Transient non-Newtonian elastohydrodynamic lubrication analysis of an involute spur gear

Abstract

The meshing of a gear is a typical example where non-stationary conditions exist. Load, velocities and curvature vary along the line of action. In this analysis, pressure and film thickness are computed at several points along the line of action by taking the transient effect into consideration. Isothermal full film lubrication is assumed and the fluid model is a non-Newtonian model which includes the effect of a limiting shear strength. The gear teeth are assumed to be rigid. The load is first assumed to be carried by either two pairs of gear teeth or by only one pair. This transition from two to one pair and vice versa is modelled as a step variation of the load. The results show that the transient effect is most pronounced at the load transitions where the previous pair of teeth goes out of action and where the next pair of teeth comes into action. Due to the squeeze effect, the minimum film thickness increases for a moment when the load is doubled. The opposite happens when the load is halved again, the film thickness decreases for a moment until it stabilises. The friction coefficient is computed at the different contact points and so are also the sub-surface stresses. Results are presented for two different lubricants, a paraffinic mineral oil and an oil of the poly-α-olefin type.