An Investigation of Inverse-Automatic Mechanical Transmission of EV Using Gear Downshift Approach

Abstract

Utilizing a two-speed I-AMT (Inverse-Automatic Mechanical Transmission) with a rear friction clutch as the research object, a gear shift strategy was developed to enhance the driving dynamics and comfort of electrical vehicles (EVs). This strategy combines the open-loop clutch position approach with the closed-loop drivetrain approach. proposal for regulating motor velocity. A two-degree-of-freedom (DOF) Smith predictor with feedforward input is developed to monitor the desired speed of the drive motor despite the system's intrinsic time delay and external disturbances. A feedback speed tracking approach is utilized to realize the speed tracking performance with the existence of time delay and external disturbance, while feedforward input is employed to remove the influence of clutch sliding friction on the speed approach of the motor. To ensure the effectiveness of the gear shift approach strategy and the precision of the two DOF Smith approach with the feedforward approach, a comparison of simulation results is performed first. Then, the most challenging working scenario to approach the transmission, downshifting at high throttle, was tested using an I-AMT-equipped lightweight pure electric vehicle. The results of the experiments show that the two-degree-of-freedom (DOF) Smith approach can remove the time-delay effect from the closed-loop approach and that the proposed whole gear shift approach strategy can limit the clutch slippage time to less than 1.5 s, resulting in a smaller shift jerk and ensuring both driving dynamics and riding comfort.