Energy efficiency of hydraulic regenerative braking for an automobile hydraulic hybrid propulsion method

A hydraulic hybrid propulsion method with the hydraulic common pressure rail for automobiles is proposed. The hydraulic regenerative braking characteristics of the hydraulic hybrid propulsion method are investigated with simulation and experiment. The dynamic responses of the system in the hydraulic regenerative braking mode are studied. The results indicate that there is an obvious correlation between the hydraulic motor speed and the hydraulic transformer speed in both driving mode and hydraulic regenerative braking mode. In the hydraulic regenerative braking mode, a greater hydraulic transformer controlled angle makes a higher braking torque applied by the hydraulic motor. The hydraulic accumulator pressure is positively correlated with the hydraulic transformer controlled angle. The energy losses include the rolling resistance energy loss, the air resistance energy loss and the hydraulic energy loss. The hydraulic energy loss is in the majority. The proportions of the rolling resistance energy loss and the air resistance energy loss become higher when the average vehicle speed becomes larger during hydraulic regenerative braking.