Engine start-up optimal control for a compound power-split hybrid powertrain

Abstract Engine start-up is the key for the control of mode transition from electric drive mode to electronic-Continuously Variable Transmission (e-CVT) mode for a compound power-split hybrid electric vehicle (HEV). With the engine shaft directly connected to the powertrain through a torsional damper spring (TDS), the engine ripple torque (ERT) before ignition is amplified by the powertrain and transmitted to the wheel, which has a significant impact on the vehicle. To improve the ride comfort of the mode transition process, an engine start-up control strategy is proposed. First, the ERT model and the dynamic model of power-split powertrain were built, and the mode transition process was analyzed. Second, an optimal crank track of engine speed was designed based on the dynamic programming aiming at ride comfort. Third, the engine reference acceleration curve was calculated according to the optimal speed track, and an optimal engine start-up control strategy was proposed. Finally, through simulations of the dynamic programming the influence factors for engine start-up were examined, and the experiment results indicate that the proposed engine start-up optimal control can effectively improve the ride comfort during mode transition.