In this study, a transient, non-Newtonian, mixed elastohydrodynamic lubrication (EHL) model of involute spur gear tooth contacts is proposed. Unlike the contact between two cylindrical rollers, spur gear contacts experience a number of time-varying contact parameters including the normal load, radii of curvature, surface velocities, and slide-toroll ratio. The proposed EHL model is designed to continuously follow the contact of a tooth pair from the root to the tip to capture the transient characteristics of lubricated spur gear contacts due to these parameter variations, instead of analyzing the contact at discrete positions assuming time-invariant parameters. The normal tooth force along the line of action is predicted by using a gear load distribution formulation and the contact radii and tangential surface velocities are computed from the kinematics and geometry of involute profiles. A unified numerical approach is adapted for handling asperity interaction in mixed EHL conditions. The differences between the transient and discrete EHL analyses are shown for a spur gear pair having smooth surfaces and different tooth profile modifications. The transient behavior predicted by the proposed model is found to be mainly due to the squeezing and pumping effects caused by sudden load changes. The lubrication behavior under rough conditions is also investigated at different operating conditions. DOI: 10.1115/1.4000270

A Transient Mixed Elastohydrodynamic Lubrication Model for Spur Gear Pairs

A model to predict friction-related mechanical efficiency losses of hypoid gear pairs is proposed in this study. The model includes a gear contact model, a friction prediction model, and a mechanical efficiency formulation. The friction model uses a friction coefficient formula obtained by applying multiple linear regression analysis to a large number of elastohydrodynamic lubrication analyses covering typical ranges of key parameters associated with surface roughness, geometry, load, kinematics, and the lubricant. Formulations regarding the kinematic and geometric properties of the hypoid gear contact are presented. The load and friction coefficient distribution predictions are used to compute instantaneous torque/power losses and the mechanical efficiency of a hypoid gear pair at any given position. Results of a parametric study are presented at the end to highlight the influence of key operating conditions, surface finish, and lubricant properties on mechanical efficiency losses of hypoid gears.

Prediction of friction-related power losses of hypoid gear pairs

Thermal elastohydrodynamic simulation of involute spur gears incorporating mixed friction

A numerical model for the solution of thermal elastohydrodynamic lubrication in coated circular contacts

In this study, the elastohydrodynamic lubrication (EHL) behaviour of high-speed spur gear contacts is investigated under dynamic conditions. A non-linear time-varying vibratory model of spur gear pairs is introduced to predict the instantaneous tooth forces under dynamic conditions within both the linear and non-linear operating regimes. In this model, the periodically time-varying gear mesh stiffness and the motion transmission error are used as excitations and a constant damping ratio is employed. This model allows the prediction of steady-state non-linear response in the form of tooth separation (contact loss). An earlier gear mixed EHL model [1] is adapted to simulate the lubrication behaviour of spur gear contacts under these dynamic loading conditions, considering the variations of the basic contact parameters, such as radii of curvature, sliding and rolling velocities, and measured roughness profiles, as the contact moves along the tooth from the start of active profile to the tip. The EHL predicti...

Jingwei Tong

Papers

Transient thermoelastohydrodynamic lubrication analysis of an involute spur gear