Patent ID: 8220609

Claim:
A torque limiter comprising: a shaft member; and a cylinder member rotatably externally fitted to the shaft member, wherein one member of the cylinder member and the shaft member has, in its inside, a hydraulic passage for pressing a circumferential surface of the one member against a circumferential surface of the other member of the cylinder member and the shaft member, and at least one circumferential surface out of the circumferential surface of the cylinder member and the circumferential surface of the shaft member has an oil-seal preventing groove opened on both sides in an axial direction of the shaft member, wherein in a cross section perpendicular to an extending direction of the oil-seal preventing groove, a line drawn by at least one of the circumferential surface of the cylinder member and the circumferential surface of the shaft member on which the oil-seal preventing groove is formed is smooth at least at both end portions of the oil-seal preventing groove.