Research On Fretting Fatigue Of Planetary Gear-Bearing Interference Fit Surface

The planetary gear transmission system is a common type of reduction mechanism typically used in applications requiring high loads,high precision,and high reliability.The planetary gear transmission system is composed of a sun gear,planetary gears,and a ring gear.Among them,the planetary gears are composed of multiple gears,and are connected to the sun gear and the ring gear through a planetary carrier.The interference fit between the planetary gears and the bearings is a common mechanical connection method,which makes the interference surface of the bearings closely contact with the mating surface of the planetary gears to achieve the transmission and support of the bearings and planetary gears.However,due to the special structure of the interference fit,slight relative sliding or micro-movement may occur between the two,resulting in local stress concentration and surface fatigue phenomena.When using a planetary gear transmission system,the interference fit between the gear and the bearing is subjected to significant forces and torques,which can cause microslip and displacement of the bearing’s interference surface,leading to fatigue damage.For a long time,micro-motion fatigue has been one of the key issues limiting the service life and reliability of planetary gear transmission systems.The micro-motion fatigue of planetary gears is caused by repeated contact stress and shear stress on the gear teeth,resulting in plastic deformation and small cracks on the gear surface.These plastic deformations and cracks gradually accumulate over time and eventually lead to gear fatigue failure.This thesis focuses on the following three aspects of research:(1)Based on the thick-walled cylinder theory and Lame’s formula,the stress and strain of the planetary gear and bearing caused by interference fit were analyzed,and the stress distribution along the depth direction was obtained.Considering the structural parameters of the planetary gear and bearing,a finite element analysis model of the planetary gear system with interference fit between the planetary gear and bearing was established.The contact pressure distribution law under different interference fit amounts was studied,and the theoretical pressure derived based on the thick-walled cylinder theory and Lame’s formula was compared to verify the accuracy of the finite element analysis.(2)The theoretical analysis of the force on the planetary gear was conducted,and the conditions for determining whether there is sliding between the interference fit surfaces of the planetary gear and the bearing were derived.The calculation method for the sliding amount of the inner wall of the planetary gear was derived based on the finite element method.The micro-slip between the planetary gear and the bearing under rated load and ultimate load was quantitatively analyzed in detail using finite element analysis,and a method for selecting the optimal interference fit amount between the planetary gear and the bearing was proposed.(3)Using matlab numerical analysis method,based on the damage parameter model proposed by Smith,the fatigue damage model is solved to obtain the stress-based damage parameter SWT values along the axis of the planetary gear,thereby determining the location of the fatigue damage of the planetary gear under the interference fit.Subsequently,the problem of slippage between the planetary gear and the bearing is analyzed from the perspectives of manufacturing errors and installation errors,and the influence of the hub thickness and mating length on the interference fit is summarized.