`
`Yimin Gao
`
`J
`
`Modern Electric,
`Hybrid Electric, and
`BUCM@iMeliaie
`Fundamentals, Theory, and Design
`
`Ali Emadi BMWv. Paice, IPR2020-00994
`
`Sebastien E. Gay
`
`BMW v. Paice, IPR2020-00994
`BM
`BMW1092
`Page 1 of 21
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`
`
`Modern Electric,
`Hybrid Electric, and
`Fuel Cell Vehicles
`Fundamentals, Theory, and Design
`
`Mehrdad Ehsani, Texas Aam University
`
`Yimin Gao, Texas A&M University
`
`Sebastien E. Gay, Texas A&M University
`
`Ali Emadii, ttlinois institute of Technology
`
`CRC PRESS
`
`Boca Raton London New York Washington, D.C.
`
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`
`General Linrary System
`University of Wisconsin -hi°
`728 State Street
`Madison, W4 §3765-1494
`U.S.A.
`oo
`
`.
`
`..
`
`Library of Congress Cataloging-in-Publication Data
`
`2004054249
`
`Modern electric, hybrid electric, and fuel cell vehicles: fundamentals,
`theory, and design/Mehrdad Ehsani... [et al.].
`p. cm. - (Powerelectronics and applications series)
`Includes bibliographical references and index.
`ISBN 0-8493-3154-4 (alk. paper)
`1. Hybrid electric vehicles. 2. Fuel cells.
`
`I. Ehsani, Mehrdad.
`
`II. Title.
`
`III. Series.
`
`TL221.15,.G39 2004
`629.22'93—dc22
`
`This book contains information obtained from authentic and highly regarded sources.
`Reprinted material is quoted with permission, and sources are indicated. A wide variety of ref-
`erences ara listed. Reasonable efforts have been madeto publish reliable data and information,
`but the author and the publisher cannot assume responsibility for the validity of all materials
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`Neitherthis book nor any part may be reproduced or transmitted in any form or by any means,
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`© 2005 by CRC Press LLC
`Noclaim to original U.S. Government works
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`Internationa! Standard Book Number 0-8493-3154-4
`Library of Congress Card Number 2004054249
`Printed in the United States of Americal 234567890
`Printed on acid-free paper
`
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`8 P
`
`
`
`arallel Hybrid Electric Drive Train Design
`
`CONTENTS
`8.1 Control Strategies of Parallel Hybrid Drive Train........ cesses261
`8.1.1 Maximum State-of-Charge of Peaking Power Source
`(Max. SOC-of-PPS) Control Strategy... ecsesesesseeeecnseenenees262
`8.1.2 Engine Turn-On and Turn-Off (Engine-On-Off)
`Control Strategy ciccscseccscesseessesssenerenetesseesssseseneenssesesesees265
`8.2 Design of Drive Train Parameters ........csccscssscsssscsessseeessesssssssneenenenees266
`8.2.1 Design of Engine Power Capacity..ccsscscssceessssseseseenenens 266
`8.2.2 Design of Electric Motor Drive Power Capacity...268
`8.2.3 Transmission Design wscesecsesssessuensessssseasesenenesaeseessnsnensness271
`8.2.4 Energy Storage Design ........cccscsscscssesesssssssseseesesenssesereeresseenseasees272
`B.S Simulations oe. cecssesesesssnscereeeeecessesseseesnsnneresressssasaneneueseoeseseeaseansneaneteses274
`References .ocssisssscscsssssrsrsssansecsssevesesesvenssssersesecennmsesensseseesssssessaaneaeeaeeeneacseaess276
`
`Unlike the series hybrid drive train, the parallel hybrid drive train has
`features that allow both the engine and traction motor to supply their
`mechanical power in parallel directly to the driven wheels. The major
`advantagesof parallel configuration over a series configuration are (1) gen-
`erator is not required, (2)
`the traction motor is smaller, and (3) multi-
`conversion of the power from the engine to the driven wheels is not nec-
`essary. Hence, the overall efficiency can be higher. However, the control of
`the parallel hybrid drive train is more complex than that of a series hybrid
`drive train, due to the mechanical coupling between the engine and the
`driven wheels.
`There are several possibilities for configurations in a parallel hybrid drive
`train, as mentioned in Chapter 5. But the design methodology for one par-
`ticular configuration may be not applicable to other configurations and the
`design result for a particular configuration may be applicable for only a
`given operation environment and mission requirement. This chapter will
`focus on the design methodology of parallel drive trains with torque
`coupling, which operate on the electrically peaking principle; that is, the
`engine supplies its power to meet the base load (operating at a given
`
`259
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
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`constant speed on flat and mild grade roads, or at the average of the load of
`a stop-and-go driving pattern) and theelectrical traction supplies the power
`to meet the peaking load requirement. Other options, such as a mild hybrid
`drive train, are discussed in Chapter 9.
`The base load is much lower than the peaking load in normal urban and
`highway driving, as mentioned in Chapter 5. This suggests that the engine
`powerrating is lower than theelectrical traction power rating. Due to the
`better torque-speed characteristics of the traction motor compared to
`the engine, the single-gear transmission for the traction motor might be the
`proper option. Thus, this chapter will focus on the design of the drive train
`as shown in Figure8.1.
`The design objectives are:
`
`1. To satisfy the performance requirements (gradeability, acceleration,
`and maximum cruising speed)
`2. To achieve high overall efficiency
`3. To maintain the battery state-of-charge (SOC) at reasonable levels
`in the whole drive cycle without charging from outside the vehicle
`4. To recover the brake energy.
`
`Vehicle
`
`Engine
`
`Torque
`coupler
`
`Vehicla speed
`
`Mechanical connection
`
`
`
`Mechanical
`
`brake
`
`
`Operation
`
`controller
`command
`
`
`
`
`
`controller
`z5
`
`
`
`Engine
`2 &
`
`
`contro!
`pe
`
`we
`
`controller
`
`
`
`
`
`Electrical power
`—— Signals
`
`FIGURE 8.1
`Configuration of the parallel torque-coupling hybrid drive train
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`261
`
`Due
`
`8.1 Control Strategies of Parallel Hybrid Drive Train
`
`The available operation modesin a parallel hybrid drive train, as mentioned
`in Chapter 5, mainly include (1) engine-alonetraction, (2) electric-alone trac-
`tion, (3) hybrid traction (engine plus motor}, (4) regenerative braking, and
`(5) peaking power source (PPS) charging from the engine. During operation,
`the proper operation modes should be used so as to meetthe traction torque
`requirement, achieve high overall efficiency, maintain a reasonable level of
`PPS SOC, and recover braking energy as much as possible.*
`The overall control scheme consists of two levels. A vehicle system level
`controller (a high-level controller) functions as a control commander and
`gives torque commands to low-level controllers (local or component con-
`trollers) based on the operator’s command, component characteristics, and
`feedback information from the components. The low-level controllers (local
`or component controllers), such as the engine controller, motor controller,
`and transmission controller in a multigear transmission, control the corre-
`sponding components to make them operate properly.
`The overall control scheme of the parallel hybrid drive train is schemati-
`cally shown in Figure8.2. It consists of a vehicle controller, engine controller,
`
`Accelerator pedal
`position signal
`
`Brake pedal
`position signal
`
`
`
`
`«—— Vehicle speed
`+~— Batteries SOC
`ToT" “Engine power| | [Motor | Friction brake
`Engine power
`command
`power command
`
`Vehicle controller
`
`
`
`
`----4—--------5
`
`|
` Friction
`Regenerating
`
`braking power
`j
`
` Transmission
`
`
`C 1 1I
`
`iL
`
`braking
`power
`
`:
`
`eneeeeere|
`Driving wheels||
`J
`
`* FIGURE 8.2
`Overall control schemeof the parallel hybrid drive train
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
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`electric motor controller, and mechanical brake controller. The vehicle con-
`troller is in the highest position. It collects data from the driver andall the
`components, such as desired torque, vehicle speed, PPS SOC, engine speed
`and throttle position, electric motor speed,etc. Based on these data, compo-
`nent characteristics, and preset control strategy, the vehicle controller gives
`its control signals to each component controller/local controller. Each local
`controller controls the operation of the corresponding component to meet
`the requirements of the drivetrain.
`The vehicle controller plays a central role in the operation of the drive
`train. The vehicle controller should fulfill various operation modes —
`according to the drive condition and the data collected from components
`and the driver’s command — and should give the correct control command
`to each componentcontroller. Hence, the preset control strategy is the key to
`the optimum successof the operation of the drive train.
`
`8.1.1
`
`MaximumState-of-Charge of Peaking Power Source (Max. SOC-of-
`PPS) Control Strategy
`Whena vehicle is operating in a stop-and-go driving pattern, the PPS must
`deliver its power to the drive train frequently. Consequently, the PPS tends
`to be discharged quickly. In this case, maintaining a high SOC in the PPSis
`necessary to ensure vehicle performance. Thus, the maximum SOC of the
`PPS control strategy may be the proper option.*
`The maximum control strategy can be explained by Figure 8.3. In this figure,
`the maximum power curves for hybrid traction (engine pluselectric motor),
`engine-alonetraction, electric motor-alone traction, and regenerative braking
`
`1 — Maximum powerwith hybrid mode
`
`Tractionpower
`
`
`Brakingpower
`
`3
`4
`
`2 — Maximum powerwith electric-alone traction
`3 — Engine poweronits optimum operating line
`4 — Engine power with partial load
`5 -— Maximum generative power of electric motor
`P.
`Vehicle speed
`P, — Load power, traction or braking
`P, — Engine power
`Pm— Motortraction power
`Pap — Motor braking power
`Pay — Mechanical braking power
`Pe — PPS charging power
`
`oa
`
`5
`
`FIGURE 8.3
`Demonstration of various operating modes based on power demand
`
`
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`263
`
`are plotted against vehicle speed. Power demandsin different conditions are
`also plotted, represented by points A, B, C, and D.
`The operation modesof the drive train are explained below:
`Motor-alone propelling mode: The vehicle speed is less than a preset value
`V4, which is considered to be the bottom line of the vehicle speed below
`which the engine cannot operate steadily. In this case, the electric motor
`alone delivers its power to the driven wheels, while the engine is shut down
`or idling. The engine power,electric traction power, and the PPS discharge
`powercan be written as
`
`P.=0,
`Py
`Pnn Thm’
`
`Pr
`Poped= He
`
`(8.1)
`
`(8.2)
`
`(8.3)
`
`where P, is the engine power output, P, is the load power demand on the
`drive wheels, n,,, is the transmission efficiency from the motorto the driven
`wheels, P,, is the power outputof the electric motor, P,,., is the PPS dis-
`charge power, and 1, is the motorefficiency.
`Hybrid propelling mode: The load power demand,represented by point A in
`Figure 8.3, is greater than what the engine can produce, both the engine and
`electric motor must deliver their power to the driven wheels at the same
`time. This is called hybrid propelling mode. In this case, the engine opera-
`tion is set on its optimum operation line by controlling the engine throttle to
`produce powerP,. The remaining power demandis supplied bythe electric
`motor. The motor power output and PPS discharge powerare
`P,-P
`P,=ete,
`
`(8.4)
`
`Pu
`Pypsd = Hor
`
`(8.5)
`
`where 7,, is the transmission efficiency from the engineto the drive wheels.
`PPS charge mode: When the load power demand, represented by point B in
`Figure 8.3, is less than the powerthat the engine can produce while operat-
`ing on its optimum operation line, and the PPS SOC is belowits top line, the
`engine is operated on its optimum operating line, producing its powerP,. In
`this case, the electric motor is controlled by its controller to function as a gen-
`erator, powered by the remaining powerof the engine. The output power of
`the electri¢ motor and PPS charge powerare
`PL
`P,, = P.- “The, Tem"ne
`Praps-c = Par
`
`(8.6)
`(8.7)
`
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
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`where 7,.,, is the transmission efficiency from the engine to the electric
`motor.
`Engine-alone propelling mode: When the load power demand (represented
`by point B in Figure 8.3) is less than the powerthat the engine can produce
`while operating onits optimum operation line, and the PPS SOC has reached
`its top line, the engine-alone propelling mode is used. In this case, the elec-
`tric system is shut down,and the engine is operated to supply the powerthat
`meets the load power demand. The power output curve of the engine with
`a partial load is represented by the dashed line in Figure 8.3. The engine
`power, electric power, and battery power can be expressed by
`P= au
`e Me?
`P,=0,
`
`8.8
`)
`‘
`(
`(8.9)
`
`Pi=O.
`
`(8.10)
`
`Regenerative-alone brake mode: When the vehicle experiences braking and the
`demanded braking poweris less than the maximum regenerative braking
`powerthat the electric system can supply (as shown in Figure 8.3 by point
`D)}, the electric motor is controlled to function as a generator to produce a
`braking power that equals the commanded braking power. In this case, the
`engine is shut downorset idling. The motor power output and PPS charge
`power are
`
`Pb = PEMmm
`
`Ppsec = Pm
`
`(8.11)
`
`(8.12)
`
`Hybrid braking mode: When the demanded braking poweris greater than the
`maximum regenerative braking powerthat the electric system can supply
`(as shown in Figure 8.3 by point C), the mechanical brake must be applied.
`In this case, the electric motor should be controlled to produce its maximum
`regenerative braking power, and the mechanical brake system should han-
`dle the remaining portion. The motor output power, battery charging power,
`and mechanical braking power are
`
`Pa» = Pvahmaxar
`
`Papse = Py
`
`(8.13)
`
`(8.14)
`
`It should be noted that for better braking performance, the front forces on
`the front and rear wheels should be proportional to their normal load on the
`wheels. Thus, braking power control will not be exactly that mentioned
`above (for more details, see Chapter 11). The control flowchart of the Max.
`SCO-of-PPSis illustrated in Figure 8.4.
`
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`265
`
` Maximum
` Traction power
`motor power
`
`command, Pie
`
`
`
`Braking power
`
`Regenerative-
`
`
`alone braking
`
`mode
`
`
`
`
`Hybrid
`braking mode
`
`P. — Tha engine power while operating
`its optimum operating ilne
`
`.
`Vehicle speed,
`
`P.e-opt
`
`SOC-ofPPS
`
`H P> Pnapt
`
`No
`
`lf S0c<806,,,
`
`Yes
`
`
`
`FIGURE 8.4
`Flowchart of Max. SOC-of-PPS control strategy
`
`PPS SOCtop line
`
`
`Engineoperation
`
` PPS SOCbottom fine
`
`
`
`FIGURE 8.5
`Iustration of engine-on-off control strategy
`
`8.1.2
`
`Engine Turn-On and Turn-Off (Engine-On—Off) Control Strategy
`
`Similar to that used in a series hybrid drive train, the engine turn-on and
`turn-off control strategy may be used in some operation conditions with low
`speed and low acceleration. In an engine-on—off controlstrategy, the opera-
`tion of the engine is controlled by the SOC of PPS, as shownin Figure 8.5.
`In the engine-on period, the control is Max. SOC-of-PPS strategy. When
`the SOC of the PPS reachesits top line, the engine is turned off and the vehi-
`cle is propelled only by the electric motor. When the SOC of the PPS reaches
`its bottom line, the engine is turned on and the control again goes into Max.
`SOC-of-PPS.
`
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
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`Que
`
`8.2. Design of Drive Train Parameters
`
`The parameters of the drive train such as engine power, electric motor power,
`gear ratios of transmission, and power and energy capacity of the peaking
`powersource are key parameters, and exert a considerable influence on vehi-
`cle performance and operation efficiency. However, as initial steps in the
`design, these parameters should be estimated based on performance require-
`ments. Such parameters should also be refined by more accurate simulations.
`In the following sections, the parameters of a passengercar are used in the
`calculations. These parameters are vehicle mass M,= 1500 kg,rolling resist-
`ance coefficient f,= 0.01, air density p,= 1.205 kg/m’, front area A, =2.0 m?,
`aerodynamic drag coefficient Cp =0.3, radius of driven wheels r=0.2794 m,
`and transmission efficiency from engine to drive wheels n,,=0.9, and from
`motorto drive wheels 7,,,=0.95.
`
`8.2.1
`
`Design of Engine Power Capacity
`
`The engine should be able to supply sufficient power to support the vehicle
`operation at normal constant speeds both on a flat and a mild grade road
`without the help of the PPS. At the same time, the engine should be able to
`produce an average power thatis larger than the average load power when
`the vehicle operates with a stop-and-go operating pattern.
`As a requirement of normal highway driving at constant speed ona flat or
`a mild grade road, the power neededis expressed as
`e 10007,, (Maoh 2 PCpAV +M,¢KW),
`p
`4
`_ Vv
`
`1
`
`,
`
`.
`
`(8.15)
`
`Figure 8.6 showsthe load powers of a 1500 kg example passengercar, along
`with vehicle speed, on a flat road and a road with 5%grade. It is seen that
`on a flat road, a speed of 160 km/h (100 mph) needs a powerof 42 kW.For
`a comprehensive analysis, the power curves of a 42 kW engine with a mullti-
`gear transmission are also plotted in Figure 8.6. From Figure 8.6, it can also
`be seen that on a 5% grade road, the vehicle can reach a maximum speed of
`about 92 and 110 km/h with the fourth gear and third gear, respectively.
`The above-designed engine powershould be evaluatedso that it meets the
`average power requirement while driving in a stop-and-go pattern. In a
`drive cycle, the average load powerof a vehicle can be calculated by
`
`1"
`
`1
`
`Poej (MugfVta PrCpAV3+6M,vr dt.
`
`dV
`
`(8.16)
`
`The average power varies with the degree of regenerative braking. The two
`extreme cases are the full and zero regenerative braking cases. Full regenera-
`tive braking recovers all the energy consumed in braking and the average
`poweris calculated by (8.16). However, when the vehicle has no regenerative
`
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`267
`
`Engine power Ona5% Ona flat
`grade road
`ad
`
`50
`45
`40
`
`35
`= 30
`o 29
`=
`
`15k
`
`Resistance
`
`0
`
`20
`
`40
`
`120
`100
`80
`60
`Vehicle speed (km/h)
`
`149
`
`160
`
`180
`
`FIGURE 8.6
`Engine powerrequired at constant speed ona flat road and a 5% grade road
`
`braking, the average poweris larger than that with full regenerative braking,
`which can be calculated from (8.16) in such a way that when the instanta-
`neous poweris Jess than zero,it is given a zero.
`Figure 8.7 showsthe vehicle speed, instantaneous load power, and aver-
`age powerswith full regenerative braking and zero regenerative braking, in
`sometypical drive cycles for a 1500 kg passenger car.
`In the engine powerdesign, the average powerthat the engine can produce
`must be greater than the average load power. Ina parallel drive train, the engine
`is mechanically coupled to the driven wheels. Hence, the enginerotating speed
`varies with the vehicle speed. On the other hand, the engine power with full
`throttle varies with engine rotating speed. Thus, the determination of the engine
`powerto meet the average powerinadrivecycleis not as straightforward as in
`a series hybrid, in which the engine operating can be fixed. The average power
`that the engine can produce with full throttle can be calculated as
`if
`(8.17)
`Pnax-ave™ T i P{v) dt,
`where T is the total time in drive cycles and P,(v) is the engine power with
`full throttle, which is a function of vehicle speed when the gear ratio of the
`transmissionis given, as shown in Figure 8.6.
`The possible operating points of the engine with full throttle and the max-
`imum possible average powers in some typical drive cycles are shown in
`Figure 8.8, in which the maximum engine poweris 42 kW and transmission
`is single gear (fourth gear only in Figure 8.6). Comparing these maximum
`possible average powersto the load average powers, as shownin Figure 8.7,
`it is concluded that the engine poweris sufficient to support a vehicle oper-
`ating in these typical drive cycles.
`
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
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`o88:|
`Speed(km/h}
`
`
`Zero regenerative
`
`
`
`
`
`
`o
`
`200
`
`460
`
`1000
`
`1200
`
`1400 Ay
`
`100
`
`800
`#600
`Time (sec)
`(a) FTP 75 urban diving cycle
`
`200
`
`600
`
`700
`
`3800
`
`500
`400
`300
`Time (sec)
`{b) FTP 75 highway diving cyclo
`
`instantaneous power Average power with
`
`En afaSee to
`pe
`Average power without
`regensrative braking
`
`
`
`Speed(kmsh}
`
`=
`3
`
`za
`
`_
`
`£&
`
`
`
`150
`E100
`Rs
`&
`
`=
`x
`:
`
`Averaga power with
`Zero regenerative
`
`100
`
`power withe
`ieecereine braking
`200
`300
`400
`Time (sec)
`(c) USO6 driving cycle
`
`500
`
`600
`
`0
`
`Average powerwith instantaneous power
`zaro regenarative
`
`Avelagepowerwithout
`2
`regensrattve braking
`100
`200
`300
`Time (89)
`(d) EGE-driving cycle
`
`400
`
`500
`
`600
`
`HM
`
`3
`a 0
`00
`¢ *
`e
`i
`- 05
`
`FIGURE 8.7
`Instantaneous power and average power with full and zero regenerative braking in typical
`drive cycles
`
`8.2.2 Design of Electric Motor Drive Power Capacity
`In HEV, the major function of the electric motor is to supply peak powerto
`the drive train. In the motor power design, acceleration performance and
`peak load powerin typical drive cycles are the major concerns.?
`It is difficult to directly design the motor power from the acceleration per-
`formance specified.It is necessary to make a good estimate based on speci-
`fied acceleration requirements, and then make a final design through
`accurate simulation. As an initial estimate, one can make the assumption
`that the steady-state load (rolling resistance and aerodynamic drag) is han-
`died by the engine and the dynamic load (inertial load in acceleration) is
`handled by the motor. With this assumption, acceleration is directly related
`to the torque output of an electric motor by
`Ti, tsm™le i
`
`rT
`~ Onn
`
`dV
`vp dt?
`
`(8.18)
`
`where T,, is the motor torque and 6,, is the mass factor associated with the
`electric motor (refer to Chapter 2).
`Using the output characteristics of the electric motor shown in Figure 8.5,
`and a specified acceleration time,t,, from zero speed to final high speed, Vy,
`
`
`
`
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`
`Maximum average
`power:
`14.5 kW
`
`Engine power~—spoed
`curve with full throttle
`
`=
`5
`=
`a
`2
`a
`ui
`
`5
`
`20
`
`40
`
`perating points
`with full throttle
`60
`8&0
`100 120 140 160 180
`Vehicle speed (km/h)
`(a) FTP 75 urban driving cycle
`
`45
`40 Maximum average
`power:
`>
`2 35
`28.3 kW
`& 30
`5
`a 25
`20
`=
`wets
`10
`5
`
`_speed
`Enai
`spec!
`ngine power-
`curve with full throttle
`
`Operating points
`with full throttte
`
`20
`
`40
`
`100 120 140 160 180
`80
`60
`Vehicle speed (kmh)
`(cb) FTP 75 highway driving cycle
`
`
`
`
`45
`45
`40
`40
`=
`=
`= 35
`= 35
`Engina power—speed
`2 30
`Engine power—speed
`= 30
`
`
`3 curve with full throttla}=3 curve with full throttle
`@ 25c
`a 25
`4 26
`B20
`Operating paints
`a
`with full throttle
`a
`18
`16
`10
`10
`
`Maximum average
`power:
`32.2 kW
`
`Maximurn average
`power:
`22.1 KW
`
`Operating points
`with full throttle
`
`550
`
`40
`
`60
`
`100 120 140 160 180
`980
`Vehicle speed (km/h}
`{c) USO6 driving cycle
`
`550
`
`40
`
`100 120 140 160 180
`80
`60
`Vehicle speed (km/h)
`(d) EGE-1 driving cycle
`
`FIGURE 8.8
`Maximum possible operating points of the engine and the maximum average powerin typical
`drive cycles
`
`and referring to Chapter 4, the motor powerrating is expressed as
`= SM,
`2
`2
`(8.19)
`Pn = Stat,VtVO.
`For a 1500 kg passenger car with a maximum speedof 160 km/h, a base speed
`of 50 km/h,a final acceleration speed of 100 km/h,acceleration time ¢,= 10
`sec, and 6,,= 1.04, the powerrating of the electric motor is 74 kW (Figure 8.9).
`It should be noted that the motor power obtained above is somewhat
`overestimated. Actually, the engine has some remaining power to help the
`electric motor to accelerate the vehicle as shownin Figure 8.6. This fact is
`also shown in Figure 8.10, in which vehicle speed, engine power with full
`throttle, resistance power(rolling resistance, aerodynamic drag, and power
`losses in transmission), and single-gear transition are plotted along the accel-
`eration time. The average remaining powerof the engine, used to accelerate
`the vehicle, can be expressed as
`
`_—1 fp
`
`P= EF l (P,—P,) dt,
`
`_
`
`(8.20)
`
`‘where P, and P, are the engine power and resistance power, respectively. It
`should be noted that the engine power transmitted to the driven wheels is
`
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
`
`6 b
`
`ha
`
`to
`
`
`
`
`
`Tractiveeffort(KN)
`
`0
`
`o
`
`20
`
`40
`
`7
`100 120 140 160 180
`80
`60
`Vehicle speed (km/h)
`
`FIGURE 8.3
`Tractive effort vs. vehicle speed of an electric motor-driven vehicle
`
`120
`
`100
`
`80
`
`60
`
`40
`
`20
`
`acceleration (kK
`
`.
`Vehicle speed (km/h)
`
`Engine power(kW)
`
`Resistance power (kW)
`
`,
`
`Englne powerfor
`
`Time (sec)
`
`FIGURE 3.10
`Vehicle speed, engine power, and resistance powervs. acceleration time
`
`associated with the transmission, thatis, the gear number and gearratios.It
`is clear from Figure 8.6 that a multigear transmission will effectively increase
`the remaining power at the driven wheels, thus reducing the motor power
`required for acceleration.
`Using the numbers of engine power and vehicle parameters mentioned
`above, the engine’s remaining power(as shown in Figure 8.10) is obtained as
`17 kW. Thus, the motor poweris finally estimated as 74-17 =57 kW,
`When the power ratings of the engine and electric motorare initially
`designed, a more accurate calculation needs to be performedto evaluate the
`
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`
`o1= 25° (46.6%)
`
`a= 20° (36.4%)
`
`(kN)
`Tractiveeffertondrivenwheels
`
`
`
`0
`
`20
`
`40
`
`60
`
`80
`
`100
`
`120
`
`140
`
`160
`
`180
`
`FIGURE8.11
`
`Tractive effort and resistance on slope road vs. vehicle speed
`
`Vehicle speed (km/h)
`
`vehicle performance, mainly maximum speed, gradeability, and accelera-
`tion. The maximum speed and gradeability can be obtained from the dia-
`gram of tractive effort and resistance vs. vehicle speed. This diagram can be
`made by using the methods discussed in Chapter2.
`The diagram (as shownin Figure 8.11) showsthe design results of an exam-
`ple passenger car. It indicates that the vehicle at 100 km/h hasa gradeability
`of 4.6% (2.65°) for the engine-alone mode, 10.36%(5.91°) for the motor-alone
`mode, and 18.14% (10.28°) for the hybrid mode (engine plus motor).
`Figure 8.12 shows the acceleration performance for the passenger car
`example.It indicates that 10.7 sec are used and 167 m are covered for accel-
`erating the vehicle from zero speed to 100 km/h.
`
`8.2.3
`Transmission Design
`Since the electric motor supplies the peak power and has high torque at low
`speed, single-gear transmission between the electric motor and the driven
`wheels can produce sufficient torque for hill climbing and acceleration (refer
`to Figure 8.11). However, a multigear transmission between the engine and
`driven wheels can indeed enhance the vehicle performance.
`The use of multigear transmission, as shown in Figure 8.6, can effectively
`increase the remaining powerof the engine. Consequently, the vehicle per-
`formance (acceleration and gradeability) can be improved. On the other hand,
`the energy storage can be charged with the large power of the engine. The
`vehicle fuel economy can also be improved, since the use of proper gears of
`the multigear transmission allows the engine to operate closer to its optimal
`speed region. Furthermore, the large remaining power of the engine can
`quickly charge the energy storage from low SOC to high SOC.'
`
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
`
`35
`
`30
`
`>
`g
`~— 25
`£
`6 20
`a
`3 15
`<
`10
`
`5
`
`0
`
`400
`
`350
`
`300 co
`3
`—
`250 §
`Cc
`200 =
`2
`150 §
`8
`too *
`
`50
`
`0
`140
`
` 40
`
`Distance
`
`0
`
`20
`
`40
`
`60
`
`80
`
`100
`
`120
`
`Vehicle speed (knvh)
`
`FIGURE8.12
`Acceleration time and distance vs. vehicle speed
`
`However, multigear transmission is much more complex, heavier, and larger
`than single-gear transmission. Moreover,it also needs a complicated gear shift-
`ing control. Thus,in the design of parallel HEV, some trade-offs must be made.
`
`Energy Storage Design
`8.2.4
`The energy storage design mainly includes the design for the power and
`energy capacity. The power capacity design is somewhat straightforward.
`The terminal power of the energy storage must be greater than the input
`electric powerof the electric motor, thatis,
`
`Pay
`Pea
`
`(8.21)
`
`where P,, and 7,, are the motor powerrating andefficiency.
`The energy capacity design of the energy storageis closely associated with
`the energy consumption in various driving patterns — mainly the full load
`acceleration and in typical drive cycles.
`During the acceleration period, the energies drawn from energy storage
`and the engine can becalculated along with the calculation of the accelera-
`tion time and distance by
`
`“a P
`E,=| —"dt
`Sto Mm
`
`(8.22)
`
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`Parallel Hybrid Electric Drive Train Design
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`273
`
`and
`
`ty
`(8.23)
`Eng | edt,
`where E, and E,,,. are the energy drawn from the energy storage and the
`engine, respectively, and P,, and P, are the powers drawn from the motor
`and engine, respectively. Figure 8.13 shows the energies drawn from the
`energy storage and the engine in the period of acceleration along the vehicle
`speed for the example passengercar. At an end speed of 120 km/h, about0.3
`kWh energy is drawn from the energy storage.
`The energy capacity of the energy storage must also meet the requirement
`while driving in a stop-and-go pattern in typical drive cycles. The energy
`changes of the energy storage can be obtained by
`t
`(8.24)
`E.=| (Pu-Paadt
`where P,, and P,, are the charging and discharging powerof the energy stor-
`age. With a given controlstrategy, the charging and discharging powerof the
`energy storage can be obtained by drive train simulation.
`Figure 8.14 showsthe simulation results of the example passenger car in an
`FTP 75 urban drive cycle with maximum SOC controlstrategy. It can be seen that
`the maximum energy change in the energy storage is about 0.11 kWh, which is
`less than that in full load acceleration (0.3 kWh). Thus, the energy consumption
`in fuel load acceleration determines the energy capacity of the energy storage.
`Actually, not all the energy stored in the energy storage can be fully used
`to deliver sufficient power to the drive train. In the case of batteries used as
`the energy storage, low SOC will limit their power output, and will at the
`same time lead to a low efficiency, due to an increaseof internalresistance. In
`the case of ultracapacitors used as the energy storage, low SOC will result in
`low terminal voltage that will affect the performance of the traction motor.
`
`From energy storage
`
`0.35
`
`0.3
`
`0.25
`
`0.2
`
`0.15
`
`0.1
`
`
`
`
`
`Energyconsumption(kWh)
`
`0.05
`
`0
`
`20
`
`100
`80
`#60
`40
`Vehicle speed (km/h)
`
`120
`
`140
`
`FIGURE 8.13
`Energies drawn from the energy storage and engine in the acceleration period
`
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