Hybrid powertrain system

A low-voltage hybrid powertrain system disposed to generate torque transferable to a vehicle driveline, comprising:

• an internal combustion engine (engine), a low-voltage electric machine, a transmission and a controller;
• wherein the engine is selectively coupled via an engine disconnect clutch to an input member of the transmission;
• wherein the low-voltage electric machine is rotatably coupled to the input member of the transmission;
• and
• wherein the controller is operatively connected to the engine and the low-voltage electric machine, the controller including an instruction set executable to:
• operate the powertrain system in an electric vehicle (EV) mode with the engine in an OFF state and with the engine disconnect clutch in a deactivated state,
• monitor an output torque request,
• determine when the output torque request indicates a command for vehicle acceleration;
• and then:
• control the low-voltage electric machine to generate torque that is transferred to the input member of the transmission in response to the output torque request, and simultaneously crank and start the engine;
• operate the engine in a speed control mode to activate the engine disconnect clutch;
• and
• control the engine and the low-voltage electric machine to generate torque in response to the output torque request when the engine disconnect clutch is activated.

A method for controlling operation of a low-voltage hybrid powertrain system for a vehicle, wherein the low-voltage hybrid powertrain system includes an engine that is selectively coupled via an engine disconnect clutch to an input member of a transmission and wherein the low-voltage electric machine is rotatably coupled to the input member of the transmission, the method comprising:

• operating the powertrain system in an electric vehicle (EV) mode with the engine in an OFF state and with the engine disconnect clutch in a deactivated state;
• monitoring an output torque request,
• determining when the output torque request indicates a command for vehicle acceleration;
• and then:
• controlling the low-voltage electric machine to generate torque that is transferred to the input member of the transmission in response to the output torque request, and simultaneously cranking and starting the engine;
• operating the engine in a speed control mode to activate the engine disconnect clutch;
• and
• controlling the engine and the low-voltage electric machine to generate torque in response to the output torque request when the engine disconnect clutch is activated.