Research On Shifting Control Strategy For Pure Electric Vehicle

In order to improve the efficiency of motor and energy efficiency of battery, automatic transmissions of electric vehicles tend to be multi-gears, but too many gears will make the structure and control system of transmission become complicated, resulting in increased costs. Therefore it is common to use mechanical automatic transmission with two gears on the light pure electric vehicles. Pure electric vehicles are driven by motor, and the control performance of motor is better than that of the engine. So the clutch can be omitted by controlling the speed and torque of the motor to achieve synchronization shift. In this paper, one kind of AMT system without clutches on a pure electric vehicle was studied and analyzed, and a shift control strategy was developed. Its main contents are as follows:1) Parameters of the motor were matched and the scope of the transmission ratio was determined. With the optimization target of higher efficiency, the optimal gear ratios of the two speed transmission were obtained with the software of ISIGHT and MATLAB, using the dynamic programming method.2) The optimal mobility and fuel economy shift schedules for the pure electric vehicle were developed, and considering the dynamic and economic property the shift points were optimized to develop a comprehensive gear shift schedule with both better economy and dynamic property.3) The shifting process of AMT without clutches was analyzed. The simulation model of shifting process was established to carry the simulation analysis combined with the model of driver, drive motor, gearbox control unit and resistance.4) The control of the shifting process was studied. The mathematical model of the drive motor was established and the closed-loop switching for the drive motor’s speed and torque was analyzed. According to the requirements of the drive motor’s speed in the shifting process, fuzzy PID controller was used to control the speed. According to the problem of sudden changes of the torque in the shifting process, with the optimal control algorithm of LQG / LTR, optimal torque control curve was obtained based on the principle that no torque was output. According to the problem of the jerk and shift time contradiction in the torque recovery process of the drive motor, one kind of torque recovery strategy based on the driver’s intention was proposed to achieve the purpose of adjusting the torque’s recovery time and smoothness.