Research On The Performance Of Cartridge Electro-hydraulic Proportional Flow Valve Controlled By Pilot Stage

As the key element in the hydraulic systems, which is widely applied in the heavy machine equipment, cartridge electro-hydraulic proportional flow valve can control the flow, pressure and other parameters continuously and proportionally according to the input control signal, which has the advantages such as large flow capacity, simple structure, low cost and so on. However, in order to reduce the influence of load pressure variety on the flow, in existing technology, a differential pressure compensator or a cartridge type flow sensor should be added on the basis of the proportional throttle valve, which will reduce the valve flow capacity and increase the system power loss and heating; the flow only can be indirectly controlled by changing valve opening area in large flow occasion and the control precision is low for the influence of load variation; the controllability is bad and dynamic response is slow when working pressure is low; the structure of three stage larger size valve is complex. So a principle that a small displacement hydraulic pump/motor driven by a low power servo-motor as pilot stage integrates with the flow amplifying characteristic of hydraulic transistor Valvistor valve to construct a new electro-hydraulic proportional flow valve, which would provide a new method for the large flow proportional control.Firstly, the working principle of the electro-hydraulic proportional flow valve was analyzed, the static and dynamic mathematic model was established, and the parameters influencing the static and dynamic characteristics was analyzed theoretically. Then, the co-simulation model of new principle valve was established in SimulationX, the static and dynamic characteristics of the valve and the influencing factors were simulated.The research results show that the static and dynamic performance of new principle valve is good, the valve flow and displacement of new principle valve is proportional to the pilot pump/motor rotational speed; for the existing of the feedback throttle slot pre-opening, the flow will decrease as the increase of differential pressure, the constant flow performance is bad. The dynamic response relates with the differential pressure, the larger the differential pressure is, the faster the response will be. The main valve core must have feedback throttle slot pre-opening, but the feedback throttle slot pre-opening will cause dead zone of main valve, and the larger the feedback throttle is, the larger the dead zone will become. The increasing of feedback throttle slot width wc will fasten the valve response speed, but will cause the increase of valve dead zone; the smaller the damping holes are, the faster the main valve respond speed will be; it’s known from the theoretical analysis that the main valve stability will be reduced when the differential pressure is large and the pilot flow is small.The leakage of pilot pump/motor has little influence on the dynamic characteristics of new principle valve and has large influence on the steady-state characteristics; the flow and displacement of diverged type valve will increase along with the increase of the internal leakage of main valve, the flow and displacement of converged type valve will decrease along with the increase of the internal leakage of main valve.The constant flow performance of new principle valve with triangle port is worse, the variety of flow along with pilot pump/motor rotational speed is nonlinear, which is not appropriate to the linear control system; the flow performance of new principle valve with rectangle port is as same as that of new principle valve with cone port, the flow area of rectangle port is proportional to the main valve displacement, the linearity of flow variety along with pilot pump/motor is good.The pilot pump/motor has flow pulsation when it works, in view of the pilot pump flow pulsation frequency is much higher than the valve natural frequency, and the research shows that the influence of flow pulsation of pilot pump on valve flow performance is very little. If a short-time high speed signal is given to servo-motor during valve opening stage and a short-time reversal signal to servo-motor during valve closing stage, the valve step response performance can be improved. The method of pressure differential pilot pump rotational speed compensation can not only improve the constant flow characteristic of the main valve and the flow control accuracy, but can also guarantee good dynamic performance and the over shoot of the flow of main valve is small under the main valve load step response.