Numerical Calculation Of Thermal Elastohydrodynamic Lubrication For Modified Herringbone Gears In Point Contact

With the advantages of smooth transmission,large bearing capacity and small axial force,herringbone gears are widely applied in the high speed reducer of the aviation gas turbine,main drive unit of the heavy lifting mechanism and ship power system.Since gear transmission is developing to high speed,heavy load and high precision,researches on gear lubrication to reduce the friction and wear of tooth surface have been paid more and more attention.In this paper,based on the non-Newtonian thermal elastohydrodynamic lubrication(EHL)theory,the modified herringbone gear EHL model in point contact is established and the complete numerical solution is acquired.The main contents includes:(1)The thermal EHL model in point contact is established.The pressure field is solved with a multilevel method,and the temperature distribution is obtained according to a column by column scanning technique.Then the effects of the load,entrainment velocity,ellipse ratio and slide-roll ratio on point contact thermal EHL are investigated.The results show that,the load and entrainment velocity have great influence on point contact EHL,and the slide-roll ratio is an important parameter for the film temperature.Moreover,the non-Newtonian behavior mainly affect the film temperature and shear stress.(2)Thermal EHL for modified herringbone gear in point contact is investigated.The contact parameters are calculated based on the meshing charact eristics of herringbone gears,and the point contact EHL model is applied to the modified herringbone gear.Then the distributions of contact force,contact line length,entrainment velocity,curvature radius and slide-roll ratio along the action line are analyzed.And the effects of work parameters,geometric parameters and gear modification on herringbone gear lubrication performance are investigated.Results indicate that,reasonable design of gear geometric parameters and working parameters may improve herringbone gear lubrication performance.(3)The transient thermal EHL in point contact is studied.The transient EHL and steady-state EHL results of the herringbone gear in a meshing cycle are compared.Then the distributions of the film central pressure,central film thickness,central temperature rise and friction coefficent are studied,and the effects of input torque and rotation speed are investigated.It is shown that there is a large difference among steady-state EHL and transient EHL of herringbone gear,transient EHL is more accurate for herringbone gear lubrication.As the rotation speed increases,the film thickness and temperature rise get larger,whereas the friction coefficient decreases.Input torque increase results in larger pressure,larger temperature rise and larger friction coefficient.(4)Transient thermal EHL model for the herringbone gear considering roughness surface is investigated.The effects of the roughness texture,roughness amplitude and roughness wavelength on the transient thermal EHL for herringbone gear are analyzed.The results show that,the central film thickness of rough tooth surface is apparently less than that of smooth tooth surface.Moreover,the pressure and film thickness distribution are usually similar to the roughness texture,and the roughness amplitude and wavelength increase result in film thickness reduction.