Hybrid powertrain with efficient electric-only mode

A hybrid powertrain includes a hybrid electro-mechanical transmission and a power source. A planetary gear set having a first, a second, and a third member connects the power source with a first and a second motor/generator. A battery is operatively connected to the motor/generators for receiving power therefrom and delivering power thereto. An input member rotates with the first member, the first motor/generator rotates with the second member, and the second motor/generator rotates with the output member. A first torque-transmitting mechanism is engagable to connect the second motor/generator for rotation with the third member. The battery and the second motor/generator provide an electric-only operating mode to power the output member when the first torque-transmitting mechanism is not engaged; the power source, planetary gear set and first motor/generator thereby being disconnected from the output member during the electric-only operating mode to prevent parasitic drag.

TECHNICAL FIELD

The invention relates to a hybrid electromechanical powertrain having an efficient electric-only mode.

BACKGROUND OF THE INVENTION

Hybrid vehicle powertrains utilize electrically-variable transmissions that combine the use of electric motors and conventional engine power to produce a more efficient vehicle via: (i) engine start-stop operation; (ii) more efficient engine operating points; and (iii) recapture of vehicle kinetic energy into a storage battery by means of regenerative braking. Some hybrid powertrains have an “input-split” architecture, whereby the engine power is split between a direct mechanical connection to the output wheels and an electric generator, with the latter both charging the onboard battery and/or delivering power to a motor connected to the output wheels. Operation with such a powerflow arrangement is referred to as an input-split operating mode. The transmission also functions as an electrically variable transmission (EVT), enabling more optimal engine operating speed and load. Some EVTs offer two EVT modes, as well as a number of fixed gear ratios, as in a conventional automatic transmission.

The intended operating mode of the aforementioned architectures is to blend the use of the conventional engine and electric motor/generators in the most efficient way possible. Therefore, unlike a purpose-built electric vehicle (EV), input-split EVT architectures are not designed to operate for an extended period of time using only battery power, and consequently are not as efficient in such an electric-only operating mode.

SUMMARY OF THE INVENTION

A hybrid powertrain is provided with a modified input-split architecture such that the powertrain has both an efficient electric-only (i.e., battery-powered) operating mode, and at least one efficient conventional hybrid vehicle operating mode. Preferably, the powertrain is suitable for a plug-in hybrid vehicle. A “plug-in” hybrid vehicle is a vehicle with a hybrid powertrain that includes a battery that can be recharged by an offboard power source. It is desirable that a plug-in hybrid vehicle is able to function both as an electric vehicle (using only battery power) with significant battery-only range and as a conventional hybrid vehicle when available battery energy is low.

The hybrid powertrain includes a hybrid electromechanical transmission and a power source, such as an engine. The electromechanical transmission includes an input member connected with the power source and an output member. A planetary gear set having a first, a second, and a third member connects the power source with a first and a second motor/generator. Each of the power source and the motor/generators are operatively connected to a different one of the first, the second, and the third members. A battery is operatively connected to the motor/generators for receiving power therefrom and delivering power thereto. The input member is operatively connected with the first member, the first motor/generator is operatively connected for rotation with the second member, and the second motor/generator is operatively connected for rotation with the output member. A first torque-transmitting mechanism is engagable to connect the second motor/generator for rotation with the third member. The battery and the second motor/generator provide an electric-only operating mode to power the output member when the first torque-transmitting mechanism is not engaged, the power source, planetary gear set and first motor/generator thereby being disconnected from the output member during the electric-only operating mode to prevent parasitic drag of these components. Preferably, the first member is a carrier member, the second member is a sun gear member, and the third member is a ring gear member.

By powering the engine and engaging the first torque-transmitting mechanism, the powertrain can transition from the electric-only operating mode to an input-split operating mode, preferably to control the speed of engagement of the first torque-transmitting mechanism by using the first motor/generator as a motor to control the speed of the third member of the planetary gear set.

Preferably, a second torque-transmitting mechanism is provided that grounds the third member so that power can flow from the engine through the planetary gear set to the first motor/generator, to the battery46and then sent from the battery to the second motor generator, establishing a series hybrid operating mode.

A method of operating a powertrain includes providing the first torque-transmitting mechanism described above, directing the stored electrical to the second motor/generator to establish the electric-only operating mode, with the first torque-transmitting mechanism disengaged during the electric-only operating mode. The method also includes powering the engine during the electric-only operating mode, with the first torque-transmitting mechanism being either automatically or selectively engaged (depending on whether it is an overrunning one-way clutch or a selectively engagable clutch capable of transmitting torque in two directions, such as a friction plate clutch) to establish an input-split operating mode. Furthermore, the method may include selectively engaging a second torque-transmitting mechanism that grounds the member of the planetary gear set connectable to the second motor/generator, powering the engine, and controlling the first motor/generator to function as a generator, to thereby establish a series hybrid operating mode. To switch from the series hybrid operating mode to the input-split operating mode, the first motor/generator is controlled to operate as a motor to synchronize the speed of the member of the planetary gear set connectable with the second motor/generator with the speed of the second motor/generator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to like components,FIG. 1Aillustrates a hybrid powertrain10including a power source, which in this embodiment is an internal combustion engine12, connected to an electrically variable transmission14. In some of its operating modes, the transmission14is designed to receive at least a portion of its driving power from the engine12, as described below. The engine12has an output shaft13drivingly connected with an input member16of the transmission14. A final drive unit17is operatively connected to an output member18of the transmission14for delivering tractive power to the wheels or tracks of a vehicle.

The electrically variable transmission14also includes a planetary gear set20having a sun gear member22, a ring gear member24, and a carrier member26that rotatably supports a plurality of pinion gears27that intermesh with both the ring gear member24and the sun gear member22. The input member16is connected for rotation with the carrier member26.

The electrically variable transmission14further includes a first motor/generator30, and a second motor generator32. The first motor/generator30has a rotor34rotatably connected with the sun gear member22via a hub36. A stator38grounded to a stationary member40, such as a transmission casing, powers the rotor34when the first motor/generator30is functioning as a motor and generates electrical power when the first motor/generator30is functioning as a generator, as is known. The second motor/generator32has a rotor42rotatably connected with the output member18. A stator44grounded to the stationary member40powers the rotor42when the second motor/generator32is functioning as a motor and generates electrical power when the second motor/generator32is functioning as a generator.

The motor/generators30,32may receive electrical power from or provide electrical power to an energy storage device, such as a battery46. An electronic controller48is in signal communication with the battery46and with a power invertor50that is also in electrical communication with the stators38,44of the motor/generators30,32, respectively. The controller48responds to a variety of input signals including vehicle speed, operator demand, the level at which the battery46is charged and the power being provided by the engine12to regulate the flow of power between the motor/generators30,32and the battery46via the inverter50, which converts between direct current provided or utilized by the battery46and alternating current provided or utilized by the stators38,44of the motor/generators30,32. An optional offboard power supply system52may be connected with the battery46for recharging of the battery46. The offboard power supply system52utilizes an offboard power supply54, an onboard charger56, and an onboard/offboard interface58, such as an electrical outlet and plug that permits selective connection of the offboard component (the offboard power supply54) with the onboard charger56. The offboard power supply54is shown in phantom inFIG. 1Ato indicate that it is offboard, and not an integrated component of the powertrain10. As used herein, “onboard” refers to a component integrated within the powertrain10such that it is carried with the powertrain10on a moving vehicle powered by the powertrain10. “Offboard” refers to a component not integrated in and not carried with the powertrain10as it moves, but that may be connected to the powertrain10.

The onboard charger56is connected with an onboard battery46. The transmission14may be referred to as a plug-in hybrid transmission as it is equipped with such an offboard power supply system52. The charger56is an onboard conductive-type charger that regulates the flow of electrical power from the offboard power supply54to the battery46. When the battery46is sufficiently recharged, the connection through interface58is terminated, and the recharged battery46is then used as discussed herein to power the motor/generators30,32, such as in an electric-only mode discussed below. Other types of offboard power supply systems may be used in lieu of offboard power supply system52, including plug-in systems that utilize an offboard conductive-type charger with an offboard power supply, and those that utilize an offboard inductive charger and offboard power supply.

The transmission14has a first torque-transmitting mechanism60and a second torque-transmitting mechanism62which are engagable and disengagable, either automatically or selectively (i.e., under the control of the controller48) as discussed below, to allow different operating modes of the powertrain10. The first torque-transmitting mechanism60is engagable to connect a hub64extending from the ring gear24for common rotation with the output member18. When the first torque-transmitting mechanism60is not engaged (as depicted inFIG. 1A), the output member18and the second motor/generator32can rotate without any physical drag caused by the planetary gear set20, the first motor/generator30, or the engine12, as those components are disconnected from the output member18and second motor/generator32by the disengaged torque-transmitting mechanism60.

The first torque-transmitting mechanism60is shown in a generic configuration as two separated portions in a disengaged state inFIG. 1A. A first portion66rotates commonly with the output member18while a second portion68rotates commonly with a hub64. In a first configuration, the first torque-transmitting mechanism60may be a one-way clutch, and is represented by one-way clutch60A inFIG. 1B. A first portion of the clutch66A connected for rotation with output member18overruns a second portion of the clutch68A when rotating relative to the second half68A in a forward direction to interrupt torque transfer between the ring gear member24and the output member18, but is engaged to rotate commonly with the second portion68A and the hub64(and ring gear member24) connected thereto when the hub64is rotating such that there is no relative rotation between the portions66A,68A, thereby permitting torque-transfer from the ring gear member24to the output member18. Such a one-way clutch60A is well known to those skilled in the art, and is advantageous as its engagement or disengagement is automatic, requiring no hydraulic or other type of actuation under the control of the controller48.

In a second configuration, the first torque-transmitting mechanism60may be a selectively engagable clutch capable of transmitting torque in two directions. That is, the first torque-transmitting mechanism60may be a selectively engaged to transmit torque between the first and second portions66,68regardless of the direction of rotation of the two portions (i.e., the first torque-transmitting mechanism60does not overrun in either direction). Well known examples of torque-transmitting mechanisms capable of transmitting torque in two directions are friction plate-type clutches and dog clutches. The first torque-transmitting mechanism60is represented by friction plate clutch60B inFIG. 1C. In such an embodiment, friction plates66B extending from the output member18may be selectively engaged with friction plates68B extending from the hub64by utilizing the controller48to control hydraulic pressure acting on a piston that applies pressure to the plates66B,68B, as is known.

The second torque-transmitting mechanism62is shown in a generic configuration as two separated portions in a disengaged state inFIG. 1A. A first portion70of the torque-transmitting mechanism62rotates commonly with the ring gear member24and the hub64, while a second portion72is grounded to the stationary member40. The torque-transmitting mechanism62may be a selectively-engagable brake-type clutch capable of transmitting torque in two directions, such as a friction plate-type stationary clutch or a band brake, both of which are well known types of torque-transmitting mechanisms. In a first configuration, the second torque-transmitting mechanism62may be a friction plate clutch, and is represented by friction plate clutch62A inFIG. 1D. In such an embodiment, friction plates70A connected for rotation with the ring gear member24and hub64may be selectively engaged with reaction plates72A extending from the stationary member40by utilizing the controller48to control hydraulic pressure acting on a piston that applies pressure to the plates70A,72A, as is known.

In another configuration illustrated inFIG. 1E, the second torque-transmitting mechanism62is a one-way clutch62B having a first portion70B connected for rotation with the ring gear member24and hub64that overruns a second portion72B when the ring gear member24rotates in a first direction, referred to as a forward direction, but automatically engages with the second portion72B, thereby grounding the clutch62B to the stationary member40, when torque applied to the ring gear member24and hub64causes those components to attempt to rotate in a second opposing direction, referred to as a reverse direction. The use of a one-way clutch for the second torque-transmitting mechanism62, such as one-way clutch62B is advantageous in that its operation is automatic, and hydraulic pressure and actuators under the control of the controller48are not required for its engagement. However, unlike the friction brake62A ofFIG. 1D, the one-way clutch62B will overrun, and is therefore not able to provide the reaction torque necessary on the ring gear member24if the first motor/generator30is operated as a motor to start the engine12.

Referring toFIG. 1F, the second torque-transmitting mechanism62may be a one-way clutch62C, functioning in the same manner as one-way clutch62B ofFIG. 1E, with an additional brake-type torque-transmitting mechanism74placed in parallel therewith. The additional brake-type torque-transmitting mechanism74may be engaged during engine starting via the first motor/generator30. This allows the use of the one-way clutch62C for forward torque transfer, without requiring a separate engine starting assembly, as the brake-type torque-transmitting mechanism74can be selectively engaged to provide reaction torque at the ring gear member24during engine starting. The brake-type torque-transmitting mechanism74may be smaller in capacity than the brake-type torque-transmitting mechanism62A ofFIG. 1D, as it would not be used for other operating modes that require ring gear member24to be grounded, such as in the series hybrid operating mode discussed below.

The powertrain10is operable in several different operating modes by controlling the operation of the engine12, the motor/generators30,32, and by engagement or disengagement of the torque-transmitting mechanisms60,62, whether such is automatic (in the case of a one-way clutch or brake) or selective (in the case of a friction plate clutch or brake). First, the powertrain10is operable in an electric-only (i.e., battery-only) operating mode when the engine12is off, the torque-transmitting mechanism62is not engaged, and the torque-transmitting mechanism60is not engaged, as illustrated inFIG. 2A. If the second motor/generator32is controlled to operate as a motor powered via electric battery stored in the battery46to supply rotary power to the output member18(depicted by arrow A), the disengaged torque-transmitting mechanism60between the ring gear member24and the motor/generator32disconnects the output member18from the planetary gear set20, the first motor/generator30and the engine12when the powertrain10is operating in an electric-only mode. By isolating the planetary gear set20, the engine12and the first motor/generator30from the driving wheels, vehicle powertrain efficiency is improved since these components are no longer a source of parasitic drag in the powertrain10. If the first torque-transmitting mechanism60is a one-way clutch such as torque-transmitting mechanism60A ofFIG. 1B, it will automatically overrun and be in a disengaged state when the motor/generator32is powering the output member18. If the first torque-transmitting mechanism60is a friction clutch capable of transmitting torque in two directions, such as friction plate clutch60B ofFIG. 1C, it will be kept in a disengaged state by the controller48, which will be programmed to not engage clutch60B when operating conditions warrant operation in the electric-only operating mode.

Additionally, the powertrain10is operable in an input-split operating mode when the engine12is on, the second torque-transmitting mechanism62is not engaged, and the first torque-transmitting mechanism60is engaged. The input-split operating mode is illustrated inFIG. 2Bwith the portions70,72of the second torque-transmitting mechanism62appearing disconnected, and the portions66,68of the first torque-transmitting mechanism60being engaged as indicated schematically by the vertical line connecting the two portions66,68. In the input-split operating mode, the engine12provides power to the output member18and to the first motor/generator30through the planetary gear set20, as depicted by arrows B and C, respectively. In the simplest preferred embodiment of this invention, the first torque-transmitting mechanism60is a one-way clutch such as clutch60A ofFIG. 1Bthat overruns while the second motor/generator32drives the output member18(as indicated by arrow D) without driving the ring gear member24. In the input-split operating mode, the second motor/generator32absorbs all power for regenerative braking of a vehicle equipped with powertrain10. In a plug-in vehicle application, the second motor/generator32will be designed with sufficient electrical capability to provide good electric-only mode performance (i.e., sufficient driving torque). The advantage of the one-way clutch60A over a selectively engagable friction-type clutch such as friction plate clutch60B is that minimal control system intervention is required to switch between the electric-only mode and the input-split operating mode. When power is sent to the ring gear member24via the engine12, the one-way clutch60A locks up, allowing the ring gear member24to drive the output member18so that the transmission14operates in an input-split hybrid operating mode. To limit driveline lash, it would be necessary to use the first motor/generator30to control the speed of engagement of the one-way clutch60A by controlling the speed of the ring gear member24. If the first torque-transmitting mechanism60were instead a friction-plate type torque-transmitting mechanism such as60B ofFIG. 1C, it could be utilized for engine-braking, as it could carry torque in a reverse direction to the ring gear member24, unlike a one-way clutch such as clutch60A which would overrun.

A third operating mode of the powertrain10is a series hybrid operating mode, illustrated inFIG. 2C, whereby the engine12is used to run the first motor/generator30(as indicated by arrow E) in order to charge the battery46and/or deliver power to motor/generator32(as indicated by arrow F). In this operating mode, engagement of the second torque-transmitting mechanism62is necessary in order to ground the ring gear member24, providing reaction torque, and allowing the engine12to send power to the first motor/generator32through the planetary gear set20. With the second torque-transmitting mechanism62engaged (as indicated schematically in FIG.2C by the vertical line connecting the two portions of the second torque-transmitting mechanism62, the powertrain10can run primarily in electric-only operating mode, and the engine12can be controlled to be on only as needed to provide recharging of battery46. In the simplest embodiment the second torque-transmitting mechanism62is a one-way clutch such as clutch62A ofFIG. 1Dthat prevents reverse rotation of the ring gear member24when the engine12comes on to shift from electric-only operating mode to the input-split operating mode. To transition to the input-split operating mode, torque and speed of the engine12as well as the speed of motor/generator30can be adjusted such that the ring gear member24is rotated in the forward direction until the first torque-transmitting mechanism60is engaged.

As per the description of the operating modes above, a method of operating a powertrain such as powertrain10, described with respect to the components ofFIGS. 1A-2C, includes providing a first torque-transmitting mechanism60between the second motor/generator32and the member (ring gear member24) of the planetary gear set20connected with the second motor/generator32. The method further includes directing stored electrical power (stored in battery46) to the second motor/generator32to drive the transmission output member18to thereby establish an electric-only operating mode, with the first torque-transmitting mechanism60being disengaged during the electric-only operating mode so that the second motor/generator32and the output member18are isolated from the planetary gear set20, the engine12and the first motor/generator30, thus eliminating drag of these latter components on the output member18. While directing stored electric power to the second motor/generator32, the method includes powering the engine12, with the first torque-transmitting mechanism60being either automatically engaged (in the case of a one-way clutch) or selectively engaged (in the case of a clutch capable of transmitting torque in two directions, such as a friction plate-type clutch), thereby directing the engine power to the output member18and establishing an input-split operating mode. Instead of an input-split operating mode, a series hybrid operating mode may be established following the electric-only operating mode by selectively engaging the second torque-transmitting mechanism62to ground the ring gear member24, powering the engine12, and controlling the first motor/generator30to act as a generator that provides the electric power to the battery46. The method may further include switching from the electric-only operating mode to the input-split operating mode by controlling the first motor/generator30to operate as a motor to synchronize the rotational speed of the ring gear member24with the rotational speed of the second motor/generator32.