| The hydraulic servo system with low viscosity oil as transmission medium is an important research direction in aerospace field.How to reduce the wear of aerospace axial piston pump(referred to as aerospace pump)is of great significance to improve the reliability and life of aerospace hydraulic servo system.However,due to the lack of research on wear mechanism under boundary lubrication with low viscosity oil and the blockade of advanced technology of aerospace pump,there is still great room to improve the wear resistance and durability of aerospace pump in China.The cylinder block/port plate pair(referred to as port plate pair)is the most critical friction pair in the aerospace pump.Because the working medium(8284aerospace kerosene)of the aerospace pump has low viscosity and high using temperature(70 ?),the lubrication performance of the port plate pair of the aerospace pump is poor.The material selection of the port plate pair,including strength,wear resistance and corrosion resistance,will directly affect the service performance and service life of the aerospace pump.Among them,polymer based coating has been widely concerned in the field of tribology because of its own lubrication characteristics and excellent mechanical properties.Howe ver,up to now,the research on the friction characteristics of polymer based coating is still limited to the field of dry friction and water lubrication,and ther e is still a lack of research under the boundary mixed lubrication state of low viscosity oil medium,which leads to a great restriction on the application of polymer based coating in aerospace pump.In this paper,based on the RP-3 medium,the material of the port plate pair of the axial piston pump is taken as the research object.Aiming at expl oring the friction and wear mechanism and life evaluation method of polymer based coating under the boundary mixed lubrication condition of the RP-3 medium,an in-depth study is carried out from the friction characteristics of polymer based coating to the key technology in the practical application in the pump.In the paper,the research object is the port plate pair of the bent-axis axial piston pump.Based on the design idea of residual compression force of cylinder block/port plate,the mechanical model of spherical port plate pair is established by the analysis of Navier-Stokes equation and continuity equation.The contact pressure and the maximum linear speed of the friction pair under the boundary lubrication condition are analyzed and calculated,which provides the reference value of loading force and velocity for the friction test.By comparing the components and performance parameters of hydraulic oil and RP-3 aviation kerosene,especially the measurement of the difficulty of oil film formation,the principle that friction pairs are easier to be in boundary lubrication in RP-3 medium under the same working condition is clarified.Based on this,a friction and wear test rig is designed to simulate the friction and wear of cylinder block/port plate under boundary lubrication and provides the calculation method of wear rate based on the "face-to-face" wear mechanism assisted.Based on the investigation of coating materials,combined with the actual working conditions of the bent-axis axial piston pump and the characteristics of RP-3 medium,the high performance coatings in the market are selected,and the PEEK based,PTFE based and PI based coatings are made by spraying.In order to investigate the scuff resistance of the coating material,the scuff test is carried out.Secondly,the Stribeck curve test is carried out to investigate the law of the lubrication state of the coating material with the changing loading speed.F inally,the constant load test is carried out to evaluate the wear resistance(the PEEK based coating is also carried out with the strengthening load test).Through a series of tests,the wear mode and wear mechanism of polymer based coating are investigated,especially the formation mechanism of the tribofilm on the counterparts and the effect on the tribological properties of the coating.By applying a series of normal force and velocity to PEEK based coating,the relationship between the wear rate and the load of PEEK based coating is quantified,and the influence mechanism between the limit pv value and wear mode(wear mechanism)of PEEK based coating is studied.On the basis of the above work,the normal load is selected as the accelerated stress,and the appropriate stress level and sample numbers are determined.The endurance life of PEEK based coating is evaluated by constant stress accelerated life test.The inverse power-law Weibull model and the inverse power-law lognormal model are used to fit the life data.The AICc and BICc rules are used to determine the optimal distribution type,and the life stress model of the coating is obtained.In the end of this paper,the accelerated test of bent-axis axial piston pump is carried out.Firstly,according to the characteristic of multiple failure modes of axial piston pump,the accelerated model of axial piston pump is established.Secondly,PEEK based coatings are sprayed to the port face of three bent-axis axial piston pumps.Then,the wear amount of PEEK based coating under the accelerated test is measured by making a detailed test plan,and the influence factor of system pressure on the coating life is evaluated. |
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