HYBRID VEHICLES: What And Why

1
HYBRID VEHICLESWhat And Why?
Michigan State University
College of Engineering

Fall 2007 - ME444

• Gerald D. Skellenger, GEDASK, LC
• Trudy R. Weber, GM RD and Planning

2
Hybrid Vehicles

• Have two (or more) energy storage devices
• Have two (or more) power paths
• Are executed to produce better emissions and fuel
  economy
• Are more costly
• Are more complex

3
In case you thought hybrids were
new
1909
4
General Concept
Fuel Converter
Power Conditioning
Storage Medium
5
Hybrid (Electric) Vehicle Arrangements
Parallel
ENGINE
MOTOR/ GENERATOR
Series
BATTERY
6
GM Car and Truck CAFE
30
Domestic Passenger Car Fleet
28
26
24
Light Truck Fleet
22
CAFE (mpg)
20
18
16
14
12
10
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
Model Year
7
Conventional Drive Vehicle
Accessories
n-Speed Automatic or CVT
Engine
FDR
Launch Device Torque Converter or Clutch
8
Energy Utilization in a Full-SizePickup Truck

Accessories
2.0
Fuel Energy
100
Engine
77.3
9
Vehicle Modeling
and Simulation Requirements

• Component models at various levels of detail
  incorporated into vehicle simulation model
• Powertrain architectures conventional electric
  hydraulic subsystems parallel series hybrid
  architectures fuel cell fuel reformer in
  direct and hybrid drives
• Link to an optimization toolbox to provide system
  design formulations
• Data integrity checks at model input data level
  (e.g., checks on speed, torque and power
  capacities, smoothness and completeness of data,
  ranges on parameters) and component compatibility
• PC-based modeling and simulation environment with
  a knowledge base to assist the beginner and
  advanced user

10
Vehicle Analysis and Simulation Model
11
Forward-driven Simulation Approach
Transmission Model
Eng Access
Launch Device Model
Final Drive Model
Engine
Transmission
S/C or T/C
Teng Weng
Analysis starts with assumed throttle or engine
output
Tire Model
Vehicle Acceleration Determined
Iterative solution required to adjust engine
output to match the cycle acceleration
12
Backward-driven Simulation Approach
Transmission Model
Eng Access
Transmission Model
Eng Access
Launch Device Model
Launch Device Model
Final Drive Model
Final Drive Model
Engine
Engine
Transmission
Transmission
S/C or T/C
S/C or T/C
Teng Weng
Teng Weng
Engine speed and torque determined by working
back through the driveline component models
Tire Model
Tire Model
Road Load Given
Note vehicle performance must be monitored in
case the engine cannot meet the cycle
requirements, the acceleration must be reduced
and the vehicle diverges from the driving cycle
Analysis starts with known velocity and
acceleration is given by the duty cycle
13
Backward vs. Forward Methods

• Backward method lends itself best to fuel economy
  simulations and energy management optimization
  and is best suited for analysis and evaluation of
  the energy and power flow in the vehicle
  driveline
• Forward method lends itself best to analyzing the
  dynamic behavior of components within the vehicle
  driveline and is better suited for looking at
  system responses assuming that all components are
  modeled to predict their output behavior
• The integrity and fidelity of the input data and
  assumptions is the most critical aspect to either
  approach for producing results within levels of
  acceptable certainty
• Both approaches are capable of predicting vehicle
  performance and fuel economy in the presence of
  good input data

14
Optimization Formulation

• Min f(x) objective function
• subject to
• g(x) lt 0 inequality
  constraints
• h(x) 0 equality constraints

active constraint
g1(x)
local optimum
g2(x)
f(x)
infeasible side
infeasible side
global optimum
15
Example Optimization Challenge
Fuel Economy (mpg)
Final Drive Ratio

• Challenge Handling simulation noise
  and discontinuities

16
Optimization Challenges

• Algorithms suited to handle inherent computer
  simulation difficulties such as
• Numerical integration noise
• Discontinuous and discrete responses
• Computationally intensive simulations
• Objective functions involving time consuming
  simulations
• Gradient methods with slow convergence and
  requiring derivative calculations

17
Vehicle System Modeling Environment at GM

• Capture the basic energy and power flow in
  vehicle
• Simulate the vehicle on all possible duty cycles
  given driveability constraints
• Provide an energy analysis of powertrain
• Develop energy management strategies to maximize
  fuel economy
• Incorporate features to maximize fuel economy,
  minimize emissions or maximize transmission
  efficiency
• Model operating mode switching and transmission
  shift dynamics
• Have access to control parameters to evaluate
  alternative scenarios and sensitivity studies
• Provide detailed output and post-processing
  features on cycle simulations displaying
  component and sub-system interactions for the
  purpose of debugging as well as understanding the
  powertrains
• Speed up execution time for optimization studies

18
Example Optimization Problem
Maximize f mpg (combined fuel
economy) Subject to g1 maximum speed 177
kph gt 10 min g2 maximum acceleration gt
5.0 m/s2 g3 0-60 mph time lt 10 seconds
g4 0-30 mph time lt 4 seconds g5 ?SOC
lt 0.5
Fuel Processor Gas Ref HEV 75 kW FPFC
52.7 A-hr NiMH 136 kW Electric Motor
Composite Fuel Economy 33.6 mpg
Note 3D design space provides feedback of
feasible region

Performance Summary


Vmax for 10 min
600 sec


2
Amax
5.17 m/s
3.0 sec
0 50 kph


10.0 sec
0 - 96 kph


No. of Failures on urban and Highway cycles
0



19
IC Engine Hybrids Parallel HEV
Launch Device Starting Clutch (Electric assist
replaces torque converter)

Engine meets cycle requirement with battery
assist as needed to operate in highest possible
gear
20
Hybrid System Issues

• Vehicle mission and technical specifications
• Degree of hybridization
• Vehicle mass (target vs. feasible or realistic
  estimate)
• Dealing with energy storage charging/discharging
• Dealing with energy and emission penalties when
  restarting engine
• Drive quality when launching vehicle and
  restarting the engine
• Component sizing for vehicle performance
  requirements
• Energy management strategy for maximum fuel
  economy gains

21
Energy Management Strategy Optimize Engine
Efficiency and Battery Losses Positive Power
Motor
Battery

• Energy stored in battery is used to
• Launch vehicle to about 30 kph without engine
• Supplement engine at high cycle requirement
• Share load with engine at high vehicle speeds

Engine
n-Speed
Drive Wheels
Cycle Requirement

• Operate engine in most efficient region
• Avoid low power operation be keeping engine off
  at low vehicle speeds
• Engine meets cycle requirement with battery
  assist if needed to keep transmission in highest
  possible gear
• Share load with battery at high vehicle speeds
  when engine efficiency is high

22
Energy Management Strategy Negative Power
Battery
Motor
Recover as much energy as possible High charging
current cannot be avoided at high deceleration
rates
Engine
n-Speed
Drive Wheels
Transmission gear selected to optimize motor
operation

• Above a specified vehicle speed the engine
  remains connected to assure driveability
• Below this speed, the engine is disconnected to
  assure maximum energy recovery

23
Optimizing Performance of Gasoline Engine in IPA
HEV
88 kW Full Sized 1.8L Gasoline Engine

• Full-size Engine
• Engine controlled by torque control to operate in
  band of good efficiency at all speeds
• Battery serves as buffer for excess engine power
  at low cycle requirements
• Engine loading levels because too much power is
  generated

• Downsized Engine
• Engine controlled by torque control to operate in
  band of high efficiency at all speeds
• Engine loading at near peak levels throughout
  cycle
• Small amount of excess power does not load
  battery

24
Applications of Approach Presented

• Studies to assess the benefits of numerous
  technologies ranging from gasoline ICEs to
  hydrogen fuel cell, from conventional to hybrid
  drives in a GM truck
• Vehicle technologies integrated into
  Well-to-Wheel energy consumption and GHG emission
  models
• Analysis performed for North America and Europe
• Reports available on these websites
• http//www.transportation.anl.gov
• http//www.lbst.de/gm-wtw

25
The General Motors HYBRID PROPULSION SYSTEMS
PROGRAM
This program was a part of the Department of
Energy's U.S. Hybrid Propulsion Systems Program,
being conducted under a cost shared
subcontract funded equally by
General Motors Corporation and
the U. S.
Department of Energy (DOE),
through the Midwest Research
Institute, the management and operating
contractor for DOE's National Renewable Energy
Laboratory in Golden, Colorado.
26
Partners Chart
Companies and Institutions
Contributing to the GM/DOE Hybrid
Vehicle Propulsion Systems Program
Program Management
Propulsion System
System Integration
GMRDC TASC NMC Exxon
GMRDC NEC DE DCS DHTS DSSS DEEMS TASC
Energy Storage
Electric Drive
Hybrid Power Unit
STM DEEMS DE
AV Optima ARA Bipolar NREL
DEEMS AV
27
Technology Neckdown
Start
Year 1
Series Parallel PM Brushless DC AC
Induction Switched Reluctance MOSFET IGBT MCT Bi
-Polar Lead Acid Spiral-Wound Lead Acid Prismatic
Lead Acid Four-Stroke Otto Cycle Gas
Turbine Stirling
Year 2
Year 3
Series AC Induction IGBT BP Lead Acid SW Lead
Acid Gas Turbine Stirling
Series AC Induction IGBT SW Lead Acid Stirling
28
Battery Pack
29
Stirling Engine HPU
30
Powertrain Cradle
31
Fuel Economy
And Emissions Testing
32
Significant Progress

• Battery pack
• Interconnects
• Structure
• Reduced assembly time
• Electric drive
• Reduced material and fabrication cost
• Production gearing
• Controls
• Production-intent system controller

33
Challenges

• Technical
• Battery Specific Energy, Charge
  Acceptance, Cycle Life
• HPU Efficiency, Emissions, Specific Power
• Economic
• Nearly All Components Need Major Cost Reduction

34
GM PRECEPT
35
GM Autonomy (Hywire)
36
GM Autonomy Powertrain
37
GM HX3
38
Four-Wheel-Motor Series Hybrid
39
HONDA INSIGHT
40
HONDA CIVIC
41
TOYOTA PRIUS
42
TOYOTA PRIUS II
43
NISSAN TINO
44
Ford Hybrids
Focus
Escape SUV
(Recently Delayed introduction)
45
Summary

• The Configuration of a Hybrid Vehicle Depends on
  the Mission it Must Fulfill
• Hybrid vehicles can contribute to cleaner air and
  reduced energy consumption.
• Parallel hybrids generally offer greatest fuel
  economy gain, but may not meet ULEV requirements
  and generally do not have a significant ZEV
  range.
• Series hybrids offer fuel economy gain and
  generally have significant ZEV range.
• The magnitude of fuel economy gain depends
  strongly on vehicle performance requirements and
  energy management strategy
• Significant challenges must still be overcome in
  cost, complexity, reliability, and customer
  acceptance.