Patent ID: 8757337

Claim:
A rotary damper comprising: an accommodating case provided with an inner peripheral surface for accommodating in its interior a viscous fluid whose viscosity declines with a temperature rise and a rotor which is disposed rotatably in the interior of said accommodating case and which partitions the interior of said accommodating case into at least two chambers in cooperation with said accommodating case, wherein said rotor has a rotor body which is rotatably supported in said accommodating case, an outer peripheral surface and an elastic vane which is provided on the outer peripheral surface of said rotor body, wherein said elastic vane includes a curved projecting surface which is continuously connected at one end to the outer peripheral surface of said rotor body and opposes at another end the inner peripheral surface of said accommodating case, and which forms one of the two chambers in cooperation with the inner peripheral surface of said accommodating case, and a curved recessed surface which is continuously connected at one end to the outer peripheral surface of said rotor body, and which forms the other one of the two chambers in cooperation with the inner peripheral surface of said accommodating case, wherein the curved projecting surface has on its other end side a circular arc-shaped projecting surface which forms a pair of wedge spaces opposing each other in a circumferential direction in cooperation with the inner peripheral surface of said accommodating case, one of the pair of wedge spaces communicating with one of the two chambers, another one of the pair of wedge spaces communicating with another one of the two chambers, the circular arc-shaped projecting surface determining a first radial width of the one wedge space such that the first radial width becomes gradually narrow in a circumferential direction from the one wedge space to the other wedge space, and a second radial width of the other wedge space such that the second radial width becomes gradually narrow in a circumferential direction from the other wedge space to the one wedge space, wherein the viscous fluid passing through the pair of wedge spaces is adapted to determine the radial width of the pair of wedge spaces by means of its viscosity by elastically deflecting the elastic vane, and wherein the inner peripheral surface of said accommodating case includes a cylindrical inner peripheral surface which forms the one wedge space in cooperation with the circular arc-shaped projecting surface and a curved recessed inner peripheral surface which is continuously connected to the cylindrical inner peripheral surface and has a complementary shape to the curved projecting surface, and the circular arc-shaped projecting surface has a smaller radius of curvature than a radius of curvature of the cylindrical inner peripheral surface.