Controlling a powertrain and a clutch of a vehicle

A vehicle includes an engine and is at least partially propelled by a fraction battery and a traction motor. A clutch is configured to be coupled to the traction motor. An electrical and/or mechanical pump provides pressure to control the clutch. At least one controller determines if the clutch is slipping. In response to the clutch slipping, the at least one controller commands an increase in speed of an input of the clutch such that the available line pressure to control the slipping of the clutch is increased. The line pressure is then applied to the clutch in order to control the slipping of the clutch.

TECHNICAL FIELD

The present disclosure relates to the control of a powertrain in a hybrid electric vehicle.

BACKGROUND

Hybrid electric vehicles (HEV's) include an internal combustion engine, an electric traction motor, and a traction battery. The engine can be connected to the motor in parallel or in series. A torque converter and/or launch clutch can couple the engine and motor to a transmission to transmit torque to wheels. When the vehicle is under relatively large loads or is traveling on an incline, the required torque to propel the vehicle is increased.

SUMMARY

According to one embodiment, a method is provided for controlling a vehicle. A current supplied to an electric machine is altered. The electric machine is coupled to wheels via a locked clutch. The altered current alters a torque output of the electric machine. In response to a slipping of the clutch due to the altered torque output, a speed of an input of the clutch is increased in order to increase a line pressure available to the clutch. In further response to the slipping of the clutch, the line pressure is applied to control the slipping of the clutch.

According to another embodiment, a vehicle includes an electric machine. A clutch is configured to be coupled to the electric machine. At least one controller is provided to respond to a slipping of the clutch. In response to the slipping, the controller is configured to increase a speed of an input of the clutch beyond a threshold speed such that an available line pressure to control the slipping of the clutch is increased.

According to yet another embodiment, a method for controlling a vehicle driveline is provided. A current to an electric machine is altered, wherein the electric machine is coupled to wheels via a locked clutch. The altering of the current alters a torque output of the electric machine. In response to a slipping of the clutch due to the altered torque output, the engine is started to increase a line pressure available to the clutch, and the line pressure is applied to control the slipping of the clutch.

DETAILED DESCRIPTION

Referring toFIG. 1, a schematic diagram of a vehicle10is illustrated according to one embodiment of the present disclosure. The vehicle10is an HEV. The powertrain or driveline of the vehicle10includes an engine12, an electric machine or motor/generator (M/G)14, and a transmission16disposed between the M/G14and wheels18. A torque converter19can optionally be provided between the M/G14and the transmission16. The torque converter19transfers rotating power from the M/G14to the transmission16. The torque converter19can include a bypass clutch that, when commanded, will transfer power from the M/G14to the remaining downstream components of the driveline while bypassing the torque converter19. A launch clutch20can also be provided, and can be disposed downstream of the M/G14in place of the torque converter19. When the launch clutch20is disengaged, the torque and rotational speed from the M/G14is not transferred to the transmission16, and when the launch clutch is at least partially engaged, torque is transferred to the transmission16. An auxiliary pump21is provided to pump fluid and control the launch clutch20. It should be understood that instead of a torque converter19, one or more clutches can be provided to selectively transfer torque from the M/G14to the transmission16. Other configurations are also possible.

The M/G14can operate as a generator by receiving torque from the engine12and supplying AC voltage to an inverter22. The inverter22converts the AC voltage into DC voltage to charge a traction battery, or battery23. The M/G14can operate as a generator by utilizing regenerative braking to convert the braking energy of the vehicle10into electric energy to be stored in the battery23. Alternatively, the M/G14can operate as a motor by receiving current or power from the inverter22and battery23, and providing torque through the torque converter19, the transmission16and ultimately to the wheels18. The battery23can also power the pump21, or the pump21can be powered from an auxiliary battery (not shown) of the vehicle10. A differential24can be provided to distribute torque from the output of the transmission16to the wheels18.

A first clutch, or disconnect clutch26, is located between the engine12and the M/G14. The disconnect clutch26can be fully open, partially engaged, or fully engaged (locked). In order to start the engine12, the M/G14rotates the engine12when the disconnect clutch26is at least partially engaged. Once the engine12is rotated by the M/G14to a certain speed (e.g., ˜100-200 rpm), fuel entry and ignition can commence. This enables the engine12to “start” and to provide torque back to the M/G14; the M/G14can charge the battery23and/or distribute torque from the engine12to the torque converter19, through the transmission16and ultimately to the wheels18. In another embodiment, a separate engine starter motor (not shown) can be provided.

The vehicle10also includes a control system, shown in the embodiment ofFIG. 1as three separate controllers: an engine control module (ECM)28, a transmission control module (TCM)30, and a vehicle system controller (VSC)32. The ECM28is directly connected to the engine12, and the TCM30can be connected to the M/G14and the transmission16. The three controllers28,30,32are connected to each other via a controller area network (CAN)34. The VSC32commands the ECM28to control the engine12and the TCM30to control the M/G14and the transmission16. Although the control system of the vehicle10includes three separate controllers, such a control system can include more or less than three controllers, as desired. For example, a separate motor control module can be directly connected to the M/G14and to the other controllers in the CAN34. Furthermore, it should be understood that references in the present disclosure to certain functions performed by the VSC32can be commanded by at least one of the ECM28and/or the TCM30.

As previously described, the M/G14is utilized to start the engine12. This is referred to as engine pull-up. It can be advantageous to pull-up the engine12in order to spin the M/G14and charge the battery23, for example. It can also be advantageous to pull-up the engine12to satisfy acceleration demands. During engine pull-up, the disconnect clutch26is at least partially engaged, and torque from the M/G14is applied through the disconnect clutch26and to the engine12. Once the engine12is pulled-up, a boost of torque can be provided through the powertrain due to, for example, sudden ignition in the engine12. The increase in speed of the engine after engine pull-up can be translated into increased rotational speed of the M/G14and increased available line pressure in the pump21to control the clutch20. Increased rotational speed of the M/G14can also cause the battery23to be charged and/or more torque to be applied to the torque converter19, as previously described. Once the battery23is sufficiently charged and the vehicle10does not require engine power for propulsion, the engine12can be disabled or pulled-down.

Referring toFIG. 2, the transmission16is shown in detail. It should be understood thatFIG. 2merely exemplifies one configuration of a transmission16. In a vehicle10utilizing the exemplified configuration ofFIG. 2, a torque converter may not be needed in the vehicle, due to the multiple clutches and planetary gear sets within the transmission. If a torque converter is not utilized in a configuration, then references to a “lockup clutch” or “launch clutch” include any clutch in the transmission capable of at least partially isolating the wheels18from the M/G14. It should therefore be understood that a simplified version of the transmission16can be utilized in combination with a torque converter19, in which fewer clutches and planetary gear sets are needed within the transmission16. Several other embodiments are contemplated with various configurations of clutches and/or planetary gear sets, with or without the use of a torque converter, as known in the art.

The transmission16ofFIG. 2includes an input shaft40that receives torque from the engine12and the M/G14either separately or in combination. The input shaft40is operatively connected to a second clutch42and a third clutch44. A portion of each of the second clutch42and third clutch44is connected to a first planetary gear set (PG)46, which is connected to a second planetary gear set (PG)48. A reverse clutch, or fourth clutch49and a low-and-reverse brake, or fifth clutch50can also be connected to the PG48. The second PG48drives a belt or chain52to transmit power to a third planetary gear set (PG)54. Each of the planetary gear sets46,48,54can include a sun gear, a ring gear, and a planetary carrier to provide various gear ratios in the transmission16. The third PG52provides a final gear ratio to transmit torque from the transmission16to the differential24.

A main pump56provides pressure to each of the clutches to engage/disengage each clutch as dictated by the TCM30. It should be understood that one or more of the clutches42,44,49,50can be controlled to be engaged (locked), partially engaged, or fully disengaged, similar to the operation of the launch clutch20and the disconnect clutch26. For example, when the second clutch42and/or the third clutch44are disengaged, the transmission16can be isolated from the M/G14such that no torque is transmitted through the transmission16and to the wheels18. It should also be understood that while clutches42,44are illustrated as being a part of the transmission16, one or more clutches can be separately utilized between the M/G14and the transmission16instead of being integral with the transmission16.

Referring toFIGS. 1 and 2, a “locked electric launch” or “locked launch” is defined as an acceleration (or attempted acceleration) of the vehicle10while the launch clutch20is locked. During a locked launch, the M/G14increases in speed to correspondingly increase the speed of a turbine in the torque converter19. This increase in speed of the turbine correspondingly adds torque to the wheels18to propel the vehicle10. The engine12can be started via the M/G14while the launch clutch20is locked during a locked launch. Any torque from the engine12and/or M/G14transfers to the transmission16while the launch clutch20is locked.

Referring toFIGS. 1 and 3, a locked launch is exemplified while the vehicle10is operating under normal conditions without a relatively large tow load or on a relatively large incline. The clutch torque capacity is defined by the pressure available for the launch clutch20as operated by the auxiliary pump21and/or main pump56. The required torque capacity is defined as the torque that is required to accelerate the torque converter19and thus accelerate the vehicle10from stopped. InFIG. 3, as there are no large external loads, for example, the M/G14can provide the necessary torque to accelerate the vehicle10as desired. Furthermore, because the clutch torque capacity exceeds the required torque capacity, power from the engine12is unnecessary to fulfill acceleration demands. While the launch clutch20is locked during acceleration, the speed of an input shaft to the clutch20is proportional to the speed of the output of the clutch20.

Referring toFIGS. 1 and 4, an attempted launch of the vehicle10is illustrated when the vehicle10is under relatively large tow load or is traveling on a relatively steep incline. Due to the large load or incline, the launch clutch20remains locked while the vehicle is stopped. As the vehicle10is commanded to accelerate, the speed and torque in the M/G14increases in an attempt to turn the turbine of the torque converter19. The torque capacity of the launch clutch20is reduced due to the lower available line pressure from the auxiliary pump21. Because the required torque capacity to accelerate the vehicle10is larger than the clutch torque capacity, the launch clutch20begins to slip, in which the input of the clutch20spins while the output of the clutch20remains generally motionless. The transferred torque from the M/G14to the launch clutch20is less than the required amount to rotate the transmission16and ultimately the wheels18. The combination of the available pressure from the pumps21,56and the power from the M/G14cannot meet the required torque capacity to propel the vehicle10. Therefore, the vehicle10remains motionless and the launch clutch20continues slipping. The VSC32continues to command the M/G14to provide torque to launch clutch20, but the load and/or incline subjected on the vehicle10is too great and thus the M/G14cannot sufficiently power the transmission16to turn the wheels18.

Referring toFIGS. 1 and 5, a commanded “slipping start” is illustrated. The vehicle10is again under large loads or is on a relatively large incline. A locked launch begins. The M/G14and the pressure available from the auxiliary pump21is initially not enough to exceed the required torque capacity and propel the vehicle10. Since the required torque capacity exceeds the clutch torque capacity, the launch clutch20begins to slip. This causes the input shaft of the clutch20to spin while the output of the clutch20remains generally motionless. The VSC32detects the slipping of the clutch. Instead of commanding the M/G14to continue to attempt to provide enough torque to propel the vehicle, the VSC32enables the launch clutch20to slip (or commands the launch clutch20to continue slipping) by reducing pressure in the launch clutch. In response to the launch clutch20slipping, the VSC32commands the M/G14to pull-up the engine12, or if already pulled-up, commands the engine12to increase its output power. An increase in torque to the clutch20(or torque converter19) may thus be provided due to the torque boost from the engine12. Once the rotational speed of the input of the clutch20has been increased beyond a threshold speed, the speed is sufficient to generate the available line pressure in the pump21to control the slipping of the clutch. Once the threshold speed has been reached and the slipping can be controlled, the VSC32can command the clutch20to remain slipping while the engine12is providing power. The boost in torque from the engine12can meet the required torque capacity to propel the vehicle10. This can be referred to as a “slipping launch” rather than a locked launch. The VSC32can command a slipping launch based upon the torque output by the M/G14being insufficient, as indicated by the detected slipping of the launch clutch20.

Once the engine12has increased its torque output, the disconnect clutch26can be locked such that the engine12provides more torque to the torque converter19. The clutch torque capacity thus increases above the required torque capacity to propel the vehicle10. The turbine speed begins to increase, transmitting torque through the transmission16and to the wheels18.

It should be understood that the references made to detecting slipping of the clutch20may include comparing a rotational speed the input and output of the clutch20. Sensors can be provided adjacent to the M/G14or the input of the clutch20to sense the rotational speed of the input of the clutch20. Similarly, rotational speed sensors can be provided near the output of the clutch20. A slip may be detected if the clutch input rotational speed is less than the clutch output rotational speed. It should further be understood that slipping can be detected by the VSC32by sensing the pressure in the clutch20and comparing the pressure to the estimated pressure necessary to lock the clutch20. Numerous other configurations can be provided in which the slipping is detected in the clutch20.

In one embodiment, the VSC32detects a slipping in the launch clutch20after an attempted locked electric launch. In response to the slipping of the clutch20, the VSC32commands an increase in speed of the input of the clutch20in order to increase a line pressure available to the clutch20. The increase in speed of the input of the clutch20can be accomplished by increasing a torque output of the engine12, or by reducing clutch pressure in the clutch20(allowing more slipping). The increase in speed of the input of the clutch20increases a speed of the pump21such that the available line pressure is increased. In further response to the slipping of the clutch20, the VSC also applies the increased line pressure to assertively control the slipping of the clutch20.

Referring toFIGS. 1 and 6, a method of providing sufficient torque to propel a vehicle subjected to high loads or inclined travel is illustrated at100. At operation102, a demanded acceleration or deceleration is detected, for example, by sensing a vehicle occupant pressing the acceleration pedal or brake pedal. At operation104, in response to the demanded tractive force, a locked launch is attempted in which the current supplied to the M/G14is altered to alter the torque output of the M/G14and thus the torque provided to a clutch, such as the launch clutch20. At operation106, slip is detected in the launch clutch20by methods previously explained. At operation108, the VSC commands a slipping start in which the launch clutch20. The engine12is pulled-up, to increase the rotational speed of the input of the launch clutch20. Shortly thereafter, the torque capacity in the launch clutch20exceeds the required torque capacity to propel the vehicle10. At operation110, once sufficient torque is provided to the launch clutch20, the VSC32can command the launch clutch20to lock, which increases the torque provided to the transmission16and to the wheels18.