| High-end electro-hydraulic servo valve(EHSV)is at the core of the industrial chain and value chain link,involving electrical,magnetic,mechanical,fluid,and many other core key technologies,the development of EHSV in China has always been subject to strict technical blockades abroad.With the needs of China’s economic development and national security,the requirement of autonomous control of EHSV has been improved.Deflector jet servo valve(DJSV)is a core control element widely used in aerospace electro-hydraulic servo system,the service performance is directly related to the reliability of the equipment.Because the jet mechanism and flow field law in the pilot stage are not clear,the morphology change analysis method of parts is lacking,result in the evolution law of the servo valve in service cannot be quantitatively analyzed.Based on this,this paper systematically studies the core basic theory of the pilot stage of DJSV,the key issues related to the morphology change of key components and the evolution of the servo valve performance,including:(1)According to the three dimensional expansion characteristics of the jet in the pilot stage,a mathematical model of pilot stage flow field is established based on the three dimensional turbulent jet.The working mechanism and fluid energy transfer process of the pilot stage of the DJSV are revealed,and the calculation method of the static characteristics such as valve coefficients of the pilot stage is obtained and verified by experiments.The results show that the pressure gain of the pilot stage can be improved by increasing the width of jet nozzle,increasing the width of guide groove outlet and decreasing the width of wedge appropriately,while the flow gain can be improved by increasing the thickness of jet-pan and the width of jet nozzle.(2)For the pressures asymmetry of pilot stage jet-pan component and high frequency noise of DJSV,the relationship between the shape factors of the jet-pan and the pressure characteristics are studied by using multiple linear regression analysis.It is found that the width of the wedge,the symmetry of the wedge,the width of the jet nozzle and the thickness of the jet-pan have obvious effects on the recovery pressure within the tolerance range,and the symmetry of the wedge is the most critical factor affecting the pressure difference between the two receiving cavities.The dynamic flow field under different deflector positions are studied.It is found that the periodic variation of the vortex in the receiving cavity which casued by the interaction between the turbulent vortex of the secondary jet flow and the jet-pan wedge is the root of the noise.When the deflector position is small,the frequency of the vortex is close to the natural frequency of the armature component,and it is easy to cause the resonance of the armature component and lead to noise.(3)The characteristics and quantitative calculation methods of the adhesive wear of feedback ball in the feedback component,the erosion wear of wedge and slide valve port are studied and verified by experiments.The calculation method of ball wear depth is obtained based on Archard adhesive wear theory,it is found that the ball in hole assembly form can avoid the spool rotation and reduce the wear of the ball effectively and high temperature environment expose the feedback ball to additional contact pressure and exacerbate wear.The calculation method of wedge erosion height is established based on average erosion rate,with the increase of erosion height,the average erosion rate of the wedge decreases gradually due to the increase of erosion area,and the increase of oil temperature enhance the inertia effect of particles and make them more likely to hit the wedge,and shorten the failure time of the wedge rapidly.Considering the influence of the morphology evolution of the valve port and the influence of particle size on the erosion process,the calculation method of single valve port erosion fillet and erosion morphology of four-side slide valve are established.It is found that the valve spool displacement has a significant impact on the erosion when the width of the valve port is small relative to the particle size,when the load of the slide valve is unsymmetrical,the erosion fillets of the four valve ports are not completely consistent,which will lead to null bias of the slide valve.(4)In view of the performance change of EHSV caused by screw creep,taking torque motor as an example,considering the elastic interaction between fastening screws,the variation rule of air gap size and performance of torque motor with service time are obtained based on the age-hardening creep model.It is found that the creep behavior of the four screws of the torque motor is relatively independent.The creep of the screws leads to the increase of the upper air gap of the torque motor and the decrease of the lower air gap,but the change of the air gap is less than 1 μm due to the large stiffness of the torque motor parts.The change of median magnetic spring stiffness and electromagnetic torque coefficient of torque motor due to screw creep is less than 0.3%,which is far less than the influence of screw preload and air gap error on torque motor performance.(5)On the basis of the morphology evolution law of the components,the nonlinear mathematical model of DJSV is established considering the factors of overlap,clearance,erosion fillet,and clearance between spool and feedback ball.The simulation platform for structural parameters and performance evolution of servo valve is created based on MATLAB GUI.The performance of positive overlap DJSV in the servo mechanism with constant load is analyzed.It is found that the null pressure gain and null flow gain of the servo valve will increase significantly due to slight port erosion and feedback ball wear in the early stage,while the null pressure gain will decrease gradually due to the increase of port leakage in the later.,and the null bias is related to the load of the servo mechanism.Asymmetrical loads will cause the servo valve to produce null bias.With DJSV as the breakthrough point,the core basic theory of pilot stage and the evolution analysis method of servo valve morphology and performance are studied in depth in this study.The results obtained are tested and applied in the development and analysis of DJSV,and provide theoretical support for the optimization and collaborative parts design of DJSV as well as the shape and performance control measures in the whole life cycle,which is helpful to improve the service performance and working reliability of DJSV,and the result also has reference value for jet pipe servo valves. |
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