Abstract: An anti-lock (ABS) hydraulic braking system for vehicles comprises a first normally open solenoid-controlled valve (4) disposed in a line between a master cylinder (3) and a brake (1), a second normally closed solenoid-controlled valve (8) disposed between the brake and expander chamber (7), and a normally-open solenoid-controlled by-pass valve (5) located between the master cylinder and the brake and by-passing the first solenoid-controlled valve (4).

Abstract: A trailer braking system for a towing vehicle has a trailer braking valve (26) is fed with a pressurized air supply which is modulated by the opening of the valve, as controlled by a first control pressure regulated by a trailer braking controller (24) in accordance with braking demand signals, to produce a trailer braking pressure. In order that a trailer braking pressure may be generated even if the above trailer braking valve control fails, the valve is supplied with a second control pressure independently of the first, and which is also capable of operating the trailer braking valve (26). In a preferred embodiment, the second control pressure is supplied from a braking line of the towing vehicle, such that the "back up" control pressure is a function of the towing vehicle braking.

Abstract: Brakes (1,2; 3,4) on the wheels (5,6; 7,8) at opposite ends of a common axle are each controlled by a separate skid control unti and a single latch valve (21) common to both units closes at the first skid point to be sensed by a sensor (9,10; 11,12) on either wheel. A control module (13) responsive to signals from at least one of the sensors is operative to operate the latch valve and the skid control unit for the respective wheel. When a skid-signal is detected from a sensor on only one wheel the latch valve closes and the brake on the skidding wheel is released and re-applied when the skid signal terminates. The brake is re-applied in a fast first stage, due to pressure from an associated memory chanber and thereafter in a slower second stage due to the latch valve restricting the increase of braking pressure when it is closed. The rate of increase of brake pressure of the non-skidding wheel is restricted to that of the slow stage from the time that the latch valve is closed due to the other wheel skidding.

Abstract: In an anti-lock braking system incorporating a solenoid-operated fluid flow control valve, the rate at which fluid can normally be dumped to release a brake is increased by the provision of a pilot valve. The pilot valve is adapted to open by a pressure drop across a diaphragm. The pressure drop is established when an exhaust valve opens upon energization of the solenoid in response to an anti-lock signal.

Abstract: Brakes (3, 4) on the wheels (7, 8) on a common axle are each controlled by a separate skid control unit (16, 17) each including a memory chamber (33, 34), and a single latch valve (21) common to both units closes at the first skid point to be sensed by a sensor (11, 12) on each wheel. The rate of re-application of the two brakes is controlled in response to signals from the individual sensors, but at rates of pressure increase determined by each respective memory chamber, and by flows of pressure controlled by restrictors (47).

Abstract: A trailer air braking system has combined spring brake and service brake actuators, and the service brake chambers of the actuators are controlled by a combined emergency relay and modulator valve assembly of known construction. In order to ensure that the spring brake function does not become operative due to a moderate loss in the pressure of the trailer reservoir, such as would occur in the event of an anti-skid test in which the reservoir is isolated from the emergency line and the modulator valve is cycled, a spring brake one-way control valve is inserted into the spring brake circuit leading from the reservoir.

Abstract: In a fluid-pressure operated anti-skid braking system operation of a brake-applying relay valve is controlled by control pressure in an application chamber. A memory chamber is charged on initial brake application with pressure from supply passage connected to a brake actuator through one-way valve and an orifice permits pressure in the memory chamber to decay when the pressure in the supply passage reduces. This reduces the effective volume of air required for initial operation of the relay valve thereby increasing its response time. Re-application of the brake following a skid is controlled by closure of a latch valve which permits only a restricted flow of control pressure into the application chamber.

Abstract: A dual brake valve assembly including two co-axial primary and secondary valves for primary and secondary braking circuits is modified to include an auxiliary exhaust valve operable in conjunction with the pressure plate and a secondary piston for controlling operation of the secondary valve in response to operation of the primary valve. When the valve assembly is operated to apply the brakes, the auxiliary exhaust valve remains closed to prevent the premature release of fluid from the primary circuit irrespective of uncontrolled relative movement between parts of the valve assembly.