Patent ID: 7677123

Claim:
An impact absorbing device, comprising: a fixed disc with a first frictional surface; and a rotary disc with a second frictional surface so as to coaxially face the first frictional surface of the fixed disc, the rotary disc being rotatable on the fixed disc against a frictional force between the fixed disc and the rotary disc in response to a load torque given to the rotary disc as an impact force, wherein the fixed disc has a plurality of first dimples on the first frictional surface, the rotary disc has a plurality of second dimples on the second frictional surface, each of the second dimples being movable along a circumferential direction of the discs in response to the load torque, a position of each of the second dimples is differentiated from a position of any of the first dimples in a radial direction of the discs substantially perpendicular to the circumferential direction, and the first dimples are arranged on the first frictional surface to form a plurality of blocks aligned with one another along the circumferential direction such that the first dimples of each block are arranged substantially at an equal pitch Pd along the radial direction, the second dimples are arranged on the second frictional surface to form a plurality of blocks aligned with one another along the circumferential direction such that the second dimples of each block are arranged along the radial direction at the same equal pitch Pd as the first dimples are arranged, and the positions of the second dimples of each block are, respectively, differentiated in the radial direction by a shift value X from the positions of the first dimples of any block so as to satisfy a relation: X=c×Pd wherein a constant c ranges from 0.1 to 0.5.