| As one of the core components of the vessels propulsion system,the down angle marine reduction gearbox is commonly widely used in the transmission system of high-speed yachts and speedboats because of the inclined angle between the input shaft and output shaft,which can be used to achieve the specific requirements of specific efficiency and space utilization.Currently crossed beveloid gear transmissions theoretically point in contact,which results in issues with the gear pair including low carrying capacity,easy wear,and short service life.Furthermore,the machining surface of beveloid gear has specialized topographical features as a consequence of repeated clamping and positioning,tool edge wear,and other machining errors.Therefore,considering the surface topography and time-varying friction force between tooth surfaces,the meshing characteristics and dynamic characteristics of crossed beveloid gear pairs are studied,and the tooth surface modification method of approximate line contact was proposed.The purpose is to improve the carrying capacity of the crossed beveloid gear transmission and reduce the vibration and noise of the beveloid gear transmission,which has important theoretical significance for the engineering application of the crossed beveloid gear transmission.The research work and achievements developed in this dissertation are as follows:(1)The mathematic equations of beveloid gear tooth surfaces are developed based on the space meshing principles and hobbing theory.The fractal characterization method of the rough tooth surface of beveloid gears with anisotropic surface topography is proposed by a series of asperities with random height and random distribution superimposed on the normal direction of the theoretical tooth surface.In addition,the measurement experiments of beveloid gear tooth surface topography are carried out,and the characterization method proposed in this dissertation is compared and analyzed with the measurement results to verify the accuracy of the method.(2)The mathematical model of the real contact area,real contact load,and normal contact stiffness of the rough tooth surface have been established,taking into account the effects of the eccentricity of the ellipsoidal asperities of the rough tooth surface and the point contact of the crossed beveloid gears.And the influence of gear tooth surface topography on the elastic-plastic contact load and normal contact stiffness of the meshing surfaces of gear pairs under different fractal parameters is investigated.(3)The teeth of the beveloid gear are discretized and analyzed by the slicing idea,and the contact stiffness,bending stiffness,shear stiffness,compression stiffness,and foundation stiffness of the beveloid gear is calculated based on the theory of material mechanics.On this basis,considering the topography characteristics of the rough tooth surface,a numerical calculation method for the time-varying mesh stiffness of the beveloid gear is proposed,and the influence of structural design parameters and tooth surface topography parameters of beveloid gears on the time-varying meshing stiffness is investigated comprehensively.(4)An 8-DOF nonlinear dynamic model of crossed beveloid gear pairs was established considering the interaction between tooth surface topography and timevarying friction.And the Runge-Kutta method was used to solve the differential equations of the system dynamics and the influence of different tooth surface topographies on the dynamic characteristics of the beveloid gear transmission system were investigated during meshing.(5)Aiming at the phenomenon of eccentric load and stress concentration in the crossed beveloid gear transmission,a modification scheme of the eccentric concave surface of the beveloid gear tooth direction is proposed,which realizes the effective improvement of the bearing capacity of the crossed beveloid gear transmission.In addition,combined with the transmission characteristics of the gearbox with a small down angle,a new type of down angle marine reduction gearbox transmission mechanism is proposed to effectively reduce product processing and manufacturing difficulties.The dynamic characteristics of the crossed beveloid gear transmission system are tested to verify the accuracy of the multi-degree-of-freedom nonlinear dynamic model established in this dissertation. |
PDF Full Text Request