Regenerative braking algorithm for the electric vehicle with a seamless two-speed transmission

Abstract

Better energy efficiency can be acquired by an appropriate shift operation during the regenerative braking process. In this work, an electric vehicle equipped with a two-speed automated transmission was used as the target vehicle. The transmission consists of two-stage planetary gear sets, a helical gear set, and two brakes. A hierarchical algorithm is presented for the electric vehicle. The upper-level algorithm was synthesized to assign braking force among regenerative braking, friction braking, front axle braking, and rear axle braking. Based on the motor external characteristic and ECE-R13 regulations, the work designed the dynamic distribution strategy for maximum use of regenerative braking. In the medium-level algorithm, the motor speed, efficiency characteristics, and assigned regenerative braking torque from upper-level algorithm were used to analyze the optimal shift points for improving regenerative efficiency. Then, a shift points table was drawn. In the lower-level algorithm, the linear control for the transmission was given to ensure seamless and smooth shifting. Finally, hardware-in-loop simulations were carried out. The results show that the proposed algorithm can improve performance in energy efficiency in the experimental braking events.