Fundamentals, Theory, and Design
`
`Mehrdad Ehsani
`
`Yimin Gao
`
`f
`
`Modern Electric,
`Hybrid Electric, and
`Fuel Cell Vehicles
`
`
`
`Sebastien E. Gay
`
`Ali Emagi
`
`BMW v. Paice, IPR2020-00994
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`

`

`Modern Electric,
`Hybrid Electric, and
`Fuel Cell Vehicles
`
`Fundamentals, Theory, and Design
`
`Mehrdad Ehsani. Texas A&M University
`
`Yimin Gao, Texas A&M University
`
`Sebastien E. Gay. Texas A&M University
`
`All Emadi, Illinois Institute of Technology
`
`CRC PRESS
`
`Boca Raton London New York Washington, DC.
`
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`

`Genera: Library Synem
`University of Wisconsin — it? .
`728 State direei
`Madison, “155306-1494-
`USA.
`"'
`
`'
`
`.
`
`.
`
`Library of Congress Cataloging-in-Publication Data
`
`2004054249
`
`Modern electric, hybrid electric, and fuel cell vehicles: fundamentals,
`theory, and design/Mehrdad Ehsani
`[et all.
`p. cm. — (Power electronics 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.
`
`11. 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 are listed. Reasonable efforts have been made to publish reliable data and information,
`but the author and the publisher cannot assume responsibility for the validity of all materials
`or for the consequences of their use.
`
`Neither this book nor any part may be reproduced or transmitted in any form or by any means,
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`mation storage or retrieval system, without prior permission in writing from the publisher.
`
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`Visit the CRC Press Web site at www.crcpress.com
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`© 2005 by CRC Press LLC
`No claim to original US. Government works
`
`International Standard Book Number 0-8493-3154—4
`
`Library of Congress Card Number 2004054249
`Printed in the United States of America 1 2 3 4 5 6 7 8 9 0
`
`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 ................................261
`8.1.1 Maximum State—of—Charge of Peaking Power Source
`(Max. SOC-of-PPS) Control Strategy ........................................262
`8.1.2 Engine Turn-On and Turn~0ff (Engine-On—Off)
`Control Strategy ............................................................................265
`8.2 Design of Drive Train Parameters .......................................................... 266
`8.2.1 Design of Engine Power Capacity .............................................. 266
`8.2.2 Design of Electric Motor Drive Power Capacity ......................268
`8.2.3 Transmission Design ....................................................................271
`8.2.4 Energy Storage Design ................................................................272
`8.3 Simulations ................................................................................................274
`References ............................................................................................................276
`
`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
`advantages of 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.5 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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`260
`
`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
`
`constant speed on flat and mild grade roads, or at the average of the load of
`a stop—and-go driving pattern) and the electrical 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
`power rating is lower than the electrical 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 Figure 8.1.
`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.
`
`Mechanical
`
`
`brake
`
`
`Operation
`
`
`controller
`command
`
`
`
`
`Peaking
`
`
`power
`U 5
`
`It}
`source
`fig
`
`
`U!
`—
`3:5»
`
`Motor
`,3 E-
`
`controller
`
`
`
`
`
`
`Vehicle speed
`
`
`
`Mechanical connection
`
`Electrical power
`
`-—Iv Signals
`
`FIGURE 8.1
`
`Configuration of the parallel torque-coupling hybrid drive train
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`Parallel Hybrid Electric Drive Train Design
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`261
`
`T—”—
`
`8.1 Control Strategies of Parallel Hybrid Drive Train
`
`The available operation modes in a parallel hybrid drive train, as mentioned
`in Chapter 5, mainly include (1) engine-alone traction, (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 meet the traction torque
`requirement, achieve high overall efficiency, maintain a reasonable level of
`PPS SOC, and recover braking energy as much as possible.4
`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 Figure 8.2. It consists of a vehicle controller, engine controller,
`
`Accelerator pedal
`position signal
`
`Brake pedal
`position signal
`
`4—— Vehicle speed
`4-"— Batteries SOC
`
`mode
`
`
`
`Engine power
`command
`
`
`Propelling
`
`mode
` Vehicle controller
`__ _...__.___.____.____ _. __ .—_.____.
`Friction brake
`
`-ower command
`
`
`.lI.. |.|||
`
`Friction brake controller
`
`
`
`.
`l
`Regenerating
`braking power
`i
`
`
`
`Friction
`braking
`power
`
`
`
`
`Motoring
`
`
`
`‘ FIGURE 8.2
`
`Overall control scheme of the parallel hybrid drive train
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`262
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
`
`electric motor controller, and mechanical brake controller. The vehicle con-
`troller is in the highest position. It collects data from the driver and all 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 drive train.
`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 component controller. Hence, the preset control strategy is the key to
`the optimum success of the operation of the drive train.
`
`8.1.1 Maximum State-of-Charge of Peaking Power Source (Max. SOC-of-
`PPS) Control Strategy
`
`When a 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 PPS is
`necessary to ensure vehicle performance. Thus, the maximum SOC of the
`PPS control strategy may be the proper option.2
`The maximum control strategy can be explained by Figure 8.3. In this figure,
`the maximum power curves for hybrid traction (engine plus electric motor),
`engine-alone traction, electric motor—alone traction, and regenerative braking
`
`Traction
`
`0
`
`power
`
`
`Brakingpower
`
`3
`4
`
`5
`
`1 — Maximum power with hybrid mode
`2 — Maximum power with electric-alone traction
`3 — Engine power on its optimum operating line
`4 — Engine power with partial load
`5 -- Maximum generative power of electric motor
`p
`eVehicle speed
`PL — Load power, traction or braking
`Pe — Engine power
`Pm— Motor traction power
`Pmb— Motor braking power
`Pm, — Mechanical braking power
`Pmc— PPS charging power
`
`FIGURE 8.3
`
`Demonstration of various operating modes based on power demand
`
`
`
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`Parallel Hybrid Electric Drive Train Design
`
`263
`
`are plotted against vehicle speed. Power demands in different conditions are
`also plotted, represented by points A, B, C, and D.
`The operation modes of the drive train are explained below:
`Motor-alone propelling mode: The vehicle speed is less than a preset value
`m, 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
`0r idling. The engine power, electric traction power, and the PPS discharge
`power can be written as
`
`g=a
`
`PL
`m_ TM,
`
`Pm
`PWM=E;,
`
`an
`
`(82)
`
`as)
`
`where P, is the engine power output, FL is the load power demand on the
`drive wheels, 772,»: is the transmission efficiency from the motor to the driven
`wheels, Pm is the power output of the electric motor, PW“f is the PPS dis-
`charge power, and nm is the motor efficiency.
`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 power Pa. The remaining power demand is supplied by the electric
`motor. The motor power output and PPS discharge power are
`P _
`m=—%E§E,
`
`no
`
`Pm
`PW = "15;:
`
`(85)
`
`where 17,; is the transmission efficiency from the engine to the drive wheels.
`PPS charge mode: When the load power demand, represented by point B in
`Figure 8.3, is less than the power that the engine can produce while operat-
`ing on its optimum operation line, and the PPS SOC is below its top line, the
`engine is operated on its optimum operating line, producing its power PE. In
`this case, the electric motor is controlled by its controller to function as a gen-
`erator, powered by the remaining power of the engine. The output power of
`the electric motor and PPS charge power are
`
`PL
`”be
`
`(8-6)
`
`P = Pa.“
`m
`
`Wigwam:
`
`Pppsf = Pm!
`
`(8'7)
`
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`264
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
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`where 11%", 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 power that the engine can produce
`while operating on its 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 power that
`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
`
`PL
`2— ”he,
`
`(8‘8)
`
`Pm= ,
`
`Pppfifl
`
`(8.9)
`
`(8.10)
`
`Regenerative—alone brake mode: When the vehicle experiences braking and the
`demanded braking power is less than the maximum regenerative braking
`power that 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 c0mrnanded braking power. In this case, the
`engine is shut down or set idling. The motor power output and PPS charge
`power are
`
`Pmb : ant,mTlm!
`
`PW}c = Pmb.
`
`(8'11)
`
`(8.12)
`
`Hybrid braking mode: When the demanded braking power is greater than the
`maximum regenerative braking power that 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
`
`Pm = Pmb’mnm,
`
`PW5,2P,,,.
`
`(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-PPS is illustrated in Figure 8.4.
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`Parallel Hybrid Electric Drive Train Design
`
`265
`
` Maximum
`Traction power
`motor power
`command. Pm
`
`Pm-max
`
`Braking power
`
`Regenerative-
`
`
`atone braking
`
`mode
`
`
`
`.
`Vehicle speed,
`
`Hybrid
`braklng mode
`
`—The engine power whlle operating
`Its optlmum operatlng llna
`
`FIGURE 8.4
`
`Flowchart of Max. SOC-of—PPS control strategy
`
`PPS SOC top line
`
`
` PPS soc bjnnom tune
`Engineoperation 0.‘3
`O:3:
`
`
`
`FIGURE 8.5
`
`Illustration 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
`tum-off control strategy may be used in some operation conditions with low
`speed and low acceleration. In an engine—on—off control strategy, the opera—
`tion of the engine is controlled by the SOC of PPS, as shown in Figure 8.5.
`In the engine-on period, the control is Max. SOC—of-PPS strategy. When
`the SOC of the PPS reaches its 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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`266
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`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
`
`——'—'——"—
`
`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
`power source 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 passenger car 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/m3, front area Af =2.0 m2,
`aerodynamic drag coefficient CD = 0.3, radius of driven wheels r= 0.2794 In,
`and transmission efficiency from engine to drive wheels The: 0.9, and from
`motor to drive wheels Tim = 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 that is 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 on a flat or
`a mild grade road, the power needed is expressed as
`
`5— 1000mm (Mugfr-l- 2 paCDAfV +Myg1)(kw).
`P
`V
`_ __
`
`l
`
`2
`
`,
`
`(8.15)
`
`Figure 8.6 shows the load powers of a 1500 kg example passenger car, 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 power of 42 kW. For
`a comprehensive analysis, the power curves of a 42 kW engine with a multi-
`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 power should be evaluated so that it meets the
`average power requirement while driving in a stop-and—go pattern. In a
`drive cycle, the average load power of a vehicle can be calculated by
`
`P —l TM v+l CAV3+6MVd—V dt
`eve—TD
`v3}; zanf
`0
`dt
`
`‘
`
`816
`(')
`
`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
`power is calculated by (8.16). However, when the vehicle has no regenerative
`
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`Parallel Hybrid Electric Drive Train Design
`
`267
`
`so
`
`45
`
`
`
`Engine power On a 5% On a flat
`
`
`‘ grae road
`rod
`
`
`.‘_..
`".
`
`
`
`
`Reslstance
`
`power
`
`0
`
`20
`
`40
`
`120
`100
`80
`60
`Vehicle speed (kmfh)
`
`140
`
`160
`
`180
`
`FIGURE 8.6
`Engine power required at constant speed on a flat road and a 5% grade road
`
`braking, the average power is larger than that with full regenerative braking,
`which can be calculated from (8.16) in such a way that when the instanta—
`neous power is less than zero, it is given a zero.
`Figure 8.7 shows the vehicle speed, instantaneous load power, and aver-
`age powers with full regenerative braking and zero regenerative braking, in
`some typical drive cycles for a 1500 kg passenger car.
`In the engine power design, the average power that the engine can produce
`must be greater than the average load power. In a parallel drive train, the engine
`is mechanically coupled to the driven wheels. Hence, the engine rotating 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
`power to meet the average power in a drive cycle is 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
`._ r T
`Pater-ace“ T In Pd”) dtr
`
`(817)
`
`where T is the total time in drive cycles and Pe(v) is the engine power with
`full throttle, which is a function of vehicle speed when the gear ratio of the
`transmission is 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 power is 42 kW and transmission
`is single gear (fourth gear only in Figure 8.6). Comparing these maximum
`possible average powers to the load average powers, as shown in Figure 8.7,
`it is concluded that the engine power is sufficient to support a vehicle oper-
`ating in these typical drive cycles.
`
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`268
`
`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
`
`
`
`(kmm) Instantaneous power Average power urtthSpeed
`zero regenerative
`
`Power(kW)
`_20
`AveragepowerwithoutTut—r
`
`
`
`
`regenerative braldng
`
`O
`
`200
`
`400
`
`600 800100012001400400100200300400500600700800
`Time (99¢)
`Time (use)
`to) FTP 75 urban driving cycle
`(in) FFP 75 hiul'rway driving cysts
`
`,_. 150
`
`E g
`
`100
`'5': 50‘
`8 0‘
`100
`Instantaneous power
`
`E 50
`e.
`g
`n.
`
`..
`0 ..
`-50
`— 00
`1
`
`0
`
`100
`
`
`
`zero regeneratlve
`braid !
`I
`_'lL. L . __,,
`.rIaul ,, -...i.-.. .. “.-".'
`powe wt _
`Arefigzmm braldng
`200
`300
`400
`Time (see)
`(1:) U306 driving cycle
`
`500
`
`4
`
`on
`
`600
`
`Ave no power Mthout
`regenerlltlv braldng
`100
`200
`300
`Time (sec)
`to) ECE-drlving cycle
`
`400
`
`500
`
`600
`
`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 power to
`the drive train. In the motor power design, acceleration performance and
`peak load power in typical drive cycles are the major concerns.3
`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-
`dled 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
`
`
`fl
`Tm itmnt m _
`1'
`#5” ”dt’
`
`(8.18)
`
`where Tm 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, ta, from zero speed to final high speed, Vf'
`
`
`
`
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`Parallel Hybrid Electric Drive Train Design
`
`269
`
`45
`
`g
`as
`i
`‘3’
`s
`E“
`“1
`
`Maximum average
`power:
`14.5 kW
`
`Engine power-speed
`curve with full throttle
`
`20
`
`pereting points
`with full throttle
`4O 60
`80
`100 120 140 160 130
`Vehicle speed (kmlh)
`(a) FI'P 75 urban driving cycle
`
`40 Maximum average
`power:
`a
`28.3 kw
`i 35
`53 30
`g
`E 25
`g, 20
`r:
`l“ 15
`10
`5
`
`a
`_
`.
`E
`ngtne power spee
`curve With full throttle
`
`Operating points
`with full throttle
`
`
`
`20
`
`40
`
`100 120 140 160 180
`80
`60
`Vehicle speed (kml'h)
`(b) i-‘l'P 75 highway driving cycle
`
`45
`
`45
`
`Maximum average
`power:
`32.2 kW
`
`Engine power—speed
`curve with full throttle
`
`Operating points
`with full throttte
`
`40
`
`E
`if 35
`g 30
`3
`a 25
`'5. 20
`E;
`
`15
`1 O
`
`40
`
`E“
`§ 35
`g 30
`3
`a, 25C
`'a 20
`tfi
`
`15
`1 0
`
`
`
`Maximum average
`power:
`22.1 kW
`
`Engine power—speed
`curve with full throttle
`
`Operating points
`with lull throttle
`
`520
`
`40
`
`60
`
`100 120 140 160 180
`80
`Vehicle speed (kmfh)
`(c) U806 driving cycle
`
`520
`
`40
`
`100 120 140 160 180
`BO
`60
`Vehicle speed (kmlh)
`(d) EOE-1 driving cycle
`
`FIGURE 8.8
`
`Maximum possible operating points of the engine and the maximum average power in typical
`drive cycles
`
`and referring to Chapter 4, the motor power rating is expressed as
`
`m
`
`SmMrJ
`= anta (V}+V§)_
`
`(8.19)
`
`For a 1500 kg passenger car with a maximum speed of 160 km/h, a base speed
`of 50 km/h, a final acceleration speed of 100 km/h, acceleration time ta=10
`sec, and 6", = 1.04, the power rating 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 shown in 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 power of the engine, used to accelerate
`the vehicle, can be expressed as
`
`Pa =
`
`a
`
`‘a
`
`1
`
`t,—t, L
`
`(Pa—Pr) (it,
`
`(8.20)
`
`-where Pa 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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`

`270
`
`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
`
`
`
`
`
`Tractiveeffort(RN)
`
`.5
`
`toto
`
`O
`
`0
`
`20
`
`40
`
`60
`
`80
`
`.
`100 120 140 160 180
`
`Vehicle speed (kmlh)
`
`FIGURE 8.9
`
`Tractive effort vs. vehicle speed of an electric motor-driven vehicle
`
`120
`
`100
`
`80
`
`60
`
`40
`
`,
`Vehicle speed (kmfh)
`
`Resistance power (kW)
`
`Engine power (kW)
`
`Time (sec)
`
`FIGURE 8.10
`
`Vehicle speed, engine power, and resistance power vs. acceleration time
`
`associated with the transmission, that is, the gear number and gear ratios. 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 power is finally estimated as 74-17 = 57 kW.
`When the power ratings of the engine and electric motor are initially
`designed, a more accurate calculation needs to be performed to evaluate the
`
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`

`Parallel Hybrid Electric Drive Train Design
`
`271
`
`mum...
`
`on = 25° (45.6%)
`.u._..._.-----—' “'
`
`(kN)
`Tractiveeffortondrivenwheels
`
`
`
`(1 = 20° (36.4%)
`
`0
`
`20
`
`4O
`
`60
`
`80
`
`100
`
`120
`
`140
`
`160
`
`180
`
`Vehlcle speed (km/h)
`
`FIGURE 8.11
`
`Tractive effort and resistance on slope road vs. vehicle speed
`
`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 Chapter 2.
`The diagram (as shown in Figure 8.11) shows the design results of an exam-
`ple passenger car. It indicates that the vehicle at 100 km/h has a gradeability
`of 4.6% (265°) for the engine-alone mode, 10.36% (591°) for the motor-alone
`mode, and 18.14% (1028") 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 power of 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 ec0nomy can also be improved, since the use of proper gears of
`the mulfigear 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.1
`
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`272
`
`Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
`
`40
`
`35
`
`30
`
`.3
`8
`v 25
`g
`
`5 20
`§
`g, 15
`3
`
`10
`
`5
`
`Distance
`
`
`
`400
`
`350
`
`300 7,-
`s
`v
`250 3
`l:
`
`200 '3
`.2
`150 E
`§
`100 <
`
`50
`
`0
`
`O
`
`20
`
`40
`
`60
`
`80
`
`100
`
`120
`
`0
`140
`
`Vehicle speed (kmlh)
`
`FIGURE 8.12
`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.
`
`8.2.4
`
`Energy Storage Design
`
`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 power of the electric motor, that is,
`
`P
`p 2—”-
`5
`37m ’
`
`(3.21)
`
`where Pm and n,” are the motor power rating and efficiency.
`The energy capacity design of the energy storage is 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 be calculated along with the calculation of the accelera-
`tion time and distance by
`
`Es: —”' dt
`
`(8.22)
`
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`

`Parallel Hybrid Electric Drive Train Design
`
`273
`
`and
`
`in
`(8.23)
`Emg= J; Peat,
`where E5 and Ems are the energy drawn from the energy storage and the
`engine, respectively, and Pm and P2 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 passenger car. At an end speed of 120 km/h, about 0.3
`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
`1
`(8.24)
`BAD (Parent.
`where PM and P5,, are the charging and disaharging power of the energy stor-
`age. With a given control strategy, the charging and discharging power of the
`energy storage can be obtained by drive train simulation.
`Figure 8.14 shows the simulation results of the example passenger car in an
`FTP 75 urban drive cycle with maximum SOC control strategy. 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 increase of internal resistance. In
`the case of ultracapacitors used as the energy storage, low SOC will result in
`low terminal