Abstract:
The present invention provides an accessory drive system for a parallel electric hybrid vehicle. The apparatus includes an engine and a motor/generator independently connectable to a transmission. At least one torque-transmitting device selectably connects an engine and a motor/generator with a transmission. A drive pulley is connected to an output shaft of the engine. A plurality of driven pulleys are each connected to an accessory. A drive belt connectively couples the drive pulley and the plurality of driven pulleys, and is operable to transfer drive forces between the drive pulley and the plurality of driven pulleys. A controller is operatively connected to the torque-transmitting device, the engine and the motor/generator, and is configured to control the torque-transmitting device, the engine and the motor/generator to ensure the plurality of accessories are adequately powered.

Description:
TECHNICAL FIELD 
     The present invention pertains generally to a method and apparatus for driving accessories on a parallel electric hybrid vehicle. 
     BACKGROUND OF THE INVENTION 
     The accessories in a conventional motor vehicle are powered by output from the engine. A hybrid electro-mechanical vehicle generally includes both an internal combustion engine and one or more electric motor/generators. Some of the accessories in a hybrid vehicle may require power while the engine is off and the vehicle is being powered by the electric motor/generator. Traditionally, in order to power hybrid vehicle accessories when the engine is off, it was necessary to provide each such accessory with a separate electric motor. 
     The typical automotive accessory drive system consists of a drive pulley connected to an output shaft of the engine, typically the crankshaft. Wrapped around this pulley is a flexible drive belt, which in turn is wrapped around a plurality of driven pulleys. This flexible drive belt transmits drive forces between the drive pulley and the driven pulleys. The driven pulleys may be fixably attached to accessories known in the art such as a power steering pump, air conditioning compressor, alternator, and water pump. 
     A parallel electric hybrid vehicle includes a transmission adapted to receive the output power from either an engine or an electric motor, or both. Additionally, in a parallel electric hybrid vehicle the power supplied by the engine and the power supplied by the source of electrical energy are independently connected to the transmission thereby forming a “parallel” type connection. 
     SUMMARY OF THE INVENTION 
     The apparatus and method of the present invention provide an accessory drive system for a parallel electric hybrid vehicle. The apparatus includes at least one torque-transmitting device selectably connecting an engine and a motor/generator with a transmission. A drive pulley is connected to an output shaft of the engine. A plurality of driven pulleys are each connected to one of a plurality of accessories. A drive belt connectively couples the drive pulley and the plurality of driven pulleys, and is operable to transfer drive forces between the drive pulley and the plurality of driven pulleys. A controller is operatively connected to the torque-transmitting device, the engine and the motor/generator, and is configured to control the torque-transmitting device, the engine and the motor/generator to ensure the plurality of accessories are adequately powered. 
     The method of the present invention allows the accessories to be driven by power from the engine or the motor-generator under all vehicle operating conditions without the need for individual accessory electric drive motors, as is often practiced, by requiring that the hybrid powertrain be operated to maintain a minimum input (engine) speed even when fuel to the engine is shut off and/or the vehicle is stopped. Energy is transferred either from the engine or the motor/generator to the plurality of accessories. The engine, motor/generator and torque transmitting devices are controlled, such as with an electronic controller, to ensure each of the accessories receive enough energy to remain fully operational. 
     According to one aspect of the invention, the apparatus includes a storage device such as a battery operatively connected to the motor/generator, the storage device being configured to store energy from the motor/generator when excess power is being produced by the engine or power is being recuperated from braking. 
     According to another aspect of the invention, the method includes establishing a predefined minimum engine speed at which all of the accessories remain fully operational. 
     According to yet another aspect of the invention, the hybrid powertrain is controlled to ensure that the input speed (therefore the engine crankshaft speed and accessory drive pulley speed) is not operated below the predefined minimum engine speed when the vehicle is in operation, including when fuel is cut off to the engine to reduce fuel consumption. 
     According to still another aspect of the invention, for engines equipped with variable valve actuation, the method includes appropriately manipulating the intake and exhaust valves (for example, keeping both intake and exhaust valves closed) when fuel to the engine is shut off and the accessories are being driven by power from the motor-generator through the engine crankshaft, in order to reduce rotational resistance and pumping losses, and so improve the efficiency of the accessory drive system. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an accessory drive system for a parallel electric hybrid vehicle in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a schematic representation of a parallel electric hybrid powertrain  10  having an accessory drive system  11 . The parallel electric hybrid powertrain  10  includes an engine  12  configured to transmit output to a drive pulley  16  and/or to a transmission  18 . The engine is connected to and controlled by a controller  34 . The drive pulley  16  is operatively connected to the crank shaft or output shaft  14 . The parallel electric hybrid powertrain  10  also includes a motor/generator  32  selectively connectable to the engine  12  and/or the transmission  18 . The controller  34  may be configured to include a hybrid control module, engine control module, transmission control module, motor-generator control modules and necessary electronic drives or power electronics circuits. The controller  34  is connected to the motor generator  32 , and to an energy storage device  36 . The storage device  36  is adapted to store energy from the motor/generator  32  when the engine  12  is producing excess power or when vehicle braking power is being recuperated. According to a preferred embodiment, the storage device  36  is a battery; however, alternate storage devices may be envisioned. The transmission  18  is operatively connected to a final drive system  38 . 
     As is known in the art, the parallel electric hybrid vehicle is so named because the engine  12  and the motor/generator  32  form a parallel type connection with the transmission  18 . In other words, the power supplied by the engine  12  and the power supplied by the motor/generator  32  are independently connected to the transmission  18 . For purposes of this disclosure, the engine  12  and the motor/generator  32  are considered to be independently connected to the transmission  18  because power from the engine  12  does not pass through the motor/generator  32  on the way to the transmission  18 , and power from the motor/generator  32  does not pass through the engine  12  on the way to the transmission  18 . 
     A first clutch  20  is disposed between the motor/generator  32  and the engine  12 , and a second clutch  22  is disposed between the motor/generator  32  and the transmission  18 . The clutches  20 ,  22  are operatively connected to and controlled by the controller  34 . The clutches  20 ,  22  are configured to operatively couple or de-couple the engine  12 , the motor/generator  32 , and the transmission  18  such that power is selectively transferable therebetween. It should be appreciated that the clutches  20 ,  22  may, alternatively, be replaced by any selectively engageable torque transmitting device. 
     The drive pulley  16  is connected to a plurality of driven pulleys  26 ,  26 ′, and  26 ″ via a drive belt  24 . Each of the driven pulleys  26 ,  26 ′,  26 ″ are connected to one of a plurality of accessories  30 ,  30 ′,  30 ″, respectively, such that the rotation of the driven pulleys  26 ,  26 ′,  26 ″ transfers power to drive the accessories  30 ,  30 ′,  30 ″ connected thereto. The accessories  30 ,  30 ′,  30 ″ may include, for example, a power steering pump, a water pump, an alternator, or an air conditioning compressor. 
     Power from the engine  12  is transferable through the output shaft  14 , through the drive pulley  16 , through the drive belt  24 , and through the driven pulleys  26 ,  26 ′,  26 ″ to power the accessories  30 ,  30 ′,  30 ″. Alternatively, when clutch  20  is engaged, power from the motor/generator  32  is transferable through the clutch  20 , through the engine output shaft  14 , through the drive pulley  16 , through the drive belt  24 , and through the driven pulleys  26 ,  26 ′,  26 ″ to power the accessories  30 ,  30 ′,  30 ″. In order to power the accessories of a hybrid vehicle when the engine is off, it was conventionally necessary to provide a separate electric motor for each such accessory. Therefore, by controlling the motor/generator  32  to power all of the accessories  30 ,  30 ′,  30 ″ when the engine  12  is off, the present invention saves the cost associated with manufacturing and installing the plurality of electric motors otherwise required to power the accessories  30 ,  30 ′,  30 ″. 
     The accessories  30 ,  30 ′,  30 ″ must each be driven above a predefined minimum speed in order to remain fully operational. Therefore, according to a preferred embodiment, the present invention establishes a predetermined minimum engine speed V m  calculated to ensure the accessories  30 ,  30 ′,  30 ″ are adequately powered and remain operational. For purposes of the present invention, the accessories  30 ,  30 ′,  30 ″ are “adequately powered” when they receive enough power to remain fully operational, and “engine speed” is defined as the rotational speed of the crankshaft  14  measured using a conventional speed sensor (not shown) attached thereto. It should be appreciated that while engine speed is preferably monitored and controlled to ensure the accessories  30 ,  30 ′,  30 ″ are adequately powered, alternate embodiments may monitor and control other characteristics of the accessory drive system  11  such as, for example, the rotational speed of one or more of the pulleys  16 ,  26 ,  26 ′,  26 ″ and/or the drive belt  24 . 
     Under operating conditions wherein the engine  12  is fueled and running normally, the accessories  30 ,  30 ′, and  30 ″ are driven by power from the engine  12 , just as in conventional vehicles. 
     Under operating conditions that normally call for the engine  12  of the hybrid vehicle to be shut down, the controller  34  shuts off the transfer of fuel to the engine  12 , controls the clutch  20  to engage fully or partially as necessary, and commands the motor/generator  32  to operate to power the accessories  30 ,  30 ′,  30 ″. More precisely, when the transfer of fuel is shut off, the controller  34  commands the motor/generator  32  to transmit power through the clutch  20 , the engine crankshaft  14 , the drive pulley  16 , the drive belt  24 , the driven pulleys  26 ,  26 ′,  26 ″, and to the accessories  30 ,  30 ′,  30 ″. This method ensures that the accessories  30 ,  30 ′, and  30 ″ remain operational under operating conditions that call for engine fuel cut-off, without the need for individual electric accessory drives. As the motor/generator  32  transfers power to the accessories  30 ,  30 ′,  30 ″ through the engine crankshaft  14 , the engine crankshaft  14  is serving as a torque/power transmitting device. For engines equipped with variable valve actuation, the controller  34  can appropriately manipulate the intake valves  13   a  and exhaust valves  13   b  (for example, but not limited to, keeping both the intake valves  13   a  and the exhaust valves  13   b  closed) when fuel to the engine  12  is shut off and the accessories  30 ,  30 ′,  30 ″ are being driven by power from the motor-generator  32  through the engine crankshaft  14 , in order to reduce crankshaft rotational resistance and engine pumping losses, and thereby improve the efficiency of the accessory drive system  11 . 
     If the engine  12  is shut down and the vehicle is decelerating to a stop, the clutch  22  can be disengaged to de-couple the motor/generator  32  from the transmission  18 . Thereafter, the controller  34  can command the motor/generator  32  to transfer additional power to maintain the engine crankshaft speed above the predetermined minimum value V m  such that the accessories  30 ,  30 ′,  30 ″ remain fully operational without affecting vehicle performance. If, however, the vehicle is being powered by the motor/generator  32 , the clutches  20  and  22  must be suitably controlled by the controller  34  to be fully or partially engaged, and the motor/generator  32  is controlled by the controller  34  to provide adequate power to run the accessories as well as meet driver demands pertaining to vehicle output. In other words, the accessories are powered to remain fully operational without sacrificing vehicle output demands such as, for example, vehicle speed and acceleration demands. 
     While the preferred embodiment of the accessory drive system  11  has been described hereinabove as including two clutches  20  and  22 , an alternate embodiment without clutch  20  may be envisioned such that only a single clutch  22  is implemented. According to the alternate embodiment, the motor generator  32  is directly connected to the engine crankshaft  14 , and is indirectly connectable to the transmission  18  via the clutch  22 . 
     The alternate embodiment wherein the accessory drive system  11  includes a single clutch  22  functions similarly to the preferred embodiment described hereinabove under operating conditions wherein the engine  12  is fueled and running normally. Under operating conditions that normally call for the engine  12  of the hybrid vehicle to be shut down, the controller  34  shuts off the transfer of fuel to the engine  12 , controls the clutch  22  to engage fully or partially as necessary, and commands the motor/generator  32  to operate to power the accessories  30 ,  30 ′,  30 ″. If the engine  12  is shut down and the vehicle is decelerating to a stop, the clutch  22  can be disengaged to de-couple the motor/generator  32  from the transmission  18  and the controller  34  can command the motor/generator  32  to transfer additional power to maintain the engine crankshaft speed above the predetermined minimum value V m  such that the accessories  30 ,  30 ′,  30 ″ remain fully operational without affecting vehicle performance. 
     A method for driving the accessories on a parallel electric hybrid vehicle includes the following. Energy from the engine  12  and/or the motor/generator  32  is transferred to the accessories  30 ,  30 ′,  30 ″ via the drive belt  24 . As energy is transferred to the accessories  30 ,  30 ′,  30 ″, the engine  12  and/or the motor/generator  32  are controlled, such as by the controller  34 , to ensure the engine speed exceeds the predetermined minimum value V m  and the accessories  30 ,  30 ′,  30 ″ remain fully operational. This may be accomplished, for example, by increasing the output of the engine  12  and/or the motor/generator  32  as required to adequately power the accessories  30 ,  30 ′,  30 ″ while meeting driver demands. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.