Control strategy for multi-mode vehicle propulsion system

1. A method for controlling a vehicle propulsion system including a transmission including a lash region coupling an engine output shaft to a vehicle drive wheel, comprising:

adjusting an operating parameter of the engine so that at least one cylinder of the engine is transitioned between a first combustion mode and a second combustion mode; and

varying a timing of said transition responsive to whether the transmission is operating within the lash region of the transmission.

2. The method of claim 1 , further comprising, adjusting an amount of torque provided to the transmission by the engine as said transmission approaches the lash region.

3. The method of claim 2 , wherein said adjusting the amount of torque includes reducing the amount of torque provided to the transmission by the engine as said transmission approaches the lash region.

4. The method of claim 1 , wherein said timing of the said transition is advanced so that the transition is performed before the transmission passes through said lash region.

5. The method of claim 1 , wherein said timing of the said transition is retarded so that the transition is performed after the transmission passes through said lash region.

6. The method of claim 1 , wherein said propulsion system includes an electric motor coupled to said transmission and wherein the method further comprises adjusting an amount of torque provided to the transmission by the motor in response to said timing of said transition.

7. The method of claim 1 , wherein said propulsion system includes an electric motor coupled to the drive wheel and wherein the method further comprises adjusting an amount of torque exchanged between the motor and the drive wheel as said transmission approaches the lash region.

8. The method of claim 1 , wherein the first mode is a spark ignition mode and the second mode is a homogeneous charge compression ignition mode.