Analysis Of Thermal EHL And Scuffing Failure Of The Gear Transmission Under An Oil Starvation Condition

The thermal EHL problem of the gear transmission under a starvation condition isthe hot issue in recent years, which is one of the EHL theory research. The traditionalEHL analysis is sufficient lubrication problems， whose upstream boundary oflubrication area is far enough away from the contact area and sufficient oil is largeenough. If the upstream boundary away from the contact area is too close, it will reducethe amount of oil and then lubricant film thickness will be smaller, which is referred toStarved lubrication.The gear starvation transmission can reduce oil film thickness andraise the average temperature, and oil film pressure distribution tends to Hertz dryfriction state. The gear scuffing is a common phenomenon, which is one of the failuremodes of the gear transmission. The temperature rise because of the starvationlubrication is the main reason of the gear scuffing failure. Therefore, analysis of thermalEHL and scuffing failure of the gear transmission under an oil starvation condition has ahigh theoretical significance and practical value. Specific research work andconclusions of this paper are as follows:1) Applying formulae of Hertz contact, contact stress analysis of meshing gearteeth with involute profiles is conducted and the variations and its related factors ofcontact stress along contact path are evaluated; The absolute velocities of the meshingteeth on pinion and gear as well as the relative sliding velocity between the tooth flanksare calculated; The approach of estimation for frictional heat flux is developed and thedistributions of frictional coefficient and heat flux on meshing tooth flank withinfluencing factors are investigated on the basis of heat transfer.2) The mathematical model for thermal EHL of the gear transmission under astarvation condition based on gear engagement theory and the non-Newtonian behavioris set up. Owe to complexity of second-order nonlinear characteristics of partialdifferential equations, some challenging numerical calculation methods are adoptedsuch as multigrid method to solve the pressure distribution of time-varying solution,multiple grid integration method to elastic deformation and the column scanningmethod to temperature distribution and then several major factors are discussed, such asthe effects of the slide-roll ratio on the pressure, the film thickness and the frictionalcoefficient, the influences of the rheological property and the thermal effects.3) Firstly, the gear lubrication oil-supply model is proposed, and the effective film thickness and contact region inlet input parameters which reflect oil supply capacity arederived with flow continuity equation, which provides a theoretical basis for thestarvation. Then, on the basis of the heat transfer, calculation criteria for the gearthermal scuffing and failure analysis theory are proposed, the difference betweenintegral temperature method and the maximum flash temperature method is discussed,and integral temperature method is used to calculate the gear scuffing load capacity withthe analysis of the various parameter changes.And then the criteria for the gear thermalscuffing and failure are also proposed, the starvation theory is divided into lubricationand cooling starvation and the formula for the critical starvation risk is determined.4) Based on the starvation thermal EHL theory and combining with the best oilsupply problems, the gear quantitative calculation of the amount of lubricating oil in thestarvation conditions is proposed,and the relationship between in the gear contact zonetemperature rise and thermal scuffing failure is analyzed. By contrast to oil mistlubrication experiments in the starvation conditions, the lubrication critical amount andstarvation EHL numerical calculation results are consistent, and the impact of thetemperature rise of full and starved oil supply on the gear transmission scuffing failureis analyzed.