System and method for engine start detection for hybrid vehicles

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.