Investigation of energy efficient hydraulic hybrid propulsion system for automobiles

The hybrid method is effective for energy savings. This paper presents an energy efficient hydraulic hybrid propulsion system for automobiles. The system consists of hydraulic common pressure rail, hydraulic transformer and hydraulic pump or motor. The parameter design and propulsion characteristics of the hydraulic hybrid propulsion system were investigated. The simulated and tested results were proposed. Based on the definition of the hydraulic transformer normal power and normal flow, an effective parameter design method was given. The increase of the degree of freedom of the system makes the parameter design become more flexible and the proposed method for the parameter design is feasible. The system achieves a constant torque output at the low speed stage and a constant power output at the high speed stage. The ideal vehicle dynamic performance is guaranteed. The hydraulic transformer speed is closely related to the vehicle speed, which should be considered in the hydraulic transformer design. During the conversion from the driving mode to the regenerative braking mode, the hydraulic transformer speed and the hydraulic motor torque fluctuate inherently, which is unhelpful for the service life and reliability of the hydraulic components. It is aimed to provide an effective method for the system design.