Effect of lubricant rheology on hypoid gear pair efficiency

Abstract

A tribo-dynamics model of a differential hypoid gear pair is presented, integrated with lubricated contact of meshing teeth pair with lubricants of varying rheological properties. Particular attention is paid to the effect of lubricant formulation and gear geometry on the system efficiency. The influence of gear torsional dynamic response is taken into account in a 4-Degree of Freedom (DoF) model. The contact geometry and kinematics of the hypoid gear pair are estimated, using Tooth Contact Analysis (TCA). Two fully formulated gear lubricants of the same viscosity grade (SAE 75W-90) blended with the same additive pack, but with different types and concentration of viscosity modifier (VM) are considered. Conjunctional friction is predicted for viscous shear of fully characterised lubricants as well as boundary interaction of rough surfaces. The results show loss of friction resulting in resonant response of the gear pair with impact of meshing teeth exhibiting non-linear jump phenomenon. The predictions also show that lubricants with higher pressure – viscosity (PV) coefficients tend to exhibit increased power loss.