Abstract: A braking system for a vehicle having primary and secondary braking circuits includes a secondary braking circuit having a secondary source of braking pressure connectable to a braking actuator and including a three-port, two-position, inlet solenoid valve having two inlet ports and one outlet port. One of the inlet ports is connected to an outlet of an inlet solenoid valve of the primary braking circuit and to the inlet of an exhaust solenoid valve of the primary braking circuit. The other inlet is connected to a secondary source of braking pressure. The outlet port is connected to the braking actuator. The inlet solenoid valve is movable by an output signal from an electronic control unit.

Abstract: A microprocessor system having two microprocessors, each of which has its own reset circuit, and a circuit being provided which detects under-voltage in the system supply voltage, each of said microprocessors having circuitry associated with it for inducing a simulated low voltage condition on the reset circuit of the other microprocessor to test said under-voltage detection circuit and to measure the resulting reset period generated.

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: A dual computer cross-checking system includes a control computer for controlling a process in accordance with input data and a monitoring computer. The two computers are interconnected to exchange check data on a cyclic basis, each computer carrying out a number of processing operations on the received check data before transmitting the data thus processed to the other computer. In addition, each computer checks the received check data against an expected value. An error condition is detected if the result of at least one of these comparisons is found to be incorrect.

Abstract: An anti-lock system for controlling the slip level on one or more wheels of a vehicle by comparing the actual wheel speed with a vehicle reference speed obtained by processing wheel speed signals through a filtering system, the filtering system comprising a selection device which produces an input signal from one or a combination of the wheel speeds, an error forming device which subtracts the required vehicle speed estimate from the input signal to produce a speed error, a non-linear device which is effective to limit the slew rate of the filtering system in both positive and negative directions in accordance with vehicle characteristics, a secondary filter which reduces transients present in the error signal, and an integration device which accumulates the error signal and whose output is fed back to the error forming device as the required vehicle speed estimate.

Abstract: In an hydraulic anti-skid braking system of the pump and de-boost type the position of the de-boost piston in the bore is determined by a volume of fluid trapped in a space by a dump valve. The dump valve operates in conjunction with a restrictor which, at least at pressures above a pre-set level, restricts the rate of release of fluid from the space when the dump valve is open. Decreasing the flow rate of the dump valve decreases the time period for each anti-skid cycle. The pump no longer has to pressurize to maximum (brake) from zero which reduces the amount of energy which otherwise would have been consumed in the re-application mode. In addition the rate of release of fluid at pressures below the pre-set level can be increased which is of particular advantage when the vehicle is travelling over surfaces having low co-efficients of friction.

Abstract: A vehicle anti-lock brake control system includes wheel speed sensors which input speed signals to a microprocessor via an interface circuit. The microprocessor is programmed to calculate the deceleration of each wheel, compare this with a threshold and output a signal to a brake release device (A,B,C) for as long as the deceleration exceeds the threshold. The threshold level is calculated by the microprocessor as a function of the time elapsed since the threshold deceleration is exceeded. Initially the threshold is relatively low, but rises with time elapsed. After a predetermined time interval the threshold falls to a new relatively low level which depends on the slip of the wheel. If the slip of the wheel remains higher than a set level following re-application of the brake, a low "fast re-trigger" threshold level is established so as to release the brakes again rapidly if excessive deceleration is again detected.