`Severinsky et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,630,761 B2
`*Jan. 14, 2014
`
`USOO863.0761 B2
`
`(54) HYBRID VEHICLES
`(71) Applicant: Alex J. Severinsky, Washington, DC
`(US)
`
`(72) Inventors: Alex J. Severinsky, Washington, DC
`(US); Theodore Louckes, Holly, MI
`US
`(US)
`(73) Assignees: PAICE LLC, Baltimore, MD (US); The
`Abell Foundation, Baltimore, MD (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`This patent is Subject to a terminal dis-
`claimer.
`
`(21) Appl. No.: 13/573,728
`
`(22) Filed:
`(65)
`
`Oct. 5, 2012
`Prior Publication Data
`US 2013/OO96752 A1
`Apr. 18, 2013
`
`Related U.S. Application Data
`(60) Division of application No. 13/065,708, filed on Mar.
`29, 2011, which is a division of application No.
`12/320,600, filed on Jan. 29, 2009, now abandoned
`which is a division of application No. 1 1/459,458, filed
`on May 8, 2006, now Pat. No. 7,520,353, which is a
`division of application No. 10/382.577, filed on Mar. 7,
`2003, now Pat. No. 7,104,347, which is a division of
`application No. 09/822,866, filed on Apr. 2, 2001, now
`Pat. No. 6,554,088, which is a continuation-in-part of
`application No. 09/264.817, filed on Mar. 9, 1999, now
`Pat. No. 6,209,672.
`(60) Provisional application No. 60/100,095, filed on Sep.
`14, 1998, provisional application No. 60/122.296,
`filed on Mar. 1, 1999.
`
`(2006.01)
`
`(51) Int. Cl.
`B60L 9/00
`(52) U.S. Cl.
`USPC ............................................. 701/22; 318/139
`(58) Field of Classification Search
`USPC ............................................. 701/22; 318/139
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`5,301,515 A
`4, 1994 Iritani et al.
`5,343,970 A * 9/1994 Severinsky ................ 18Of 65.25
`5,430,432 A * 7/1995 Camhi et al. .................. 340,438
`5,483,939 A
`1/1996 Kamura et al.
`5,497,941 A
`3/1996 Numazawa et al.
`5,501,267 A
`3, 1996 Iritani et al.
`5,695,722. A
`12/1997 Myers et al.
`5,785,137 A * 7/1998 Reuyl ...................... 18O, 65.245
`5,806,617 A
`9/1998 Yamaguchi
`(Continued)
`Primary Examiner — Calvin Cheung
`(74) Attorney, Agent, or Firm — Michael de Angeli
`(57)
`ABSTRACT
`A hybrid vehicle comprises an internal combustion engine, a
`traction motor, a starter motor, and a battery bank, all con
`trolled by a microprocessor in accordance with the vehicle's
`instantaneous torque demands so that the engine is run only
`under conditions of high efficiency, typically only when the
`load is at least equal to 30% of the engine's maximum torque
`output. In some embodiments, a turbocharger may be pro
`vided, activated only when the load exceeds the engine's
`maximum torque output for an extended period; a two-speed
`transmission may further be provided, to further broaden the
`vehicle's load range. A hybrid brake system provides regen
`erative braking, with mechanical braking available in the
`event the battery bank is fully charged, in emergencies, or at
`rest; a control mechanism is provided to control the brake
`system to provide linear brake feel under varying circum
`StanceS.
`
`12 Claims, 17 Drawing Sheets
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`Page 1 of 48
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`US 8,630,761 B2
`Page 2
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,825,283 A * 10/1998 Camhi .......................... 340,438
`5,927,829 A
`7/1999 Saga
`5,939,794. A * 8/1999 Sakai et al. ................. 290/40 A
`5,942,879 A * 8/1999 Ibaraki ............................ 322/16
`5,982,045 A * 1 1/1999 Tabata et al. .................... 29Of 17
`
`5.984,033 A * 1 1/1999 Tamagawa et al. ........ 180/65.28
`6,070,680 A *
`6/2000 Oyama ...................... 18Of 65.25
`6,089,310 A
`7/2000 Toth et al.
`6,104.282 A * 8/2000 Fragoso et al. ............ 340,309.8
`6,314,347 B1 * 1 1/2001 Kuroda et al. .................. TO1/22
`2001/0044683 A1* 11/2001 Takaoka et al. .
`701/22
`2004/0230376 A1* 11/2004 Ichikawa et al. .................. 702/2
`
`
`
`* cited by examiner
`
`BMW1001
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`1.
`HYBRD VEHICLES
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation-in-part of Ser. No.
`09/264,817, filed Mar. 9, 1999, now U.S. Pat. No. 6,209,672,
`issued Apr. 3, 2001, which in turn claims priority from pro
`visional application Ser. No. 60/100,095, filed Sep. 14, 1998,
`and is also a continuation-in-part of Ser. No. 09/392,743, filed
`Sep. 9, 1999, which in turn claims priority from provisional
`application Ser. No. 60/122.296, filed Mar. 1, 1999.
`
`FIELD OF THE INVENTION
`
`This application relates to improvements in hybrid
`vehicles, that is, vehicles in which both an internal combus
`tion engine and one or more electric motors are provided to
`supply torque to the driving wheels of the vehicle. More
`particularly, this invention relates to a hybrid electric vehicle
`that is fully competitive with presently conventional vehicles
`as regards performance, operating convenience, and cost,
`while achieving Substantially improved fuel economy and
`reduced pollutant emissions.
`
`DISCUSSION OF THE PRIOR ART
`
`10
`
`15
`
`25
`
`2
`coal-fired powerplants, so that using electric Vehicles merely
`moves the source of the pollution, but does not eliminate it.
`Furthermore, comparing the respective net costs per mile of
`driving, electric vehicles are not competitive with ethanol
`fueled vehicles, much less with conventional gasoline-fueled
`vehicles. See, generally, Simanaitis, “Electric Vehicles',
`Road & Track, May 1992, pp. 126-136: Reynolds, “AC Pro
`pulsion CRX, Road & Track, October 1992, pp. 126-129.
`Brooks etal U.S. Pat. No. 5,492,192 shows such an electric
`vehicle; the invention appears to be directed to incorporation
`of antilock braking and traction control technologies into an
`otherwise conventional electric vehicle.
`Much attention has also been paid over the years to devel
`opment of electric vehicles including internal combustion
`engines powering generators, thus eliminating the defect of
`limited range exhibited by simple electric vehicles. The sim
`plest 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 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
`between the engine and the wheels of the vehicle.
`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 operating range. Accord
`ingly, all vehicles driven directly by an internal combustion
`engine (other than certain single-speed vehicles using friction
`or centrifugal clutches, and not useful for normal driving)
`require a variable-ratio 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 mechani
`cally 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 practical to provide a diesel locomo
`tive, for example, with a multiple speed transmission, or a
`clutch. Accordingly, the additional complexity of the genera
`tor and electric traction motors 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
`increase 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, and as dis
`cussed in detail below in connection with FIGS. 1 and 2, it is
`well known that a gasoline or other internal combustion
`engine is most efficient when producing near its maximum
`output torque. Typically, the number of diesel 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 locomo
`tives can be operated at nearly full torque production. More
`over, such locomotives 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,
`involving many short trips, frequent stops in traffic, extended
`low-speed operation and the like.
`So-called “series hybrid’ electric vehicles have been pro
`posed for automotive use, wherein batteries are used as
`energy storage devices, so that an internal combustion engine
`provided to power a generator can be operated in its most
`fuel-efficient output power range while still allowing the elec
`tric traction motor(s) powering the vehicle to be operated as
`required. Thus the engine may be loaded by Supplying torque
`
`30
`
`35
`
`45
`
`For many years great attention has been given to the prob
`lem of reduction of fuel consumption of automobiles and
`other highway vehicles. Concomitantly very substantial
`attention has been paid to reduction of pollutants emitted by
`automobiles and other vehicles. To a degree, efforts to solve
`these problems conflict with one another. For example,
`increased thermodynamic efficiency and thus reduced fuel
`consumption can be realized if an engine is operated at higher
`temperatures. Thus there has been substantial interest in
`engines built of ceramic materials withstanding higher com
`bustion temperatures than those now in use. However, higher
`combustion temperatures in gasoline-fueled engines lead to
`increase in certain undesirable pollutants, typically NO.
`40
`Another possibility for reducing emissions is to burn mix
`tures of gasoline and ethanol ("gasohol), or straight ethanol.
`However, to date ethanol has not become economically com
`petitive with gasoline, and consumers have not accepted etha
`nol to any great degree. Moreover, to make an alternate fuel
`Such as ethanol available to the extent necessary to achieve
`appreciable improvements in nationwide air quality and fuel
`conservation would require immense costs for infrastructure
`improvements; not only the entire nation's motor fuel pro
`duction and delivery system, but also the vehicle manufac
`ture, distribution, and repair system, would have to be exten
`sively revised or substantially duplicated.
`One proposal for reducing pollution in cities is to limit the
`use of vehicles powered by internal combustion engines and
`instead employ electric vehicles powered by rechargeable
`batteries. To date, all such “straight electric' cars have had
`very limited range, typically no more than 150 miles, have
`insufficient power for acceleration and hill climbing except
`when the batteries are substantially fully charged, and require
`substantial time for battery recharging. Thus, while there are
`many circumstances in which the limited range and extended
`recharging time of the batteries would not be an inconve
`nience, such cars are not suitable for all the travel require
`ments of most individuals. Accordingly, an electric car would
`have to be an additional vehicle for most users, posing a
`substantial economic deterrent. Moreover, it will be appreci
`ated that in the United States most electricity is generated in
`
`50
`
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`
`60
`
`65
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`BMW1001
`Page 20 of 48
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`3
`to a generator charging the batteries while Supplying electri
`cal power to the traction motor(s) as required, so as to operate
`efficiently. This system overcomes the limitations of electric
`vehicles noted above with respect to limited range and long
`recharge times. Thus, as compared to a conventional vehicle,
`wherein the internal combustion engine delivers torque
`directly to the wheels, in a series hybrid electric vehicle,
`torque is delivered from the engine to the wheels via a serially
`connected generator used as a battery charger, the battery, and
`the traction motor. However, energy transfer between those
`components consumes at least approximately 25% of engine
`power. Further, Such components add substantially to the cost
`and weight of the vehicle; in particular, an electric motor
`capable of providing Sufficient torque to meet all expected
`demand, e.g., to allow reasonable performance under accel
`eration, during hill-climbing and the like, is rather heavy and
`expensive. Thus, series hybrid vehicles have not been imme
`diately successful.
`A more promising “parallel hybrid” approach is shown in
`U.S. Pat. Nos. 3,566,717 and 3,732,751 to Berman et al. In
`Berman et al an internal combustion engine and an electric
`motor are matched through a complex gear train so that both
`can provide torque directly to the wheels, the vehicle being
`operated in several different modes. Where the output of the
`internal combustion engine is more than necessary to drive
`the vehicle (“first mode operation') the engine is run at con
`stant speed and excess power is converted by a first motor/
`generator ('speeder') to electrical energy for storage in a
`battery. In “second mode operation', the internal combustion
`engine drives the wheels directly, and is throttled. When more
`power is needed than the engine can provide, a second motor/
`generator or “torquer” provides additional torque as needed.
`Berman et all thus show two separate electric motor/gen
`erators separately powered by the internal combustion
`engine; the “speeder charges the batteries, while the
`“torquer” propels the vehicle forward in traffic. This arrange
`ment is a source of additional complexity, cost and difficulty,
`as two separate modes of engine control are required. More
`over, the operator must control the transition between the
`several modes of operation. Such a complex vehicle is
`unsuited for the automotive market. Automobiles intended
`for mass production can be no more complicated to operate
`than conventional vehicles, and must be essentially “fool
`proof, that is, resistant to damage that might be caused by
`operator error. Further, the gear train shown by Berman etal
`appears to be quite complex and difficult to manufacture
`economically. Berman etal also indicate that one or even two
`variable-speed transmissions may be required; see, e.g., col.
`3, lines 19-22 and 36-38 of U.S. Pat. No. 3,566,717, and col.
`2, lines 53-55 of U.S. Pat. No. 3,732,751.
`Lynch et al U.S. Pat. No. 4,165,795 also shows an early
`parallel hybrid drive. Lynch argues that maximum fuel effi
`ciency can be realized when a relatively small internal com
`bustion engine is provided, such that when the engine is
`operated at an efficient speed, it produces approximately the
`average power required over a typical mission. The example
`given is of an engine producing 25hp maximum and 17 hp at
`its most efficient speed, about 2500 rpm. This is to be com
`bined with an electric motor-generator of about 30 peak hp.
`This vehicle requires a variable-ratio transmission to achieve
`reasonable performance. It appears that the engine is to be run
`continuously, at a steady speed, with additional torque pro
`vided by the motor when needed and excess torque produced
`by the engine being used to charge the batteries. In a first
`embodiment, torque provided by the motor is transmitted to
`the drive wheels through the engine, while in a second
`embodiment their respective positions are reversed.
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`Nishida U.S. Pat. No. 5,117,931 shows a parallel hybrid
`vehicle where torque from an electric motor may be com
`bined with torque from an internal combustion engine in a
`“torque transmission unit comprising paired bevel gears and
`means for controlling the relative rates of rotation of the
`motor and engine, so that the motor can be used to start the
`engine, absorb excess torque from the engine (by charging a
`battery), or provide additional propulsive torque. A variable
`speed transmission is coupled between the torque transmis
`sion unit and the propelling wheels. Both the torque transmis
`sion unit and the variable-speed transmission are complex,
`heavy, and expensive components, the use of which would
`preferably be avoided.
`Helling U.S. Pat. No. 3,923,115 also shows a hybrid
`vehicle having a torque transmission unit for combining
`torque from an electric motor and an internal combustion
`engine. However, in Helling the relative rates of rotation of
`the motor and engine input shafts are fixed; a flywheel is
`provided to store excess mechanical energy as well as a bat
`tery to store excess electrical energy. Albright, Jr. etal U.S.
`Pat. No. 4,588,040 shows another hybrid drive scheme using
`a flywheel in addition to batteries to store excess energy;
`various complicated mechanical connections are provided
`between the various components. Capacitors have also been
`proposed for energy storage; see Bates et al U.S. Pat. No.
`5,318,142.
`Fjällström U.S. Pat. No. 5,120,282 shows a parallel hybrid
`drive train wherein torque from two electric motors is com
`bined with torque produced by an internal combustion
`engine; the combination is performed by a complex arrange
`ment of paired planetary gearsets, and unspecified control
`means are alleged to be able to allow variation of road speed
`without a variable-ratio transmission.
`Hunt U.S. Pat. Nos. 4,405,029 and 4,470.476 also disclose
`parallel hybrids requiring complex gearing arrangements,
`including multiple speed transmissions. More specifically,
`the Hunt patents disclose several embodiments of parallel
`hybrid vehicles. Hunt indicates (see col. 4, lines 6-20 of the
`476 patent) that an electric motor may drive the vehicle at
`low speeds up to 20 mph, and an internal combustion engine
`used for speeds above 20 mph, while “in certain speed ranges,
`such as from 15-30 mph, both power sources may be ener
`gized.... Additionally, both power sources could be utilized
`under heavy load conditions.” Hunt also indicates that “the
`vehicle could be provided with an automatic changeover
`device which automatically shifts from the electrical power
`Source to the internal combustion power Source, depending
`on the speed of the vehicle' (col. 4, lines 12-16).
`However, the Hunt vehicle does not meet the objects of the
`present invention, as discussed in detail below. Hunt's vehicle
`in each embodiment requires a conventional manual or auto
`matic transmission. See col. 2, lines 6-7. Moreover, the inter
`nal combustion engine is connected to the transfer case
`(wherein torque from the internal combustion engine and
`electric motor is combined) by a “fluid coupling or torque
`converter of conventional construction'. Col. 2, lines 16-17.
`Such transmissions and fluid couplings or torque converters
`are very inefficient, are heavy, bulky, and costly, and are to be
`eliminated according to one object of the present invention,
`again as discussed in detail below.
`Furthermore, the primary means of battery charging dis
`closed by Hunt involves a further undesirable complexity,
`namely a turbine driving the electric motor in generator con
`figuration. The turbine is fueled by waste heat from the inter
`nal combustion engine. See col. 3, lines 10-60. Hunt's inter
`nal combustion engine is also fitted with an alternator, for
`additional battery charging capability, adding yet further
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`complexity. Thus it is clear that Hunt fails to teach a hybrid
`vehicle meeting the objects of the present invention—that is,
`a hybrid vehicle competitive with conventional vehicles with
`respect to performance, cost and complexity, while achieving
`substantially improved fuel efficiency.
`Kawakatsu U.S. Pat. Nos. 4,305,254 and 4,407,132 show a
`parallel hybrid involving a single internal combustion engine
`coupled to the drive wheels through a conventional variable
`ratio transmission, an electric motor, and an alternator, to
`allow efficient use of the internal combustion engine. As in the
`Hunt disclosure, the engine is intended to be operated in a
`relatively efficient range of engine speeds; when it produces
`more torque than is needed to propel the vehicle, the excess is
`used to charge the batteries; where the engine provides insuf
`ficient torque, the motor is energized as well.
`A further Kawakatsu patent, U.S. Pat. No. 4.335,429,
`shows a hybrid vehicle, in this case comprising an internal
`combustion engine and two motor/generator units. A first
`larger motor/generator, powered by a battery, is used to pro
`vide additional torque when that provided by the engine is
`insufficient; the larger motor-generator also converts excess
`torque provided by the engine into electrical energy, to be
`stored by the battery, and is used in a regenerative braking
`mode. The second Smaller motor/generator is similarly used
`to provide additional torque and additional regenerative brak
`ing as needed.
`More particularly, the latter Kawakatsu patent asserts that
`a single electric motor sized to provide Sufficient torque to
`propel the vehicle would not be capable of providing suffi
`cient regenerative braking force; see col. 1, line 50-col. 2 line
`8. Accordingly, Kawakatsu provides two separate motor/gen
`erators, as noted; a separate engine starting motor is also
`provided. See col. 6, lines 22-23. In the embodiment shown,
`the larger motor/generator is connected to the wheel drive
`shaft, while the engine and the Smaller motor/generator are
`35
`connected to the wheels through a complex mechanism com
`prising three separately-controllable clutches. See col. 5,
`lines 50-62.
`Numerous patents disclose hybrid vehicle drives tending to
`fall into one or more of the categories discussed above. A
`40
`number of patents disclose systems wherein an operator is
`required to select between electric and internal combustion
`operation; for example, an electric motor is provided for
`operation inside buildings where exhaust fumes would be
`dangerous, and an internal combustion engine provided for
`operation outdoors. It is also known to propose a hybrid
`vehicle comprising an electric motor for use at low speeds,
`and an internal combustion engine for use at higher speed.
`The art also Suggests using both when maximum torque is
`required. In several cases the electric motor drives one set of
`wheels and the internal combustion engine drives a different
`set. Seegenerally Shea (U.S. Pat. No. 4,180,138): Fields etal
`(U.S. Pat. No. 4,351,405); Kenyon (U.S. Pat. No. 4,438,342):
`Krohling (U.S. Pat. No. 4,593,779); and Ellers (U.S. Pat. No.
`4,923,025).
`Many of these patents show hybrid vehicle drives wherein
`a variable speed transmission is required, as do numerous
`additional references. A transmission as noted above is typi
`cally required where the internal combustion engine and/or
`the electric motor are not capable of Supplying Sufficient
`torque at low speeds. See Rosen (U.S. Pat. No. 3,791,473);
`Rosen (U.S. Pat. No. 4,269,280); Fiala (U.S. Pat. No. 4,400,
`997); and Wu et al (U.S. Pat. No. 4,697,660). Kinoshita (U.S.
`Pat. No. 3,970,163) shows a vehicle of this general type
`wherein a gas turbine engine is coupled to the road wheels
`through a three-speed transmission; an electric motor is pro
`vided to supply additional torque at low speeds.
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`For further examples of series hybrid vehicles generally as
`discussed above, see Bray (U.S. Pat. No. 4,095,664); Cum
`mings (U.S. Pat. No. 4,148,192); Monaco etal (U.S. Pat. No.
`4,306,156); Park (U.S. Pat. No. 4.313,080); McCarthy (U.S.
`Pat. No. 4,354,144); Heidemeyer (U.S. Pat. No. 4,533,011):
`Kawamura (U.S. Pat. No. 4,951.769); and Suzuki etal (U.S.
`Pat. No. 5,053,632). Various of these address specific prob
`lems arising in the manufacture or use of hybrid vehicles, or
`specific alleged design improvements. For example, Park
`addresses certain specifics of battery charging and discharge
`characteristics, while McCarthy shows a complex drive sys
`tem involving an internal combustion engine driving two
`electric motors; the torque generated by the latter is combined
`in a complex differential providing continuously variable
`gear ratios. Heidemeyer shows connecting an internal com
`bustion engine to an electric motor by a first friction clutch,
`and connecting the motor to a transmission by a second fric
`tion clutch.
`Other patents of general relevance to this subject matter
`include Toy (U.S. Pat. No. 3.525,874), showing a series
`hybrid using a gas turbine as internal combustion engine;
`Yardney (U.S. Pat. No. 3,650.345), showing use of a com
`pressed-air or similar mechanical starter for the internal com
`bustion engine of a series hybrid, such that batteries of limited
`current capacity could be used; and Nakamura (U.S. Pat. No.
`3,837.419), addressing improvements in thyristor battery
`charging and motor drive circuitry. Somewhat further afield
`but of general interest are the disclosures of Deane (U.S. Pat.
`No. 3,874,472); Horwinski (U.S. Pat. No. 4,042,056); Yang
`(U.S. Pat. No. 4,562,894); Keedy (U.S. Pat. No. 4,611,466);
`and Lexen (U.S. Pat. No. 4,815,334); Mori (U.S. Pat. No.
`3,623.568); Grady, Jr. (U.S. Pat. No. 3,454,122); Papst (U.S.
`Pat. No. 3,211,249); Nims etal (U.S. Pat. No. 2,666,492); and
`Matsukata (U.S. Pat. No. 3,502,165). Additional references
`showing parallel hybrid vehicle drive systems include
`Froelich (U.S. Pat. No. 1,824,014) and Reinbeck (U.S. Pat.
`No. 3,888,325).U.S. Pat. No. 4,578,955 to Medina shows a
`hybrid system wherein a gas turbine is used to drive a gen
`erator as needed to charge batteries. Of particular interest to
`certain aspects of the present invention is that Medina dis
`closes that the battery pack should have a Voltage in the range
`of 144, 168 or 216 volts and the generator should deliver
`current in the range of 400 to 500 amperes. Those of skill in
`the art will recognize that these high currents involve Substan
`tial resistance heating losses, and additionally require that all
`electrical connections be made by positive mechanical means
`such as bolts and nuts, or by welding. More specifically, for
`reasons of Safety and in accordance with industry practice,
`currents in excess of about 50 amperes cannot be carried by
`the conventional plug-in connectors preferred for reasons of
`convenience and economy, but must be carried by much
`heavier, more expensive and less convenient fixed connectors
`(as used on conventional starter and battery cable connec
`tions). Accordingly, it would be desirable to operate the elec
`tric motor of a hybrid vehicle at lower currents.
`U.S. Pat. No. 5,765,656 to Weaver also shows a series
`hybrid wherein a gas turbine is used as the internal combus
`tion engine; hydrogen is the preferred fuel.
`U.S. Pat. No. 4,439,989 to Yamakawa shows a system
`wherein two different internal combustion engines are pro
`vided, so that only one need be run when the load is low. This
`arrangement would be complex and expensive to manufac
`ture.
`Detailed discussion of various aspects of hybrid vehicle
`drives may be found in Kalberlah, “Electric Hybrid Drive
`Systems for Passenger Cars and Taxis, SAE Paper No.
`910247 (1991). Kalberlah first compares “straight” electric,
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`series hybrid, and parallel hybrid drive trains, and concludes
`that parallel hybrids are preferable, at least when intended for
`general use (that is, straight electric Vehicles may be useful
`under certain narrow conditions of low-speed, limited range
`urban driving). Kalberlah then compares various forms of
`parallel hybrids, with respect to his FIG.4, and concludes that
`the most practical arrang