Patent GB-1463894-A (GB)
Title: Anti-lock control system for fluid pressure operated vehicle  brakes
IPC: B60T8/60
Filed: 1974-02-14
Abstract: 1463894 Anti-lock braking system WABCO WESTINGHOUSE GmbH 14 Feb 1974 [15 Feb 1973] 6724/74 Heading F2F An anti-lock fluid pressure braking system has a signalling device to supply signals - b,  #V, + b 1 , +b 2  indicative of the rotational behaviour of the wheel to an electronic control device comprising a normally open inlet solenoid valve 17 and a normally closed outlet solenoid valve 18 operable to control the braking pressure in a brake cylinder wherein the control device also includes a time control device 28 responsive to the start of a renewed increase in brake pressure caused by a re-opening of the valve 17 following a relaxation of that pressure under the control of a signal from the signalling device to control the valves 17, 18 to cause a rapid increase in brake pressure during a time determined by the time control device 28. The signal - b is generated when wheel deceleration exceeds a threshold value, the signal #V is generated when wheel speed falls below a threshold value, the signal +b 1  is generated when wheel acceleration exceeds a first threshold value, and the signal +b 2  is generated when wheel acceleration exceeds a second higher threshold value: as shown in Fig. 1 these signals are applied to OR gates 19, 20, 21 and to AND gates (having negated inputs) 22, 23, 24, 25, 27 of the electronic control device as illustrated. When the - b signal is evolved the signal passes through OR gate 19 and AND gate 25 to close valve 17 and through OR gate 21 to open valve 18 to reduce brake pressure in the cylinder ; when signal - b is terminated the valve 18 is closed although the #V signal if present keeps valve 17 closed to hold the brake pressure constant. If the subsequent wheel acceleration exceeds the first threshold value, the + b 1  signal is produced and via the OR-gate 20, a slowrelease circuit 26, the AND-gate 27, the OR- gate 19 and the AND-gate 25 keeps valve 17 closed even after the #V signal has been terminated. Should signal +b 2  be generated the valve 17 is opened by the action of gate 25. If the wheel acceleration falls below the first acceleration threshold, the +b 1  signal stops but the circuit 26 maintains its output for a period adequate for the subsequent control action. Since no +b 1  signal appears at the corresponding negated input of the AND-gate 23, the AND-gate 23 applies a signal to the AND-gate 27 terminating the closure of valve 17. This signal also actuates device 28 which in this embodiment is in the form of a slow-response circuit, and until the end of the delay time determined by the circuit 28 neither of the valves 17, 18 is actuated and the brake pressure increases rapidly-the increase may be determined by a modulating valve in series with valves 17, 18. At the end of the delay time the circuit 28 applies an output signal to a slow-release circuit 30 which determines the pulse duration of pulses from a generator 29 which are applied via AND- gate 22, OR-gate 19 and AND-gate 25 to the inlet solenoid valve 17. In this pulsed phase the brake pressure rises in a series of steps. When the next - b signal appears, a new control cycle begins. In the modification of Fig. 3 the circuit 28 is replaced by an arrangement 28<SP>1</SP> which is controlled by means of a pressure switch 31 acted upon by the pressure p of the brake cylinder. When the +b 1  signal stops, the signal from gate 23 is applied to the inputs of AND-gates 32, 33 36. If switch 31 is open AND-gate 36 will actuate a slow-release circuit 37, the output signal, of which blocks AND-gate 33 and enables AND- gate 32. Gate 32 actuates a slow-response circuit 34 which has a relatively short delay time at the end of which, via OR-gate 38, the slowrelease circuit 30 is actuated. Should the brake pressure be sufficient to close switch 31, a signal from AND-gate 23 is applied via AND-gate 33 to a slow-response circuit 35 which has a longer delay time. Several pressure switches having different closing pressures with respective slowresponse circuits may be provided. In the modification of Fig. 4 the circuit 28 is replaced by an arrangement 2811 responsive to the - b signal which is applied through a lining circuit 44 having a slow-response and a slowrelease to control gates 39, 40. If the duration of the - b signal lies below the response delay time of circuit 44, the short response delay time of a circuit 41 is used for the brake pressure reestablishment because the gate 39 is open. If the duration of the - b signal is above the delay time of the first stage of the circuit 44, the long response delay time of a circuit 42 is used for the brake pressure re-establishment because the gate 40 is open.