Patent ID: 8523690

Claim:
A boot for a constant velocity universal joint, the boot comprising: a large diameter section to be mounted to an outer joint member of a constant velocity universal joint; a small diameter section to be mounted to a shaft coupled to an inner joint member of the constant velocity universal joint; and a bellows section arranged between the large diameter section and the small diameter section, wherein the bellows section comprises three or more peak portions, three or more valley portions arranged alternately with the three or more peak portions along an axial direction, and coupling portions coupling the peaks portions and the valley portions that are respectively adjacent to each other, wherein the coupling portions are inclined portions in a stress-free state, and a radially outer portion of each of the three or more peak portions in vertical cross-section of the boot is formed into a round shape, wherein a stress distributing and equalizing structure and a smooth fold-deformation enabling structure are configured by one or two of the three or more peak portions positioned at a central portion between the large diameter section and the small diameter section, wherein the stress distributing and equalizing structure is configured by setting a curvature radius of a radially outer portion of a peak portion that is positioned only at the central portion between the large diameter section and the small diameter section to be larger by 1.3 times or more and less than 4 times than curvature radii of the radially outer portions of others of the three or more peak portions including a peak portion arranged adjacent to the large diameter section and a peak portion arranged adjacent to the small diameter section, and the smooth fold-deformation enabling structure is configured by having a radially outer end of the peak portion at the central portion between the large diameter section and the small diameter section and having the larger curvature radius positioned at a radially inner side with respect to a straight line connecting a radially outer end of a peak portion on a large diameter section side and a radially outer end of a peak portion on a small diameter section side that are adjacent to the peak portion having the larger curvature radius, and wherein one stress distributing and equalizing structure and one smooth fold-deformation enabling structure are provided at the central portion between the large diameter section and the small diameter section.