Coordinated Control of Downshift Powertrain of Combined Clutch Transmissions for Electric Vehicles

To improve the shift quality of electric vehicles equipped with two-gear automatic transmissions, the coordinated control of the combined clutch and the motor is proposed. The dynamic model of shift process is built up, the dynamic characteristics of each phase of downshift process are analyzed, and linear quadratic optimal control is used to optimize the shift process. As a result, the optimal trajectories of the motor torque and oil pressure of the combined clutch are obtained. Compared to the clutch control only, the simulation results indicate that shift quality is improved remarkably by employing the proposed coordinated control. Specifically, the shift jerk and sliding friction work are decreased by 43% and 44%, respectively, with accelerator pedal angle 50%. In contrast, the reduced percentages are 57% and 89% when accelerator pedal is not depressed.