Patent ID: 7967091

Claim:
A method for controlling a hybrid electric vehicle powertrain having an engine, at least one motor-generator, a multiple-ratio transmission defining parallel power flow paths to vehicle traction wheels and a controller for effecting a transition from motor-generator drive operation to engine drive operation, the method comprising the steps of: determining whether the powertrain is operating in motor-generator drive operation with the engine off; determining whether a desired power is less than a calibrated engine-on power threshold value; calculating a predicted time to start the engine in advance of a transmission ratio shift; calculating a predicted time to shift the transmission from one ratio to another ratio; comparing the predicted time to shift the transmission to the predicted time to start the engine; shifting the transmission if the predicted time to shift the transmission is not greater than the predicted time to start the engine; and starting the engine first if the predicted time to shift the transmission is greater than the predicted time to start the engine, a time separation between an engine start and a transmission shift effecting a smooth transition from motor-generator drive operation to engine drive operation.