Analysis and control of engine starting process based on a novel single-motor power-reflux hybrid electric vehicle

In this study, a novel single-motor hybrid electric vehicle (HEV) equipped with a power-reflux coupling transmission system is proposed for improving the fuel economy of HEVs. The structural characteristics and operating principles of the proposed HEV were analyzed, and a detailed driveline dynamic model was established. Then, a rule-based energy management strategy regulated by the optimal comprehensive energy economy was adopted to divide its working mode regions. As a result, the engine starting process in vehicle motion may involve not only a driving mode switch but also a speed regulation mode conversion, resulting in noticeable jerks and an unpleasant driving sensation. To address this problem, this study presents a multilevel torque coordination method that synergizes the transient intervention of torques from two power sources and clutches and changes the transmission ratio. Compared with the simulation results of the dynamic performance of a vehicle under conventional control strategy, the results of the proposed control strategy demonstrate a better control effect, which can ensure the smoothness of power transmission during engine startup to effectively minimize the impact on the system and improve the ride comfort.