| Electro-hydraulic servo valve is the precise key component of hydraulic servo system,which is widely used in special equipment,aerospace,ships and other important fields.As its power stage,the hydraulic servo spool valve usually works near zero position,generally the opening is 0～0.5mm.This servo-type hydraulic valve orifice is easily eroded by solid particles sticked by high-speed liquid flow,which leads to collapse and an increase in the leakage of the servo valve,changes in zero offset or even failure.At present,there is still a lack of regular understanding of the internal relationship between the performance inconsistency,performance degradation and micromorphology of servo spool va lve.In view of the above problems,this paper found and established the concept of the “variance” parameter of the spool valve working edge through the high-speed visualization of the particle motion,the simulation of particle erosion,the analysis of th e erosion micromorphology and the performance experiment of the servo valve,and the influence mechanism of fillet variance on servo valve performance and erosion degradation were revealed.The effect of variance on servo valve performance and erosion degradation provided basic theoretical guidance and new ideas for performance prediction,quality evaluation,design and manufacture of servo valve and high performance proportional valve.The main work s and conclusions are as follows:(1)Characteristic of solid particles in oil medium of typical hydraulic servo system.The particle size distribution and particle morphology of solid particles in10 oil samples were studied using a cleanliness analysis system.The research showed that the main distribution range of particle size in the hydraulic servo system was 5～50μm,and the number of 5～15μm solid particles was the largest,up to90.89%;the shape of solid particles was close to ellipsoid.(2)Particle motion in valve orifice and simulation research on e rosion factors.The particle motion visualization experiment and the numerical calculation results of solid-liquid two-phase flow showed that the high-speed collision and scraping with the working edge during the movement of the particles were the main forms for erosion.The working edge erosion rate and "Erosion rate variance" increased with the increasement of the pressure difference at the valve orifice,the particle concentration and the oil viscosity,and decrease d with the increasement of particle size,density and shape factor.The frequency of contact between the particles and the working edge increase d greatly under small opening,resulting in a significant increasement in the erosion rate of the working edge.(3)Erosion micro-morphological characteristics of the valve orifice working edge and the causes.The erosion morphology of the spool working edge was mainly characterized by surface peeling,gaps and grooves by the optical non-contact precision measurement.The contou r of the working edge was approximately rounded,and the radius of the rounded corner change d sharply along the circumferential direction and the test spool fillet radius range was 5.9558～89.1091μm.The concept of the rounded corner variance of working edge was defined.Explicit dynamic calculations showed that the impact of a single solid particle on the working edge produced high stress at the collision center point instantaneously,When the pressure difference at the valve orifice was 3.5MPa,it can reach up to 1500 MPa.The working side was subjected to the high-frequency pulse cyclic stress of particles,resulting in fatigue erosion.(4)Accurate calculation model and method of valve orifice area.Based on the simulation calculation of the flow field of the tiny valve orifice,the calculation models of the valve orifice area were proposed and the variation relationship between the area and the opening were analyzed.The research showed that near the zero position,with the increase of the working edge fillet radius of the sleeve or the spool,the valve orifice area in the small opening range increased nonlinearly and greatly compared with the ideal sharp edge,and the nonlinear region expand ed,which led to the change of the valve orifice zero position parameters and the performance degradation.(5)The essential relationship between the working edge micro-morphology of the spool and the performance degradation of the servo valve.The working edge fillets of the spool were changed to study the effect of working edge erosion on the performance of the servo valve.The results show ed that when the average fillet radius increased by 2.71 times and the mean fillet variance increased by 2.55 times,the maximum leakage increased by 5.08 times.T he flow gain decreased slightly with the increase of the fillet radius and was asymmetric in the positive and negative directions,decreasing by 7.78% and 1.75%,respectively.The pressure gain change d significantly with the increase of the fillet radius,decreasing by 40.30%. |
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