Theoretical modeling and transmission characteristics analysis of a novel double-roller hourglass worm drive based on enveloping principle

Traditional planar double-enveloping hourglass worm pairs have the characteristics such as the strong bearing capacity, high transmission efficiency and long life-span. However, the high relative sliding velocity and the serious agglutination or abrasion may also occur at the contact point on tooth surfaces. In this paper, a novel type of double-roller hourglass worm pair is proposed and analyzed, wherein, the worm part adopts from the planar double-enveloping worm pair, the corresponding meshing tooth surface of worm gear is replaced by two rows of cylinder rollers for reducing friction and enhancing meshing efficiency. That is, the original meshing tooth surfaces in worm gear are replaced by the common tangent plane of rollers to form a special type of meshing drive, the original line-contact form between tooth surfaces was changed to point-contact so that the sliding friction was transformed into rolling friction, and the meshing efficiency can be greatly improved. The theoretical model of double-roller hourglass worm pair was established based on spatial enveloping principle, the meshing equation and tooth surface equations were derived. The solid models of worm and gear were established and assembled. The parameters of enveloping surface angle, roller radius and friction coefficient, which affecting relative motion velocity at meshing contact point and efficiency during the whole transmission process was analyzed and discussed systematically. The results showed that comparing to the traditional worm pair, the roller’s rotation greatly reduced the relative sliding velocity and improved meshing efficiency at the contact point in this double-roller hourglass worm pair.