Feed forward and feedback adjustment of motor torque during clutch engagement

1. A hybrid vehicle comprising:

a motor;

a clutch configured to couple the motor to an engine; and

a controller programmed to,

increase motor torque by a specified value prior to engagement of the clutch during clutch pressure boost and starter motor cranking of the engine,

decrease motor torque during clutch engagement by the specified value, and

adjust motor torque during post engine start engagement of the clutch based upon clutch pressure and slip speed and vehicle acceleration to maintain vehicle acceleration.

2. The hybrid vehicle of claim 1 wherein the period of clutch engagement is terminated when a disconnect clutch between the motor and the engine is fully engaged.

3. The hybrid vehicle of claim 1 wherein the period of clutch engagement is terminated when a speed of rotation of the motor and a speed of rotation of the engine are substantially equal thereby indicating that the disconnect clutch is fully engaged.

4. The hybrid vehicle of claim 1 wherein the period of clutch engagement begins when a disconnect clutch between the motor and the engine begins to drag the engine, wherein a calibrated time window is provided prior to the beginning of the clutch engagement.

5. The hybrid vehicle of claim 4 wherein a clutch pressure signal is provided to a gain scheduling processor that obtains a feed forward torque command based upon a stored value table.

6. The hybrid vehicle of claim 1 wherein the clutch slip speed value is provided to a proportional controller that is based upon a speed of rotation of the motor and a speed of rotation of the engine, and wherein the proportional controller provides a signal requesting a change in motor torque.

7. The hybrid vehicle of claim 1 wherein the motor torque is decreased by the specified value gradually during clutch engagement until full engagement of the clutch is complete, in response to detection of negative engine torque being transferred through the clutch.

8. A hybrid vehicle comprising:

a motor;

a starter motor;

an engine and a battery for supplying power to the motor;

a clutch configured to selectively couple the motor and engine;

a torque converter configured to couple the motor to a transmission; and

at least one controller programmed to,

increase motor torque by a specified value prior to a period of clutch engagement during clutch pressure boost and starter motor cranking of the engine,

decrease motor torque during clutch engagement by the specified value, and

adjust motor torque during the period of clutch engagement after an engine start, based upon clutch pressure, clutch slip speed, and vehicle acceleration such that engine inertia drag is compensated for and vehicle acceleration is maintained.

9. The hybrid vehicle of claim 8 wherein the controller is configured to record the vehicle acceleration immediately prior to the period of clutch engagement, wherein the vehicle acceleration is provided to a proportional integral (PI) controller as a set point of the PI controller.

10. The hybrid vehicle of claim 9 wherein a filtered vehicle acceleration signal is provided to the PI controller for closed loop control.

11. The hybrid vehicle of claim 8 wherein the controller detects a change in driver demand associated with removing pressure from an accelerator pedal or by requesting application of a brake while the controller is controlling motor torque to maintain vehicle acceleration, wherein upon detecting a change in driver demand the controller discontinues maintaining vehicle acceleration.

12. The hybrid vehicle of claim 8 wherein the controller starts controlling the motor torque to maintain vehicle acceleration at the start of the period of clutch engagement and stops controlling the motor torque to maintain vehicle acceleration when the period of clutch engagement has ended.

13. The hybrid vehicle of claim 8 wherein the motor torque is decreased by the specified value gradually during clutch engagement until full engagement of the clutch is complete, in response to detection of negative engine torque being transferred through the clutch.

14. A method of operating a hybrid vehicle with a control unit, the hybrid vehicle having an engine that is selectively connected to a driveline by a disconnect clutch and a secondary power source that is coupled to a transmission by a torque converter comprising:

increasing secondary power source torque by a specified value prior to a period of clutch engagement during disconnect clutch pressure boost and starter motor cranking of the engine

decrease secondary power source torque during clutch engagement by the specified value, and

adjusting secondary power source torque during the period of clutch engagement after an engine start with the control unit, based upon a disconnect clutch pressure, a clutch slip speed, and vehicle acceleration such that engine inertia drag is compensated for and vehicle acceleration is maintained.

15. The method of claim 14 further comprising terminating the period of clutch engagement with the control unit when the disconnect clutch between the secondary power source and the engine is fully engaged.

16. The method of claim 14 wherein the period of clutch engagement begins when the disconnect clutch between the secondary power source and the engine begins to drag the engine, wherein the method further comprises inputting a calibrated time preparation window into the control unit prior to the beginning of the clutch engagement, increasing torque requested from the secondary power source prior to the beginning of the clutch engagement with the control unit, and decreasing the torque requested from the secondary power source after the beginning of clutch engagement with the control unit.

17. The method of claim 14 further comprising monitoring the vehicle acceleration with the control unit immediately prior to the period of clutch engagement, wherein the vehicle acceleration is provided as an input to a proportional integral (PI) controller as a set point of the PI controller.

18. The method of claim 14 further comprising outputting a filtered vehicle acceleration signal from the control unit and inputting the filtered vehicle acceleration signal to a PI controller for closed loop control.

19. The method of claim 14 further comprising detecting a change in driver demand associated with removing pressure from an accelerator pedal or a request for application of a brake with the control unit, while the control unit is also controlling motor torque to maintain vehicle acceleration, wherein upon detecting the change in driver demand maintaining vehicle acceleration is discontinued by the control unit.

20. The method of claim 14 wherein the secondary power source torque is decreased by the specified value gradually during clutch engagement until full engagement of the clutch is complete, in response to detection of negative engine torque being transferred through the clutch.