Regenerative braking algorithm for a hybrid electric vehicle with CVT ratio control

Abstract

A regenerative braking algorithm is proposed for a hybrid electric vehicle with a continuously variable transmission (CVT) to make the maximum use of the regenerative braking energy. In the regenerative braking algorithm, the regenerative torque is determined by considering the motor capacity, battery state of charge (SOC), and vehicle velocity. The regenerative braking force is calculated from the brake control unit by comparing the demanded brake torque and the motor torque available. The wheel pressure is reduced by the amount of the regenerative braking force and is supplied from the hydraulic brake module. In addition, the CVT speed ratio control algorithm is suggested during braking for optimal motor operation. The optimal operation line is proposed to operate the motor in the most efficient region while keeping the motor speed as low as possible by considering engine noise and friction. It is found from the experiments that the regenerative braking algorithm with CVT ratio control offers an improved battery SOC, which provides increased recuperation energy by 8 per cent for the federal urban driving schedule compared with that of the conventional CVT ratio control.