Study On Gear Strength Of Automobile Transmission Based On FEM

Gears are important parts in the transmission.Gear failure is the main realization of the failure of the automobile transmission,so the strength and reliability of gear directly affects the strength and reliability of transmission.The failure methods mainly include broken tooth,worn tooth,and tooth surface glued.These failures reflect ultimately in root bending stress and contact pressure.The classical theory method of tooth root stress and contact pressure is tedious and has some limitations,so this paper discusses the method of obtaining reliable root bending stress and contact pressure by FEM,laying the foundation for analysis of gear fatigue.In this paper,the following main jobs have been done:(1)Establishing FEA gear model and considering two effects of deformation of shafts and transmission box on gear: center distance enlarged and axis deflected.The simulation results show that the center distance enlarged has obvious influence on root bending stress,the axis deflected has obvious influence on contact pressure.The results of study show that the advantage of analyzing gear strength by FEA is to reflect the influence of shaft and transmission box deformation on gear strength,considering the actual meshing condition.(2)Establishing different mesh size FEA gear model,and root bending stress and contact pressure.The results show that the smaller mesh size,the closer the root stress and contact pressure are to the theoretical solution,the higher accuracy.The results of study show that the difficulty of analyzing gear strength by FEA is that the accuracy and efficiency of simulation results are contradictory.The higher the simulation accuracy,the lower computational efficiency.(3)First,this paper study the maximum z-stress of cantilever beam which is simple and has theoretical solution.The modeling method of cantilever beam is applied to analyze gear root bending stress.The study shows: five or more solid elements are distributed at the root transition curve.Add a shell element on the surface of solid elements can get the exact root bending stress.(4)Combining ANSA?LS-PREPOST and MATLABT,this paper presents a local model of gear contact.Using the local model for gear contact analysis can improve both the simulation accuracy and efficiency.Different mesh size are used for local model.The study shows that the exact solution of contact pressure can be obtained by distributing 27 or more mesh in the gear contact area.In summary,this paper presents two methods to get actual root bending stress and contact pressure,which make a pave for the analysis of gear failure.At the same time,based on the above conclusions,this paper builds a whole transmission FEA model to analyze and evaluate the root bending stress in the condition of reverse gear and analyzes the influence of shafts and transmission box deformation on root bending stress and contact stress.