Single planetary hybrid powertrain with at least three electrically-variable operating modes

A hybrid powertrain has an engine, an input member, an output member, and a stationary member, and includes a single planetary gear set having a first, a second, and a third member. The input member is connected for common rotation with the engine. The output member is connected for common rotation with the second member. A first and a second motor/generator are provided, as well as five torque-transmitting mechanisms, including only one brake. The torque-transmitting mechanisms are engagable in different combinations to establish at least two electric-only operating mode, at least two engine-only operating mode, and at least three electrically-variable operating modes. In one embodiment, an electric torque converter operating mode is provided, and may be the default mode in case of motor/generator failure.

TECHNICAL FIELD

The invention relates to a hybrid powertrain, and specifically to a hybrid powertrain with two motor/generators, an engine, and a single planetary gear set.

BACKGROUND OF THE INVENTION

Hybrid powertrains for vehicles utilize different power sources under different vehicle operating conditions. An electro-mechanical hybrid powertrain typically has an internal combustion engine, such as a diesel engine, gasoline engine, air engine, or fuel cell, and one or more motor/generators. Different operating modes, such as an engine-only operating mode, an electric-only operating mode, and an electrically-variable operating mode are established by engaging brakes and/or clutches in different combinations and controlling the engine and motor/generators. The various operating modes are advantageous as they may be used to improve fuel economy. However, the additional components required for a hybrid powertrain, such as the motor/generators, planetary gear sets, brakes and/or clutches may increase overall vehicle cost.

SUMMARY OF THE INVENTION

A hybrid powertrain is provided with a minimal number of components without sacrificing available operating modes and performance advantages. For example, the powertrain has only one planetary gear set, two motor/generators, and five torque-transmitting mechanisms, including only one band clutch (i.e., only one brake), and is operable in at least two electric-only operating modes, at least two engine-only operating modes; and at least three electrically-variable operating modes. This configuration permits the engine to be used for vehicle launch in low battery state of charge conditions, therefore allowing a smaller battery to be used relative to other two motor/generator hybrid powertrain architectures. Furthermore, system failures, such as a failure affecting the motor/generator, may be detected and the powertrain controlled to protect against damage to the motor/generator under such circumstances. Because only one of the torque-transmitting mechanisms is a brake (i.e., a band clutch), heat generation and clutch maintenance are minimal.

Specifically, the hybrid powertrain has an engine, an input member, an output member, and a stationary member. The powertrain has only a single planetary gear set with a first, a second, and a third member, preferably a ring gear member, a carrier member and a sun gear member, respectively. The input member is connected for common rotation with the engine. The output member is connected for common rotation with the second member. A first and a second motor/generator are provided, as well as five torque-transmitting mechanisms, including only one brake. The first torque-transmitting mechanism is selectively engagable to ground the first member to the stationary member. The second torque-transmitting mechanism is selectively engagable to connect the first motor/generator for common rotation with the first member. The third torque-transmitting mechanism is selectively engagable to connect the input member for common rotation with the first member. The fourth torque-transmitting mechanism is selectively engagable to connect the input member for common rotation with the third member. The fifth torque-transmitting mechanism is either selectively engagable to connect the second motor/generator for common rotation with the third member, or is selectively engagable to connect the first motor/generator for common rotation with the output member. The torque-transmitting mechanisms are engagable in different combinations to establish at least two electric-only operating modes, at least two engine-only operating modes; and at least three electrically-variable operating modes. In one embodiment, the torque-transmitting mechanisms are engaged in different combinations to establish two engine-only (fixed gear) operating modes, two electric-only operating modes, and four electrically-variable operating modes. In another embodiment, the torque-transmitting mechanisms are engaged in different combinations to establish three engine-only (fixed gear) operating modes, four electric-only operating modes, three electrically-variable operating modes, and an electric torque converter operating mode.

One or more controllers are operable to monitor operating conditions of the motor/generators such as failures of components associated with the motor/generators or failure of the motor/generators. Under predetermined operating conditions indicative of such a failure, the controller will engage those torque-transmitting mechanisms that establish one of the engine-only operating modes (or the electric torque converter operating mode) in response to the monitored operating conditions. By relying on power from the engine, damage to the motor/generators is prevented. Additionally, the one or more controllers may monitor the state of charge of an energy storage device used to provide stored energy to the motor/generators (such as a battery), and engage those torque-transmitting mechanisms that establish one of the engine-only operating modes when the state-of-charge falls below a predetermined minimum state of charge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,FIG. 1shows a hybrid powertrain10for a vehicle. The powertrain10includes an engine12as one power source. The engine12may be a diesel engine, a gasoline engine, an air engine, a fuel cell or other type of power source other than an electric motor/generator. The powertrain10further includes a first electric motor/generator15(labeled M/G A inFIG. 1) and a second electric motor/generator14(labeled M/G B inFIG. 1).

The powertrain10includes a single planetary gear set20that has a sun gear member22, a ring gear member24, and carrier member26. The carrier member26rotatably supports a plurality of pinion gears (not shown) that mesh with both the sun gear member22and the ring gear member24, as is well understood by those skilled in the art. A person of ordinary skill in the art will readily understand the function and operation of planetary gear sets. As used herein, the ring gear member24is referred to as a first member of the planetary gear set20, the carrier member26is referred to as a second member of the planetary gear set20, and the sun gear member22is referred to as a third member of the planetary gear set20. The members of the planetary gear set20may be arranged differently without departing from the scope of the claimed invention. Furthermore, a compound planetary gear set may be used in lieu of the simple planetary gear set20, or a differential gear set may be used instead of a planetary gear set.

The engine12has an engine output member, such as a crankshaft, that is connected for common rotation with an input member30. An output member32is connected for common rotation with the carrier member26and with transmission gearing34, which may be a final drive or a transmission gearbox having additional intermeshing gears and torque-transmitting mechanisms (not shown).

Five torque-transmitting mechanisms are provided, including a first stationary-type clutch C1, also referred to as a band clutch or as brake C1. The other four torque-transmitting mechanisms, clutch C2, clutch C3, clutch C4and clutch C5are rotating-type clutches. Brake C1is selectively engagable to ground the ring gear member24to the stationary member35, which may be a transmission casing or other non-rotating member. Clutch C2is selectively engagable to connect the motor/generator15for common rotation with the ring gear member24. As used herein, “common rotation” means rotation at the same speed, including zero speed, or no rotation. Clutch C3is selectively engagable to connect the input member30(and thereby the engine12) for common rotation with the ring gear member24. Clutch C4is selectively engagable to connect the engine12for common rotation with the sun gear member22. Clutch C5is selectively engagable to connect the motor/generator14for common rotation with the sun gear member22.

Each of the motor/generators14and15has both a stator and a rotor. The stators are connected with an energy storage device, such as a battery36through a power inverter38that converts direct current supplied from the battery36to alternating current used for powering the motor/generators14,15when the respective motor/generator14, functions as a motor, or converts alternating current from the stator to direct current to be stored in the battery36when the respective motor/generators14,15functions as a generator, as is well understood by those skilled in the art. The advantages of the powertrain10could be achieved if a hydraulic or pneumatic chamber were used in lieu of a battery as the energy storage device for the motor/generator.

A motor control processor40is connected to the motor/generators14,15to control electrical energy flow between the stators of the motor/generators14,15and the battery36to control whether the respective motor/generator14,15functions as a motor or as a generator, and the amount of torque and speed of the rotor thereof according to stored algorithms and vehicle operating conditions, as is well understood by those skilled in the art. The motor/generators14,15may be configured to be rechargeable from a power grid, so that the powertrain10may be a plug-in hybrid.

An engine control module (ECM)37is operatively connected with the engine12and with other vehicle components, such as an accelerator position sensor, a wheel speed sensor, etc., to control operation of the engine12(such as engine speed, starting or stopping) in accordance with a stored algorithm. A hybrid control processor (HCM)39is operatively connected to the ECM37and to the motor control processor40.

A transmission control module (TCM)41that may be part of a transmission electro-hydraulic control module (TEHCM) including a valve body and solenoid valves is used to control engagement of torque-transmitting mechanisms, brake C1and clutches C2, C3, C4and C5, such as by actuating valves that control hydraulic fluid used to engage the torque-transmitting mechanisms C1, C2, C3, C4and C5. Some or all of the ECM37, HCM39, CONT40and TCM41may be integrated as a single controller.

The powertrain10is operable in eight different modes. A mode is established by engagement of different torque-transmitting mechanisms and by providing power from one or more of the power sources. The torque-transmitting mechanism engagement schedule for the eight operating modes is set forth inFIG. 2. Launch of a vehicle with powertrain10may be accomplished with power supplied by the motor/generator14in a one motor/generator electric-only operating mode, referred to inFIG. 2as One M/G EV. To establish the one motor/generator electric-only operating mode, brake C1is engaged to provide reaction torque at the ring gear member24, and clutch C5is engaged with the motor/generator14controlled to operate as a motor, providing torque to sun gear member22, which is provided to the output member32through the planetary gear set20to propel the vehicle. The single motor/generator electric-only operating mode may be used for launching the vehicle to achieve better fuel economy, as engine friction is high at vehicle launch. The single motor/generator electric-only operating mode may also be used to capture kinetic energy during braking and deceleration by feeding electric power back the into the battery36to recover expended charge.

A second electric-only operating mode using both motor/generators14,15is referred to inFIG. 2as Two M/G EV. To establish the second electric-only operating mode, clutches C2and C5are engaged to connect motor/generator14for common rotation with sun gear member22, and motor/generator15for common rotation with ring gear member24. Both motor/generators14,15can thus provide torque to propel the vehicle. The second electric-only operating mode provides extended electric operating range to the vehicle. The second electric-only operating mode may be more efficient than extended range electric vehicles that rely on the engine to provide power to a motor/generator functioning as a generator that then in turn powers a second motor to drive the vehicle. Such extended range vehicles always require an electro-mechanical path, with associated losses in converting from mechanical power to electrical power.

Four different electrically-variable operating modes are provided in which both the engine12and one or both motor/generators14,15provide power at the output member32through the planetary gear set20. In the electrically-variable operating modes, the engine12can be controlled to operate at its most efficient operating speed, while the speed of one or both motor/generators14,15is controlled to meet vehicle operating conditions. To establish a first electrically-variable operating mode, referred to inFIG. 2as EVT1, clutches C2, C3and C5are engaged. The engine12provides torque at ring gear member24, while motor/generator14provides torque at sun gear member22, with the torque combined through the planetary gear set20at output member32. Motor/generator15can provide torque or receive torque, as needed to maintain the engine12at its optimal speed.

To establish a second electrically-variable operating mode, referred to inFIG. 2as EVT2, clutches C2, C4and C5are engaged. Thus, torque of the engine12and motor/generator14is combined at sun gear member22, and motor/generator15provides torque at ring gear member24, with the torque combined through the planetary gear set20at the output member32. The engine12may be operated at its optimal speed, and its torque is multiplied from the sun gear member22to the carrier member26.

To establish a third electrically-variable operating mode, referred to inFIG. 2as EVT3, clutches C3and C5are engaged. The engine12provides torque at the ring gear member24, and may be operated at its optimal speed as the motor/generator14provides torque at sun gear member22.

To establish a fourth electrically-variable operating mode, referred to inFIG. 2as EVT4, clutches C2and C4are engaged. The engine12provides torque to the sun gear member22, while motor/generator15functions as a motor or as a generator as necessary to provide torque at the ring gear member24, such that the requisite torque at the output member32for vehicle operating conditions is provided while still allowing the engine12to operate at its optimal speed.

Two different engine-only, fixed gear operating modes are provided. A first engine-only, fixed gear operating mode, referred to inFIG. 2as Engine-Only Fixed Gear1is established by engaging brake C1and clutch C4. The engine12provides torque at the sun gear member22while brake C1provides reaction torque at ring gear member24. Engine torque is multiplied through the planetary gear set20. The first engine-only mode may be appropriate when relatively high torque is demanded. The motor/generators14,15need not be held stationary in the first engine-only operating mode, and the engine12can be used to recharge the battery36through motor/generator14as necessary during this mode by engaging clutch C5if the battery state of charge is outside of a predetermined range.

A second engine-only, fixed gear operating mode, referred to inFIG. 2as Engine-Only Fixed Gear2is established by engaging clutches C3and C4. The engine12provides torque at the output member32in a direct drive ratio, as engine torque is provided to both the ring gear member24and the sun gear member22.

The engine-only operating modes may be selected when the temperature of battery36is outside of a predetermined acceptable temperature range for supplying power (i.e., when the battery36is considered to be too cold (below a predetermined minimum temperature) or too hot (above a predetermined maximum temperature). Additionally, if the battery36is at a full state of charge, and the vehicle is cruising at relatively high speeds, it may be more efficient to operate in an engine-only operating mode than to discharge the battery36, as electromagnetic losses are higher and the electro-mechanical path is not as efficient. The engine-only, fixed gear operating modes are efficient during high speed cruising, when torque requirements are relatively low.

If the powertrain10is launched in the second electric-only operating mode, it may remain in that mode until vehicle speed requires peak power of the motor/generators14,15and/or the battery state of charge falls below a specified minimum state of charge due to heavy usage. The engine12may then be started in an engine start/stop operating mode by engaging clutch C4so that motor/generator14cranks the engine12. Once the engine12gains starting speed, torque from the engine12may be added to the output member32by releasing clutch C4and engaging clutch C3(while clutches C2and C5remain engaged) to establish the first electrically-variable operating mode in which torque from both the engine12and the motor/generators14,15is combined through the planetary gear set20at the output member32to meet higher acceleration demand from the driver. During the first electrically-variable operating mode, the motor/generator14may be controlled to operate as a generator, converting torque from the sun gear member22into stored electrical energy in the battery36to slow the output member32, such as during vehicle braking.

Furthermore, the powertrain10is designed to transition to the engine-only operating mode in the event of the battery conditions described above, or motor-related failures, such as a failure of the motor control processor40, the failure of a motor for an auxiliary pump used to provide lubricating fluid flow to the torque-transmitting mechanisms C1, C2and C3when the engine12is off, or a failure of motor contactor controls. In the event of such a failure, which may be indicated to the ECM37, HCM39, CONT40or TCM41by various sensors configured to sense vehicle operating conditions, the TCM41provides a control signal to cause engagement of either brake C1and clutch C4(first engine-only mode), or clutches C3, C4(second engine-only mode). The motor/generators14,15are protected from damage that may otherwise occur if operated during the failure event.

The powertrain10is of a reduced cost compared to other hybrid powertrain configurations that provide four electrically-variable operating modes, as it requires only one planetary gear set20, and only one rotating clutch C1. Packaging may thus be simpler. Overall weight is also reduced in comparison to a hybrid powertrain with two motor/generators. Because reaction torque is available at the ring gear member24, the powertrain10can be operated in an engine-only operating mode in the event of motor-related failures. The battery36may be downsized relative to a typical battery configured to power two motor/generators, as the engine12may be used to launch in low state of charge conditions, due to its direct connection with the output member32in the second engine-only operating mode. A desirable electric range and fuel economy of the powertrain10are still provided with the low cost design, due to the availability of the engine-only and electrically-variable operating modes. The electric range is comparable to other existing architectures that have two motor/generators because the motor/generator14is connected to the sun gear member22to provide higher torque and hence range. Because the engine-only operating modes are as efficient as the electrically-variable operating modes, the fuel economy achieved should remain comparable to that of other two motor/generator architectures.

Second Embodiment

FIG. 3shows a hybrid powertrain110for a vehicle. The powertrain110includes the same components as shown and described with respect to the powertrain10ofFIG. 1, except that clutch C5is selectively engagable to connect the first motor/generator15(M/G A) for common rotation with the output member32.

The powertrain110is operable in eleven different modes. The torque-transmitting mechanism engagement schedule for the eleven operating modes is set forth inFIG. 4. Launch of a vehicle with powertrain110may be accomplished with power supplied by the motor/generator14in a one motor/generator electric-only operating mode, referred to inFIG. 4as EV1. To establish the one motor/generator electric-only operating mode, brake C1is engaged to provide reaction torque at the ring gear member24with the motor/generator14controlled to operate as a motor, providing torque to sun gear member22, which is provided to the output member32through the planetary gear set20to propel the vehicle. The single motor/generator, electric-only operating mode may be used for launching the vehicle to achieve better fuel economy, as engine friction is high at vehicle launch. The single motor/generator, electric-only operating mode may also be used to capture kinetic energy during braking and deceleration by feeding electric power back the into the battery36to recover expended charge.

A second electric-only operating mode using both motor/generators14,15is referred to inFIG. 4as EV2. To establish the second electric-only operating mode, clutch C2is engaged to connect motor/generator15for common rotation with ring gear member24. Both motor/generators14,15can thus provide torque to propel the vehicle using controllable motor speeds. The second electric-only operating mode provides extended electric operating range to the vehicle. The second electric-only operating mode may be more efficient than extended range electric vehicles that rely on the engine to provide power to a motor/generator functioning as a generator that then in turn powers a second motor to drive the vehicle. Such extended range vehicles always require an electro-mechanical path, with associated losses in converting from mechanical power to electrical power.

A third electric-only operating mode using both motor/generators14,15is referred to inFIG. 4as EV3. To establish the third electric-only operating mode, clutches C1and C5are engaged to ground the ring gear member24to the stationary member35and to connect motor/generator15for common rotation with the output member32. The speed of the output member32is thus equal to the speed of motor/generator15. The third electric-only operating mode is an ideal mode in which to launch the vehicle as the speed of the output member32is easily controlled by controlling the speed of motor/generator15. Because the motor/generator15can be selectively attached to the output member32by engaging C5, torque may be provided by both of the motor/generators14,15, with torque multiplication for motor/generator14.

A fourth electric-only operating mode using both motor/generators14,15is referred to inFIG. 4as EV4. To establish the fourth electric-only operating mode, clutches C2and C5are engaged to connect motor/generator15for common rotation with both the ring gear member24and the output member32, thus causing the sun gear member22, the carrier member26and the ring gear member24of the planetary gear set20to rotate at the same speed, establishing an electric, direct drive mode in which the output member32rotates at the same speed as the motor/generator15(i.e., there is no torque multiplication through the planetary gear set20). The fourth electric-only operating mode EV4is ideally suited for low speed cruising.

Three different electrically-variable operating modes are provided in which both the engine12and one or both motor/generators14,15provide power at the output member32through the planetary gear set20. To establish a first electrically-variable operating mode, referred to inFIG. 4as EVT1, clutches C3and C5are engaged. The engine12provides torque at the ring gear member24, while motor/generator14provides torque at sun gear member22. Motor/generator15provides torque to or receives torque from the output member32such that the first electrically-variable operating mode is a low speed, input split operating mode.

To establish a second electrically-variable operating mode, referred to inFIG. 4as EVT2, clutches C2and C3are engaged. The engine12provides torque at the ring gear member24, while motor/generator15provides torque to the ring gear member24to share loading with the engine12. Motor/generator14provides torque at or receives torque from the sun gear member22to enable the engine12to maintain an optimal operating speed while meeting vehicle operating conditions. The second electrically-variable operating mode is an output split mode ideal for high speeds.

To establish a third electrically-variable operating mode, referred to inFIG. 4as EVT3, clutches C2and C4are engaged. The engine12provides torque at the sun gear member22, while motor/generator15provides torque at ring gear member24to enable the engine12to maintain an optimal operating speed. Motor/generator14provides torque to or receives torque at the sun gear member22to share loading with the engine12. The third electrically-variable operating mode is an output split mode ideal for high speeds, but with less speed reduction than EVT2.

Three different engine-only, fixed gear operating modes are provided. A first engine-only, fixed gear operating mode, referred to inFIG. 4as Engine-Only Fixed Gear1is established by engaging brake C1and clutch C4. The engine12provides torque at the sun gear member22while brake C1provides reaction torque at ring gear member24. Engine torque is multiplied through the planetary gear set20. The first engine-only mode may be appropriate when relatively high torque is demanded. The motor/generator14need not be held stationary in the first engine-only operating mode, and the engine12can be used to recharge the battery36through motor/generator14as necessary during this mode if the battery state of charge is outside of a predetermined range.

A second engine-only, fixed gear operating mode, referred to inFIG. 4as Engine-Only Fixed Gear2is established by engaging clutches C2, C3and C4. The engine12provides torque at the ring gear member24and the sun gear member22. Because the engine12is connected for rotation with both the ring gear member24and the sun gear member22, Engine-Only Fixed Gear2is a direct drive operating mode (i.e., with no torque multiplication from the engine12to the output member32). This operating mode is well suited for cruising at a constant vehicle speed. The motor/generators14,15need not be held stationary in the second engine-only operating mode, and the engine12can be used to recharge the battery36through either or both motor/generators14,15as necessary during this mode if the battery state of charge is outside of a predetermined range.

A third engine-only, fixed gear operating mode, referred to inFIG. 4as Engine-Only Fixed Gear3is established by engaging brake C1and clutches C4and C5. The engine12provides torque at the sun gear member22while the ring gear member24is held stationary, resulting in high torque multiplication through the planetary gear set20, ideal for acceleration, vehicle launch, or wide open throttle conditions. Motor/generators14,15need not be held stationary in the second engine-only operating mode, and the engine12can be used to recharge the battery36through motor/generators14,15as necessary during this mode if the battery state of charge is outside of a predetermined range.

An electric torque converter operating mode, referred to inFIG. 4as eTC mode, is established by engaging clutch C3. The engine12provides torque at the ring gear member24, resulting in torque multiplication at the output member32through the planetary gear set20. Motor/generator14provides reaction torque at the sun gear member22to enable the engine12torque to be multiplied through the planetary gear set20. The eTC mode may be a default mode established under the control of the controller40in the event of monitored vehicle operating conditions indicative of a failure of motor/generator15.

As with powertrain10, powertrain110is of a reduced cost compared to other hybrid powertrain configurations that provide three electrically-variable operating modes, as it requires only one planetary gear set20, and only one rotating clutch C1. Packaging may thus be simpler. Overall weight is also reduced in comparison to a hybrid powertrain with two motor/generators. The four electric-only operating modes provide good electric range capability in comparison to other hybrid vehicles having only a single planetary gear set. Vehicle launch is available in many different operating modes, including electric-only operating mode EV3, two engine-only, fixed gear operating modes (FG1and FG2), and electrically-variable operating mode EVT1.

Because reaction torque is available at the ring gear member24, the powertrain110can be operated in an engine-only operating mode in the event of motor-related failures. If motor/generator14fails, either of Engine-Only Fixed Gear1or Engine-Only Fixed Gear3operating modes are available to provide either of two levels of torque multiplication. In the event of a failure of motor/generator15, the electric torque converter eTC mode is available with the planetary gear set20allowing torque multiplication of the engine torque as motor/generator14provides reaction torque at the sun gear member22. Two different direct drive modes are available, such as for during vehicle cruising, one as an electric-only operating mode (EV4), and the other as an engine-only operating mode (FG2). Two of the engine-only, fixed gear modes (Engine-Only Fixed Gear2and Engine-Only Fixed Gear3) are operable with both motor/generators14and15on, allowing an opportunity for battery charging or balancing. For example, if battery SOC is full (at or above 90%), the battery36cannot take any more charging current. In such situations, if the vehicle110is cruising, the engine-only modes are more efficient than electric-only modes. However, if the engine12is providing an amount of power that suffices to meet output requirements as well as to charge the battery36and still operate at an efficient point, the electromechanical path may be used with the engine12driving the vehicle wheels directly as well as through motor/generator14, without using the battery36. In case of cold conditions or hot battery conditions, the battery36may not be ready to charge immediately, and engine-only modes may be used.

Finally, two of the electrically-variable operating modes (EVT2and EVT3) are load-sharing modes in that one of the motor/generators is connected with the engine12and can assist the engine12in providing torque.

The battery36may be downsized relative to a typical battery configured to power two motor/generators, as the engine12may be used to launch the vehicle in low state of charge conditions, due to its direct connection with the output member32in the second engine-only operating mode. Desirable electric range and fuel economy of the powertrain110are still provided with the low cost design, due to the availability of the engine-only and electrically-variable operating modes. The electric range is comparable to other existing architectures that have two motor/generators because the motor/generator14is connected to the sun gear member22to provide higher torque and hence range. Because the engine-only operating modes are as efficient as the electrically-variable operating modes, the fuel economy achieved should remain comparable to that of other two motor/generator architectures.