Research On Mechanical-Hydraulic Coupling Dynamics Of Opposing Cylinder Controlled By Servo Valve Considering Oil Dynamic Stiffness

The hydraulic opposing cylinder controlled by servo valve is a typical electro-hydraulic load simulator.It has many advantages such as large power-to-weight ratio,wide frequency bandwidth,good stability and high reliability.It has been widely used in aviation,aerospace,navigation and construction machinery,etc.field.The current rapid development of science and technology has put forward higher requirements for the dynamic performance of the electro-hydraulic load simulator.At present,there are two main factors restricting the further improvement of the performance of the electro-hydraulic load simulator:(1)The large compressibility of the working medium,the small bulk modulus,low stiffness,and obvious mechanical nonlinear characteristics;(2)The change of the flow and pressure of the fluid causes the movement and deformation of the load cylinder,similarly,the movement and deformation of the load cylinder causes the change of the fluid state,these two factors influence and restrict each other,so there is a mechanical-hydraulic coupling characteristic in the system.Low stiffness and mechanical-hydraulic coupling characteristics cause the electro-hydraulic load simulation hydraulic system to have large response deviations,system delay,working dead zone,nonlinear vibration,etc.,especially when the load frequency changes in a wide range and runs for a long time,the excitation frequency of the system tends to be closed to its natural frequency and resonance occurs,which seriously affects the normal operation of the system.In view of this,this article takes the mechanical-hydraulic coupling system of the hydraulic opposing cylinder controlled by servo valve as the research object,and studies its modal characteristics,vibration laws and other dynamic issues.Analysis of dynamic bulk modulus of oil.Using the lumped parameter method,based on the polytropic process of gas,introducing thermodynamic parameters,combined with Henry’s law in the form of five-order interpolation,a dynamic bulk modulus model of oil is established.The influence law of the initial mass content of gas,pressure change period and temperature on the dynamic bulk modulus of oil is analyzed,and the correctness of the theoretical model is verified by comparison with experimental data.Free vibration analysis of the system of the hydraulic opposing cylinder controlled by servo valve.Based on the oil dynamic bulk modulus model,the free vibration dynamic model and equations are established.The modal analysis of the system has been completed,and the influence law of the main parameters of the system on the natural frequency and the sensitivity change law of the natural frequency to the main parameters are determined.Forced vibration analysis of the system of the hydraulic opposing cylinder controlled by servo valve.Introducing the internal damping and pulsating excitation force of the system,the dynamic model and equation of the forced vibration of the system are established.The forced vibration response analysis of the system when the excitation frequency is close to the steady-state value of the natural frequency is completed.Parametric vibration analysis of the system of the hydraulic opposing cylinder controlled by servo valve.Considering that the oil stiffness has the characteristics of simple harmonic pulsation under the pressure fluctuation of the pump,the parameter vibration dynamic equation of the system is deduced.Based on the multi-scale method,the theoretical analytical solutions of the main resonance and the combined resonance of the system are determined,and the parametric vibration response of the system is analyzed.Experimental research on dynamics of the system of the hydraulic opposing cylinder controlled by servo valve.A vibration signal test system is developed based on Labview,and the experimental modal frequency of the system is tested.The experimental modal frequency is compared with the theoretical modal frequency to verify the correctness of the dynamic model of the system of the hydraulic opposing cylinder controlled by servo valve.