Pseudo-spectral optimisation of smooth shift control strategy for a two-speed transmission for electric vehicles

The shift quality of two-speed planetary of electric vehicle is closely related to the characteristics of shift oil pressure. In this paper, the smooth shift control strategy of electric vehicle with two-speed planetary transmission is studied. Firstly, the dynamic models of the two-speed planetary gear train, the shift oil pressure of the hydraulic system and the clutch friction torque are established. The analysis results show that there are three jerks during the shift process, of which the shift jerk during the clutch/brake engaging process is most obvious, thus a six-stage shift control scheme is proposed. The shift jerk degree is constructed as an optimal control problem during the clutch/brake engaging process, of which the performance function presents higher order nonlinearity. Then the optimal oil pressure trajectory is obtained by using the Radau pseudo-spectral method and the sliding mode variable structure controller of oil pressure is designed. The HIL simulation results show that by optimising the control, the degree of shift jerk is reduced by approximately 60% during the clutch/brake engaging process; and the shift oil pressure can track the optimal trajectory better and stably, the real-time and validity of the shift optimisation strategy are verified.