Opposed-piston type disk brake device

An opposed-piston disk brake device, comprising:

• a caliper including
• an outer body part and an inner body part which are arranged across a rotor rotatable together with a wheel,
• a pair of connecting parts connecting together peripheral-direction two ends of the outer body part and inner body part at a position existing more outward in a radial direction than an outer peripheral edge of the rotor, and
• at least one set of cylinders respectively arranged in the outer body part and inner body part to be opposed to each other, the caliper being fixed to a suspension device while straddling over the rotor;
• pistons respectively fitted in the cylinders to be liquid-tight and movable along the axial direction;
• at least a pair of pads respectively arranged on opposite sides of the rotor and supported by the caliper to be movable along an axial direction with respect to the caliper;
• and
• a parking mechanism part including
• a clamp member including a pressure part in an outer side end thereof and a base part in an inner side end thereof, interposed between the connecting parts along a peripheral direction, supported by the caliper to be movable in the axial direction with respect to the caliper while straddling from outward in the radial direction over the pair of pads and the inner body part respectively intervening between the pressure part and the base part along the axial direction of the pads, and
• a thrust generation mechanism including a member supported on the base part and movable toward the inner side with respect to the caliper when a parking brake is operated and a member arranged in the cylinders provided in the inner body part and movable toward the outer side when the parking brake is operated,
• wherein a braking force by a service brake is generated when pressure oil is supplied into the cylinders and the pads are pressed against opposite side surfaces of the rotor by the pistons,
• wherein a braking force by the parking brake is generated by that an inner side pad of a pair of the pads over which the clamp member straddles from outward in the radial direction is pressed against a side surface of the rotor directly or indirectly by the member movable toward the outer side, and an outer side pad of the pair of the pads is pressed by the pressure part against a side surface of the rotor when the clamp member is moved toward the inner side with respect to the caliper due to a reacting force caused by the pressing action of the inner side pad, in accordance with operation of the thrust generation mechanism,
• wherein an inner side piston of the pistons which is fitted in a same cylinder as the member moving toward the outer side has a stepped shape including an outer side large diameter part, an inner side small diameter part and a step surface formed continuously with the large and small diameter parts and configured to receive a pressure of the pressure oil, and
• wherein a pressure receiving area of the step surface is equal to a pressure receiving area of an outer side piston of the pistons which is arranged opposed in the axial direction to the inner side piston.