Patent ID: 7458445

Claim:
A parking brake system comprising: a casing having a hollow bore formed therein to accommodate a parking piston; a parking piston slidably fitted into the casing so that a parking brake activation state can be achieved by forward movement of said parking piston 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 to the rear side of the parking piston, said lock mechanism configured and arranged 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; 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; the lock mechanism comprising a hydraulically actuatable lock piston that is disposed to the rear of the parking piston while having an axis orthogonal to the axis of the parking piston and that makes a forward urging force act on the parking piston when the parking piston moves forward, and opposite end parts of the lock piston being slidably fitted into and supported on the casing.