Research On Pressure Balanced Water Hydraulic Proportional Valve With A Ball Core

The water hydraulic proportional valve is the core component of the water hydraulic proportional control system,and its dynamic response directly affects the control effect of the entire system.However,higher density,lower viscosity,poor lubricity and higher vaporization pressure of water have brought many challenges to the development and application of water proportional valves,which are shown in difficulty of sealing,higher friction,larger flow force and cavitation.These factors will cause serious non-linear interference to the closed-loop control system,influencing the closed-loop control performance of proportional valve.For the above technical difficulties,this paper proposes a water proportional valve with a ball core,performs a simulation analysis of flow field based on flow force,studies the key parameters affecting the response speed of the valve,and test a prototype.The main contents are as follows:(1)Considering the influences of water’s properties,this paper designs a water proportional pilot valve.The valve is a converging flow ball valve,solving the water seal problem.A drainage pressure balance structure and a lever amplification method are adopted,a voice coil motor drive and,which greatly reduces the requirements of driving force of the electro-mechanical converter and the volume of the entire valve.(2)The steady flow force of converging flow cone/ball valve was theoretically discussed,and the valve port flow field was simulated by CFD numerical calculation method.According to the mechanism of cavitation,the influence of back pressure on flow force is analyzed.The flow force of the water proportional valve is compensated by adjusting the outlet length of the valve seat and the slope of the push rod flange.The simulation results show that the flow force can be compensated to within 10 N under a working condition within the pressure of21 MPa and the flow rate of 140L/min.The non-linear interference by flow force of the proportional control of the valve is significantly reduced.(3)This paper establishes a physical simulation model of the water proportional valve based on AMESim and analyzes the control performance under Conventional PI control strategy to study the influences of proportional valve’s own parameters on its response performance.We study the response characteristics of the water proportional valve under the influence of the nonlinear characteristics of friction,analyzes the influence of key parameters on system response.By increasing the damping coefficient to improve the stability margin of the system and reducing the mass of mover to enhance the driving force’s ability to follow fast-changing signals,the system can be controlled by larger PI parameters,reducing the overshoot and improving the response..The simulation results show that after parameter optimization,the 100% signal step response of the water proportional valve can reach 40 ms.(4)A water proportional valve performance test bed is built and the dynamic performance test of a prototype is carried out.Experiments show that the 100% signal step response can reach 40-65 ms within a pressure of 4Mpa,but the performance decreases with the pressure increasing.By analyzing the PI control performance of the prototype under different pressure differences,a further performance improvement plan is proposed.