PROPULSION SYSTEM DESIGN OF ELECTRIC VEHICLES
`
`Mehrdad Ehsani
`Fellow, IEEE
`
`Khwaja M. Rahman
`Student Member, IEEE
`
`Hamid A. Toliyat
`Member, IEEE
`
`Texas Applied Power Electronics Center
`Department of Electrical Engineering
`Texas A&M University
`College Station, TX 77843-3 128
`Fax: (409) 845-6259
`to its self starting capability. However, soon after the
`Abstract:
`introduction of electric starter for ICE early this century,
`There is a growing interest in electric vehicles due to
`despite being energy efficient and nonpolluting, EV lost the
`environmental concems. Recent efforts are directed toward
`battle completely to ICE due to its limited range and
`developing an improved propulsion system for electric vehicle
`inferior performance. Since then ICE has evolved,
`applications. This paper is aimed at developing the system design
`improved in design, and received wide spread acceptance
`philosophies of electric vehicle propulsion systems. The vehicle’s
`and respect, Although this
`being the case, EV
`in an
`dynamics are
`to find an Optima1 torque-
`interest never perished completely, and whenever there has
`speed profile for the electric propulsion system. This study
`been any crisis regarding the operation of ICE automobiles,
`reveals that the vehicle’s operational constraints such as: initial
`rating if we have seen a renewed interest for EV. The early air
`acceleration and grade
`be met with minimum
`quality COncernS in the 60’s and the energy Crisis in the
`the powertrain can be operated mostly in constant power region.
`70’s have brought EVs back to the street again. However,
`Several examples are presented to demonstrate the importance of
`the constant power operation. Operation of several candidate
`the most recent environmental awareness and energy
`motors in the constant power region are also examined. Their
`concerns have imposed, for the first time since its
`behaviors are compared, and conclusions are made.
`introduction, a serious threat to the use of ICE automobiles.
`I. Introduction
`Electric Vehicles offer
`the most promising
`ICE automobile at the Present 1s a
`solutions to reduce vehicular emission. Electric vehicles
`constitute the only commonly known group of automobiles
`source of urban pollution. According to figures released by
`the US Environmental Protection Agency @PA),
`that qualify as Zero Emission Vehicle (ZEV). These
`conventional ICE vehicles currently contribute 40-50% of
`vehicles use an electric motor for propulsion, and batteries
`ozone, 80-90% of carbon monoxide, and 50-60% of air
`as electrical energy storage devices
`toxins found in urban areas [l]. Besides air pollution, the
`This paper presents the EV propulsion system
`other main objection regarding ICE automobiles
`its
`design philosophies. The paper is organized as follows,
`extremely low efficiency use of fossil fuel- Hence, the Section I1 describes the design constraints and the variables
`problem associated with ICE automobiles are three fold,
`for E v system. Design philosophies of EV propulsion
`environmental, economical, as well as Political. These
`systems are presented in sections 111. Section IV examines
`concerns have forced governments all Over the world to
`several most commonly used motors for EV system design.
`Section v compares our designed EV with the General
`consider alternative vehicle Concepts. The CalifOrnia Air
`Resource €hmd ( C A B ) is among the few Who acted first Motors IMPACT. Summary and conclusions are presented
`in Section VI.
`through the declaration of the Clear Air Act of September,
`1990. This act requires that 52% Of dl vehicles sold in that
`11. Specifications ofEV Propulsion System Design
`state be either Low Emission Vehicles (LEV’S)- 48%, Ultra A. system ~~~i~~ const,-aints
`Low Emission Vehicles (ULEV’s)- 2%, or Zero Emission
`Vehicle operation consists of three main segments.
`Vehicles (ZEV’s)- 2%, by the year of 1998 [21. Similar These are, i) the initial acceleration, ii) cruising at vehicle
`measures are considered in Other States and nations, as Well.
`rated speed, and iii) cruising at the maximum speed. These
`The concept of Electric Vehicle (Ev) Was
`three operations provide the basic design constraints for the
`conceived in the middle of previous century. After the EV drivetrain, A drivetrain capable of meeting these
`introduction of internal combustion engine (ICE), EvS
`constraints will function adequately in the other operational
`remained in existence side by side with ICE for several
`regimes. Refinements to these basic design constraints are
`years. The energy density of gasoline is far more than what
`necessary for an actual commercial product, but those are
`beyond the scope of this paper. The objective here is to
`the electrochemical battery could Offer. Despite this fact,
`the EV continued to exist, egpecially in the urban arem due
`
`0-7803-2775-6196 $4.00 0 1996 IEEE
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`meet these constraints with minimum power. The variables
`defining the above design constraints are:
`(i) Vehicle rated velocity, v,.
`(ii) Specified time to attain this velocity, tf.
`(iii) Vehicle maximum velocity, vma.
`(iv) Vehicle mass, and other physical dimensions.
`B. System Design Variables:
`The main component of EV is its electrical
`powertrain. The electric propulsion design variables are:
`i) Electric motor power rating.
`ii) Motor rated speed.
`iii) Motor maximum speed.
`iv) The extend of constant power speed range,
`beyond the rated speed.
`v) Gear ratio between motor shaft and the wheel
`shaft (transmission).
`As mentioned earlier, the main design objective is
`to find the minimum drive weight, volume and cost that will
`meet the design constraints with minimum power.
`C. Road Load Characteristics
`The road load (Fw) consists of rolling resistance
`(fro), aerodynamic drag (fi), and climbing resistance (fs3 [3].
`Fw = fro + f l + fst
`(1)
`The rolling resistance (fro) is caused by the tire
`
`deformation on the road:
`fro =f"g
`(2)
`where f is the tire rolling resistance coefficient. It increases
`with vehicle velocity, and also during vehicle turning
`maneuvers. Vehicle mass is represented by m, and g is the
`gravitational acceleration constant.
`Aerodynamic drag, fi, is the viscous resistance of
`air acting upon the vehicle.
`f, = 0.5ECwA(v + v0)*
`(3)
`where 5 is the air density, Cw is the aerodynamic drag
`coefficient, A is the vehicle frontal area, v is the vehicle
`speed, and vo is the head wind velocity.
`The climbing
`resistance
`(fst with positive
`operational sign) and the down grade force (fSt with
`negative operational sign) is given by
`f,, = m-g-sina
`where a is the grade angle.
`The following assumptions will be made in the
`analysis prsented in the following sections, unless otherwise
`specified.
`
`(4)
`
`(i) velocity independent rolling resistance
`(ii) zero head wind velocity
`(iii) level ground
`These assumptions do not change the general trend
`of the solution and can be easily relaxed.
`The motive force F available from the propulsion
`system is partially consumed in overcoming the road load,
`Fw. The net force, F-Fw, accelerates the vehicle (or
`
`a=-
`
`(5)
`
`decelerates when Fw exceeds F). The acceleration is given
`bY
`
`F-Fw
`k;m
`where k, is the rotational inertia coefficient to compensate
`for the apparent increase in the vehicle's mass due to the
`on-board rotating mass.
`PIP. EV System Design
`The main component of EV drivetrain is its
`electric motor. The electric motor in its normal mode of
`operation can provide constant rated torque up to its base or
`rated speed. At this speed, the motor reaches its rated
`power limit. The operation beyond the base speed up to the
`maximum speed is limited to this constant power region.
`The range of
`the constant power operation depends
`primarily on the particular motor type and its control
`strategy. However, some electric motors digress from the
`constant power operation, beyond certain speed, and enter
`the natural mode before reaching the maximum speed. The
`maximum available torque in the natural mode of operation
`decreases inversely with the square of the speed. This range
`of operation is neglected in the analysis presented in this
`section, unless otherwise specified. It is assumed that the
`electric motor operates in the constant power region beyond
`the base speed and up to the maximum speed. Nevertheless,
`for some extremely high speed motors the natural mode of
`operation is an appreciable part of its total torque-speed
`profile. Inclusion of this natural mode for such motors may
`result in a reduction of the total power requirement. Of
`course, power electronic controls allow the motor to
`operate at any point in the torque speed plane, below the
`envelop defined by the mentioned limits. However, it is the
`profile of this envelop that is important in the motor drive
`selection and design.
`In order to free up the motor speed from the
`vehicle speed, for design optimization, gearing between the
`motor shaft and the drive shaft is required. In our design,
`we will make the following assumptions.
`(i) single gear ratio transmission operation: power
`electronic control allows instantaneous matching of the
`available motor torque with the required vehicle torque, at
`any speed. Therefore, multiple gearing in order to match
`the motor torque-speed to the vehicle torque-speed is no
`longer a necessity.
`(ii) ideal loss free gear: without loss of generality,
`the gear losses can be incorporated at the end of analysis.
`The gear ratio and size will depend on the
`maximum motor speed, maximum vehicle speed, and the
`wheel radius. Higher maximum motor speed, relative to
`vehicle speed, means a higher gear ratio and a larger gear
`size. The selection criterion for the maximum motor speed
`will be further discussed later. The torque speed diagram of
`a typical motor is drawn in Fig. 1, but in terms of tractive
`force and vehicular speed for different gear ratios. Notice
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`form solution for the motor rated power P,. The insight
`gained from the closed form solution is also valid for the
`more practical design involving running resistances.
`With these simplifying assumptions the governing
`differential equation reduces to:
`dv F
`a = - = - (assuming k,=l)
`dt m
`
`now the electric motor base speed and maximum speed, in
`terms of the vehicle speed, depend on the gear ratio. A
`design methodology based on the three regions of operation
`will now be presented.
`A. Initial Acceleration:
`The force-velocity profile of a typical motor is
`redrawn once again in Fig. 2. In this figure, v,
`is the
`is the vehicle rated speed
`electric motor rated speed, v,
`and v,,
`is the vehicle maximum speed. The motor
`maximum speed must correspond to this v,,,
`after the gear
`ratio transformation.
`
`1:13.2
`
`1mh
`
`wheel Radius=li inch
`
`I
`
`I
`
`Velide Speed (mph)
`
`Fig. 1. Torque-speed diagram of an electrical motor in terms of
`tractive force and vehicular speed with gear size as the parameter
`The range of operation for initial acceleration is 0-
`v,. For now, we will focus our attention only on this
`interval. For maximum acceleration the motor operates in
`constant rated force (torque), Fmd=P,,,/v,
`up to the motor
`rated speed v,,
`and in constant power (Fv=P,,,/v) at speeds
`beyond the base speed, up to the vehicle rated speed v,.
`Here, P, is the motor rated power. We assume v,>v,.
`The
`wisdom of this assumption will become clear, shortly. The
`differential equation describing the perforpance of the
`system is given by eq. (5) and is repeated here for
`convenience.
`
`dv F-Fw
`a=-=
`k m . m
`dt
`F is the motive force available from the propulsion
`system and Fw is the running resistance (road load). The
`boundary conditions are
`at t=O, vehicle velocity v=O.
`at t=tf, vehicle velocity v=v,.
`To gain insight, we will solve eq. (5) under the most
`simplifying assumptions:
`i) The vehicle is on a level ground.
`ii) The rolling resistance is zero.
`iii) Aerodynamic drag is zero.
`we will relax these assumptions later for a more realistic
`solutiorf. The above assumptions will result in a closed
`
`“0
`
`20
`
`80
`
`Vmax
`100
`
`40
`60
`Vehicle Speed (mph)
`Fig. 2. Typical torque-speed profile of electric motor in terms of
`tractive force and vehicular speed.
`This differential equation is solved with the
`previous boundary conditions and the force-speed profile of
`Fig. 2. The differential equation is integrated within the
`acceleration interval of 0-v, in 0-4 seconds, in order to get
`a closed form solution for the rated power P,.
`
`o 1
`0
`The left hand side integral is broken into two parts, the 0-
`v,
`constant force operation and the v,-v,
`constant power
`operation
`
`Now solving for P,, we get
`
`For minimum motor power, differentiating P, with
`respect to v,
`and setting it to zero gives
`v, = o
`(9)
`This establishes a theoretical limit for minimum
`motor power. For v,=O,
`the electric motor operates entirely
`in the constant power region. Therefore, if the motor is
`performing 0-v, in tf seconds in constant power alone, the
`power requirement is minimum, On the other hand, if the
`motor operates in the constant torque (force) region during
`In this case, eq.
`the entire 0-tf period, we will have v,=v,.
`(8) shows that the power requirement is twice that of
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`constant power operation. The solid line curve of Fig. 3
`shows an example of the motor power requirements
`between these two extremes. Of course, operation, entirely
`in constant power regime, is not practically realizable.
`However, this theoretical discussion demonstrates that
`longer constant power range of operation will lower the
`motor power.
`Having discussed the simplified resistanceless
`case, we now solve the more realistic case, involving the
`running resistance. The vehicle differential equation (5) can
`
`llO/
`
`p o o -
`
`g 90-
`
`a
`
`-
`
`1
`
` h the Prasence of Road Load ’ / I
`
`“V 0
`
`10
`
`30
`20
`40
`Motor Rated Speed Vfm (mph)
`
`50
`
`60
`
`Fig. 3. Acceleration power requirement as a function of
`motor rated speed. Solid line curve- resistanceless case,
`dashed curve- in the presence of road load.
`
`be solved under the same boundary conditions as before
`with the presence of the running resistance Fw. In this case,
`a closed form solution is feasible. However, the result is a
`transcendental equation involving rated motor power P,,
`rated motor velocity v,,
`rated vehicle velocity v,,
`acceleration time tf, and all the other system constants, e.g.;
`vehicle mass m,
`rolling
`resistance coefficient
`f,
`aerodynamic drag coefficient Cw, etc. The resulting
`equation can be solved numerically for P,
`for a specific
`motor rated velocity v,,
`using any standard root seeking
`method such as the secant method [4].
`Let’s assume that it is desired to obtain P, for the
`following case
`- 0-26.82 m / s (0-60 mph) in 10 seconds.
`- vehicle mass of 1450 kg.
`- rolling resistance coefficient of 0.013.
`- aerodynamic drag coefficient of 0.29.
`- wheel radius of 0.2794 m (1 1 inch).
`- level ground.
`- zero head wind velocity.
`a plot of the resulting motor rated power vs. motor rated
`speed, in terms of vehicle speed, is shown in Fig. 3 (the
`dashed curve).
`Examination of Fig. 3 (the dashed curve) results in
`the following conclusions:
`
`curve shows the same
`i) Rated power versus v,
`general trend of the resistanceless case.
`ii) Rated motor power requirement is minimum for
`continuous constant power operation (v,=O).
`iii) Rated motor power is roughly twice that of
`continuous constant power operation for constant force
`(torque) operation (v,=v,>.
`iv) Rated motor power remains close to its
`minimum up to about 20 mph of rated motor speed and
`then grows rapidly.
`B. Cruising at Rated VehkEe Velocity:
`A powertrain capable of accelerating the vehicle to
`the rated velocity v, will always have sufficient cruising
`power at this speed. Hence, the constraint of cruising at
`rated vehicle speed is automatically met for the case of
`EV. Of course, cruising range is another issue, related to
`the battery design, which is outside the scope of this paper.
`However, minimizing power of the drive will help the
`battery size.
`C. Cruising at Maximum Vehicle Velocity:
`The power requirement to cruise at maximum
`vehicle speed can be obtained as
`
`G n a x = (fro + f,,) * v,, + f, ( V I . vmax
`(10)
`Since aerodynamic drag dominates at high speeds,
`this power requirement increases with
`the cube of
`maximum vehicle velocity. If
`this vehicle power
`requirement is greater than the motor power calculated
`previously (P,,>P,),
`then P,,
`will define the motor
`power rating. However, in general P, will dominate P,,,
`since modern vehicles are required to exhibit a high
`acceleration performance. As mentioned before, some
`extremely high speed motors usually have three distinct
`modes of operation. The initial constant torque operation,
`followed by a range of constant power operation, then to
`the maximum speed in natural mode (see Fig. 2). For such a
`motor it may be advantageous to use the entire constant
`power range for initial acceleration of the vehicle. The
`operation beyond that would be in the natural mode. This
`would allow a longer constant power operation in the initial
`acceleration. Consequently, the motor power requirement
`will be lower. This scheme will work provided the motor
`has adequate torque in natural mode to meet the constraints
`at the maximum vehicle speed. Otherwise some part of the
`constant power operation has to be used for the vehicle
`operation beyond the rated vehicle speed.
`Natural mode of motor operation is not the
`preferred mode beyond
`rated vehicle speed,
`the
`unfortunately no control algorithm exists, presently, to
`operate some high speed motors entirely in constant power
`beyond their base speed. However, the natural mode, if
`included, can lower the overall power requirement. The
`speed at which the electric motor can enter the natural
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`off between maximum motor speed and the gear size.
`However, this tends to be more in favor of selecting a
`medium or high speed motors. For an extremely high speed
`motor, a sophisticated gear arrangement might be necessary
`for speed reduction. Planetary gear arrangement [5] could
`be the choice, that is compact but allows high speed
`reduction. Extended constant power range, on the other
`hand, will increase drive shaft torque and stress on the
`gear. Hence, another design tradeoff is involved between
`the gear stress and the extended constant power range. It
`can be seen from the results of table I that after a certain
`point there is not any appreciable power reduction with
`extended constant power range. Any further extension of
`constant power range beyond this point will only adversely
`
`12000, n
`
`~ l w 0 0
`
`!g 8000
`
`' 0 4
`
`'
`
`mode and still meet the power requirement at maximum
`vehicle speed is obtained from
`
`In
`
`Note that the initial acceleration power is also a function of
`VN (extended constant power range). Hence, vN and P,,, have
`to be solved iteratively. Also, the gear ratio between the
`drive shaft and the motor shaft is to be determined by
`matching VN with the motor speed at which it enters the
`natural mode. More discussion about the natural mode of
`operation appears in section IV. The rest of the analysis is
`done assuming constant power operation beyond the base
`speed up to the maximum speed.
`The importance of extending the constant power
`speed range can be better understood by comparing the
`required motor power for different constant power speed
`ranges (as a multiple of its base speed). Table I shows an
`example of power requirement for several constant power
`ranges for the following case:
`i) Maximum motor speed is 10,000 rpm.
`ii) Maximum vehicle speed is 44.7 m/s (100 mph).
`iii) Other system variables and constants are the
`same as the previous example.
`Here, the required gear ratio, to match the
`maximum motor speed to the maximum vehicle speed, for a
`wheel radius of 0.2794 m (11 inches), is 1:6.55. The
`results of Table I suggest an extended range of 4 to 6 times
`the base motor speed in order to significantly lower the
`motor power requirement.
`Finally, we examine the effect of maximum motor
`speed and the extended constant power range on the overall
`system performance. The power requirement is not a
`function of the motor maximum speed. Motor maximum
`speed only affects the gear size. However, maximum speed
`
`EMnded Speed Range
`Madmum Motor Speed (krpm)
`Fig. 4. Rated motor shaft torque as a function of maximmum motor
`speed.
`affect the gearing and drive shaft appreciably without
`reducing the power requirement. This will set the upper
`limit of the extended range of the constant power operation.
`Overall, the EV drive system design philosophy
`can be summarized as:
`i) Power requirement for acceleration decreases as
`Table I: EV Power requirement as a function of constant power range,
`Extended Constant HP Speed Range
`1 :4
`1 :3
`74
`67
`
`Motor Rated Power (KW)
`
`1:l
`110
`
`1:2
`95
`
`I
`
`15
`64
`
`1:6
`62
`
`has a pronounced effect on the rated torque of the motor.
`An example of this is illustrated in the surface plot of Fig.
`4. Low speed motors with extended constant power speed
`range have a much higher rated shaft torque. Consequently,
`they need more iron to support this higher flux and torque.
`Furthermore, higher torque is associated with higher motor
`and power electronics currents. This will also impact the
`power converter silicon size and conduction losses.
`Extended speed range, however, is necessary for initial
`acceleration as well as for cruising intervals of operation.
`Therefore, the rated motor shaft torque can only be reduced
`through picking a high speed motor. This would however
`affect the gear ratio. A good design is the renult of a trade
`
`the range of constant power operation increases. More
`specifically, as the ratio of the vehicle rated speed to motor
`rated speed increases.
`ii) The gear ratio between the electric motor and
`the drive shaft is determined by the motor and. vehicle
`maximum speeds.
`the
`iii) Power requirement for cruising at
`maximum vehicle speed is obtained directly from the road
`resistance at maximum speed. In general, this power
`requirement will be
`lower than the initial acceleration
`power requirement.
`iv) High speed motors would be more favorable
`for EV spplication, in general.
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`IV. Electric Propulsion Systems for EV Design
`the BLDC motor makes it appear inferior to the induction
`motor, despite its high power factor and high efficiency.
`An electric propulsion system comprises of three
`The extremely high speed operation of the SRM and its
`elements: power electronic converter, motor, and its
`main
`relatively longer constant power range helps it to overcome
`controller. This section is devoted to examining several
`some of the difficulty associated with its lower power factor
`for EV propulsion. The
`most commonly used motors
`operation. Furthermore, the SRM converter is simpler and
`importance of extended speed range, under constant power
`easier to control.
`operation of electric motors in EV system design was
`Table 11: Motor data.
`
`is referred to as field weakening, from its origin in dc motor
`drives. Therefore, this section will concentrate mainly on
`the field weakened extended speed operation of the EV
`motors. A more detailed study of these motors for EV
`propulsion application is presented in [6].
`
`Motors IMPACT.
`In this section an EV prototype is discussed. The
`actual design specifications of this vehicle are compared
`with our theoretical design of the same vehicle, based on
`the ideas presented in this paper. The EV is the General
`uirements for the motors of
`
`Design Example
`We present a design example of some most
`commonly used motors in the constant power region. This
`example will help clarify the capabilities of these motors
`for vehicle applications.
`EV data: - Vehicle Rated Speed of 26.82 m/s (60 mph).
`- Required acceleration of 26.82 m/s
`in 10
`seconds.
`- Vehicle maximum speed of 44.7 m / s (100 mph).
`- Vehicle mass of 1450 kg.
`- Rolling resistance coefficient of 0.013.
`- Aerodynamic drag coefficient of 0.29.
`- Frontal Area of 2.13 m2.
`- Wheel radius of 0.2794 m (1 1 inch).
`- level ground.
`- zero head wind.
`The motor data are shown in Table 11. The motor
`data chosen are for the commercially available samples of
`these motors. Clearly, more specific motors can be
`designed for vehicle applications, but such data were not
`available for this paper. Based on the vehicle data. the
`powerequirement to cruise at the maximum speed is 41 kW.
`The motor power for acceleration and converter volt-
`ampere (VA) requirement for each motor are shown in
`Table 111.
`The extended constant power range available from
`the induction motor clearly makes it highly favorable for
`vehicle application. The limited constant power range of
`
`Motor corporation IMPACT car.
`General Motors Electric Vehicle IMPACT
`General Motors announced the first version of its
`electric vehicle, IMPACT, in January, 1990. Over the years
`there have been several modifications of the IMPACT. The
`following are the most recent specifications of the
`IMPACT. We have included only those features which are
`pertinent to this study.
`Performance:
`0-26.82 m/s (0-60 mph) acceleration in 8.5
`seconds.
`Top speed of 35.76 m/s (80 mph).
`Dimensions:
`Frontal area 2.2578 m2.
`Drag coefficient 0.19.
`Curb weight 1347.17 kg.
`Design Features:
`102.16 kW three phase induction motor.
`IGBT power inverter module- 102 kW.
`High speed rated 205/50 R15 tires.
`Our propulsion system is to meet the same
`performance specifications as that of IMPACT. In light of
`the design methodologies presented in section I11 and the
`electric propulsion system performance analysis presented
`in section IV, we pick an induction motor with maximum
`speed of 14000 rpm and the rated speed of 3500 rpm
`(extended constant power range of 1:4). A comparison of
`our design EV with that of General Motors IMPACT is
`presented in Table IV. The cogent result of this exercise is
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`that our motor power rating for this vehicle is only 73 kW,
`as compared to the 102 kW motor in the prototype. This
`demonstrates the importance of
`the design approach
`presented in this paper.
`VI. Conclusions
`A design methodology for EV propulsion systems
`is presented based on
`the vehicle dynamics. This
`methodology is aimed at finding the optimal torque-speed
`profile for the electric powertrain. The design is to meet the
`operational constraints with minimum power requirement.
`The study reveals that the extended constant power
`operation is important for both the initial acceleration and
`
`The design methodology of this paper was applied
`to an actual EV to demonstrate its benefits. Clearly the
`detailed design of a vehicle propulsion system is more
`complicated
`than
`in our ex&ples. However,
`this
`methodology can serve as the foundation of the detailed
`design.
`
`Referencs
`[l] A. Alison, “Searching for perfect fuel ... in the clean air act”,
`Conference Proceedings of Environmental Vehicles, 94, pp. 61-87,
`Dearbom, Jan, 1994.
`[2]1 S. Barsony, “Infrastructure needs for EV and H E V , NIST
`Workshop on Advanced Components for Electric and Hybrid
`Electric Vehicles, pp. 14-23, Gaithensburg, MD, Oct., 1993.
`
`Table IV: Comparison of General Motor EV, IMPACT and our designed EV.
`The rotational inertia constant km=l.l.
`
`cruising intervals of operation. The more the motor can
`operate in constant power, the less the acceleration power
`requirement will be.
`Several types of motors are studied in this context.
`It is concluded that the induction motor has clear
`advantages for EV, at the present. Brushless dc motor must
`be capable of high speeds to be competitive with the
`induction motor. The switched reluctance motor may be
`superior to both of these motors, for vehicle application,
`both in size and cost. However, more desigo and evaluation
`data is needed to verify this possibility.
`
`[3] Aufomorive Handbook, Robert Bosch Gmbh, Germany, 1986.
`[4] A. Ralston and P. Rabinowitz, A first Course in Numerical
`Analysis, 2nd ed., New York, McGraw Hill, 1978.
`[51 A. G. Erdman, G. N. Sandor, Mechanism Design: Analysis and
`Synthesis, Vol. I, New Jersy, Prentice-Hall, 1984.
`[6] H. A. Toliyat, K. M. Rahman, and M. Ehsani, “Electric machines in
`electric and hybrid vehicle applications,” Proceedings of the 1995
`International Conference on Power Electronics, Oct. 10-14, Seoul,
`Korea..
`
`Page 7 of 7
`
`FORD EXHIBIT 1132
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`13
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