Contact and elastohydrodynamic analysis of worm gears Part 2: Results

Abstract

The paper presents the results of modelling the contact and elastohydrodynamic lubrication (EHL) effects between the teeth of worm gears. A number of different practical worm gear designs have been studied covering a wide range of sizes and potential applications, from small instrument drives to high power units. All the designs are of the popular ZI type, in which the worm is an involute helicoid, with deliberate mismatch of tooth conformity in order to avoid damaging edge contact. The results cover loaded tooth contact analysis (‘loaded TCA’) under dry conditions, predicted film-generating behaviour with lubrication, surface and oil film temperatures, and calculated values of friction and transmission efficiency. It is demonstrated that regions of poor film formation may be predicted in a qualitative way on the basis of loaded TCA together with consideration of the kinematics of entrainment at the contacts.