An air brake control system for use in truck trailers, including tandem trailers, having at each axle compressed-air spring brakes and service brakes with each trailer being coupled to receive compressed air through an emergency (supply) gladhand and to receive service brake signals through a service (control) gladhand and which includes an integrated brake valve system for each trailer within a common valve housing. Each integrated brake control valve includes a spring brake valve cluster having a non-return check valve connected to receive and pass air pressure from the emergency supply and deliver it to the spring brakes and an air pressure responsive shuttle operative to open the check valve whenever the emergency supply line pressure falls below a predetermined spring brake isolation pressure above which the spring brake holding pressure is not affected by fluctuations of the emergency supply pressure; an air tank supply valve cluster connected between the emergency supply and a reservoir and operative to sense pressure in the emergency supply and to open at a spring brake threshold pressure above the predetermined spring brake isolation pressure to pass air to the reservoir and to close air passage to the reservoir to prevent supply line pressures from dropping below the threshold level during failure of the system elements; and a non-compounding valve cluster for releasing service brake pressure to atmosphere whenever, due to a loss of pressure in the emergency supply lines, the spring brakes have been activated.

A limited service application of the service brakes of the trailer portion of a tractor trailer combination vehicle is applied and held while the vehicle operator gets out of the cab to make a pre-trip inspection. The service actuation is initiated by releasing the trailer parking brakes while the tractor parking brakes remain applied and then making a momentary service brake actuation by use of the vehicle dual control valve. A control valve assembly responds to the service actuation to hold a service actuation of the trailer brakes until either the tractor parking brakes are released or the trailer parking brakes are applied.

A control valve for a fluid pressure braking system includes a housing which receives a pair of identical plungers and corresponding springs acting on the plunger which activate automatically at different trip pressures. The differential trip pressures are attained by providing different valve seating areas on the housing and spring cavities of different depths.

An pneumatic system (10) for a tractor trailer truck (6) which increases compressed air flow to the trailer reservoir (52) whenever the tractor (7) is parked. This decreases the time it takes to charge the trailer reservoir (52) to a sufficient pressure to release the trailer brakes allowing the truck (6) to move. In normal over the road operation the trailer reservoir (52) is charged through a tractor protection control valve (14) which is mounted on the tractor dash. However when the tractor (7) is parked and a tractor park valve (12) which is mounted on the tractor dash is pulled out compressed air from the tractor secondary reservoir (42) is delivered with an increased flow rate to the trailer supply line (50). When the tractor park control valve (12) is pushed in releasing the tractor parking brake the trailer charging reverts back to charging through the dash mounted tractor protection control valve (14). Pulling the tractor protection control valve (14) out vents the trailer supply line (50) in both the fast and normal charge mode.

An electronic braking system in a motor vehicle capable of towing a standard trailer not having its own EBS system has a separate pressure control channel for the generation of a trailer service brake pressure signal in the event that a driver's braking demand is sensed at any axle of the towing vehicle. The pressure signal level is set in the towing vehicle so as to be a function of the driver's electrical demand signal modified in dependence upon the load exerted by the trailer on the towing vehicle as measured at a towing link therebetween. Separate adaptive loops are provided in respect of the towing vehicle braking and the trailer braking, with the towing vehicle adaptive loop being responsive to deceleration error established by a comparison of vehicle retardation against driver braking demand, and with the trailer adaptive loop being responsive to towing link load, such as to obtain error signals which cause the adaptive adjustments to be made in the two loops in a mutually co-ordinated manner in order to achieve the required overall vehicle retardation.