Method of operating a hybrid powertrain

1. A method of operating a hybrid powertrain of a vehicle, the hybrid powertrain including an engine, an electric motor and a high voltage battery, the method comprising:

monitoring a state of charge of the high voltage battery to determine if the state of charge is above a pre-defined upper limit;

preventing fuel flow to the engine to stop engine torque production when the state of charge of the high voltage battery is greater than the pre-defined upper limit, and when the hybrid powertrain is operating in a second fueling condition in which fuel flow to the engine is preferably maintained; and

rotating the engine with torque supplied by the electric motor while the fuel flow to the engine is prevented and the hybrid powertrain is operating in the second fueling condition to maintain rotation of the engine.

2. A method as set forth in claim 1 further comprising monitoring an engine torque of the engine.

3. A method as set forth in claim 2 further comprising comparing the engine torque to an output power request to determine if the engine torque is capable of producing an output torque of the hybrid powertrain that is greater than the output power request.

4. A method as set forth in claim 3 wherein preventing a fuel flow to the engine when the state of charge of the high voltage battery is greater than the pre-defined upper limit is further defined as preventing a fuel flow to the engine when the state of charge of the high voltage battery is greater than the pre-defined upper limit and the engine torque produces an output torque of the hybrid powertrain greater than the output power request.

5. A method as set forth in claim 1 further comprising defining a first fueling condition and the second fueling condition.

6. A method as set forth in claim 5 further comprising monitoring an operating parameter to determine if the engine is operating in the first fueling condition or the second fueling condition.

7. A method as set forth in claim 6 wherein the operating parameter includes one of a speed of the vehicle and a temperature of the high voltage battery.

8. A method as set forth in claim 1 further comprising re-establishing the fuel flow to the engine when the state of charge falls to a pre-defined lower limit.

9. A method of operating a hybrid powertrain of a vehicle, the hybrid powertrain including an engine, an electric motor and a high voltage battery, the method comprising:

monitoring a state of charge of the high voltage battery to determine if the state of charge is above a pre-defined upper limit;

comparing an engine torque of the engine to an output power request to determine if the engine torque is capable of producing an output torque of the hybrid powertrain greater than the output power request;

preventing fuel flow to the engine to stop torque production when the state of charge of the high voltage battery is greater than the pre-defined upper limit, the engine torque produces an output torque greater than the output power request, and when the hybrid powertrain is operating in a second fueling condition in which fuel flow to the engine is preferably maintained; and

rotating the engine with torque supplied by the electric motor while the fuel flow to the engine is prevented and the hybrid powertrain is operating in the second fueling condition to maintain rotation of the engine and to discharge the high voltage battery.

10. A method as set forth in claim 9 further comprising monitoring an engine torque of the engine.

11. A method as set forth in claim 10 further comprising defining a first fueling condition and the second fueling condition.

12. A method as set forth in claim 11 further comprising monitoring an operating parameter to determine if the engine is operating in the first fueling condition or the second fueling condition.

13. A method as set forth in claim 12 wherein the operating parameter includes one of a speed of the vehicle and a temperature of the high voltage battery.

14. A method as set forth in claim 9 further comprising re-establishing the fuel flow to the engine when the state of charge falls to a pre-defined lower limit.

15. A method of operating a hybrid powertrain of a vehicle, the hybrid powertrain including an engine, an electric motor and a high voltage battery, the method comprising:

monitoring a state of charge of the high voltage battery to determine if the state of charge is above a pre-defined upper limit;

comparing an engine torque of the engine to an output power request to determine if the engine torque produces an output torque of the hybrid powertrain that is greater than the output power request;

preventing fuel flow to the engine to stop torque production when the state of charge of the high voltage battery is greater than the pre-defined upper limit, the engine torque produces an output torque greater than the output power request, and when the hybrid powertrain is operating in a second fueling condition in which fuel flow to the engine is preferably maintained;

rotating the engine with torque supplied by the electric motor while the fuel flow to the engine is prevented and the hybrid powertrain is operating in the second fueling condition to maintain rotation of the engine; and

re-establishing the fuel flow to the engine when the state of charge falls to a pre-defined lower limit.

16. A method as set forth in claim 15 further comprising defining a first fueling condition and the second fueling condition.

17. A method as set forth in claim 15 further comprising monitoring an operating parameter to determine if the engine is operating in the first fueling condition or the second fueling condition, wherein the operating parameter includes one of a speed of the vehicle and a temperature of the high voltage battery.

18. A method as set forth in claim 15 further comprising monitoring an engine torque of the engine.