Research On Lubrication Performance Of VH-CATT Cylindrical Gear Transmission

The cylindrical gear transmission with a variable hyperbolic circular-arc-toothtrace(VH-CATT cylindrical gear transmission)is a new type of gear transmission developed from Gleason spiral bevel gear transmission.Because of its excellent performance such as strong bearing capacity,higher transmission efficiency,lower installation precision requirements,and no axial force,it is expected to be widely used in aerospace,ship vehicles,and other occasions.In engineering practice,the VHCATT cylindrical gear transmission is operated under high-speed or heavy-load conditions,and the lubricant is introduced to prevent direct contact of the rough peaks between gears.Since the physical quantities such as spatial geometry,contact load,and speed of each meshing instant of the gear transmission are constantly changing,and under the joint influence of tooth surface roughness and thermal effect,the elastic deformation of the gear surface and the viscosity and density changes of the lubricant will be significantly enhanced,thus forming a complex and unknown lubrication state in the contact area.The quality of the lubrication state will directly affect the transmission performance and service life of the VH-CATT cylindrical gear transmission.At present,some progress has been made in the research on the forming principle and meshing principle of VH-CATT cylindrical gear transmission.However,due to the limitation of theoretical analysis and numerical calculation,the research on the lubrication characteristics of the gear transmission is few,and its lubrication mechanism has not been fully revealed.Therefore,based on the forming principle and meshing principle of VH-CATT cylindrical gear,starting from the tooth surface contact characteristics and considering the influence of various dynamic and static factors,this paper systematically studies and analyzes film-forming property and the thermal elastohydrodynamic lubrication(TEHL)characteristics of smooth and rough tooth surface under elliptical contact in a meshing period,and further reveals the lubrication mechanism of the gear transmission.The main contents and results are as follows:(1)Combined with the forming principle of VH-CATT cylindrical gear,the tooth surface equation and three-dimensional accurate modeling method of it under the double-edged cutting mode of rotary cutterhead are expounded.(2)Based on the forming principle and tooth surface equation of VH-CATT cylindrical gear,the meshing space coordinate system simulating the assembly and transmission process of the gear pair is established,and the equation expressions of tooth surface and unit normal vector in the meshing space coordinate system are derived according to the gear meshing principle and differential geometry principle.Through the analysis of tooth profile meshing process,the rotation angle range of meshing surface in one meshing cycle is obtained.Therefore,the tooth contact analysis(TCA)model of VH-CATT cylindrical gear transmission is established,the numerical calculation method and the corresponding program of the model are determined.After numerical calculation,the full numerical solution of instantaneous contact point,unit normal line,and contact trace in a meshing period is obtained.(3)According to the principle of gear geometry,the numerical calculation methods of some dynamic parameters(instantaneous contact point curvature,entrainment velocity,and rolling ratio,etc.)affecting the lubrication performance of the contact area are derived based TCA results.The analysis model of elastohydrodynamic lubrication(EHL)minimum and center oil film thickness is established by introducing dynamic parameters.The variation law of EHL oil film thickness in a meshing period of VH-CATT cylindrical gear transmission under constant input load and rotational speed is studied,and the lubrication film forming performance of different contact areas on the tooth surface during transmission is revealed.In view of the static factors(input parameters and design parameters)that may affect the lubrication performance of VH-CATT cylindrical gear transmission,through lubrication film-forming property under different input torque under different input torques,rotational speeds,pressure angles and tooth radiuses is analyzed parametrically,and its influence on the overall lubrication film-forming performance and the weak lubrication contact area is quantified.(4)Based on the TCA model of VH-CATT cylindrical gear transmission,according to the elastic mechanics and Hertz contact theory,the loaded tooth contact analysis(LTCA)model is established,and the numerical calculation method of another part of the dynamic parameters affecting the lubrication performance is deduced,including the maximum Hertz contact stress and Hertz contact ellipse at each meshing instant.After introducing all the dynamic parameters,and considering the three-dimensional roughness,contact temperature rise,elastic deformation,lubricant rheological properties and other physical quantities,the elliptical contact TEHL analysis model of VH-CATT cylindrical gear transmission interface considering various factors is established,and the numerical solution and the corresponding program of the model is derived.Through the model,the TEHL numerical solutions(oil film thickness,pressure,and temperature distribution)of VH-CATT cylindrical gear transmission under smooth and rough tooth surfaces in a meshing period are obtained.The evolution law of the lubrication state along the contact trace in a meshing period is studied in detail,and the comprehensive lubrication characteristics of VH-CATT cylindrical gear transmission are further revealed when considering various dynamic factors.