Patent GB-1527629-A (GB)
Title: Antiskid braking system for a wheeled vehicle
IPC: B60T8/1761
Filed: 1975-12-08
Abstract: 1527629 Anti-skid braking systems BENDIX CORP 8 Dec 1975 [9 Dec 1974 (2)] 50263/75 Heading F2F  An antiskid fluid pressure braking system has a skid detecting circuit 16 responsive to a signal from a wheel speed sensor 12 to generate a signal at an output terminal 18 when incipient skidding of the wheel 14 is detected, which signal is supplied to a signal modifying circuit 20 and also to a set terminal of a flip-flop 32, the signal modifying circuit 20 has an input terminal 26 connected via a switch 28 closed when the brakes are operated to a voltage source 30 and the terminal 26 is also connected to a reset terminal of flip-flop 32 via an inverter, and the signal modifying circuit 20 is operable to supply via an output terminal 22 a signal proportional to the desired pressure level in brake actuators 36 to a duty cycle translator 24 which is operable to generate an adaptive control signal fed to one input terminal of an AND gate 33, the other input terminal of which is connected to the output terminal of flip-flop 32. Thus when incipient skidding is sensed by circuit 16 flip-flop 32 is set thereby enabling duty cycle translator 24 to control via AND gate 33 actuation of a modulator 34 modulating fluid pressure in the actuators 36. The modulator may be a modulating relay valve having an electrically actuated valve responsive to the adaptive control signal from duty cycle translator 24. The duty cycle translator 24 shown in Fig. 2 includes an amplifier having a negative terminal 40 connected to the output terminal 22 of the circuit 20 to receive the signal proportional to the desired pressure level, and a positive terminal 42 to receive a pseudo-pressure feedback signal, the adaptive control signal being generated when the value of signal on the positive terminal 42 exceeds the value of signal on negative terminal 40. The pseudo-pressure feedback signal is generated by circuit whose input is connected to the output terminal 44 of the amplifier 44 and whose output is a capacitor 86 connected to the positive terminal 42. This circuit includes amplifiers 52, 68 with respective voltage divider networks 58, 72 and respective associated components 46, 48, 54 and 62, 64, 70, and resistor-diode combinations 80, 79 and 82, 84 constituting charging and discharging paths for capacitor 86. The signal modifying circuit shown in Fig. 4 comprises a transistor 88 whose base is connected to terminal 18, whose collector is connected to terminal 22 and whose emitter is connected to ground. A capacitor 94 connected in parallel with transistor 88 is charged with a charge corresponding to what is termed an auxiliary signal. The signal proportional to the desired pressure level is equated to the auxiliary signal at the instant when the skid detecting signal is extinguished. When incipient skidding of wheel 14 is detected by circuit 16 the brake pressure control signal at output 22 drops to its lowest possible value by grounding of transistor 88, and when this occurs the value of the adaptive control signal on terminal 44 switches to a high state to cause actuation of valve 34 to initiate a brake pressure reduction in actuators 36. The pseudo-pressure feedback signal generating circuit provides such signal to terminal 42, which after a time interval, begins to decay in an exponential manner, and when this signal drops below the value of the brake pressure control signal the adaptive control signal is turned off; this in turn causes increase in the pseudopressure feedback signal to initiate another brake pressure decay cycle.