Method to reduce lash clunk in a hybrid electric vehicle

Method for starting an internal combustion engine of a powertrain system including a hybrid transmission having a selectable clutch device effective when engaged to mechanically couple the engine to a first axle at a desired fixed gear ratio, comprising:

• monitoring an output torque request and a vehicle speed;
• operating the hybrid transmission in an electric vehicle mode comprising:
• terminating engine operation,
• commanding the transmission to a neutral state, and
• controlling an electric machine to provide tractive torque to a second axle;
• executing an engine start event in response to detecting a predetermined condition during operation in the electric vehicle mode, said engine start event comprising:
• spinning and fueling the engine such that engine speed is increased to exceed a predetermined engine speed to enable synchronization of the selectable clutch device and to achieve the desired fixed gear ratio effective when the selectable clutch device is engaged;
• and
• engaging said selectable clutch device after the engine speed exceeds the predetermined engine speed.

Apparatus, comprising:

• an internal combustion engine;
• a transmission including a selectable clutch device effective when engaged to mechanically couple the engine to a first axle at a fixed engine speed to axle speed ratio;
• a first electric machine mechanically coupled to a second axle and configured to provide tractive torque to the second axle;
• an electrical energy storage device (ESD) configured to provide power to the first electric machine;
• and
• a control module:
• monitoring an operator torque request, vehicle speed, and a state of charge (SOC) of the ESD;
• terminating engine operation, commanding the transmission to a neutral state, and controlling the electric machine to provide tractive torque to the second axle;
• and
• executing an engine start event in response to detecting a predetermined condition when the transmission is in the neutral state and tractive torque is provided to the second axle by the first electric machine, said engine start event comprising:
• spinning and fueling the engine such that an engine speed to axle speed ratio exceeds the fixed engine speed to axle speed ratio;
• and
• engaging said selectable clutch device after the engine speed to axle speed ratio exceeding the fixed engine speed to axle speed ratio by a predetermined magnitude.