Engine Crank Stop Position Control to Reduce Starting Vibration of a Parallel Hybrid Vehicle

Engine off control is conducted on parallel hybrid vehicles in order to reduce fuel consumption. It is efficient in terms of fuel economy, however, noise and vibration is generated on engine cranking and transferred through engine mount on every mode transition from EV to HEV. Engine crank position control has been studied in this paper in order to reduce vibration generated when next cranking starts. System modeling of an architecture composed of an engine, P1 and P2 motors has been conducted. According to the prior studies, there exists correlation between crank vibration level and the crank angle. Thus a method to locate pistons on a specific crank angle which results in a local minimum of vibration magnitude could be considered. The P1 motor facilitates this crank position control when engine turns off, for its location directly mounted on a crankshaft allows the system model to obtain more precise crank position estimation and improved linearity in torque control as well. For the sake of robustness, a position-speed controller considering active damping has been designed, and verified by simulations on frequency and time domains analyses. The controller suggested in this paper shows better response to load disturbance compared to conventional P-PI position-speed controller, and is able to operate robustly on fluctuating static and dynamic friction of an engine. Vehicle tests have been conducted to prove the control performance, which resulted in 50% reduction of vibration magnitude in average.