Patent ID: 7350602

Claim:
A method for operating a hybrid vehicle having a primary power generating system and a secondary power generating system coupled via a power transmission assembly for delivery of tractive force for the vehicle, the method comprising: determining acceleration of input speed to the power transmission assembly when the primary power generating system is deactivated; and inferring activation of the primary power generating system based at least in part on the acceleration of the power transmission assembly, wherein the primary power generating system comprises an internal combustion engine, the secondary power generating system comprises an electric machine that performs as a motor in one mode of operation, and performs as a generator in another mode of operation: operating the hybrid vehicle comprises engine start detection and activation of the primary power generating system comprises engine start; determining acceleration of input speed to the power transmission assembly comprises determining a transmission input speed, filtering the transmission input speed, determining a derivative of the filtered transmission input speed, and filtering the derivative of the filtered transmission input speed; and inferring activation of the primary power generating system comprises determining an engine speed and a transmission input torque; generating a first trigger signal when the filtered derivative of the filtered transmission input speed is greater than a first predetermined acceleration for a first predetermined time; generating a second trigger signal when the engine speed is greater than a second predetermined speed; generating a third trigger signal when the transmission input torque is greater than a predetermined torque level; and asserting an engine start signal when the first, second, and third trigger signals are substantially simultaneously generated.