Hybrid Torque Converter Control During Rolling Engine Start For Driveline Damping

A hybrid electric vehicle, comprising:

• an engine;
• an automatic transmission having a torque converter with an impeller, a turbine, and a bypass clutch;
• a traction motor coupled to the impeller and selectively coupled to the engine by a disconnect clutch;
• a controller configured to control the bypass clutch to vary a speed difference between the impeller and the turbine to maintain turbine torque substantially constant while starting the engine using traction motor torque.

A method for controlling a hybrid vehicle having an engine selectively coupled by a disconnect clutch to a traction motor coupled to an automatic transmission having a torque converter with an impeller, a turbine, and a torque converter clutch, comprising:

• operating the vehicle to provide a driver demanded torque in an electric drive mode using only the traction motor with the disconnect clutch disengaged and the torque converter clutch locked with zero slip speed between the impeller and the turbine;
• engaging the disconnect clutch to start the engine using traction motor torque;
• controlling torque converter clutch apply pressure to control the slip speed and provide an associated converter torque ratio that maintains a substantially constant turbine torque to compensate for the traction motor torque used while starting the engine;
• controlling torque converter clutch apply pressure to control the slip speed and provide an associated converter torque ratio based on a combined engine torque and traction motor torque to provide the driver demanded torque after starting the engine;
• and
• controlling torque converter clutch apply pressure to lock the torque converter clutch and reduce the slip speed to zero after starting the engine.