| Gear transmission system is one of the key transmission components of aero-engine,so it is particularly important to ensure that it is in a good lubrication state.Aviation gear usually operates under high speed and heavy load.If the gear lubrication design is defective and unreasonable,it can not form a reliable and effective oil film,and can not isolate the direct contact of the gear surface,it will lead to increased tooth wear and friction coefficient,which will produce huge heat,reduce the transmission efficiency of the gear transmission system,affect the stability of the transmission system,and make the system failed.Therefore,it is of great significance to study the elastohydrodynamic lubrication of aviation gears.In this paper,taking the aviation gear as the research object,the three-dimensional finite element simulation analysis technology of elastohydrodynamic lubrication of gear is proposed.Considering the influence of non-Newtonian effect on gear lubrication characteristic parameters,the elastohydrodynamic lubrication characteristic parameters of gear meshing interface are calculated,the influence law of working condition change on gear lubrication characteristic is revealed,and the influence of roughness on gear lubrication characteristic is explored.Firstly,the simulation method of gear line contact elastohydrodynamic lubrication is verified.According to the meshing characteristics of gears,the necessary boundary conditions of gear elastohydrodynamic lubrication are obtained;the simulation model,numerical theoretical model and empirical formula model of line contact elastohydrodynamic lubrication are established respectively,and the accuracy and reliability of the simulation method of gear line contact elastohydrodynamic lubrication are verified by comparing the simulation results,theoretical calculation values and empirical formula values under the same working condition.Secondly,the simulation of gear non-Newtonian fluid elastohydrodynamic lubrication is carried out.Taking the gear meshing point as the research object,considered the influence of non-Newtonian effect on gear lubrication characteristics,Ree-Eyring fluid is selected for simulation analysis,and the influence rules of Ree-Eyring fluid on lubrication characteristics are obtained.The results show that the oil film thickness calculated by Ree-Eyring is consistent with that of Newtonian fluid,but the friction coefficient is smaller than that of Newtonian fluid.Based on the Ree-Eyring fluid model,the lubrication characteristics parameters of the whole gear surface are studied,the friction coefficient of the meshing side is the largest,reaching0.0120.Thirdly,the influence of working conditions on gear lubrication characteristics and the EHL characteristics of gear with roughness are studied.Taking the gear meshing point as the research object,the gear lubrication simulation model under different parameters is established,and the influence of different speeds,different sliding rolling ratios,different loads and different ambient temperatures on the gear lubrication characteristic parameters is studied.Based on the ideal roughness model and the real gear surface roughness model measured by experiment,the elastohydrodynamic lubrication simulation model of rough surface is established.The influence of the amplitudes,directions and contact peak types of gear surface roughness on the lubrication characteristics is studied,and compared with the calculation results of smooth surface,the results show that when the H_P increases from 0 to 0.64um,the friction coefficient increases from 0.0120 to 0.0187,and the film thickness ratio decreases from 1.96 to 1.42.Due to the so-called"pump effect"produced by the transverse roughness,the film thickness can be increased by 0.024um under the transverse roughness condition.Finally,combined with the engineering practice,the influence of different oil-gas ratios on the lubrication characteristics of gears with rough surface is discussed,the results show that when the oil gas ratio decreases from 1.0 to 0.6 and the Ra is 0.30um,the friction coefficient increases from 0.0132 to 0.00250 and the film thickness ratio decreases from 2.13 to 1.55;when the Ra is 0.35um,the friction coefficient increases from 0.0144 to 0.0274,and the film thickness ratio decreases from 1.81 to 1.33.In addition,when the oil-gas ratio is less than 0.9,the friction coefficient decreases linearly with the increase of the oil-gas ratio at a slope of-0.03;when the oil-gas ratio is greater than 0.9,the decrease of the friction coefficient tends to be gentle.It is suggested that the oil-gas ratio should be controlled at about 0.9 to achieve a smaller friction coefficient. |
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