Importance

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Abstract

A warning circuit generates warning signals in response to conditions of a vehicle brake system which includes main and back-up brake fluid pumps. The main pump is engine-driven and ignition-switch controlled. The back-up pump is relay actuated and battery powered. A sensor switch opens upon operation of the main pump and a brake switch closes during an operator brake application. The warning circuit includes a first OR gate with inputs coupled to the ignition and brake switches. The output of the first OR gate is coupled to the relay and to a first warning lamp. The output of the first OR gate is capacitively coupled to the set input of a set-reset flip-flop and is coupled to the reset input of the flip-flop. The reset input is also coupled to a terminal of the back-up source. The Q output of the flip-flop is coupled to an input of a second OR gate through an inverter. The other input of the second OR gate is coupled to the terminal of the back-up source, to the reset input and to the output of the first OR gate. The output of the second OR gate is coupled to a controlled switch which becomes conducting to turn on the first warning lamp. A second warning lamp is coupled to the ignition switch and is coupled to a ground potential through an interruptible connection provided by the sensor switch.

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First Claim