Research On Plasto-elasto Hydrodynamic Lubrication Of Helical Gears Considering Real Tooth Surface Roughness

As a fundamental category of mechanical components,gear drives are used extensively to transmit power and motion.With the ever-growing requirement for better performance of mechanical equipment,it has been increasingly urgent to improve the reliability of gear pair and to extend its fatigue life.Therefore,proper description of gear serving performance,especially the status of lubricated contact and subsurface stress field,becomes particularly important.Surface roughness left on gear teeth by manufacturing processes has significant influences on both the status of lubricated contact and the subsurface condition of stresses and strains of gear pair.Heavy duty or a certain extent of dry contact between roughness peaks are likely to incur plasticity in the teeth,and alter both macro and micro topography of tooth surfaces,thus influencing the serving performance of gear pair.However,traditional gear design methods are mainly based on Hertz contact theory,assuming pure elasticity and ignoring the effect of lubrication and surface roughness on contact performances,which as a result is far from sufficient to reflect the true serving status of gear drives.Focused on the lubricated contact problem of helical gears,this work takes into account both real surface roughness produced by four different surface finishing processes,namely Form Gringding,Generating Grinding,Super Finishing and Grinding&Coating,and the plasticity that could occur during tooth engagement.A non-Newtonian Plasto-Elasto Hydrodynamic Lubrication(PEHL)contact model is established for helical gear pair,which is intended to investigate the characteristics of lubricated contact of involute helical gears,to provide the lubrication design of modern gears with theoretical support,and to underpin the reasonable estimate of gear fatigue life with a reliable description of tooth contact status.The main contents are as follows:(1)The establishment of a PEHL contact model for helical gear pair,considering surface micro topography.The geometries and kinematics of helical gear drive are equivalently simplified into a finite line contact model.A PEHL contact model for helical gear pair is constructed by alternating iteratively between the analysis of lubricated contact status on tooth surfaces and the analysis of subsurface stresses and strains,and a numerical solving scheme is provided featuring both realiability and efficiency.(2)Comparison between results from the PEHL contact model developed in this work and from the relatively mature EHL contact model based on the pure-elasticity assumption,under ideally smooth tooth surface and generating ground tooth surface,respectively.The comparisons are performed in order to show the differences in their ability to characterize the status of lubricated contact.(3)The influence of surface micro topography on the lubricated contact performance of helical gear pair.On the one hand,comparisons are drawn between the lubricated contact performances of four measured types of tooth surfaces with different roughness originating from surface finishing processes.On the other hand,each of the measured types of tooth roughness is scaled to a same series of RMS(root mean square)values,and the effect of RMS value can be investigated,and meanwhile,the influence of the distribution characteristics of micro topography extracted from different tooth surfaces can be observed under equal RMS values.(4)The influence of operating conditions on the lubricated contact performance of helical gear pair.When both surface roughness and plasticity of material are taken into account,the way in which operating conditions affect the lubricated contact performance differs from that under ideally smooth surface and that under the pure-elasticity assumption.Therefore,it is necessary to investigate the influences of input torque and input rotational speed on the lubricated contact performance of helical gear pair,using the PEHL contact model developed.In this thesis,a non-Newtonian mixed PEHL contact model is established for helical gear pair,and the patterns in which surface micro topography affects the characteristics of its lubricated contact are investigated,based on four different types of tooth roughness measured.The effects of the root mean square of roughness,input torque and input rotational speed are also analyzed.The reported work contributes to the theories of lubrication design for modern gears and the reasonable description of lubricated contact status of gear pair.