Transmission downshift input torque modulation for a hybrid electric vehicle

1. A method for controlling transmission input torque during an downshift, comprising:

(a) using an engine to produce transmission input torque;

(b) during a ratio change phase of the downshift, operating an electric machine as a motor to increase the transmission input torque; and

(c) during a torque transfer phase of the downshift following the ratio change phase, operating the electric machine as a generator to decrease the transmission input torque.

2. The method of claim 1 further comprising the steps of:

determining whether a temperature of the electric machine is less than a reference temperature;

executing steps (b) and (c) if the temperature of the electric machine is less than the reference temperature; and

discontinuing use of the electric machine if the temperature of the electric machine is equal to or greater than the reference temperature.

3. The method of claim 1 further comprising the steps of:

determining whether a speed of the electric machine is less than a reference speed;

executing step (b) and (c) if the speed of the electric machine is less than the reference speed; and

discontinuing use of the electric machine if the speed of the electric machine is equal to or greater than the reference speed.

4. The method of claim 1 further comprising the steps of:

determining whether a desired magnitude of torque modulation is less than a current torque capability of the electric machine;

executing step (b) and (c) if the desired magnitude of torque modulation is less than the current torque capability of the electric machine; and

discontinuing use of the electric machine if the desired magnitude of torque modulation is equal to or greater than the current torque capability of the electric machine.

5. The method of claim 1 further comprising the steps of:

determining whether a desired magnitude of torque modulation is less than a current torque capability of the electric machine;

executing step (b) and (c) if the desired magnitude of torque modulation is less than the current torque capability of the electric machine; and

using the electric machine and the engine if the desired magnitude of torque modulation is equal to or greater than the current torque capability of the electric machine.

6. The method of claim 1 further comprising the steps of:

if a torque modulation request is negative, determining whether a battery state of charge is less than a reference maximum state of charge;

executing step (c) if the battery state of charge is less than the reference maximum state of charge; and

discontinuing use of the electric machine if battery state of charge is equal to or greater than the reference maximum state of charge.

7. The method of claim 1 further comprising the steps of:

if a torque modulation request is positive, determining whether a battery state of charge is less than a reference minimum state of charge;

executing step (b) if the battery state of charge is greater than the reference minimum state of charge; and

discontinuing use of the electric machine if the battery state of charge is equal to or less than the reference minimum state of charge.

8. A method for controlling transmission input torque during an downshift, comprising:

(a) using an engine to produce transmission input torque;

(b) during a ratio change phase of the downshift, operating an electric machine as a motor to increase the transmission input torque; and

(c) during the ratio change phase of the downshift, controlling transmission input torque by using the engine to drive the transmission and the electric machine concurrently.

9. The method of claim 8 further comprising the step of operating the electric machine as a generator to decrease said net magnitude of torque, during a torque transfer phase of the downshift following the ratio change phase.

10. The method of claim 9 further comprising the step of storing in a battery energy produced by the electric machine during the torque transfer phase of the downshift.

11. The method of claim 8 wherein step (c) further comprises the step of varying a magnitude of torque required to drive the electric machine.

12. The method of claim 8 further comprising the steps determining whether a temperature of the electric machine is less than a reference temperature;

determining whether a temperature of the electric machine is less than a reference temperature;

executing step (b) if the temperature of the electric machine is less than the reference temperature; and

discontinuing use of the electric machine if the temperature of the electric machine is equal to or greater than the reference temperature.

13. The method of claim 8 further comprising the steps of:

determining whether a speed of the electric machine is less than a reference speed;

executing step (b) if the speed of the electric machine is less than the reference speed; and

discontinuing use of the electric machine if the speed of the electric machine is equal to or greater than the reference speed.

14. The method of claim 8 further comprising the steps of:

determining whether a desired magnitude of torque modulation is less than a current torque capability of the electric machine;

executing step (b) if the desired magnitude of torque modulation is less than the current torque capability of the electric machine; and

discontinuing use of the electric machine if the desired magnitude of torque modulation is equal to or greater than the current torque capability of the electric machine.

15. The method of claim 8 further comprising the steps of:

determining whether a desired magnitude of torque modulation is less than a current torque capability of the electric machine;

executing step (b) and (c) if the desired magnitude of torque modulation is less than the current torque capability of the electric machine; and

using the electric machine and the engine if the desired magnitude of torque modulation is equal to or greater than the current torque capability of the electric machine.

16. The method of claim 8 further comprising the steps of:

if a torque modulation request is negative, determining whether a battery state of charge is less than a reference maximum state of charge;

operating the electric machine as a generator to decrease said net magnitude of torque during a torque transfer phase of the downshift following the ratio change phase, if the battery state of charge is less than the reference maximum state of charge; and

discontinuing use of the electric machine if battery state of charge is equal to or greater than the reference maximum state of charge.

17. The method of claim 8 further comprising the steps of:

if a torque modulation request is positive, determining whether a battery state of charge is less than a reference minimum state of charge;

executing step (b) if the battery state of charge is greater than the reference minimum state of charge; and

discontinuing use of the electric machine if the battery state of charge is equal to or less than the reference minimum state of charge.

18. A method for controlling transmission input torque during an downshift, comprising:

(a) using an engine to produce transmission input torque;

(b) during a ratio change phase of the downshift, operating the electric machine as an electric motor;

(c) during the ratio change phase, varying the torque produced by the engine; and

(d) producing a net torque transmitted to the transmission input by using the engine to drive the transmission input and the electric machine.

19. The method of claim 18 further comprising the step of operating the electric machine as a generator to decrease said net magnitude of torque, during a torque transfer phase of the downshift following the ratio change phase.

20. The method of claim 19 further comprising the step of storing in a battery energy produced by the electric machine during the torque transfer phase of the downshift.

21. The method of claim 18 wherein step (d) further comprises the step of varying a magnitude of torque required to drive the electric machine.

22. The method of claim 18 further comprising the steps determining whether a temperature of the electric machine is less than a reference temperature;

determining whether a temperature of the electric machine is less than a reference temperature;

executing step (b) if the temperature of the electric machine is less than the reference temperature; and

discontinuing use of the electric machine if the temperature of the electric machine is equal to or greater than the reference temperature.

23. The method of claim 18 further comprising the steps of:

determining whether a speed of the electric machine is less than a reference speed;

executing step (b) if the speed of the electric machine is less than the reference speed; and

discontinuing use of the electric machine if the speed of the electric machine is equal to or greater than the reference speed.

24. The method of claim 18 further comprising the steps of:

determining whether a desired magnitude of torque modulation is less than a current torque capability of the electric machine;

executing step (b) if the desired magnitude of torque modulation is less than the current torque capability of the electric machine; and

discontinuing use of the electric machine if the desired magnitude of torque modulation is equal to or greater than the current torque capability of the electric machine.

25. The method of claim 18 further comprising the steps of:

if a torque modulation request is negative, determining whether a battery state of charge is less than a reference maximum state of charge;

operating the electric machine as a generator to decrease said net magnitude of torque during a torque transfer phase of the downshift following the ratio change phase, if the battery state of charge is less than the reference maximum state of charge; and

discontinuing use of the electric machine if battery state of charge is equal to or greater than the reference maximum state of charge.

26. The method of claim 18 further comprising the steps of:

if a torque modulation request is positive, determining whether a battery state of charge is less than a reference minimum state of charge;

executing step (b) if the battery state of charge is greater than the reference minimum state of charge; and

discontinuing use of the electric machine if the battery state of charge is equal to or less than the reference minimum state of charge.