Dynamics of a hydraulic-transformer-controlled hydraulic motor system for automobiles

This paper presents a hydraulic-transformer-controlled hydraulic motor system for automobiles. The system consists of a hydraulic common pressure rail, a hydraulic transformer and a hydraulic pump-motor. The inherent dynamic characteristics of the system are investigated by an analytical method. The results are validated by simulations and tests. Because of the symmetrical mechanical structure of the valve plate in the hydraulic transformer, the system has both minimum-phase characteristics and non-minimum-phase system characteristics. The negative response characteristics of the system appear if the controlled angle is larger than 30°. The non-minimum phase of the system is unavoidable and should be considered in the controller design of the system. The stiffness of the system is also lower than those of the pump-controlled and valve-controlled systems. The stiffness changes with the variation in the controlled angle and becomes higher with increasing controlled angle.