Patent GB-1371164-A (GB)
Title: Apparatus for reducing the skiding of vehicle wheels
IPC: B60T8/36
Filed: 1972-01-13
Abstract: 1371164 Anti-skid systems WABCO WESTINGHOUSE GmbH 13 Jan 1972 [18 Jan 1971] 1671/72 Heading F2F  In apparatus for reducing the skidding of a vehicle wheel during braking comprising a valve arrangement, for controlling the braking pressure effective on a wheel, which responds to the occurrence of predetermined values of a factor indicating the onset of skidding of the wheel, first to reduce the braking pressure and then permit it to rise again, and a flow restrictor with a movable flow restrictor element in a line feeding braking pressure to the wheel for retarding the renewed rise in braking pressure, the movable flow restrictor element includes piston means controlling the effectiveness of the flow restrictor, which piston means is subjected to a pressure differential across the flow restrictor tending to maintain the flow restrictor effective, and means tending to return the piston means to a position such that the flow restrictor is not effective, when the pressure differential falls below a particular value. In the Fig. 1 embodiment, the Figure shows the situation when the brake is not being applied. When brake valve 7 is actuated, compressed air passes from reservoir 2 via lines 4, 5, annular grooves 11, 12, and line 6 to brake cylinder 3. If wheel deceleration exceeds a value indicative of skidding, a signal transmitting unit 34 energizes an electromagnetic valve 19, opening a compressed air path to a piston 18. Piston 25 and valve slide 14 (including part 16) are thereby forced to the right against the force of spring 22 until communication between grooves 11 and 12 is cut off and brake cylinder 3 is vented via line 6 and grooves 12 and 13. When the wheel accelerates, unit 34 energizes an electromagnetic valve 24, opening a compressed air path to a piston 20 which (spring 22 being compressed) bears against slide part 16 and pushes it to the left (piston 20 being of greater area than piston 18). Slide part 16 reengages bore 10, thus interrupting the venting of cylinder 3, while slide part 28 first compresses a spring 30 inside piston 25, and then contacts an internal shoulder in the piston, the piston still being held in engagement with bore 9 partly by inlet pressure in groove 11. The pressure in brake cylinder 3 is thereupon stabilized as the wheel accelerates. When the acceleration, rises above a predetermined level, valve 19 is deenergized, and then valve 24 is also de-energized (but more slowly), so valve slide 14 is rapidly moved left by spring 22 (part 16 remaining in engagement with bore 10), and piston 25 is moved a distance such that a reduced portion 26 on it lies opposite bore 9. Piston 25 is now held by the pressure difference between grooves 11, 12 (such pressure difference opposing spring 30), and air flows from groove 11 via flow restrictor 9, 26 to groove 12 and thus to cylinder 3, the rise in brake pressure being thus retarded by the restrictor. If braking pressure in cylinder 3 rises to a certain value less than the maximum and determined by the force of spring 30, the differential pressure is overcome by the spring, piston 25 is forced leftwards, and restriction 9, 26 becomes inoperative. In Fig. 3, compressed air flows, on braking, via line 105, ribs 150, bore 149, easing 141 and line 106. At excessive deceleration, unit 156 energizes actuator 155, so diaphragm 143 moves downwards, venting brake cylinder 103, and piston 135 moves downwards, compressing spring 152 and cutting off the inflow. In the next phase (compare Fig. 1), actuator 155 is deenergized, and diaphragm 143 closes against seat 144 again, while piston 135 returns, but to an intermediate position where a reduced portion 136 on it forms a flow restrictor with bore 149, so the new rise in brake pressure is retarded. The final phase (as in Fig. 3) is reached in the manner described for Fig. 1. In Fig. 4 compressed air flows during brake application from line 205 to the underside of a diaphragm 265, through bore 262 and line 206 to brake cylinder 203. On excessive deceleration, valves 265 and 268 are reversed from the positions shown by electromagnetic actuators 274, 275, respectively (268 being the venting valve), but the piston 263 forming the seat for diaphragm 265 is forced down against spring 264 until it partially encloses fixed member 272. Upon excessive acceleration occurring, as previously described, actuators 274, 275 are deenergized, but piston 263 is maintained in the position last reached by the pressure differential across it, so the flow to the brake is via the restriction formed by the lower end 271 of the piston and fixed member 272. In Fig. 5 the admission and vent valves are in a single structure 380 electro-magnetically actuated at 383 under the control of signal unit 389, while the restrictor device 381 is upstream. The actual restriction, coming into operation when appropriate, consists of the interaction of piston 385 with radial bores 396 in a sleeve 386. Control is effected by a spring-loaded piston 392 and stem 388 governed by a chamber 400 which is either pressurized from reservoir 302, or vented, by electromagnetic valve 387, which is also under control of the signal unit 389. In Fig. 6, the flow restrictor 451 is in series with an electromagnetically-operated admission, venting and stabilizing valve 450. The restrictor element consists of flange 459 and ribs  458 on a member 456 and an internal flange 460 in casing 455; part 461 of member 456 constitutes the flow restrictor piston. Member 456 is subject on the left to brake-applying pressure 405, and on the right to brake cylinder pressure 406 and to the pressure of a spring 457. Signal unit 462 acts on the admission &c. valve 450 only.