A four-step control algorithm and downshift schedule of a seamless shift transmission equipped on electric vehicles during the regenerative braking process

Abstract

To improve dynamic performance and energy efficiency of electric vehicles, various methods are adopted, one of which is to equip each electric vehicle with a seamless shift transmission that can maintain comfort. This paper focuses on when to downshift during the regenerative braking process and designs an algorithm to decrease the torque interrupt and reduce the dependence on the changes of friction braking during downshift. First, the author shows a seamless shift transmission structure and builds the dynamic model of the transmission, motor model, vehicle model and so on. Next, a four-step control algorithm of downshifting is proposed, upon which a downshift schedule is created. Finally, on the basis of the above-mentioned methods, a simulation model and a Hardware-in-the-loop test platform are established. The results of the simulation and the Hardware-in-the-loop test show that the algorithm not only maintains the accuracy of control and seamless shift, but also has strong robustness. In addition, the shift schedule also satisfies the needs of dynamic performance, energy efficiency, and comfort.