Study On The Modification Of Low Speed And Heavy Load Involute Straight Cylindrical Gears

Full-section hard rock tunnel boring machines(shield machines)are subject to geological conditions when tunneling,and their main bearings drive gears are constantly exposed to shock,excessive loads and other external loads,resulting in failure problems such as tooth fracture and tooth surface pitting,leading to uninterrupted construction and huge economic losses.At present,there is more research on gears under high speed and light load conditions,while large gears under low speed and heavy load require further in-depth research due to their relatively complex loading conditions.Therefore,this thesis to improve the smoothness of internal gear transmission and load capacity for the purpose of shield machine main bearing drive gear tooth profile modification and tooth direction modification analysis,a 3m-level shield machine main bearing involute straight cylindrical gear as the research object,the following research work.Summarize the principles of profile and axial modification,and preliminarily determine the distribution of profile modification quantity allocation,modification length,and axial modification method based on low speed and heavy load conditions.According to the condition that involute straight tooth cylindrical gear can not be fully meshed under bad working conditions,the calculation formula of meshing askew degree is used to calculate the axis parallelism error and simulate gear bias,which provides theoretical basis for further analysis.Parametric modeling of gear pair is carried out,and contact fatigue strength analysis and quasi-static contact analysis under multi-objective evaluation of unmodified gear under deflection are carried out based on the worst working conditions in the load spectrum provided by the project.Then,used the permutation combination increment method to optimize the tooth profile and tooth orientation shape modification parameters to determine the optimal shape modification parameters under single factors,then combine the optimal shape modification parameters to determine the three comprehensive shape modification schemes to compare the transverse and determine the final shape modification scheme,and conclude that reasonable shape modification parameters can eliminate tooth surface deflection,reduce meshing impact and effectively improve transmission stability and bearing capacity.Perform gear strength verification under eccentric load on the final shape modification plan to determine the design rationality of the modified gear.And based on the implicit algorithm,the modified gear was re-modeled for transient dynamic analysis.The results showed that the dynamic meshing stress and vibration acceleration of the modified gear were reduced,and the dynamic characteristics of the transmission process were optimized.Design and construction of a gear test stand,using a scaled-down model approach.The similarity criterion for root bending stresses in spur gears was derived based on the second theorem of similarity and dimensional analysis,and the accuracy of the reduced ratio model was verified by comparing the root nominal stresses of the gears before and after reduction.Establishment and design of a tooth root strain test based on resistive strain measurement before and after machining of a reduced ratio gear,the results show that the root strain of the reshaped gear is lower than the root strain of the unshaped gear,verifying the reliability of the reshaped gear.