Investigation On Axial Vibration Characteristics Of Pilot-stage Poppet Valve Core

In the hydraulic system,poppet valve is a commonly valve construction,mainly composed of poppet,valve seat and spring.When used as pressure regulating valve,it can be used as direct-acting pressure valve or as pilot stage of a pilot-operated pressure valve to control the motion of the main poppet.For the pilot poppet valve,its own damping coefficient is small and connected to the main circuit,the flow pulsation in the system and the out-of-roundness of the valve seat cause uneven force on the poppet,which often leads to undesired working conditions such as axial vibration and lateral oscillation of the poppet,thereby affecting the pressure regulation accuracy and working stability of the entire valve.In severe cases,the system pressure may fluctuate drastically,affect the function of the entire hydraulic system,it may even cause an accident,which seriously reduces the stability,reliability and safety of the hydraulic system.This subject adopts the research method combining theoretical analysis,experiment and simulation calculation.Studied the dynamic characteristics of the opening and adjusting process of the pilot-level poppet valve and the axial equal-amplitude vibration phenomenon of the poppet.The main contents are as follows:Firstly,combining the mechanical balance equation of the poppet,the continuity equation and the valve flow equation.The dynamic performance of the pilot-stage poppet valves with and without the orifice structure was analyzed by the transfer function method.It is concluded that adding the orifice can effectively improve the smoothness for the opening process of the poppet valve.At the same time,under the premise of not affecting the static characteristics of the poppet valve,properly reducing the half cone angle of the poppet can improve the smoothness of the opening process of the poppet valve.Secondly,according to the poppet force balance equation,a User-Defined-Function(UDF)program that can be loaded into the solver is developed by C language,which can improve the accuracy of the simulation results.Using Fluent dynamic mesh technology,under the control of UDF,the pilot-stage poppet opening adjustment process of different structures was simulated by step signal excitation.Comparing the change of the valve opening degree of each calculation model during the opening adjustment process.It is concluded that adding the orifice and appropriately reducing the half cone angle of the poppet valve can reduce the valve opening degree overshoot,shorten the transition process time,and raise the poppet valve opening process smoothness.Furthermore,the flow in the valve after reaching the steady state is analyzed,and the influence of the change of the structural parameters on the dynamic characteristics of the poppet valve is further explained.Thirdly,the axial vibration characteristics of the valve core during the opening process of the pilot-stage cone valve were studied by experimental methods: Through the experimental data,it can be concluded that after adding the orifice,the valve opening overshoot can be significantly reduced,and the transition process time can be shortened.Through the spectrum analysis method,the vibration of the poppet during the opening process is caused by the coupling resonance between the poppet valve and the inlet piping system.Fourth,for the axial equal amplitude vibration phenomenon of the poppet which occurs during the experiment.When the poppet has an equal amplitude vibration phenomenon during the working process,the flow pulsation flowing through the poppet valve is in a sinusoidal form.The sinusoidal flow condition is used to simulate the pilot stage poppet valve.By analyzing the force on the surface of the poppet valve body of each calculation model,it was found that the oil viscous force played a damping role during the movement of the poppet.This subject studied the dynamic characteristics of the pilot-stage poppet valve opening adjustment process and the axial equal-vibration phenomenon of the poppet.Has reference significance for the optimization of pilot poppet valve and stability study of the dynamic performance of the poppet valve.