Tripod type constant velocity universal joint

Abstract

A tripod type constant velocity universal joint comprises an outer joint member having three track grooves with roller-guiding surfaces opposing each other circumferentially, a tripod member with three trunnions protruding in a radial direction, a plurality of rollers each inserted into a corresponding track groove and a plurality of rings each fitted on the corresponding trunnion for supporting the roller rotatably. An outer surface of the trunnion is formed to take on a straight shape in a longitudinal section and an ellipse shape in a cross-section. A contact ellipse shape between the trunnion and the ring is modified so as to render the radius of curvature r smaller while keeping an aspect ratio b/a stable in comparison with a contact ellipse shape being defined to minimize contact pressure between a ring inner surface and a trunnion outer surface.

1 - 2 . (canceled) 
   
   
       3 . A method of forming a tripod type constant velocity universal joint, wherein the tripod type constant velocity universal joint includes: an outer joint member having three track grooves, each of the track grooves having a pair of roller-guiding surfaces opposing each other in a circumferential direction; and a tripod member having three trunnions protruding in a radial direction, the method of forming the tripod type constant velocity universal joint comprising:
 inserting a plurality of rollers into a corresponding one of the track grooves, each of the rollers being movable in an axial direction of the outer joint member along the corresponding pair of roller-guiding surfaces;   fitting each of a plurality of rings on a corresponding one of the trunnions for rotatably supporting one of the rollers, an inner surface of each of the rings being formed as a convex arc R in longitudinal section;   forming, for each of the trunnions, an outer surface of the trunnion to take on a straight shape in a longitudinal section and an ellipse shape in a cross-section to render the outer surface thereof contiguous to the inner surface of the corresponding ring in a direction perpendicular to a joint axial direction and to provide play between the inner surface of the ring and the outer surface of the trunnion in the joint axial direction; and   modifying, for each of the trunnions, a contact ellipse shape between the trunnion and the corresponding ring so as to render a radius of curvature r smaller while keeping an aspect ratio b/a stable in comparison with the contact ellipse shape being defined to minimize contact pressure between the inner surface of the ring and the outer surface of the trunnion,   wherein r is a radius of curvature r of the convex arc R in a longitudinal section of the inner surface of the ring, a is a major axial length of trunnion cross-section ellipse, b is a minor axial length of trunnion cross-section ellipse, and b/a is an aspect ratio of trunnion cross-section.   
   
   
       4 . The method of forming a tripod type constant velocity universal joint according to  claim 3 , wherein the radius of curvature r is from 1.9a to 2.5a, and the aspect ratio b/a is from 0.8 to 0.9.