Study On Fretting Wear Mechanism Of Gear Shaft Under Complex Operating Conditions And Its Prediction Method

Gear assembly is the main component of power machinery, it mainly plays therole of supporting the rotating parts and transmitting the motion, torque or bending.Due to the torsional vibration of gear shaft shoulder caused by the cyclical changes inthe gear meshing force, the stick-slip friction instability phenomenon between gearshaft shoulder and bearing inner ring is caused by the torsional vibration. With thecontinuous operation under complex operating conditions, it then causes the frettingwear of gear shaft shoulder. Fretting wear exists in all kinds of mechanicalequipments, it usually reduces the material fatigue limit. It is one of the main reasonsfor the failure of key components. During the operation of gear shaft, the motionsystem composed by gear shaft and bearing has the friction disturbances with theinternal parameter variations, external load disturbances and the complexcharacteristics of uncertain and nonlinear. Its torsional vibration has low speed, highload and typical characteristics of dry friction, therefore, the vibration amplitude andnoise are greatly increased in the operation process of gear shaft. The above factorslead to poor operation of gear shaft, it is prone to cause the fretting wear of gear shaftshoulder. The serious fretting wear causes the fatigue fracture of gear shaft, resultingin the mechanical failure of power machinery.Therefore, based on the National863Program Grant of China (2008AA11A116)and the Advanced Research of the Weapon Equipment Key Fund Project(9140A2011QT4801) and the enterprise project ‘performance analysis andoptimization design research for reducer’s gear assembly’, the fretting wearphenomenon between the contact surfaces between gear shaft shoulder and bearinginner ring of gear components of power machinery is researched by mechanismanalysis and numerical calculation, the main research works are as follows:(1) By establishing the finite element simulation model of the gear assembly ofpower machinery, the stress field, strain field and temperature field are obtained byanalyzing the simulation results of the fretting phenomenon of gear shaft shoulder.The simulation results show that, the contact stress increases with the height of theshaft shoulder; the axial and radial deformation increases with the height of gear shaftshoulder; the temperature field and thermal stress field of gear shaft shoulderincreases with the rotational speed of gear shaft. (2) By establishing the fretting friction instability model and the kinematicequations of gear shaft shoulder under complex operating conditions, the frettingfriction instability condition of gear shaft shoulder are obtained by introducing thefriction instability damping ratio. By establishing the calculation model of frettingtorsional vibration of gear shaft shoulder, the effects of the main influencing factorson fretting torsional vibration of gear shaft shoulder are analyzed based on the above.The results show that, the tightening torque and rotational speed are the main factorsfor causing the fretting friction instability of gear shaft shoulder, and the frettingfriction instability of gear shaft shoulder is the main reason for causing the frettingwear of gear shaft shoulder.(3) Based on the analysis of contact characteristics of torsional vibration frictionmotion characteristics between gear shaft shoulder and bearing inner ring undercomplex operating conditions, the fretting wear mechanism of gear shaft shoulderunder complex operating conditions are analyzed and the fretting wear depths of gearshaft shoulder are calculated by the modified Archard formula. The results show that,the wear depth of gear shaft shoulder is maximum at gear meshing position; the weardepth of gear shaft shoulder increases with the height of gear shaft shoulder. The mainfactors for fretting wear of gear shaft shoulder under complex operating conditions are:transmission power, torsional stiffness, torsional inertia, torsional damping ratio,tightening torque, the amount of interference, the friction coefficient and rotationalspeed, etc.(4) The fuzzy grey correlation analysis model for the affecting factors of frettingwear in the gear assembly under complex operating conditions is established based onthe grey theory methodology. The performance characteristics of gear shaft shoulderunder different working conditions as the model’s comparison sequence, the importantdegrees of characteristic indexes affecting the fretting wear of gear assembly undercomplex operating conditions are analyzed by the grey relational analysis. Based onthe grey correlation degrees of affecting factors of fretting wear of gear assemblyunder complex operating conditions, the comprehensive performances of fretting wearof gear assembly under complex operating conditions are analyzed. The main factors’grey correlation for fretting wear of gear transmission under complex operatingconditions were calculated and analyzed, the results show that the influencing degreesof the major factors for fretting wear under complex operating conditions aretransmission power> rotational speed> tightening torque> interference> frictionfactor. (5) A forecasting method of support vector machine for the fretting wear of gearassembly under complex operating conditions is established and the forecastingmethod is be optimized by the adaptive mutation particle swarm optimizationalgorithm. The results show that the mean squared error and the mean relative error ofprediction method for the fretting wear of gear assembly under complex operatingconditions based on the adaptive mutation particle swarm optimization algorithmsupport vector machine are0.103%and2.06%, respectively. It means that theprediction method has higher precision. Then, the influencing factors of fretting wearof gear assembly under complex operating conditions have been analyzed andverified.