Method and apparatus for executing engine autostart in a powertrain system employing multiple torque generating devices

A method for controlling a powertrain system for a vehicle that includes an internal combustion engine and an electric machine configured to generate propulsion torque and electric power storable on an energy storage device, wherein a maximum torque capability of the electric machine is greater than a maximum torque capability of the internal combustion engine, the method comprising:

• requesting execution of an engine autostart operation during operation in a charge depletion mode;
• evaluating, via a controller, whether a driveline torque sag will occur during the execution of the engine autostart operation prior to the engine autostart operation;
• forgoing via the controller the execution of the engine autostart operation when the driveline torque sag will occur if the engine autostart operation is executed unless a superseding condition compels the execution of the engine autostart operation;
• and
• executing via the controller the engine autostart operation upon occurrence of the superseding condition;
• wherein the superseding condition is associated with a state of charge (SOC) of the energy storage device;
• and
• wherein the driveline torque sag comprises a decrease in the propulsion torque without a corresponding decrease in the driver torque request.

A powertrain system, comprising:

• an internal combustion engine and an electric machine mechanically coupled to a transmission to transfer torque to a driveline;
• an energy storage device electrically connected to the electric machine;
• and
• a controller including a control routine in response to a, the control routine including executable code operative to:
• request execution of an engine autostart operation during powertrain operation in a charge depletion mode;
• evaluate whether a driveline torque sag will occur during execution of the engine autostart operation prior to the engine autostart operation;
• forgo the execution of the engine autostart operation when the driveline torque sag will occur during execution of the engine autostart operation unless a superseding condition compels the execution of the engine autostart operation;
• and
• execute the engine autostart operation upon occurrence of the superseding condition;
• wherein the superseding condition is associated with a state of charge (SOC) of the energy storage device;
• and
• wherein the driveline torque sag comprises a decrease in the propulsion torque without a corresponding decrease in the driver torque request.