Undercutting mechanism of worm wheel in offsetting normal arc-toothed cylindrical worm drive

Abstract

The worm wheel whose undercutting characteristic is researched is a member of offsetting normal arc-toothed cylindrical worm drive. The tooth profile of the worm in its offsetting normal section is a circular arc. The normal vector used to calculate the first-type limit function is determined in the natural frame without the aid of the curvature parameter of worm helicoid. The first-type limit line is ascertained via solving the nonlinear equations iteratively. It is discovered that one first-type limit line exists on the tooth surface of worm wheel by numerical simulation, and such a line is normally located out of the meshing zone. Only one intersection point exists between the first and second-types of limit lines, and this point is a lubrication weak point. The undercutting mechanism is essentially that a part of the meshing zone near the conjugated line of worm tooth crest will come into the undercutting area and will be cut off during machining the worm wheel. The machining simulation verifies the correctness of undercutting mechanism. Moreover, a convenient and practical characteristic quantity is proposed to judge whether the undercutting exists in the whole meshing zone via computing the first-type limit function values on the worm tooth crest.

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Central South University