Investigation On Tooth Wear Considering The Dynamic Load And Contact Temperature For Spur Gears In Mixed EHL

The tooth wear has been one of the main failure forms of gears,especially under loss-of-lubrication condition.The dynamic characteristics and temperature rise of gear have an important influence on its lubrication performance,which leads to the increase of friction and wear.The tooth wear is closely related to the lubrication,gear dynamics and temperature field.Hence,it is of important significance to investigate the interaction between gear tribology,dynamics and heat transfer.In this work,the involute spur gear is taken as the research object.The gear wear model in mixed elastohydrodynamic lubrication(EHL)is established considering the film defect coefficient and asperity contact ratio.Combining the gear dynamics and heat transfer,the effects of gear dynamics and contact temperature on gear wear are investigated for spur gears in mixed EHL,it provides the theoretical basis for enhancing the gear wear resistances.The primary contents and conclusions include:(1)The models of oil film stiffness and friction coefficient are established based on the mixed EHL model.The effects of surface roughness on the quasi-static film thickness,film pressure,film stiffness and friction coefficient are investigated.The result illustrates that the film thickness and friction coefficient increase with the increased surface roughness,but the film pressure and film stiffness reduce.(2)The gear dynamic model is proposed in mixed EHL.The dynamic force is obtained by introducing the film stiffness and friction into gear dynamic model.The dynamic time-variant meshing stiffness,film thickness,film pressure,film stiffness and friction coefficient compare with those under the quasi-static load.The dynamic results fluctuate around those under the quasi-static load.The effects of surface roughness on the dynamic film thickness,time-variant meshing stiffness,film stiffness,friction coefficient and film pressure are analyzed.The results show that dynamic gear meshing stiffness,film stiffness and pressure decrease with the increased surface roughness,but the film thickness and friction coefficient increase,which is consistent with the variant law under the quasi-static load.(3)The thermal network model is presented for spur gears in mixed EHL.The gear bulk temperature is determined.The effects of non-involute error reduced by thermal deformation on the load distribution coefficient and equivalent curvature radius are analyzed.According to the thermal network model and formula of flash temperature rise,the contact temperatures of driving and driven gears are obtained.It is found that the contact temperature,bulk temperature and non-involute error of driving gear are larger than those of driven gear.Combining the gear contact temperature and dynamic models,the dynamic gear contact temperature,bulk temperature and flash temperature rise compare with those under the quasi-static load.The dynamic contact temperature and flash temperature rise fluctuate around that under the quasi-static load.The gear bulk temperature is basically similar under the dynamic and quasi-static loads.The effects of surface roughness on dynamic gear contact temperature,bulk temperature and flash temperature rise are investigated.The results indicate that the lower surface roughness is beneficial for reducing the contact temperature and enhancing the scuffing resistance of gear pairs.(4)The gear wear considering the gear dynamic load and contact temperature is calculated and analyzed.The dynamic load and contact temperature are introduced into the wear model considering the film defect coefficient and asperity contact ratio in mixed EHL,and then the gear wear considering the dynamic load and contact temperature is calculated.It is found that the dynamic film defect coefficient,asperity contact pressure and relative sliding distance have a synthetic influence on dynamic wear depth,and the effect of film defect coefficient,related to the gear contact temperature,is maximum,which illustrates that gear contact temperature is one of main factors determined gear wear depth.The effects of surface roughness and gear geometric parameters(tooth width,module and pressure angle)on dynamic wear depth are studied.The results show that the lower surface roughness and larger gear geometric parameters are advantageous to the improvement of tooth wear resistance.In summary,the tooth wear depth considering the gear dynamic load and contact temperature is calculated by combining the gear dynamic model,contact temperature model and wear model in mixed EHL.The calculated method of tooth wear are preliminarily explored through the coupling of gear dynamics,heat transfer and tribology.