Dynamic and tribological study of a planetary gearbox with local nonlinearities

Abstract

A planetary gearbox model comprising five spur gears (sun, ring and three planets) and the carrier has been developed and analysed. The influence of gear teeth backlash and friction during mixed regime of lubrication has been taken into consideration. Greenwood and Tripp model is employed, while viscous friction is calculated analytically using the functions of Evans and Johnson. A combined tribodynamics modeling approach has been implemented and modal analysis is performed in order to predict the coupled mechanism of tribological and dynamic behavior, subjected to backlash and excited at the gear meshing frequency. The software used for the simulations is ADAMS MSc (Student Edition), where the model variables (concerning gear geometry and forcing functions) have been added in a parametric way. The results showed that small variations of the dynamic transmission error affect notably the viscous friction through changing the contact load between the engaged teeth pairs. Also, higher values of the Stribeck oil parameter due to higher film thickness or lower surface roughness in the mixed lubrication regime lead to reduction of the boundary friction, whereas a reduction of the total generated friction occurs when increasing the angular velocity of the input gear body (due to higher film thickness and smaller asperity interactions). The above lead to reduced power loss of the mechanism. Finally, a characterization of the system dynamics is presented using the calculated eigenvalues and eigenmodes of the corresponding linearized system. Potential interactions with the gear meshing frequency of the system are also examined.