Modelling lubrication in gear pairs

The lubrication regime in gear pairs is usually elasto-hydrodynamic, i.e. solid deformations due to the fluid pressure are not negligible. It is well known that lubrication in gear pairs depends upon a number of kinematical parameters, so that it is a non stationary EHD problem. Moreover, it depends upon the dynamic response (i.e. the dynamic load) of the gear pair [1-5]. The problem of finding the dynamic response in gear systems, especially spur gears, has been studied by many research works. Most of them consider as the main source of vibration the time variation of the number of teeth pairs that are in contact at the same time. This fluctuation makes the transmission more stiff, when two pair of teeth are in contact, more deformable when only one pair is in contact. This behaviour can cause oscillations of the gears, and eventually detachment of the teeth in contact, with impacts and noise. The purpose of the present work is to investigate the effect of the varying rotational velocity of the gear pair on the film thickness and the contact pressure distribution. The lubrication regime in spur gear pairs is investigated using an EHL lubrication model. The solver described by Venner and Lubrecht [6] is adapted to the specific transient problem. Different test cases at different speeds are presented, in order to point out the role of the dynamic coupling on the lubricated contact.