Regenerative Braking Algorithm for a HEV with CVT Ratio Control during Deceleration

A regenerative braking algorithm is proposed to make maximum use of regenerative brake for improvement of fuel consumption. In the regenerative braking algorithm, the regenerative torque is determined by considering the motor capacity, battery SOC and vehicle velocity. The regenerative braking force is calculated from the brake control unit by comparing the demanded brake force(torque) and the motor torque available. The wheel pressure that is reduced by the amount of the regenerative braking force is supplied form the hydraulic brake module. In addition, CVT speed ratio control algorithm is suggested during the braking. The optimal operation line is obtained to operate the motor in the most efficient region. It is found from the simulation that the regenerative braking algorithm including the CVT ratio control provides improved fuel economy as much as 4 percent for federal urban driving schedule.