Steady-State Characteristics Study of a Power Split Hydraulic Transmission

The steady-state characteristics of a power split hydraulic transmission were carefully studied in this article. The hydraulic transmission is an alternative power split device for power split hydraulic hybrid drivetrain. It was built from a balanced vane pump, where an output shaft is added and coupled to its floating ring. The internal friction torques due to the relative motion between floating ring and vanes help to drive the output shaft. This improves the mechanical transfer efficiency from input to output shaft, making it more competitive than conventional hydrostatic transmission. The steady-state characteristics of the hydraulic transmission were investigated through both theoretical analysis and experimental studies. Mathematical models of the input and output shaft torques, and the outlet flow rate of the hydraulic transmission were developed. Studies show that the input and output shaft torques are not only dependent on outlet pressure, but also dependent on differential shaft speed. The outlet flow rate is proportional to the differential shaft speed. Finally, a hydro-mechanical transmission based on power split hydraulic transmission was introduced. The characteristics and system application of the hydro-mechanical transmission were given.