Theoretical And Experimental Study On Soft Elastohydrodynamic Lubrication Of Hydraulic Linear Reciprocating Seals

Due to its good trace ability and eccentricity compensation,and low friction resistance,hydraulic linear reciprocating seals(HLRSs)have been widely used in hydraulic devices in the fields of aviation,aerospace,ship,automobile,engineering machinery and other applications,to prevent the oil leakage and the invasion of external pollutants.The failure of seals will directly affect the efficiency of hydraulic system,leading to produce huge economic loss,and even threaten the human safety.Therefore,the research on mechanism revealing and performance prediction of HLRSs combined by theoretical and experimental,is helpful to the development of high-life and highreliability seals,and the improvement of seal design method and theoretical system,which have great significance not only in guaranteeing the safety and reliability of key hydraulic equipments in China,but also in achieving the localization of high-end seals.The multi-scale multi-physics isothermal soft elastohydrodynamic lubrication(SEHL)model have been developed based on SEHL theory,which was solved by finite element method.This model combines fluid mechanics,static contact mechanics,asperity contact mechanics and micro-deformantion analysis.The distributions of fluid pressure and film thickness in the sealing zone of O-ring seal and step seal under different condition parameters have been compared,using to reveal the seal mechanism under mixed lubrication.The influences of rod speed,sealed pressure and roughness on sealing performance have also been analyzed.The results show that the lip structure of step seal responsible for its superior performance comparing to O-ring seal.The thermo-SEHL model have been developed by considering the influence of friction heat.The distributions of oil film temperature,viscosity and O-ring seal temperature under different condition parameters was analyzed,the functionary mechanism of temperature-viscosity wedge effect caused by the oil temperature and pressure was discussed.The thermal effect on oil film behavior and sealing performance was revealed,the influences of rod speed,sealed pressure and roughness on thermohydrodynamic lubrication characteristics of O-ring seal was also analyzed.And the reasons why high sealed pressure or rough surface is unfavorable are explained.The non-Newtonian fluid characteristics was introduced in thermo-SEHL model based on power law fluid model.By comparing the distributions of oil film pressure and velocity of pseudoplastic fluid and dilatant fluid,the influence of nonlinear rheological properties on oil film behaviors and the lubrication mechanisim of nonNewtonian fluids were revealed.In addition,the influence of power law index on thermohydrodynamic lubrication characteristics of O-ring seal was discussed.The transient thermos-SEHL model have been developed,which was used to perform the evolution law of oil temperature,pressure,thickness and O-ring seal temperature under variable speed conditions.The influence mechanism of thermal accumulation on oil film behavior under transient conditions was revealed.The influence of oil film water pollution on transient thermodynamic lubrication characteristics of O-ring is further analyzed.It is pointed out that slight water pollution is beneficial to improving lubrication characteristics and sealing performance.In order to further verify the numerical results,a novel hydraulic reciprocating seal device have been built,which can measure the friction force both during outstroke and instroke,the net leakage and the average rod-seal interface temperature simultaneously.The influences of rod speed,sealed pressure and rod surface roughness on sealing performance of O-ring seal were experimental analyzed under quasi-constant speed conditons,which made a validation of thermos-SEHL model.In addition,the sealing performance under continuously changing speed conditions and frequent start-stop operation conditions were compared.Showing that the later is more like to leak,restart after stop process will result a lager friction force,and inducing a seal failure.These research results systematically expound the influence mechanism of interfacial friction heat,fluid rheological properties and water pollution on oil film behavior,which can improve the design method and theoretical system of HLRSs,and also provide theoretical guidance and design basis for the engineering selection of HLRSs,contributing to the development of high-life and high-reliability seals.