Anti-skid brake control system and failsafe circuit therefor

Claim 1

An anti-skid brake control system comprising: a land vehicle having first and second wheels; first and second electromagnetic pick-ups mounted on said vehicle for producing first and second series of pulses, respectively, at first and second respective pulse repetition frequencies directly proportional to the respective speeds of said first and second wheels, said first and second pick-ups including first and second inductive windings, respectively; an air brake valve; a brake pedal assembly; a supply of fluid under pressure connected to said valve and to said brake pedal assembly; a set of fluid pressure operable brakes connected from said valve, said valve being operable by fluid under pressure supplied in response to pressure on said brake pedal assembly, said valve having an electrical input lead, said valve being deactuable by predetermined electrical signals applied to said input lead thereto; an anti-skid brake system controller connected from both of said first and second windings to said valve input lead to supply signals to the latter on predetermined conditions to override the fluid pressure supplied to said brakes in response to pressure on said brake pedal assembly; and for override means connected from both of said windings for interrupting control of said valve by said controller when at least one of said windings develops an open, a regulated source of potential being provided having a first output lead connected to a point of reference potential, and a second output lead, said windings each having a first lead connected from the second output lead of said source, and a second lead, first and second transistors each having a collector, an emitter and a base, a first resistor connected from the second output lead of said source to said first transistor base, an amplifier having an input lead and an output lead, a second resistor connected from said amplifier input lead to the second output lead of said source, a third resistor connected from said amplifier output lead to said first transistor base, a diode connected from said first transistor base to said point of reference potential, both of said emitters being connected to said point of reference potential, a fourth resistor connected from the second lead of said first winding to said second transistor base, a fifth resistor connected from the second lead of said second winding to said second transistor base, a capacitor connected from said amplifier output lead to said second transistor base, said amplifier means output signals being produced on said amplifier output lead, said first transistor collector being connected from said second transistor base, said second transistor collector being connected to said amplifier input lead, and control means connected from said amplifier output lead to suppress the output of said controller and the input to said valve which would otherwise be impressed on said valve input lead by said controller, said control means being actuable to suppress said controller output and said valve input when either one of said windings develop an open either one at a time or both together.