Abstract: A booster for a vehicle braking system has an input piston, a boost piston and an output piston working a bore, the boost piston being advanced in the bore in response to pressure fluid from a source pressurizing a boost chamber under control of a valve.The operation of the valve is dependent on the pressure in the system, and the valve has a valve mechanism working in a bore in the boost piston of which one part has a pressure-responsive face, the valve being operative, on initial movement of the input piston to cause pressurization of the braking system to the threshold level, and application of pressure fluid to the pressure-responsive face to move the part relative to the input piston to place the boost chamber in communication with the pressure source. Threshold pressurization of the braking system may be achieved by pressurization of the boost chamber, or an auxiliary chamber forward of the boost piston to a predetermined level.

Abstract: The present invention provides an actuator mechanism comprising an axially rotatable actuator shaft and an actuator member which, in use, can be moved axially to actuate a brake. The actuator shaft and actuator member are interconnected by an assembly which comprises a first fast thread and a second fast thread. The first fast thread has a greater pitch angle than said second fast thread and is arranged to, in use, move the actuator member to take up any slack to cause friction surfaces of the brake to interengage. Said second thread subsequently moves the actuator member to apply the brake. By this arrangement the advantages of the two types of fast thread are utilized, the first fast thread quickly taking up the shock and the second fast thread being capable of applying the brake.

Abstract: In an hydraulic system an unloader valve is located in a line between a pump and an hydraulic accumulator. The unloader valve is operative to prevent the accumulator from being overcharged and to allow the pump to re-charge the accumulator should the pressure stored therein fall below a desired minimum value. The unloader valve incorporates a control valve comprising a spool, and a pressure responsive slave which is operated by fluid pressure under the control of the control valve. A spring acts to bias the spool into a first position against pressure in a control chamber into which fluid is pumped through a first one-way valve. A second valve in series with the first valve is located between the first valve and an exhaust port for connection to a tank for fluid. The slave comprises inner and outer concentric piston parts which are relatively movable axially and of which the inner part is adapted to open the valve to unload the pump.

Abstract: The present specification discloses a friction pad assembly and disc brake incorporating such an assembly, wherein the friction pad assembly comprises a backing plate and a pad of friction material secured thereto, a wire spring being secured to the backing plate. The wire spring comprises a coiled region from which two arms extend in generally opposite directions. The coiled region of the spring is located in a recess in the backing plate with the arms extending from the recess on opposite sides of the backing plate. Thus the spring arms are the only parts of the spring extraneous to the dimensions of the backing plate so that in a simple manner the optimum amount of design space for constructional strength, is available in a brake incorporating such a friction pad assembly. Also, by virtue of the spring arms extending one on each side of the backing plate, stable spring biassing of the friction pad assembly is achieved in the brake.

Abstract: A hydraulic brake actuator having a piston slidable in a cylinder for hydraulic service brake operation also incorporates a mechanical linkage for handbrake operation. The mechanical linkage comprises a cranked shaft journalled in a closed end wall of the cylinder, a linearly displaceable peg and a strut interconnecting the cranked shaft and peg such that rotation of the cranked shaft causes linear displacement of the peg. The cranked part of the shaft of the strut and the peg are preferably contained wholly within a hydraulic working chamber defined by the piston and cylinder so that when the service brake and handbrake are applied simultaneously, movement of the mechanical components does not cause a change in the volume of the chamber and prevailing hydraulic fluid pressure will not therefore affect such movement.

Abstract: A pressure control valve for a braking system having two separate pressure circuits comprises two valves for connection in the respective circuits. Each valve has a valve closure member, the members being axially aligned and coupled together for movement in unison for simultaneous opening and closing of the valves.