Multi-axial Fatigue Life Model For Involute Gear Contacts Based On The EHL Lubrication

Gear is a very important transmission element and widely used in various industrial equipment.This paper presents a starved elastohydrodynamic lubrication model for involute spur gear tooth contacts,with considering the change of entrainment speed,radii of curvature,load during engagement process.As gear experiences multi-axial cyclic loading and complicated work environment during its service life,in this paper,a multi-axial fatigue life model based on the gear elastohydrodynamic lubrication is established to analyze fatigue life of gears.The main contents and conclusions are as follows:By simplifying the meshing process of spur gear into the contact between two cylindrical rollers,the elastohydrodynamic lubrication analysis of spur gear is conducted.Considers effects of different operating conditions and results show that,oil pressure increases sharply on the boundary of single tooth meshing area and double teeth meshing area,and induces stress concentration on both ends along the direction of tooth face width.The effects of revolution speed,load and fillet radius at the tooth ends on the lubrication performance are investigated.Based on the elastohydrodynamic lubrication calculation and subsurface stress,a multi-axial fatigue life model of involute spur gear is developed,which considers the effect of both the stress history of certain point under tooth surface and material properties,and obtains the fatigue life distribution of entire gear contacts.The fatigue life predictions for smooth and rough tooth surfaces are conducted.The results show that: oil pressure obviously increases and fluctuates due to surface roughness,and becomes serious with the increase of roughness amplitude.Tooth surface roughness has a significant effect on gear fatigue life;with the increase of the amplitude of surface roughness,subsurface maximum stress moves to the teeth surface,which results in the extension of low fatigue life region to the teeth surface and further extension to the entire single tooth meshing area;however,it has little effect on gear fatigue life if the surface roughness reduces to a certain extent.The starved EHL lubrication model of involute spur gear is established and gear fatigue life is investigated under starved lubrication condition.The results show that: under starved lubrication condition,oil pressure distribution is more like the Hertzian dry contact pressure,at the free boundary the pressure is discontinuous and pressure gradient rises and pressure region reduces with the decrease of supplied oil.Because oil film thickness is smaller under starved lubrication condition,asperities on the teeth surface will get into contact directly,which increases the oil pressure and reduces gear fatigue life,and has significant effects in subsurface of teeth.