Compound optimal control for shift processes of a two-speed automatic mechanical transmission in electric vehicles

Public interest in pure electric vehicles equipped with two-speed automatic mechanical transmission is increasing because of not only widened high-efficiency operation zone but also reduced speed range and cost of electric drive system. In this paper, transient dynamic behaviors of an e-drive passenger car including clutch-free two-speed automatic mechanical transmission are analyzed during up and down shifts. Bench tests for the proposed electric driveline are conducted, by which the dynamic model and the shift control strategy are validated. In experiments, severe jerking phenomena are observed when the drive motor torque sharply decreases before the separation with current gear meanwhile fast increases after the engagement with target one. For alleviation of the torsional shocks, feed-forward control in combination with optimal torque feedback control is developed for the drive motor according to torque estimation of the half shaft using extended Kalman filtering method. Meanwhile, a sliding mode control is employed for precise positioning of the shift fork for the transmission. By comparisons of the simulation and test results, it is demonstrated that the proposed control strategy reduces the jerking intensity of driveline as well as the shift period effectively in shift process.