Mesh Characteristic Analysis And Dynamic Performance Optimization Of Gear Transmission System With Small Shaft Angle

Beveloid gears are adopted in usual marine gearbox with small shaft angle,which has both helical angle and cone angle,so its modification coefficient varies along the axes,realizing the power transmission of intersected and crossed axes transmission.Because the contact form of beveloid gear tooth surface is point contact,the contact area is small and the sliding speed is large,causing many problems such as large vibration,high noise and serious wear on tooth surface occur during working procedure.Therefore,developing mesh characteristic analysis and dynamic performance optimization of gear transmission system with small shaft angle is of great theoretical significance and engineering application valuation for improving the dynamic performance of gearbox.Focusing on the gear transmission system with small shaft angle,research on the modeling and dynamic contact analysis of beveloid gear pairs,analysis of the influence factors of meshing stiffness,nonlinear dynamic simulation and dynamic performance optimization of the transmission system are conducted.The main research work in this thesis can be summarized as follows:(1)Using the rack cutter profile equations,the coordinate transformation matrix of imitating machining beveloid helical gear is derived,and then the tooth surface equations of beveloid helical gear are built up.According to the spatial geometric relation,the assemble model of the crossed axes beveloid helical gear pair is constructed,and the contact finite element model can be created by ANSYS/LS-DYNA software.Through the dynamic contact finite elements simulation,the dynamic contact force,dynamic stress and transmission error of beveloid gear pairs during engagement process are studied.(2)The contact ellipse is simplified as the contact line on the long axis,then the gear meshing stiffness is deduced and calculated by the material mechanics theory and the integral idea,comparing with the finite element results,the accuracy of the stiffness calculation method is verified.On this basis,the influence of normal pressure angle,pitch angle and external load on meshing stiffness is analyzed and discussed.(3)Taking time-varying mesh stiffness,clearance,transmission error and mesh damping into overall consideration,a nonlinear dynamic model of transmission system under complex excitation is established based on lumped parameter method.The dimensionless dynamic differential equations are solved by Runge-Kutta method.Then the bifurcation maps,time history curves,spectrum,phase traces,Poincaré and dynamic load coefficient curve are analyzed to study the effect of different parameters on nonlinear dynamics characteristics of gear transmission system.(4)On the basis of gear transmission system lumped parameter model,the analytical solution of vibration response of each component of transmission system is obtained by harmonic balance method.A multi-objective mixed discrete optimization model with objectives of minimizing RMS value of vibration acceleration and total mass is established by taking structural parameters of gear pairs as design variables,and through writing discrete optimization program,the optimal design variables are obtained based on the branch-bound algorithm.