Abstract: A hydraulic parking brake device is selectively switched between a braking state and a non-braking state. A braking force decreases as a pressure in the control oil chamber increases and increases as the pressure in the control oil chamber decreases. The device includes a discharged oil restrictor located in a discharge passage and an accumulator connected to the control oil chamber. The accumulator is capable of releasing hydraulic oil to the control oil chamber when the braking force is greater than that at the time when the parking brake device is switched from the non-braking state to the braking state and the braking force can further be increased during the braking state of the parking brake device. Thus, the parking brake device can gradually brake the vehicle from the running state.

Abstract: An emergency vent valve including a piston responsive to the differential pressure between the brake pipe and a control volume to open a vent valve to vent the brake pipe to atmosphere and includes an exhaust valve responsive to the differential pressure between brake pipe and control volume to connect the control volume to atmosphere through a service check and when the vent valve is opened through a second blow-down choke of a lesser rate which limits the exhausting of the control chamber. A choke valve connected to the piston connects the blow-down choke in series with the service choke when the vent valve becomes fully open.

Abstract: In an oil pressure controlled brake system, wherein the brake oil contained within a wheel cylinder is returned to an oil reservoir associated with a master cylinder when the wheel lock or impending lock is detected. In a preferred form, an electromagnetic cross valve responsive to the detected wheel lock or impending lock is provided for returning the brake oil from the wheel cylinder to the master cylinder via the electromagnetic cross valve and a pressure control valve.