Fail safe circuit for an anti-skid control apparatus

Claim 1

In the anti-skid control apparatus for an automobile brake system adapted to operate with the brake system of an automobile and prevent it from skidding with an actuable valve operatively coupled to a brake shoe for applying brake force against a wheel of the automobile in motion to slow it down and an anti-skid control circuitry controlling the operation of the actuable valve for applying brake forces against the wheel in a controlled manner to avoid skidding, said anti-skid control circuitry including means for sensing the rate of deceleration of the moving wheel and providing an output signal when the rate exceeds a predetermined rate indicative of skidding conditions and means for deactuating the valve to release the brake shoe in response to the output signal to prevent skidding, the improvement which comprises fail safe circuitry for actuating the valve when the brake shoe is released by said anti-skid control circuitry for a predetermined time period whereby the brake shoe is prevented from being released for more than said time period, said fail safe circuitry including an R-C timer adapted to have applied thereto a regulated voltage, said timer including a timing capacitor coupled to the regulated voltage and through additional circuitry providing an actuating signal to the valve when the voltage stored in said timing capacitor reaches a predetermined value, and semiconductor means coupled across said timing capacitor for discharging said capacitor before the voltage stored therein reaches the predetermined value when the regulated voltage dips below a predetermined amount.