| In this paper,a fatigue-resistant parallel gear structure and its design method are proposed for the fatigue fracture problem of transmission gears.Moreover,the reliability optimization design method of fatigue-resistant parallel gears is further proposed with the minimization of manufacturing cost as the objective function and the satisfaction of reliability index as the constraint.Meanwhile,a gear reliability calculation method considering the related failure modes is proposed to analyze the reliability of parallel gear structures with strong nonlinear characteristics and related failure modes.Finally,a gear fatigue reliability test bench based on a spatial linkage mechanism is developed and designed to save test costs and better simulate gear loading conditions.The main research contents include:(1)A fatigue-resistant parallel gear structure scheme and its design method are proposed.In response to the current problems that cracks in gears are not easily detected under high speed and heavy load conditions and that fatigue fracture failure has serious consequences,a fatigue-resistant parallel gear structure was developed and designed by using friction welding technology to weld multiple sub-gear structures that can theoretically complete their work independently.At the same time,according to the principle of parallel system reliability analysis,combined with the traditional gear design process,the parallel gear design method was proposed.Moreover,the effectiveness of parallel gears in improving the reliability of tooth root bending fatigue strength is illustrated by specific examples.(2)A reliability optimization design method for anti-fatigue parallel gears is proposed.In order to further optimize the design parameters of parallel gears,a reliability optimization model of parallel gears is established based on the reliability averaging point method,the bending fatigue strength of the tooth root is taken as the constraint,and the gear material cost and manufacturing cost are minimized as the objective function.After that,the design parameters of parallel gears are optimized by using MATLAB’s Optimization Toolbox.Moreover,through case analysis,the feasibility of this method is verified.(3)A reliability calculation method of parallel gear structure considering the relevant failure modes is proposed.In order to accurately and efficiently analyze the structural reliability of parallel gears with relevant failure modes and strong nonlinear characteristics,a structural reliability calculation method considering the relevant failure modes is proposed.Firstly,the state equation corresponding to different failure modes of the gear is constructed,and the mean point is used as the initial point,and the verification points on different failure boundaries are obtained by a reliability analysis method.After that,a hyperplane is established through each verification point,the initial point of high order(m-times)is determined,and the high order(m-times)test points are obtained.Then,the fitting function is established according to the verification points on different failure boundaries and the respective high-order(m-times)verification points,and the reliability of the parallel gear structure of the relevant failure mode is calculated.Finally,the Monte Carlo method is used to verify the calculation results.The final calculation example shows that the method not only has high calculation accuracy,but also has few sampling times and high calculation efficiency.(4)A gear fatigue reliability test bench based on a spatial linkage mechanism was developed and designed.In response to the problems of high cost of gear fatigue reliability test and inconvenient load adjustment,a gear fatigue reliability test bench was developed and designed which is close to the actual working condition and saves the test cost.The test stand is mainly composed of driving part,loading part and center distance adjustment part.The driving part adopts the space linkage mechanism to provide the driving force for the driven gears close to the actual working conditions,the loading part adjusts the load on the driven gears through the double-piston rod hydraulic cylinder with relief valve and check valve,and the center distance adjustment part adjusts the center distance through the screw and threaded bore structure to expand the size range of the tested gears.At the same time,the superiority of using the space linkage mechanism as the driving mechanism of the test bench is explained through the kinematic analysis of the space linkage mechanism and the common plane crank rocker mechanism. |
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