Fluid coupling for a hybrid powertrain system

1. A hybrid powertrain system, comprising:

an internal combustion engine;

an electric machine coupled to a transmission,

a fluid coupling including an impeller and a turbine, the impeller mechanically coupled to a rotatable member of the electric machine, the turbine mechanically coupled to a rotatable member of the internal combustion engine;

said fluid coupling effective to fluidically couple torque from the electric machine to the internal combustion engine when the impeller and turbine are not mechanically locked.

2. The hybrid powertrain system of claim 1 , wherein the fluid coupling is a torque converter further comprising a stator.

3. The hybrid powertrain system of claim 2 , wherein the torque converter is further effective to multiply the fluidically coupled torque from the electric machine to the internal combustion engine.

4. The hybrid powertrain system of claim 1 , wherein the electric machine is configured to effect an engine autostart during ongoing operation of the powertrain system.

5. A method for controlling a hybrid powertrain system comprising an internal combustion engine coupled to a torque machine through a torque converter including an impeller, a turbine, a stator, and a torque converter clutch, the method comprising:

transferring torque produced by the torque machine coupled to the impeller of the torque converter to the internal combustion engine coupled to the turbine of the torque converter through a fluidic coupling of the impeller to the turbine during an engine start event.

6. The method of claim 5 further comprising increasing torque produced by the torque machine so long as the internal combustion engine remains below a predetermined minimum firing speed whereafter the engine is fueled and fired and the torque converter clutch is locked.

7. The method of claim 5 further comprising increasing torque produced by the torque machine so long as the internal combustion engine remains below a predetermined minimum firing speed and the torque produced by the torque machine remains below a predetermined torque sufficient to spin and maintain the engine to the minimum firing speed.

8. The method of claim 7 further comprising applying the torque converter clutch after the torque produced by the torque machine exceeds the predetermined torque sufficient to spin and maintain the engine to the minimum firing speed.

9. The method of claim 8 further comprising fueling and firing the engine after the internal combustion engine exceeds the predetermined minimum firing speed and thereafter locking the torque converter clutch.

10. The method of claim 5 further comprising fueling and firing the engine after the internal combustion engine exceeds a predetermined minimum firing speed and thereafter locking the torque converter clutch.

11. A hybrid powertrain system, comprising:

an internal combustion engine;

an electric machine;

a torque converter comprising an impeller coupled to the electric machine, a turbine coupled to the internal combustion engine, and a selectively engageable torque converter clutch;

a control module disengaging the torque converter clutch and rotating the electric machine to fluidically transfer torque through the torque converter to the internal combustion engine for the purpose of spinning the engine prior to fueling and firing the internal combustion engine.

12. The hybrid powertrain system of claim 11 wherein the control module further increases torque produced by the electric machine so long as the internal combustion engine remains below a predetermined minimum firing speed whereafter the engine is fueled and fired and the torque converter clutch is locked.

13. The hybrid powertrain system of claim 11 wherein the control module further increases torque produced by the electric machine so long as the internal combustion engine remains below a predetermined minimum firing speed and the torque produced by the electric machine remains below a predetermined torque sufficient to spin and maintain the engine to the minimum firing speed.

14. The hybrid powertrain system of claim 13 wherein the control module further applies the torque converter clutch after the torque produced by the electric machine exceeds the predetermined torque sufficient to spin and maintain the engine to the minimum firing speed.