Abstract: A wheel slip control system generates one level of brake relief when a fixed threshold of wheel deceleration is exceeded. The system generates a second level of brake relief when a variable threshold, dependent upon both deceleration and velocity, is exceeded. A fixed acceleration threshold circuit monitors wheel acceleration during brake relief. Under normal road and load conditions, where wheel acceleration is great enough to exceed the fixed acceleration threshold, termination of brake relief is initiated by the increase in wheel velocity past a variable reference threshold which has a fixed part and a variable part. The fixed part is an a priori prediction of the minimum vehicle velocity decrease under normal stopping conditions. The variable part is dependent on wheel acceleration alone. When the acceleration threshold is not exceeded, as with slippery roads or very light loads, termination of brake relief is delayed until wheel acceleration decreases to a low value.

Abstract: A fault detection system containing three modes of system shutdown, temporary, latching, or permanent disables an automotive wheel slip control system upon detecting faults in the speed sensors, control valves or interconnecting cables. Temporary shutdown is performed immediately following turn on and whenever certain supply voltages drop below threshold levels. Temporary shutdown is automatically terminated at the end of a predetermined time after turn on or when the supply voltages return to normal. Latching, resettable shutdown is performed in response to excessive apparent speed difference between a pair of wheels where the apparent difference endures too long. Latching shutdown is also performed in response to excessive actuation time of one or the other of two wheel slip control system solenoid valves and in response to actuation of a second solenoid valve in the absence of cycling of the first solenoid valve.