Accessory drive system and method for a belt-alternator-starter electric hybrid vehicle

The method and apparatus of the present invention provide an accessory drive system for a belt-alternator-starter electric hybrid vehicle. The apparatus includes a drive pulley connected to an engine output shaft, a plurality of accessories that are each connected to a driven pulley, and a selectively engageable torque transmitting device disposed between the engine crankshaft and a transmission. A belt-alternator-starter system is connected to another driven pulley. A drive belt connectively couples the drive pulley and the driven pulleys and is operable to transfer drive forces between the drive pulley and the driven pulleys. A controller is operatively connected to the torque transmitting device, the engine and the belt-alternator-starter system. The controller is configured to control the torque transmitting device, the engine and the belt-alternator-starter system to ensure the accessories are adequately powered.

TECHNICAL FIELD

The present invention pertains generally to a method and apparatus for driving accessories on an electric hybrid vehicle having a belt-alternator-starter (BAS) system.

BACKGROUND OF THE INVENTION

The accessories in a conventional motor vehicle are powered by output from the engine. An electric hybrid 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 belt-alternator-starter (BAS) system employs a combined starter and alternator motor/generator mounted with respect to the other components of the accessory drive system. This system combines the alternator and starter motor/generator into one device that can be mounted in effectively the same way and in effectively the same packaging space as a traditional alternator.

SUMMARY OF THE INVENTION

The method and apparatus of the present invention provide an accessory drive system for a belt-alternator-starter electric hybrid vehicle. The apparatus includes a torque transmitting device selectively connecting an engine with a transmission. A drive pulley is connected to an engine crankshaft. A plurality of driven pulleys are each connected to one of a plurality of accessories. A belt-alternator-starter system is connected to another driven pulley. A drive belt connectively couples the drive pulley and the driven pulleys and is operable to transfer drive forces between the drive pulley and the driven pulleys. A controller is operatively connected to the torque transmitting device, the engine and the belt-alternator-starter system. The controller is configured to control the torque transmitting device, the engine and the belt-alternator-starter system to ensure the accessories are adequately powered.

The method of the present invention allows the accessories to be driven by power from the engine or the belt-alternator-starter system 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 belt-alternator-starter system to the plurality of accessories. The engine, belt-alternator-starter system, and torque transmitting device 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 belt-alternator-starter system, the storage device being configured to store energy from the belt-alternator-starter system when excess power is being produced by the engine or power is being recuperated from braking.

According to 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 yet 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 belt-alternator-starter system, in order to reduce rotational resistance and pumping losses, and so improve the efficiency of the accessory drive system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to like components,FIG. 1shows a schematic representation of an electric hybrid powertrain10having an accessory drive system11. The accessory drive system11includes an engine12configured to transmit output to a drive pulley16and/or to a transmission18. The drive pulley16is operatively connected to the engine12via a crankshaft or output shaft14. The engine12is connected to and controlled by a controller such as the controller34. The controller34may 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.

A selectively engageable torque transmitting device such as the clutch20is disposed between the engine12and the transmission18. The clutch20is operatively connected to and controlled by the controller34. The clutch20is configured to operatively couple or de-couple the engine crankshaft14from the transmission18such that power is selectively transferable therebetween. More precisely, when the clutch20is engaged torque and power are transferable from the engine crankshaft14through the transmission18to drive or power the hybrid vehicle by means of a final drive21. Conversely, when the clutch20is disengaged, torque and power from the engine crankshaft14are not transferred to the transmission18.

The drive pulley16is operatively connected via a drive belt24to a plurality of driven pulleys26,26′ and to a driven pulley28. Each of the driven pulleys26,26′ are operatively connected to one of a plurality of accessories30,30′, respectively. The driven pulley28is operatively connected to a belt-alternator-starter (BAS) system32. The accessories30,30′ may include, for example, a power steering pump, a water pump, or an air conditioning compressor. The BAS system32preferably includes a combined alternator and starter motor/generator (not shown), and is operatively connected to the controller34and a storage device36. The storage device36is adapted to store energy from the BAS system32when the engine12is producing excess power or when vehicle braking power is being recuperated. According to a preferred embodiment, the storage device36is a battery; however, alternate storage devices may be envisioned.

Power from the engine12is transferable through the crankshaft14, through the drive pulley16, and through the drive belt24to power the accessories30,30′ and the BAS system32. Power transferred to the BAS system32is convertible from the rotational motion of the drive belt24to electric energy by the alternator portion of the BAS system32, and this electric energy can be stored in the storage device36. Additionally, the BAS system32is operable to transmit power through the driven pulley28, through the drive belt24, and through the driven pulleys26,26′ to power the accessories30,30′. 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 BAS system32to power all of the accessories30,30′ when the engine12is off, the present invention saves the cost associated with manufacturing and installing the plurality of electric motors otherwise required to power the accessories30,30′.

The accessories30,30′ 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 Vmcalculated to ensure the accessories30,30′ are adequately powered. For purposes of the present invention, the accessories30,30′ are “adequately powered” when they receive enough power to remain fully operational, and “engine speed” is defined as the rotational speed of the crankshaft14measured 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 accessories30,30′ are adequately powered, alternate embodiments may monitor and control other characteristics of the accessory drive system11such as, for example, the rotational speed of one or more of the pulleys16,26,26′,28, and/or the drive belt24.

Under operating conditions wherein the engine12is fueled and running normally, the accessories30and30′ are driven by power from the engine12, just as in conventional vehicles.

Under operating conditions that normally call for the engine12of the hybrid electric vehicle to be shut down, the controller34shuts off the transfer of fuel to the engine12and the BAS system32is operated to power the accessories30,30′. More precisely, after the transfer of fuel is shut off, the controller34commands the BAS system32to transmit power through the driven pulley28, through the drive belt24, through the pulleys26,26′, and to the accessories30,30′. As the BAS system32transfers power to the accessories30,30′ via the drive belt24, the driving pulley16and the crankshaft14attached thereto are also necessarily being driven. For engines equipped with variable valve actuation, the controller34can appropriately manipulate the intake valves13aand exhaust valves13b(for example, but not limited to, keeping both the intake valves13aand the exhaust valves13bclosed) when fuel to the engine12is shut off and the accessories30,30′ are being driven by power from the BAS system32, in order to reduce crankshaft rotational resistance and engine pumping losses, and thereby improve the efficiency of the accessory drive system11.

If the engine12is shut down and the vehicle is decelerating to a stop, the clutch20can be disengaged to de-couple the engine12from the transmission18. Thereafter, the controller34can command the BAS system32to transfer additional power to maintain the engine crankshaft speed above the predetermined minimum value Vmsuch that the accessories30,30′ remain fully operational and without affecting vehicle performance. If, however, the vehicle is being powered by the BAS system32, the clutch20must be suitably controlled by the controller34to be fully or partially engaged, and the BAS system32is controlled by the controller34to provide adequate power to run the accessories as well as meet driver demands pertaining to vehicle output. In other words, the accessories30,30′ are powered to remain fully operational without sacrificing vehicle output demands such as, for example, vehicle speed and acceleration demands.

A method for driving the electronic accessories on a hybrid electric vehicle having a belt-alternator-starter (BAS) system includes the following. Energy from the engine12and/or the BAS system32is transferred to the accessories30,30′ via the drive belt24. As energy is transferred to the accessories30,30′, the engine12and/or the BAS system32are controlled by the controller34to ensure the engine speed exceeds the predetermined minimum value Vmand the accessories30,30′ remain fully operational. This may be accomplished, for example, by increasing the output of the engine12and/or the BAS system32as required to adequately power the accessories30,30′ while meeting driver desires.