Analysis Of Contact Stress And Modal Of The Helical Gear With Root Crack

With the advantages of compact structure,strong bearing capacity and stable transmission,helical gear is widely used in mechanical transmission.However,the facts of manufacturing error,installation error,deformation of gears,shafts,bearings after loading can lead to partial gear surface stress concentration or excessive contact stress,thus,pitting and fatigue damage become two kinds of common failure phenomenon in gear transmission.Therefore,carry out research on the contact characteristics of involutes helical gear,stress variation of contact tooth surface and the effect on the inherent characteristics of gear when root crack occurs,which has important theoretical significance to master the running state of helical gear,find and locate fault accurately,predict the change trend of gear meshing state,improve the reliability of gear meshing.With the object of involutes helical gear,we have done some research as follows:(1)A precise finite element model of the helical gear meshing is established.Based on the software ANSYS 15.0 and a certain type of diesel engine front timing gears as example,use the ANSYS Parametric Design Language(APDL)to establish the 3D geometric model of involutes helical gear meshing through the determination of the end surface of the helical gear tooth profile of involutes tooth root transition curve,and arc line,spiral and cylindrical coordinates equation,meshing by manual method to establish the grid model of high quality,and established the finite element analysis model of gear meshing based on the multi point constraint(MPC)technology.(2)Precise static and dynamic contact stress finite element model of the helical gear meshing are established.The model is excellently verified by the calculation formula of Hertz and AGMA the contact stress of the gear contact stress and the stress analysis model.As for the dynamic contact stress finite element model of the helical gear meshing,tooth surface contact stress values of several meshing position are gained by solving and post processing,the results show that the dynamic contact stress varies along the time with certain regularity,and tooth tip is the most possible position that serious meshing impact occurs.(3)Based on the 3D model of helical gear meshing using APDL,add different length of gear root crack,and solve dynamic contact stress finite element models of the helical gear meshing respectively in the same solution settings to study the effect of different size of root crack on the dynamic contact performance of the gear meshing,so as to learn the relationship between dynamic contact stress and length of root crack changes.(4)The finite element model of the entire helical gear meshing is established,and the first 10 natural frequencies and mode shapes is obtained by modal analysis.Furthermore,the influence of the crack size on the natural frequency and vibration mode is studied.Results show that the impact of root crack on gear vibration mode is not obvious,but little effect can be observed on the natural frequency with certain regularity.