United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,823,280
`
`Lateur et al.
`
`[45] Date of Patent:
`
`Oct. 20, 1998
`
`US005823280A
`
`......................... .. 74/859
`3/1971 Berman et al.
`3,566,717
`.. 310/61
`5/1979 Weghaupt
`4,155,019
`290/27
`2/1980 Etienne ............ ..
`4,187,436
`60/716
`4,407,132 10/1983 Kawakatsu et al.
`. . . . .. 475/5
`5,067,932 11/1991 Edwards . . . . . . . . . . . . .
`5,365,153
`11/1994 Fujita et al.
`............................ .. 318/34
`
`
`
`..
`
`Primary Exami/1er—Richard M. Camby
`Attorney, Agent, or Firm—Flehr Hohbach Test Albritton &
`Herbert LLP
`
`[57]
`
`ABSTRACT
`.
`.
`.
`.
`.
`.
`A hybrld elecmc d“V‘°~ System 15 descrlbed that Includes a
`heat engine having a drive shaft, and two electric motor/
`generators having rotors that are coaxially connected to the
`drive shaft. Acontrol arrangement for these elements is also
`described that provides a relatively simple combined opera-
`tion for driving a vehicle.
`
`[54] HYBRID PARALLEL ELECTRIC VEHICLE
`
`[75]
`
`Inventors: Michel J. Lateur, Redwood City;
`Danie] P_ Pliskjn, Palo Alto, both of
`Calif.
`
`[73] Assignee: Nevcor, Inc., Stanford, Calif.
`
`[21] App1' N07 372’173
`[22]
`Filed:
`Jan. 12, 1995
`
`Int. Cl.5 ..................................................... .. B60K 1/00
`[51]
`[52] U.S. Cl.
`....................... .. 180/65.2; 180/65.4; 180/165
`[58] Field of Search .............................. 60/716; 180/652,
`180/651, 65.4, 65.3; 475/3, 5; 364/426.041;
`318/141’ 149’ 34’ 41’ 46’ 53’ 59’ 61
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,122,696
`
`2/1964 Graybeal et al.
`
`....................... .. 322/20
`
`19 Claims, 9 Drawing Sheets
`
`28
`
`10
`
`1
`
`22
`
`82
`
`12
`
`1
`
`Heat Engine
`
`'
`
`_
`
`First Elect
`Mtr/Gen
`
`Torque Trans,
`
`
`
`3 0
`
`62
`
`
`
`76
`
`$3
`
`5
`
`0
`
`First rotor
`speed sensor
`
`Second rotor
`speed sensor
`
`4
`
`3
`
`Engine speed
`sense,
`
`40
`
`Brake pedal
`sensor
`
`
`
`14
`4
`2
`.
`Second Ele t
`
`
`Accelerator I E Powercontroller
`
`sensor
`
`' MU/Gen
`
`C
`
`
`
`
`Cruise control Cljinj
`switch
`Driver
`
`
`
`Control
`Display
`
`
`34
`
`State of charge
`sensor
`
`
`
`
`
`
`
`storage gens
`
`32
`
`A/C Mains
`
`charger Aux fl
`
`1 of 18
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`

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`U.S. Patent
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`Oct. 20, 1998
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`Sheet 1 of9
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`5,823,280
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`0
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`.t_o.m_._S._.wage...
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`mm
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`Bmcmw
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`mmfico699m
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`Bmcmw
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`

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`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 2 of 9
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`5,823,280
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`N O
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`E
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`Ne
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`¢mmm?3.:
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`U.S. Patent
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`Oct. 20, 1998
`
`Sheet 3 of 9
`
`5,823,280
`
`Figure3
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`4 of 18
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`4 of 18
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`

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`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 4 of 9
`
`5,823,280
`
`1st Motor/generator
`
`2nd Motor/generator
`
`1¢(-————x———9[€——x/2
`
`92
`
`
`
`Figure 4 21
`
`A I I
`
`Output shaft
`
`Heat éngme
`
`2nd Motor/generator
`
`2k————x-————)!(——-x/2
`4
`T
`
`
`
`2
`
`.1 st Motor/generator
`
`Output 9 shaft
`
`Figure 4 b
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`5of18
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`U.S. Patent
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`Oct. 20, 1998
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`Sheet 5 of 9
`
`5,823,280
`
`Read accelerator and brake
`
`pedal sensors
`
`Determine output speed
`
`Read Rotational speed sensors
`
`Accelerate
`
`yes
`
`Control commutation of 1st & 2nd
`motorlgenerators to increase speed of
`output shaft.
`
`no
`
`no
`
`
`
`Control commutation of 1st & 2nd
`yes
`
`
`output shaft by producing regenerative
`
`
`braking forces
`
`
`motor/generatorstodecreasespeed at
`
`
`
`Determine desired acceleration or
`
`deceleration characteristics.
`
`Figure 5
`
`
`
`Control current flow to balanace torques
`being prodvided by 1st & 2nd
`motor/generators
`
`
`
`
` Control current flows to provide sum of
`torques desired for acceleration or
`deceleration characteristics
`
`End
`
`6 of 18
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`

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`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 6 of 9
`
`5,823,280
`
`
`
`Sense battery
`state of charge
`
`
`
`inimum
`
`Operate in
`State of
`ail-electric mode
`
`
`
`
`
`
`
`
`
`Stop 1st rotor while maintaining
`speed & torque to output shaft by
`controlling current flow to 2nd
`
`motor/generator
`
`Engage Ctutch
`
`Start heat engine by
`applying torque from
`1st motor/generator
`
`
`
`
`
`Control commutation of 1st
`motor/generator to operate heat
`engine at first load and speed
`
`
`
`
`
`Warm-up heat engine
`
`Controi commutation of
`
`
`
`1st motor/generator to
`operate in charge mode
`
`
`
`
`
`
`
`
`Read accelerator and brake
`pedal sensors
`
`V
`
`E
`
`Figureea
`
`7 of 13
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`U.S. Patent
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`Oct. 20, 1998
`
`Sheet 7 of 9
`
`5,823,280
`
`Read rotational
`
`speed sensors
`
`
`
`
`
` Control generative load of first
`
`motor/generator to balance
`torque of 2nd motor/generator and
`to increase speed of output shaft at
`
`desired rate.
`
`
`
`
`
`I10
`
`no
`
`Sense battery
`state of charge
`
`tate 0
`
`charge
`greater than
`- redetermined
`onstan
`
`
`yes
`
`Disengage clutch
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Control generative load of first
`motor/generator to balance torque of
`2ndmotor/generator and to decrease
`speed of output shaft at desired rate.
`
`
`
`
`
`Turn off heat engine
`
`Return to all-electric
`
`
`
`
`
`Figure 6 b
`
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`U.S. Patent
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`Oct. 20, 1998
`
`Sheet 8 of 9
`
`5,823,280
`
`Read cruise master control switch
`
`no
`
`s
`
`ye
`
`Read brake pedal sensor
`
`De
`
`I
`t
`ce era e
`
`NO
`
`yes
`
`Control commutation of 1st & 2nd
`motor/generator to produce
`regenerative braking force
`to slow rotation of output shaft at
`desired rate.
`
`
` Control commutation of 1st &
`
`
`
`
`2nd motor/generators to
`increase speed of rotation of
`output shaft at desired rate.
`
`
`
`
`
`
`
`
`
`
`Read accelerator sensor
`
`Accelerate
`
`no
`
`Control commutation of 1st
`& 2nd motor/generators to
`maintain speed of rotation
`of output shaft.
`
`
`
`
`
`
`Figure 7 i
`
`9 of 18
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`U.S. Patent
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`Oct. 20, 1998
`
`Sheet 9 of 9
`
`5,823,280
`
`Read cruise control
`master switch
`
`
`
` Operate in cruise control
`
`no
`
`Read Rotational speed sensors
`
`
`
`Control commutation of 1st & 2nd
`
`Read brake pedal sensors
`
`
`
`motor/generators to decrease speed of
`output shaft via regererative braking
`
`Read accelerator sensor
`
`
`
`Control commutation of 1st & 2nd
`
`
`
`
`motor/generators to increase speed of
`output shaft
`
`
`
`
`
`
`
`
`motorlgenerators to decrease speed of
`output shaft via regererative braking
`
`
`Control commutation of 1st & 2nd
`
`Accelerate
`
`no
`
`Decelerate
`
`no
`
`Control commutation at 1st & 2nd motor
`
`generators to maintain output shaft speed
`
`End
`
`Figure 8
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`10 of18
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`5,823,280
`
`1
`HYBRID PARALLEL ELECTRIC VEHICLE
`
`TECHNICAL FIELD
`
`The invention relates generally to electric vehicles, and
`drive arrangements which include both a fuel powered
`engine and a pair of coaxial electric motor/generators.
`
`PRIOR ART
`
`Most of today’s motor vehicle carry an internal combus-
`tion engine that functions optimally at high speeds only. It
`is by necessity larger than an engine required for “in town”
`operation. Therefore a penalty is paid for the luxury of broad
`range operation, including the deterioration of our environ-
`ment. Emissions during warm-up and low speed operations
`are not negligible. A large engine requires longer warm-up
`time, and short trips may not achieve warm-up in many
`cases, increasing the pollution problem.
`There exists, at the moment, much effort in addressing the
`basic need for an efficient power source at all operating
`conditions. One such effort, known as series hybrid electric,
`approaches the problem by carrying an on-board generator,
`which supplies electrical power to recharge batteries for an
`electric drive mechanism. This allows for “range extending”
`at the cost of the additional weight of added components. In
`this scheme each of the power elements must be individually
`capable of the peak demands of the vehicle. An example of
`a series hybrid electric vehicle is set forth in U.S. Pat. No.
`4,187,436, issued Feb. 5, 1980 to Etienne.
`Another effort, known as parallel hybrid electric, holds a
`significant amount of promise. Aparallel system allows the
`output from power components to be added together as
`required and therefore, each of the power components need
`only produce a portion of the power required of the series
`system components. Similarly, each of the power compo-
`nents is substantially lighter than its counterpart in the series
`hybrid. This reduction in weight also reduces power
`requirements, necessitating fewer batteries for the same
`range.
`
`One such parallel hybrid electric system is described in
`U.S. Pat. No. 4,407,132 issued Oct. 4, 1983 to Kawakatsu et
`al. This particular arrangement, however,
`is not without
`disadvantages. For example, the rotational speed of the rotor
`of the single electric motor generator must always rotate at
`a multiple of the speed of the drive shaft which will result
`in the motor stopping its rotation whenever the drive shaft
`stops. If the rotor of the motor/generator turns at substan-
`tially the same speed as the drive shaft, such motor/generator
`will not operate as efficiently as possible since electric
`motors/generators operate most efficiently when rotating at
`relatively high speeds. When the motor/generator is con-
`verting electrical energy to mechanical rotation of the shaft,
`at low speeds, the torque must be high in order to reach high
`mechanical power outputs. Since torque is proportional to
`current, this leads to large IZR losses and increased degra-
`dation of the electric storage device.
`If the drive shaft is maintained at high speeds, though, a
`transmission is required to transform the high drive shaft
`speed to a lower speed to be applied to the differential. A
`clutch is also needed to disengage the drive shaft from the
`transmission. The addition of the clutch and transmission
`
`necessarily adds weight and complexity to the drive system.
`Another parallel arrangement is set forth in U.S. Pat. No.
`3,566,717 issued Mar. 2, 1971 to Berman et al. While this
`system eliminates some of the problems associated with the
`Kawakatsu arrangement, the Berman et al. arrangement also
`
`5
`
`10
`
`15
`
`20
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`25
`
`30
`
`35
`
`40
`
`50
`
`55
`
`60
`
`65
`
`2
`has a number of shortcomings. For example, since the
`motor/generators are not disposed coaxially with the output
`shaft from the internal combustion engine, substantially
`more space is utilized than would otherwise be required.
`Also, additional support structures must be added and more
`bearings are required. There are no provisions made,
`moreover, for disengaging the internal combustion engine so
`the system can run in an all electric mode,
`the most
`environmentally sound mode.
`In most hybrid electric vehicle motors, an internal com-
`bustion engine is used to run the generator to produce
`electricity. If the exhaust emissions from the engine when it
`is operating are maintained at ultra low levels, the actual
`average emissions from the vehicle can be maintained close
`to zero since the engine will be rarely used, i.e., only during
`relatively lengthy trips in which the batteries are signifi-
`cantly discharged. The internal combustion engine can be
`operated inherently cleaner by being maintained at a con-
`stant speed and constant load,
`independent of the time-
`varying need for road horsepower. During most city driving
`it will not operate at all, i.e., the hybrid electric vehicle will
`operate in an all-electric mode and be recharged at night by
`plugging the batteries into a standard 120V or 240V elec-
`trical outlet.
`
`Hybrid electric vehicles have substantially different aver-
`age power levels in many driving situations. For example,
`the average power consumed when operating “in-town” is
`substantially less than the average power consumed when
`operating at full highway speed. Similarly, substantially
`more power is consumed when climbing an extended grade,
`such as in the mountains, than is required when travelling on
`level highways. Thus to provide an electric generating
`system capable of charging the vehicle batteries in all travel
`situations would require operating the generating system at
`a higher, and potentially less efficient, power level than
`would be required for typical driving conditions.
`SUMMARY OF THE INVENTION
`
`The invention avoids the disadvantages of known parallel
`hybrid electric vehicles. In its broad aspects,
`it includes
`providing a pair of motor/generators (converters) whose
`rotors are coaxial with the ultimate drive shaft of,
`for
`example, the ground vehicle to be powered. A source of
`electrical energy, e.g., a battery pack, is also included. It has
`been found that the coaxial relationship of the converter
`rotors with the drive shaft results in a driving arrangement
`that is quite compact and is easily usable to electrically drive
`most ground vehicles.
`Most desirably, both converters are also generators, i.e.,
`capable of changing mechanical energy to electrical energy,
`as well as changing electrical energy to mechanical energy
`(from the broad standpoint, the term “generator” encom-
`passes alternators), and the source includes a heat engine.
`The output shaft of the heat engine is connected to the
`generator-converter to provide the mechanical energy the
`latter needs to produce electricity for the driving arrange-
`ment. Again, the combination is quite compact. To enhance
`such compactness, it is most desirable that the heat engine
`output shaft also be coaxial with the ultimate drive shaft and,
`hence, with the converter rotors.
`The invention includes many features and advantages,
`some of which are claimed, that will become apparent from
`a more detailed study of the drawings and the following
`description.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`For a better understanding of the present invention, ref-
`erence may be made to the accompanying drawings,
`in
`which:
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`3
`FIG. 1 is a block diagram of the major components of an
`embodiment of the present invention;
`FIG. 2 is a cut-away, side View of one embodiment of a
`parallel hybrid electric drive arrangement incorporating the
`invention;
`FIG. 3 is an exploded, isometric view of the embodiment
`of FIG. 2;
`FIGS. 4a and 4b illustrate the torque distribution of a
`hybrid electric drive arrangement of the invention;
`FIG. 5 is a logic flow chart illustrating an all-electric
`operation of an embodiment of the invention;
`FIGS. 6a and 6b illustrate a logic flow chart of the
`transition portion of the operation;
`FIG. 7 is a flow chart illustrating the speed control portion
`of the operation; and
`FIG. 8 is a logic flow chart illustrating a standard opera-
`tion incorporated in an embodiment of the invention.
`DETAILED DESCRIPTION
`
`An embodiment of a hybrid electric drive arrangement of
`the invention is shown in FIG. 1. For simplicity in showing,
`the various elements are not shown in their physical rela-
`tionships. This implementation of the invention can be used
`to power an automobile,
`truck, bus, delivery van, work
`vehicle, etc.
`First and second motor/generators represented at 12,14
`are electrically connected to a power controller represented
`at 16. In the preferred embodiment,
`the first and second
`motor/generators 12,14 are multi-pole, direct current, per-
`manent magnet motors; however, it should be appreciated
`that other types of motors may be used, for example mul-
`tiphase alternating current motors. Advantageously, the first
`and second motor/generators 12,14 are selected to have low
`mass rotors for high speed response, minimum cogging and
`high torque. The windings of the first and second motor/
`generators 12,14 are such that series-parallel combinations
`can be switched, and the commutation of the motor/
`generators can be controlled by the power controller 16 in a
`manner well-known in the art. Advantageously, the power
`controller 16 includes a plurality of power semiconductor
`switching devices, for example power MOSFETs or IGBTs.
`First and second motor/generators 12,14 are coupled via
`planetary gear system 18 (described in detail below) to the
`vehicle’s drive transmission 20 through which forces from
`the planetary gear system are transferred to the drive wheels
`of the vehicle, and vice versa.
`Heat engine 22 includes a drive shaft 78 (FIG. 2) coupled
`via clutch 82 to the first motor/generator 12 for driving the
`latter at a speed and load sufficient to produce an output
`voltage capable of recharging an electric power storage
`device 24, such as a plurality of batteries, via power con-
`troller 16. In a preferred implementation, heat engine 22 is
`a rotary engine of a type well-known in the art; however, it
`will be appreciated by those skilled in the art that four-stroke
`engines, two-stroke engines, gas turbines and the like may
`be used. In the embodiment being described, heat engine 22
`is fuel injected and is controlled via microprocessor 26 to
`operate at its maximum efficiency.
`Microprocessor 26 serves to process a plurality of control
`algorithms for controlling operation of the hybrid electric
`drive system in response to a plurality of sensed parameters.
`A memory device 28 is coupled to microprocessor 26 for
`storing sensed parameters, limit values, and various flags
`used in operation of the control algorithms, as well as, in one
`implementation, the instructions for carrying out the algo-
`
`10
`
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`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`rithms. In this embodiment, power controller 16, micropro-
`cessor 26, and memory device 28 are powered by the electric
`storage device 24, and appropriate isolation and voltage
`regulation circuitry is utilized to provide the appropriate
`power level and regulation to those devices.
`An operator display 30 is coupled to microprocessor 26
`for receiving signals representative of operating conditions
`and the levels of sensed parameters. Charger unit 32 is
`connected to the electric power storage device 24 and
`includes a power inlet cord allowing charger unit 32 to be
`connected to an external power source, such as a 120 or 240
`volt AC line. Charger unit 32 converts, if necessary, the
`external power signal to an appropriate DC level and deliv-
`ers the electrical energy to electrical storage device 24 for
`recharging. For example, when the operator returns the
`vehicle to a fixed location having a standard electrical outlet,
`electrical storage device 24 can be recharged by plugging
`charger unit 32 into a standard AC electrical outlet, with
`charger unit 32 rectifying the AC power to provide a DC
`charging voltage.
`A state of charge sensor 34 of a type well-known in the art
`and is provided for sensing the state of charge of the electric
`power storage device 24 and delivering an appropriate signal
`to the microprocessor 26.
`A plurality of switch inputs are provided within the
`operator compartment of the vehicle to allow the operator to
`control the drive system 10. A speed “cruise” control switch
`36 is one of them. It is provided for producing a “cruise
`control on” signal or a “cruise control off” signal in response
`to a selection made by the operator. Similarly,
`in one
`embodiment, trip parameter inputs 38 are provided to allow
`the operator to modify operation of the control algorithms by
`transmitting information regarding the characteristics of the
`trip to be undertaken to microprocessor 26. For example,
`information pertaining to the length of the trip, whether there
`is a downhill portion near the end of the trip, whether the trip
`is predominated by “in-town” driving, etc., can be inputted.
`Similarly, brake pedal and accelerator sensors 40,42 of
`types typically found in automobiles are included connected,
`respectively, with the brake pedal and accelerator pedals.
`Such sensors 40,42 produce signals indicative of the relative
`displacement of the brake pedal and accelerator,
`respectively, and deliver them to microprocessor 26. A
`plurality of rotational speed sensors 48,50,52 are also pro-
`vided. They are included for indicating the rotational speed
`of the output shaft 62 (related by gear ratio to the drive
`motors), and the rotors of the first and second motor/
`generators 12,14.
`Referring now primarily to FIG. 2 and FIG. 3, the first and
`second motor/generators are shown and include first and
`second stators 54,56, and first and second rotors 58,60,
`respectively. In one implementation of the invention, first
`and second rotors 58,60 each include a plurality of perma-
`nent magnets; however, as described above other types of
`motors may be used.
`Output shaft 62 includes a plurality of spindles 64 at its
`end within the torque transmission. A plurality of planet
`gears 68 are rotatably mounted to the spindles 64. (In the
`design shown, four planet gears 68 and four spindles 64 are
`used.) Output shaft 62 is axially aligned and constrained to
`the first rotor 58 via a first set of needle bearings 72.
`The first rotor 58 includes a sun gear 74 in engagement
`with the planet gears 68. On the other hand, the second rotor
`60 includes a ring gear 76 engaged with such planet gears.
`By virtue of this arrangement, the rotational speed of output
`shaft 62 is dependent upon the difference between the
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`rotational speeds of the first and second rotors 58 and 60. It
`may be manually input by the operator, or the hybrid electric
`drive system 10 may be controlled in a completely automatic
`mode and require no upgrade or input. For example, if the
`circumference of ring gear 76 is three times the circumfer-
`ence of sun gear 74, then where first rotor 58 is spinning at
`3000 RPM in the clockwise direction and second rotor 60 is
`
`spinning at 1000 RPM in the counterclockwise direction,
`output shaft 62 will remain stationary. Similarly, when the
`first rotor 58 is rotating at 3000 RPM in the clockwise
`direction and the second rotor 60 is not rotating, output shaft
`62 will rotate at 1000 RPM in the clockwise direction.
`
`The first rotor 58 is coaxially aligned with output shaft 78
`of heat engine 22 via a second set of needle bearings 80. In
`accordance with the invention, shafts 78 and 62, and first and
`second rotors 58,60 are disposed along substantially the
`same axis of rotation. And because of the planet gear
`arrangement, it can be said that both of the motor/generators
`have output shafts which are coaxial with the drive shaft.
`Clutch 82 is connected to first rotor 58 via spline 83 and
`is movable between engaged and disengaged positions.
`When engaged, clutch 82 is coupled to both first rotor 58 and
`output shaft 78 such that first rotor 58 and the output shaft
`78 rotate at
`the same speed. When in the disengaged
`position, clutch 82 remains engaged with first rotor 58 but is
`not in contact with the output shaft 78. Thus output shaft 78
`and first rotor 58 are allowed to rotate independently. Clutch
`82 may be moved between the engaged and disengaged
`positions by a solenoid coil 84 as shown which receives
`control signals from microprocessor 26. Detent mechanism
`85, for example, of a type well-known in the art, is included
`for maintaining clutch 82 in the engaged or disengaged
`positions without further expenditure of electrical energy by
`solenoid coil 84. While only a simple form of clutch 82 with
`extended pins 86 is shown engaged in bores in the flange of
`output shaft 78, it should be apparent that many variations
`of clutch 82 will be suitable.
`
`The torque applied to output shaft 62 and, hence, to the
`automobile differential, is directly related to the torque of the
`first and second rotors 58,60. This output torque when the
`system is operated in an all-electric mode, i.e., with clutch
`82 (FIG. 2) disengaged and both the first and second
`motor/generators 12,14 driving the output shaft 62, is equal
`in this embodiment to X times the torque of the first rotor 58
`plus X/2 times the torque of second rotor 60, where X is
`equal to the gear reduction to output shaft 62 of sun gear 74.
`The actual gear reduction chosen is a matter of design choice
`and depends upon the desired performance characteristics of
`the drive system. One of ordinary skill in the art easily can
`choose an appropriate gear reduction to provide selected
`characteristics. In general,
`the power (u)C'cC) is equal to
`u)A('cA+~cE)+u)B*cB), where:
`u)=rotational speed;
`'c=torque;
`A represents the first rotor;
`B represents the second rotor;
`E=the heat engine; and
`C=the output shaft 62;
`FIGS. 4a and 4b are force diagrams which show the
`relationships. FIG. 4a shows the relationships when the
`drive arrangement of the invention is in an all-electric mode,
`whereas FIG. 4b shows the relationships when the heat
`engine is part of such arrangement.
`Recharge Mode
`The torque characteristics of the drive system when the
`clutch 82 is engaged and motor/generator 12 is being used
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`as a generator are now discussed. (This is known as the
`recharge mode.) In this case, the torque on the output shaft
`62 is equal to the sum of X/2 times the torque of the second
`rotor 60 plus X times the difference of the torque of output
`shaft 78, less the torque absorbed by the first rotor 58 (the
`generative load). Thus the difference of torque from the
`combination of the first rotor and the engine acts to drive the
`output shaft 62.
`In the exemplary embodiment of FIG. 2, the torque of the
`first rotor 58 times the gear reduction of sun gear 74 equals
`the torque of second rotor 60 times the gear reduction of ring
`gear 76. This is necessary to balance the torques applied to
`output shaft 62 to prevent one source of torque from
`overdriving the other. In addition, it is desirable to maintain
`the currents flowing in both of the motor/generators 12,14 at
`relatively low levels. Since torque is proportional to current,
`the current in each motor/generator is minimized by causing
`each of motor/generators 12,14 to produce one-half of the
`torque required at output shaft 62. Since torque is propor-
`tional to current,
`it is advantageous to keep the current
`flowing in the first motor/generator 12 multiplied by the gear
`reduction of sun gear 74, substantially equal to the current
`flowing in second motor/generator 14 multiplied by the gear
`reduction of ring gear 76. Thus, by causing both electric
`motor/generators 12,14 to drive output shaft 62, losses are
`minimized and the lifespan of electric power storage device
`24 is improved. Thus, in one embodiment, the maximum
`torque available is equal to twice the torque of the least
`torque producing element.
`First and second motor/generators 12,14 are preferably
`operated at relatively high speeds. Since back electromotive
`force (EMF) increases in proportion to rotational speed, by
`maintaining the rotational speed of first and second rotors
`58, 60 at relatively high levels, currents are maintained at
`lower levels and voltages are maintained at relatively high
`levels. By minimizing currents,
`the lifespan of electric
`power storage device 24 is improved and the I2R losses are
`minimized. In addition, the control of the voltages by power
`controller 16 is improved when the voltages of the motor/
`generators are relatively high since a smaller proportion of
`the voltage is dissipated across the switching devices within
`power controller 16.
`As is well-known in the art of electric motors, for any
`given rotor speed there is a current-load relationship in
`which the speed for a given current will increase as the load
`decreases, and vice versa. In addition, each rotor 58,60 has
`a maximum allowable speed and a maximum allowable
`current which is stored in memory device 28. Microproces-
`sor 26 maintains rotors 58,60 within their allowable oper-
`ating limits by comparing the operating characteristics of the
`motor/generators 12,14 with their respective operating lim-
`its.
`All Electric Mode
`
`Referring now to FIG. 5, an exemplary flow chart show-
`ing operation in an all-electric mode is illustrated. Micro-
`processor 26 receives signals from brake pedal and accel-
`erator sensors 40,42 and from the output shaft speed sensor
`46 and responsively determines the desired output shaft
`speed and torque.
`In one embodiment, memory device 28 includes a look-up
`table of a type well-known in the art for determining the
`desired speed and torque of output shaft 62. The desired
`speed and torque determined by microprocessor 26 is a
`function of the signals from the brake pedal and accelerator
`sensors 40, 42, the speed of the vehicle, and information
`stored in the memory device 28. The precise values included
`in the look-up table are determined in response to the desired
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`for
`operating characteristics of the vehicle and reflect,
`example, desired acceleration and deceleration characteris-
`tics and operational limits of system components. Whenever
`acceleration is desired, power controller 16 changes the
`commutation of the motor/generators 12,14 as appropriate to
`increase torque and to change the relative rotational speed of
`the first and second rotors 58,60 to achieve a higher rota-
`tional speed for the output shaft 62. Similarly, whenever
`deceleration is desired, power controller 16 changes the
`commutation phasing of first and second motor/generators
`12,14 to apply torque to output shaft 62 counter to its
`direction of rotation and to change the relative rotational
`speed of the first and second rotors 58,60 to achieve a lower
`rotational speed for output shaft 62.
`The rotational speed of the output shaft 62 is a function of
`the difference between the rotational speeds of the rotors
`58,60. The speed of rotor 60 increases (or the speed of rotor
`58 decreases) as the demand for greater forward vehicle
`speed increases. To decrease the forward speed of the
`vehicle, the difference between the rotational speeds of the
`first and second rotors 58, 60 is decreased. The rate of
`acceleration and deceleration are determined in response to
`the signals from brake pedal and accelerator sensors 40,42.
`Microprocessor 26 receives the signals from brake pedal and
`accelerator sensors 40,42 and, by way of data reflecting the
`desired operating characteristics of the vehicle stored in a
`look-up table in memory device 28, responsively determines
`the desired change of relative rotation of the first and second
`rotors.
`
`Microprocessor 26 processes the signals from the first and
`second rotor speed sensors 50,52 to determine whether the
`difference between the speeds of such rotors 58,60 is such
`that the rotational speed of the output shaft 62 is substan-
`tially equal to the desired output speed. If not, micropro-
`cessor 26 delivers a signal to power controller 16 to change
`the switching characteristics of power being delivered to the
`first and second motor/generators 12,14 so that the appro-
`priate torque is applied to provide the appropriate accelera-
`tion or deceleration characteristic for the vehicle such that
`
`the rotational speeds of the first and second rotors 58,60 will
`change to cause output shaft 62 to rotate at
`the desired
`velocity.
`Power controller 16 senses the amount of current flowing
`in each of motor/generators 12,14 and sends signals to
`microprocessor 26 indicative of the current levels in the
`motor/generators 12,14. Microprocessor 26 determines
`whether the currents in such motor/generators 12,14 will
`cause the sum of the torques being produced by the first and
`second motor/generators 12,14, multiplied by their respec-
`tive gear reductions, to be substantially equal to the desired
`torque on output shaft 62. If not, microprocessor 26 sends a
`signal to power controller 16 to change appropriately the
`current in the first and second motor/generators 12,14.
`Microprocessor 26 also determines whether the torques
`being produced by the motor/generators 12,14 multiplied by
`their respective gear reductions are substantially equal.
`Microprocessor 26 sends signals to power controller 16 to
`correct for any sensed torque imbalances by making the
`appropriate changes to the commutation of motor/generators
`12,14.
`Transition to Recharging Mode
`Referring now to FIGS. 6a and 6b, the transition from the
`all-electric mode to a recharging mode is illustrated. Micro-
`processor 26 receives a signal from state of charge sensor 34
`indicating the state of charge of electric power storage
`device 24. If the state of charge is greater than a predeter-
`mined level,
`the system continues to operate in the all-
`electric mode.
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`The predetermined level selected, is based on the desired
`degree of discharge of electrical storage device 24 prior to
`recharge and, if desired, in response to the trip parameter
`inputs. For example, if there is a large downhill portion near
`the end of the trip which will be coming up shortly, the
`operator may direct microprocessor 26 to allow electrical
`storage device 24 to remain at a low state of charge to take
`full advantage of the upcoming regenerative braking
`described below. Similarly, if the vehicle is nearing the end
`of a trip, the o