Patent ID: 8348023

Claim:
A disk brake comprising: a pair of pads disposed on the respective sides of a disk; a piston adapted to press at least one of the pair of pads against the disk; a caliper body including a cylinder capable of containing the piston such that the piston is movable in the cylinder, the caliper body adapted to advance the piston by a supply of a fluid pressure into the cylinder; an electric motor disposed at the caliper body; and a parking brake mechanism disposed at the caliper body, the parking brake mechanism operable to advance the piston based on a rotation of the electric motor and maintain the advanced piston at a parking brake applying position, the parking brake mechanism comprising a speed reducing mechanism for increasing a rotational force from the electric motor, a rotation/linear motion converting mechanism for converting a rotation of the speed reducing mechanism into a linear motion, and a rotation preventing mechanism for preventing a rotation of the speed reducing mechanism in a direction causing the piston to return, the speed reducing mechanism comprising an input member adapted to rotate in response to an input from the motor, and a pair of output members adapted to rotate in opposing directions so as to increase a rotational input from the input member to provide a rotational output, the speed reducing mechanism constituted by an input-output coaxial type speed reducer in which the pair of output members and the input member are coaxially disposed; wherein one output member of the pair of output members transmits a rotation to the rotation/linear motion converting mechanism; the rotation preventing mechanism prevents a rotation of the one output member in the direction causing the piston to return; the other output member of the pair of output members rotates by a predetermined range to act on the rotation preventing mechanism; when the motor causes the input member to rotate so that the piston moves in a return direction, a rotation of the other output member according to the rotation of the input member releases rotation prevention of the rotation preventing mechanism to the one output member; the rotation preventing mechanism is supported by the caliper body, and comprises an engagement member adapted to be engaged with and disengaged from the one output member according to a rotational direction of the other output member; and the other output member includes at least one contact portion, and when the motor rotates so that the piston moves in the return direction, the other output member rotates and the at least one contact portion contacts the engagement member to move the engagement member from an engagement position, where the engagement member is engaged with the one output member, to a disengagement position, where the engagement member is disengaged from the one output member.