Abstract: A supervisory circuit for an anti-lock brake system (ABS) unit. The circuit includes an independent internal voltage reference source that provides power to the circuit components. The circuit also includes an external power source monitor powered by the internal voltage reference source which inhibits the ABS unit when an external power source voltage exceeds a predetermined level. The circuit also includes a system voltage monitor powered by the internal voltage reference source that inhibits the ABS unit when a system voltage deviates from predetermined system voltage parameters. The circuit also includes an electronic control unit (ECU) monitor powered by the internal voltage reference source that monitors a periodic signal generated by an ECU and that inhibits the ABS unit if an ECU timing signal deviates from a predetermined threshold level. The supervisory circuit helps to prevent spurious operation of ABS modulators due to race conditions.

Abstract: A speed signal conditioning and test circuit includes a comparator which is connected to a digital input port of a microprocessor and which switches its output in response to the alternating current generated by the sensor when sensing wheel speed. A test sequence is initiated by injecting a signal into a tuned circuit formed by the inductance of the sensor coil, the filtering capacitors, and associated circuit resistances. The voltage output of the tuned circuit increases exponentially and switches the comparator to provide a test pulse of a predetermined time period. The microprocessor times the pulse to establish that an operative sensor is present. Since the inductance of the coil is switched out of the circuit in the case of an open or shorted sensor coil, no pulse is generated and the microprocessor accordingly determines that a defective sensor is present.

Abstract: A test for an electronically controlled braking system, such as an adaptive braking system, is made to assure that the solenoids of each of the modulators are properly wired. According to the test, each modulator is tested in sequence. The exhaust solenoid of a modulator is actuated for 10 milliseconds, and the hold solenoid is then actuated for 30 milliseconds. If the modulator has been miswired, the exhaust solenoid will have been actuated for 30 milliseconds, thus generating a much louder "popping" sound than that generated by the other modulators will be immediately noticed and corrected.

Abstract: A proportional modulator includes valve elements actuated by a proportional solenoid that controls communications between an inlet port, an outlet port, and an exhaust port. The pressure level at the outlet port is controlled to vary directly with the current applied to the coil of the solenoid controlling the valve elements.