Importance

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Abstract

Anti-skid brake control systems are described in which anti-skid brake control modules associated with the braked axles are each provided with a failsafe circuit and these failsafe circuits are connected in cascade fashion to form a chain so that an input signal applied to a first failsafe circuit will propagate through the chain of failsafe circuits to the output of the last failsafe circuit only if the wiring connecting the modules is correct, the failsafe circuits are themselves operating correctly and electrical power is being supplied to each module, a warning being given to the driver of the vehicle if the output signal from the last failsafe circuit fails. In a previously proposed system the warning given is only produced in the event of a fault, and there is no positive indication of correct operation of the system at switch on. Circuits are here described in which the vehicle ignition switch is arranged to apply a fault pulse to the input of the first failsafe circuit in the chain at switch-on of the ignition and the response of the output of the last failsafe circuit to the pulse is monitored by a suitable monitor unit. Some of the failsafe circuits incorporate switch-off circuits which are so arranged that, on the occurence of a fault in the chain upstream of that failsafe circuit, the switch-off circuits operate an inhibit device to inhibit operation of one or more of the brake release circuits which are downstream of the point at which the fault exists.

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First Claim