Patent ID: 8651254

Claim:
An apparatus for a disk brake comprising: a piston; a seal; a caliper body having an inner peripheral surface defining an opening dimensioned to slidably receive the piston therein, wherein the piston moves in a direction of a braking direction axis in response to hydraulic fluid applied to the opening; a seal groove disposed at the inner peripheral surface of the opening and dimensioned to receive the seal therein so that the seal can seal a space between the inner peripheral surface and the piston, wherein the seal groove comprises: a seal groove inner peripheral surface; a movement restricting surface that extends radially inwardly from the seal groove inner peripheral surface and that restricts axial movement of a radially outer portion of the seal in the direction of the braking direction axis; and a movement permitting part that permits axial movement of a radially inner portion of the seal upon movement of the piston in the direction of the braking direction axis, wherein the movement permitting part comprises: a stepped surface formed radially inwardly from the seal groove inner peripheral surface; and a side surface that extends radially inwardly from the stepped surface; wherein a corner is formed between the movement restricting surface and the stepped surface of the movement permitting part to form a fulcrum for bending the radially inner portion of the seal; wherein the stepped surface is oriented relative to the corner such that a fulcrum position of the seal for a bending portion of the seal is always near the corner so that the seal does not progressively contact the stepped surface adjacent to the corner as the radially inner portion of the seal moves toward the side surface; and wherein the first corner has a radius of curvature in a range of from approximately 0.1 millimeter to approximately 0.5 millimeter.