1V6I‘Slty
`
`g e 5 Q
`
`Un
` %
`
`Durham E—Theses
`
`Some drive train control problems in hybrid ale
`engine/boitery electric vehicles
`
`l\/Iascling5 Philip Wilson
`
`HOW to cite:
`
`Masding5 Philip Wilson (1988) Some drive train control problems in hybrid is engine/battery electric
`vehicles, Durham theses, Durham University. Available at Durham E—Theses Online:
`httpii/fetlleses.dur.ac.uk,-’6408f
`
`Use policy
`
`The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or
`charge, for personal research or study, educational, or not—for~pmfit purposes provided that:
`
`o a full bibliographic reference is made to the original source
`a a link is made to the metadata record in Durham E—Theses
`
`a the full—text is not changed in any way
`
`The fullrtext must not be sold in any format or medium without the formal permission of the copyright holders.
`Please consult the full Durham E-Theses policy for further details.
`
`1
`
`PAICE 2104
`Ford v. Paice & Abell
`
`|PR2014—00579
`
`1
`
`PAICE 2104
`Ford v. Paice & Abell
`IPR2014-00579
`
`

`

`Academic Support Office, Durham University, University Office, Old Elvct, Durham JJH‘i. BHP
`eimaii: eitheses.admin‘ifljduriacmk Tel: +44 0191 334 6107'
`htf'p:{781116565‘dul‘izLL'JJl:
`
`2
`
`

`

`Some Drive Train Controi Problems In
`
`Hybrid i.c Engine/Battery Electric Vehicles
`
`The copyright of this thesis rests with the author.
`
`No quotation from it should be published without
`
`his prior written consent and information derived
`
`from it should be acknowledged.
`
`by Philip Wilson Masding B.Sc.
`
`A Thesis Submitted for the Degree of Doctor of Philosophy
`
`School of Engineering and Applied Science
`
`University of Durham
`
`1988
`
`""t
`I
`
`D U
`4. .
`lil‘ESfiwir-
`I
`XX? Vim—513%
`Aka-r.“my”
`
`"“
`
`I? NW 1983
`
`3
`
`

`

`Declaration
`
`None of the work contained in this thesis has been previously submitted
`
`for a. degree in this or any other university.
`
`It is not part of a joint research
`
`project.
`
`Copyright
`
`The copyright of this thesis rests with the author. No quotation
`
`from it should be published without his prior written consent and information
`
`derived from it should be acknowledged.
`
`4
`
`

`

`Acknowledgements
`
`I Would like to acknowledge the tremendous support and encouragement I
`
`have had from my supervisor, Dr.
`
`JAR. Bumby, throughout this research.
`
`I
`
`am also grateful to Mr N. Herron and Mr K‘ McGee for their assistance in
`
`maintaining and building the rig and to Mr N. Herron in particular who designed
`
`the mechanical system for the gearbox. Finally I would like to thank Mr C. Dart
`
`for his help with electrical work on the rig.
`
`I am also grateful to the Ford Motor Company, Lucas Chloride E.V. Systems
`
`Ltd, and Shell Research Ltd. for the provision of equipment.
`
`5
`
`

`

`Abstract
`
`This thesis describes the development of a microprocessor based control
`
`system for a parallel hybrid petrol/ electric vehicle.
`
`All
`
`the fundamental‘
`
`systems needed to produce an operational vehicle have been developed and
`
`tested using a full sized experimental rig in the laboratory.
`
`The work begins with a review of the history of hybrid vehicles,
`
`placing emphasis on the ability of the petrol electric design to considerably
`
`reduce the consumption of oil based fuels, by transferring some of the load
`
`to the broad base of fuels used to generate electricity.
`
`Efficient operation of a hybrid depends on the correct scheduling of
`
`load between engine and motor, and correct‘choice of gear ratio. To make
`
`this possible torque control systems using indirect measurements provided
`
`by cheap sensors, have been developed. Design of the control systems is
`
`based on a theoretical analysis of both the engine and the motor. Prior to
`
`final controller design, using the pole placement method, the transfer functions
`
`arising from the theory are identified using a digital model reference technique.
`
`The resulting closed loop systems exhibit well tuned behaviour which agrees
`
`well with simulation.
`
`To complete the component control structure, a pneumatic actuation
`
`system was added to a ‘manual gearbox’ bringing it under complete computer
`
`control. All aspects of component control have been brought
`
`together so
`
`that an operator can drive the system through simulated cycles. Transitions
`
`between modes of operation during a cycle are presently based on speed, but
`
`the software is structured so that efficiency based strategies may be readily
`
`incorporated in future.
`
`Consistent control over cycles has been ensured by the development
`
`of a computer speed controller, which takes the 'place of an operator. This
`
`system demonstrates satisfactory transition between all operating modes.
`
`ii
`
`6
`
`

`

`CONTENTS
`
`Page
`
`List of Symbols
`[list of Figures
`
`CHAPTER 1:
`
`INTRODUCTION
`
`.
`
`1.]. Possible Improvements or Alternatives to LC. Engine Vehicles
`1.1-1 NOVel Engines
`
`1.1.2 The Electric Vehicle
`
`1.2 The History of Hybrid LC. Engine/Electric Passenger Cars
`
`1.3 The Context of the Present Work
`
`CHAPTER 2: THE LABORATORY TEST SYSTEM
`
`2.1 Loan Emulation
`
`2.2 The Hybrid Drive System
`
`2.3 Computer Control and Signal Monitoring
`
`2.3.1 Motorola M68600 System
`
`2.3.2 Duet 16 Personal Computer
`
`2.4 Instrumentation
`
`2.5 Software System
`
`2.5.1 System Initialisation
`
`2.5.2 Active Rig Control
`
`2.5.3 Data Logging
`
`2.5.4 Data Transfer
`
`-
`
`2.5.5 Data. Analysis
`
`-
`
`2.6 Discussion
`
`2.7 Software Documentation
`
`vii
`x
`
`1
`
`5
`6
`
`7
`
`9
`
`17
`
`32
`
`32
`
`34
`
`36
`
`36
`
`38
`
`38
`
`40
`
`40
`
`43
`
`44
`
`45
`
`46
`
`47
`
`50
`
`CHAPTER 3: PHYSICAL ANALYSIS OF THE ENGINE AND MOTOR 57
`
`3.1 Analysis of the Electric Traction System
`
`3.1.1 D.C. Machine Analysis
`
`3.1.2 Motor Torque Equation
`
`3.1.3 The Effects of the Power Electronic Controller
`
`59
`
`59
`
`61
`
`62
`
`iii
`
`7
`
`

`

`3.2 Physical Analysis of the LC. Engine
`
`3.2.1 Inlet Manifold Pressure Variations
`
`3.2.2 Transfer Function for Engine Torque
`
`3.2.3 Throttle Servo-System
`
`3.2.4 Engine Speed on No—Load
`
`3.3.5 Transfer Function for Engine No—Load Speed
`
`CHAPTER 4: EXPERIMENTAL IDENTIFICATION RESULTS
`
`4.1 Calibration of Indirect Torque Measurements
`
`4.1.1 Engine Torque Model Calibration
`
`4.1.2 Engine Torque Model Testing
`
`4.1.3 Motor Torque Model Calibration and Testing
`
`4.2 Gain Functions for the Three Operating Modes of the Motor
`
`4.2.1 Field Boost Mode
`
`4.2.2 Full Field Mode
`
`4.2.3 Field Weakening Mode
`
`4.3 Transfer Function Identification
`
`4.4 Transfer Function Identification for the Motor
`
`4.4.1 The Closed Loop Transfer Functions for Current
`
`-_4.4.2 Direct Identification of the Motor Torque
`
`Transfer Function
`
`4.5 Manifold filling Delay and Engine Torque Variations
`
`4.6 Engine NodLoad Speed Transfer Function
`
`4. 7 Discussion
`
`CHAPTER 5: CONTROLLER DESIGN
`
`5.1 Controller Design Method
`
`5.2 Control Algorithm
`
`5.3 Design of Individual Controllers
`
`. 5.3.]. Engine Torque
`
`5.3.2 Electric Motor Torque Control
`
`5.3.3 Motor Torque Control Test Results
`
`5.3.4 Mode Determination
`
`iv
`
`66
`
`66
`
`69
`
`71
`
`71
`
`72
`
`79
`
`80
`
`80
`
`81
`
`82
`
`83
`
`84
`
`85
`
`86
`
`88
`
`92
`
`92
`
`93
`
`97
`
`99
`
`100
`
`118
`
`118
`
`121
`
`123
`
`123
`
`126
`
`127
`
`128
`
`8
`
`

`

`5.3.5 Engine Speed Synchronisation
`
`53.6 Engine Starting and Load Transfer
`
`5.4 Quantisation Errors and Noise
`
`5.5 Model Reference Controller Design
`
`5.5.1 Application of the Model Reference Technique
`
`to the Motor
`
`5.6 Discussion
`
`CHAPTER 6: THE AUTOMATED GEAR CHANGING SYSTEM
`
`6.1 The Case for a Variable Transmission in Road Vehicles
`
`6.2 Variable Transmission Systems
`
`.
`
`6.3 Transmission System Hardware on the Hybrid Vehicle Rig
`
`6.4 Interface Circuitry
`
`6.5 Software Control
`
`6.5.1 Stage 1: Shift into Neutral
`
`6.5.2 Stage 2: Speed Matching
`
`6.5.3 Stage 3: Engaging the New Gear
`
`6.5.4 Error Handling
`
`6.5.5 Location on Power Up
`
`6.6 Results
`
`6. 7 Discussion
`
`CHAPTER 7:
`
`INTEGRATED DRIVE TRAIN CONTROL AND
`
`DRIVE CYCLE TESTING
`
`7.1 Component Sequencing Control
`
`7.2 A Speed Based Mode Controller
`
`7.3 Drive Cycle Testing
`
`7.3.1 Speed Conversions
`
`7.4 Complete Computer Control
`
`7.4.1 The Speed Contro1 Loop
`
`7.5 Automated Cycle Control Using the
`
`Speed Based Mode Controller
`
`7.5.1 Preliminary All Electric Performance
`
`130
`
`131
`
`133
`
`136
`
`139
`
`140
`
`159
`
`159
`
`16?.
`
`166
`
`168
`
`168
`
`169
`
`171
`
`172
`
`172
`
`174
`
`174
`
`175
`
`186
`
`187 '
`
`189
`
`190
`
`192 .
`
`193
`
`194
`
`197
`
`197
`
`9
`
`

`

`7.5.2 Calibration of the Expert System
`
`7.5.3 All Electric Performance with Expert Controi
`
`7.5.4 Effect of Mode Transitions and Gear Changes
`
`7.6 Discussion
`
`CHAPTER 8: CONCLUSIONS AND PROPOSALS
`
`FOR FUTURE WORK
`
`8.1 General Conclusions
`
`8.2 Proposals for Future Work
`
`REFERENCES
`
`199
`
`200
`
`200
`
`202
`
`216
`
`216
`
`222
`
`226
`
`vi
`
`10
`
`10
`
`

`

`Liet of Symbols
`
`a
`
`Cd
`
`Cr
`
`ea
`
`fC
`
`f,
`
`9
`
`G43)
`
`gc(w’)
`
`96(2)
`
`9,:
`
`Zero of 9410’).
`
`Coefficient of drag
`
`Coefficient of rolling resistance
`
`Back e.rn.f. voltage, V
`
`Counter value from flywheel speed probe
`
`Number of teeth on the flywheel speed probe gear
`
`Gain ms yew).
`
`Armature closed loop transfer function
`
`P—i—l Controller in w'-plane form.
`
`Bilinear discretisation of gc(w’).
`
`Final drive ratio
`
`GAS)
`
`Field closed loop transfer function
`
`id
`
`1';
`
`3,:
`
`J
`
`ng
`
`K
`
`KC
`
`Ka
`
`k,-
`
`K;
`
`KP
`
`Kg;
`
`KT
`
`K2
`
`Armature current, A
`
`Field current, A
`
`Mean field current during a transient, A
`
`Flywheel inertia, 1(ng
`
`Equivalent inertia of vehicle mass M, 1(ng
`
`Constant relating dynamometer speed to load
`
`Scaling factor, flywheel count
`
`to roadspeed
`
`Back e,n1.f. constant (= 27%)
`
`galls/2
`
`Manifold filling delay gain
`
`Gain of armature controller
`
`Power stroke delay gain
`
`Motor torque constant
`
`Gain of engine torque/speed transfer function
`
`kg(9,pm)
`
`Manifold pressure/throttle gain
`
`vii
`
`11
`
`11
`
`

`

`Armature inductance, H
`
`Field inductance, H
`
`Mass air flow into inlet manifold, kg/s
`
`Mass charge flowing out of inlet manifold, kg/s
`
`Vehicle mass, kg
`
`Mass of gaseous mixture in the inlet manifold, kg
`
`Engine or motor speed, r.p.m.
`
`Speed at which linearisation takes place, rpm.
`
`Adaptive gain matrix
`
`Engine power, kW
`
`Inlet manifold depression, mbar _
`
`Manifold depression at no load and N r.p.m., mbar
`
`Armature resistance,
`
`(2
`
`Field resistance, 9
`
`Vehicle wheel radius,
`
`in
`
`Motor torque, Nm
`
`Torque in gearbox output shaft, Nm
`Eng-fine torque, Nm
`
`Vehicle aerodynamic and rolling; resistance loss torque, Nrn
`
`Controller design criteria:
`
`rise time, sec
`
`Control system sampling period, sec
`
`Armature voltage, V
`
`Field voltage, V
`
`Adaptive error at j‘h sampling point
`
`Field current set-point function
`
`Plant model coeflicient vector
`
`Armature current set-point function
`
`Signifies small change in variable
`
`viii
`
`12
`
`12
`
`

`

`Controller design criteria clamping factor
`
`Engine throttle position, 0.9” steps
`
`Demand throttle position, (19° steps
`
`Electric motor accelerator/ brake demand
`
`Mean demand value during transient
`
`Inlet manifold filling time constant, sec
`
`Engine inertia time constant, sec
`
`Field flux, Wb
`
`Plant model input/output vector
`
`Controller torque demand
`
`ix
`
`13
`
`13
`
`

`

`List of Figures
`
`Fig.
`
`1.1 Series Hybrid Electric Vehicle Drive Train
`
`Fig.
`Fig.
`
`1.2 Parallel Hyhrid Electric Vehicle Drive Train
`1.3 Typical Engine Efficiency Map for a BUliVV LC. Engine
`
`Page
`
`28
`
`28
`29
`
`Fig.
`
`1.4 Influence of
`
`\Neighting Factor on the Performance of
`
`the Hybrid
`
`Vehicle
`
`30
`
`Fig.
`
`1.5 Use of the Engine Over an Urban Driving Cycle for an Optimailly
`
`Controlled Hybrid Vehicle
`
`Fig.
`
`1.6 Possible Hybrid Vehicle Control System
`
`Fig. 2.1 Test Bed Layout
`
`Fig. 2.2 Power Loading Provided by the Dynamometer
`
`Fig. 2.3 Test Bed Computing and Interface Equipment
`
`Fig.
`
`2.4 Software Structure
`
`.
`
`Fig. 3.] Elements of the Electric. Traction Drive
`
`Fig. 3.2 Block Diagram of Electric Motor Equations
`
`r
`
`Fig. 3.3 Variation oleield Current With Operating Mode
`
`Fig.
`
`3.4] Block Diagram for Motor Current Control
`
`Fig. 3.5 Engine Physical Processes
`
`Fig. 3.6 Block Diagram for the Throttle Servo—System
`Fig. 4.1 11‘. Engine Power Characteristics
`
`F
`
`30
`
`31
`
`53
`
`54
`
`55
`
`56
`
`72’.
`
`74
`
`75
`
`T6
`
`77
`
`78
`103
`
`Fig.
`
`4.2. LC. Engine POWer Characteristics: Variation of Regression Con-
`
`stants irith Speed
`
`.
`
`103
`
`Fig.
`4.3 Comparison of Torque Transducer
`Torque Prediction
`‘
`
`it‘leasurenients with LC. Engine
`104
`
`I
`
`Fig. 4.4 The Effect of the Engine Cooling Fan on Torque Measurements 104
`
`Fig. 4.5 \‘uriation of Motor Torque Constant with Field Current
`
`10.5
`
`14
`
`14
`
`

`

`Fig.
`
`4:5 Verification of the indirect. Torque hlleasnreniems for the Motor 11.15
`
`Fig.
`
`l.?(a.) Variation oli Field Current Witli input Demand in the Field Borist.
`
`M i )(l e
`
`11') 6
`
`Fig.
`
`415(1)) Variatirm oi Armature Current. with Input Demand in the Field
`
`Boost Mode
`1116
`Fig.
`4.8 Variation of Current with input Demand in the Full Field Mode
`
`107
`
`Fig.
`
`4.9(a) Variation of Field Current with Input Demand in the Field
`
`Weakening Mode
`
`107
`
`F ig. 4,9(li) Variation of Armature Current. with Input Demand in the Field
`
`\Neakening Mode
`
`Fig. 4.10 Adaptive Identification System
`
`108
`
`109
`
`Fig. 4.11 Model Identification for the Closed Loon Armature Current. Control
`
`Response GJ(:)
`
`110
`
`Fig.
`
`4.12 Comparison of Torque Transfer Functions with Experimental Data
`
`for the Field Boost Mode
`
`110
`
`Fig.
`
`4.13 Comparisons of Gains for the Manifold Filling Delay and Steady
`
`State Data Relating Manifold Depression to Throttle Opening
`
`Fig. 4.14 Block Diagram of the Linearised Engine Model
`
`' Fig. 4.]5 Engine Behaviour at
`
`10011 r.p.1n.
`
`Fig. 4.16 Engine Behaviour at. 3000 rpm.
`
`11]
`
`112
`
`113
`
`113
`
`Fig. 4.17 li‘erification of Transfer Functions for Engine Speed on No-Load 114
`
`Fig.-
`
`4.16 Predicted and Measured Torque and Current Responses for a
`
`Transient in the Field Boost Mode
`
`_-
`
`__
`
`114
`
`Fig.
`
`4.1!I Predict-ed and Measured Torque and Current Responses for
`
`a
`
`Transient in the. Fnli Field Mode
`
`,
`
`I
`
`115
`
`Fig.
`
`4.20 Predicted and Measured Torque and Current Responses for 3
`
`Transient
`
`in the Field Vv’eakening Mode
`
`11.5
`
`xi
`
`15
`
`15
`
`

`

`Fig. 4.2l Motor Torque Model: Test for the Direct lclentifit‘aition in the Fielcl
`
`Boost Mode
`
`116
`
`Fig. 423 Mom;- Torque Model: Tesl
`
`for the Direrl‘
`
`identification in the Full
`
`Field Mode
`
`'
`
`116
`
`Fig.
`4.23% Moioi‘ Torque Muriel: Test
`Weakening Mode
`
`for the Direct
`
`ltlen’rifiration in the Field
`7
`11?
`
`Fig. Filler) Unrompensatecl Lorna for Control of Engine Torque at 2000 rpm.
`
`145
`
`Fig. 5.]{l)) Compensated Locus for Control of Engine Torque at 2000 rpm.
`
`145
`
`Fig.
`
`5.2(a) Simulate-cl and Experimental Performance of the Engine Torque
`
`Control System at. 2000 r.p.ni.
`
`145
`
`Fig.
`
`52(1)) Sin'iulatetl and Experimental Performance of the Engine Torque
`
`Control System at 3000 r.p.1n.
`
`146
`
`Fig.
`
`5.3 Engine Torque Control System: Comparison oi'lntlirect. and Direct.
`
`Torque l\'le‘a5lll'€'1116nl5 During a Large Step Disturbance
`
`‘
`
`Fig.
`
`5.4 Motor Torque Control System
`
`.i.
`
`147
`
`148
`
`Fig.
`
`5.5(a) chompensatecl Locus [0: Motor Torque Control
`
`in the Field
`
`Boost Mode
`
`149
`
`Fig. 5.5{13}Compensated Locus for Motor Torque Control in the Field Boost
`Mode _
`i
`149
`
`5.6(a) Motor Torque Control Test
`Fig.
`Conditions
`
`in the Field Boost Mode at Design
`I
`I
`.
`150
`
`Fig.
`
`513(1)) Motor Torque Control Test.
`
`in the Field Boost Mode Away From
`
`Design (‘onclil-ioue
`Fig. 5.? Motor Torque Control Test.
`
`in ilie Full Field Mode
`
`1.50
`151
`
`Fig.
`
`5.3(a) Nlotor Torque Control Test
`
`in the Field W’eakening Mode at
`
`Design Conditions
`
`152
`
`xii
`
`16
`
`16
`
`

`

`Fig.
`
`5.8(l3) Motor Torque Control Test
`
`in the Field W’eakening Mode Away
`
`From Design Conditions
`
`552
`
`Fig. 5.9 l‘v’lotor Torque Control Demonstrating Satislnctory Transition Between
`
`Operating Modes
`
`153
`
`Fig. 5.10 hrlotor Torque Control:
`the Field Boost Mode
`
`lfllik=~ct of Using Field Wealiening Gains in
`'
`153
`
`Fig. 5.11 Engine Speed Control Block Diagram
`
`154
`
`Fig. 5.12M) Uncoinpensated Locus for Control of Engine Speed on No~Loztd
`
`Fig.
`
`3112(1)) Compensated Locus for Control of Engine Speed on No-Load
`
`Fig. 5.13 Step Test for
`
`the Engine Speed Control System
`
`Fig. 5.14 Analysis of the Engine Starting and Load Transfer Process
`
`Fig.
`
`5.1-5 Hill Climbing Control Design Process
`
`156
`
`1336
`
`133?
`
`Fig. 5.16 Lorne of Control Parameters During a. Hill Cliinh Design Procedure
`
`158
`
`Fig.
`
`5.17 Comparison of Reference Model Performance snide Control System
`
`Designed by the Hill Climb Method
`
`158
`
`Fig.
`
`6.1 Road Load and Motor Operating Curves for All Electric Vehicles
`
`17 00
`
`6.2 Tractive Effort and Road Load Curves for All Electric Vehicles
`Fig.
`Showing the Eliect of Gear Ratio
`'
`i
`179
`Fig. 6.3 The Gearchange Mechanism
`130
`
`.
`
`'
`
`Fig. 6.4 The Pneuinatic’Circuit
`
`Fig. 6.5 Regions Covered by the Position Sensors
`Fig. 6.6 Gear Change Algciritlnn FlDl-‘u'flli‘ftft
`,
`
`,
`
`181
`
`182
`183
`
`Fig. 6.7(a) Torque and Speed Profiles During a Down Change from rThird to
`
`Second
`
`184
`
`XIII
`
`17
`
`17
`
`

`

`Fig. 67(1)} Torque and Speed Profiles During an Up Change from Second to
`
`Third
`
`I
`
`Fig.
`
`6.8M.) Silage Timings for a. Down Change from Third in Second
`
`Fig.
`
`6.8(l3) Stage Timings l‘or an Up Change from Second lo Third
`
`Fig.
`
`7.1 (f‘oniplele \I’elir‘irlo Component Control System
`
`Fig, 7.2 Flowchart
`
`for Component Sequencing Logic
`
`Fig. T3 EC'E'l-S Cycle with Manual Accelerator and Brake Conf-rol
`
`Fig.
`
`7.4- Blocl: Diagram for Automatic Cycle Speed Control
`
`184
`
`[85
`
`1235
`
`20+
`
`205
`
`206
`
`20?
`
`Fig.
`
`7.5 Identification Experiment for the Flywheel and Dynamoineter
`
`208
`
`Fig. T.6 Compensated Locus for the Flywheel and Dynaniometer
`
`Fig. 7.7 Step Tea}. for the Cycle Speed Control System
`
`Fig. 7.8[al ECElB Cycle Using the Unmodified Speed Controller
`
`Fig.
`
`7.8{li'} Variation in Motor Torque
`
`Fig.
`
`7.9 Flywheel Inertia Calibration
`
`Fig. 7.lfl(a) ECEl-fi Cycle Using the Expert Control System
`
`2053
`
`209
`
`210
`
`21(7)
`
`211
`
`1212
`
`Fig.
`
`7.100)) Variation in Motor Torque Showing Immediate Drop at Break
`
`Points
`
`,
`
`212
`
`Fig.
`
`T.11(a) EC—EJS Cycle Using Speed Based Mode. and Gear Shifting
`
`Strategy
`
`Fig. 7.110)) Variation in Motor Torque
`
`Fig. T.11(r) Variation in Engine Torque
`
`Fig. 7.12m ECEIB Cycle Using Battery Recharge Mode
`
`l
`
`Fig. 7.120)) Variation in Engine and Motor Torque
`
`213
`
`213
`
`214'
`
`21 n
`
`21-5
`
`Bill;
`
`18
`
`18
`
`

`

`CHAPTER 1
`
`INTRODUCTION
`
`Conventional internal combustion (i.c.) engine vehicles, based on the
`
`Otto and Diesel cycles, have dominated road vehicle transport for the greater
`
`part of this century. Among their many advantages are unlimited range, ease
`
`of refuefling, good power characteristics and the low cost materials required for
`
`their construction [JPL, 1975 pp 3-2][Unnewehr and Nasar, 1982 pp 214-217]
`
`Despite these facts conventional vehicles bring with them problems of air
`
`pollution and inefficient use of dwindling fuel resources, which at the present
`
`rates may be depleted early in the twenty—first century [Foley, 1976]. Although
`
`diminishing energy resources, and in particular depletion of fossil fuels, poses
`
`a problem to many areas of technology it
`
`is particularly pronounced in the
`
`transport sector where the choice of fuels is most restricted. This dependence
`
`on one type of fuel
`
`is
`
`illustrated by examining figures
`
`for
`
`total energy
`
`consumption in Britain over
`
`recent years. Energy consumption in Britain
`
`peaked in about 1973 [Bumby and Clarke, 1982] subsequently falling by 11%
`
`in the years up to 1981 as a result of price rises, conservation measures and
`
`recession.
`
`Price rises were particularly great
`
`for oil based fuels and many
`
`non transport users switched to gas or coal over‘this time period. As a
`
`result of this switch over amongst more flexible users, the transport sector has
`
`become responsible for using a progressively greater proportion of the total
`
`amount of oil used in the UK. Over
`
`the period 1973—1981 this proportion
`
`rose dramatically from 29% to 47%. Further analysis of the transport sector
`
`itself shows that most fuel is used by passenger cars.
`
`In 1978 such vehicles
`
`accounted for 63% of all
`
`fuel used in vehicles, whilst
`
`the public transport
`
`sector for example, including taxis, coaches and buses used only 4.4% of the
`
`total [Dept
`
`of Energy, 1978}.
`
`Faced with this heavy dependence on oil,
`
`inspite of its likely exhaustion in the relatively near term,
`
`there has been
`
`19
`
`19
`
`19
`
`

`

`increasing interest
`
`in possible alternative vehicle propulsion systems over the
`
`last twenty years. Amongst
`
`the many possible alternative power plants are
`
`the Stirling engine,
`
`the Brayton engine (gas turbine) the all electric vehicle
`
`and the hybrid vehicle [JPL, 1975]. Of these alternatives the hybrid power
`
`plant is the subject of the present study. A hybrid power plant maybe defined
`
`as one that is powered by two or more energy sources and as such there are
`
`a multitude of possible combinations. Examples of some which have been
`
`investigated are:
`
`Heat engine/battery electric
`
`Flywheel/ battery electric
`
`Heat engine/flywheel/battery electric _
`
`Pneumatic/ battery electric
`
`Battery/ battery
`
`The purpose of this study is to consider the control problems relating to the
`
`heat engine/battery electric power train in particular. As many authors have
`
`pointed out
`
`[Mitcham and Bumby, 19??”Unnewehr and Nassar, 1982] using
`
`two power plants adds considerably to the complexity and cost of the whole
`
`vehicle and hence the power
`
`train must offer other compensating factors
`
`such as lower running costs,
`
`reduced pollution and less noise in sensitive
`
`areas. Of the alternatives to conventional
`
`i.c.
`
`vehicles mentioned earlier,
`
`the electric vehicle would seem to offer all
`
`these advantages without
`
`the
`
`added complexity of a duel power source. Unfortunately, due to current
`
`battery technology, electric vehicles are basically ‘energ‘y deficient’ [Unnewehr
`
`and Nassar, 1982]. Despite the fact that many types of advanced batteries
`
`have been the subject of much research and development, many people still
`
`feel
`
`that
`
`for
`
`the present, at
`
`least,
`
`the only practical storage battery for
`
`use in electric vehicles is the lead/acid type [van Niekerk et
`
`a1, 1980][Dell,
`
`1984], which has an energy density of 40 Wh/kg as opposed to the energy
`
`20
`
`20
`
`

`

`density of petroleum which is 12300 Wh/kg [Unnewehr and Nassar, 1982].
`
`In addition the energy density of lead/acid batteries falls at high discharge
`
`rates which always occur in vehicle applications during acceleration. As a
`
`consequence of these factors even advanced electric 'vehicles such as the ETV‘
`
`1, developed for the US. Department of Energy by Chrysler and General
`
`Electric, suffer from severe range limitations varying in this case from 160 km
`
`at 60 kin/h down to 95 km at 90 km/h even under
`
`favourable steady
`
`cruise conditions [Knrtz et al, 1981]. One Way of reducing the severe range
`
`restrictions of the straightforward all electric vehicle is to combine it with
`
`some secondary energy source in a hybrid design. As can be seen in the
`
`list of hybrid drives above, all
`
`incorporate an electrical system. Of these
`
`systems the flywheel/battery electric,
`
`the pneumatic battery/electric and the
`
`battery/battery can be considered as primarily electric since the secondary
`
`energy storage device has very limited capacity. Nevertheless this secondary
`
`device can make a substantial
`
`improvement
`
`to the vehicle range simply by
`
`providing energy for short bursts of acceleration.
`
`For example flywheel
`
`systems, despite their modest energy storage capacity, can easily provide
`
`enough energy to accelerate a. vehicle up to 30 mph once,
`
`thus protecting
`
`the batteries from the damaging high discharge rates which normally occur
`
`during such operation.
`
`In one such study simulatioris showed that electric
`
`vehicle range could be extended by 80% by using a flywheel of about 0.5 kWh
`
`capacity [Burrows et a1, 1980].
`
`On the other hand the hybrid heat engine/ battery electric is by no
`
`means primarily electric, with the power and stored energy capacity of the
`
`engine typically exceeding that of the electrical system.
`
`In this case the motor
`
`takes on a secondary role in shielding the engine from operating conditions
`
`which are particularly unfavourable to it. Typically this means that such
`
`a vehicle will operate electrically when the total power requirement
`
`is low.
`
`21
`
`21
`
`

`

`Since lovvr loading is typical of urban driving this vehicle has the potential to
`
`reduce pollution and noise in the urban environment whilst at the same time
`
`still offering the extended range capability characteristic of the engine.
`
`In
`
`general this system seeks to emphasise the particular strengths of each power
`
`source whilst playing down the disadvantages.
`
`When considering any type of hybrid electric vehicle two basic me-
`
`chanical configurations form the basis of nearly all designs. These are the
`
`series and parallel configurations, which are illustrated by figures 1.1 and
`
`1.2 respectively.
`In the parallel hybrid both the engine and the motor are
`connected directly to the roadwheels.
`Provision is usually made for them
`
`to operate either independently or jointly in powering the vehicle.
`
`In the
`
`series hybrid however, only the motor is connected to the road Wheels and
`
`must therefore be sized to meet all vehicle acceleration and top speed power
`
`requirements.
`
`In this case the engine supplies powor indirectly via the gen-
`
`erator battery combination. Although the series system has been considered
`for large bus applications [Brusaglino, 1982][Bader, 1981}[Roan, 1976], on the
`
`grounds that
`
`it gives greater flexibilty in positioning components and ease
`
`of controlling the Le. engine,
`
`the multiple energy chnversions invariably lead
`
`to a low overall efficiency. Consequently almost all designs for passenger car
`
`applications have tended to favour the parallel configuration. As seen previ-
`
`ously this latter application is most important because passenger cars offer the
`
`greatest potential fuel savings in the country as a Whole. Clearly if hybrid
`
`vehicles could offer significant fuel savings in this transport sector, the benefit
`
`to society would be substantial. Before considering What potential the hybrid
`
`heat engine/electric has for making fuel savings in this sector it is important
`
`to consider what it is competing against in terms of likely improvements to
`
`conventional vehicles and other alternative vehicle power systems.
`
`22
`
`22
`
`

`

`1.1 Possible improvements or Alternatives to LC. Engine Vehicles
`
`It is important to recognise that any alternative to i.c. engine vehicles
`
`is competing against a mature, established technology backed up by a large
`
`industrial
`
`research base.
`
`As a result conventional vehicles have shown a
`
`steady improvement over the years and seem likely to continue to do so.
`
`It is
`
`therefore pointless to compare possible economic and environmental advantages
`
`of a new vehicle technology against the i.c.
`
`engine vehicles which are being
`
`built
`
`today. A more realistic comparison is to judge the new technology
`
`against an estimate of what conventional vehicles will achieve 10-15 years
`
`from now. This 10'15 year period will then allow a reasonable time span for
`
`the new technology to be put
`
`into production on a worthwhile scale. Some
`
`of the likely improvements in i.c.
`
`engine design which might be made over
`
`the next few years are discussed by Blackmore and Thomas [Blackmore and
`
`Thomas, 1979]. This review suggests that major economy improvements could
`
`be achieved by using higher compression ratios coupled with leaner mixtures
`
`thus saving 20% of fuel use over all operating conditions.
`
`Lean mixtures
`
`must be used in conjunction with the higher compression ratios to avoid
`
`problems with knocking. Other savings can be achieved by improvements to
`
`cold starting ( saving 25% on short
`
`trips ), power modulation by variable
`
`mixture strength as opposed to the inefficient throttling method ( saving 20%
`
`on average ) and finally up to 10% can be saved by improving fuel and
`
`lubricants. Apart
`
`from changes to the engine itself further improvements
`
`can be made by altering vehicle aerodynamics and designing better tyres and
`
`gearboxes.
`
`Electronic engine control systems also offer substantial improvements
`
`in fuel economy.
`
`One major application for electronics is
`
`in Optimising
`
`ignition timing. Standard mechanical distributors produce a crude variation
`
`in spark timing on the basis of engine speed, as sensed by a centrifugal weight
`
`23
`
`23
`
`

`

`system, and engine load1 as determined indirectly by a vacuum diaphragm
`
`lever system connected to the inlet manifold. Load and speed are in fact
`
`the correct indicators needed to optimise ignition timing, but the mechanical
`
`system can never re-produce the complex function relating them to optimum
`
`spark advance.
`
`In contrast,
`
`in an electronic system,
`
`it
`
`is possible to store
`
`the best spark advance as a function of manifold depression and speed in a
`
`two dimensional look-up table. As described by Main [Main, 1986] Ford have
`
`produced a microprocessor system which not only controls spark timing but
`
`also controls a continuously variable transmission system (CVT).
`
`Unlike some proposed vehicle systems the hybrid heat engine/battery
`
`electric can incorporate all
`
`the changes mentioned above in its own engine
`
`and so its potential advantages remain undiminished.
`
`1.1 .1 Novel Engines
`
`Apart
`
`from all electric and hybrid vehicles which may generally be
`
`considered as the electric alternative, whether partial or complete,
`
`there are
`
`two other major possibilities; alternative fuels and novel engines. Leading
`
`examples of alternative fuels are those based on agricultural products such as
`
`alcohol made from sugar. This has been successfully applied in Brazil with 95%
`
`alcohol by volume being used in cars with modified carburetters. According
`
`to the Jet Propulsion Laboratory (JPL) [JPL, 1975] lesser concentrations, up
`
`to 28%, maybe used in ordinary cars without any such modifications. A
`
`second alternative is to produce synthetic petroleum from coal as has already
`
`been done in S. Africa. Neither of these alternatives are without drawbacks
`
`though, alcohol for example is particularly prone to absorb water in storage
`
`and the petrol from coal process is undesirable on both environmental and
`
`efficiency grounds [Mitcham and BmmbyJ 1977].
`
`Amongst the most
`
`likely novel engines are the gas turbine, based on
`
`24
`
`24
`
`

`

`the Joule Brayton cycle, and the Stirling engine. Gas turbines are already
`
`highly successful as aero-engines but need much development for small scale
`
`use in cars.
`
`in addition they use more expensive materials in order
`
`to
`
`withstand the high temperatures associated with a continuous combustion
`
`process [Bumby and Clarke, 1982]. External combustion engines such as the
`
`Stirling design promise a broader choice of fuels and the ability to optimise
`
`combustion conditions for better efficiency and reduced emissions. Despite
`
`improvements to heat exchangers however the Stirling engine still suffers from
`
`large thermal inertia.
`
`In their study of alternative vehicle pourer systems, JPL concluded
`
`that the Stirling engine and the gas turbine might achieve gains of 20% and
`
`30% respectively when compared with the conventional vehicles of the time
`
`(1975). When such improvements are viewed in the light of the predicted
`
`improvements to the conventional car itself, these figures are not outstanding,
`
`particularly when it is considered that in all cases the alternative engine costs
`
`more to produce.
`
`1.1.2 The Electric Vehicle
`
`Although of somewhat
`
`limited range the all electric vehicle must
`
`not be dismissed prematurely as a likely replacement means of transport,
`
`particularly in certain applications. Fleet trials of electric vehicles have shown
`
`them to be very useful
`
`in applications with a well defined use pattern and
`
`limited range requirement, such as the small delivery vehicle. Volksivagen
`
`[Altendorf et al, 1982] undertook one such trial with 40 electric vehicles
`
`beginning in 1978 and found them to be reliable and acceptable to their
`
`operators. Unfortunately this success will not be‘repeated in the car market
`
`until improved battery technology is widely available. Although many battery
`
`types such as nickel/zinc and nickel/iron offer considerable improvements in
`
`25
`
`25
`
`

`

`energy storage capacity over
`
`lead-acids,
`
`they still do not give an electrical
`
`vehicle comparable performance with a conventional vehicle. One possible
`
`battery technology which does promise large vehicle range, up to 200 km,
`
`is
`
`sodium/sulphur. Here the main problem is that battery operating temperature
`
`must be above 300°C.
`
`Assuming that some battery technology such as sodium/ sulphur could
`
`provide vehicle performance that was acceptable to the consumer, a Whole new
`
`problem is created when the infrastructure needed for refuelling is considered.
`
`To assess this problem Watson [Watson et al, 1986] carried out a computer
`
`simulation study to determine the cost of the vehicle refuelling infrastructure
`
`that Would be needed for an all electric car
`
`fleet of