Lubricated contact analysis of a spur gear pair with dynamic loads

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Abstract

In the present research study, a comprehensive spur gear lubrication analysis has
been carried out to understand the gear contact behaviour under lubrication
conditions. The modelling works have been extended to consider the effects of
thermal mechanical, non-Newtonian fluid, surface roughness, transient squeeze and
dynamic load conditions.
First, the elastohydrodynamic lubrication theory is studied and relevant
numerical approaches are introduced. The reduced Reynolds equation technique is
applied to deal with any potential "asperity contacts" or any other ultra-thin film
situations. Those situations could be a result of the surface roughness or the dynamic
load effect. This approach allows us to capture local information about pressure,
traction, film thickness, etc., within the nominal contact zone. Influence of working
conditions, i.e. load, rolling speed, as well as the sliding to roll ratio are discussed
with those models (Newtonian or non-Newtonian fluids, isothermal or thermal
conditions). The non-Newtonian fluid effect has been investigated with a
Ree-Eyring fluid model and a power-law fluid model and the thermal effect is
studied by solving energy equations of interacting solids and the film numerically
with the sequential sweeping technique.
The dynamic effect on contact performance is also studied. The dynamic load is
calculated using a two degree-of-freedom lumped parameter system dynamic model
in which the varying mesh stiffness is considered as the excitation. The dynamic
model is solved using the Runge-Kutta method. The effects of the dynamic load
effect on pressure distribution and film thickness in a whole mesh period are
discussed. The normal contact stiffness of a spur gear pair is also predicted based on
the deterministic tribology models.
The main contributions from the present research could be summarized as follows:
i. An elastohydrodynamic lubrication model for a spur gear pair is developed
by taking into account the effects of transient squeeze, the non-Newtonian fluid, the
rough surface and the thermal mechanical contacts which makes the proposed model
one of the most advanced models currently evaluating gear lubrication performance.
This model can also be applied to bearings, cams, or other gear types with some
modifications.
ii. The friction behaviour, which is not investigated as extensively as the film
thickness in existing work, is studied. The effects of the working conditions (the
load, the rolling speed, the slide/roll ratio), the non-Newtonian conditions, the rough
surface conditions, as well as the thermal conditions on friction behaviour are
discussed. The conclusions suggest controlling surface topography patterns and
working conditions aiming at a reduced friction coefficient and a longer service life.
iii. The dynamic effect on lubrication performance and effect of lubrication on
normal contact stiffness of a spur gear pair are studied. The work provides a
potential gateway for a more comprehensive evaluation of spur gear pair working
performance using a tribology-dynamic coupled method which is the next area this
author would like to explore.

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