`Lateur et al.
`
`I IIIII IIIIIIII Ill lllll lllll lllll lllll lllll lllll lllll lllll 111111111111111111
`US005823280A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,823,280
`Oct. 20, 1998
`
`[54] HYBRID PARALLEL ELECTRIC VEHICLE
`
`[75]
`
`Inventors: Michel J. Lateur, Redwood City;
`Daniel P. Pliskin, Palo Alto, both of
`Calif.
`
`[73] Assignee: Nevcor, Inc., Stanford, Calif.
`
`[21]
`
`Appl. No.: 372,173
`
`[22]
`
`Filed:
`
`Jan. 12, 1995
`
`[51]
`[52]
`[58]
`
`[56]
`
`Int. Cl.6
`....................................................... B60K 1/00
`U.S. Cl. ......................... 180/65.2; 180/65.4; 180/165
`Field of Search .............................. 60/716; 180/65.2,
`180/65.1, 65.4, 65.3; 475/3, 5; 364/426.041;
`318/141, 149,3~41,4~53,59, 61
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,566,717
`4,155,019
`4,187,436
`4,407,132
`5,067,932
`5,365,153
`
`3/1971 Berman et al. ........................... 74/859
`5/1979 Weghaupt ................................. 310/61
`2/1980 Etienne ..................................... 290/27
`10/1983 Kawakatsu et al. ...................... 60/716
`11/1991 Edwards ...................................... 475/5
`11/1994 Fujita et al.
`.............................. 318/34
`
`Primary Examiner-Richard M. Camby
`Attorney, Agent, or Firm----Flehr Hohbach Test Albritton &
`Herbert LLP
`
`[57]
`
`ABSTRACT
`
`A hybrid electric drive system is described that includes a
`heat engine having a drive shaft, and two electric motor/
`generators having rotors that are coaxially connected to the
`drive shaft. A control arrangement for these elements is also
`described that provides a relatively simple combined opera(cid:173)
`tion for driving a vehicle.
`
`3,122,696
`
`2/1964 Graybeal et al. ......................... 322/20
`
`19 Claims, 9 Drawing Sheets
`
`50
`
`First rotor
`speed sensor
`
`Second rotor
`speed sensor
`
`48
`Engine speed
`sensor
`
`sensor
`
`sensor
`
`36
`
`34
`
`sensor
`
`28
`
`Memory
`
`22
`
`Heat Engine
`
`Microprocessor
`
`! 30
`
`Driver
`Control
`Display
`
`12
`
`First Elect
`Mtr/Gen
`
`74
`
`Torque Trans.
`
`62
`
`76
`
`14
`
`Second Elect
`Mtr/Gen
`
`32
`
`A/C Mains
`
`Storage Cells
`
`Charger Aux.
`
`BMW1051
`Page 1 of 18
`
`
`
`50
`
`First rotor
`speed sensor
`
`....
`
`52")
`
`Second rotor
`speed sensor
`
`....
`
`48")
`Engine speed ....
`sensor
`
`40")
`
`28"'1
`
`- Memory
`
`22"'1
`
`'
`
`Heat Engine
`
`a
`
`a
`
`82
`;:::II
`
`• Ill
`
`._
`
`Brake pedal -
`
`sensor
`
`26")
`
`_....
`
`-
`.,...
`-~
`-
`
`101
`
`-
`C_ <=> "'l
`
`p~
`
`62")
`
`Diff.
`
`C es> 'Ji
`
`l
`-
`
`12"'1
`
`1~
`
`74 ")
`
`First Elect
`Mtr/Gen
`
`Torque Trans.
`
`!,6~
`
`Power controller -
`.....
`
`j ~
`
`'-76
`
`14 ")
`'
`Second Elect
`Mtr/Gen
`
`--
`--
`
`d •
`r:JJ.
`•
`~
`~ .....
`~ = .....
`
`0
`I")
`t"""
`
`N ~=
`"'""
`\C
`\C
`00
`
`'JJ. =(cid:173)~
`~ ....
`"'"" 0 ....,
`
`\C
`
`Ul
`....
`00
`N
`~ ....
`N
`00 =
`
`~ '
`-
`I Accelerator ~ Microprocessor
`
`!
`
`42")
`
`....
`
`sensor
`
`36)
`
`Cruise control
`switch
`
`-
`
`34")
`
`State of charge I
`
`sensor
`
`I
`
`30")
`'
`
`Driver
`Control 14
`Display
`
`~ • 24 '1
`
`Storage Cells
`
`....
`
`-.....
`
`32")
`
`A/C Mains
`
`Charger Aux .
`
`I/
`I"-
`
`-,
`
`Figure 1
`
`BMW1051
`Page 2 of 18
`
`
`
`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 2 of 9
`
`5,823,280
`
`N
`
`(.'.)
`G::
`
`I I I I
`I I I I
`I I I I
`I I I I
`I I I I
`I I I I
`I
`I
`I I I I
`I I I I
`I
`I
`I I I I
`I I I I
`I I I I
`I I I I
`I I I I
`
`I I I I
`I I I I
`I
`I
`I I I I
`I I I I
`I I I I
`I I I I
`I I I I
`I I I I
`I I I I
`I I I I
`I
`I
`I I I I
`
`'<t-
`
`N
`(0
`
`0
`(0
`
`(0
`l.()
`
`N
`..--
`
`s:;t-
`l.()
`
`CX)
`l.()
`<.D
`I'
`'<t-
`<.D
`
`BMW1051
`Page 3 of 18
`
`
`
`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 3 of 9
`
`5,823,280
`
`BMW1051
`Page 4 of 18
`
`
`
`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 4 of 9
`
`5,823,280
`
`1 st Motor/ generator
`
`2nd Motor I generator
`
`1~
`
`X---)IE~-X/212
`
`t I
`
`Output shaft
`
`Figure 4 a
`
`Heat engine
`
`2nd Motor/generator
`
`z IE----- X ----)1(•:----X/ 212
`t
`
`1st Motor/generator
`
`Output shaft
`
`Figure 4 b
`
`BMW1051
`Page 5 of 18
`
`
`
`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 5 of 9
`
`5,823,280
`
`Start
`
`Read accelerator and brake
`pedal sensors
`
`Determine output speed
`
`Read Rotational speed sensors
`
`yes Control commutation of 1st & 2nd
`">-----1M motor/generators to increase speed of
`output shaft.
`
`yes
`
`Control commutation of 1st & 2nd
`motor/generators to decrease speed at
`>-----1-.t output shaft by producing regenerative
`braking forces
`
`Determine desired acceleration or
`deceleration characteristics.
`
`Control current flows to provide sum of
`torques desired for acceleration or
`deceleration characteristics
`
`Control current flow to balanace torques
`being prodvided by 1st & 2nd
`motor/generators
`
`End
`
`Figure 5
`
`BMW1051
`Page 6 of 18
`
`
`
`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 6 of 9
`
`5,823,280
`
`Sense battery
`state of charge
`
`no
`
`Operate in
`all-electric mode
`
`Stop 1st rotor while maintaining
`speed & torque to output shaft by
`controlling current flow to 2nd
`motor/generator
`
`Engage Clutch
`
`t
`
`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
`
`Control commutation of
`1st motor/generator to
`operate in charge mode
`
`Read accelerator and brake
`
`pedal sensors •
`
`B
`
`Determine desired output speed I ,--,
`' - - - - - - - - - - - - - -~
`
`Figure 6 a
`
`BMW1051
`Page 7 of 18
`
`
`
`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 7 of 9
`
`5,823,280
`
`T
`
`Read rotational·
`speed sensors
`
`yes
`
`Control generative load of first
`motor/generator to balance
`torque of 2nd motor/generator and
`to increase speed of output shaft at
`desired rate.
`
`~__;;_ye_s __ .....i Control generative load of first
`motor/generator to balance torque of
`2ndmotor/generator and to decrease
`speed of output shaft at desired rate.
`
`Sense battery
`state of charge
`
`1 ... 4a - - - - - - - - - - - - - l
`
`Disengage clutch
`
`Turn off heat engine
`
`Return to all-electric
`
`Figure 6 b
`
`BMW1051
`Page 8 of 18
`
`
`
`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 8 of 9
`
`5,823,280
`
`Read cruise master control switch
`
`Cruise control on
`
`no
`
`Operate in standard mode
`
`yes
`
`Read brake pedal sensor
`
`Control commutation of 1st & 2nd
`motor/generator to produce
`yes
`~ - - -~ regenerative braking force
`to slow rotation of output shaft at
`desired rate.
`
`no
`
`Read accelerator sensor
`
`Control commutation of 1st
`& 2nd motor/generators to
`maintain speed of rotation
`of output shaft.
`
`yes
`
`Control commutation of 1st &
`2nd motor/generators to
`increase speed of rotation of
`output shaft at desired rate.
`
`Figure 7
`
`BMW1051
`Page 9 of 18
`
`
`
`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 9 of 9
`
`5,823,280
`
`Start
`
`Read cruise control
`master switch
`
`Operate in cruise control
`
`Read Rotational speed sensors.._-----------------.
`
`Read brake pedal sensors
`
`yes Control commutation of 1st & 2nd
`=>----1.i motor/generators to decrease speed of
`output shaft via regererative braking
`
`Read accelerator sensor
`
`Control commutation of 1st & 2nd
`=>-----i.i motor/generators to increase speed of
`output shaft
`
`Control commutation of 1st & 2nd
`~-~~ motor/generators to decrease speed of
`output shaft via regererative braking
`
`no
`
`Control commutation at 1st & 2nd motor
`generators to maintain output shaft speed
`
`End
`
`Figure 8
`
`BMW1051
`Page 10 of 18
`
`
`
`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(cid:173)
`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(cid:173)
`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 25
`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. A parallel 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(cid:173)
`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(cid:173)
`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(cid:173)
`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 I2R losses and increased degra(cid:173)
`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 60
`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 65
`system eliminates some of the problems associated with the
`Kawakatsu arrangement, the Berman et al. arrangement also
`
`10
`
`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.
`5 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
`15 relatively lengthy trips in which the batteries are signifi(cid:173)
`cantly discharged. The internal combustion engine can be
`operated inherently cleaner by being maintained at a con(cid:173)
`stant speed and constant load, independent of the time(cid:173)
`varying need for road horsepower. During most city driving
`20 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(cid:173)
`trical outlet.
`Hybrid electric vehicles have substantially different aver(cid:173)
`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,
`30 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
`40 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
`45 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
`50 (from the broad standpoint, the term "generator" encom(cid:173)
`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-
`55 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.
`
`35
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`For a better understanding of the present invention, ref(cid:173)
`erence may be made to the accompanying drawings, in
`which:
`
`BMW1051
`Page 11 of 18
`
`
`
`5,823,280
`
`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(cid:173)
`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(cid:173)
`tionships. This implementation of the invention can be used
`to power an automobile, truck, bus, delivery van, work 25
`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(cid:173)
`manent magnet motors; however, it should be appreciated
`that other types of motors may be used, for example mul(cid:173)
`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 50
`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(cid:173)
`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 alga-
`
`4
`rithms. In this embodiment, power controller 16, micropro(cid:173)
`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
`5 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
`10 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(cid:173)
`ers the electrical energy to electrical storage device 24 for
`15 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
`20 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
`30 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,
`35 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
`40 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
`45 plurality of rotational speed sensors 48,50,52 are also pro(cid:173)
`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-
`55 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
`60 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
`65 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
`
`BMW1051
`Page 12 of 18
`
`
`
`5,823,280
`
`5
`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(cid:173)
`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 30
`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 (We-cc) is equal to
`wA(i:A +i:E)+ws"ts), where:
`w=rotational speed;
`"t=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 60
`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
`
`6
`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
`5 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
`10 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
`15 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-
`20 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
`25 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
`35 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/
`40 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
`45 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(cid:173)
`sor 26 maintains rotors 58,60 within their allowable oper-
`50 a ting limits by comparing the operating characteristics of the
`motor/generators 12,14 with their respective operating lim(cid:173)
`its.
`All Electric Mode
`Referring now to FIG. 5, an exemplary flow chart show-
`55 ing operation in an all-electric mode is illustrated. Micro(cid:173)
`processor 26 receives signals from brake pedal and accel(cid:173)
`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
`65 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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`operating characteristics of the vehicle and reflect, for
`example, desired acceleration and deceleration characteris(cid:173)
`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(cid:173)
`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 15
`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(cid:173)
`tially equal to the desired output speed. If not, micropro(cid:173)
`cessor 26 delivers a signal to power controller 16 to change
`the switching characteristics of power being delivered to the 35
`first and second motor/generators 12,14 so that the appro(cid:173)
`priate torque is applied to provide the appropriate accelera(cid:173)
`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(cid:173)
`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 appropriate