Analysis On Gearing Roughness Effect Based On Measured Roughness Data

At present, the contact fatigue strength design of the involute cylinder gearing drive is only based on Hertz theory, as is known to all, this theory is only fit for the smooth surfaces without lubrication. With the existence of tooth surface roughness, it will have an effect on the the contact stress of gear. Therefore, the tooth surface roughness effects must be considered when in the study of gear transmission with elastohydrodynamic lubrication.Explore the tooth surface roughness effects, most scholars tend to assume that the tooth surface roughness peak and valley were sine (cosine) distribution or artificially assumed the tooth surface single (multi) asperity, which may help to reduce the difficulty of computation, but there is a large gap with the actual situation of trough surface peak and valley distribution. The surface roughness data of a test-piece are firstly measured by a roughness profile measuring analyzer. With the help of the Fourier approximation the measured data are used to form a roughness function which is then added to the oil film thickness equation and a gearing mixed Elastohydrodynamic Lubrication model is established.At last,using multiple grid method to solve EHL pressure distribution,using multiple grid integration method to solve oil film thickness distribution,using the sequential column sweeping scheme to solve the temperature distribution. Based on this,the application of the elastic contact theory, and seek a tooth contact area sub-surface stress distribution. Through135sets of values calculated,explore the affect of lubricant viscosity,size and texture direction of tooth surface roughness to tooth contact stress and tooth surface oil film thickness from theory, and the formation of the main findings as follows:(1) Premise other gear parameters fixed,with the increase of the lubricant viscosity,the fluctuations of pressure and film thickness, sub-surface stress concentration are waning; gear transmission lubrication condition gradually from boundary lubrication after mixed lubrication to full-film lubrication. When the oil film thickness λ≤4.0, the tooth contact stress reduce with the parabolic law when film thickness increases. This shows that:under certain working conditions, increased the viscosity of the lubricant is helpful to improve the contact fatigue life of the gear.(2) Different machining methods will form a different texture of surface roughness. With the same roughness values, the fluctuations of tooth surface pressure and subsurface stress concentration with vertical rough texture is violently than the lateral tooth surface rough texture. The value of average film thickness under longitudinal rough texture tooth face is less than the thickness of the smooth tooth surfaces, and to the contrary, the value of average film thickness under the transverse rough texture of the tooth surface is greater than the thickness of the smooth tooth surfaces. With the increase of the tooth surface roughness rms value σ, the average of oil film thickness under the tooth surface of longitudinal rough texture hav gradually decreases, while the lateral rough texture tooth surface hav increasing. With the increase of λ, the change of the rough ratio of the average film thickness and a smooth tooth surface hav/has amplitude gradually slowing down; when λ>5, hav/has gradually approaches1, the average of film thickness under rough tooth surface and smooth tooth surface are gradually consistency.(3) When the the rough tooth contact, regardless of the rough texture direction is vertical or horizontal, the maximum principal shear stress τmax in the sub-surface of the tooth contact area is always greater than the corresponding values with smooth tooth surface contact. When the tooth surface roughness rms value σ<0.2(μm), τmax almost do not vary with σ changes; when σ>0.2(μm), with σ increases, τmax significantly increase; especially when σ>0.55(μm), the τmax under rough tooth surface contact increased by70-90% than the corresponding value of smooth tooth surface contact, and wherein the τmax under the longitudinal rough texture is greater than the corresponding under lateral rough texture. Here is important to note that, in order to consider the impact of the tooth surface roughness, the international standard of involute cylindrical gear carrying capacity (ISO/6336:1996) and the National Institute of Standards (GB3840-1997) recommended roughness coefficient ZR, when the tooth surface roughness value is doubled, the value of ZR is only5%change, and obviously difficult to reflect the tooth significant effects on tooth contact stress of the surface roughness, so that the coefficient of Science is questionable.(4) In summary, in conditions of the same roughness values, the lubricating effect under the tooth surface with horizontal rough texture is superior to that with longitudinal rough texture.In the end, through the regression analysis with the calculation results, establish a quantitative relationship between the average film thickness, the tooth contact stress,film ratio and tooth surface roughness under the state of lateral, vertical rough texture.The innovation of this paper is to establish the quantitative relationship Among the size of the grain direction,the tooth contact stress and tooth surface roughness based on the measured surface roughness. In addition, in the numerical calculation consider the lubrication, the tooth surface friction, the influence of the roughness and thereby causing the dynamic characteristics of a variety factors, such as, the results closer to the actual working conditions.The inadequacies of theoretical research is that the research results has not yet been experimental verification.