Study On The Grease Lubrication Theory And Failure Mechanism Of Wheel Hub Bearing

With the development of industrial, harsh conditions are widely exists in machinecomponents, for example: high temperature，over loading and high speed shearing,therebythe demands on lubricant properties and relative theory research increasingly high. After alarge number of scholars efforts, the lubrication theory and measuring apparatus for slidersurface contact, line contact and point contact problems of liquid lubrication had beenresolved well; furthermore, comprehensive investigation on the lubrication mechanism fromthe macro and micro sides respectively, all these works made a positive influence on theapplication of liquid lubricant. As a main part of automotive, wheel hub bearings usuallyadopt grease for the lubricant, due to the special structure and property, the distinguishes ofapplication and theory study for grease are noticeable which compared to liquid lubricant. Atpresent, the study of grease puts particular emphasis on application sides, such asdevelopment of high-performance grease and relatively additive, the methods ordinarilyaccording to the experience and lots of experiment investigations. Consequently, discussingthe lubrication mechanism and perfect the lubrication theory of grease, and applying thetheory study conclusions to practices, there are a lot of problems still need to be resovled.Firstly, a generalized form of Reynolds equation for grease lubrication is derived, andaims at the lubrication failure which discovered in the statistical analysis of the failured wheelhub bearings, the effects of lubrication factor on bearing life and capability are analyzed. Then,the final expression forms of lubrication failure for wheel hub bearing are summarized:defects on race-way and solid particles in grease. Finally, the influences of defect and solidparticles on grease EHL are discussed by theory and experimental method. Consequently, thispaper may perfect the study of grease EHL theory, and guide the analysis of bearing failureand application of grease additive. The research works of this paper mainly consist offollowing parts:1、A generalized form of Reynolds equation for grease lubrication is derived, andaccording to the different grease lubrication problems, put out the correspongding greaselubrication equation. 2、The failure wheel hub bearings are counted, the effects of lubrication on bearing lifeand several failure modes which caused by the undesirable lubrication are analyzed. Used thegrease EHL analysis the phenomenon that for the outer ring fixed, inner ring rotating with theshaft ball bearing type, the inner ring race-way compared with the outer ring race-way ismore likely to appearance wear and fatigue failure.3、The effect of surface defects on film pressure and thickness of grease EHL areanalyzed, and the correctness of numerical calculation is proved by experimental methods.Theeffect of dents and bumps in the race-way surface on the distribution of film pressure andthickness for line contact and point contact grease EHL are analyzed by numerical calculationmethod, include the size and location of the dents and bumps.Furthermore, through the SEMand EDS analyzing for the edge and core of surface dent and bump to proving the correctnessof numerical calculation.4、The Reynolds equation of line contact and point contact grease EHL for exist a solidparticle in grease is detailed derived. The source of solid particles in wheel hub bearing grease,and the relationship between the particle number and diameter are analyzed by experimentalmethod and statistical theory. The effect of center location, velocity and size of solid particleon line contact grease EHL, and the velocity and size of solid particle on point contact greaseEHL are analyzed.5、The influence of different physical property, diameter and massfraction of submicroparticle on lubricating property of grease are analyzed. In order to prevent the influence ofgrease additive on the experiment results, self-made a lithium complex grease withoutadditive, and offer the formula and preparation process. The test samples are the grease whichmixed by brittle particle SiO2and ductile particle Cu with different diameter and massfraction,and the friction coefficient and the relationship between the test temperature and times ofsamples are tested by used four-ball tester.