i

STUDY ON AIR SUSPENSION SYSTEMS

A PROJECT REPORT

SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE

AWARD OF THE DEGREE OF

―BACHELOR OF TECHNOLOGY‖

IN

MECHANICAL ENGINEERING

(MECHATRONICS)

BY

G.O. ABHISHEK (08261A1421)

TARIQ KAREEMULLA (08261A1455)

UNDER THE ESTEEMED GUIDANCE OF

Ms. K. C. Sabitha

Asst. Professor, Mechatronics

DEPARTMENT OF MECHANICAL ENGINEERING (MECHATRONICS)

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY

(Affliated to Jawaharlal Nehru Technological University, Hyderabad)

Accredited by National Board of Accreditation, New Delhi

GANDIPET, HYDERABAD – 500075(A.P)

www.mgit.ac.in

2012

ii

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY Accredited by National Board of Accreditation, New Delhi,

(Affiliated to Jawaharlal Nehru Technological University, Hyderabad)

Gandipet, Hyderabad – 500 075 (A.P)

www.mgit.ac.in

CERTIFICATE

This is to certify that the project report entitled

STUDY ON AIR SUSPENSION SYSTEMS

Submitted by

G.O. ABHISHEK (08261A1421)

TARIQ KAREEMULLA (08261A1455)

In partial fulfillment for the award of the Degree of Bachelor of Technology in

Mechanical Engineering (Mechatronics) is a record of bonafide work carried out by him

under my guidance and supervision during the academic year 2011– 12. The results

embodied in this project report have not been submitted to any other University or

Institute for the award of any Degree or Diploma.

Internal Guide Dr. K. Sudhakar Reddy

Ms. K. C. Sabitha Head of the Department

Asst. Professor

Internal Examiner External Examiner

iii

iv

ACKNOWLEDGEMENT

This Dissertation report would be considered complete with

acknowledging the names of the people who have helped us immensely in preparing it.

We would like to express our profound gratitude to our guide and mentor

Ms. K.C. Sabitha. We would also like to thank Dr. K. Sudhakar Reddy (Professor

and HOD Mechanical Engg., MGIT) and Principal Dr. G. Chandra Mohan Reddy, for

permitting us to do the project at Ashok Leyland, Chennai whose encouragement,

guidance and valuable suggestions are of great importance in successful completion of

the project.

We are very thankful to Mr. Sundaram Parthasarathi (Special Director -

Business Planning), Ashok Leyland, Sardar Patel Road, Chennai and Ms. J

Sumathy(Human Resources Manager), Ashok Leyland Technical Centre,

Vellivoyalchavadi, Chennai for granting us permission to do project in the plant by

extending facilities and motivating us through all the difficulties that came our way.

We express our special gratitude and thanks to Mr. C Prakash, General

Manager (Product Development), Ashok Leyland Technical Centre,

Vellivoyalchavadi, Chennai for his kind co-operation without whom the project training

would not have been completed.

We would like to thank Mr. Siva Lingam S, Sr. Manager (Protoshop), Ashok

Leyland Technical Centre, Vellivoyalchavadi, Chennai for providing us with an

interesting project work in their firm. His encouragement, guidance and valuable

suggestions are of great importance in successful completion of this project. He helped

us at every stage in understanding and solving many problems encountered during the

course of project. On the whole, working with him was a great learning experience.

We would also like to thank all the people in the organisation for their help. We

would cherish our experiences in this organization for our life time.

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ABSTRACT

Air ride suspension carries the load on each axle with a pressurized air bag much

like a high pressure balloon. Air ride suspension systems have been in common use for

over forty years and have proven to provide the smoothest and most shock-free ride of

any known vehicle suspension system. Modern air bags are constructed using the same

methods as a tire by using high strength cords which are then encapsulated in rubber.

These units are very durable in service and have a proven life of many years.

In addition to providing extremely smooth ride quality, air ride suspension also

provides other important features. First, the system automatically adjusts air pressure in

the air bag so that the trailer always rides at the same height, whether lightly loaded or

heavily loaded. This allows the suspension system to always provide the maximum

usable wheel travel independent of trailer load. In addition, the higher air bag pressure

associated with higher trailer loads automatically provides a stiffer suspension which is

exactly what is required for a smooth ride. The lower air bag pressure for lightly loaded

conditions automatically provides for a softer suspension, thus providing the same ride

quality for all trailer loading conditions. Since each axle is independently supported by

its own air bag, the air ride suspension is a truly, fully independent suspension system.

The automatic control of the air bag pressure is accomplished by a solid state

electronic control system specifically designed and packaged for vehicle use. This

system continuously monitors the "ride height" of the trailer suspension and increases

air pressure if the ride height is too low, by turning on an on-board air compressor. The

air compressor stops automatically when the proper ride height is reached. If the ride

height is too high, an automatic vent valve vents excess air pressure and stops venting

when the proper ride height is reached. All required electrical power is provided by a 12

volt battery contained in the trailer equipment compartment.

The subject of study of this project was ―CITY BUS- Semi low floor- entry +

two steps‖. And a study on the rear Air-suspension system of the vehicle was carried

out.

vi

TABLE OF CONTENTS

CHAPTER 1: INTRODUCTION TO SUSPENSION SYSTEMS

1.1 SUSPENSION SYSTEM 1

1.1.1 INTRODUCTION TO SUSPENSION SYSTEM 1

1.1.2 OBJECTIVE OF SUSPENSION SYSTEM 2

1.1.3 CLASSIFICATION OF SUSPENSION SYSTEM 3

CHAPTER 2: AIR SUSPENSION

2.1 AIR SUSPENSION 15

2.2 BASIC AIR SUSPENSION 16

2.2.1 WHAT IS AN AIR SUSPENSION? 16

2.2.2 COMPONENTS OF THE AIR SUSPENSION 17

2.2.3 AIR SUSPENSION ADVANTAGES 22

2.2.4 APPLICATIONS 22

2.3 ECAS (ELECTRONICALLY-CONTROLLED AIR SUSPENSION) 23

2.3.1 AUTOMATIC LEVEL CONTROL 25

2.3.2 ELECTRONIC CONTROL UNIT (ECU) 26

2.3.3 SOLENOID VALVE 27

2.3.4 HEIGHT SENSORS 27

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2.3.5 ECAS APPLICATIONS 28

CHAPTER 3: THE ECAS SYTEM IN COMMERCIAL VEHICLES

3.1 ECAS SYTEM IN BUSES: ELECTRONIC HEIGHT CONTROL AND

LEVELING FUNCTION 29

3.1.1 KNEELING FUNCTION 29

3.1.2 HIGH RIDE FUNCTION 30

3.1.3 LOW RIDE FUNCTION 30

3.1.4 DOOR AND TRANSMISSION INTERLOCK 30

3.1.5 SIMPLE DIAGNOSTICS 30

3.2 ECAS SYSTEM IN TRUCKS 31

3.2.1 ELECTRONICALLY CONTROLLED AIR SUSPENSION

FOR HEAVY-DUTY TRUCKS 31

3.3 ECAS BENEFITS 32

CHAPTER 4: SUSPENSION SYSTEM FOR SEMI LOW FLOOR BUS

4.1 CITY BUS- SEMI LOW FLOOR- ENTRY + TWO STEPS 33

4.2 DIMENSIONS 33

4.3 FRAME ASSEMBLY 34

4.4 SUSPENSION SYSTEM 35

4.4.1 SUSPENSION CHARACTERISTICS 36

4.4.2 FRONT SUSPENSION 37

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4.4.3 REAR SUSPENSION 38

4.4.3.1 REAR AIR SUSPENSION-KINEMATIC ANALYSIS 39

4.4.3.2 LOADING CONDITIONS 40

4.4.3.3 REAR SPRING VARIABLE STIFFNESS GRAPH 42

4.4.3.4 REAR AIR SUSPENSION BRACKETS FEA 43

4.4.3.5 REAR AIR SUSPENSION- AXLE BRACKET

ANALYSIS 44

4.4.3.6 REAR AIR SUSPENSION - RIG TESTING 45

4.5 SUMMARY 46

CHAPTER 5: CONCLUSION 47

BIBLIOGRAPHY 49

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LIST OF FIGURES

CHAPTER1:

Fig. 1.1 Basic suspension system 2

Fig. 1.2 Control Arm 4

Fig. 1.3 Steering knuckle for front-wheel-drive 5

Fig. 1.4 Tapered stud provides a force fit into the steering knuckle or bearing support 5

Fig. 1.5 This shock uses pressurized gas, acting on the oil to reduce foaming 6

Fig. 1.6 Shock Absorber Action 6

Fig. 1.7 Strut Assembly 7

Fig. 1.8 Sway Bar 8

Fig. 1.9 Track Rod 8

Fig. 1.10 Independent and Non-independent Suspension Systems 9

Fig. 1.11 Bogie Suspension 14

Fig. 1.12 NRS 14

CHAPTER2:

Fig. 2.1 Stout-Scarab 15

Fig. 2.2 Locating Suspension Units 16

Fig. 2.3 Advanced Air Suspension 17

Fig. 2.4 Components of air suspension 18

x

Fig. 2.5 Air spring, which is a rubber cylinder or air bag filled

with compressed air. 18

Fig. 2.6 Working of an Air Spring 19

Fig. 2.7 Air-Shock Absorber 20

Fig. 2.8 Actual Working of Air Suspension 21

Fig. 2.9 A lift axle using air bags 22

Fig. 2.10 An air-suspension system with air springs at all four wheels. 23

Fig. 2.11 Construction of an air-strut, which includes air spring,

solenoid, and internal height sensor 24

Fig. 2.12 Electronic automatic-level-control system. 25

Fig. 2.13 ECU 26

Fig. 2.14 A sample ECU circuit 26

CHAPTER3:

Fig. 3.1 A modern day bus using ECAS for Kneeling 29

Fig. 3.2 High Ride function 30

Fig. 3.3 Low Ride function 30

Fig. 3.4 Illustration of a heavy-duty truck highlighting the electronically

controlled air suspension. 31

xi

CHAPTER4:

Fig. 4.1 CITY BUS- Semi low floor- entry + two steps 33

Fig. 4.2 Dimensions 33

Fig. 4.3 Frame assembly 34

Fig. 4.4 Front & Rear Suspension 35

Fig. 4.5 Front Suspension 37

Fig. 4.6 Front spring 37

Fig. 4.7 Rear Air suspension 38

Fig. 4.8 Kinematic Analysis 39

Fig. 4.9 Loading Conditions 40

Fig. 4.10 Variable stiffness graph of Rear spring 42

Fig. 4.11 Rear Air suspension brackets Finite Element Analysis 43

Fig. 4.12 Rear Air suspension- Axle Bracket Analysis 44

Fig. 4.13 Rig Testing 45

xii

LIST OF TABLES

CHAPTER3:

Table 4.1 Suspension Characteristics 36

1

CHAPTER 1

INTRODUCTION TO SUSPENSION SYSTEMS

1.1 Suspension system:

1.1.1 Introduction of Suspension system

Suspension is the term given to the system of springs, shock absorbers and

linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose

— contributing to the car's road holding handling and braking for good active safety and

driving pleasure, and keeping vehicle occupants comfortable and reasonably well

isolated from road noise, bumps, and vibrations, etc. These goals are generally at odds,

so the tuning of suspensions involves finding the right compromise. It is important for

the suspension to keep the road wheel in contact with the road surface as much as

possible, because all the forces acting on the vehicle do so through the contact patches

of the tires. The suspension also protects the vehicle itself and any cargo or luggage

from damage and wear. The design of front and rear suspension of a car may be

different.

A suspension system comprises springs, shock absorbers and linkages. This

suspension connects an automobile to its wheels. The suspension systems not only help

in the proper functioning of the car's handling and braking, but also keep vehicle

occupants comfortable and make your drive smooth and pleasant. It also protects the

vehicle from wear and tear. To know about the suspension system, one needs to know

about the spring rate or suspension rate. Various spring types are used for different

vehicles. In case of heavier suspension loads, the spring rate is higher and vice versa.

Spring rate is measured as a ratio used to measure how resistant a spring is to being

compressed or expanded during the spring's deflection Besides spring rate, one needs to

take in account the wheel rate. Wheel rate is the effective spring rate when measured at

the wheel. It is generally equal to or considerably less than the spring rate.

2

1.1.2 Objectives of Suspension system:

To absorb the road shocks

To maintain required frame height

Supports the weight of the vehicle

Allows the wheels to move up and down

Allows rapid cornering without extreme body roll

Keeps the tires in firm contact with the road

Prevents excessive body squat when accelerating or heavily loaded

Prevents excessive body dive when braking

Allows the front wheels to turn left or right for steering

Helps keep the wheels in correct alignment

Basic Suspension System

A basic suspension system is described in the Fig. 1.1

Fig. 1.1 Basic suspension system

3

1.1.3 Classification of Suspension System:

1. Based on spring medium

2. Based on Suspension Mounting

Rigid axle Suspension

a. UnderSlung Suspension

b. Overslung Suspension

Independent Suspension

Sandwich type

Lump Mass

Rubber Spring

Semi-Elliptic Parabolic

Single Stage Two Stage Progressive Stage

Shackle Type Slipper Type Weveller

Leaf Spring

Normally wound

Progressively wound

Coil Spring

Mechanical Suspension

Double Wishbone

Single Wishbone

Pneumatic Suspension

Hydrolastic

Hydropneumatic

Hydra Gas

Electromagnetic

Hybrid

SUSPENSION SYSTEM

4

Suspension System Construction

Control Arms

Used to hold the steering knuckle, bearing support, or axle housing in position as

the wheel moves up and down

Inner end contains bushings

Outer end contains a ball joint (independent) or bushing (solid axle)

(See Fig. 1.2)

Fig. 1.2 Control Arm

Strut Rod

Fastens to the outer end of the lower control arm and to the body or frame

Keeps the control arm from swinging toward the front or rear of the vehicle

Rod ends contain rubber bushings that soften the action of the rod and permit a

controlled amount of lower control arm front-to-rear flex

5

Ball Joints

Connections that allow limited rotation in every direction

Filled with grease for lubrication

Grease fitting may be provided

Grease seal holds grease in and prevents water and contaminant entry

(See Fig. 1.3, 1.4)

Fig. 1.3 Steering knuckle for front-wheel-drive

Fig. 1.4 Tapered stud provides a force fit into the steering knuckle or bearing support

6

Shock Absorbers

Limit spring oscillations to smooth a vehicle‘s ride

One end is connected to the body or frame, the other to the axle or control arm

When compressed or extended, oil inside the shock is forced through small

orifices, absorbing energy, damping spring action

Shock Absorber Construction

Fig. 1.5 This shock uses pressurized gas, acting on the oil to reduce foaming

Fig. 1.6 Shock Absorber Action

7

Strut Assembly

Consists of a shock absorber, a coil spring, and an upper damper unit

Replaces the upper control arm

Only the lower control arm and the strut are needed to support the wheel

assembly

(See Fig. 1.7)

Fig. 1.7 Strut Assembly

Sway Bar (Stabilize Bar)

Used to keep the body from leaning excessively in sharp turns

Made of spring steel

Fastens to both lower control arms and to the frame

When the body leans, it twists the bar

The bar‘s resistance to twisting limits body lean in corners

Sway bar links connect the bar to the control arms

(See Fig. 1.8)

8

Fig. 1.8 Sway Bar

Track Rod

Used on the rear axle to prevent side-to-side movement during cornering

Uses control arms of different lengths

Minimizes tire tilting (camber change) with suspension action

Reduces tire scuffing and wear

Upper control arms are shorter than the lower control arms

(See Fig. 1.9)

Fig. 1.9 Track Rod

9

Independent and Non-independent Suspension Systems

Non-independent

Fig. 1.10 Independent and Non-independent Suspension Systems

Independent Suspension

Allows one wheel to move up and down with minimal effect on the other wheels

Each wheel is attached to its own suspension unit

Movement of one wheel does not cause direct movement of the wheel on the

other side of the vehicle

Non-independent Suspension

Both left and right wheels are attached to the same solid axle

When one tire hits a bump in the road, its upward movement causes a slight

upward tilt of the other wheel

Neither wheel is independent of the other

Independent

10

Understeer and Oversteer

Understeer:

Vehicle is slow to respond to steering changes in a turn

rear tires retain traction

front tires may slip on the road surface due to lack of downforce or other factors

Oversteer:

Rear tires try to skid around sideways in a sharp or hard turn

front tires retain traction

Suspension systems are designed to balance understeer and oversteer

Neutral steering is the result, where all four wheels have equal traction in turns

Suspension System Springs

Springs must jounce (compress) and rebound (extend) as a vehicle travels over

bumps and holes in the road surface

Springs must support the weight of the vehicle while still allowing suspension

travel (movement)

11

Leaf Spring System

12

Semi Elliptic Vs Parabolic Springs

13

Load Vs. Deflection Graph:

14

Suspension Type and Application

Suspension Type Application

Single Stage Bus/Truck Front Suspension-where

Unladen to Laden load variation is less

Two Stage Bus/Truck Rear Suspension- where

Unladen to Laden load variation is more

Progressive Stage Bus Rear Suspension- helps smooth

stiffness transition from Unladen to

Laden

Bogie System

Fig. 1.11 Bogie Suspension

Non-Reactive Suspension

Fig. 1.12 NRS

15

CHAPTER 2

AIR SUSPENSION

2.1 Air Suspension

Air suspension, which Lincoln ballyhooed for some models in 1984 was

introduced in 1909 by the Cowey Motor Works of Great Britain. It did not work well

because it leaked.

Fig. 2.1 Stout-Scarab

The first practical air suspension was developed by Firestone in 1933 for an

experimental car called the Stout-Scarab (Fig. 2.1). This was a rear-engined vehicle that

used four rubberized bellows in place of conventional springs. Air was supplied by

small compressors attached to each bellow. As you might imagine, the air bag

suspension was an expensive setup -- still is, in fact.

The first automobile to use torsion bar suspension was the 1921 Leyland. Most

of the credit for the wide acceptance of torsion bars in Europe goes to Dr. Ferdinand

Porsche who made it standard on most of his cars, beginning with the 1933 Volkswagen

prototypes. By 1954, 21 makes of European cars were equipped with torsion bars.

16

2.2 BASIC AIR SUSPENSION

2.2.1 What is an air suspension?

‗The air suspension system is an air-operated, microprocessor controlled

suspension system. This system replaces the conventional coil spring suspension

and provides automatic front and rear load leveling. The 4 air springs, made of

rubber and plastic, support the vehicle load at the front and rear wheels‘.

Fig. 2.2 Locating Suspension Units

1. Right shock strut 2. Air compressor

3. Left shock strut 4. Rear height sensor

5. Air suspension switch 6. Air line

7. Air springs 8. Lower control arm

9. Front height sensor

An air suspension supports the vehicle on the axles with an arrangement of air

bags instead of some type of steel spring, leaf or coil, or some type of torsion

spring arrangement. The air bags are sometimes referred to as air springs or

bellows. Suspensions that have steel or torsion springs that are supplemented by

the use of air bags are not considered air suspensions. There are combination

17

systems that have both air and steel springs. Usually the air suspension

components are used on the rear of the vehicle.

Fig. 2.3 Advanced Air Suspension

Depending on the situation, this type of air suspension will probably have

to be dealt with for leveling purposes. Normally, the air suspension is just one

part of the air system on the vehicle. Most (but not all) vehicle with an air

suspension also have air brakes along with other equipment that may be operated

with air. Any of these other systems can cause problems with the air suspension.

Other air systems including the brake systems in general, will not be discussed

in this school. It is important to understand that on vehicles with air systems,

especially with air brakes, manufacturers must follow specific regulations when

designing their air systems. The brake system will always be the main concern

for the air system. There will be safety features installed in the system that make

the brake system the main priority for the air system.

2.2.2 Components of the air suspension

An air suspension has three basic components. The air supply, the air bags and

the height control valves (see Fig. 2.4). As stated before, there are many

different types of these components and different arrangements of how these

components are used. In the following section, we will discuss several different

arrangements of these components but this is by no means a complete discussion

of all of the possible arrangements.

18

Fig. 2.4 Components of air suspension

Air Spring

The air spring (Fig. 2.5) is a rubber cylinder or air bag filled with compressed

air. A plastic piston on the lower control arm moves up and down with the lower

control arm. This causes the compressed air to provide spring action. If the load

in the vehicle changes, a valve at the top of the air bag opens to add or release

air. An air compressor connected to the valve keeps the air springs inflated.

Fig. 2.5 Air spring, which is a rubber cylinder or air bag filled with compressed

air.

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Working

Fig. 2.6 Working of an Air Spring

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Air Shock Absorbers

Air shock absorbers have a rubber boot surrounding the shock absorber (Fig.

2.7). This forms a sealed air chamber which is filled with compressed air. The

compressed air increases the load-carrying capacity of the vehicle while maintaining

proper rear-end height. Some air shock absorbers are filled through an air valve by

attaching a service-station air hose. When the load is removed, enough air should be

bled from the shock absorber to lower the vehicle to its normal ride height.

Fig. 2.7 Air-Shock Absorber

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Fig. 2.8 Actual Working of Air Suspension

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2.2.3 Air suspension advantages

Maintains uniform Chassis height at all loads

Air Spring offers Variable stiffness

Natural frequency is constant hence better Ride is offered at all loads.

Reduces Driver and Passenger fatigue

2.2.4 Applications

Street rods, trucks, cars, and even motorcycles

Luxury vehicles

Lift axle mechanisms in trucks(see Fig. 2.9)

ECAS buses(with Kneeling function)

Fig. 2.9 A lift axle using air bags

23

2.3 ECAS (Electronically-Controlled Air Suspension)

The air-suspension system has air springs that replace coil springs at all four

wheels (Fig. 2.10). The system controls spring rates and provides automatic height and

level control. The rear air springs mount ahead of the rear axle on the lower suspension

arms. The front air springs are part of the strut assemblies. These air struts (Fig. 2.11)

mount between the vehicle body and the steering knuckle.

Fig. 2.10 An air-suspension system with air springs at all four wheels.

An electric air compressor supplies the air pressure that operates the system

(Fig. 2.11). An air dryer mounted on the compressor removes any moisture from the air.

This prevents water-which could damage the system-from entering it. An air line runs

from the dryer to each air spring. A solenoid on each air spring opens and closes to

control the air pressure and volume within the spring. The control module switches the

compressor and the solenoids on and off.

24

Fig. 2.11 Construction of an air-strut, which includes air spring, solenoid, and internal

height sensor

The system includes three height sensors. These are magnetic sensors in the

front air struts (Fig. 2.11) and in the right-rear shock absorber (Fig. 2.7). When weight is

added to the body, the body settles. The height sensors respond by signaling the control

module. It then starts the air compressor and opens the solenoid valves at the air springs.

The increased air pressure ―pumps up‖ the air springs. This raises the body back up to

its original height or trim height. Then the control module turns off the air compressor

and closes the solenoid valves.

25

When the load is removed, the body rises above the trim height. The height

sensors signal the control module. It responds by opening the solenoid valves to allow

some air to escape from the springs. When the body settles back down to the trim

height, the control module closes the solenoid valves.

2.3.1 Automatic Level Control

Many vehicles have automatic level control or electronic level control (Fig.

2.12). The two rear air-shock absorbers are connected by air lines to an air compressor

on the vehicle. At least one of the shock absorbers includes a height sensor (Fig. 2.7 and

Fig. 2.12). It signals the electronic control module (ECM) when a load in either the rear

or front of the vehicle has caused a change in the vehicle height. The ECM then

switches on the air compressor to add air to the shock absorber. Removing the load

causes the ECM to open air valve. This bleeds air from the system.

Fig. 2.12 Electronic automatic-level-control system. A height sensor in the

shock absorber switches the electric air compressor on and off.

26

2.3.2 Electronic Control Unit (ECU)

[See Fig. 2.13(a)]

• State-of-the-art electronics function as the ―brain‖ of the ECAS

• Compact design

• Receives driver input from control panel

• Controls solenoid valve to ensure proper vehicle height

• Constantly monitors system performance

Fig. 2.13 (a) (b) (c)

Fig. 2.14 A sample ECU circuit

27

2.3.3 Solenoid Valve

[See Fig. 2.13(b)]

• Modular system that reduces pneumatic piping required

• Reduces leveling response times to seconds

• Less hardware and fewer leak points

• Minimal space requirements

2.3.4 Height Sensors

[See Fig. 2.13(c)]

• Three-sensor system

• Maintains level vehicle body under every vehicle load

28

2.3.5 ECAS applications

Due to its modular design, ECAS can be used in:

Trucks with air suspended rear axles, with air suspended rear and lifting axles,

with air suspended front and rear axles, with air suspended front, rear and lifting

axles

Buses with air suspension systems

Trailers with air suspension systems

Light-duty commercial vehicles and passenger cars

ECAS offers clear benefits

ECAS is available with or without a remote control unit and offers:

Vehicle superstructure in parallel to the road at a pre-set level even if the

load is not spread evenly

Constant level for loading ramp operation with no need of manual re-

adjustment; stand-by operation possible

Automatic traction control in compliance with the latest European legal

requirements

Traction control as an option for the maximum utilization of permissible

axle loads

Rapid lifting and lowering times

Low air consumption as brief dynamic spring motion does not affect the

control process

CAN bus capability

Load indication

Long service life

In addition, ECAS only requires little space for installation and pipes.

29

CHAPTER 3

THE ECAS SYTEM IN COMMERCIAL VEHICLES

3.1 THE ECAS SYTEM IN BUSES: ELECTRONIC HEIGHT CONTROL AND

LEVELING FUNCTION

The height sensors constantly measure the distance between the axles and the

vehicle body sending the data to the electronic control unit (ECU). The data will change

whenever the vehicle is loaded or unloaded. These changes are registered by the ECU,

which through the use of a solenoid valve will automatically adjust the suspension air

bags to ensure proper ride height level, enhancing ride, handling and control.

3.1.1 KNEELING FUNCTION

When stationary, the vehicle can be raised and lowered to facilitate the

passengers‘ entry and exit – all at the press of a button (see Fig. 3.1).

Fig. 3.1 A modern day bus using ECAS for Kneeling

30

3.1.2 HIGH RIDE FUNCTION

Allows the driver to raise the vehicle in driving conditions where sharp break

overs (e.g., railroad tracks) or steep road angles (e.g., driveways, entrance

ramps) occur. This will prevent the vehicle from bottoming out. A limited height

feature prevents the driver from overinflating the suspension air bags when

adjusting vehicle height.

Fig. 3.2 High Ride function

3.1.3 LOW RIDE FUNCTION

Allows the driver to lower the vehicle for access to areas where low overhangs

and canopies exist.

Fig. 3.3 Low Ride function

3.1.4 DOOR AND TRANSMISSION INTERLOCK

Built-in passenger safety feature requiring the door to be shut, parking brake

applied and vehicle in neutral prior to kneeling.

3.1.5 SIMPLE DIAGNOSTICS

Your choice of two simple, user-friendly methods:

• Standard blink code

• PC-based diagnostics

31

3.2 THE ECAS SYTEM IN TRUCKS

3.2.1 Electronically Controlled Air Suspension for Heavy-Duty Trucks

The air suspension in a large truck performs two important duties: It lifts and drops the

chassis to couple the trailer, and it helps stabilize vehicles that have a high center of

gravity. Leading truck manufacturers like Ashok Leyland, etc. develop an electronically

controlled air suspension (ECAS) for its next generation of heavy-duty trucks, it

presented the engineers with a set of 1360 stringent system requirements. In addition,

the ECAS had to ensure the safety and comfort of drivers operating 40-ton vehicles.

Fig. 3.4 Illustration of a heavy-duty truck highlighting the electronically controlled air

suspension.

32

3.3 ECAS BENEFITS

ECAS benefits include

• Enhanced ride, handling and control

• Reduced vibration and wear on the driveline

• Ease of entrance and exiting for passenger

• Allows vehicle access to normally inaccessible areas

• Reduced air consumption

• Level vehicle body, even with uneven weight distribution

• Makes vehicle more adaptable to road environment

33

CHAPTER 4

Suspension System for Semi Low Floor Bus

4.1 CITY BUS- Semi low floor- entry + two steps

Fig. 4.1 CITY BUS- Semi low floor- entry + two steps

4.2 Dimensions:

Fig. 4.2 (a)

Fig. 4.2 (b)

34

4.3 Frame Assembly

Fig. 4.3 Frame assembly

35

4.4 Suspension System

Figure 4.4 depicts the type(s) of suspension system used in the bus.

Fig. 4.4 Front & Rear Suspension

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4.4.1 Suspension Characteristics

Sl.No Description

1 FAW-Kg 5460

2 RAW-Kg 10200

3 Front Leaf-Spring stiffness-Kg/mm 34.7

4 Rear Air-spring Stiffness-Kg/mm 15.42

5 Front Suspension Natural Frequency - Hz 1.7

6 Rear Suspension Natural Frequency - Hz 1.3

7 Front Suspension (Leaf Spring) Roll Stiffness-Nm/deg 1960

8 Rear Air spring Roll Stiffness-Nm/deg 7415.6

9 Rear ARB Roll Stiffness-Nm/deg 5554.7

10 Rear Suspension Roll Stiffness-Nm/deg 12970.3

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4.4.2 Front Suspension

Fig. 4.5 Front Suspension

Fig. 4.6 Front spring

38

4.4.3 Rear Suspension

Fig. 4.7 Rear Air suspension: (a)

(b)

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4.4.3.1 Rear Air suspension- Kinematic Analysis

Fig. 4.8 Kinematic Analysis

40

4.4.3.2 Loading Conditions

Fig. 4.9 (a) Vertical Loading

41

Fig. 4.9 (b) Braking Loading

Fig. 4.9 (c) Cornering Loading

42

4.4.3.3 Rear spring variable stiffness graph

Fig. 4.10 Variable stiffness graph of Rear spring

43

4.4.3.4 Rear Air suspension Brackets FEA

Fig. 4.11 Rear Air suspension brackets Finite Element Analysis

44

4.4.3.5 Rear Air suspension- Axle Bracket Analysis

Fig. 4.12 Rear Air suspension- Axle Bracket Analysis

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4.4.3.6 Rear Air suspension - Rig testing

Fig. 4.13 (a) Rig testing Air Suspension System Rig testing is done for the following conditions

•Case-1: 0.5g-2g Vertical load for 1 Lac Cycles

•Case-2: 1g Vertical & 0.8g (+/-) Braking for 1 Lac Cycles

•Case-3: 1g Vertical & 0.6g (+/-) Cornering for 1 Lac Cycles

Fig. 4.13 (b) Rig testing

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4.5 Summary

Rubber ended Leaf spring suspension at Front and Air suspension at Rear is a

new concept driven by Ashok Leyland.

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CHAPTER 5

Conclusion

Our Contribution:

We contributed to the research facility as trainees and volunteered in the shop

floor work, which were mostly study, assembly and movement of parts of the

automobile.

Our Study:

A study was carried out on the conventional suspension system and air

suspension system. The advancements in Air Suspension Systems were

observed.

The benefits of using air suspension system and additional features and

advantages that could be added by using ECAS:

The ECAS provides variable height suspension for on and off road applications.

The air springs are designed to provide a luxurious ride quality and provide the

ability to raise the body of the vehicle for off road clearance and lower the

vehicle when driving at higher speeds on highways.

Also it has a kneeling function so as to make it easy for elderly citizens and the

physically challenge to get into the vehicle easily.

In addition the various aspects of production and automation in real-time testing

(viz. 4-poster and 6-poster) were observed.

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Observations:

The basic suspension system, air suspension system, ECAS components and

function of each component for providing a smooth ride were observed. Also it

was seen how the conventional suspension springs have been replaced by air

springs, which are par superior as they act as a smoother suspension to the

vehicle.

Conclusions derived from this study:

ECAS is the new technology in Air Suspension Systems and is superior to any

other suspension system and it provides additional features like:

• Enhanced ride, handling and control

• Reduced vibration and wear on the driveline

• Ease of entrance and exiting for passenger

• Allows vehicle access to normally inaccessible areas

• Reduced air consumption

• Level vehicle body, even with uneven weight distribution

• Makes vehicle more adaptable to road environment

49

BIBLIOGRAPHY

Central Library, Ashok Leyland Technical Centre, Vellivoyalchavadi.

Automotive Mechanics by Crouse, Anglin, Donald L. Anglin and William

H. Crouse.

Slide show on ―Suspension System for Semi Low Floor Bus‖ by Mr. V. Vijay

Kumar (Manager-Product Development).

Project ―Jan Bus‖, headed by Mr. Siva Lingam S, Sr. Manager (Protoshop).

"Magneshocks..Future Of Shock Absorbers Is Here Today!"

"Cadillac.com - ESV -Stability Enhancement System."