Control system for a hybrid powertrain system

1. Method for operating a vehicle including a hybrid transmission having first and second torque machines, comprising:

decreasing a clutch pressure of an off-going clutch associated with operating the hybrid transmission in a first continuously variable mode and decreasing a clutch torque holding capacity of the off-going clutch and applying a friction braking torque to a wheel of the vehicle coincident with decreasing the clutch pressure of the off-going clutch;

operating the hybrid transmission in a neutral operating mode and synchronizing an oncoming clutch associated with operating the hybrid transmission in a second continuously variable mode; and

applying the oncoming clutch and coincidentally releasing the applied friction braking torque when the oncoming clutch is synchronized.

2. The method of claim 1 , wherein synchronizing the oncoming clutch comprises controlling torque of the first and second torque machines to synchronize the oncoming clutch.

3. The method of claim 2 , wherein synchronizing the oncoming clutch comprises synchronizing the oncoming clutch at a predetermined rate.

4. The method of claim 1 , wherein applying the oncoming clutch when the oncoming clutch is synchronized comprises increasing a clutch pressure of the oncoming clutch and increasing a clutch torque holding capacity of the oncoming clutch.

5. The method of claim 4 , further comprising pre-filling the oncoming clutch prior to applying the oncoming clutch.

6. Method for operating a vehicle including a powertrain including an engine, first and second torque machines, and a hybrid transmission, comprising:

operating the engine in an unfueled state;

releasing an off-going clutch which when engaged effects operation of the hybrid transmission in a first continuously variable mode;

applying a friction braking torque to a wheel of the vehicle to compensate for an increase in an output torque of the hybrid transmission resulting from releasing the off-going clutch;

subsequent to releasing the off-going clutch, releasing the applied friction braking torque and synchronizing an oncoming clutch which when engaged effects operation of the hybrid transmission in a second continuously variable mode; and

subsequent to synchronization of the oncoming clutch, engaging the oncoming clutch.

7. The method of claim 6 , wherein operating the engine in the unfueled state comprises operating the engine in an off state.

8. The method of claim 6 , wherein operating the engine in the unfueled state comprises operating the engine in a fuel cut-off mode.

9. The method of claim 6 , wherein synchronizing the oncoming clutch comprises controlling torque of the first and second torque machines to synchronize the oncoming clutch.

10. The method of claim 9 , wherein synchronizing the oncoming clutch comprises synchronizing the oncoming clutch at a predetermined rate.

11. Hybrid vehicle system, comprising:

an internal combustion engine;

at least one electric machine;

a transmission operatively coupled to said internal combustion engine and said at least one electric machine, said transmission including a first clutch which when engaged effects operation of the transmission in a first continuously variable mode and a second clutch which when engaged effects operation of the transmission in a second continuously variable mode;

a friction brake operative on a wheel operatively coupled to the transmission;

a control module effecting a shift of the transmission from the first continuously variable mode to the second continuously variable mode, comprising

operating the engine in an unfueled state;

releasing the first clutch;

applying the friction brake to compensate for an increase in an output torque of the transmission resulting from releasing the first clutch;

subsequent to releasing the first clutch, synchronizing the second clutch; and

subsequent to synchronization of the second clutch, releasing the applied friction brake and engaging the second clutch.