Patent GB-1297680-A (GB)
IPC: B60T8/1761
Filed: 1970-02-17
Abstract: 1297680 Anti-skid braking systems WESTINGHOUSE BREMSEN UND APPARATE. BAU GmbH 17 Feb 1970 [2 April 1969] 7644/70 Heading F2F In a vehicle braking system for limiting the rate of change of revolution of a wheel of a vehicle under braking action of a first means including a second means operative to determine when the wheel attains a chosen value of rate of change of revolution and in response thereto produce a first signal to initiate the operation of a third means operative to reduce the action of the first means, a fourth means, operative on the attainment thereafter of a selected degree of operation of the first means, starts to time an interval and to produce thereafter a signal to initiate the curtailing of the operation of the third means and thereby permit recovery of the action of the first means. As shown in Figs. 1, 2 and 3 a single-action pneumatic or hydraulic brake cylinder 1, for actuating the wheel brake 3 of a wheel 4, is connected to a 3/2 way magnetic valve 7 acting as a brake pressure control valve and a pedal-type brake valve 9, and a differential pressure switch 11 has a membrane 12 acted on one side by the brake pressure obtaining in the brake cylinder 1 and on the other side by atmospheric pressure and connected with an electrical switch 13. An electric control unit 15 with a relay switch 18 is connected with the valve 7, the switch 11 and a gauge 16 which determines the rotary deceleration of the wheel 4. In operation, with the valve 7 in the position, as shown, wherein the cylinder 1 is connected with the valve 9 and brake pressure, varying in accordance with the curve P 0  to P B3 , is introduced into the cylinder, when the difference between the pressure P B  and atmospheric pressure P 0  reaches a pressure P B1 -P 0  corresponding to the threshold of response of the switch 11, the switch 13 closes whereby the unit 15 is ready for operation. When the pressure reaches a value P B2  where the wheel 4 undergces a rotary deceleration corresponding to the response threshold of the gauge 16 the switch 17 closes and a voltage is applied to solenoid 19 of switch 18 so that the switch 21 closes and the valve 7 is operated to connect the cylinder to atmosphere whereby after the pressure has risen to a valve P B3  the pressure continuously decreases. Simultaneously, with closing of the switch 21, the switch 20 closes so that the voltage applied to the solenoid 19 is maintained independently of the behaviour of the gauge 16 and is also applied to a circuit 22 to charge a capacitor 23. When the difference between the decreasing pressure and atmospheric pressure reaches a valve P B4 -P 0  corresponding to the response threshold of the switch 11 the switch 13 opens and the solenoid 19 is maintained under voltage until the capacitor is discharged, the impulse released by the switch 11 determining the commencement of a retaining time (t 5 -t 4 ), Fig. 3, provided by the discharge time of the capacitor and being of a length such that the wheel 4 is brought to a rotational speed corresponding to a given slip which is below the critical slip. With elapse of the retaining time [t 5 ) the solenoid 19 is de-energized and the switches 20, 21 open so that the valve 7 is moved (at time t 6 ) to a position wherein the brake cylinder is connected to the valve 9 and the pressure rises until a pressure P B7 -P 0  is reached corresponding to the response threshold of the switch 11 (time t 7 ) when the switch 13 again closes to commence a new period of readiness in which the control unit 15 is again ready for operation. In modifications, (a) a double-acting brake cylinder, Fig. 4 (not shown), and a 4/2 way magnetic valve is used, the sides of the membrane of the switch 11 being respectively connected to the brake pressure and counterpressure chambers of the cylinder, (b) the 4/2 way magnetic valve is actuated in each direction by separate electromagnets, (c) in one position of the 4/2 way magnetic valve the pressure chamber of the brake cylinder is connected to the valve 9 and the counterpressure chamber is connected to atmosphere and in the other position of the valve the chambers are connected with each other whereby the pressures balance out at a value which remains constant until the second switching over of the magnetic valve, (d) a differential pressure switch 411, Fig. 10, is connected such that the membrane 412 thereof is subject on opposite sides to the brake pressure and counterpressure in the double-acting brake cylinder 450 and a differential pressure switch 460 has a membrane 461 acted upon on its opposite sides by the brake pressure and atmospheric pressure, a flow direction switch 463 being connected in series with the switch 411, the arrangement permitting independent adjustment of the switch 460 which determines the commencement of the period of readiness for operation and the switch 411 which determines the commencement of the retaining time and (e) the differential pressure switch 590, Fig. 13, consists of two pistoncylinder units 591, 592, the membrane 570 of unit 591 being acted upon by the brake pressure on one side and on the other side by the pressure in the counterpressure chamber of the brake cylinder 550, and having a rod 571, carrying an adjustment screw 573, and the membrane of the unit 592 carrying an electric switch 576; a magnetic valve 580, as shown, is located in a switching position in which the chambers of the units 591, 592 are interconnected, and when the membrane 570 of the unit 591 is subject to decreasing brake pressure on one side and increasing counterpressure on the other, the switch 576 is opened to commence the retaining time.