Patent ID: 8140204

Claim:
An energy management method for a plug-in hybrid electric vehicle powertrain having an engine, at least one electric machine, a battery, and a power transmission mechanism for delivering engine power and battery power to vehicle traction wheels, the method comprising: monitoring battery state-of-charge; controlling the battery state-of-charge whereby battery power discharge is below a power discharge limit; monitoring driver demand for power at the vehicle traction wheels; maintaining the engine in an engine-off state to achieve an all-electric drive when battery state-of-charge is greater than a predetermined battery charge threshold and driver demand for power is less than a minimum calibrated engine power threshold level for an engine start below which engine thermal efficiency becomes low; controlling the engine to turn the engine on when the driver demand for power is equal to or greater than the minimum calibrated engine power threshold level; and increasing engine power when a driver demand for power is greater than a sum of minimum engine power and the power discharge limit whereby the engine operates at an engine power level greater than the minimum engine power.