Functional monitoring of vehicular brake warning lamp switch - indicating failure when number of braking operations, not accompanied by closure of switch, exceeds predetermined limit

摘要

A data bus (10) conveys acceleration measurements (A) to two threshold comparators (11, 12) with negative and positive references (B1, B2) respectively, setting and resetting a flip-flop (13) whose output trailing edge drives a counter (14) reset by the deriv. pulse (17) from the switch (15) in question. The count (Z) is compared (18) with a fixed limit (B3). An AND gate (19) gives warning (22) when this is exceeded while the throttle flap (21) is at a positive angle (20). ADVANTAGE - Continuous monitoring with plausibility check affords earlier warning of switch fault, using measurements made by antilock braking system at no extra cost.