulically activated and controlled via integrated AWD Electronic Control

Unit (ECU). It does not have a driveline disconnect system.

Figure 5-58: Volkswagen Tiguan / Haldex Gen IV Hydraulic System

Figure 5-58 shows the hydraulic system schematics: An electrically driven axial piston

pump draws oil from a reservoir and delivers it into the high pressure system. An

accumulator stores energy and a check valve prevents high pressure from bleeding back

into the reservoir when the pump is not running.

A solenoid controlled by the AWD ECU is proportioning the pressure delivered to the

multi plate clutch according to the torque level requested by the control algorithms.

186

The systems described above are combined into an add-on module to the RDM. Tight

packaging is shown in Figure 5-59.

Figure 5-59: Volkswagen Tiguan AWD Coupler – Haldex Gen IV114

The AWD coupler module is produced by BorgWarner under the Haldex brand (Haldex

Gen IV). For model year 2017 Tiguan Volkswagen is moving to a Gen V system, which

basically eliminates the accumulator and the solenoid but has the same functionality. In

Gen V the clutch pressure is controlled via a patented combination of an axial piston

pump and a unique ‘centrifugal pressure control valve’.115 Cost and mass savings have

been achieved with the transition to the Gen V system.

Basic AWD torque control follows the example shown in section 5.1.1 for the Ford

system.

114 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf 115 https://www.youtube.com/watch?v=CDRVTjMPK9Q

187


Mass116 [kg] 17.5


Lubricant117 [L] 0.9


Gear ratio 1.588

Gear manufacturing process Face milled/ground







Table 5-14: Volkswagen Tiguan Power Transfer Unit – Technical Data

Figure 5-60: Volkswagen Tiguan Power Transfer Unit118

116 Includes lubricant 117 Nominal, per service information 118 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf

188

Table 5-15: Volkswagen Tiguan Power Transfer Unit, Bill of Material rotating parts [input]/[output]

119 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel 120 Not part of the AWD drivetrain 121 Mass included in PTU housing

Volkswagen Tiguan Power Transfer Unit – Bill of Materials


inertia

kg Kg.m2

1 PTU housing Al 3.920

2 Bolt, hex hd with shoulder (0.009 ea.) 4 0.036

3 seal Syn/Mix 0.050

4 seal bolt (combination) (0.004 ea.) 2 0.008

5 double collared stud 0.046

6 cap for transmission breather Syn

7 sealing cap Syn

8 seal G Syn/Mix 0.014


10 O-ring Syn 0.000

11 cover Al 0.586

12 Screw, hex. Hd. (0.003 ea.) 6 0.018


14 flange 0.798 9.54E-04

15 hex nut 0.066 1.70E-05

16 Intermediate shaft120 1.702

17 lock ring 0.000

18 O-ring Syn 0.000

19 needle sleeve 0.026

20 needle sleeve 0.026

21 circlip 0.000

22 lock ring 0.000

23 V4 side cover Al 1.636

24 O-ring for V4 side cover Syn 0.000

25 65 mm hex nut 0.144 1.20E-04

26 outer shim V4 side 0.030

27 outer bearing V4 0.254 1.60E-04

28 inner bearing V4 0.254 1.60E-04

29 Hollow shaft with ring gear 4.044 8.76E-03

30 output pinion gear 2.344 2.27E-03

31 outer shim for pinion 0.016

32 pinion tail bearing 0.200 1.10E-04

33 pinion head bearing 0.160 5.18E-05

34 Pinion nose bearing121 3.00E-05

35 Lubricant (850 ml) Lub. 0.704

189

Figure 5-61: Volkswagen Tiguan Power Transfer Unit - Parts

190

Figure 5-62: VW Tiguan PTU, Top View

Figure 5-63: VW Tiguan Ring Gear (left) and Pinion (right)

191

5.3.3 Propshaft & Axles122

Propshaft

Mass [kg] 11.4




Left Axle Shaft

Mass [kg] 6.2




Right Axle Shaft

Mass [kg] 6.4




Table 5-16: Volkswagen Tiguan Propshaft/Axle Technical Data

122 Inertias and equivalent mass are estimates based on mass and design features

192


Mass123 [kg] 35.6



Lubricant coupler [L] 0.7


Gear ratio 1.588

Gear manufacturing process Face milled/ground






Equivalent mass factor 1.008 Table 5-17: Volkswagen Tiguan Rear Drive Module – Technical Data

Figure 5-64: Volkswagen Tiguan Rear drive Module125

123 Includes lubricant 124 Nominal, per service information 125 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf

193

Table 5-18: Volkswagen Tiguan Rear Drive Module, Bill of Materials rotating parts [input]/[output]

126 Materials code: Al – Aluminum, Syn – Synthetics, Mix – several different materials, lub – lubricant, no indication - steel

Volkswagen Tiguan Rear Drive Module – Bill of Materials


inertia

kg Kg.m2


2 housing drain screw 0.026

3 input flange 0.560 6.52E-04

4 input flange nut 0.040 0.00E+00

5 input flinger Syn 0.020 0.00E+00

6 hex flange bolt for module (0.008 ea.) 2 0.016

7 AWD control module Syn/Mix 0.204

8 Actuator Steel/Mix 1.000

9 hex flange bolt for pump 0.008

9 hex flange bolt for pump 0.008

10 clutch assembly 4.832 4.58E-03

11 hexagon flange screw (0.044 ea.) 4 0.176

12 retain clip for outer bearing pinion gear 0.008

13 shim for outer bearing pinion gear 0.030

14 Outer tapered roller bearing for pinion127 0.164 6.12E-05

15 Inner tapered roller bearing for pinion 0.388 2.21E-04

16 pinion gear 3.408 2.26E-03

17 RDM cover Al 3.524

18 drain plug for cover (0.008 ea.) 3 0.024

19 Screw, hex. hd. for cover (0.036 ea.) 12 0.432

20 output flange V2 side with c-clip 1.218 1.12E-03

21 seal V2 side Syn/Mix 0.030

22 outer tapered bearing V2 side 0.286 2.18E-04

23 output flange V4 side with c-clip 1.888 1.58E-03

24 seal V4 side Syn/Mix 0.030

25 outer tapered bearing V4 side 0.198 1.08E-04

26 differential case w ring gear 5.578 9.66E-03

27 differential inner gear shim 0.018

28 side gear 0.418 2.19E-04

29 side gear 0.418 2.19E-04



32 differential cross shaft 0.218 2.33E-04

33 shear pin for differential small gear pin 0.000

34 Lubricant main case (840 ml) Lub. 0.698

35 Lubricant AWD Coupler (1000 ml) Lub. 0.792

194

Figure 5-65: Volkswagen Tiguan Rear Drive Module - Parts

127 All tapered roller bearings w/o cup

195

Figure 5-66: VW Tiguan RDM, Top View

Figure 5-67: VW Tiguan Ring Gear (left) and Pinion (right)

Parting line

196

Figure 5-68: VW Tiguan RDM, AWD Coupler Module with Multi Plate Clutch Assembly and Actuator

5.3.4.1 AWD Coupler

Volkswagen Tiguan AWD Coupler – Bill of Materials

ID Part Name Qty Mass

kg

1 housing 1.330

2 seal 0.018

3 retainer clip 0.008

4 thrust bearing housing side 0.094

5 thrust bearing plate holder side 0.094

6 Hub 1.030

7 ball bearing gear shaft 0.110

8 cage 0.886

9 Thrust plate128 0.152

10 friction plate (0.05 ea.) 13 0.650

11 reaction plate (0.034 ea.) 12 0.408 Table 5-19: Volkswagen Tiguan AWD Coupler rotating parts [input]/[output]

128 End side thrust plate same size as reaction plates

197

Figure 5-69: Volkswagen Tiguan AWD Coupler129/130

129 http://www.freel2.com/gallery/albums/userpics/11383/tiguan_haldex_gen4.pdf 130 Piston and spring plate are part of the housing and are not listed in the coupler BoM

198

Figure 5-70: Volkswagen Tiguan AWD Coupler - Parts

Figure 5-71: VW Tiguan AWD Coupler Assembly

199

Figure 5-72: VW Tiguan AWD Coupler, Cage (left), Multi Plate Clutch and Hub (right)

200

Figure 5-73: VW Tiguan AWD Coupler, Outer (left) and Inner (right) Plate

201


Figure 5-74: Volkswagen Tiguan Mass Analysis131/132

VW Tiguan AWD adds 78 kg or 5.0% to the 2WD base vehicle. The right hand image in

Figure 5-74 details mass contributions. Equivalent mass based on rotational inertias and

gear ratios is shown in Figure 5-75 below.

Figure 5-75: Volkswagen Tiguan Equivalent Mass Analysis

131 Source: Vehicle mass: Dealer website, AWD components measured 132 The category ‘other’ includes any parts not directly related to driveline components (e.g. body structure reinforcements, etc.)

202

Table 5-20: Volkswagen Tiguan Mass Distribution Analysis

Except for 0.9 kg all of the added mass is due to AWD driveline components


Mass [kg]

Total front rear

FWD133 1550 910 640

AW

D

add

ed

par

ts1

34 PTU 17.5 17.5

Propshaft135 11.4 5.7 5.7

RDM 35.6 35.6


Other136 0.9 -1.2 2.1

AWD110 1628 932 696

203


5.3.6.1 Power Transfer Unit

The VW Tiguan PTU is a single stage unit with a laser welded ring gear, as shown in

Figure 5-76.

Figure 5-76: VW Tiguan PTU – Laser Welded ring Gear

204

5.3.6.2 Rear drive Unit

The Tiguan RDM features a laser welded ring gear.

Figure 5-77: VW Tiguan RDM, Ring Gear/Differential Case Laser Welding

Figure 5-78: VW Tiguan RDM Pinion

The pinion appears to have a unique bearing arrangement. The inner tapered roller bearing is leaning against a thrust bearing on the back side of the pinion to take up axial load. This might aid in reducing parasitic losses due to bearing preload in the pinion setup.

205

5.3.6.3 AWD Coupler

Figure 5-79: VW Tiguan AWD Coupler, Friction and Reaction Plates

The MY 2015 Tiguan has a Haldex Gen IV AWD coupler. Friction plates, as shown in

Figure 5-79, have dual sided sinter metal coated friction plates and smooth reaction

plates.

Figure 5-80: VW Tiguan AWD Coupler Hub

The coupler hub features lubrication paths to aid oil flow through the multi plate clutch

and support thermal management of the AWD system (Figure 5-80).

206

Figure 5-81: VW Tiguan AWD Coupler Cage

The Tiguan AWD coupler cage is a very cost and mass effective net formed steel part

with minimal machining.

207

6 Disconnect System Cost Analysis

Cost analysis in this section is based on Pilot System’s expert knowledge and peer

discussions and is considered directional. No purchasing activities or forensic cost

analyses have been performed.

Production volumes, technology content and market conditions may vary significantly

and lead to different cost structures.

Cost as indicated in this section is considered to be a mix of Direct Manufacturing Cost

(DMC) for parts made in-house by a tier 1 supplier and, where applicable, purchasing

cost for parts and subsystems from a tier 1 supplier perspective. These costs do not

include engineering recovery, initial tooling cost, investment for capital equipment and

tier 1 profit and SG&A. Depending on the percentage of vertical integration for a tier 1

supplier the additional margin can range from 25 – 40 % up to the final selling price to

an OEM. For comparison purpose In the tables below the incremental cost to the OEM

was calculated with 25% cost added to the tier 1 cost.

All costing has been done on an incremental basis compared to an actual or conceptual

non-disconnect system.

208

6.1 Jeep Cherokee

The Jeep Cherokee AWD system has been designed with the intent of adding a low gear

option for the Trailhawk™ version. Due to the FWD based drivetrain the PTU and RDM

architectures had to be capable of supporting the standard version and the addition of a

planetary gear reduction for Trailhawk™.

Figure 6-1: Jeep Cherokee AWD Configuration

Although the PTU cost is not significantly increased, the RDM should be seen as a

compromise between cost and the flexibility of including a low gear option.

Considerable complexity has been added by adopting a parallel RDM architecture rather

than a half-shaft disconnect (see also section 1.3.5). Figure 6-1 shows the driveline

architecture of the Jeep Cherokee Sport (standard version).

There is no non-disconnect version of this drivetrain available, so cost estimates are

based on design assumptions rather than direct comparisons.

Total AWD Disconnect system cost of $150.00 US includes PTU and RDM adaptations. A

cost breakdown is given in the following sections. Although midsize crossover vehicles

are among the best selling vehicles in today’s market, because of the specific

requirements for the low gear option this should not be considered a mainstream

example of an AWD disconnect system.

209


Major changes to the PTU include splitting the primary shaft (into primary and input

shaft) to provide for a disconnect point and adding the shift mechanics/mechatronics

(shift sleeve and smart linear actuator). The case had to be designed to house the

additional elements and allow access for the actuator, as shown in Figure 6-2.

Figure 6-2: Jeep Cherokee PTU, Bottom Front View137

Incremental cost estimates total $86.00 US, with a breakdown shown in Table 6-1. The major cost additions are the shift actuator and mechanism. Additional

mechanical changes and assembly procedure adjustments are minor.


210

Jeep Cherokee PTU Component Add/change Cost

Actuator assembly Add smart actuator $ 60

Input shaft / Primary shaft Split up primary shaft, add shift tooth profile & bearing

$ 17

Shift sleeve Add $ 5

Housing Added volume to house disconnect mechanism $ 1

Assembly Added complexity $ 3

Total $ 86

Total cost to OEM $ 107 Table 6-1: Jeep Cherokee AWD Disconnect Incremental Cost estimate – PTU


The RDM is designed to accommodate a planetary gear set offering a low gear option. A

parallel coupler arrangement (see also section 1.3.5) has therefore been chosen. In this

RDM architecture the AWD coupler has to carry the entire axle torque (as opposed to

in-line, which carries axle torque divided by the axle ratio, or a half shaft disconnect that

carries only half the axle torque due to balancing across the differential). This requires

significantly increased coupler torque capacity and consequently size.

Additional complexity is added with the ring gear and transfer shafts, as shown in Figure

6-3, and resized ball bearings to accommodate larger shaft diameters and increased

reaction forces.

Estimated incremental cost totals $64.00 US, with a breakdown shown in Table 6-2. Major contributors are the shafts and the increased AWD coupler capacity.

The AWD coupler’s actuation subsystem does not require significant modifications and

therefore contributes only marginally to the cost of the disconnect system.

211

Figure 6-3: Jeep Cherokee RDM138

Jeep Cherokee RDM Component Add/Change Cost

Ring gear shaft Add $ 15

Increased size of AWD coupler

Change, needs full axle torque capacity $ 12

Larger housing for hydraulic system

Change $ 1

Transfer shaft Add, 2 splines, 2 bearing journals, length $ 18

Increase complexity of output shaft

Asymmetrical design $ 8

2 Ball bearings for differential and transfer shaft

Added size compared to in-line design $ 4

Complex assembly process $ 6

Total $ 64

Total cost to OEM $ 80 Table 6-2: Jeep Cherokee AWD Disconnect Incremental Cost estimate - RDM


212

6.2 Alternative Disconnect Systems

6.2.1 Side Shaft Disconnect

One very cost efficient RDM option to provide full AWD disconnect capabilities is the

rear half-shaft disconnect as shown in Figure 6-4. The AWD coupler still needs to be

upgraded to half the axle torque (as opposed to an inline coupler that carries only axle

torque divided by the axle ratio). With this solution the differential side gears will spin in

opposite directions, but the ring and pinion as the main contributors to parasitic losses

would be at standstill while the vehicle is in motion and the system is in disconnect

mode.

Total incremental system cost (assuming the use of a Cherokee type PTU disconnect

system) would be $93.00 US.

Figure 6-4: Side Shaft Disconnect, Parallel System in the Background for Comparison

Side Shaft Disconnect Component Add/Change Cost

PTU Disconnect Add 86

Increased size of AWD coupler

Change, needs half axle torque capacity $ 7

Total $ 93

Total cost to OEM $ 116 Table 6-3: AWD Disconnect Incremental Cost Estimate – Side Shaft Disconnect

213

6.2.2 Front Axle Center Disconnect

Front axle center disconnect is used for RWD based vehicles. Frontrunners were the

light duty trucks, with passenger cars following recently. Figure 6-5 shows the system

used in the Chrysler 300 (see also section 1.2.2.5). It basically splits up the left hand half-

shaft between the cross-shaft, as shown in the figure, and the actual half-shaft driving

the LH wheel. A simple shift sleeve solution was chosen, since the AWD coupler in the

transfer case is providing synchronization of the front drivetrain in order to enable

reconnect without driveline clunk or damage to the clutch components. The cross shaft

reaches through the structural engine oil pan to connect with the front axle located on

the RH side of the engine and is part of the original AWD system.

Figure 6-5: Front End Center Disconnect (Chrysler 300)139

The system is very cost effective since the only parts added are the front end disconnect unit and minimal modifications to the transfer case to allow for ‘wide open’ mode to reduce drag in the multi plate clutch. The fact that Chrysler 300 moved from a mechanical center differential transfer case to an on-demand unit was not considered part of the incremental cost since this follows a trend away from permanent AWD to on-demand independently from the increased use of disconnect systems.

139 Source: http://www.magna.com/capabilities/powertrain-systems/products-services/driveline-systems and Warn Industries


214

The cost breakdown is shown in Table 6-4 below. The AWD coupler in the transfer case needs to be adjusted to allow for ‘wide – open’ mode. No significant cost should be expected with that modification.

Front Axle Center Disconnect Component Add/Change Cost

Actuator Add $ 60

Housing Add $ 15

Shaft modifications, shift sleeve, bearing, assembly etc.

Add/modify $ 20

Transfer case modify $ 1

Total $ 97

Total cost to OEM $ 121 Table 6-4: Front End Center Incremental Disconnect Cost Estimate

6.2.3 Others

The dual clutch RDM architecture (as shown in the Range Rover Evoque in section 1.3.5)

has not been included in this cost assessment. The system basically eliminates a

mechanical differential and adds a second clutch, with all cost associated with an active

coupler system. Increased cost compared to a more basic disconnect system may be

offset by added functionality since the pair of clutches provides limited slip capabilities

across the rear axle and some limited torque vectoring. These features are provided in

most vehicles by brake traction control to a comparable level.

215

7 Summary and Conclusions

7.1 AWD/4WD Systems and Components

7.1.1 Current and Future AWD Systems

AWD systems have been classified by SAE in Standard J1952, most recently updated in October 2013. There are three basic types of systems as shown in Table 7-1. Some vehicles also have combinations of the below listed types that are driver

selectable. Trucks and SUVs for example can have a 2WD normal operating mode (2Hi), an on-

demand AWD mode (4AUTO) and with a fully locked transfer case a non-synchro 4WD mode

(4Hi).

Figure 7-1: AWD System Classification per SAE J1952 (Oct 2013) Standard

AWD system architecture is not included in the SAE classification. Figure 7-2 shows a lineup of

characteristic AWD system architectures:

The FWD based systems are by far the most prevalent, mainly because of the dominance of

FWD base vehicles. Added components are the Power Transfer Unit (PTU), the Rear Drive

Module (RDM), propshafts and halfshafts, an Electronic Control Unit (ECU) and modifications to

the rear suspension and subframe.

The RWD based systems are typically found in large and luxury cars and in light trucks and full

size SUVs. Added components are a transfer case, a front axle, the front propshaft, a modified

rear propshaft and an ECU.

Recently some OEMs have introduced a front wheel drive based hybrid AWD system using an

electrical Rear Axle Drive (eRAD). One example is the Volvo XC90, introduced in early 2016. This


capable

Longitudinal

speed

differentiation

capable

Longitudinal

torque

distribution

mode

Torque

modulation

System Designation










Part Time

(PT)

Full Time

(FT)

On-Demand

(OD)

n/a Yesvariable

yes yes variable

216

architecture is currently only a niche product since the added component cost make the vehicle

expensive. Enablers for a more widespread use of hybrid technology would be cost reductions in

components due to higher volumes and advances in battery and power electronics technology,

or a dramatically changed economic environment.

Electric AWD, as introduced by Tesla in their Model S, should be considered exotic at this time.

Further development in the battery sector might pave the way for purely electric propulsion.

Figure 7-2: AWD System Architecture: (1) FWD based; (2) RWD based; (3) FWD based, through the Road PHEV; (4) Electric

1 2 3 4

217

7.1.2 Component and System Function

On-Demand Systems – The Torque Transfer Device (TTD)

The core element in an on-demand driveline is the TTD, also known as AWD coupler. Passive

systems (e.g. viscous couplers, gerotor couplers et.) have been replaced in the past decade with

active systems capable of electronically controlling torque flow between the front and rear axle.

Active units can be of 4 different types with similar functionality:

hydraulic

electro-hydraulic

electro-mechanic

electro-magnetic

The electro-magnetic system is contained in a completely sealed unit and is controlled via a

stationary electric coil. Torque is generated in a control clutch by magnetic flux. A ball cam

mechanism augments the control torque and pressurizes the multi plate clutch to transfer

driveline torque to the axles.

Figure 7-3: Active AWD Coupler Systems: Electro-magnetic (left), Electro-hydraulic (right)140

Due to its modular design and the lack of an active hydraulic system this type of AWD coupler is

very cost effective. However, the small lubricant volume and limited heat exchange make it

challenging to manage the unit’s temperature under demanding driving conditions. The system

reverts to 2WD mode if temperature limits are reached. That makes this type of AWD coupler

more attractive to smaller vehicles without off-road capability.

140 Source: www.borgwarner.com

218

Electro-hydraulic AWD couplers are used in all vehicle segments. They can be sized to handle

high torque and extended use by increasing the lubricant volume and provide extra cooling by

designing oil reservoirs with cooling fins.

Electro-mechanic actuators use a mechanical cam or gear mechanism to apply axial pressure to

a multi plate clutch. Due to packaging constraints this type of actuator is mainly found in

transfer cases. It is very robust and can handle driveline torque levels typically found in light

trucks and SUVs.

Full Time Systems

Full time AWD systems feature a center differential to distribute torque between the front and

rear axle permanently with a preset torque bias. An active or passive locking device may be

added to improve the traction potential of the system.

Full time systems are taking advantage of sophisticated Brake Traction Control (BTC) systems.

BTC offers a very cost effective way of maintaining traction in adverse conditions by using the

brake system and with specific control logics to keep wheel slip within dynamic limits.

AWD Disconnect Systems

Disconnect systems (shown in Figure 7-4 for a FWD based AWD system) have two main

components: the front axle disconnect and an AWD coupler that acts as an axle disconnect

device and also as a synchronizer to allow reengagement while the vehicle is in motion.

Figure 7-4: AWD Disconnect System Schematic

219

The engagement/disengagement sequences are controlled via Electronic Control Unit (ECU) and

in most applications do not require driver intervention (trucks and SUVs are an exception). The

driver can override the controls and dial in continuous on-demand operation. Automatic control

draws information from the vehicle sensors and reacts on vehicle dynamic status and

environmental conditions (e.g. ambient temperature, etc.).

1.1.2 Comparative Assessment of Positives and Negatives

This chapter provides a snapshot of positive and negative effects of vehicle architecture and

AWD system characteristic with respect to efficiency and performance.

The facts & features are color coded for positive or negative effects as follows;

FWD based AWD

RWD based AWD

Very efficient base architecture due to lack of hypoid gears

Not as efficient base architecture as FWD

Secondary drivetrain is very inefficient due to two hypoid sets, high use of AWD drives total efficiency down significantly

Front drivetrain has nearly the same efficiency as rear, permanent use has little negative effect on efficiency

Packaging allows for hybridization by adding an independent electric rear axle

Typically offers more torque capacity

Active coupler technology enables driveline downsizing by limiting peak torque and managing duty cycles in the secondary driveline

Table 7-1: FWD/RWD Architecture Positives and Negatives

220

Full Time

On-Demand

Superior vehicle handling potential Handling compromise at low speed if RWD based (torque oversteer)

No torque management devices necessary if used with Brake Traction Control (BTC)

AWD coupler (passive or active) required to manage torque transfer

Proven mechanical torque biasing devices work well with BTC

Electronic Limited Slip Differentials (eLSD) provide additional flexibility

Always transfers torque across at least one less efficient hypoid set

Primary driveline is highly efficient (FWD based vehicles)

Always transfers torque across a less efficient hypoid set (RWD based vehicle)

No downsizing because of permanent torque transfer; driveline sizing needs to account for biasing devices

Active coupler technology enables driveline downsizing by limiting peak torque and managing duty cycles in the secondary driveline Driveline sizing based on torque split if

used with BTC only

2WD vehicle dynamics characteristics can be preserved (understeer for FWD, oversteer for RWD)

Table 7-2: Full Time vs. On-Demand AWD Positives and Negatives

221

7.2 AWD Vehicles by Make & Model

7.2.1 The North American AWD Vehicle Market – Overview

In this report all major vehicle manufacturers that offer AWD vehicles in the North

American Market are captured.

Table 7-1 lists the OEMs with their platform structure and number of nameplates.

Table 7-3: AWD Market Overview; AWD Systems per OEM and Number of Platforms/Nameplates141/142

The most prevalent AWD system is the on-demand system with offerings from all OEMs. This

includes FWD and RWD based vehicle architectures, with most of the systems being active

electronic control AWD systems. This type of AWD offers great flexibility in terms of torque bias,

vehicle dynamics, peak and duty cycle torque management, vehicle integration (packaging,

electronic control system etc.) and cost control.

141 Niche vehicles and models with small sales volumes not included 142 (FCA) – Fiat Chrysler Automobili; (GM) – General Motors; (JLR) – Jaguar – Land Rover; (VW) - Volkswagen

Platforms Nameplates Platforms Nameplates Platforms Nameplates

Total 5 9 15 27 57 140

Audi 3 8 2 3

BMW 8 17

Daimler 6 13 1 4

FCA 1 2 1 1 7 11

Ford 1 1 4 16

GM 1 1 8 23

Honda 4 10

Hyundai 2 7

JLR 2 2 3 6

Mazda 3 3

Mitsubishi 1 2

Nissan 6 16

Subaru 1 6

Tesla 1 1

Toyota 2 5 2 2 1 4

VW 1 1 2 3

Volvo 3 8

Part Time Full Time On-Demand

222

The field of full time systems is dominated by Audi and Daimler Benz, both of which rely heavily

on this type. Daimler Benz vehicles are predominantly RWD based, whereas Audi builds on a

longitudinal FWD platform. While Daimler Benz relies solely on BTC, Audi offers a torque

sensitive center differential with asymmetric torque bias to further enhance the tractive

potential and vehicle dynamics.

Audi has just introduced an on-demand system as a replacement for their full time systems. The

extent of this change is not known as of today.

Part time systems, also known as 4WD systems, are mainly found in dedicated off-road vehicles,

like Jeep Wrangler, or work trucks as an entry model. Part time systems require driver

intervention to select the appropriate driving mode. Although they provide great traction they

are not supposed to be driven in 4WD mode on surfaces with high friction coefficients (e.g. dry

pavement).

223

7.2.2 Fuel Consumption and Vehicle Mass Data

Added mass and increased torque and parasitic losses result in an increase of fuel consumption

for AWD vehicles. The following charts are based on EPA’s annually published fuel efficiency

estimates for city, highway and combined cycles. The left hand column shows the increase of

fuel consumption over the added mass from the AWD components. The fact that the data points

are scattered over a broad band indicates that mass is not the only factor for the increase of fuel

consumption, although the trend lines follow a common pattern.

The right hand side shows fuel consumption over total vehicle mass. The trend lines are

comparable with the AWD-only data.

Figure 7-5: Increase of Fuel Consumption over AWD Mass Increase (LH Column of Charts) Compared to the Total Fuel

Consumption over Vehicle Mass for a Selection of AWD Vehicles [the Red Dot Indicates Vehicles with AWD Disconnect]143

143 Source: http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf; dealer websites

224

It is interesting to note that vehicles with AWD disconnect (red dotted in the left hand

charts) do not show any improvements over conventional drivetrains. EPA test

procedures capture spin losses in an AWD drivetrain during coastdown; however,

torque related losses in the secondary driveline are not measured. Testing of

electronically controlled AWD systems on a chassis dyno in fully active mode would be

complicated.

7.3 AWD Efficiency Improvement Potentials

The documentation of efficiency improvement potentials was broken down into

System level

Component level

Design

Materials

Manufacturing Process

Advanced engineering/development process

Advanced operating and control strategies The following sections cover the more influential measures to improve driveline efficiency and

performance.

7.3.1 System Level

Architecture

AWD systems have traditionally been seen as add-ons to existing platforms which required

compromises in design and packaging of components. More recent vehicles have been designed

with the AWD option in mind from the beginning and take advantage of simpler, light mass and

more efficient components like a single shaft PTU (see also 3.4.4). The difference between a

single shaft PTU and a 2-shaft PTU can be shown by comparing Ford Fusion and Jeep Cherokee

PTUs:

Jeep Cherokee (2-shaft): 22.6 kg

Discount for disconnect system: 144 -0.6 kg

Ford Fusion (single shaft): 12.20 kg

Net Difference: 9.8 kg

Savings can also be achieved with the integration of the Rear Drive Module (RDM) into the rear

axle subframe.

144 Jeep Cherokee has an AWD disconnect system, which adds 0.6 kg to the base mass of the PTU

225

Disconnect System

The AWD disconnect systems can reduce total fuel consumption by 2.4 – 7%145 depending on

driving conditions. However, a sophisticated, fully automated disconnect strategy is required to

balance fuel efficiency with vehicle dynamics, traction and safety requirements in real-life

driving. Driver override options (‘Sport’, ‘Off-road’, etc.) can further reduce the actual

effectiveness of disconnect systems.

Downsizing

The torque capacity of secondary drivetrains in FWD based AWD vehicles is a major

factor for increased mass and decreased efficiency. The relative amount of torque

required to drive on snowy surfaces is far lower than what is typically provided by the

AWD system. Downsizing therefore provides a high potential for improvements with

minimal impact on overall vehicle performance. Downsizing also reduces drivetrain cost

and, with proper algorithms to manage the duty cycle of the secondary drivetrain, has

no negative effect on strength and durability.

Electric Rear Axle Drive (eRAD)

The eRAD carries probably the biggest potential for reducing overall fuel consumption.

The effectiveness largely depends on the size of the battery in a plug-in hybrid

configuration and the individual mission profile. The system would be most effective in

urban driving with frequent recharging stops.

Sales volumes of the several systems on the market have been disappointing partly

explained by the high price for this type of system.

7.3.2 Component Level and Design

On the component level many small improvements in bearing technology, seals, shaft joints and

lubrication strategies add up to measurable savings in fuel consumption.

Design optimizations on hypoid offset and bearing preload have the potential to further improve

efficiency.

145 http://articles.sae.org/13610/; http://articles.sae.org/13615/; http://papers.sae.org/2015-01-1099/

http://articles.sae.org/13610/

http://articles.sae.org/13615/

http://papers.sae.org/2015-01-1099/

226

7.3.3 Materials

The material of choice for AWD component housings today is aluminum (Al). As an alternative,

magnesium (Mg) alloys have been proven to provide significant mass savings on housings when

properly designed.146

In the AWD drivetrain transfer cases would be prime candidates and Rear Drive Modules (RDMs)

could be potential candidates for the application of magnesium alloys147. The following example

assumes an average mass savings of 30% compared to an aluminum housing:

Table 7-4: Mass Comparison between Aluminum and Magnesium on an RDM148

Under the above assumptions a mass savings of 2kg, which is 8.1% of the total RDM mass or

0.12% of the total vehicle mass, could be achieved.

Another area of potential improvements is the formulation of lubricants. Friction enhancing

additives can significantly improve parasitic losses, especially at temperatures below the normal

operating range of 90 - 120° C.

7.3.4 Manufacturing Process

Two areas in manufacturing appear to offer a good potential for mass savings and efficiency

improvements:

Aluminum die cast processes have been refined such that very thin walled sections can be cast

in areas with low stress. Vacuum high pressure die casting is an example.

Certain applications allow for squeeze casting, where partially molten aluminum is forced into a

die. The result is a high strength aluminum part with minimal porosity.

On the component side, hypoid manufacturing has been improved: ground (vs. hobbed &

lapped) gears promise advantages in efficiency and noise performance. Coatings and micro

finished surfaces can improve friction parameters and result in highly efficient gear sets.

146 The old Volkswagen Beetle from the 50’s era had an engine block and a transmission housing made from magnesium 147 PTUs have a very high power density and limited external cooling due to the proximity to transmission, engine block and the exhaust system and should not be considered ideal for a conversion to magnesium 148 Estimate only; for accurate results design changes need to be considered

Ford Fusion RDM Component Al Mass [kg] Mg Mass [kg] Savings [kg]

RDM housing 4.096 2.867 1.229

AWD coupler cover 1.064 0.745 0.319

Differential cover 1.888 1.322 0.566

Total 7.048 4.934 2.114

227

7.3.5 Summary of Efficiency Improvement Potentials

The biggest gains in efficiency and mass loss can be achieved on system level:

Highly integrated components (e.g. single shaft PTUs) can reduce system mass

significantly and, as an added benefit, reduce cost and improve driveline

efficiency.

Disconnect systems eliminate AWD driveline parasitic losses during times when

AWD is not needed. Real world efficiency depends highly on the engagement

algorithms and driving conditions.

On the high end, hybrid and electric systems can provide a breakthrough in overall

system efficiency. Vehicle pricing has so far proven prohibitive and widespread

use of this type of vehicles remains dependent on cost reductions and changes in

the economic environment.

228

7.4 Trend Analysis

7.4.1 Technical Trend Analysis in AWD Research and Development

Three major technology trends can be identified:



Electric Rear Axle Drives, (eRAD) Actively controlled MPC are the dominant technology in AWD driveline systems. Every OEM in

the North American market offers at least one vehicle platform equipped with this technology.

This type of AWD offers great flexibility in terms of torque bias, vehicle dynamics, peak and duty

cycle torque management, vehicle integration (packaging, electronic control system etc.) and

cost control.

Active AWD disconnect systems are a more recent trend in AWD systems. Driver activated

center axle disconnect devices have been in use in pick-up trucks and full size SUVs for a long

time, preceded by manual locking hubs and similar devices. The current trend favors fully

automated, electronically controlled devices. Their main operating mode is without driver

intervention, although an override option usually exists.

Electric Rear Axle Drives are the latest emerging technology to dramatically improve fuel

economy. Volvo was the most recent entry into the market with the XC90 Hybrid SUV. The

electric rear axle is completely independent from the conventionally powered front axle, and

adds additional power and the ability to recuperate energy during braking. A front end

starter/generator enhances front axle drive efficiency. System cost is currently limiting this

application to luxury vehicles and first adopters as customers.

7.4.2 AWD Market Trend Analysis

Figure 7-6: MY 2015 Driveline Architecture Distribution in NA, All Segments149


229

The popularity of CUV/SUV in North America is driving an increase in the adaption of AWD/4WD

systems. About one third of all vehicles sold in North America in 2015 were AWD. The AWD take

rate varies extremely between vehicle segments and equipment levels. Sedans throughout the

segments are the least likely to be sold with an AWD system. In the SUV and pick-up segments

AWD outnumber 2WD drivelines, with the luxury vehicles having the highest take rate in their

respective segments.

Regional differences in the USA are also very distinctive, with northern and rural states having

the largest percentage of AWD vehicles (Figure 7-7). This fact suggests similar Canadian trends.

Figure 7-7: AWD Take Rate [%] by State, Sorted by High (AK) to Low (FL) AWD150


230

7.5 AWD System Teardown Analysis

Three vehicles were selected for AWD component teardown analysis:

Ford Fusion

Jeep Cherokee

Volkswagen Tiguan

All three vehicles have a FWD based AWD system architecture with the AWD coupler

incorporated in the rear drive module as shown in Figure 5-1. One of the vehicles, Jeep

Cherokee, includes an AWD disconnect system.

Figure 7-8: AWD System Architecture

Power Transfer Units (PTU) and Rear drive Modules (RDM) were purchased and disassembled to

a level that did not require destructive methods. The following tables and charts compare

component data and analysis results.

231

7.5.1 Component Data Comparison

151 As received, Includes lubricant 152 Nominal, per service handbook

PTU Ford Jeep VW

Mass151 [kg] 12.2 22.6 17.5

Lubricant152 [L] 0.450 0.700 0.900

Gear tooth count 31/11 38/33 29/13 27/17

Gear ratio 2.818 1.152 + 2.231 /2.735

1.588

Gear cutting process Hobbed / lapped

Hobbed / lapped

Milled / ground

Mass of rotating parts [kg] 7.287 11.008 9.966

Total rotational inertia input shaft

[kg.m2] 9.041e-03 4.36e-03 9.20e-03

Total rotational inertia secondary shaft

6.42e-03

Total rotational inertia output shaft

[kg.m2] 3.48e-03 7.16e-04 3.59e-03

Dynamic tire radius [m] 0.334 0.362 0.343

Equivalent mass of rotational inertias

[kg] 0.329 0.111 0.152

Equivalent mass factor 1.027 1.005 1.009

RDM

Mass151 [kg] 26.1 33.1 35.6

Lubricant main152 [L] 1.15 0.800 0.900

Lubricant Coupler152 [L] 0.28 0.400 0.700

Gear tooth count (ring/pinion)

31/11 41/15 27/17

Gear ratio 2.818 2.733 1.588

Gear cutting process Hobbed / lapped

Hobbed / lapped

Milled / ground

Mass of rotating parts [kg] 16.002 19.2 19.946

Total rotational inertia input shaft

[kg.m2] 1.30e-02 2.07e-03 7.77e-03

Total rotational inertia output shaft

[kg.m2] 1.34e-02 3.56e-02 1.36e-02


[kg] 1.046 0.389 0.282


232

Table 7-5: Component Data Comparison (notable differences highlighted)

Propshafts Ford Jeep VW

Mass [kg] 9.5 13.1 11.4

Rotational Inertia [kg.m2] 7.556e-03 1.043e-02 9.083e-03


[kg] 0.537 0.595 0.195


Halfshafts

left

Mass [kg] 6.0 8.3 6.2



[kg] 0.046 0.055 0.046


right

Mass [kg] 6.0 8.5 6.4



[kg] 0.046 .055 0.047


233

7.5.2 Mass & Rotational Inertias

Figure 7-9 illustrates significant differences in component masses:

Ford Fusion (midsize car) has a very efficiently designed PTU with a mass probably near the

optimum. The RDM also has the lowest mass although some design features indicate further

potential for improvement (bolted vs. welded ring gear). Together with a magnesium housing

the RDM could save approximately 3kg without compromising structural integrity or function.

Jeep Cherokee (small SUV) has the heaviest PTU since it is the only one in this comparison with

a two shaft design for packaging reasons. The RDM adds considerable mass because it was

designed to accommodate a low gear planetary set for the Trailhawk™ version. Mass was added

to the shafts to provide torque capacity for off-roading. A significant amount of incremental

mass is not accounted for in the analysis and most likely was used to adapt chassis parts.

VW Tiguan (small SUV) has a very complex RDM which adds mass to the system. The rear axle

torque rating is higher than with Ford Fusion.

Figure 7-9: AWD Component Mass Comparison

For this comparison vehicles with matching powertrains and trim levels have been selected. The

category ‘other’ includes any parts not directly related to driveline components (e.g. driveline

variations, body structure reinforcements, suspension subframes etc.)

234

Figure 7-10: AWD Component Rotational inertia Equivalent Mass

Ford Fusion has the highest equivalent mass due to the fact that a 5 kg AWD coupler with

considerable diameter is rotating at propshaft speed. Although that is the case for VW Tiguan as

well, Tiguan has a much lower axle gear ratio (1.588 vs. 2.818) and therefore a much smaller

rotational inertia effect.

For comparison, a wheel with a total mass (tire + rim) of 26kg and a dynamic tire radius of 0.334

m would have an rotational inertia equivalent mass of approximately 13.5 kg, which for the

wheel subsystem equals to 54 kg compared to 0.7 – 2 kg for the entire AWD system in the above

chart.

Rotational inertia effects in the AWD driveline are therefore negligible with respect to fuel

efficiency. However, rotational inertias play a major role in disconnect systems since the

synchronizing unit (i.e. the AWD coupler) must accelerate the non-moving part of the driveline

to the equivalent of vehicle speed within a very short period of time (approximately 200 - 400

ms).

235

7.6 AWD Disconnect System Cost Assessment

The following tables show a summary of the cost associated with upgrading a conventional AWD

system to accommodate fuel efficient disconnect capability. Cost is incremental to the base

system without disconnect.

The total cost includes the actual mechanical disconnect system including a smart actuator plus

any changes to the AWD coupler necessary to minimize parasitic losses (i.e. architecture, AWD

coupler clutch plate separation etc.).

The total system cost associated with disconnect devices is in the range of $90.00 to $100.00

US. The Jeep Cherokee system may be an exception since design perspectives included the

option of a low gear which adds unrelated cost to the system.

Pricing is from a tier 1 cost perspective. Sales price for a basic system to an OEM would be in the

range of $110.00 to $130.00 US with the addition of engineering, capital investment, SG&A,

profits and volume considerations.

Jeep Cherokee Sport Component Cost

PTU $ 86

RDM $ 64

Total $ 150 Table 7-6: Jeep Cherokee AWD Disconnect Cost Summary

Side Shaft Disconnect Component Cost

PTU $ 86

RDM $ 7

Total $ 93 Table 7-7: Generic Side Shaft Disconnect Cost Summary

Front Axle Center Disconnect (Chrysler 300) Component Cost

Front axle center disconnect $ 96

T-case $ 1

Total $ 97 Table 7-8: Chrysler 300 Front Axle Center Disconnect Cost Summary

236

8 Appendix A: List of Tables and Figures

Table 1-1: AWD Systems Classification ....................................................................................... 16

Table 1-2: FWD/RWD Architecture Positives and Negatives ..................................................... 40

Table 1-3: Disconnect Systems Positives and Negatives ............................................................ 40

Table 1-4: Torque Limitation Positives and Negatives ............................................................... 41

Table 1-5: Full Time vs. On-Demand AWD Positives and Negatives .......................................... 41

Table 1-6: RDM Architecture Positives and Negatives ............................................................... 42

Table 2-1: AWD System Classification (SAE J1952, Oct 2013) .................................................... 47

Table 2-2: Audi Platforms and Models ........................................................................................ 48

Table 2-3: Audi AWD Classification ............................................................................................. 48

Table 2-4: Audi A6 Basic Information .......................................................................................... 50

Table 2-5: BMW Platforms and Models ...................................................................................... 52

Table 2-6: BMW AWD Classification ............................................................................................ 52

Table 2-7: BMW Active Tourer Basic Information ...................................................................... 53

Table 2-8: BMW 3/4/5/6/7 Series Basic Information ................................................................. 54

Table 2-9: BMW X3/4/5/6 Basic Information ............................................................................. 56

Table 2-10: Daimler Benz Platforms and Models ........................................................................ 58

Table 2-11: Daimler Benz AWD Classification ............................................................................. 58

Table 2-12: Mercedes CLA/GLA Basic Information ..................................................................... 60

Table 2-13: Mercedes C, E and S-Class Basic Information .......................................................... 62

Table 2-14: FCA Platforms and Models ....................................................................................... 64

Table 2-15: FCA AWD Classification ............................................................................................. 64

Table 2-16: Jeep Cherokee Basic Information ............................................................................. 66

Table 2-17: Jeep Cherokee Trailhawk Basic Information............................................................ 67

Table 2-18: Jeep Grand Cherokee Basic Information .................................................................. 68

Table 2-19: Jeep Wrangler Basic Information ............................................................................. 70

Table 2-20: Jeep Wrangler Rubicon Basic Information ............................................................... 71

Table 2-21: Chrysler 300 Basic Information ................................................................................ 72

Table 2-22: Ford Platforms and Models ...................................................................................... 74

Table 2-23: Ford AWD Classification ........................................................................................... 74

Table 2-24: Ford Fusion Basic Information .................................................................................. 75

Table 2-25: General Motors Platforms and Models ................................................................... 76

Table 2-26: General Motors AWD Classification ......................................................................... 76

Table 2-27: Chevrolet Equinox Basic Information ....................................................................... 77

Table 2-28: Chevrolet Silverado / GMC Sierra Basic Information .............................................. 78

Table 2-29: Honda Platforms and Models ................................................................................... 80

Table 2-30: Honda AWD Classification ........................................................................................ 80

Table 2-31: Honda CR-V Basic Information ................................................................................. 81

237

Table 2-32: Hyundai Platforms and Models ................................................................................ 82

Table 2-33: Hyundai AWD Classification ..................................................................................... 82

Table 2-34: Hyundai SantaFe Basic Information ......................................................................... 83

Table 2-35: Jaguar Land Rover Platforms and Models ............................................................... 85

Table 2-36: Jaguar Land Rover AWD Classification ..................................................................... 85

Table 2-37: Range Rover Evoque Basic Information ................................................................... 86

Table 2-38: Mazda Platforms and Models .................................................................................. 88

Table 2-39: Mazda AWD Classification ........................................................................................ 88

Table 2-40: Mitsubishi Platforms and Models ............................................................................ 89

Table 2-41: Mitsubishi AWD Classification.................................................................................. 89

Table 2-42: Nissan Platforms and Models ................................................................................... 92

Table 2-43: Nissan AWD Classification ........................................................................................ 92

Table 2-44: Nissan Rogue Basic Information ............................................................................... 93

Table 2-45: Subaru Platforms and Models .................................................................................. 94

Table 2-46: Subaru AWD Classification ....................................................................................... 94

Table 2-47: Subaru Outback Basic Information .......................................................................... 96

Table 2-48: Tesla Model S Basic Information .............................................................................. 97

Table 2-49: Toyota Platforms and Models .................................................................................. 98

Table 2-50: Toyota AWD Classification ....................................................................................... 98

Table 2-51: Toyota Rav4 Basic Information ................................................................................ 99

Table 2-52: Toyota Highlander Basic Information .................................................................... 100

Table 2-53: Volkswagen Platforms and Models ........................................................................ 101

Table 2-54: Volkswagen AWD Classification ............................................................................. 101

Table 2-55: Volkswagen Tiguan Basic Information ................................................................... 102

Table 2-56: Volvo Platforms and Models .................................................................................. 103

Table 2-57: Volvo AWD Classification ....................................................................................... 103

Table 2-58: Volvo XC 90 Basic Information ............................................................................... 104

Table 2-59: Volvo XC90 T8 PHEV Basic Information ................................................................. 105

Table 3-1: Summary of Efficiency Improvement Potentials ..................................................... 120

Table 3-2: Summary of Efficiency Improvement Potentials (continued) ................................. 121

Table 5-1: Ford Fusion Power Transfer Unit – Technical Data ................................................. 136

Table 5-2: Ford Fusion Power Transfer Unit, Bill of Material rotating parts

[input]/[output] ......................................................................................................................... 137

Table 5-3: Ford Fusion Propshaft/Axle Technical Data ............................................................. 141

Table 5-4: Ford Fusion Rear Drive Module – Technical Data .................................................... 142

Table 5-5: Ford Fusion Rear Drive Module, Bill of Material rotating

parts [input]/[output] ................................................................................................................ 144

Table 5-6: Ford Fusion AWD Coupler, Bill of Materials rotating parts

[input]/[output] ......................................................................................................................... 148

Table 5-7: Ford Fusion Mass Distribution Analysis ................................................................... 153

Table 5-8: Jeep Cherokee Power Transfer Unit – Technical Data ............................................. 161

238

Table 5-9: Jeep Cherokee Power Transfer Unit, Bill of Material rotating parts

[input]/intermediate/[output] .................................................................................................. 163

Table 5-10: Jeep Cherokee Propshaft/Axle Technical Data ...................................................... 167

Table 5-11: Jeep Cherokee Rear Drive Module – Technical Data ............................................. 168

Table 5-12: Jeep Cherokee Rear Drive Module, Bill of Materials rotating

parts [input]/[output] 171

Table 5-13: Jeep Cherokee Mass Distribution Analysis ............................................................ 180

Table 5-14: Volkswagen Tiguan Power Transfer Unit – Technical Data ................................... 187

Table 5-15: Volkswagen Tiguan Power Transfer Unit, Bill of Material rotating

parts [input]/[output] ................................................................................................................ 188

Table 5-16: Volkswagen Tiguan Propshaft/Axle Technical Data .............................................. 191

Table 5-17: Volkswagen Tiguan Rear Drive Module – Technical Data ..................................... 192

Table 5-18: Volkswagen Tiguan Rear Drive Module, Bill of Materials rotating parts

[input]/[output] 193

Table 5-19: Volkswagen Tiguan AWD Coupler rotating parts [input]/[output] .............. 196

Table 5-20: Volkswagen Tiguan Mass Distribution Analysis .................................................... 202

Table 6-1: Jeep Cherokee AWD Disconnect Incremental Cost estimate – PTU ....................... 210

Table 6-2: Jeep Cherokee AWD Disconnect Incremental Cost estimate - RDM ...................... 211

Table 6-3: AWD Disconnect Incremental Cost Estimate – Side Shaft Disconnect ................... 212

Table 6-4: Front End Center Incremental Disconnect Cost Estimate ....................................... 214

Table 7-1: FWD/RWD Architecture Positives and Negatives ................................................... 219

Table 7-2: Full Time vs. On-Demand AWD Positives and Negatives ........................................ 220

Table 7-3: AWD Market Overview; AWD Systems per OEM and Number of

Platforms/Nameplates/ ............................................................................................................. 221

Table 7-4: Mass Comparison between Aluminum and Magnesium on an RDM ..................... 226

Table 7-5: Component Data Comparison (notable differences highlighted) ........................... 232

Table 7-6: Jeep Cherokee AWD Disconnect Cost Summary ...................................................... 235

Table 7-7: Generic Side Shaft Disconnect Cost Summary ......................................................... 235

Table 7-8: Chrysler 300 Front Axle Center Disconnect Cost Summary ..................................... 235

Table 10-1: Vehicle Data ............................................................................................................ 249

Figure 1-1: AWD Nomenclature ................................................................................................... 15

Figure 1-2: FWD Based AWD System Architecture ..................................................................... 17

Figure 1-3: RWD Based AWD System Architecture ..................................................................... 18

Figure 1-4: FWD Based ‘Through the Road’ Hybrid AWD ........................................................... 20

Figure 1-5: Electric AWD .............................................................................................................. 21

Figure 1-6: Power Transfer Unit ................................................................................................... 22

Figure 1-7: PTU Architecture; Single Shaft (center), Two Shaft (left) and Three Shaft (right) .. 23

Figure 1-8: Power Flow in a PTU (2015 VW Tiguan).................................................................... 24

239

Figure 1-9: RDM with integrated Torque Transfer Device ......................................................... 25

Figure 1-10: Electro-magnetically actuated AWD coupler ......................................................... 26

Figure 1-11: Rear Drive Module Architecture Variants .............................................................. 27

Figure 1-12: Torque Vectoring ..................................................................................................... 29

Figure 1-13: Audi Sport Differential............................................................................................. 30

Figure 1-14: Front Axle Disconnect System, Integrated in the PTU ........................................... 31

Figure 1-15: Rear axle disconnect via AWD coupler ................................................................... 32

Figure 1-16: AWD System Status Before (left) and after (right) Disconnect – FWD based

vehicles ......................................................................................................................................... 33

Figure 1-17: AWD System Status Before and After Disconnect – RWD based vehicles ............ 34

Figure 1-18: Front Wheel Hub Disconnect .................................................................................. 34

Figure 1-19: Active 2-speed transfer case ................................................................................... 36

Figure 1-20: Torque Flow in an On-demand Transfer case ......................................................... 36

Figure 1-21: High Level AWD System Disconnect Algorithm ...................................................... 38

Figure 2-1: Fuel Consumption Comparison between 2WD and AWD, MY 2015 ....................... 44

Figure 2-2: Fuel Consumption Comparison between 2WD and AWD, MY 2015 (continued) ... 45

Figure 2-3: Vehicle Mass Comparison between 2WD and AWD versions, MY 2015 ................. 46

Figure 2-4: Audi 8-Speed Automatic Transmission with Integrated Torsen Differential .......... 51

Figure 2-5: BMW 3/4/5/6/7 Series Transfer Case with Geared Drive ....................................... 55

Figure 2-6: BMW X3 / X4 / X5 / X6 Single Speed Active On-demand Transfer Case with Chain

Drive .............................................................................................................................................. 57

Figure 2-7: Mercedes CLA/GLA 4-Matic Power Transfer Unit .................................................... 61

Figure 2-8: Mercedes CLA/GLA Rear Drive Module .................................................................... 61

Figure 2-9: Mercedes C, E and S-Class 4-Matic Powertrain ........................................................ 63

Figure 2-10: Jeep Grand Cherokee Single Speed (left) and 2-speed (right) Transfer Cases ...... 69

Figure 2-11: Chrysler 300 Axle Disconnect Unit (left) and Front Axle (right) ............................. 73

Figure 2-12: Chevrolet Silverado / GMC Sierra Transfer Cases: 4WD Base Model (left) and

AWD Premium Model (right) ....................................................................................................... 79

Figure 2-13: Magna Dynamax AWD Coupler ............................................................................... 84

Figure 2-14: Evoque Rear Drive Module and RDM Architecture (insert) ................................... 87

Figure 2-15: Mitsubishi S-AWC (‘Super – All Wheel Control’) .................................................... 90

Figure 2-16: Lancer Evolution Rear Drive Module with Active Yaw Control (AYC) .................. 91

Figure 2-17: Subaru AWD CVT Transmission ............................................................................... 95

Figure 3-1: Volvo XC90 T8 Hybrid .............................................................................................. 108

Figure 3-2: Angular Contact Double Row Ball Bearing (left) as a Replacement for Tapered

Roller Bearings, Power Loss Comparison (Under Lab Conditions, right) ................................. 109

Figure 3-3: Substitution of Tapered Roller Bearings (red) with Angular Contact Ball Bearings

(blue) ........................................................................................................................................... 110

Figure 3-4: Power Loss Distribution between Gears, Bearings and Oil Splash in a Single Stage

Axle under Load .......................................................................................................................... 110

240

Figure 3-5: Low Drag Seal; Conventional Seal with Garter Spring on the Right Hand Side for

Comparison ................................................................................................................................. 111

Figure 3-6: Spin Loss Comparison between Standard and Disconnect AWD Systems ............ 112

Figure 3-7: Advanced Driveshaft Joint for Reduced Friction and Mass ................................... 113

Figure 3-8: Hypoid Offset ........................................................................................................... 114

Figure 3-9: PTU Architecture; Single Shaft (center), Two Shaft (left) and Three Shaft (right) 115

Figure 3-10: Influence of Lubricants and Temperature on Driveline Torque Losses ............... 117

Figure 3-11: Influence of Micro Finishing and Coating on the Friction Coefficient in Gears ... 118

Figure 4-1: Global Light Vehicle Production Forecast by Region, total numbers .................... 122

Figure 4-2: Global Light Vehicle Production Growth between 2014 and 2021 ........................ 123

Figure 4-3: Average Fuel Efficiency of U.S. Light Duty Vehicles (CAFE) .................................... 124

Figure 4-4: Adjusted CO2 Emissions (left) and Adjusted Fuel Economy (right) for MY 1975-2015

..................................................................................................................................................... 124

Figure 4-5: Fuel Economy, Horsepower and Mass Changes between 1975 and 2015 ............ 125

Figure 4-6: MY 2015 Driveline Architecture Distribution in NA, All Segments ........................ 127

Figure 4-7: AWD Take Rate by Vehicle Segment in MY 2015 ................................................... 128

Figure 4-8: AWD Take Rate [%] by US State, Sorted by Regions, MY 2015 ............................. 129

Figure 4-9: AWD Take Rate [%] by State, Sorted by High (AK) to Low (FL) AWD Content64 ... 129

Figure 5-1: AWD System Architecture ....................................................................................... 130

Figure 5-2: Chassis Integration of an RDM (Ford Fusion) ......................................................... 132

Figure 5-3: Ford Fusion AWD Coupler/ ...................................................................................... 133

Figure 5-4: Electro-magnetic Clutch - Operating Principle ....................................................... 134

Figure 5-5: Ford Fusion AWD Basic Control Logic ..................................................................... 135

Figure 5-6: Ford Fusion Power Transfer Unit ............................................................................ 137

Figure 5-7: Ford Fusion Power Transfer Unit - Parts ................................................................. 138

Figure 5-8: Ford Fusion PTU, Top View ...................................................................................... 139

Figure 5-9: Ford Fusion PTU Input Shaft Figure 5-10: Ford Fusion PTU Output

Shaft 139

Figure 5-11: Ford Fusion PTU, Output Shaft with Pinion in Main Housing .............................. 140

Figure 5-12: Ford Fusion Rear Drive Module ............................................................................. 142

Figure 5-13: Ford Fusion Rear Drive Module - Parts ................................................................. 145

Figure 5-14: Ford Fusion Rear Drive Module ............................................................................. 146

Figure 5-15: Ford Fusion Rear Axle Differential Assembly ....................................................... 146

Figure 5-16: Ford Fusion Rear Axle Assembly: Pinion in the Center Part [1] of the 3-piece

Housing ....................................................................................................................................... 147

Figure 5-17: Ford Fusion AWD Coupler Assembly..................................................................... 147

Figure 5-18: Ford Fusion AWD Coupler, Control Clutch and Ball Ramp Mechanism ............... 149

Figure 5-19: Ford Fusion AWD Coupler, Input Case .................................................................. 149

Figure 5-20: Ford Fusion AWD Coupler Control Clutch Plates .................................................. 150

Figure 5-21: Ford Fusion Main Clutch Plates ............................................................................. 150

Figure 5-22: Ford Fusion AWD Coupler - Parts .......................................................................... 151

241

Figure 5-23: Ford Fusion AWD Mass Analysis/ ......................................................................... 152

Figure 5-24: Ford Fusion ............................................................................................................. 152

Figure 5-25: Ford Fusion PTU Laser Welded Ring Gear ............................................................. 154

Figure 5-26: Ford Fusion Rear Axle Differential ........................................................................ 155

Figure 5-27: Ford Fusion Rear Axle Pinion with High Efficiency Tandem Ball Bearings .......... 156

Figure 5-28: Ford Fusion AWD coupler - Input Case Detail .......................... 157

Figure 5-29: Jeep Cherokee AWD Hydraulic System ................................................................. 158

Figure 5-30: Jeep Cherokee AWD Coupler ................................................................................ 159

Figure 5-31: Jeep Cherokee PTU Disconnect Cross-section, Shift Fork Actuator Module on the

Right ............................................................................................................................................ 160

Figure 5-32: Jeep Cherokee Power Transfer Unit ..................................................................... 162

Figure 5-33: ................................................................................................................................. 164

Figure 5-34: Jeep Cherokee PTU Assembly, Shift Actuator (black) .......................................... 165

Figure 5-35: Jeep Cherokee PTU, View of Input Shaft and Primary Shaft (w/ Shift Sleeve,

Actuator Removed) .................................................................................................................... 165

Figure 5-36: Jeep Cherokee PTU, View of Helical Gear Stage, Primary Shaft (large) and

Secondary Shaft (small) ............................................................................................................. 166

Figure 5-37: Jeep Cherokee PTU, Primary Shaft (left) and Secondary Shaft (right) ................ 166

Figure 5-38: Jeep Cherokee PTU, Pinion .................................................................................... 167

Figure 5-39: Jeep Cherokee Rear Drive Module ........................................................................ 168

Figure 5-40: ................................................................................................................................. 172

Figure 5-41: Jeep Cherokee RDM, Top View with Actuator and Oil Reservoir Cover ............. 173

Figure 5-42: Jeep Cherokee RDM, Hydraulic System Body with Ring Gear and Clutch Pack .. 173

Figure 5-43: Jeep Cherokee RDM, Pinion with inner TRB and Crush Sleeve ............................ 174

Figure 5-44: Jeep Cherokee RDM, Ring Gear ............................................................................. 174

Figure 5-45: Transfer Shaft with Ball Bearing ............................................................................ 175

Figure 5-46: Jeep Cherokee RDM, Differential .......................................................................... 175

Figure 5-47: Jeep Cherokee AWD Coupler - Parts ..................................................................... 176

Figure 5-48: Jeep Cherokee Clutch Assembly, Hydraulic System Body, and Transfer Shaft Ball

Bearing ........................................................................................................................................ 177

Figure 5-49: Jeep Cherokee AWD Coupler, Outer (left) and Inner (right) Plate, Reaction Side

..................................................................................................................................................... 177

Figure 5-50: Jeep Cherokee RDM, Outer (left) and Inner (right) Plate, Friction Side .............. 178

Figure 5-51: Jeep Cherokee Mass Analysis/ .............................................................................. 179

Figure 5-52: Jeep Cherokee ........................................................................................................ 179

Figure 5-53: Jeep Cherokee PTU, Laser Welded Ring Gear ....................................................... 181

Figure 5-54: Jeep Cherokee RDM Ring Gear Laser Weld .......................................................... 182

Figure 5-55: Jeep Cherokee Hydraulic System Body with Integrated Strainer ........................ 182

Figure 5-56: Jeep Cherokee AWD Clutch Assembly .................................................................. 183

242

Figure 5-57:

Jeep Cherokee AWD Inner and Outer Clutch Plates, Friction Side on the left, Reaction side on

the right ...................................................................................................................................... 184

Figure 5-58: Volkswagen Tiguan / Haldex Gen IV Hydraulic System ....................................... 185

Figure 5-59: Volkswagen Tiguan AWD Coupler – Haldex Gen IV ............................................. 186

Figure 5-60: Volkswagen Tiguan Power Transfer Unit .............................................................. 187

Figure 5-61: Volkswagen Tiguan Power Transfer Unit - Parts .................................................. 189

Figure 5-62: VW Tiguan PTU, Top View ..................................................................................... 190

Figure 5-63: VW Tiguan Ring Gear (left) and Pinion (right) ...................................................... 190

Figure 5-64: Volkswagen Tiguan Rear drive Module ................................................................ 192

Figure 5-65: Volkswagen Tiguan Rear Drive Module - Parts .................................................... 194

Figure 5-66: ................................................................................................................................. 195

Figure 5-67: VW Tiguan Ring Gear (left) and Pinion (right) ...................................................... 195

Figure 5-68: VW Tiguan RDM, .................................................................................................... 196

Figure 5-69: Volkswagen Tiguan AWD Coupler/ ....................................................................... 197

Figure 5-70: Volkswagen Tiguan AWD Coupler - Parts ............................................................. 198

Figure 5-71: VW Tiguan AWD Coupler Assembly ...................................................................... 198

Figure 5-72: VW Tiguan AWD Coupler, Cage (left), Multi Plate Clutch and Hub (right) .......... 199

Figure 5-73: VW Tiguan AWD Coupler, Outer (left) and Inner (right) Plate ............................ 200

Figure 5-74: Volkswagen Tiguan Mass Analysis/ ...................................................................... 201

Figure 5-75: Volkswagen Tiguan Equivalent Mass Analysis.................................................... 201

Figure 5-76: VW Tiguan PTU – Laser Welded ring Gear ............................................................ 203

Figure 5-77: VW Tiguan RDM, Ring Gear/Differential Case Laser Welding ............................. 204

Figure 5-78: VW Tiguan RDM Pinion ......................................................................................... 204

Figure 5-79: VW Tiguan AWD Coupler, Friction and Reaction Plates ................................. 205

Figure 5-80: VW Tiguan AWD Coupler Hub ............................................................................... 205

Figure 5-81: VW Tiguan AWD Coupler Cage .............................................................................. 206

Figure 6-1: Jeep Cherokee AWD Configuration ......................................................................... 208

Figure 6-2: Jeep Cherokee PTU, Bottom Front View ................................................................. 209

Figure 6-3: Jeep Cherokee RDM ................................................................................................. 211

Figure 6-4: Side Shaft Disconnect, Parallel System in the Background for Comparison ......... 212

Figure 6-5: Front End Center Disconnect (Chrysler 300) ........................................................... 213

Figure 7-1: AWD System Classification per SAE J1952 (Oct 2013) Standard ............................ 215

Figure 7-2: AWD System Architecture: (1) FWD based; (2) RWD based; (3) FWD based, through

the Road PHEV; (4) Electric ........................................................................................................ 216

Figure 7-3: Active AWD Coupler Systems: Electro-magnetic (left), Electro-hydraulic (right) .. 217

Figure 7-4: AWD Disconnect System Schematic ........................................................................ 218

Figure 7-5: Increase of Fuel Consumption over AWD Mass Increase (LH Column of Charts)

Compared to the Total Fuel Consumption over Vehicle Mass for a Selection of AWD Vehicles

[the Red Dot Indicates Vehicles with AWD Disconnect] .......................................................... 223

Figure 7-6: MY 2015 Driveline Architecture Distribution in NA, All Segments ........................ 228

243

Figure 7-7: AWD Take Rate [%] by State, Sorted by High (AK) to Low (FL) AWD .................... 229

Figure 7-8: AWD System Architecture ....................................................................................... 230

Figure 7-9: AWD Component Mass Comparison ....................................................................... 233

Figure 7-10: AWD Component Rotational inertia Equivalent Mass ......................................... 234

Figure 9-1: AWD couplers - Power transfer units - Transfer cases - Integrated rear drive

modules (left to right) ................................................................................................................ 244

Figure 9-2: Transfer cases - AWD couplers - Electric rear drive modules (left to right) .......... 245

Figure 9-3: Power Transfer Units - AWD couplers - Electric drive modules (left to right) ...... 246

Figure 9-4: Light trucks / SUVs - FWD based passenger cars - RWD based passenger cars (left

to right) ....................................................................................................................................... 247

Figure 9-5: Hybrid drives - Power Transfer Units - Rear drive modules - Engineered gears (left

to right) ....................................................................................................................................... 248

Figure 11-1: Relative Rotational inertia Effects on Vehicle Dynamics ..................................... 251

Figure 12-1: Evaluation of Rotational inertia ............................................................................ 253

Figure 12-2: Spreadsheet to Support Evaluation of Rotational inertia .................................... 254

244

9 Appendix B: Major North American AWD System

Suppliers

________________________________________________________________________

Magna Powertrain (Source: Magna website)

Magna, one of the largest and most diversified Tier 1 suppliers worldwide, develops and

manufactures a full line of AWD products, from cost effective solutions up to top of the

line systems. Magna has a large market share in transfer cases for SUVs, mainly in North

America, and FWD based AWD systems, mainly in Europe and increasingly in Asia.

Magna has joined the group of hybrid and electric drive developers and has AWD

technology available in the hybrid field.

Figure 9-1: AWD couplers - Power transfer units - Transfer cases - Integrated rear drive modules (left to right)

‘Magna Powertrain is a premier supplier for the global automotive

industry with full capabilities in powertrain design, development, testing

and manufacturing. Offering complete system integration sets us apart

from our competitors’

Magna Website

245

________________________________________________________________________

Borg Warner (Source: BorgWarner website)

The Borg Warner TorqTransfer group delivers a complete line of products for FWD and

RWD based AWD vehicles. The group offers cost effective systems as well as top of the

line AWD systems with electronic limited slip functions. With their recent acquisition of

Haldex they have top technology in their portfolio.

Electric drives capable of converting a FWD based vehicle into a through the road AWD

hybrid are also in the lineup, as well as transmission systems for purely electric vehicles.

Figure 9-2: Transfer cases - AWD couplers - Electric rear drive modules (left to right)

‘BorgWarner is a global product leader in powertrain solutions. We focus

on developing leading powertrain technologies that improve fuel

economy, emissions and performance. Our facilities are located across

the globe to provide local support for our diverse customer base’

Borg Warner Website

246

________________________________________________________________________

GKN Automotive (Source: GKN website)

GKN’s Driveline group concentrates on FWD based AWD vehicles with power transfer

units, AWD couplers, axles and e-drives. Advanced disconnect devices have been

developed. No transfer cases are in the product lineup.

GKN is also a major supplier of propshafts and CV joints.

Figure 9-3: Power Transfer Units - AWD couplers - Electric drive modules (left to right)

‘The global leader in efficient all-wheel drive systems, GKN Driveline

continues to deliver driveline systems and solutions to the world’s

premier automotive manufacturers.

With an enviable world class reputation since the emergence of the motor

car, GKN Driveline is committed to the unique development and

manufacture of full AWD systems.

GKN Driveline is a solutions provider, with advanced technology centred

on continuous improvement, innovation and a depth of understanding in

systems integration to optimise the very best components’

GKN Website

247

________________________________________________________________________

American Axle Manufacturing (Source: AAM website)

AAM is developing and manufacturing a full line of driveline products for light trucks /

SUVs (Front axles, rear beam axles, transfer cases with various functional levels), FWD

based passenger cars (power transfer units, rear axles including torque transfer devices,

propshafts) and RWD passenger cars (rear axles, transfer cases).

Most notably, AAM is the manufacturer of the Jeep Cherokee AWD system, with state of

the art disconnect system for fuel efficiency and a unique low gear option for enhanced

off-road capabilities.

Figure 9-4: Light trucks / SUVs - FWD based passenger cars - RWD based passenger cars (left to right)

‘AAM is a leading, global Tier-One automotive supplier of driveline and

drivetrain systems and related components for light trucks, SUVs,

passenger cars, crossover vehicles and commercial vehicles with a

regionally cost competitive and operationally flexible global

manufacturing, engineering and sourcing footprint. Through highly-

engineered, advanced technology products, processes and systems and

industry leading operating performance, the AAM team provides a

competitive advantage to our customers’

AAM Website

248

________________________________________________________________________

Linamar (Source: Linamar website)

Linamar has an impressive array of manufacturing plants for powertrain and driveline

parts, mainly acting as a Tier 2 supplier. A large gear manufacturing operation is capable

of supplying quality gears for in-house products and Tier 1 customers.

As a Tier 1 they are supplying power transfer units and a highly integrated rear drive

module with a sophisticated electronic limited slip differential.

Linamar has recently developed an electric rear drive module that can be used to

convert a FWD based vehicle into an AWD hybrid. The RDM has two electric motors,

each driving one wheel, and is capable of providing torque vectoring.

Driveline product groups

Figure 9-5: Hybrid drives - Power Transfer Units - Rear drive modules - Engineered gears (left to right)

‘As a leading edge Tier 1 supplier to the automotive markets, Linamar

provides core engine components including cylinder blocks & heads,

camshafts and connecting rods. For transmission, Linamar builds

differential assemblies, gear sets, shaft & shell assemblies, as well as

clutch modules. For the vehicle's driveline, Linamar is a full service

supplier of gears and gear driven systems such as PTUs and RDUs for use

in all-wheel drive systems. From single machine components to complex

assemblies, Linamar is the supplier of choice for OEM customers’

Linamar Website

10 Appendix C: Vehicle Data153

Table 10-1: Vehicle Data

153 Source: mass & price: dealer websites, EPA data: http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf, converted from original mpg into L/100 km

Base vehicle

architecture Model Price Curb Weight city hwy combined Price Curb Weight city hwy combined

USD kg l/100 l/100 l/100 USD kg l/100 l/100 l/100

Audi A4 FWD 2.0L 35,900$ 1567 9.9 7.4 8.8 1632 10.8 7.7 9.5

X3 RWD 2.0L 38,950$ 1814 11.3 8.5 9.9 40,500$ 1868 11.3 8.5 9.9

X5 RWD 53,900$ 2106 12.5 8.8 10.8 56,200$ 2156 13.2 8.8 11.3

C-Class RWD C350 38,950$ 1538 9.5 7.0 8.5 40,950$ 1617 9.9 7.7 8.8

E-Class RWD E350 53,100$ 1721 11.9 8.2 10.3 55,600$ 1791 11.9 8.5 10.3

Cherokee FWD 2.4L 23,395$ 1645 10.8 7.7 9.5 25,395$ 1779 11.3 8.5 9.9

Grand Cherokee RWD Laredo 29,995$ 2045 14.0 9.5 11.9 31,995$ 2105 14.0 9.9 12.5

300 RWD 3.6L 32,015$ 1813 12.5 7.7 10.3 34,515$ 1890 13.2 8.8 11.3

Fusion FWD SE 2.0L 23,680$ 1598 10.8 7.2 9.1 1670 10.8 7.7 9.5

Escape FWD 1.6L 25,300$ 1576 10.3 7.4 9.1 27,050$ 1640 10.8 8.2 9.5

F150 RWD XL 28,610$ 1989 14.0 9.9 11.9 33,255$ 2089 14.0 10.3 12.5

ATS RWD 2.oL Turbo 35,215$ 1518 11.3 7.9 9.9 37,245$ 1594 11.9 8.5 10.3

Acadia FWD 3.6L 34,175$ 2095 14.0 9.9 12.5 36,175$ 2183 14.8 10.3 12.5

Equinox FWD 2.4L 25,210$ 1705 10.8 7.4 9.1 26,960$ 1767 11.9 8.2 10.3

MDX FWD 43,015$ 1782 11.9 8.5 10.3 45,015$ 1888 13.2 8.8 11.3

CR-V FWD LX 23,595$ 1524 8.8 7.0 8.2 24,895$ 1575 9.1 7.2 8.5

Hyundai SantaFe FWD Sport 2.0L 24,950$ 1557 12.5 8.8 10.8 26,700$ 1627 13.2 9.9 11.3

Mazda CX-5 FWD Sport automatic 21,795$ 1545 9.1 7.4 8.2 24,445$ 1615 9.5 7.7 8.5

Rogue FWD S 23,290$ 1534 9.1 7.2 8.5 24,640$ 1596 9.5 7.4 8.5

QX60 FWD 42,400$ 1973 11.3 8.8 10.3 43,800$ 2036 12.5 9.1 10.8

Subaru Outback RWD 2.5L n/a n/a n/a n/a n/a 31,245$ 1635 9.5 7.2 8.5

Toyota Rav4 FWD 23,680$ 1546 10.3 7.9 9.1 25,080$ 1598 10.8 8.2 9.5

Highlander FWD 3.5L LE 23,681$ 1910 12.5 9.5 11.3 25,081$ 1979 13.2 9.9 11.9

VW Tiguan FWD S 24,890$ 1532 11.3 9.1 10.3 26,865$ 1616 11.9 9.1 10.3

AWD

EPA L/100 km EPA L/100 km

2WD

GM

Honda

Nissan

BMW

Daimler

FCA

Ford

http://www.fueleconomy.gov/feg/pdfs/guides/FEG2015.pdf

250

11 Appendix D: Equivalent Mass Definition

11.1 Equivalent Mass

A driveline component’s moment of rotational inertia directly affects vehicle dynamics

and subsequently system efficiency. One easy way to show this effect is to convert

rotational inertia into an equivalent mass. This gives us an understanding of the

magnitude of influence on the vehicles dynamic capabilities, expressed relative to the

actual vehicle mass.

Equation [1] represents the total energy 𝑬 stored in a driveline component at the speed

𝒗 as a combination of translational and rotational kinetic energy. The introduction of the

equivalent mass 𝒎𝒆𝒒 in equation [2] allows us to describe the rotational energy

equivalent in a system with no rotating parts.

𝐸 = 𝑚𝑣2

2 +

𝐼𝜔2

2 [1]

𝑚𝑒𝑞𝑣2

2=

𝐼𝜔2

2 [2]

𝑣 = 1

𝑖𝜔𝑅𝑑𝑦𝑛 [3]

𝑚𝑒𝑞 = 𝐼 (𝑖

𝑅𝑑𝑦𝑛)

2

[4]

𝑚𝑡𝑜𝑡𝑎𝑙 = 𝑚 + 𝑚𝑒𝑞 [5]

𝑚𝑓 = 𝑚𝑡𝑜𝑡𝑎𝑙 / 𝑚 [6]

Equation [3] describes the ratio between a vehicle’s speed 𝒗 and the rotational speed 𝝎

of an individual driveline component. The gear ratio 𝒊 represents the speed ratio

between the wheels and the actual location of the component within the driveline (e.g.

an axle or transmission ratio or a combination of all driveline components).

Combining equations [2] and [3] allows us to isolate 𝒎𝒆𝒒 and express the rotational

inertia equivalent mass based on the value of the rotational inertia. The results are

cumulative, with every component being calculated using its moment of rotational

inertia and the actual gear ratio.

E Total system energy 𝑚 Static component mass 𝑣 Vehicle speed I Rotational inertia ω Rotational speed

𝑚𝑒𝑞 Equivalent mass

𝑖 Gear ratio 𝑅𝑑𝑦𝑛 Dynamic tire radius

𝑚𝑡𝑜𝑡𝑎𝑙 Total equivalent mass 𝑚𝑓 Equivalent mass factor

251

Total [equivalent] mass 𝒎𝒕𝒐𝒕𝒂𝒍 is the sum of actual mass and 𝒎𝒆𝒒 from rotational inertia

calculation (equations [4] and [5]). The Equivalent Mass Factor is defined per equation

[6].

11.2 Relative Effects of Rotational inertia on Vehicle Dynamics

Figure 11-1 shows the effects of rotational inertia on vehicle dynamics relative to the

location of a component in the drivetrain. Since equivalent mass grows by the square of

the gear ratio (per equation [4] in section 11.1), the rotational inertia I of propshaft

elements (medium) may have an influence up to 10+ times as much as wheel speed

level components (low), based on the axle ratio (here shown as 3.0, which would give a

factor of 9).

Figure 11-1: Relative Rotational inertia Effects on Vehicle Dynamics

Transmission ratios are typically in a range of 0.8 to 3.5. Any component upstream of

the transmission (high) would have again an equivalent mass growing with the square of

the total gear ratio, including transmission gear stage. This is obviously variable,

depending on the actual gear selected. The effects are highest in low gears and would

give a maximum factor of (3 * 3.5)2 = 110 in the above example. That means a flywheel

or a torque converter (high level) for instance would have 110 times the equivalent

mass of a component with the same rotational inertia at wheel speed level (low) in 1st

gear.

AWD components fall into the medium or low categories and have very limited

influence on fuel consumption based on their rotational inertia.

252

However, disconnect systems for example have to quickly accelerate driveline

components in order to synchronize them with the wheel speeds when engaging the

AWD systems. Rotational inertias have to be taken into consideration to ensure smooth

transition from 2WD to AWD. In other driveline components, e.g. transmissions, even

small reductions in rotational inertia can improve performance significantly.

AWD disconnect systems do not eliminate all effects of rotational inertia since there are

still some added components spinning, depending on architecture (e.g. half shafts

unless there is a wheel hub disconnect. However, effects are minimal and eliminating

them would not justify added complexity.

253

12 Appendix E: Evaluation of Rotational Inertia and

Equivalent Mass

Rotational inertia have been evaluated for all rotating parts in the RDMs and PTUs of all

three vehicles listed in the teardown part of this report. Measurements have been done

with simple lab methods, i.e. electronic calipers and high definition scales.

The evaluation was executed in the following steps:

1. All parts, components and subsystems were weighed (0.002 kg accuracy)

2. Component measurement: All rotating components were broken down into

cylindrical segments as shown in Figure 12-1. Segments with non-cylindrical

shapes (e.g. gears, differential cases etc.) were estimated.

3. From the measurements the mass was calculated. The results were compared to

the actual mass measured in step 1, and a correction factor was applied to

correlate dimensional values with measured masses.

4. A second correction factor was estimated for complex geometries to reflect mass

offset in the calculation of rotational inertias (e.g. voids in clutch plates,

differential cases, bearings etc.)

5. Rotational inertias were calculated for every segment by the formulas listed in

Figure 12-2. The rotational inertias were finally multiplied by the estimated

factor from step 4

6. The actual rotational inertia for each component is the sum of all segments and

is listed in the BoM for each individual part in section 5 of this report.

Figure 12-1: Evaluation of Rotational inertia

254

Figure 12-2: Spreadsheet to Support Evaluation of Rotational inertia

This process makes the listed rotational inertias estimates rather than exact

measurements. However, the method should be considered accurate enough to

produce values very close to the actual numbers.

The equivalent mass was calculated with the formulas listed in Appendix D. The actual

gear ratio was determined for all parts to account for the exact location in the driveline.

That means RDMs and PTUs have two groups of rotational inertias, one on wheel speed

level and one upstream of the hypoid set with the axle ratio taken into account.

Mass Inertia

ffactor … form factor to compensate for non-uniformity 7850 steel density [kg/m3] [kg] [kg m2]

Ifactor … orm actor or partially rotating parts (bearings) 3.14159 Pi Total: 1.655 6.279E-04C

[kg] [kg m2]

Dinner Douter L Offset ffactor Ifactor m I

1 0 25.2 35.7 1 1 0.140 1.110E-05

1 0 27.1 51.8 1 1 0.235 2.153E-05

1 0 30.2 29.2 1 1 0.164 1.872E-05

1 0 31.8 19.1 1 1 0.119 1.505E-05

1 0 33.4 24.6 1 1 0.169 2.359E-05

1 0 72.1 31.5 0.82 1 0.828 5.379E-04

1 0 1 1 0.000 0.000E+00

1 0 1 1 0.000 0.000E+00

1 0 1 1 0.000 0.000E+00

1 1 0.000 0.000E+00

Total 1.654646 6.279E-04

[kg] [kg m2]

L d Offset ffactor m I

1 1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

Total 0 0.000E+00

[kg] [mm] [kg] [kg m2]

m Offset ffactor m I

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

1 0.000 0.000E+00

Total 0 0.000E+00

Point Mass(Parallel Axis Theorem)

Qty

Cylinder TubeQty

[mm]

RodQty [mm]

255

13 Appendix F: List of Terms and Acronyms

2WD Two Wheel Drive

4WD Four Wheel Drive, used per SAE definition for part time systems

4x4 Four by Four – general term, equivalent to AWD for 4-wheeled vehicles

ABS Anti-lock Braking System

ADS Active Disconnect System, a driveline setup that allows one or more sections of the driveline to be disconnected from the torque flow and brought to a standstill while the vehicle is in motion

AWD All Wheel Drive, general term for vehicles where all wheels (4X4, 6X6 etc.) receive torque

BoM Bill of Materials

BTC Brake Traction Control, a set of algorithms that allows the use of selective braking of individual wheels to enhance traction and vehicle dynamics

CAFE Corporate Average Fuel Economy

CD Center Differential

CUV Cross-over Utility Vehicle

CV Joint Constant Velocity Joint, a driveline joint type that minimizes rotational speed oscillations in a multi piece shaft at an angle

CVT Continuously Variable Transmission, a transmission type that does not have individual gear ratios or steps across a predefined range

DCT Dual Clutch Transmission, a mechanical transmission type using two clutches that allows automatic shifts between gears without interrupting torque flow

DMC Direct Manufacturing Cost, the cost to manufacture a component from base materials, including direct labor cost

EC Environment Canada

ECU Electronic Control Unit, an electronic device containing a set of algorithms to control torque flow in a driveline

eLSD electronic Limited Slip Differential, a device that allows the controlled redistribution of torque across a differential in a ratio different from the mechanically predefined torque bias

EPA U.S. Environmental Protection Agency

Equivalent Mass Factor

The Equivalent Mass Factor is defined as [(component or vehicle mass) + equivalent mass of rotational inertias] divided by (component or vehicle mass)

eRAD electric Rear Axle Drive, an electric drive unit to drive the rear axle independently (with no mechanical connection) from the front axle drive

256

eTV Transport Canada’s ecoTECHNOLOGY for Vehicles Program

EV Electric Vehicle

FE Fuel Efficiency

FWD Front Wheel Drive

GHG Green House Gases

HDV Heavy Duty Vehicle, typically heavy trucks and SUVs up to class 8 tractor/trailers

LDV Light Duty Vehicle, typically passenger cars and light trucks and SUVs

LH Left Hand

LSD Limited Slip Differential, a device that redistributes torque across a differential based on predefined design features and vehicle status with no external controls

MPC Multi Plate Clutch, a stack of multiple pairs of friction plates and reaction plates, alternately connected to the hub and the housing of a clutch; integral part of an AWD coupler

NVH Noise Vibration & Harshness

OEM Original Equipment Manufacturer – the vehicle manufacturers

PHEV Plug In Hybrid Electric Vehicle, an electric hybrid vehicle with a battery pack large enough to provide a significant amount of electric propulsion in addition to the internal combustion engine

PTU Power Transfer Unit, a mechanical device that picks up torque from the front axle and provides a mechanical connection to the rear axle

RDM Rear Drive Module, a mechanical device to drive the rear axle of a vehicle, typically contains a torque transfer device to control the amount of torque delivered

RH Right Hand

RWD Rear Wheel Drive

SG&A Sales, General and Administrative, part of the component cost structure

SUV Sport Utility Vehicle

TC Transport Canada

T-Case Transfer Case, a mechanical device typically found in RWD based AWD vehicles; splits torque between the front and rear axles in a fixed or controlled way

Tier 1 A Tier 1 Supplier sells parts and components directly to the car companies, also called the OEMs.

TRB Tapered Roller Bearing, roller bearings that can take substantial axial and radial loads, typically found in axles and PTUs

TTD Torque Transfer Device, also known as AWD coupler; a mechanical device that actively or passively controls the amount of torque passing through

awd component analysis · 2019. 4. 29. · 2.2.6 general motors ... a general trend analysis for...

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