5,586,613
`[11] Patent Number:
`[19]
`Unlted States Patent
`
`Ehsani
`[45] Date of Patent:
`Dec. 24, 1996
`
`l|||||l|||lll|llllllllllllllllll||||l|||||Illll||||llllllllllllllllllllllll
`U3005586613A
`
`[54] ELECTRICALLY PEAKING HYBRID
`SYSTEM AND METHOD
`
`[75]
`
`Inventor: Mehrdad Ehsani, Bryan, Tex.
`
`-
`.
`-
`-
`[73] ASSlgnee' ggficgggfafighirg‘mversrty SyStem’
`’
`'
`
`[21] Appl. No.: 312,438
`.
`Filed:
`
`[22]
`
`Sep. 26, 1994
`
`Related U-S- Application Data
`
`[63] Continuation of Ser. No. 51,156, Apr. 22, 1993, abandoned.
`
`[51]
`Int. C16 ....................................................... B60K 6/04
`[52] U.S. Cl.
`............................................ ISO/65.2, 318/139
`[58] Field of Search ..................................... 123/352, 399;
`290/9; 180/65.1, 65.2, 65.3, 65.4, 65.8;
`318/139
`
`[55]
`
`References CitEd
`U.S. PATENT DOCUMENTS
`
`3,493,066
`3,732,751
`3,791,473
`3’792’327
`3’837’419
`3,842,287
`3 888 325
`3:898:893
`3,923,115
`4,042,056
`4,165,795
`4,187,436
`4,187,741
`4,216,420
`
`2/1970 Dooley ...................................... 180/54
`5/1973 Berman et a1.
`........................... 74/675
`2/1974 R059" ------------
`- 180/65-2
`
`2/1974 Waldorf
`318/139
`9/1974 Nakamura '
`ISO/65
`10/1974 Nakamura .....
`. 290/16
`
`6/1975 Reinbeck ______
`. 180/65
`
`8/1975 Hashimoto et a1.
`__
`74/859
`
`12/1975 Helling ....................... 180/65
`
`8/1977 Horwinski ,
`,,,,, 180/65
`
`8/1979 Lynch et a1.
`180/65
`2/1980 Etienne .......... 290/27
`2/1980 Nyman ......
`74/751
`8/1980 Jinbo et a1.
`............................. 318/370
`
`
`
`
`
`ISO/65.2 X
`4,305,254 12/1981 Kawakatsu et a1.
`..
`..
`4,313,080
`1/1982 Park ........................... 320/61
`
`9/1982 Fields et a1. ........... 180/65
`4,351,405
`
`
`4,407,132 10/1983 Kawakatsu et al.
`..... 60/716
`4,438,342
`3/1984 Kenyon ...................... 290/45
`
`8/1985 Heidemeyer et al. ......... 180/65
`4,533,011
`
`4,588,040
`5/1986 Albright, Jr. et al.
`180/165
`
`4,591,016
`5/1986 Matthews ..........
`180/165
`4,923,025
`5/1990 Ellers .................. ISO/65.2
`5,053,632 10/1991 Suzuk et al.
`......
`..
`ISO/65.2 X
`5,213,077
`5/1993 Nishizawa et a1.
`..................... 123/352
`
`Primary Examiner—Brian L. Johnson
`Assistant Examiner—Michael Mar
`Attorney, Agent, or Finn—Baker & Botts, L.L.P.
`
`[57]
`ABSTRACT
`A series hybrid electric—combustion system is provided
`which includes an engine (16) operable to generate mechani-
`cal energy and translate it to a drive shaft (21). Abattery (24)
`is included that is operable to store electrical energy and to
`deliver electrical energy. Also provided is a electric machine
`(18) mechanically coupled to engine (16) and electrically
`coupled to battery (24). Electric machine (18) has. two
`modes of operations. In the first mode rt translates electrical
`energy from battery (24) into additional mechanical energy
`at drive shaft (21)_ In the second mode of operation, electric
`machine (18) delivers electrical energy to battery (24) for
`storage. Converter (22) is also included in the system to
`convert the electrical energy from electric machine (18) for
`.
`.
`storage and battery (24) and also for converting electrical
`energy from battery (24) for use by electric machine 18. The
`System also includes command (12) for inputting System
`power requirements and controller (14) to control converter
`(22) and engine (16) in the modes of operation of the system.
`
`8 Claims, 3 Drawing Sheets
`
`E
`
`MACHINE
`
` ELECTRIC
`
`Page 1 of 9
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`US. Patent
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`Dec. 24, 1996
`
`Sheet 1 of 3
`
`5,586,613
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`
`
`ELECTRIC
`MACHINE
`
`15
`
`BATTERY
`
`25
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`Page 2 of 9 7
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`EM [I
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`ICE
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`RB
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`US. Patent
`
`Dec. 24, 1996
`
`Sheet 2 of 3
`
`5,586,613
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`20
`
`F]G. 3
`
`42
`
`\
`
`§0 21
`
`18
`
`
`
`COMMAND
`
`12/
`
`22
`
`24
`
`\ 38
`
`16
`
`14
`
`16
`
`
`
`
`
`ELECTRIC
`MACHINE
`
`COMMAND
`/
`
`48a
`
`FIG. 5
`
`2°
`
`1 6
`
`ENGINE
`
`
`
`
`
`1 2
`
`\
`COMMAND
`
`
`
`CONTROLLER
`
`AC/DC
`14
`
`CONVERTER
`
`52
`
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`US. Patent
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`Dec. 24, 1996
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`Sheet 3 of 3
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`5,586,613
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`56
`
`N
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`.
`
`FIG. 6
`
`MECHANICAL
`COUPLER
`
`19
`
`
`
`
`ELECTRIC
`MOTOR
`
`16
`
`
`
`ENGINE
`
`2°
`
`
`
`
`
`
`
`I 2
`
`\
`COMMAND
`
`CONTROLLER
`
`CONVERTER
`
`DC/AC
`
`64
`W
`
`FIG. 7
`
`74
`
`ENGINE
`
`19
`
`/
`
`77
`
`ELECTRIC
`
`MACHINE
`
`21
`
`/
`
`78
`
`VEHICLE
`MASTER
`
` CONTROLLER
`
`COMMAND
`/
`I 2
`
`OC/AC
`CONVERTER
`
`70
`
`ELECTRIC
`
`MACHINE
`
`DC/AC
`CONVERTER
`
`76
`..—_———
`fl—
`
`80
`
`‘I’
`
`fl
`__—____——
`
`72
`
`24
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`1
`ELECTRICALLY PEAKlNG HYBRID
`SYSTEM AND METHOD
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of application Ser. No.
`08/051,156 filed Apr. 22, 1993, entitled “ELECTRICALLY
`PEAKING HYBRID SYSTEM AND METHOD” by
`Mehrdad Ehsani, now abandoned.
`
`TECHNICAL FIELD OF THE INVENTION
`
`This invention relates generally to the field of electrical-
`mechanical systems, and more particularly to an electrically
`peaking hybrid system and method of generating hybrid
`electric-combustion power.
`
`BACKGROUND OF THE INVENTION
`
`Technical publications describing developments in tech-
`nology for electric vehicles are abundant. Some, however,
`fail to recognize the fundamental limitations in the perfor-
`mance of the electric vehicle in comparison to the internal
`combustion engine (ICE). Thus, most of the improvements
`reported are of a short term, single issue nature and fail to
`address the overall vehicle as a commercial product that is
`to be competitive with the ICE vehicle. Because of the
`performance advantages to the ICE,
`transportation will
`continue to depend primarily on some form of internal
`combustion for many years to come.
`The electric vehicle does present, however, certain impor-
`tant a advantages. For example, electric vehicles are suitable
`for applications that require zero emissions. There is a
`growing recognition that the discharge from ICE vehicles is
`a significant contributor to the global atmospheric degrada—
`tion. To make a short term impact in reducing the atmo-
`spheric contamination caused by ICE vehicle exhaust emis—
`sions in urban areas, electric vehicles have been mandated
`by law in some places in this country and around the world.‘
`However, this requirement can only be met with sacrifices of
`performance and at a cost premium, when compared to the
`conventional ICE vehicle.
`
`2
`The drive train of the conventional ICE automobile con-
`sists of an engine, a transmission and a drive shaft that
`connects to the wheel axle. All of the required power and
`torque are supplied by the engine at all times. The engine is
`sized to deliver the maximum power that the driver is likely
`to ask for, even though most of the time the driver requires
`much less than the maximum power. This makes the engine
`much larger than the average demand required. The basic
`problem with such a large engine is that most of the time it
`will be running at far less than its maximum power, and
`therefore below its maximum efliciency. Having a large
`engine and running it far below its optimum efi‘iciency are
`the two fundamental reasons for the poor fuel economy of
`the conventional ICE vehicle.
`
`To partially overcome this problem, a transmission is
`added to the drive train. This helps to match the variations
`of speed and power of the vehicle to the engine to some
`extent. However, the transmission introduces its own inef—
`ficiencies which are substantial. The result of this conven-
`tional design is that a typical American full-size sedan is
`equipped with an engine of 160 horsepower or larger. Most
`of the time, however,
`the vehicle requires less than 30
`horsepower to operate in the city or on the highway. At these
`power levels, the conventional engine is operating at two to
`four times below its optimum efficiency. This results in an
`average fuel economy of about 20 miles per gallon.
`Today, no hybrid electric-ICE vehicle drive system has
`been developed that is competitive with the conventional
`ICE vehicle both in cost and performance. Therefore, a need
`has arisen for a hybrid electric-ICE vehicle drive system
`which provides performance and range comparable to con—
`ventional ICE vehicles. Furthermore, to be viable, such a
`system should operate within the existing infrastructure of
`fuel supply and distribution, make use of existing compo-
`nent technology, and be price and operating cost competitive
`with conventional ICE vehicles.
`
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`SUMMARY OF THE INVENTION
`
`In accordance with the present invention, an electrically
`peaking hybrid system and method are provided which
`substantially eliminate or reduce disadvantages and prob-
`lems associated with prior systems.
`Limitations in electric storage batteries present the great-
`est obstacle to the development of an all electric vehicle that
`In accordance with the teachings of the present invention,
`is cost and performance competitive with the ICE vehicle.
`a series-mechanical hybrid electric-combustion system is
`While progress has been made in battery development, it
`provided that includes an engine to generate mechanical
`appears that chemical—electrical storage batteries cannot
`energy. The engine is coupled to a drive mechanism. The
`match the energy storage density and convenience of today’s
`system also includes a battery to store and deliver electric
`petroleum-based fuels.
`energy, and an electric machine coupled to the engine and
`the battery. The electric machine has two operating modes.
`The design of an all electric vehicle is driven by the need
`In the first mode of operation, the electric machine translates
`to minimize the load on the limited battery supply. This has
`mechanical energy from the engine and electrical energy
`forced extreme designs to reduce road friction, aerodynamic
`from the batteries to drive the drive mechanism. In the
`drag, vehicle weight and power requirements of the various
`second mode of operation,
`the electric machine delivers
`auxiliary systems. Since no significant
`improvement
`in
`electrical energy to the battery for storage.
`battery performance is expected for the near future, these
`design constraints tend to force the introduction of undesir—
`An important technical advantage of the present invention
`able vehicle tradeoffs. This, in turn, can lead to user dissat-
`is the reduction in size of the ICE to approximately one
`isfaction, which can adversely affect the long-term accept—
`quarter the size used in conventional ICE vehicles. Another
`ability of the electric vehicle concept.
`'
`important technical advantage of the present invention is the
`series coupling between the drive train, electric machine,
`The present state of the art in electric motor drives has
`reached a level of maturity. A high level of development has
`and engine, thereby eliminating the need for a transmission
`and associated power losses. An additional technical advan-
`also been reached in batteries and microcomputer controls.
`tage of the present invention is its fuel efficiency, which is
`However, to have both suitable range and performance, the
`typically 2.8 times the current ICE vehicle. Another techni-
`electric vehicle needs to incorporate some additional energy
`cal advantage of the system of the present invention is that
`source. The hybrid electric vehicle is presently the best
`solution with the existing technology.
`‘
`it provides full acceleration and the range of conventional
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`ICE vehicles. Another technical advantage of the present
`invention is that it can be manufactured from currently
`available technologies and therefore no research into new
`technologies is required.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`For a more complete understanding of the present inven—
`tion and the advantages thereof, reference is now made to
`the following description taken in conjunction with the
`accompanying drawings in which the reference numbers
`indicate like features and wherein:
`
`FIG. 1 illustrates an electrically peaking hybrid system
`constructed according to the teachings of the present inven-
`tion;
`
`FIG. 2 illustrates typical dynamic power requirements of
`a vehicle as a function of time;
`FIG. 3 illustrates an altemate embodiment of an electri-
`cally peaking hybrid system including at least one clutch;
`FIG. 4 illustrates an alternate embodiment of an electri-
`
`cally peaking hybrid system including a transmission;
`FIG. 5 illustrates an alternate embodiment of the present
`invention where the electric machine functions of electric
`propulsion and battery charging are divided between two
`electric machines;
`
`FIG. 6 illustrates an alternate embodiment of the present
`invention where the engine, electric motor, and electric
`generator are decoupled and operate at separate speeds; and
`FIG. 7 illustrates an alternate embodiment of the present
`invention where the electric motor is divided into two
`motors and placed on each of the individual drive trains to
`provide all wheel drive.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`vehicles. For example, for a full-size sedan, the size of the
`ELPH engine 16 may be about 40 horsepower.
`FIG. 2 illustrates typical dynamic power requirements for
`a vehicle as a function of time. Line 36 represents the
`“power curve,” or power required by the vehicle overtime.
`Zone 26 represents the power required by the vehicle during
`acceleration. Zone 28 represents the power requirement of
`the vehicle once it reaches its cruising speed. Zone 30 shows
`a sudden drop in power requirements, which occurs for
`example during braking. The power requirement would then
`remain low while the vehicle is in a full stop at zone 32.
`Once the vehicle starts in motion again, continuing cycles of
`acceleration, cruising, and stopping continue on in time for
`the vehicle. The average power requirement of the system 10
`is shown by straight line 34. For the ELPH vehicle of the
`present invention, the average power level represented by
`line 34 is used to determine the appropriate size of the
`engine 16.
`The system 10 has two modes of operation. In the first
`mode, the power requirements of the system exceed the
`power available from engine 16, and in the second mode the
`power requirements of the system are less than that being
`supplied by engine 16. In operation of system 10 of FIG. 1,
`the modes are determined by power demands on the system
`input by command 12. In a preferred embodiment, command
`12 is an accelerator pedal, but any input mechanism may be
`used without departing from the intended scope of the
`present invention. When additional power is required by
`command 12, the system enters its first mode of operation
`when the power required by the system exceeds the power
`of engine 16. Controller 14 responds by requiring converter
`22 to provide electrical energy from battery 24 to electric
`machine 18. Electric machine 18 has dual functionality to
`act as a motor and as a generator. In the first mode, electric
`machine 18 draws electrical energy from battery 24 to
`provide the additional required power and torque to drive
`The present invention is illustrated in FIGS. 1—7 of the
`shaft 21 above that delivered to the drive shaft 21 by engine
`drawings, like numerals being used to refer to the like and
`16. Converter 22 converts the DC electrical energy stored in
`corresponding parts of the various drawings. Throughout the
`battery 24 to AC electrical energy which is used by electric
`following description the present invention will be discussed
`machine 18 in the first mode of operation.
`in connection with a vehicle, it being understood that the
`In the second mode of operation of system 10, the power
`present invention may also be included in other applications.
`demands of the system are less than power provided by
`FIG. 1 shows a series-mechanical hybrid electric com-
`engine 16. Electric machine 18 performs as a generator and
`bustion system 10 of an electrically peaking hybrid (ELPH)
`converts any excess mechanical energy from engine 16 to
`electrical energy. Converter 22 converts this AC electrical
`vehicle constructed according to the teachings of the present
`invention. System 10 includes command 12 which is elec-
`energy to DC electrical energy for storage in battery 24. In
`trically coupled to controller 14. Controller 14 is electrically
`certain situations the drive shaft 21 and propulsion device 20
`coupled to engine 16 and converter 22. Engine 16 is
`will also provide mechanical energy that can be converted
`mechanically coupled to electric machine 18 through link
`into electrical energy for storage. For example, when the
`19. Electric machine 18 and engine 16 are mechanically
`vehicle is traveling down hill, the drive train 21 will actually
`coupled through drive shaft 21 to propulsion device 20.
`be driving electric machine 18, allowing for generation and
`Thus,
`the engine 16 is directly—mechanically coupled, in
`storage of electrical energy.
`series, to the drive shaft 21 and propulsion device 20 and can
`The controller 14 controls the system such that the electric
`directly drive the drive shaft 21. Link 19 may be considered
`machine 18 delivers power to drive shaft 21 only at peak
`part of drive shaft 21.
`power requirements (thus the term peaking), that is, during
`In the preferred embodiment, propulsion device 20 are the
`the first mode of operation. During the second mode, electric
`wheels of a vehicle. Electric machine 18 is also electrically
`machine 18 generates electrical energy for storage to the
`battery 24.
`coupled to converter 22. Converter 22 is also electrically
`coupled to battery 24. As shown in FIG. 1, the electric
`Engine 16 may comprise any one of many available
`machine 18 is in series with the engine 16 and the drive shaft
`thermal engines,
`such as
`the conventional
`four-stroke
`21. Electric machine 18 could also be geared into the drive
`engine, a gas turbine, a Wankle engine, and a two-stroke
`shaft 21, such that the engine 16 is still directly coupled to
`engine, for example. Other thermal engines may also be
`the drive shaft 21, but not through electric machine 18.
`used without departing from the intended scope herein. Each
`In system. 10, the power of engine 16 is chosen to meet
`of these engines offers unique advantages to the overall
`the average power required by the system. Thus, engine 16
`ELPH drive which may be more or less appropriate for
`is about one-quarter the size of engines of conventional ICE
`particular vehicles.
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`may be used. Electronic harmonic noise cancellation tech-
`niques may be implemented through specific pulse with
`modulation (PWM) motor control strategies. For example, a
`PWM technique with switching angles selected to cancel
`lower order harmonics may be programmed into the motor
`drive control system.
`Generally, PWM control techniques are used throughout
`the motor speed range to keep the harmonic noise under
`control. However, a six step converter wave form mode,
`without harmonic cancellation, is used under transient con—
`ditions, when voltage forcing is performed by the controller.
`The PWM control strategy also compensates for the dead
`time resulting from the electric machine minimum on and off
`switching time. Furthermore, the switching frequency of the
`PWM control should be sufficiently high, relative to the
`transient reactance of the motor, so that the current output of
`the converter is sufficiently filtered. This is particularly
`important when a field oriented induction motor control is
`used. The outputs of the coordinate transformation subrou—
`tines in the field oriented motor controller should be
`adequately filtered by the motor
`reactance, without
`adversely affecting system bandwidth over an operating
`frequency range of about 30 to l. The frequency of the PWM
`switching, used to eliminate all nontriplen odd harmonics up
`to sixty—first, at rated speed,
`is about 2924 hertz. This
`switching frequency may vary directly with motor starter
`frequency, except at crawl speeds. When two motors are
`used for front and rear wheels as in the embodiment shown
`
`in FIG. 7, the applied frequencies for the two motors are
`displaced in phase by 180 degrees.
`In the preferred embodiment, converter 22 of system 10
`is a solid state switching high power DC to AC power
`converter. Converter 22 has a dual function of (1) driving
`electric machine 18 during the first mode of operation, and
`(2) recharging battery 24 during the second mode of opera-
`tion. Converter 22 also senses that battery 24 is firlly charged
`in the second mode of operation of system 10 and discon-
`tinues charging battery 24. High efiiciency solid state
`switching inverters of many ldnds have been developed and
`are available for AC motor drives and are suitable for
`converter 22.
`
`An important element of converter 22 is a solid state
`power switch. Several types of power switches are currently
`available. At present, the insulated gate bipolar transistor
`(IGBT) is the power device of choice for the medium
`frequency and medium power levels in which most appli-
`cations of system 10 fall. The IGBT combines the high speed
`and low switching loss attributes of the gate voltage con-
`trolled unipolar field eifect transistor with the low conduc-
`tion losses of the base current controlled bipolar transistor.
`However, in the long run, MOS-controlled thyristors (MCT)
`may be the preferred choice, due to their conduction losses
`and higher voltage and gain capabilities.
`An alternative for converter 22 involves the application of
`simple converters, which use fewer power devices, in com-
`bination with a switched reluctance motor.
`
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`For example, the gas turbine is very good at fixed speeds
`and constant power applications. By modifying the basic
`ELPH architecture, the advantages of a gas turbine engine
`can be used in large vehicles such as tanks and personnel
`carriers. As another example, the two-stroke engine offers
`the advantage of compactness, with existing 800 CC two-
`cylinder units available that weigh 88 pounds and produce
`54 horsepower.
`Because of the widespread availability of two or four—
`cycle engines, and of gasoline fuel, these engines will be the
`least expensive in the near future. However,
`the use of
`natural gas or propane in all of the above engines can reduce
`their emissions by at least 50 percent. Thus, propane, natural
`gas and other low emission fuels are attractive fuels for the
`ELPH system, and will be even more attractive as their
`availability increases.
`At the present time, the most practicable and economical
`choice for battery 24 is lead acid. Nickel-cadmium and
`nickel-iron batteries may also be used. Since the battery
`power is only used for peaking power demands and not for
`driving the vehicle continuously, its capacity and size are
`small when compared to existing electrical driven vehicles.
`Other battery systems could be used without departing from
`the intended of the present invention.
`The electric machine 18 has the dual functionality of
`providing additional mechanical energy to drive shaft 21
`from energy from the battery 24 in the first mode of
`operation (motor function), and providing electrical energy
`for storage in battery 24 in the second mode of operation
`(generator function). In the preferred embodiment, electric
`machine 18 is a single AC electric motor.
`In the first mode of operation, mechanical power from the
`engine 16 is delivered to drive shaft 21. Furthermore,
`additional mechanical power is imparted to the drive shaft
`21 by electric machine 18 from energy from battery 24.
`Electrical energy from battery 24 is converted to electric
`machine 18 from energy from battery 24. Electrical energy
`from battery 24 is converted to mechanical energy by the
`motor function of the electric machine 18. In the second
`mode of operation, any excess mechanical energy, whether
`from the drive shaft 21 or engine 16, will be converted to
`electrical energy by the generator function of electric
`machine 18. The link 19 and drive shaft 21 may be coupled
`directly to the rotor of the electric machine 18, or may be
`indirectly coupled, for example, through a clutch or trans-
`mission, as will be discussed.
`
`Many presently available AC motors are appropriate for
`electric machine 18 of system 10, depending on the cost,
`performance and type of vehicle. For example, the squirrel
`cage induction motor, permanent magnet electronically
`commutated motor, and the variable or switched reluctance
`motor provide suitable alternatives for electric machine 18.
`The induction motor drive is the most mature and com-
`
`monly used drive for many applications. A high efiiciency
`induction motor drive with vector controlled strategy can
`effectively satisfy system requirements of system 10. Per-
`manent magnet motors have the added advantage of com-
`pactness and relatively high efficiency. A switched reluc-
`tance motor drive offers the advantages of high performance,
`low cost, simplicity, ruggedness and easy control. Other AC
`or DC motor drives may be used without departing from the
`intended scope of the present invention.
`Because of the frame and airborne vibrational noises of
`
`Manufacture of converter 22 can be based on printed
`circuit board technology. This approach significantly sim-
`plifies the manufacturing of complex electronic circuits.
`However, the use of this technology may limit the maximum
`current carrying capability of the conductors to about 70
`amperes. Therefore, for example, to build converters for 60
`horsepower motor drives, the DC bus voltage of the con-
`verter should be about 700 volts. This is somewhat higher
`having a motor in a vehicle, a motor drive control system is
`than the conventional currently available converter voltages
`desirable for motor 18. To arrest
`these problems, both
`of this horsepower rating. However, it requires no new or
`mechanical isolation and electronic harmonic cancellation
`unknown techniques.
`Page 7 of 9
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`65
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`FMC 1017
`FMC 1017
`
`

`

`7
`
`5,586,613
`
`Controller 14 manages the system power by controlling
`engine 16, converter 22, and battery 24. Controller 14 may
`also monitor and control the energy used by the traction
`motors, coolant pump, air conditioner compressor, and other
`system loads in a vehicle. Controller 14 may control engine
`16 through several alternative control techniques.
`One technique operates engine 16 at an average power
`level at all times. This technique can be modified such that
`power level of engine 16 is decreased to a level below the
`average power level of the system 10 when the batteries are
`fully charged and the power requirements of the system are
`below the average power requirements. Other control tech-
`niques may also be used without departing from the intended
`scope herein.
`For example, to meet the various acceleration and decel—
`eration scenarios of a vehicle traveling on various roads,
`some learning control and fuzzy control system elements
`may be included in controller 14. With fuzzy logic, for
`example, the output of the engine 16 can be adjusted as the
`average power of the system changes, for example from a
`long highway trip to city driving. The objectives of control-
`ler 14 are to satisfy the acceleration requirements of the
`driver, as a conventional vehicle would, while maintaining
`energy balance in the charging and discharging of battery 24.
`Because of the design of the present invention, battery 24
`does not need external charging. For best efliciency and
`lowest emissions, controller 14 controls engine 16 such that
`it operates within a predetermined trajectory of speed and
`power output.
`To provide good vehicle performance, maximum electric
`motor torque is obtainable at any speed. One approach to
`achieve this would be to operate the electric motor of electric
`machine 18 at rated rotor flux at all times. However, this also
`requires the maximum rated magnetizing current, which is a
`source of inefficiency. A motor with high magnetization
`reactance is desirable to reduce magnetizing current. This
`allows for operating the electric motor at reduced levels of
`flux, under normal conditions, and increasing the flux level
`only when higher than normal levels of torque are required.
`The higher levels are required, for example, during accel-
`eration, deceleration and climbing steep grades.
`During normal operation, the electric machine 18 operates
`at about 50% of its rated flux value. When sudden speed
`change is commanded by the driver, the initial speed accel-
`eration rate is limited by controller 14 to about 50% of the
`maximum rate. However, at the same time, the motor flux
`level is ramped to its rated value. Thus, the acceleration is
`correspondingly increased. Once the vehicle speed reaches
`about 95% of the command value, the flux is allowed to
`relax to its original value. The option of maintaining the
`motor at the higher rate of the flux may be provided to the
`driver, for example, by a switch, so that the normal momen-
`tary degradation of acceleration can be avoided. Further—
`more, the operator can have the option of boost flux at low
`speed operation, for emergencies.
`invention are
`Alternate embodiments of the present
`shown in FIGS. 3—7. FIG. 3 shows ELPH drive 38 including
`Shown in FIG. 7 is an embodiment of the present inven-
`clutch 40. Clutch 40 is mechanically coupled between
`tion in which an ELPH drive system 64 is appropriate for an
`electric machine 18 and propulsion device 20 in drive shaft
`all-wheel drive vehicle. In this embodiment, there is a first
`21. Clutch 40 may be a slipping or catching clutch. Clutch
`electric machine 66 and a second electric machine 68, as
`well as a first converter 70 and a second converter 72. First
`40 allows for decoupling of drive shaft 21 from propulsion
`device 20. Clutch 40 also adds some flexibility to the speed
`electric machine 66 is mechanically coupled between the
`at which engine 16 torque will be coupled to the drive shaft
`engine 16 and the first propulsion device 74. First electric
`21. Furthermore, with the presence of clutch 40, the engine
`machine 66 is also electrically coupled to first converter 70.
`16 can continue to charge battery 24 or idle, while the
`Second electric machine 68 is also mechanically coupled to
`vehicle is at a stop. Additional clutch 42 can be added
`second propulsion device 76 through drive shaft 80 and to
`Page 8 of 9
`Page 8 of 9
`
`ment, ELPH system 48 also includes clutch 53 mechanically
`coupled between generator 50 and electric motor 51. Fur—
`thermore, generator 50 is mechanically coupled to engine 16
`and electric motor 51. Generator 50 is also electrically
`coupled to first converter 52. First converter 52 is an AC to
`DC converter. First converter 52 is also electrically coupled
`to controller 14 and battery 24. Second converter 54 is
`electrically coupled to controller 14, electric motor 51 and
`battery 24.
`In operation of this embodiment, generator 50 can be
`much smaller than electric motor 51 because it only provides
`steady state charging at a much lower level than the peaking
`power of electric motor 51. This allows charging of battery
`24 even during idling of engine 16. Furthermore, engine 16
`can be started by generator 50, while it is disengaged from
`the drive shaft 21 by clutch 51.
`Referring to FIG. 6, an alternate embodiment of the
`present invention, ELPH drive system 56, is depicted. In this
`embodiment, mechanical
`coupler 62 is mechanically
`coupled to engine 16 and electric motor 57. Additionally,
`electric generator 58 is mechanically coupled to mechanical
`coupler 62 and first converter 52. Also, second converter 54
`is electrically coupled to controller 14, electric motor 53 and
`battery 24.
`In operation, decoupling of separate generator 58 and
`electric motor 57 through mechanical coupler 62 allows for
`maintaining different torque and speed at engine 16 and
`drive shaft 21. Mechanical coupler 62 between engine 16
`and motor 57 and generator 58 allows each of these respec-
`tive shafts to run at different speeds. Thus, in this embodi-
`ment of the present invention, engine 16 could be a high
`speed gas turbine or a piston engine, running at a constant
`speed, while drive shaft 21 and the shaft of generator 58 are
`running at slower speeds to meet the needs of the vehicle.
`This is useful in large military vehicles such as tanks, which
`require large amounts of mechanical energy and also have
`very large electrical loads, such as on-board weapon sys-
`terns.
`
`8
`between engine 16 and electric machine 18. Clutch 42
`provides the flexibility of driving the vehicle temporarily
`from the electrical system only, for example, during emer—
`gencies. Clutch 42 may comprise a catching or slipping
`clutch.
`
`FIG. 4 illustrates an alternate embodiment, ELPH system
`44, with transmission 46. In this embodiment, transmission
`46 is mechanically coupled between engine 16 and the
`electric machine 18. Transmission 44 gives ELPH system 44
`the ability of uncoupled speeds between drive shaft 21 and
`engine 16. In this embodiment,