Patent ID: 7210546

Claim:
A method for controlling a hybrid electric vehicle powertrain having an internal combustion engine, a battery, an electric generator, an electric motor and transmission gearing; the battery, the motor and the generator being electrically coupled to define an electrical driving power source; the engine defining a mechanical power source; the generator being drivably connected to a first element of the gearing and the engine being drivably connected to a second element of the gearing to define separate power flow paths through the gearing to vehicle traction wheels; the method comprising the steps of: determining desired input torque, vehicle speed and the state-of-charge of the battery; determining whether the state-of-charge is less than a predetermined high value above which charging of the battery is not allowable; determining whether the state-of-charge is greater than a predetermined target value; operating the powertrain using both the engine and the electrical power source when the state-of-charge is less than the high value and less than the target value; and operating the powertrain using solely the motor, the generator and the battery as a power source with the engine off when the state-of-charge is greater than the high value; operating the powertrain using both the engine and the electrical power source when the vehicle speed is greater than a maximum value and the state-of-charge is less than the target value; and using solely the engine, the battery and the motor as a power source when the state-of-charge is greater than the target value; the generator being braked to condition the powertrain for operation with the engine, the battery and the motor as a power source.