A General Modification Theory for Double-Enveloping Hourglass Worm Drives
A universal modification theory is developed for all kinds of hourglass worm drives, no matter what shape the generating surface of the worm is. Based on the theory established, toroidal worm drives can be classified into two main categories: with singular points and without singular points. That is to say, the unmodified hourglass worm gearing is merely a special case of the modified one in essence. Furthermore, the meshing characteristics of a double-enveloping toroidal worm drive are entirely up to the situation of the solution of the meshing equation of the second envelope.
Daizhong Su, Kai Xue and Shifan Zhu
Y. P. Zhao and T. C. Wu, "A General Modification Theory for Double-Enveloping Hourglass Worm Drives", Key Engineering Materials, Vol. 486, pp. 279-282, 2011