Adhesive Wear Model For Helical Gears Under Dry Friction And Mixed Lubrication

This paper takes the perfect involute helical gear drive as the research object,based on Archard's wear formula and the line-contact mixed elastohydrodynamic lubrication(EHL)theory,the adhesive wear models for helical gears both under dry friction and mixed EHL are established.The wear depth of the pinion and the gear is calculated,then the presented models are verified by the comparative results of the wear depth curves from the proposed models and relative published papers.Effects of geometrical and working parameters on wear are discussed.Moreover,effects of surface roughness and lubricant properties on tooth surface tribology characteristics are analyzed,which provides theory basis for wear resistance and stationarity enhancement of gear drive.The main research contents include:(1)Geometrical model of perfect involute helical gears.Based on the generating principle of gear machining,the equations for the helical gear tooth profile are deduced according to the coordinate conversion method,then the equations are solved by using MATLAB.(2)Adhesive wear model for helical gear drive under dry friction.According to the equivalent contact model of tapered rollers in opposite orientation and Archard's wear formula,an adhesive wear model for helical gears under dry friction is proposed.Face loads are firstly determined by the time-varying contact ratio,and then the tooth pressure and the sliding distance are evaluated based on the equivalent contact model and Hertz's theory.The presented model is verified by the comparative results of the wear depth curves from itself and relative published papers.The wear depth calculating results of the pinion and the gear show that larger wear depths are generated at the root and the tip,while the wear depth at the root is larger than that at the tip,and that it trends to zero at the pitch line.From front transverse plane to rear one of the driving pinion or driven gear,the wear depth of the pinion becomes smaller whereas that of the gear turns larger.However,the wear depth of wide-faced helical gears trends to a uniform along face width.Additionally,the parameters analysis show that the wear depth decreases as modules,transmission ratios,face widths or input torques are increased,while helical angle variation has little influence on the wear depth reduction.(3)Line-contact mixed EHL model.Based on the modified Reynolds equation and the surface deformation and the statistical elasto-plastic asperity micro-contact model,the line-contact mixed EHL model is established.The influence of parameters such as dimensionless load,speed,surface hardness and surface roughness on film thickness and asperity load ratio is discussed.(4)Steady-state adhesive wear model for helical gear drive under mixed lubrication.Based on the modified Archard's wear formula and the line-contact mixed EHL model,the traction coefficient and wear rate caculating model for the contacting surfaces is established.The presented model is verified by comparing its simulation results with experimental data and simulation examples in relative published papers.Simulation results show that the wear depth is three orders of magnitude lower than that under dry friction,which indicates that wear can be significantly reduced with good lubrication.Parameters analysis show that as surface roughness increased,the center film thickness,the flash temperature,the traction coefficient and the wear depth also increased,while the film parameter decreased significantly,and the asperity load ratio increased largely,the fractional film defect almost remained the same.The effect of tooth profile and operating parameters on wear is similar to that under dry friction,in addition,wear depth under mixed lubrication can be reduced significantly by appropriately increase the input rotational speed.