VWGoA - Ex. 1006
`Volkswagen Group of America, Inc. - Petitioner
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`U.S. Patent
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`U.S. Patent
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`Sep. 6, 1994
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`Sheet 3 of 12
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`5,343,970
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`Sep. 6, 1994
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`HYBRID ELECIRIC VEHICLE
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`BACKGROUND OF THE INVENTION
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`tween the diesel engine and the wheels of the locomo-
`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
`operating range. Accordingly, all vehicles driven di-
`rectly by an internal combustion engine (other than
`certain single-speed vehicles using friction or centrifu-
`gal clutches, and not useful for normal driving) require
`a multiple speed transmission between the engine and
`the wheels, so that the engir1e’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-
`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.
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`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,
`it is well known that a gasoline or other internal com-
`bustion engine is most efficient when producing near its
`maximum output torque. Typically, the number of die-
`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 rim 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-
`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-
`tor(s) as required, so as to operate efliciently. This sys-
`tem overcomes the limitations of electric vehicles noted
`above with respect to limited range and long recharge
`times.
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`However, such series hybrid electric vehicles are
`inefficient and grossly uneconomical, for the following
`reasons. In a conventional vehicle, the internal combus-
`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-
`proximately 25% of engine power. Further such com-
`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
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`1. Field of the Invention
`This invention is in the field of hybrid electric vehi-
`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-
`larly, this invention relates to a hybrid electric vehicle
`that is fully competitive with presently conventional
`vehicles as regards performance, operating conve-
`nience, and cost, while achieving substantially im-
`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-
`biles and other highway vehicles. Concomitantly very
`substantial attention has been paid to reduction of pol-
`lutants emitted by automobiles and other vehicles. To a
`degree, efforts to solve these problems conflict with one
`another. For example, increased thermodynamic effi-
`ciency and thus reduced fuel consumption can be real-
`ized if an engine is operated at higher temperatures.
`Thus there has been substantial interest in engines built
`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-
`cally NO,,.
`Another possibility for reducing emissions is to burn
`mixtures of gasoline and ethanol (“gasoho1”) or straight
`ethanol. However, to date ethanol has not become eco-
`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-
`tion engines and instead employ electric vehicles pow-
`ered by rechargeable batteries. To date, all such electric
`cars have a very limited range, typically no more than
`l50‘miles, have insufficient power for acceleration and
`hill climbing except when the batteries are fully
`charged, and require substantial time for battery re-
`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-
`stantial economic deterrent. Moreover, it will be appre-
`ciated that in the United States most electricity is gener-
`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-
`spective net costs per mile of driving, electric vehicles
`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-
`ing the defect of limited range exhibited by simple elec-
`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
`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-
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`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.
`In Berman et al, the internal combustion engine is run
`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 constant speed and excess power is converted by
`a first 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.
`The present invention relates to such a parallel hybrid
`vehicle, but addresses certain substantial deficiencies of
`the Berman et al design. For example, Berman et al
`show two separate electric motor/generators powered
`by the internal combustion engine to charge batteries
`and to drive 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, and the operator must control the transition
`between the several modes of operation. Further the
`gear train shown by Berman et al appears to be quite
`complex and difficult
`to manufacture economically.
`Berman et al also indicate that one or even two variable-
`speed transmissions may be required; see col. 3, lines
`19-22 and 36-38.
`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 energized.
`.
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`. 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. Hunt’s vehicle in each embodi-
`ment requires a conventional manual or automatic
`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.
`Furthermore, the primary means of battery charging
`disclosed by Hunt involves a further undesirable com-
`plexity, namely a turbine driving the electric motor in
`generator configuration. The turbine is fueled by waste
`heat from the internal combustion engine. See col. 3,
`lines 10-60. Hunt’s internal combustion engine is also
`fitted with an alternator, for additional battery charging
`capability, adding yet further complexity. Thus it is
`clear that Hunt fails to teach a hybrid vehicle meeting
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`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. No. 4,335,429 shows a parallel
`hybrid involving a single internal combustion engine
`and two electric motors to allow efficient use of the
`electric motors, and is directed principally to a complex
`control scheme.
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`Numerous patents disclose hybrid vehicle drives
`tending to fall into one or more of the categories dis-
`cussed above. A number of patents disclose systems
`wherein an operator is required to select between elec-
`tric and internal combustion operation; for example an
`electric motor is provided for operation inside buildings
`where exhaust fumes would be dangerous. In several
`cases the electric motor drives one set of wheels and the
`internal combustion engine drives a different set. See
`generally, U.S. Pat. Nos.; Shea (4,180,138); Fields et al
`(4,351,405); Kenyon (4,438,342); Krohling (4,593,779);
`and Ellers (4,923,025).
`Numerous other patents show hybrid vehicle drives
`wherein a variable speed transmission is required. A
`transmission as noted above is typically required where
`the electric motor is not capable of supplying sufficient
`torque at
`low speeds. See U.S. Pat. Nos.; Rosen
`(3,791,473); Rosen (4,269,280); Fiala (4,400,997); and
`Wu et al (4,697,660). For further examples of series
`hybrid vehicles as discussed above, see generally Bray
`(4,095,664); Cummings (4,148,192); Kawakatsu et al
`(4,305,254 and 4,407,132); Monaco et al (4,306,156);
`Park (4,313,080); McCarthy (4,354,144); Heidemeyer
`(4,533,011); Kawamura (4,951,769); and Suzuki et al
`(5,053,632). Other patents of general relevance to this
`subject matter
`include Toy (3,525,874); Yardney
`(3,650,345); Nakamura (3,837,419); Deane (3,874,472);
`Horwinski
`(4,042,056); Yang
`(4,562,894); Keedy
`(4,611,466); and Lexen (4,815,334).
`U.S. Pat. No. 4,578,955 to Medina shows a hybrid
`system wherein a gas turbine is used as the internal
`combustion engine to drive a generator as needed to
`charge batteries. Of particular interest to certain aspects
`of the present invention is that Medina discloses that the
`battery pack should have a voltage in the range of 144,
`168 or 216 volts and the generator should deliver cur-
`rent in the range of 400 to 500 amperes. Those of skill in
`the art will recognize that these high currents involve
`substantial resistance heating losses, and additionally
`require that all electrical connections be made by posi-
`tive 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 carmot be carried by the conventional
`p1ug—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
`electric motor of a hybrid vehicle at lower currents.
`U.S. Pat. No. 4,439,989 to Yamakawa shows a system
`wherein two different internal combustion engines are
`provided so that only one need be run when the load is
`low. This arrangement would be complex and expen-
`sive to manufacture.
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`Detailed discussion of various aspects of hybrid vehi-
`cle drives may be found in Kalberlah, “Electric Hybrid
`Drive Systems for Passenger Cars and Taxis”, SAE
`Paper No. 910247 (1991), and in Bullock, “The Techno-
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`logical Constraints of Mass, Volume, Dynamic Power
`Ra.nge 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
`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-
`bustion engine in its most efficient operating range, and
`that a battery may be provided to store energy to be
`supplied to a.n electric motor in order to even out the
`load on the internal combustion engine, there remains
`substantial room for improvement. In particular, it is
`desired to obtain the operational flexibility of a parallel
`hybrid system, while optimizing the system’s opera-
`tional parameters a.nd providing a substantially simpli-
`fied parallel hybrid system as compared to those shown
`in the prior art.
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`OBJECTS AND SUMMARY OF THE
`INVENTION
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`It is a.n object of the invention to provide a.n im-
`proved hybrid electric vehicle realizing substantially
`increased fuel economy and reduced pollutant emis-
`sions as compared to present day vehicles while suffer-
`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
`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-
`cent of the rated output power of the internal combus-
`tion engine, and more preferably up to about 150-200
`percent thereof, so that the engine operates under sub-
`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-
`vide the average power required for operation at mod-
`erate and highway speeds, with the electric motor sized
`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
`30-50 amperes maximum current, whereby resistance
`heating losses are greatly reduced, and whereby inex-
`pensive and simple electrical manufacturing a.nd con-
`nection techniques ca.n be employed.
`It is a further object of the invention to provide a
`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-
`verting mechanical energy provided to the induction
`motor when operated as a generator to DC energy for
`charging the batteries as required.
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`Other aspects a.nd objects of the invention will be-
`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-
`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-
`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-
`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, a.nd 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-
`ventional vehicles idle uselessly at stop lights or in traf-
`fic. This source of inefficiency and pollution is elimi-
`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 a.n
`automatic transmission. However, during highway
`cruising and in traffic, that is, under the most common
`operating conditions, only 2-30 hp is required. There-
`fore, the intemal combustion engine of a conventional
`vehicle rarely operates near maximum efiiciency. More-
`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-
`tion provides acceleration and hill climbing perfor-
`mance equivalent to a conventional vehicle with a 165
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`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
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`7
`hp internal combustion engine with automatic transmis-
`sion, while yielding a 200—300% improvement in net
`fuel efficiency and at least a similar reduction in pollut-
`ants emitted. Moreover, the vehicle of the present in-
`vention is no heavier, no more bulky and no more ex-
`pensive to manufacture than conventional vehicles
`using standard internal combustion engines.
`More particularly, according to the invention, the
`internal combustion engine is operated only under the
`most efficient conditions of output power and speed.
`When the engine can be used efficiently to drive the
`vehicle forward, e.g. in highway cniising, it is so em-
`ployed. Under other circumstances, e.g. in traffic, the
`electric motor alone drives the vehicle forward and the
`internal combustion engine is used only to charge the
`batteries as needed. No transmission is required, thus
`effecting a very substantial saving in both weight and
`cost. The AC electric motor is controlled to operate as
`a constant torque source at low motor speeds, and as a
`constant power source at higher speeds. The motor
`operates at relatively low currents and relatively high
`voltage and frequency, as compared with conventional
`practice. Connections between the battery and the elec-
`tric motor are substantially simplified through the use of
`relatively low maximum current, and at relatively resis-
`tance heating losses are likewise reduced substantially.
`The above and still further objects, features and ad-
`vantages of the present invention will become apparent
`upon consideration of the following detailed description
`of a specific embodiment thereof‘, especially when taken
`in conjunction with the accompanying drawings
`wherein like reference numerals in the various figures
`are utilized to designate like components.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a plot of output power versus rotational
`speed (RPM) for a typical internal combustion engine,
`illustrating the relative fuel consumption of the engine
`as used in a conventional automobile in gallons/horse-
`power-hour;
`FIG. 2 is a similar plot describing operation of a
`relatively small internal combustion engine used in the
`present invention under circumstances similar to those
`depicted in FIG. 1;
`FIG. 3 is a block diagram of the parallel hybrid drive
`system of the invention;
`FIGS. 4-9 are schematic diagrams of the hybrid drive
`system according to the invention operating in different
`modes and showing flow of energy,
`in the form of
`stored electrical energy or fossil fuel, and of power, as
`torque from either the electric motor or the internal
`combustion engine;
`FIG. 10 is a schematic cross-sectional view of a
`
`clutch forming a frictional coupling between one input
`shaft of a torque transfer unit and either the internal
`combustion engine or the frame of the vehicle;
`FIG. 11 is a schematic cross-sectional view of the
`torque transfer unit;
`FIG. 12 is a schematic circuit diagram of the solid-
`state switching unit providing AC/DC power conver-
`sion, with indication of the control signals provided
`thereto;
`FIG. 13 illustrates the manner of control of the motor
`as a motor or generator; and
`FIG. 14 illustrates the preferred torque versus speed
`characteristics of the motor as operated with the corre-
`sponding preferred AC/DC power converter, and of
`the internal combustion engine.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`Referring specifically to FIG. 1, curve 10 represents
`the output power versus engine speed (RPM) of a typi-
`cal spark ignition gasoline-fueled internal combustion
`engine as used with an automatic transmission in a typi-
`cal sedan of 3,300 pounds. As can be seen, the maximum
`engine power available is about 165 horsepower at
`about 5,000 RPM. Also shown in FIG. 1 by curve 12
`are the average power requirements of such a vehicle.
`Points C, S and H on curve 12 show average fuel con-
`sumption in city, suburban and highway driving, re-
`spectively. Point C on curve 12 shows that the average
`power required in typical city driving is less than 5 hp.
`Point S shows that the average power consumed in
`suburban driving is 10 hp, and point H shows that the
`power needed for steady-speed highway driving is only
`about 30 hp. Thus, the vehicle is vastly overpowered at
`all times except during acceleration or hill-climbing.
`FIG. 1 also includes curves indicating the relative
`fuel consumption of the engine. As can be seen, reason-
`able fuel efficiency, that is, at least about 105 percent
`relative fuel consumption (l00% being ideal), is reached
`only when the engine is operated at between about
`2,000 and 4,000 RPM, when producing between about
`75 and 150 horsepower. FIG. 1 thus indicates that the
`typical internal combustion engine operates with rea-
`sonable efficiency only when producing between about
`50 and about 90% of its maximum output power. The
`typical automobile only requires such substantial power
`under conditions of extreme acceleration or hill climb-
`ing. Thus, only during relatively brief intervals is the
`engine operating efficiently. As can be seen, during
`typical highway driving, shown by point H on curve 12,
`the relative fuel consumption is on the order of 190
`percent of that required during the most efficient opera-
`tion of the engine. The situation is even worse in subur-
`ban driving, where the relative fuel consumption is
`nearly 300 percent of the most efficient value, and in
`city driving, where the relative fuel consumption is
`almost 350 percent of that required at most efficient
`operation.
`FIG. 1 thus demonstrates that an internal combustion
`engine having sufficient horsepower for adequate accel-
`eration and hill climbing capability must be so oversized
`with respect to the loads encountered during most nor-
`mal driving that the engine is grossly inefficient in its
`consumption of fuel. As noted, FIG. 1 further shows
`that only about 30 horsepower is needed to cniise on
`the highway even in a relatively large car.
`FIG. 2 is similar to FIG. 1, and illustrates the opera-
`tional characteristics of the same 3,300 pound car if
`driven by a relatively small engine having a maximum
`horsepower rating of about 45 horsepower at 4,000
`RPM. The power requirement of the vehicle during
`highway cruising, shown by point H on curve 14, is in
`the center of the most efficient region of operation of
`the engine. However, even with this small engine thus
`optimized for highway cruising, there is a substantial
`gap between the engine operating power line 16 and the
`average power requirement line 14. That is, even this
`small engine produces substantially more power at low
`RPM than needed for city driving (point C) or for sub-
`urban driving (point S). Accordingly, even with a small
`engine sized appropriately for highway cniising, sub-
`stantial inefficiencies at lower speeds persist. Moreover,
`of course, such a vehicle would have unsatisfactory
`
`17
`
`17
`
`

`
`9
`acceleration and hill climbing ability. Therefore, the
`answer is not simply to replace large internal combus-
`tion engines with smaller internal combustion engines.
`The prior art recognizes that there are substantial
`advantages to be gained by combining the virtues of a
`gasoline or other internal combustion engine with those
`of an electric motor running from a battery charged by
`the internal combustion engine. However the prior art
`has failed to provide a solution which is directly price
`and performance competitive with vehicles now on the
`market.
`
`As indicated above, “straight” electric vehicles, that
`is, vehicles having electric traction motors and batteries
`requiring recharge at the end of each day’s use, do not
`have sufficient range and require too much time to
`recharge to fully replace conventional automobiles.
`Further, the operational costs of such vehicles are not
`competitive with internal combustion vehicles operated
`on fuels derived from renewable resources such as etha-
`nol, and are even less competitive with gasoline-fueled
`automobiles.
`
`A first type of series hybrid vehicles, involving a
`gasoline engine driving a generator charging a battery
`powering an electric traction motor, are limited in ac-
`celeration and hill climbing ability unless the electric
`motor is made very large, costly, and bulky. The alter-
`native series hybrid approach, involving a transmission
`between a relatively smaller electric motor and the
`wheels to provide the torque needed to accelerate
`quickly, loses the virtue of simplicity obtained by elimi-
`nation of a multi-speed transmission. These vehicles fail
`to realize the advantages provided by the parallel hy-
`brid system in which both an internal combustion en-
`gine and an electric motor provide torque to the wheels
`as appropriate. However, the prior art relating to paral-
`lel hybrid vehicles fails to disclose a system sufficiently
`simple for economical manufacture. The art further has
`failed to teach the optimum method of operation of a
`parallel hybrid vehicle.
`Moreover, the art relating to parallel hybrids does
`not teach the appropriate operational parameters to be
`employed, relating to the relative power outputs of the
`internal combustion engine and the electric motor; the
`type of electric motor to be employed; and the fre-
`quency, voltage, and current characteristics of the mo-
`tor/battery system.
`According to one aspect of the invention, the internal
`combustion engine of a hybrid vehicle is sized to supply
`adequate power for highway cruising, preferably with
`some additional power in reserve, so that the internal
`combustion engine operates only in its most efficient
`operating range. The electric motor, which is substan-
`tially equally efficient at all operating speeds, is used to
`supply additional power as needed for acceleration and
`hill climbing, and is used to supply all power at low
`speeds, where the internal combustion engine is particu-
`larly inefficient, e.g., in traffic.
`FIG. 3 shows a block diagram of the