| The stress calculation of the high contact mechanical parts such as gear transmission is based on the assumption of smooth surface. In engineering practice, however, absolutely smooth surfaces are not present; The oil film thickness of contact surface is usually in the same order of magnitude with the surface roughness of the general metal cutting process, these roughness peak and valley will inevitably cause the dynamic changes of contact stress. In view of this, domestic and foreign scholars have made a deep study on the roughness effect of the contact surface. However, In order to reduce the difficulty of research, computing mostly assumes one surface is rough and the other surface is smooth, this obviously has a great difference with the actual working conditions. Therefore, further research on this subject is necessary.In this paper, based on the two gear tooth surface roughness is all assumed cosine distribution, constructs involute gears mixed thermal elastohydrodynamic lubrication model. Based on this model, under the condition that the other parameters are kept constant, this paper analyses the influence of roughness peak height, wavelength and transmission ratio on the lubrication parameters of gear transmission by using the elastic contact theory and the multi grid method; Then, through 102 sets of numerical calculation, The quantitative relation between the average oil film thickness av,rh at pitch point, the maximum principal shear stress max,rt at pitch with the peak heights ratio /b aA A, the wavelength ratio are respectively established. Analyzing and summarizing the content of this study, we can draw the following conclusions:(1) From the approach point to the separate point at the meshing line along the gear drive, the main shear stress of rough tooth surface fluctuation rise as serrated at first, the maximum value obtained near the pitch point, and then fluctuation decrease; With the increase of roughness peak or the decrease of roughness length, The numerical solution of max,rt is increasing and the fluctuation range of main shear stress distribution tends to be violent.(2) Because the “pump effect†of transverse rough texture, the average oil film thickness of the rough tooth surface av,rh is bigger than the film thickness of the smooth tooth surface av,sh.The greater roughness height, the greater difference between av,rh and av,sh; But there was no significant relationship between roughness wavelength and the differences between av,rh and av,sh. In addition from the approach point to the separate point at the meshing line along the gear drive, av,rh overall fluctuation rise as serrated, This means that a minimum of av,rh occurred at the meshing point. Therefore, the current practice of using the oil film thickness of the node as the gear lubrication design reference is worth to be discussed.(3) Under the condition that other parameters are fixed, with the increase of gear transmission ratio, the average oil film thickness increases but the maximum principal shear stress is decreased.Therefore, it is beneficial to improve the contact fatigue life of gear transmission that increase the gear transmission ratio appropriately.(4) With the increase of two tooth surface roughness wavelength ratio /b aL L, the average thickness of the oil film av,rh oscillation changes; The volatility gradually leveled off after /b aL L >3.75. For the maximum principal shear stress on the contact zone subsurface, when /b aL L <0.8, max,rt decrease sharply with the increase of /b aL L; when 0.87< /b aL L <3.75, max,rt keep small amplitude oscillation; when /b aL L >3.75, max,rt basically tend to be stable.So keep /b aL L >3.75 can not only reduce the fluctuation of the film thickness of the tooth surface and the principal shear stress on the subsurface but also can be beneficial to reduce the contact fatigue stress of gear drive.(5) The average oil film thickness and roughness peak heights ratio /b aA A showed a two curve relationship, similarly to the roughness synthesis peak height A( A =2 2a bA +A).When /b aA A <1.5( A <0.36),av,rh decreases monotonically,when /b aA A ≈1.5( A ≈0.36), av,rh obtain the minimum value;when /b aA A >1.5( A >0.36)av,rh rise monotonically.(6) the maximum principal shear stress on the contact zone subsurface max,rt and roughness peak heights ratio /b aA A showed a linear relationship, similarly to the roughness synthesis peak height A.max,rt corresponding to /b aA A ≈3 is more than 70% larger than that of /b aA A ≈1. Accordingly, in order to improve the contact fatigue life of gear transmission, machining accuracy should be improved, meanwhile, two tooth surface roughness size as far as possible to maintain consistency.In addition, the numerical results are analyzed by regression analysis in this paper, The functional relationship between the tooth contact stress, the average oil film thickness and the roughness peak heights ratio,the roughness synthesis peak height is established respectively. The research results have positive significance for improving the theory of contact strength design of gear transmission.The innovation of this paper is to discuss the gear lubrication effect of the double rough tooth surface contact. The deficiency is that there are some limitations in roughness peak height and roughness wavelength due to the convergence problem of numerical settlement. In addition, although the cosine function has been relatively close to the real rough surface topography, but there are some differences between each other, resulting in the numerical results are difficult to fully reflect the actual working conditions of gear transmission. |
