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MECA0500 ELECTRIC & HYBRID VEHICLES
Pierre DuysinxResearch Center in Sustainable Automotive
Technologies of University of Liege
Academic Year 2017-2018
1
References
C.C. Chan and K.T. Chau. « Modern Electric Vehicle Technology » Oxford Science Technology. 2001.
M. Ehsani, Y. Gao, S. Gay, and A. Amadi. Modern Electric, Hybrid Electric, and Fuel Cell Vehicles. Fundamentals, Theory, and Design. CRC Press. 2005.
I. Husain. Electric and hybrid vehicles. Design fundamentals. Second edition. CRC Press. 2011.
R. Kaller & J.-M. Allenbach. Traction électrique. Presses Polytechniques et Universitaires Romandes. Vol 1 et 2. 1995.
B. Multon. Motorisation des véhicules électriques. Les techniques de l’ingénieur. Dossier E 3 996.
Michel Kant. La voiture électrique. Les techniques de l’ingénieur. Dossier D 5 560.
2
Outline
Introduction
History
Electric powertrain of road vehicles
Electric powertrain in railway vehicles
Architectures of electric powertrains
Centralized electric drivetrain
Distributed electric drivetrain
Hybrid
3
Introduction
4
Introduction
The electric car exist from the eve of automobile in the end of 19th century
After a rather erratic period that ends up in the 30ies, the piston engine has definitively won the contest and has been, since that time, the dominating solution for road vehicles
Electric machines has intrinsically superior characteristics superior to piston engines: Constant power in a large range of operation
No idle regime
Easy maintenance
Reliability
5
Introduction
However the energy storage system based on batteries appears to be less efficient than petrol that was abundant and cheap: Higher specific energy so longer range and autonomy
Easiness of maintenance
Not expensive
Abundant
Nowadays, while one might have believed that electric drivetrain was forgotten for ever, piston engine is the victim of its success story: Reduction of petrol resources
CO2 emissions
Emissions of pollutants from combustion
6
Introduction
In the beginning of the 21st century, the electric motor could be the final winner.
Indeed, in order to preserve individual mobility, on needs vehicles with:
Less pollutants
Less noise
Less fuel consumption
7
Electric powertain for road vehicles
Advantages:
Zero emissions on site urban application
Zero (low) noise emissions
Simple mechanical transmission
(no or simplified gear box)
Torque and speed regulation possible
Energy recovery while braking
High torque at low and zero speed
Smooth operation
No range limitation if external power supply (catenaries for trains)
Disadvantages:
Weight penalty and cost of batteries
Limited autonomy is batteries (Max 200 km)
Charging time8
Electric Powertrain Architecture
9
Electric powertrain
Basic electric traction architecture usually mounted on light and heavy vehicles, as well as industrial vehicles (fork lifters, airfield vehicles…) and two wheelers
10
Electric powertrain
A modern electric drive is conceptually more complicated.
It is made of 3 subsystems
Electric motor propulsion
Energy source
Auxiliary
11
Electric powertrain
Electric propulsion system
Vehicle controller
Power electronic converter
Electric motor
Mechanical Transmission
Driving wheels
Energy source subsystem
Energy source or storage
Energy management unit
Energy refueling unit
Auxiliary
Power steering
Hotel climate control
Auxiliary supply unit
12
Electric powertrain components
Electric machine: Converting electric energy into mechanical energy (motor regime)
and vice versa (generator regime)
Types of electric machines DC shunt or series or separately excited
AC synchronous
AC induction machines; 1 phase or 3 phase machines
Switched Reluctance Machine
Power electronics Modulation of power, speed, torque
Control of machine mode (motor, generator)
Types Chopper, DC / DC converters, etc.
Inverter
13
Electric powertrain components
Batteries:
Storing electric energy
Power source
Peak power source
Types
Lead-acid,
Nickel – Cadmium,
Ni – MH (metal hydride),
Li ions
Super capacitors
Flywheels
14
Electric powertrain components
Transmission (mechanical)
Gear box
Differential
Wheels
15
Electric powertrain architrectures
One can distinguish 2 different solutions:
Centralized motorization: similar to ICE configuration = one single motor and the power is transmitted to the wheels via a transmission line including gear boxes, transfer boxes, differentials, shafts.
Decentralized motorization: electric motors are located on each wheels or against each wheel sets (boogie).
On can further distinguish motors actuating the shaft or using direct drive technique
16
Electric powertrain architrectures
17
Centralized motorization
Similar concept to ICE engine
May be not adapted to modern electric motorization18
Centralized motorization
19
Decentralized motorization
20
Decentralized motorization
21
Need for a gear box and a clutch?
For piston engines (ICE), the gear box + clutch is necessary because of the unfavorable speed-torque of the engine
ICE
Wheels
Wheels
Shafts
Gear box
Differential
Clutch
Typical drivetrain architecture with an ICE propulsion system
22
Need for a gear box and a clutch?
v
I
II
III
IV
Envelop of the tractive force curves for different gear ratio is defining a constant power (1/v)
23
Need for a gear box and a clutch?
In a naïve conversion of ICE cars to electric, one keeps the gear box and may be the clutch.
However electric machines have
No idle speed
Large range of operating speed (0 to 3.000 rpm - 12.000 rpm)
Electronic controllers can regulate torque and speed easily
Electric drivetrain can be equipped with a simple gear box: one or two gear ratios
24
Need for a gear box and a clutch?
25
Need for a gear box and a clutch?
Advantages of gear box with a fixed reduction ratio : No shock during operations. Smooth driving.
Planetary gear boxes can achieve important reduction ratios in a single stage with a good efficiency
Cost of electric motor strongly depends on the maximum torque: Using a high speed motor is favorable to reduce the cost
But the acceleration factor is affected by high gear ratio
Selection of single or multiple gear ratios depending on: Acceleration requirements
Max slope and max drawbar pull requirements
Speed range of the motor
26
Unique or multiple motors configuration?
The unique motor configuration is typical from ICE.
With electric motors, on can imagine more innovative design and it is possible to actuate each degrees of freedom independently as in robotics and mechatronic systems.
With distributed motorization with multiple motors, one can even abandon the concept of differential and replace it by 2 or 4 motors, one per each wheel.
The mechanical differential is replaced by an electronic differential systems with control loop.
27
Multiple motors configurations
28
Unique or multiple motor configuration?
Advantages of multiple motor configurations
Reduction of the weight and volume constraints
Electronic differential system opens new possibilities to control the torque and speed differences at each individual wheels
New possibilities in controlling the vehicle dynamics:
Longitudinal dynamics: antiskid and anti lock braking (ABS) systems
Lateral dynamics: extended electronic stability program
Inconvenient
Using additional electronic systems
Reliability of the overall system?
Additional cost
Increasing system complexity
29
In-wheel motor concept
The concept of in-wheel motors minimizes or avoids completely the mechanical transmission by placing directly the motors inside the wheels
One distinguishes :
Inner in-wheel motors whose rotation speed is rather high and is reduced using a fixed gear ratio
Outer in-wheel motors whose rotation speed is low and that are connected in direct-drive
Both approaches generally use permanent magnet (PM) motors because of their high specific power.
30
Inner in-wheel motor
31
Outer in-wheel motor
32
TM4 in-wheel motor Mitsubishi in-wheel motor
Read more at: http://www.electricvehiclesresearch.com/articles/3108/in-wheel-electric-motors-gain-market-share
In-wheel motor concept
The inner in-wheel motor
The max rotation speed is rather high (for instance 10 000 rpm)
Requires a gear box (about 10:1) for instance a planetary gear mounted on the wheel hub
Smaller size and smaller weight
Smaller cost
The outer in-wheel motors
Simplicity of the concept
No reduction of speed nor gear box
Larger size and higher weight: might have some impact on comfort and road holding
High cost
33
In-wheel motor concept
In-wheel motor from TM4
Motor wheel specifications in brief(other versions are available)Peak Power 80 kW 107 hpNominal Power: @950rpm 18.5kW (25hp)Peak torque 670 Nm 494 lb ftNominal torque @ 950 rpm 180 Nm (133lbft)Peak speed: 1385 rpmMax continuous speed: 1235 rpmEfficiency under continuous load @ 950rpm h=96.3 %Maximum supply voltage 500 VDC
34
In-wheel motor concept
MIEV Lancer Evolution equipped by 4 in-wheel motors
35
In-wheel motor concept
MIEV Lancer Evolution equipped by 4 in-wheel motors
Motor
(outer-rotor
type)
Type
Permanent
magnetic
synchronous
MakerToyo Denki
Seizo K.K.
Max. output 50 kW
Max. torque 518 Nm
Max. speed 1500 rpm
Dimensions445 mm (dia.)
x 134 mm
No. fitted 4
36
In-wheel motor concept
MIEV Lancer Evolution equipped by 4 in-wheel motors
37
In-wheel motor concept
Bike applications:
www.smart-bike.netwww.acclivity.ca
38
Hybrid Electric Powertrain Architecture
39
Definitions
Definition of hybrid vehicle: vehicle equipped with a propulsion system that combines two or several energy sources, storages and converters.
Hybrid electric vehicle: a vehicle in which the propulsion energy is available from two or more types of energy stores, sources and converters, and at least one of them can deliver electrical energy (Chan, 2002) There are many kinds of HEV: petrol/diesel/CNG/H2 ICE & battery,
fuel cell & battery, battery & supercaps/flywheels…
Hybrid hydraulic vehicle: same as HEV but in this case one of the energy sources, storage and converters are hydraulic systems
40
Definitions
One also distinguish two basic configurations of the hybrid powertrain
In a parallel hybrid, both types of motorization are connected to the wheels and can propel the car independently or in combination.
Typically the fuel tank supplies the ICE while the batteries are the energy source for the electric motor.
In a series hybrid, the prime mover and its energy source are used to spin a generator that supplies electrical energy to either the batteries or directly the electric motor that is the only one to be geared with the wheels.
41
Parallel hybrid electric powertrains
TWO MODE TRACTION or PARALLEL HYBRID
The ICE powertrain is used outside of the cities while electric powertrain is more efficient for urban driving
Series hybrid electric powertrains
SERIE ELECTRIC POWERTRAIN
The ICE (piston engine or gas turbine) is used to power a generator that continuously feeds in batteries
The battery supplies the electric motor that is the only one to be connected to the wheels
43
Definitions
Other more complex configurations are possible (Chan, 2002)
The series-parallel configuration: both energy sources can propel the vehicle. Nonetheless the system is designed to allow recovering series architecture by inserting a generator between the ICE engine and the batteries.
The complex hybrid configuration extends also the couplings between the two kinds of propulsion chains. The more complex lay-out allows using the electric machine to receive from (generator mode) or to deliver (starter mode) energy to ICE engine.
44
Parallel Hybrid
E
B
P M
G
T
F
Series Hybrid
F
E
B MP
T
Complex HybridSeries-Parallel Hybrid
B: BatteryE: Internal Combustion EngineF: Fuel TankG: GeneratorM: Electric MotorP: Power ConverterT: Transmission to wheels
F
M/G
M M
T
E
T
P
P
P
B
B
G
E
F Electric link
Hydraulic link
Mechanical link
Torque coupling: Two shaft configuration
In the parallel hybrid configuration, a classical option is to use two separate shafts, one for the e-motor and one for the engine.
The transmission and mechanical reduction components can be placed before or after the torque coupling device
45
Fig. 5.8 Eshani et al. (2010) Fig. 5.10 Eshani et al. (2010)
Torque coupling: single shaft configuration
46
In the parallel hybrid configuration, the alternative option is to have a single shaft mounting.
The drawback is that the e-motor and the engine rotation speed are linked.
Decoupling the engine and e-motor rotation speeds requires clutches
Fig. 5.12 Eshani et al. (2010)Fig. 5.11 Eshani et al. (2010)
Torque coupling: separated axles
47
A third alternative option is to use the road as the mechanical coupling. Each motor is placed on a different axle.
The drawback if that coupling efficiency is impacted by the road tire efficiency.
The advantage is that one gets a all-wheel drive vehicle for free…
Fig. 5.13 Eshani et al. (2010)
Speed coupling: planetary gear
48
Among the complex coupling architectures, the torque coupling using a planetary gear train is the most famous one.
The difficulty lies in the complex algorithm necessary to deal with the rotation speed constraint between the three input / output velocities
Fig. 5.18 Eshani et al. (2010)
Toyota Prius transmission
Transmission of Toyota Prius II
49
Toyota Prius transmission
Transmission of Toyota Prius II
50
Speed coupling: transmotor configuration
51
Finally it is also possible to use non mechanical devices to realize the speed coupling.
Transmotors are typically used to perform this task.
Fig. 5.19 Eshani et al. (2010)
Key components of electric and hybrid electric vehicles
52
Key components of hybrid vehicles
The components of electric and hybrid vehicles are the following:
A prime mover, generally a internal combustion engine
An auxiliary power source: electric machines (generator / motor) or hydraulic motor/pump…
An storage system for the auxiliary energy : a battery pack, a fly wheel, or hydraulic accumulator…
Electronic Control Unit for power modulation of power source and converters: modulation of speed, torque, power…
Mechanical transmission and transfer box: mechanical system to connect the different motors to the wheels
Energy management unit (power electronic): optimization of energy flow…
53
Prime mover
The prime mover is the main energy source of the vehicle.
Most of the time the prime mover is an internal combustion engine, and often a piston engine.
Gasoline, diesel, CNG, H2 piston engine
High energy density of liquid fuel
High autonomy of ICE
Reliable technology, taking benefit of a century of continuous developments
Established infrastructure
Modern developments to improve ICE performances and reduce the consumption and the emissions: catalytic converters, variable injection, direct injection, PM filters, etc.)
54
Prime mover
Other combustion engines: Possibility to operate the engine at given fixed load and constant
rotation speed
New focus on gas turbines and steam engines
55
Prime mover
In mid or long term, fuel cells could be the prime mover: Fast growing technology
Hydrogen or methanol fuel cell
Major issues: storage or on-board production of the fuel Reforming process
Storage under high pressure, under liquefied, adsorption, etc.
Retail and distribution network to be established
Problems still to be addressed : reliability, life time…
56
Electric machines
For hybrid electric vehicles, the secondary / auxiliary energy source is electricity.
The electric converters are reversible machines, working as motor or generators.
The electric machines used for HEV are very similar to those used in pure electric vehicles.
Remind that most popular electric traction machines are the following: DC series motors or separately excited DC machines
AC induction machines
AC synchronous machines
Motor with electronically commanded commutation: Permanent Magnet (PM) electric machines, Switched Reluctance (SR) machine…
57
Electric machines for HEV
DC motor Induction machine
Brushless motor
SR motor Hybrid PM motor
Specific power 2,5 3,5 5 3,5 4
Efficiency 2,5 3,5 5 3,5 5
Controllability 5 4 4 3 4
Reliability 5 4 4 3 4
Maturity 5 5 4 4 3
Cost 4 5 3 4 3
Total 22 26 25 23 23
Evaluation of electric motor for HEV by Chan (2002)
Electric machines
The study conducted by Chan (2002) shows that induction machines and synchronous PM motors seems to be the most interesting technologies for hybrid electric vehicles.
The smaller cost of induction machines makes them the most suited choice for starter alternator used in integrated motor assist systems but also in Start & Stop systems.
The focus on hybrid vehicles rises a growing interest to electric machines and to an important research effort:
Ultra thin motors: e.g. electric IMA for Honda Insight
Permanent Magnet AC motors as in the new THSII of the Prius
59
Electric machines
DC brushless motor of the Honda IMA
The motor is mounted directly on fly wheel at the end of the crankshaft
The electric machine must be short and develop a large torque so the thin multi pole configuration
60
Electric machines
61
Electric machines
62
PM e-machines of Toyota Prius
Electric machines
Motor / generator AC synchronous Permanent Magnet of the Prius II
63
Electric machines
64
Electric machines: torque ripple
Problem of NVH generator by electric machines: torque ripple
65
Simple DC machine
Torque ripple for a SR machine
Electric machines: torque ripple
Problem of NVH generator by electric machines: torque ripple for PM and SR machines
66
Electric machines: torque ripple
Shape optimization of an Interior Permanent Magnet machine
Minimization of Torque Ripple
St. Minimum Torque
Design Variables: parameters of CAD entities
67
Electric machines: torque ripple
Approach in FEDO project:
User friendly design tool based on the ONELAB project
Simulation based on GETDP tool
Optimization based on free optimization packages and Python scripts (e.g. NLOPT)
68
Electric machines: torque ripple
Optimization algorithm: MMA (NLOPT)
Optimized geometry (iteration 20)
Reduction of torque ripple -71%
Reduction of average torque -18%
In blue: original geometry
In red: optimized geometry
69
Transmissions
For series hybrid vehicles, the wheels are only connected to the electric machine so that generally as in pure electric vehicle, there is no need for a gear box and a clutch.
When internal combustion engine is connected to the wheels as in parallel hybrid, then a clutch and a gear box are needed:
To allow the vehicle to start from rest
To allow the vehicle to stop without blocking the engine
To allow gear ratio change if a manual gear box is used
To adapt the rotation speed and the torque to the driving conditions to take benefit of the full power
The different types of transmission systems can be applied to hybrid vehicles
70
Transmissions
The transmissions with manual gear box have the best mechanical efficiency but they require some expertise of the user to reduce the fuel consumption.
The transmissions with automatic gear box are providing the best driving comfort, gear changes without power interruption to the wheels, they remain more complex and more expensive. Their mechanical efficiency is generally lower than manual gear box because of the hydraulic torque converter.
The continuous variable transmissions (CVT) are promising. They allow the engine working in rotation speed and torque conditions that are (nearly) independent of the speed and torque of the wheels. They are more expensive and heavier. They also lead to unusual working conditions for the driver.
71
Friction Clutch
Clutch in closed position Clutch in open position
72
Hydraulic coupling
Principle: use hydro kinetic energy of the fluid to transfer smoothly the power from the source to the load while amplifying the output torque
The input wheel plays the role of a pump whereas the output wheel acts as a turbine
One may add a fixed wheel (stator) to improve the efficiency
73
Manual gear boxes
Gear box principles
Input shaft
Output shaft
Intermediateshaft
Direct transmission
74
Manual gear boxes
75
Manual gear boxes
Neutral
1st 2nd
3rd
Reverse76
Manual gear boxes
Gear selection77
Automatic gear boxes
The basic element of automatic gear boxes is the planetary gear train
Sun = planétaire Planet = satellite Annulus = Couronne78
Automatic gear box
Principle of an automatic gear box based on double planetary gear trainsMèmetaux Fig 5.9
79
CVT : Van Doorne System
Pulleys with variable radii
80
CVT : Van Doorne System
Working principle
By modifying the distance between the two conical half shells, one modifies the effective radii of the pulleys and so the reduction ratio
Originally the system was based on the centrifugal forces, but nowadays the system is actuated by depression engines and controlled by microprocessors
PERFORMANCES
Variable reduction ratios varying between 4 to 6 are achieved
Variable efficiency variable with the input torque and the rotation speed
81
Differential system
During turn, the inner and outer wheels have different rotation speeds because of different radii.
Differential systems allow a different speed in left / right wheels while one single input torque
Differential systems can be studied as planetary gears with equal number of teeth for sun and annulus.
Input shaft (engine)
Output shafts (wheels)
82
Differential system
Working principle of differential system83
Torque coupling devices
Torque coupling devices realize the sum of the input torques and transmit the result to wheel shafts
With the reduction ratios
84
Torque coupling devices
85
Torque coupling can be carried out by two gear trains meshing to the final shaft or by single gear train.
Torque coupling devices
86
Torque coupling can be realized also using chains or pulleys
Planetary gear
Speed coupling Kinematic relation
between the sun, the planet carrier and the annulus
With the gear ratio
One finds the Willys formula
Or alternatively
87
Planetary gear sets
Equilibrium and conservation of power are given by
After some algebra one finds
88
Toyota Prius transmission
89
Van Doorme system
90
Honda IMA transmission
CVT de la Honda Civic
91
Energy storage and peak power source
The requirements on batteries and energy storage devices depend on the hybrid vehicle configuration.
For full hybrid, the energy storage capacity must be sufficiently large to level the energy demand and supply for the energy necessary to drive a given distance in pure electric mode (zero emission mode)
For mild hybrids, the energy storage can have a smaller capacity and sufficient to assist the prime mover when accelerating or recovering braking energy. However because of frequent fluctuation, the batteries plays more as peak power source and specific power has a greater influence
For both lay-out, the braking energy is a major factor of batteries sizing.
92
Energy storage and peak power source
As for electric vehicle, the following parameters have to be considered for battery selection:
Specific energy [Wh/kg]
Volumetric energy [Wh/m³]
Specific power [W/kg]
Energy efficiency: the ratio between output energy over input energy [%]
Self discharge rate: the time necessary to loose 20% of the state-of-charge
The life time in number of charge – discharge cycles
93
Energy storage and peak power source
Spec. En.
[Wh/kg]
En. Dens.
[Wh / l]
Spec. Pow.
[W /kg]
# Cycles
[Cycles]
Cost
[$/kWh]
VRLA 30-45 60-90 200-300 400-600 150
Ni-Cd 40-60 80-110 150-350 600-1200 300
Ni-Zn 60-65 120-130 150-300 300 100-300
Ni-MH 60-70 130-170 150-300 600-1200 200-350
Zn–Air 230 269 105 NA 90-120
Al–Air 190-250 190-200 7-16 NA NA
Na–S 100 150 200 800 250-450
Na-NiCl2 86 149 150 1000 230-350
Li-ions 90-130 140-200 250-450 800-1200 >200
USABC 200 300 400 1000 <100
Comparison of HEV batteries by Chan & Chau 2001 94
Energy storage and peak power source
Battery Pack of Toyota Prius II
95
Energy storage and peak power source
Battery Pack of Toyota Prius II
96
Control systems
Electronic control systems are of a primary importance in hybrid electric vehicles.
The hybrid management system is in charge of the strategy to minimize the fuel consumption and emissions while guaranteeing the best performances to the vehicle
One major issue is to maintain state-of-charge of the batteries and accumulators
Hybrid management system rules the energy flux between the different components and powertrains
97
Control systems
Besides the hybrid management system, one has the subordinated controllers that control the particular components
Electronic engine Control Unit (ECU) is in charge of engine management
Battery management System supervises the battery operations controlling the state-of-charge, current density, the cell temperature, etc.
The Electric Motor control units are the chopper or the inverter that carries out electric machine behavior
98
Control systems
Hybrid management system (synergy drive) of Toyota Prius II
99
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