Patent GB-1472915-A (GB)
Title: Anti-lock braking system
IPC: B60T8/72
Filed: 1974-06-28
Abstract: 1472915 Anti-lock braking systems WABCO WESTINGHOUSE GmbH 28 June 1974 [29 June 1973] 28791/74 Heading F2F An anti-lock braking system incorporates a sensor producing output signals -b, #v, +b indicative of the rotational behaviour of a wheel; the -b signal is generated when the deceleration of the wheel exceeds a threshold level and is actuable on an electronic control circuit to reduce the braking pressure (air or hydraulic) in a cylinder by the actuation of two solenoid valves 17, 18; the -b signal, however, is applied to the control circuit via an evaluation unit 11 which acts to prevent pressure reductions by spurious -b signals caused not by excessive braking pressure but by uneven road surfaces or oscillations in the vehicle drive mechanism. The evaluation unit 11 comprises an AND- gate 12 and a delayed response circuit 13 which both receive the -b signal as input. The output signal of the circuit 13 is applied to a delayed release or pulse stretching circuit 14 and to an OR-gate 15 and the output signal of circuit 14 is applied to the negated input of AND-gate 12, the output signal of which forms a second input to the OR-gate 15. The output signal from the OR-gate 15 of unit 11 is supplied directly to inputs of an OR-gate 19, an OR-gate 20, and an OR-gate 21 and to negated inputs of an AND-gate 22 and an AND-gate 23. The #v signal which is produced when the wheel speed falls below a certain value is applied to an input of OR-gate 19, and to negated inputs of AND-gate 23 and an AND- gate 24. The +b signal which is produced when the acceleration of the wheel exceeds a particular value is fed to OR-gate 20 and to other negated inputs of AND-gates 23, 24. The electronic control circuit further incorporates an AND-gate 27, a delayed release circuit 26, a delayed response circuit 28, a delayed release circuit 30, and a pulse generator 29 connected as shown. The solenoid valves 17, 18 are respectively connected in an inlet and an outlet line to the brake cylinder. During a braking operation, a - b signal is applied to the evaluation unit 11 and passes during the delay time of the delayed response circuit 13 via the AND-gate 12 and the OR-gate 15 to the gates 19, 20, 21, 23 in the control circuit. As soon as the delay time of circuit 13 has ended the -b signal passes through the circuit 13 and the OR-gate 15 to the control circuit, and the signal from circuit 13 also acts on the delayed release circuit 14, the delay time from which is selected so that succeeding occurrences of -b signals are only passed on by unit 11 if they follow another such signal after more than a predetermined interval determined by circuit 14 or they are of a duration longer than the delay time of circuit 13. The -b signal from OR-gate 15 effects via OR-gate 19 the closure of inlet valve 17 and via OR-gate 21 the opening of outlet valve 18. The pressure in the wheel brake cylinder falls and the -b signal terminates and valve 18 closes; the AND-gate 12 remains blocked for the delay time of circuit 14. A #v signal acts on valve 17 via OR-gate 19 and thus the braking pressure is held constant. A +b signal keeps the valve 17 closed after termination of the #v signal and when the +b signal stops the delayed release circuit 26 maintains an output signal for a period Z 1 . With no +b signal AND-gate 23 blocks AND- gate 27 and also excites the circuit 28. During time Z 2  neither valve 17, 18 is actuated so that brake pressure increases quickly but after Z 2  circuit 30 acts on generator 29 which gives brake pressure rises in steps. Before the brake pressure has been built up so far that the wheel again shows a tendency to lock the blocking signal of circuit 14 ends and when the -b signal appears a new control cycle begins. Brief duration -b signals caused, e.g. by axle oscillations cannot cause a response from circuit 13 and all signals during the delay time Z 5  are thus ignored.