Patent ID: 8565949

Claim:
A method of controlling a powertrain on a vehicle, wherein the powertrain has an engine, a transmission with an output member, and a motor, comprising: determining an amount of power currently available from a battery for tractive torque; wherein the amount of power currently available from the battery for tractive torque is an amount of power stored in the battery less an amount of power required to power at least some other electrically-powered vehicle components, and less an amount of power required to start the engine, the amount of power currently available from the battery for tractive torque thereby ensuring battery power reserve to start the engine; determining an output torque limit at the output member when torque is provided only by the motor, and an amount of power required to provide the output torque limit based on stored test data and current operating conditions; calculating a power-based maximum output torque that ensures a reserve of power required to start the engine by multiplying the amount of power determined to be currently available from the battery for tractive torque by a ratio of the output torque limit of the motor to the amount of power required to provide the output torque limit; and selecting the lesser of the power-based maximum output torque and the output torque limit as the maximum operating output torque of the powertrain to reduce torque sag when the engine is started.