Gear downshift control of inverse-automatic mechanical transmission of electric vehicle

Abstract

In order to improve the driving dynamics and riding comfort of pure electric vehicles, taking a two-speed I-AMT (Inverse-Automatic Mechanical Transmission) with rear friction clutch as the research object, a gear shift strategy, which consists of the open-loop control of the clutch position control and the closed-loop control of the drive motor speed control, is proposed. Considering the inherent time-delay and external disturbances within the motor speed adjustment system, a two DOF (degree-of-freedom) Smith predictor with feedforward input is designed to track the target speed of the drive motor. The feedforward input is used to eliminate the influence of clutch sliding friction on the motor speed control, while the feedback speed tracking controller is applied to realize the speed tracking performance with the existence of time-delay and the external disturbance. In order to verify the effectiveness of the gear shift control strategy and the accuracy of the two DOF Smith controller with feedforward control, simulation results comparison is firstly carried out to illustrate the effectiveness of the control scheme. Then, a light pure electric vehicle equipped with I-AMT was used for downshift experiments under large throttle, which is the most difficult working scenario to control the transmission. The experimental results show that the two DOF Smith controller can eliminate the influence of time-delay on the closed-loop control, and the proposed whole gear shift control strategy can limit the clutch slippage time within 1.5 s, resulting in a smaller shift jerk, thus guarantee the driving dynamics and riding comfort simultaneously.