Mesh Performance Analysis And Fatigue Life Prediction Of Crossed Axes Beveloid Helical Gears

Beveloid helical gears are adopted in usual marine gearbox with small shaft angle, the main characteristic of this kind of gear is its modification coefficient varies along the axes, the need of intersecting and crossed axes transmission in marine gearbox can be well met by this feature. This paper takes the crosssed axes beveloid helical gear pair as research object, applies the spatial gears meshing theory, Hertz point contact theory, dynamic contact analysis method and fatigue life evaluation theory comprehensively, and carries out research about gear pair parameter design, gear tooth profile generation and finite element modeling, meshing performance analysis and fatigue life prediction of the beveloid helical gear pair. Correlational research will be of great theoretical significance and engineering application valuation in choosing the appropriate beveloid gears' parameter, improving the bearing capacity and extending the service life.The research work in this thesis can be summarized as follows:(1) According to the processing principle of the beveloid helical gear, introducing the concept of fictitious public rack, according to the principle of spatial gear meshing, the tooth shape parameters of the crossed axes beveloid gear pair are calculated, and according to the size requirements of the marine gearbox with small shaft angle, a pair of crossed axes beveloid gears are designed.(2) Using the rack cutter profile equations, the coordinate transformation matrix of imitating machining beveloid helical gear is derived, then the tooth surface equations of beveloid helical gear are built up. According to the bevel gear meshing theory, the assembly relation of the crossed axes beveloid helical gear pair are determined, the assemble model of the crossed axes beveloid helical gear pair is constructed by the Matlab and UG software.(3) Applying the conjugate surface theory, the main curvature and principal direction of the crossed axes beveloid helical gear are calculated, and combining with Hertz contact theory, the tooth contact strength of the gear pair is checked. Deriving the tooth root bending stress calculation formula of beveliod helical gear, the tooth root bending strength is checked. In the ANSYS software, the static contact finite element model of the crossed axes beveloid helical gear pair is established, through the simulation, the tooth contact stress and tooth root bending stress of the gear pair are obtained and coincident with the results obtained by thoretical calculation very well, the theoretical calculation and simulation method are proved to be correct thereby.(4) With the help of ANSYS/LS-DYNA software, the solid model of the crossed axes beveloid helical gear pair is discretized and the boundary conditions are applied, then the contact finite element model can be created. Through the dynamic contact finite elements simulation, the dynamic contact stress contour of the gear pair is gained, the dynamic contact force and transmission error of the crossed axes beveloid helical gear pair during engagement process are studied.(5) Taking the dynamic contact force of the crossed axes beveloid helical gear pairs during meshing process as load spectrum,calculating the S-N curve of gear material based on GL standard, combining the stress and strain result from static simulation, fatigue life analysis of the crossed axes beveloid helical gear pair are conducted by ANSYS/FE-SAFE software, the logarithmic fatigue life and the fatigue safety factors of the crossed axes beveloid helical gears are obtained, the influence of tooth surface roughness and load magnitude on fatigue life of gear pair are analysed as well.