Abstract:
An aspect of the present invention involves a system and method for providing parallel power in a hybrid-electric vehicle. The system includes a compact motor coupled to the input shaft of the vehicle&#39;s transmission. Advantageously, the compact motor and the engine use the same drivetrain. Both the compact motor and the engine are able to apply power to the portion of the drivetrain from the transmission to the wheels. Since the motor is compact and does not require a separate drivetrain, the parallel power system can be installed in an otherwise conventional vehicle without packaging difficulties.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The field of the invention relates to systems and methods for providing parallel power in a hybrid-electric vehicle.  
           [0002]    Hybrid electric vehicles (HEVs) combine the internal combustion engine of a conventional vehicle with the battery and electric motor of an electric vehicle, and provide better fuel economy than comparable conventional vehicles. This combination offers the extended range and rapid refueling that consumers expect from a conventional vehicle, with a significant portion of the energy and environmental benefits of an electric vehicle. The practical benefits of HEVs include improved fuel economy and lower emissions compared to conventional vehicles.  
           [0003]    A hybrid&#39;s efficiency and emissions depend on the particular combination of subsystems, how these subsystems are integrated into a complete system, and the control strategy that integrates the subsystems. Existing HEVs use complex integration systems, which, while efficient, have not yet proven to be economically feasible. The commercial success of HEVs has been hindered by the economics of producing a complex hybrid power system rather than by the inherent capabilities of the technology. Complexity is a major disadvantage of existing HEV configurations, and has inhibited the acceptance of HEVs in the marketplace.  
           [0004]    HEV configurations fall into two basic categories: series and parallel. In a series hybrid, the internal-combustion engine drives a generator that charges the batteries, which power an electric motor. Only the electric motor can directly turn the vehicle&#39;s wheels to propel the vehicle. In contrast, in a parallel hybrid either the engine or the motor can apply torque to the wheels. Both the parallel and the series hybrid can be operated with propulsion power supplied only by the internal-combustion engine. But in a series hybrid, this power is inefficiently applied through the generator and the electric motor. Parallel HEVs do not require a generator, because the motor generates electricity when driven by the engine. Parallel HEVs are thus less complex than series HEVs. Another advantage of the parallel scheme is that a smaller engine, electric motor, and battery pack can be used, because the engine and the motor work together to drive the vehicle.  
           [0005]    Turning to series HEVs, an advantage of series configurations is that the internal-combustion engine can be located anywhere in the vehicle because it does not transmit power mechanically to the wheels. This is advantageous for designing the vehicle because the designer has more freedom of choice in determining where the internal combustion engine should be located. In contrast, parallel configurations must connect both the motor and the engine to the drivetrain. This requires the motor and the engine to be in proximity to each other. Though parallel configurations are generally preferred for their flexible power output, the difficulty of packaging both a conventional engine and a conventional electric motor in a drivetrain has been a major disadvantage of existing parallel HEVs.  
         SUMMARY OF THE INVENTION  
         [0006]    An aspect of the present invention involves a system and method for providing parallel power in a hybrid-electric vehicle. The system includes a compact motor coupled to the input shaft of the vehicle&#39;s transmission. Advantageously, the compact motor and the engine use the same drivetrain. Both the compact motor and the engine are able to apply power to the portion of the drivetrain from the transmission to the wheels. Since the motor is compact and does not require a separate drivetrain, the parallel power system can be installed in an otherwise conventional vehicle without packaging difficulties.  
           [0007]    Other and further objects, features, aspects, and advantages of the present invention will become better understood with the following detailed description of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    The following drawings illustrate both the design and utility of preferred embodiments of the invention.  
         [0009]    [0009]FIG. 1 is a top diagram view of a hybrid electric vehicle constructed in accordance with an embodiment of the present invention.  
         [0010]    [0010]FIG. 2 is a front perspective view of a compact electric motor constructed in accordance with an embodiment of the present invention.  
         [0011]    [0011]FIG. 3 is a schematical view of a system constructed in accordance with an embodiment of the present invention for providing parallel power in a hybrid-electric vehicle. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    [0012]FIG. 1 shows a diagram of a parallel hybrid electric vehicle (HEV)  10  constructed in accordance with an embodiment of the present invention. The vehicle  10  comprises an engine  20 , a coupling  30 , a compact motor  40 , a transmission  50 , fuel tanks  60 , auxiliary components  70 , an inverter system  80 , drive shaft  90 , differential  100 , wheels  110 , and an energy storage pack  120 . A parallel hybrid electric drivetrain  122  may include one or more of the engine  20 , the coupling  30 , the compact motor  40 , the transmission  50 , the drive shaft  90 , and the differential  100 .  
         [0013]    The vehicle  10  shown in FIG. 1 is a heavy-duty vehicle. A heavy-duty vehicle is preferably a vehicle having a gross vehicle weight (GVW) of at least 10,000 lbs. Examples of heavy-duty vehicles that the parallel hybrid electric drivetrain  122  may be used with include, but not by way of limitation, a tractor, a tow tractor, a tug, a pull tractor, a push-back tractor, a truck (e.g., class  6 , class  7 , class  8 , etc.), a dump truck, a semi truck, a bobtail truck, a school bus, a transit bus, a pick-up truck, a shuttle van, a refuse-collection vehicle, a recycling-collection vehicle, and a tram vehicle. The parallel hybrid electric drivetrain  122  may be used with vehicles other than heavy-duty vehicles, and, thus, is not limited to heavy-duty vehicles.  
         [0014]    The engine  20  may comprise a spark ignition engine, compression ignition engine, turbine engine, or any other engine that transmits power through a rotating shaft. The coupling  30  couples the engine  20  to the compact motor  40 . The coupling  30  is preferably capable of connecting and disconnecting the engine power from the compact motor  40 . The coupling  30  may include, but is not limited to, a clutch, torque converter, or positive mechanical link. In FIG. 1, the coupling  30  is understood to be housed in a bellhousing. The HEV system is a parallel system, meaning that the engine  20  and compact motor  40  can simultaneously provide power to the drivetrain, and thus to the wheels  110 .  
         [0015]    [0015]FIG. 2 shows an embodiment of a compact motor  40  constructed in accordance with the present invention. The compact motor  40  is preferably a pan-type motor to minimize axial length. It is to be understood that motor specifications will vary with vehicle requirements, with smaller vehicles typically requiring smaller motors and larger vehicles normally requiring larger motors. The compact motor  40  shown in FIG. 2 is illustrative of compact motors adapted for use in heavy duty HEVs. The compact motor  40  is eighteen inches in diameter, four inches long, and meets the following specifications:  
         [0016]    Motor Type: PM Brushless DC  
         [0017]    Maximum Torque: 1000 Nm@250 Arms/ph for 2 min.  
         [0018]    Maximum speed: 2500 rpm  
         [0019]    Peak efficiency: 92%  
         [0020]    Coolant: Weg 50  
         [0021]    Coolant flow rate: 5 gpm  
         [0022]    Pressure drop: 5 psi  
         [0023]    Max. Inlet temperature: 75 C.  
         [0024]    Max. Ambient temperature: 65 C.  
         [0025]    Weight: 95 lb  
         [0026]    A suitable liquid cooled traction motor is available from Precision Magnetic Bearing Systems, Inc. of Cohoes, N.Y. Such pan-type motors use powerful permanent magnets to reduce size, and employ thin-stator designs to allow the motors to be compact.  
         [0027]    In heavy-duty embodiments comprising digital controller area networks (CANs), the compact motor  40  is preferably driven by a 250 kW CANverter inverter  80 . When used with the compact motor  40  specified above, the inverter  80  preferably meets the following specifications:  
         [0028]    Motor Options: PM Brushless or AC  
         [0029]    Continuous Power: 250 kW  
         [0030]    Input Voltage: 600 Vdc  
         [0031]    Output Current (Apk/ph.): 600A@25 C.; 420A@70 C.  
         [0032]    Peak Efficiency: 97.50%  
         [0033]    Coolant: Ethylene/Glycol 50-50  
         [0034]    Coolant Flow: 5 gpm  
         [0035]    Pressure Drop: 5 psi  
         [0036]    Inlet Temperature: 167° F. (75° C.)  
         [0037]    Size: 14.4×8.7×4.2 in  
         [0038]    Weight: 27 lbs (12 kg)  
         [0039]    A suitable CANverter inverter  80  is available from Precision Magnetic Bearing Systems, Inc. of Cohoes, NY. It is to be understood that inverter specifications will vary with motor requirements.  
         [0040]    Since the compact motor  40  can provide power to the drivetrain, the engine  20  can be reduced in size proportionally to the output of the motor  40 . For instance, given the specifications above, the heavy-duty HEV would have approximately two-hundred additional horsepower when the compact motor  40  was providing full assist. If the engine in a comparable conventional vehicle produced, for instance, four-hundred horsepower, the engine  20  in the embodiment described above need only produce half as much power. Lower power requirements permit the use of smaller, less polluting, more efficient engines.  
         [0041]    The transmission  50  is preferably an automated manual shift transmission (shift by wire). Also, in this embodiment, the coupling  30  can be a conventional clutch mechanism (including flywheel), or it can be a positive mechanical link. The clutch may be optional during use because at low speeds, the engine is preferably off, and the motor is driving the vehicle. Therefore, engine stalling is not an issue. Though disengaging a clutch during motor-only operation would advantageously prevent the motor from spinning the engine, re-engaging the clutch while moving would likely jerk the vehicle, similar to a push start. Nevertheless, a clutch would be advantageous in applications where the vehicle operates at very low, motor-only speeds for extended lengths of time (so the motor would not have to expend energy spinning the engine).  
         [0042]    In applications where no clutch is used, the motor  40  turns the engine  20  without injecting fuel until the engine speed reaches approximately 1000 RPM. The engine  20  starts immediately when fuel is introduced into the engine  20  when it is spinning at 1000 RPM. By not running the engine  20  at low speeds or at idle, noise and pollution is abated, and clutch wear is prevented. This embodiment requires electrically driven accessories so that accessories can operate with the engine off.  
         [0043]    By placing the coupling  30  between the engine  20  and the compact motor  40 , the motor is capable of operating independently of the engine, for instance when the coupling  30  comprises a disengaged clutch. It is also advantageous to place the coupling  30  between the engine  20  and the motor  40  to move the motor  40  away from the heat and vibration of the engine  20 .  
         [0044]    In various embodiments, the energy storage pack  120  may include, but is not limited to, ultracapacitors, high power prismatic NIMH batteries, or lead-acid batteries. The compact motor  40  preferably also acts as a generator to charge the energy storage pack  120 . The compact motor  40  generates electricity during regenerative braking, and as needed by spinning the motor with energy from the engine. Regenerative braking also reduces wear on brake components.  
         [0045]    Though it is desirable to convert vehicles to parallel HEVs, converting a conventional vehicle to a parallel HEV has, until now, proven to be expensive and time consuming. For instance, the parallel drive systems produced by Allison Transmission and Enova require many new components and significant changes to the drivetrain. Similarly, the parallel drive systems employed in the Toyota Prius and Honda insight are vehicle specific; entirely new vehicles were built around the HEV components.  
         [0046]    In contrast to the existing expensive and time consuming systems and methods for converting vehicles to parallel HEVs, the present inventor has found that conventional vehicles can be easily converted into parallel HEVs by installing a compact motor  40  between the coupling  30  and the transmission  50 .  
         [0047]    The process of converting a conventional vehicle to a parallel HEV according to an embodiment of the present invention comprises the following steps: removing the transmission  50  and driveshaft  90 ; replacing the transmission input shaft with one that is long enough to accommodate the additional axial length of the compact motor  40 ; providing a compact motor  40  that is machined on one side to mount to the transmission, and is machined on the other side to mount to the bellhousing; assembling the compact motor  40  to either the transmission  50  or the bellhousing; reinstalling the transmission in the vehicle; and replacing the driveshaft  90  with one that is shortened appropriately to compensate for the offset of the transmission  50 . Once the compact motor  40  is installed, a conventional HEV control system, energy storage system, and inverter are utilized to complete the conversion.  
         [0048]    Though a retrofit application is discussed above, it is clear that the design principles of the present invention could easily be applied to original equipment manufacturing (OEM) applications. For instance, original equipment manufacturers are motivated to continue using existing parts when possible; redesign and retooling are expensive. The present invention is advantageous in both aftermarket and OEM contexts because it provides a system for converting current production drivetrains to parallel HEV drivetrains with a minimal number of new parts or design changes.  
         [0049]    With reference to FIG. 3, an embodiment of a parallel hybrid electric drivetrain and control system  124  will now be described. In this embodiment, a 330 horsepower internal combustion engine  125  is connected in parallel with a compact  140  Kw electric motor/generator  126 , which is mounted on one side to a seven-speed powershift transmission  128 . A vehicle dynamics controller  130  receives inputs from vehicle systems  140  such as anti-lock breaking system (ABS) and speed sensors, and from driver interface  150 , which may include acceleration/braking, driver controls, and driver information. Based on those inputs, the vehicle dynamics controller  130  controls power distribution between the engine  125  and the motor  126 , and may provide input to the transmission  128 .  
         [0050]    The vehicle dynamics controller  130  does not communicate directly with the motor  126 , but instead communicates with a motor controller  160 , in this case a 180 kVA motor controller  160 . Also in communication with the motor controller  160  is the energy storage system  170 , which is managed by an energy management system  180 . The energy storage system  170  in this embodiment comprises between 28 and 50 twelve volt batteries each rated at 80-90 amp-hours, for approximately 40 kW/h of energy storage. Since batteries are used, a battery management system  190  equalizes and maintains the batteries. The energy management system  180  monitors the amount of power or energy available in the energy storage system  170 , and provides this information to the vehicle dynamics controller  130 . In vehicles utilizing SAE CAN J 1939  networks, the vehicle dynamics controller  130  can be connected to the network, completing the system.  
         [0051]    Although the present invention has been described above in the context of certain preferred embodiments, it is to be understood that various modifications may be made to those embodiments, and various equivalents may be substituted, without departing from the spirit or scope of the invention.