Adaptive anti-lock brake control apparatus

Abstract

An anti-lock brake control apparatus especially suited to heavy duty trucks with air brakes senses the wheel speeds on a given axle and cyclically releases and applies the brakes on that axle as required to avoid undesirable wheel slip during braking. In one control channel, a deceleration switch responsive to a wheel speed signal produces a brake release signal when wheel deceleration exceeds a predetermined threshold. A second parallel channel, also responsive to wheel speed, derives a velocity error signal representing the difference between wheel speed and an estimated vehicle speed and produces a release signal when the velocity error exceeds a value which varies as a function of wheel speed. The velocity error is determined by comparing the wheel deceleration with an estimated vehicle deceleration and integrating the difference. The second channel also includes an acceleration switch connected to the release integrator to quickly remove the velocity error signal when a predetermined wheel acceleration occurs to effect brake reapplication. A self-check circuit includes a timer producing an output signal which increases with time and a synchronous reapply circuit connected to the second channel to effect brake reapplication when a time period has expired. The timer is operative when a self-check accelerometer indicates that the wheels experience low positive or negative acceleration and when a self-check logic circuit indicates that the control circuit calls for a brake release. A comparator and latch circuit responsive to the timer output signal is actuated when a second larger time period has expired and is effective to illuminate a warning lamp and to disable the control circuit. The timer is retarded when a large velocity error signal is present to extend the time periods for brake reapplication and disabling of the circuit.