GB1324236A - Control valve units for vehicle braking systems - Google Patents

Abstract

1324236 Valve unit for vehicle braking systems CLAYTON DEWANDRE CO Ltd 14 Jan 1971 [26 Jan 1970] 3648/70 Heading F2F A control valve unit is provided for a vehicle braking system in which a mechanical locking device is associated with an output member of a fluid pressure operated brake motor, fluid pressure fed through a lock line holding the device in an inoperative position. The control valve unit comprises a hand-operated reaction valve 12, 13 operable against the action of a graduated spring 9 for controlling the brake motor so that a delivery pressure proportional to the load on the valve operating member 4 is produced. A releasable ratchet mechanism 7, 26 is operable to retain the valve operating member 4 in a set position when the lock line is vented by a valve 24. In the construction shown the lock line venting valve is actuated by a flick lever 22 acting through a plunger 23. The pawl 26 of the ratchet mechanism is held in its inoperative position when the lock line is under pressure by a lever 28 associated with a spring-loaded piston 29 which is in communication with the lock line pressure. If, in a vehicle braking system, all brakes except one associated with the driving axle are to be actuated for service braking and all for parking, a valve associated with ratchet mechanism actuator is provided which valve isolates the brake actuator of the driving axle until the lock line is vented for parking purposes (Fig. 5, not shown). The pressure for holding the pawl of the ratchet mechanism in its inoperative position in this construction is derived from a port 65 of brake actuator (Fig. 6), which port 65 is connected to the lock line only when the lock line is under pressure. The brake actuator has both a service and an auxiliary piston 42, 41 acting on the brake push-rod 50 initially through spring discs 46. A warning device comprising a micro or similar switch 58 is associated with the parking lock so that a warning is given should an attempt be made to drive away the vehicle with the parking brake in its operative condition. A further micro-switch 72 may be provided in the warning circuit to prevent misuse of the control valve unit.