Automatic parking brake device

An automatic parking brake system comprising:

• a parking piston (23, 103) which is slidably fitted into a casing (22, 102) and has a parking control fluid pressure chamber (28, 106) defined between a rear face of the parking piston (23, 103) and the casing (22, 102) so that a parking brake state can be obtained by forward movement in response to a parking control fluid pressure acting on the parking control fluid pressure chamber (28, 106);
• a lock mechanism (25, 105) having a lock piston (24, 104) which is slidably fitted into the casing (22, 102) so as to be capable of advancing or retreating relative to the parking piston (23, 103), has a parking release control fluid pressure chamber (44, 109) defined between a front face of the lock piston (24, 104) and the casing (22, 102), and is urged forward by a spring (48, 114), the lock mechanism (25, 105) automatically locking in response to forward movement of the parking piston (23, 103) in order to mechanically lock the parking piston (23, 103) at a forward position and unlocking in response to a parking release control fluid pressure acting on the parking release control fluid pressure chamber (44, 109);
• a fluid pressure source (10C;
• 10A, 10B);
• and fluid pressure control means (56;
• 66A, 66B) for controlling a fluid pressure generated by the fluid pressure source (10C;
• 10A, 10B) so that the parking control fluid pressure and the parking release control fluid pressure can be obtained and separately controlled.