Study On Pressure Balancing And Clearance Flow Characteristic Of Helical Grooved Piston-copper Pair

Piston-copper pair is one of the most important friction pair of swash-plate axial piston pump,its pressure balancing and clearance flow characteristic affect the overall efficiency of equipment.In order to improve working performance of the piston pair,more and more scholars have explored extensively research on applying smooth surface characteristics to piston pairs,so as to improve the bearing capacity of the oil film of friction pair,enhance lubrication,and reduce leakage.The influence of helical groove piston on copper sleeve work performance and design parameters are researched.According to the results,tow improvement scheme are proposed.The main contents are as follows:1)A numerical simulation method was used to analyze the flow field characteristics of piston-copper pair.Combining with the actual structure of the swash plate piston pump and the working condition,setting the appropriate physical parameters and boundary conditions,numerical simulation was carried out to investigate the piston-copper pair by CFD software FLUENT.Static-dynamic method was proposed to test rationality of numerical simulation using theoretical formula and experimental measurement.2)Through comparing helical groove piston,ring groove piston and smooth piston,the influence mechanism of helical groove on the performance of piston was analyzed from three aspects: pressure distribution,inclination moment and gap flow.Flow guiding of helical groove reduces resistance of the flow of the oil in the piston pair and the pressure of the rate of decline,and improves the distribution of the oil film pressure,increased automatic alignment in working process of the piston,however,the sealing of column plug is influenced by increasing the gap flow.With three helical groove piston as the basic mechanism,the influence of the length,location and connectivity of the helical grooves were explored.The depth,angle and pitch on the piston pair were also investigated.The helical groove has a large length and connected distribution,which is helpful to reduce the pressure decline speed.The position of helical groove is close to pressure chamber,which is helpful to increase pressure distribution uniformity.The greater the depth and angle of the groove,and the larger the gap leakage,the better the lubrication performance.The screw pitch is mainly used to change the line length of the helical groove and influence the performance of the piston.3)According to the research results,the two improvement scheme of helical groove piston with compound type and discontinuous type is presented and ansysed by CFDnumerical method.The compound helical groove piston combines the advantages of two kinds of structure of helical groove and ring groove,the lubrication of piston,stability and sealing are more balanced.The intermittent helical groove piston retains the characteristics of the pressure lubrication of helical grooves.Meantime,the leakage of piston-copper paire is effectively reduced,and the design and application of helical groove structure is promoted further.