The double enveloping toroidal worm drive (DT worm drive) is a typical representative of spatial mechanical drives with complex tooth surfaces, and the lubrication performance is difficult to know precisely. This study aims to investigate the lubrication performance of the DT worm drive during meshing and provide a theoretical basis for understanding the elastohydrodynamic lubrication (EHL) characteristics.
An EHL model of the DT worm drive is developed based on the gear geometry and kinematics, where the contact between the tooth surfaces is simplified as a dual-line contact EHL problem. Numerical calculation of the lubrication model over a complete meshing cycle is conducted using the multigrid method.
The results show that the lubrication quality at the entrance and exit of the worm gear tooth surface is better, while the lubrication quality at the middle position between the entrance and exit of the contact area is relatively poor, making it more prone to lubrication failure. The film thickness at each contact point is significantly influenced by the equivalent curvature radius, and this kind of toroidal worm drive exhibits preferable lubrication performance.
This paper reveals why the DT worm drive exhibits more advantageous EHL performance than other worm drives and how it plays a role. Consequently, this sheds new light on a comprehensive understanding of the interaction between gearing geometry, kinematics and EHL performance. In addition, the EHL characteristic analysis method based on the meshing theory proposed in this paper can be easily extended to other worm drives with complex surface types.
