United States Patent [191
`Severinsky
`
`[56]
`
`[54] HYBRID ELECTRIC VEHICLE
`Inventor: Alex J. Severinsky, 10904 Pebble
`[76]
`Run, Silver Spring, Md. 20902
`[21] Appl. No.: 947,691
`Sep. 21, 1992
`[22] Filed:
`Int. Cl.s ................................................ B60K 6/04
`[51]
`[52] U.S. CI •.................................. 180/65.2; 180/65.6;
`180/165; 60/718; 475/2; 475/5
`[58] Field of Search .................... 180/65.2, 65.3, 65.4,
`180/65.6, 165; 60/716, 718; 475/2, 5, 8, 9
`References Cited
`U.S. PATENT DOCUMENTS
`3,525,874 8/1970 Toy .................................... 180/65.2
`3,566,717 3/1971 Berman et al ...................... 180/65.2
`3,650,345 3/1972 Yardney ............................. 180/65.2
`3,732,751 5/1973 Berman et al ...................... 180/65 .. 2
`3,791,473 2/1974 Rosen ................................. 180/65.2
`3,837,419 9/1974 Nakamura .......................... 180/65.4
`3,874,472 4/1975 Deane ................................ 180/65.4
`3,923,115 12/1975 Helling ............................... 180/65.2
`4,042,056 8/1977 Horwinski .......................... 180/65.2
`4,095,664 6/1978 Bray ................................... 180/65.4
`4,148,192 4/1979 Cummings ......................... 180/65.2
`4,180,138 12/1979 Shea : .................................. 180/65.2
`4,269,280 5/1981 Rosen ................................. 180/65.2
`4,305,254 12/1981 Kawakatsu et al ................ 180/65.2
`4,306,156 12/1981 Monaco et al ..................... 180/65.2
`4,313,080 1/1982 Park ................................... 180/65.2
`4,335,429 6/1982 Kawakatsu ......................... 180/65.2
`4,351,405 9/1982 Fields et al ........................ 180/65.2
`4,354,144 10/1982 McCarthy .......................... 180/65.4
`4,400,997 8/1983 Fiala ................................... 180/65.2
`4,405,029 9/1983 Hunt ................................... 180/65.2
`4,407,132 10/1983 Kawakatsu et al ................ 180/65.4
`4,438,342 3/1984 Kenyon .............................. 180/65.2
`4,439,989 4/1984 Yamakawa ............................ 60/718
`4,470,476 9/1984 Hunt ................................... 180/65.2
`4,533,011 8/1985 Heidemeyer et al. ............. 180/65.2
`4,562,894 1/1986 Yang .................................. 180/65.2
`4,578,955 4/1986 Medina ............................... 180/65.4
`
`I IIIII IIIIIIII Ill lllll lllll lllll lllll lllll lllll lllll lllll 111111111111111111
`US005343970A
`5,343,970
`[11] Patent Number:
`Sep. 6, 1994
`[45] Date of Patent:
`
`4,593,779 6/1986 Krohling ............................ 180/65.4
`4,611,466 9/1986 Keedy ................................... 60/718
`4,697,660 10/1987 Wu et al ............................. 180/65.2
`4,815,334 3/1989 Lexen .................................... 74/661
`4,923,025 5/1990 Ellers ................................. 180/65.2
`4,951,769 8/1990 Kawamura ......................... 180/65.4
`5,053,632 10/1991 Suzuki et al ....................... 180/65.2
`5,117,931 6/1992 Nishida .............................. 180/65.2
`5,120,282 6/1992 Fjallstrom ...................... 180/65.4 X
`
`OTHER PUBLICATIONS
`SAE Technical Paper Series 891659, Bullock, pp.
`11-26, Aug. 7-10, 1989.
`SAE Technical Paper Series 910247, Kalberlah, pp.
`69-78, Feb. 25-Mar. l, 1991.
`Primary Examiner-Margaret A. Focarino
`Assistant Examiner-Peter C. English
`ABSTRACT
`[57]
`An improved hybrid electric vehicle includes an inter(cid:173)
`nal combustion engine and an electric motor. Both the
`motor and the engine provide torque to drive the vehi(cid:173)
`cle directly through a controllable torque transfer unit.
`Typically at low speeds or in traffic, the electric motor
`alone drives the vehicle, using power stored in batteries;
`under acceleration and during hill climbing both the
`engine and the motor provide torque to drive the vehi(cid:173)
`cle; and in steady state highway cruising, the internal
`combustion engine alone drives the vehicle. The inter(cid:173)
`nal combustion engine is sized to operate at or near its
`maximum fuel efficiency during highway cruising. The
`motor is operable as a generator to charge the batteries
`as needed and also for regenerative braking. No trans(cid:173)
`mission is employed. The motor operates at signifi(cid:173)
`cantly lower currents and higher voltages than conven(cid:173)
`tionally and has a rated power at least equal to that of
`the internal combustion engine. In this manner a cost
`efficient vehicle is provided, suffering no performance
`disadvantage compared to conventional vehicles.
`
`40 Claims, 12 Drawing Sheets
`
`32
`
`34
`
`AIR
`
`EFI
`
`56
`
`CONIROUABLE
`TORQUE(cid:173)
`TIWlSFER UNIT
`
`>r./DC
`CONVERIER
`
`FREQUENCY
`JJP
`POLARITY
`L...-----lCON1ROUER 1----.:..::.::..::.=.c__ _ _ __,
`CURRENT
`
`FUEL
`~
`36
`
`OPERATOR {
`COMMANDS
`
`ACCELERATION
`DIRECTION
`DECELERATION
`
`}
`
`ENGINE SPEED
`MOTOR SPEED
`~TIERY VOLTAGE
`~TIERY CHARGE
`~BIENT TEMP.
`
`DATA INPUT
`
`BMW1013
`Page 1 of 27
`
`

`

`180 - , - - - - - - - - - - - - - - - - - - - - - - - - - - - ,
`
`r , t ·
`-
`ea ive fuel consum~tion
`( gal/hp-hour)
`100%
`/
`--- '
`) / /
`/
`.,/"' /
`
`----
`
`/
`
`-125%
`
`(160%
`
`105°h
`"
`r'
`o
`I
`
`/
`
`/
`
`--------
`
`/
`115%
`v-.,,
`r
`
`/
`
`/
`
`/
`
`/""'
`
`___,,,,,
`
`y/
`( 210 %
`k
`- - 1250%
`
`-----
`
`~300°/o
`
`I
`6,000
`
`I
`5,000
`
`~ • 00 •
`~ a a
`
`tll
`~
`
`,.(1\
`
`i,,.i.
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`IC :
`
`tll go
`a
`
`i,,.i.
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`~
`i,,.i.
`N
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`UI
`"' ~
`~
`"' \C
`-....l
`0
`
`150
`
`ci:
`.::S
`
`~ 120
`Cl>
`LaJ z
`(.!) 90
`ffi
`L&J
`i=
`z
`0 ;
`
`60
`
`~ 30 - t - - -
`
`maximum
`engine
`power
`
`\
`
`/
`(_____ ----
`
`'--- -- ----- /
`....__ - -- ---
`-----
`
`_.,,,.,,-
`
`~
`
`0 I ~ I
`I
`- - - - -
`I
`2,000
`1,000
`4,000
`3,000
`ENGINE SPEED, {RPM)
`FIG.1
`(PRIOR ART)
`
`BMW1013
`Page 2 of 27
`
`

`

`~ • 00 •
`~ a a
`
`... (/1\
`
`00
`~
`i-f
`
`r a
`
`N
`a,
`I(cid:173)
`N
`
`...
`UI
`CH
`~ ...
`'° ....J =
`
`50-,--~~~~~~~~~~~~~~~~~~~~~----.
`
`maximum engine power,
`during 98°/o of city driving
`
`~ _g- 40 -
`~ en
`LL.I 30
`z
`6 as
`i:!: 20
`
`La.I
`
`~ ;
`
`~ 10
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`0 ~
`1,000
`
`1
`2,000
`
`1
`5
`~
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`----...
`
`/125%
`
`% I
`,00% y I _95% !-./
`/ / 160°/0
`/ / y
`
`(
`
`210°k
`I
`_J ,250%
`
`-- -relative fuel
`
`consumption, (gal /
`
`1
`3,000
`ENGINE SPEED, (RPM)
`FIG.2
`
`I
`
`1h
`
`p -hour}
`
`4,000
`
`BMW1013
`Page 3 of 27
`
`

`

`~
`
`34'
`
`32
`
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`~4
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`61
`)
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`THROTilE ._
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`ENGINE
`
`1-....1 TWO-WAY
`CLUTCH
`
`-
`
`\
`~ I
`
`2~
`CONTROLLABLE
`TORQUE(cid:173)
`TRANSFER UNIT
`
`48
`
`EA h I
`
`I JJP
`
`CONTROLLER
`
`56
`
`~ FUEL
`36
`
`OPERATOR {
`COMMANDS
`
`ACCELERATION
`DIRECTION
`DECELERATION
`
`'-' 20;
`
`44
`
`MOTOR I
`
`AC/DC
`I CONVERTER
`
`I
`
`r:J'..l
`~
`... °'
`~ !
`
`FREQUENCY
`POLARllY
`CURRENT
`
`ENGINE SPEED
`MOTOR SPEED
`BATIERY VOLTAGE
`BATIERY CHARGE
`AMBIENT TEMP.
`
`r:J'..l i
`
`~
`
`s,
`~
`
`DATA INPUT
`
`FIG.3
`
`...
`CII
`~
`~ ...
`\C
`-...l
`Q
`
`BMW1013
`Page 4 of 27
`
`

`

`U.S. Patent
`
`Sep. 6, 1994
`
`Sheet 4 of 12
`
`5,343,970
`
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`BMW1013
`Page 5 of 27
`
`

`

`U.S. Patent
`
`Sep. 6, 1994
`
`Sheet 5 of 12
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`5,343,970
`
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`BMW1013
`Page 6 of 27
`
`

`

`U.S. Patent
`
`Sep. 6, 1994
`
`Sheet 6 of 12
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`5,343,970
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`BMW1013
`Page 7 of 27
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`

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`U.S. Patent
`
`Sep. 6, 1994
`
`Sheet 7 of 12
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`5,343,970
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`BMW1013
`Page 8 of 27
`
`

`

`U.S. Patent
`U.S. Patent
`
`Sep.6, 1994
`Sep. 6, 1994
`
`Sheet 8 of 12
`Sheet 8 of 12
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`5,343,970
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`BMW1013
`Page 9 of 27
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`

`

`U.S. Patent
`U.S. Patent
`
`Sep. 6, 1994
`Sep. 6, 1994
`
`Sheet 9 of 12
`Sheet 9 of 12
`
`5,343,970
`5,343,970
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`Page 10 of 27
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`BMW1013
`Page 10 of 27
`
`

`

`TORQUE
`TRANSFER
`UNIT
`
`.LL
`
`~I I
`
`FROM ENGINE
`( VIA CLUTCH 5°)
`40 )
`
`,------Fl
`
`86
`
`TO
`
`WHEELS 1.
`
`FIG. 10
`
`30
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`-
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`41
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`/ 50
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`104
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`~106
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`MOTOR
`FROM
`1 - - - · l ~ 20)
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`\ 28
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`FIG. 1 f
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`BMW1013
`Page 11 of 27
`
`

`

`U.S. Patent
`
`Sep. 6, 1994
`
`Sheet 11 of 12
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`5,343,970
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`BMW1013
`Page 12 of 27
`
`

`

`U.S. Patent
`
`Sep. 6, 1994
`
`Sheet 12 of 12
`
`5,343,970
`
`+ TORQUE
`
`MOTOR
`
`~
`
`SLIP ANGLE
`
`~-----i-----------+
`
`GENERATOR
`
`FIG. 13
`
`TORQUE
`
`0 ""'t'--"--~------------.__ ........
`FIG. 14
`
`0
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`
`RPM
`
`BMW1013
`Page 13 of 27
`
`

`

`1
`
`HYBRID ELECTRIC VEHICLE
`
`5,343,970
`
`2
`tween the diesel engine and the wheels of the locomo(cid:173)
`tive. More particularly, an internal combustion engine
`produces zero torque at zero engine speed (RPM) and
`reaches its torque peak somewhere in the middle of its
`5 operating range. Accordingly, all vehicles driven di(cid:173)
`rectly by an internal combustion engine ( other than
`certain single-speed vehicles using friction or centrifu(cid:173)
`gal clutches, and not useful for normal driving) require
`a multiple speed transmission between the engine and
`the wheels, so that the engine's torque can be matched
`to the road speeds and loads encountered. Further,
`some sort of clutch must be provided so that the engine
`can be decoupled from the wheels, allowing the vehicle
`to stop while the engine is still running, and to allow
`some slippage of the engine with respect to the drive
`train while starting from a stop. It would not be practi-
`cal to provide a diesel locomotive with a multiple speed
`transmission, or a clutch. Accordingly, the additional
`complexity of the generator and electric traction mo(cid:173)
`tors is accepted. Electric traction motors produce full
`torque at zero RPM and thus can be connected directly
`to the wheels; when it is desired that the train should
`accelerate, the diesel engine is simply throttled to in-
`crease the generator output and the train begins to
`move.
`The same drive system may be employed in a smaller
`vehicle such as an automobile or truck, but has several
`distinct disadvantages in this application. In particular,
`30 it is well known that a gasoline or other internal com(cid:173)
`bustion engine is most efficient when producing near its
`maximum output torque. Typically, the number of die(cid:173)
`sel locomotives on a train is selected in accordance with
`the total tonnage to be moved and the grades to be
`overcome, so that all the locomotives can be operated at
`nearly full torque production. Moreover, such locomo-
`tives tend to be run at steady speeds for long periods of
`time. Reasonably efficient fuel use is thus achieved.
`However, such a direct drive vehicle would not achieve
`good fuel efficiency in typical automotive use, involv(cid:173)
`ing many short trips, frequent stops in traffic, extended
`low-speed operation and the like.
`So-called "series hybrid" electric vehicles have been
`proposed wherein batteries are used as energy storage
`devices, so that the engine can be operated in its most
`fuel-efficient output power range while still allowing
`the electric traction motor(s) powering the vehicle to be
`operated as required. Thus the engine may be loaded by
`supplying torque to a generator charging the batteries
`while supplying electrical power to the traction mo(cid:173)
`tor(s) as required, so as to operate efficiently. This sys-
`tem overcomes the limitations of electric vehicles noted
`above with respect to limited range and long recharge
`times.
`However, such series hybrid electric vehicles are
`inefficient and grossly uneconomical, for the following
`reasons. In a conventional vehicle, the internal combus(cid:173)
`tion engine delivers torque to the wheels directly. In a
`series hybrid electric vehicle, torque is delivered from
`the engine via a serially connected generator, battery
`charger, inverter and the traction motor. Energy trans-
`fer between those components consumes at least ap(cid:173)
`proximately 25% of engine power. Further such com(cid:173)
`ponents add substantially to the cost and weight of the
`vehicle. Thus, series hybrid vehicles have not been
`immediately successful.
`A more promising "parallel hybrid" approach is
`shown in U.S. Pat. Nos. 3,566,717 and 3,732,751 to
`
`15
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention is in the field of hybrid electric vehi(cid:173)
`cles incorporating both an internal combustion engine,
`such as a gasoline engine, and an electric motor as
`sources of torque to drive the vehicle. More particu(cid:173)
`larly, this invention relates to a hybrid electric vehicle 10
`that is fully competitive with presently conventional
`vehicles as regards performance, operating conve(cid:173)
`nience, and cost, while achieving substantially im(cid:173)
`proved fuel economy and reduced pollutant emissions.
`2. Discussion of the Prior Art
`For many years great attention has been given to the
`problem of reduction of fuel consumption of automo(cid:173)
`biles and other highway vehicles. Concomitantly very
`substantial attention has been paid to reduction of pol(cid:173)
`lutants emitted by automobiles and other vehicles. To a 20
`degree, efforts to solve these problems conflict with one
`another. For example, increased thermodynamic effi(cid:173)
`ciency and thus reduced fuel consumption can be real(cid:173)
`ized if an engine is operated at higher temperatures.
`Thus there has been substantial interest in engines built 25
`of ceramic materials withstanding higher combustion
`temperatures than those now in use. However, higher
`combustion temperatures in gasoline-fueled engines
`lead to increase in certain undesirable pollutants, typi(cid:173)
`cally NOx,
`Another possibility for reducing emissions is to bum
`mixtures of gasoline and ethanol ("gasohol") or straight
`ethanol. However, to date ethanol has not become eco(cid:173)
`nomically competitive with gasoline and consumers
`have not accepted ethanol to any great degree.
`One proposal for reducing pollution in cities is to
`limit the use of vehicles powered by internal combus(cid:173)
`tion engines and instead employ electric vehicles pow(cid:173)
`ered by rechargeable batteries. To date, all such electric
`cars have a very limited range, typically no more than 40
`150'miles, have insufficient power for acceleration and
`hill climbing except when the batteries are fully
`charged, and require substantial time for battery re(cid:173)
`charging. Thus, while there are many circumstances in
`which the limited range and extended recharge time of 45
`the batteries would not be an inconvenience, such cars
`are not suitable for all the travel requirements of most
`individuals. Accordingly, an electric car would have to
`be an additional vehicle for most users, posing a sub(cid:173)
`stantial economic deterrent. Moreover, it will be appre- 50
`ciated that in the United States most electricity is gener(cid:173)
`ated in coal-fired power plants, so that using electric
`vehicles merely moves the source of the pollution, but
`does not eliminate it. Furthermore, comparing the re(cid:173)
`spective net costs per mile of driving, electric vehicles 55
`are not competitive with ethanol-fueled vehicles, much
`less with conventional gasoline-fueled vehicles.
`Much attention has also been paid over the years to
`development of electric vehicles including internal
`combustion engines powering generators, thus eliminat- 60
`ing the defect of limited range exhibited by simple elec(cid:173)
`tric vehicles. The simplest such vehicles operate on the
`same general principle as diesel-electric locomotives
`used by most railroads. In such systems, an internal
`combustion engine drives a generator providing electric 65
`power to traction motors connected directly to the
`wheels of the vehicle. This system has the advantage
`that no variable gear ratio transmission is required be-
`
`35
`
`BMW1013
`Page 14 of 27
`
`

`

`5,343,970
`
`4
`3
`Berman et al. In Berman et al an internal combustion
`the objects of the present invention-that is, a hybrid
`vehicle competitive with conventional vehicles with
`engine and an electric motor are matched through a
`respect to performance, cost and complexity, while
`complex gear train so that both can provide torque
`achieving substantially improved fuel efficiency.
`directly to the wheels.
`In Berman et al, the internal combustion engine is run 5 Kawakatsu U.S. Pat. No. 4,335,429 shows a parallel
`in several different modes. Where the output of the
`hybrid involving a single internal combustion engine
`internal combustion engine is more than necessary to
`and two electric motors to allow efficient use of the
`drive the vehicle ("first mode operation") the engine is
`electric motors, and is directed principally to a complex
`run at constant speed and excess power is converted by
`control scheme.
`a first generator ("speeder") to electrical energy for 10 Numerous patents disclose hybrid vehicle drives
`storage in a battery. In "second mode operation", the
`tending to fall into one or more of the categories dis-
`internal combustion engine drives the wheels directly,
`cussed above. A number of patents disclose systems
`and is throttled. When more power is needed than the
`wherein an operator is required to select between elec-
`engine can provide, a second motor generator or
`tric and internal combustion operation; for example an
`"torquer" provides additional torque as needed.
`15 electric motor is provided for operation inside buildings
`The present invention relates to such a parallel hybrid
`where exhaust fumes would be dangerous. In several
`vehicle, but addresses certain substantial deficiencies of
`cases the electric motor drives one set of wheels and the
`the Berman et al design. For example, Berman et al
`internal combustion engine drives a different set. See
`show two separate electric motor/generators powered
`generally, U.S. Pat. Nos.; Shea (4,180,138); Fields et al
`by the internal combustion engine to charge batteries 20 (4,351,405); Kenyon (4,438,342); Krohling (4,593,779);
`and to drive the vehicle forward in traffic. This arrange-
`and Ellers (4,923,025).
`ment is a source of additional complexity, cost and
`Numerous other patents show hybrid vehicle drives
`difficulty, as two separate modes of engine control are
`wherein a variable speed transmission is required. A
`required, and the operator must control the transition
`transmission as noted above is typically required where
`between the several modes of operation. Further the 25 the electric motor is not capable of supplying sufficient
`gear train shown by Berman et al appears to be quite
`torque at low speeds. See U.S. Pat. Nos.; Rosen
`complex and difficult to manufacture economically.
`(3,791,473); Rosen (4,269,280); Fiala (4,400,997); and
`Berman et al also indicate that one or even two variable- Wu et al (4,697,660). For further examples of series
`speed transmissions may be required; see col. 3, lines
`hybrid vehicles as discussed above, see generally Bray
`19-22 and 36-38.
`30 (4,095,664); Cummings (4,148,192); Kawakatsu et al
`Hunt U.S. Pat. Nos. 4,405,029 and 4,470,476 also
`(4,305,254 and 4,407,132); Monaco et al (4,306,156);
`disclose parallel hybrids requiring complex gearing
`Park (4,313,080); McCarthy (4,354,144); Heidemeyer
`arrangements, including multiple speed transmissions.
`(4,533,011); Kawamura (4,951,769); and Suzuki et al
`More specifically, the Hunt patents disclose several
`(5,053,632). Other patents of general relevance to this
`embodiments of parallel hybrid vehicles. Hunt indicates 35 subject matter include Toy (3,525,874); Yardney
`(see col. 4, lines 6-20 of the '476 patent) that an electric
`(3,650,345); Nakamura (3,837,419); Deane (3,874,472);
`motor may drive the vehicle at low speeds up to 20
`Horwinski
`(4,042,056); Yang
`(4,562,894); Keedy
`mph, and an internal combustion engine used for speeds
`(4,611,466); and Lexen (4,815,334).
`above 20 mph, while "in certain speed ranges, such as
`U.S. Pat. No. 4,578,955 to Medina shows a hybrid
`from 15-30 mph, both power sources may be energized. 40 system wherein a gas turbine is used as the internal
`... Additionally, both power sources could be utilized
`combustion engine to drive a generator as needed to
`charge batteries. Of particular interest to certain aspects
`under heavy load conditions." Hunt also indicates that
`"the vehicle could be provided with an automatic
`of the present invention is that Medina discloses that the
`changeover device which automatically shifts from the
`battery pack should have a voltage in the range of 144,
`electrical power source to the internal combustion 45 168 or 216 volts and the generator should deliver cur-
`power source, depending on the speed of the vehicle"
`rent in the range of 400 to 500 amperes. Those of skill in
`(col. 4, lines 12-16).
`the art will recognize that these high currents involve
`However, the Hunt vehicle does not meet the objects
`substantial resistance heating losses, and additionally
`of the present invention. Hunt's vehicle in each embodi-
`require that all electrical connections be made by posi-
`ment requires a conventional manual or automatic 50 tive mechanical means such as bolts and nuts, or by
`transmission. See col. 2, lines 6-7. Moreover, the inter-
`welding. More specifically, for reasons of safety and in
`nal combustion engine is connected to the transfer case
`accordance with industry practice, currents in excess of
`(wherein torque from the internal combustion engine
`about 50 amperes cannot be carried by the conventional
`and electric motor is combined) by a "fluid coupling or
`plug-in connectors preferred for reasons of convenience
`torque converter of conventional construction". Col. 2, 55 and economy, but must be carried by much heavier,
`lines 16-17. Such transmissions and fluid couplings or
`more expensive and less convenient fixed connectors (as
`torque converters are very inefficient, are heavy, bulky,
`used on conventional starter and battery cable connec-
`and costly, and are to be eliminated according to one
`tions). Accordingly, it would be desirable to operate the
`object of the present invention.
`electric motor of a hybrid vehicle at lower currents.
`Furthermore, the primary means of battery charging 60 U.S. Pat. No. 4,439,989 to Yamakawa shows a system
`disclosed by Hunt involves a further undesirable com-
`wherein two different internal combustion engines are
`plexity, namely a turbine driving the electric motor in
`provided so that only one need be run when the load is
`generator configuration. The turbine is fueled by waste
`low. This arrangement would be complex and expen-
`heat from the internal combustion engine. See col. 3,
`sive to manufacture.
`lines 10-60. Hunt's internal combustion engine is also 65 Detailed discussion of various aspects of hybrid vehi-
`fitted with an alternator, for additional battery charging
`cle drives may be found in Kalberlah, "Electric Hybrid
`capability, adding yet further complexity. Thus it is
`Drive Systems for Passenger Cars and Taxis", SAE
`clear that Hunt fails to teach a hybrid vehicle meeting
`Paper No. 910247 (1991), and in Bullock, "The Techno-
`
`BMW1013
`Page 15 of 27
`
`

`

`5,343,970
`
`5
`logical Constraints of Mass, Volume, Dynamic Power
`Range and Energy Capacity on the Viability of Hybrid
`and Electric Vehicles", SAE Paper No. 891659 (1989).
`Further related papers are collected in Electric and
`Hybrid Vehicle Technology, volume SP-915, published 5
`by SAE in February 1992. Reference herein to the latter
`volume does not concede its effectiveness as prior art
`with respect to the claims of the present application.
`It can thus be seen that while the prior art clearly
`discloses the desirability of operating an internal com- 10
`bustion engine in its most efficient operating range, and
`that a battery may be provided to store energy to be
`supplied to an electric motor in order to even out the
`load on the internal combustion engine, there remains
`substantial room for improvement. In particular, it is 15
`desired to obtain the operational flexibility of a parallel
`hybrid system, while optimizing the system's opera(cid:173)
`tional parameters and providing a substantially simpli(cid:173)
`fied parallel hybrid system as compared to those shown
`·
`· h
`m t e pnor art.
`
`20
`
`6
`Other aspects and objects of the invention will be(cid:173)
`come clear as the discussion below proceeds.
`The present invention satisfies the needs of the art
`and objects of the invention mentioned above by provi(cid:173)
`sion of an improved parallel hybrid electric vehicle. An
`internal combustion engine and an AC induction motor
`are arranged to supply torque through a controllable
`torque transfer unit to the driving wheels of the vehicle.
`The motor is driven at relatively high voltage, rela(cid:173)
`tively high frequency, and relatively low maximum
`current. Energy stored in batteries is transformed into
`AC drive pulses of appropriate frequency and shape by
`a solid state switching unit comprising metal oxide semi(cid:173)
`conductor (MOS) controlled thyristors. No variable
`gear ratio transmission is required by the vehicle of the
`present invention, as the AC electric motor provides
`adequate torque at low RPM. Inefficiencies particularly
`inherent in automatic transmissions are thus eliminated.
`A microprocessor receives control inputs from the
`driver of the vehicle and monitors the performance of
`the electric motor and the internal combustion engine,
`the state of charge of the battery, and other significant
`variables. The microprocessor determines whether the
`internal combustion engine or the electric motor or
`both should provide torque to the wheels under various
`monitored operating conditions. Typically, the electric
`motor operates under battery power during low speed
`operation, e.g., in traffic, during reverse operation, or
`the like. In this mode of operation, the energy transfer
`efficiency from the batteries to the wheels is very high.
`By comparison, it will be appreciated that a vast amount
`of fuel is wasted as internal combustion engines of con(cid:173)
`ventional vehicles idle uselessly at stop lights or in traf(cid:173)
`fic. This source of inefficiency and pollution is elimi(cid:173)
`nated according to the invention.
`As the road speed increases, the internal combustion
`engine is started, using torque provided by the electric
`motor through the torque transfer unit, such that no
`separate starter is required. The internal combustion
`engine is sized to operate near maximum efficiency
`during steady state cruising on the highway, at between
`about 35 and 65 mph; at these times the electric motor is
`not powered. When necessary for acceleration or hill
`climbing, the electric motor is operated to add its torque
`to that provided by the internal combustion engine.
`Under braking or coasting conditions, the electric
`motor may be operated as a generator to charge the
`batteries.
`For comparison to an example of the hybrid electric
`vehicle of the invention, a conventional 3,300 pound
`sedan is typically powered by a 165 horsepower internal
`combustion engine driving the rear wheels through an
`automatic transmission. However, during highway
`cruising and in traffic, that is, under the most common
`operating conditions, only 2-30 hp is required. There(cid:173)
`fore, the internal combustion engine of a conventional
`vehicle rarely operates near maximum efficiency. More(cid:173)
`over, as noted, such vehicles are normally driven
`through notoriously inefficient automatic transmissions;
`specifically, such transmissions are typically only about
`60% efficient during operation in the indirect gears, i.e.,
`during acceleration.
`A comparable 3,300 pound sedan according to the
`invention has an internal combustion engine of about 45
`horsepower working in concert with a 65 horsepower
`electric motor, without a transmission. This combina(cid:173)
`tion provides acceleration and hill climbing perfor(cid:173)
`mance equivalent to a conventional vehicle with a 165
`
`25
`
`30
`
`OBJECTS AND SUMMARY OF THE
`INVENTION
`It is an object of the invention to provide an im-
`proved hybrid electric vehicle realizing substantially
`increased fuel economy and reduced pollutant emis(cid:173)
`sions as compared to present day vehicles while suffer(cid:173)
`ing no significant penalty in performance, operating
`convenience, cost, complexity, or weight.
`It is a more particular object of the present invention
`to provide an improved parallel hybrid electric vehicle
`wherein an internal combustion engine and an electric
`motor can separately or simultaneously apply torque to
`the driving wheels of the vehicle, controlled to realize 35
`maximum fuel efficiency at no penalty in convenience,
`performance, or cost.
`It is a further object of the invention to provide a
`parallel hybrid electric vehicle wherein the electric
`motor provides output power equal to at least 100 per- 40
`cent of the rated output power of the internal combus(cid:173)
`tion engine, and more preferably up to about 150-200
`percent thereof, so that the engine operates under sub(cid:173)
`stantially optimum conditions in order to realize sub-
`stantial fuel economy of operation.
`More particularly, it is an object of the invention to
`provide a parallel hybrid electric vehicle wherein the
`internal combustion engine is sized to efficiently pro(cid:173)
`vide the average power required for operation at mod(cid:173)
`erate and highway speeds, with the electric motor sized 50
`to deliver the additional power needed for acceleration
`and hill climbing.
`Still another object of the invention is to provide a
`hybrid electric vehicle wherein the electric motor and
`battery charging circuits operate at no more than about 55
`30-50 amperes maximum current, whereby resistance
`heating losses are greatly reduced, and whereby inex(cid:173)
`pensive and simple electrical manufacturing and con(cid:173)
`nection techniques can be employed.
`It is a further object of the invention to provide a 60
`solid-state switching power converter for converting
`DC power provided by the batteries of a parallel hybrid
`electric vehicle to AC power of higher frequency than
`conventionally employed for supply to an AC induction
`motor for powering the vehicle as needed, and for con- 65
`verting mechanical energy provided to the induction
`motor when operated as a generator to DC energy for
`charging the batteries as required.
`
`45
`
`BMW1013
`Page 16 of 27
`
`

`

`5,343,970
`
`7
`8
`hp internal combustion engine with automatic transmis(cid:173)
`DESCRIPTION OF THE PREFERRED
`sion, while yielding a 200-300% improvement in net
`EMBODIMENTS
`fuel efficiency and at least a similar reduction in pollut(cid:173)
`ants emitted. Moreover, the vehicle of the present in-
`Referring specifically to FIG. 1, curve 10 represents
`vention is no heavier, no more bulky and no more ex- 5 the output power versus engine speed (RPM) of a typi-
`pensive to manufacture than conventional vehicles
`cal spark ignition gasoline-fueled internal combustion
`using standard internal combustion engines.
`engine as used with an automatic transmission in a typi-
`More particuJarly, according to the invention, the
`cal sedan of 3,300 pounds. As can be seen, the maximum
`internal combustion engine is operated only under the
`engine power available is about 165 horsepower at
`most efficient conditions of output power and speed. 10 about 5,000 RPM. Also shown in FIG. 1 by curve 12
`When the engine can be used efficiently to drive the
`are the average power requirements of such a vehicle.
`vehicle forward, e.g. in highway cruising, it is so em-
`Points C, S and H on curve 12 show average fuel con-
`ployed. Under other circumstances, e.g. in traffic, the
`sumption in city, suburban and highway driving, re-
`electric motor alone drives the vehicle forward and the
`spectively. Point Con curve 12 shows that the average
`in