Anti skid braking system

Claim 2

In an anti-skid control system for the brake of at least one wheel of a vehicle, of the type comprising an angular velocity transducer for detecting the angular velocity of said wheel and for producing an output signal representing said angular velocity, a braking control circuit connected between the output of said angular velocity transducer and said brake, said braking control circuit including means for differentiating said signal representing said angular velocity, and operating to release said brake when the derivative of said angular velocity signal exceeds a predetermined negative threshold value, the improvement wherein: said braking control circuit comprises a first transistor, the base of said first transistor being coupled to said output of said angular velocity transducer, a threshold circuit having a first state and a second state, and operating to produce an output signal in said second state, brake pressure control means for controlling the braking pressure applied to said brake, said output signal of said threshold circuit being applied to said brake pressure control means to effect release of said braking pressure when said threshold circuit is in said second state, the emitter of said first transistor being earthed and also being connected to said threshold circuit, said threshold circuit commuting to said second state whenever the derivative of said angular velocity signal exceeds said predetermined negative threshold value, a reference signal generating circuit connected to the output of said threshold circuit, said reference signal generating circuit operating to produce a reference signal which is delayed by a predetermined time interval after the commutation of said threshold circuit to said second state of an angular velocity signal at the instant when said threshold circuit commutes to said second state and the value of said angular velocity signal after said predetermined time interval from said instant when said threshold circuit commutes to said second state, and detector means sensitive to both said reference signal and said angular velocity signal, said detector means operating to return said threshold circuit to said first state thereof, when said angular velocity signal and said reference signal both attain the same value, whereupon said brake pressure control means allow reapplication of said brakes, said angular velocity transducer produces an output signal the voltage of which represents said angular velocity of said wheel, and said braking control circuit comprises a capacitor connected between said emitter of said transistor and earth, a monostable multivibrator connected to the output of said threshold circuit, a second transistor of a type complementary to said first transistor, the base of said second transistor being earthed, the collector of said second transistor being connected to said emitter of said first transistor, and a second capacitor connected between the emitter of said second transistor and the output of said monostablE multivibrator, the period of said monostable multivibrator being equal to said predetermined time interval and the output of said monostable multivibrator multiplied by the ration of capacities of said first and second capacitors determining the decrement by which said reference signal is less than said angular velocity signal at the instant when said threshold circuit commutes from said first state to said second state, said reference signal being constant.

Claim 3

In an anti-skid control system for the brake of at least one wheel of a vehicle of the type comprising an angular velocity transducer for detecting the angular velocity of said wheel and for producing an output signal representing said angular velocity, a braking control circuit connected between the output of said angular velocity transducer and said brake, said braking control circuit including means for differentiating said signal representing said angular velocity, and operating to release said brake when the derivative of said angular velocity signal exceeds a predetermined negative threshold value, the improvement wherein: said braking control circuit comprises a first transistor, the base of said first transistor being coupled to said output of said angular velocity transducer, a threshold circuit having a first state and a second state, and operating to produce an output signal in said second state, brake pressure control means for controlling the braking pressure applied to said brake, said output signal of said threshold circuit being applied to said brake pressure control means to effect release of said braking pressure when said threshold circuit is in said second state, the emitter of said first transistor being earthed and also being connected to said second state whenever the derivative of said angular velocity signal exceeds said predetermined negative threshold value, a reference signal generating circuit connected to the output of said threshold circuit, said reference signal generating circuit operating to produce a reference signal which is delayed by a predetermined time interval after the commutation of said threshold circuit to said second state the value of said reference signal lying between the value of said angular velocity signal at the instant when said threshold circuit commutes to said second state and the value of said angular velocity signal after said predetermined time interval from said instant when said threshold circuit commutes to said second state, and detector means sensitive to both said reference signal and said angular velocity signal, said detector means operating to return said threshold circuit to said first state thereof, when said angular velocity signal and said reference signal both attain the same value, whereupon said brake pressure control means allow reapplication of said brakes, said angular velocity transducer produces an alternating output signal the frequency of which represents the angular velocity of said wheel, a pulse shaping circuit connected to the output of said angular velocity transducer, said pulse shaping circuit producing a train of pulses of constant width the pulse repetition frequency of which represents the frequency of said signal from said transducer, said reference signal generating circuit comprising: a capacitor to the output of said pulse shaping circuit so as to be periodically charged by said signal pulses therefrom, a discharge circuit by means of which said capacitor can periodically discharge, said discharge circuit including a normally closed switching device, said threshold circuit comprising a differentiator circuit connected in parallel with part of said discharge circuit and a trigger circuit coupled to the output of said differentiator circuit, said trigger circuit having a first state and a second state and commuting to said second state when said output from said differentiator circuit exceeds said predetermined negative threshold, said trigger circuit being conneCted to said brake pressure control means and operating to control release of said brakes when in said second state, a timing circuit connected between said output of said trigger circuit and said switch device of said discharge circuit, said timing circuit operating to produce an output pulse to open circuit said switching device for said predetermined time interval after said trigger circuit has commuted to said second state to prevent discharge of said capacitor for this time interval.

Claim 4

In an anti-skid control system for the brake of at least one wheel of a vehicle of the type comprising an angular velocity transducer for detecting the angular velocity of said wheel and for producing an output signal representing said angular velocity, a braking control circuit connected between the output of said angular velocity transducer and said brake, said braking control circuit including means for differentiating said signal representing said angular velocity, and operating to release said brake when the derivative of said angular velocity signal exceeds a predetermined negative threshold value, the improvement wherein: said braking control circuit comprises a first transistor, the base of said first transistor being coupled to said output of said angular velocity transducer, a threshold circuit having a first state and a second state, and operating to produce an output signal in said second state, brake pressure control means for controlling the braking pressure applied to said brake, said output signal of said threshold circuit being applied to said brake pressure control means to effect release of said braking pressure when said threshold circuit is in said second state, the emitter of said first transistor being earthed and also being connected to said second state whenever the derivative of said angular velocity signal exceeds said predetermined negative threshold value, a reference signal generating circuit connected to the output of said threshold circuit, said reference signal generating circuit operating to produce a reference signal which is delayed by a predetermined time interval after the commutation of said threshold circuit to said second state the value of said reference signal lying between the value of said angular velocity signal at the instant when said threshold circuit commutes to said second state and the value of said angular velocity signal after said predetermined time interval from said instant when said threshold circuit commutes to said second state, and detector means sensitive to both said reference signal and said angular velocity signal, said detector means operating to return said threshold circuit to said first state thereof, when said angular velocity signal and said reference signal both attain the same value, whereupon said brake pressure control means allow reapplication of said brakes, said angular velocity transducer produces an alternating output signal the frequency of which represents the angular velocity of said wheel, a pulse shaping circuit connected to the output of said angular velocity transducer, said pulse shaping circuit producing a train of pulses of constant width the pulse repetition frequency of which represents the frequency of said signal from said transducer, said reference signal generating circuit comprising: a capacitor to the output of said pulse shaping circuit so as to be periodically charged by said signal pulses therefrom, a discharge circuit by means of which said capacitor can periodically discharge, said discharge circuit including a normally closed switching device, said threshold circuit comprising a differentiator circuit connected in parallel with part of said discharge circuit and a trigger circuit coupled to the output of said differentiator circuit, said trigger circuit having a first state and a second state and commuting to said second state when said output from said differentiator circuit exceeds said predetermined negative threshold, said trigger circuit being conneCted to said brake pressure control means and operating to control release of said brakes when in said second state, a timing circuit connected between said output of said trigger circuit and said switch device of said discharge circuit, said timing circuit operating to produce an output pulse to open circuit said switching device for said predetermined time interval after said trigger circuit has commuted to said second state to prevent discharge of said capacitor for this time interval.

Claim 5

The anti-skid control system of claim 2 wherein said switching device comprises a transistor the base of which is earthed and the emitter of which is connected to said timing circuit.