Optimization to reduce fuel consumption in charge depleting mode

1. A method for controlling a powertrain comprising an internal combustion engine, a first motor, a second motor, an energy storage device providing electrical energy to the first and second motors, and a plug-in connection, the method comprising:

providing a planetary gear set within the powertrain, said planetary gear set coupled to the engine, the first motor and the second motor;

monitoring a fuel cut mode;

ceasing a fuel flow to the engine based upon the fuel cut mode;

permitting the engine to spin freely during the fuel cut mode;

selectively maintaining a zero engine speed comprising balancing a first torque applied to the planetary gear set by the first motor and a second torque applied to the planetary gear set by the second motor; and

through a period of operation including acceleration of the powertrain, the first motor and the second motor each providing motive torque that cooperatively provide an entirety of propelling torque to the powertrain with the electrical energy from the energy storage device based upon the fuel cut mode.

2. The method of claim 1 , further comprising permitting the engine to spin freely in a forward direction during the fuel cut mode.

3. The method of claim 1 , wherein providing the entirety of propelling torque to the powertrain comprises maintaining an engine speed at zero.

4. The method of claim 3 , further comprising:

monitoring an end to the fuel cut mode;

increasing the engine speed with the motor before the monitored end to the fuel cut mode; and

starting the engine based upon the monitored end to the fuel cut mode.

5. The method of claim 1 , further comprising:

determining a first efficiency associated with maintaining a zero engine speed;

determining a second efficiency associated with permitting the engine to spin freely; and

selectively maintaining the zero engine speed based upon a comparison of the first and second efficiencies.

6. The method of claim 5 , wherein determining the second efficiency comprises determining a fuel cost to reheat an aftertreatment catalyst.

7. The method of claim 1 , further comprising:

monitoring a state of charge of the energy storage device;

comparing the monitored state of charge to a low state of charge threshold; and

terminating the fuel cut mode based upon the comparing.

8. The method of claim 1 , further comprising initiating the fuel cut mode immediately when the powertrain is started.

9. The method of claim 1 , wherein monitoring the fuel cut mode comprises:

monitoring a planned route of travel;

determining a preferred portion of the planned route of travel to operate the fuel cut mode; and

initiating the fuel cut mode based upon the determined preferred portion of the planned route of travel.

10. The method of claim 9 , wherein determining the preferred portion of the planned route of travel comprises determining a portion of the planned route of travel in which the fuel cut mode will result in a greatest fuel savings over the entire planned route of travel.

11. The method of claim 9 , wherein determining the preferred portion of the planned route of travel comprises a terminal portion of the planned route of travel.

12. The method of claim 1 , further comprising:

monitoring an output torque of the powertrain; and

suspending the fuel cut mode based upon the monitored output torque of the powertrain exceeding a torque limit for the motor.

13. The method of claim 12 , wherein monitoring the output torque of the powertrain comprises monitoring an output torque request.

14. The method of claim 12 , wherein monitoring the output torque of the powertrain comprises predicting an output torque.

15. The method of claim 12 , wherein suspending the fuel cut mode comprises temporarily suspending the fuel cut mode.

16. The method of claim 1 , wherein the powertrain comprises an electric drive powertrain and the engine comprises a range extender.

17. The method of claim 1 , wherein the powertrain comprises a hybrid drive powertrain wherein the engine and the motor are operable in a powersplit mode.

18. The method of claim 1 , further comprising:

monitoring a state of charge of the energy storage device;

comparing the state of charge to a maximum state of charge; and

utilizing engine braking based upon the comparing.

19. The method of claim 18 , wherein utilizing engine braking comprises controlling the powertrain to increase an engine speed.

20. The method of claim 19 , wherein utilizing engine braking comprises modulating a valve control strategy for the engine to increase a torque required to spin the engine.

21. An apparatus for controlling a powertrain comprising an internal combustion engine, a first motor, a second motor, an energy storage device providing electrical energy to the first and second motors, and a plug-in connection, the apparatus comprising:

a planetary gear set within the powertrain, said planetary gear set coupled to the engine, the first motor and the second motor;

a control module:

monitoring a fuel cut mode;

ceasing a fuel flow to the engine based upon the fuel cut mode;

permitting the engine to spin freely during the fuel cut mode;

selectively maintaining a zero engine speed comprising balancing a first torque applied to the planetary gear set by the first motor and a second torque applied to the planetary gear set by the second motor; and

through a period of operation including acceleration of the powertrain, commanding the first motor and the second motor to each provide motive torque that cooperatively provides an entirety of propelling torque to the powertrain with the electrical energy from the energy storage device based upon the fuel cut mode.