Patent ID: 7823983

Claim:
A parking brake system comprising: a casing having a hollow bore formed therein; a parking piston slidably fitted into the casing, said parking piston configured and arranged so that a parking brake state of a wheel brake can be obtained by forward movement of the parking piston in the bore in response to a parking control fluid pressure acting on a rear face side of the parking piston; a lock mechanism provided within the casing so as to automatically lock in response to forward movement of the parking piston in order to mechanically lock the parking piston at a forward position and unlock in response to a parking release control fluid pressure acting on the lock mechanism, the lock mechanism comprising a lock piston that is slidably fitted into the casing to the rear of the parking piston so that the parking release control fluid pressure can act on the lock piston toward the rear and a spring provided in a compressed state between the lock piston and the casing so as to exhibit a spring force that urges the parking piston to move forward; a fluid pressure source; and a fluid pressure control mechanism for controlling a fluid pressure generated by the fluid pressure source so that the parking control fluid pressure and the parking release control fluid pressure can be obtained; an opening provided in a portion of the casing that the rear side of the lock piston faces being closed by a separate, detachable lid member, a tool connection part being provided in a rear portion of the lock piston, and the tool connection part enabling a tool inserted through the opening to be detachably connected to the tool connection part, wherein the tool is configured to be inserted through the opening from the outside of the casing and connected to the tool connection part to enable manual operation of the lock piston via the tool, a front face of the parking piston faces an air chamber defined within the casing, the spring is provided in a spring chamber formed between a rear face of the lock piston and the casing, a first communication passage communicating with the spring chamber extends axially through the lock piston, and a second communication passage communicating the first communication passage with the air chamber is provided in the parking piston, the opening provided in the casing communicates with the spring chamber, and the tool connection part is an internal thread formed on a rear part of an inner face of the first communicating passage.