Characteristic analysis of valve-pump parallel connection in a variable frequency hydraulic system

摘要

To solve the problems existing in variable frequency hydraulic system (VFHS), such as bad low speed stability, low response and bad speed smooth at start-up and stop, a valve-pump parallel connection variable frequency hydraulic system (V-PVFHS) is proposed, in which a flow valve is parallel to a variable speed pump to form a bypass leakage path. Mathematical model and simulation model are constructed. Results indicate that the throttle governing has small contribution to response speed because the introduction of valve control cannot improve hydraulic natural frequency; the valve low-pressure coefficient has significant influence on damping ratio and speed stiffness; compared with V-PVFHS using a throttle valve, that using a speed control valve is similar to VFHS, and is less subject to variation with valve stroke with more constant damping ratios and harder stiffness, and should be a preferable scheme for V-PVFHS; the bypass throttle governing contributes lo improve low speed stability, speed smooth and reduction in pressure impact at start-up and stop; the system flow is unlimited since the throttle circuit is placed in branch with small leakages. Therefore, V-PVFHS has great potential in applications requiring lower speed, larger power and higher efficient.