Patent GB-442518-A (GB)
Title: Improvements in or relating to compressed air brakes
IPC: B60T8/32
Filed: 1934-07-07
Abstract: 442,518. Fluid-pressure brakes. KNORR-BREMSE AKT.-GES., 9, Neue Bahnhofstrasse, Lichtenberg, and HILDEBRAND, F., 2, Waldmannstrasse, Lankwitz, both in Berlin. July 7, 1934, No. 20004. [Class 103 (i)] In a compressed-air brake for railway vehicles adapted to establish a greater cylinder pressure at speeds above a predetermined value than at speeds below that value the control valve mechanism comprises a triple valve which controls a second valve device comprising piston operated cylinder supply and exhaust valves the triple valve when the brakes are applied supplying an ante-chamber connected to a piston chamber of the second valve device. The second valve device may comprise pistons subject to opposing pressures in the cylinder and ante-chamber and to render the cylinder pressure dependent upon the speed a further piston may be subject to the cylinder pressure or to the ante-chamber or other pressure only at one of the speed ranges or the pistons may act through a lever the arms of which are varied. The cylinder pressure may also be varied automatically with the load. The system shown in Fig. 3 comprises a triple valve 1 adapted when the pressure in the brake pipe 2 is reduced to supply from a reservoir 3, an ante-chamber 14 connected to the chamber below one piston 11 of the second valve device 10 which comprises also a piston 11<b> the chamber above which is connected to the cylinder 5 and a piston 11<a> the chamber above which is connected at high speeds to atmosphere by valve 21 operated by the governor 7. The pistons operate a cylinder exhaust valve 17 and a supply valve 12 which connects a reservoir 4 to the cylinder. Thus in braking the cylinder pressure is dependent upon the pressure established in the chamber 14 by the triple valve and by the area of the pistons 11, 11<b> but when the speed falls to a predetermined value the governor 7 opens the valve 22 to connect the chamber above piston 11<a> with the reservoir 4 so that the cylinder pressure is reduced to a lower value. The chamber above piston 11<a> may instead be connected to the cylinder 5 at low speeds. To retard the rise of cylinder pressure at low speed braking a valve device 33 may be interposed between the valve 1 and chamber 14. This comprises a piston 31 which under the pressure of spring 32 holds open a valve 30 at high speeds but at low speeds is depressed by the pressure supplied by the valve 22 through pipe 19 to close the valve 30 so as to provide only a restricted port 29 for the supply to chamber 14. Fig. 2 shows a system adapted to effect a gradual fall of the cylinder pressure with the speed to a minimum value. The valve 10 comprises two sets of pistons of which those 11<b>, 11<c> of the one set only are operative at low speeds, the cylinder pressure acting on piston 11<b> being determined by the pressure in chamber 14 acting on piston 11<c>. The chambers above pistons 11<d>, 11<a> of the other set are connected respectively to the cylinder 5 and reservoir 3 and the chamber below piston 11 to chamber 14. At low speeds the chamber below piston 11<a> is connected to atmosphere by the governor operated valve 21. The lower set of pistons is not positively connected to the upper set and is so dimensioned that with the pressures acting on it at low speed braking it remains in the lower position and is inoperative. At speeds above a predetermined value the governor 7 compresses a spring 26 against a diaphragm 27 thereby opening a valve 22 to establish in the chamber below piston 11<a> a pressure dependent upon the speed whereby the pistons 11, 11<a>, 11<d> co-operate with pistons 11<b>, 11<c> to establish in the cylinder 5 a pressure which is also dependent upon the speed. With the system shown in Fig. 4, the cylinder pressure is dependent both upon the speed and upon the load. The valve device 10 comprises pistons 11, 15 acting on a lever 37 the arms of which are adjustable in effective length by shifting the pivot 38 of the lever. For this purpose the pivot is carried by a lever 41 angularly adjustable automatically according to the load by connections 39, 40 and also by a piston 35 which when the speed falls to the lower value is connected by the governor 7 to the reservoir 4. In a modification of this arrangement adapted to give the same cylinder pressures in braking at high as at low speeds with light brake pipe pressure reductions up to, say, 5 atm. while giving higher cylinder'pressures at high speeds than at lower speeds with greater pressure reductions an additional piston subject to the pressure in chamber 14 acts with the piston 11 in opposition to the piston 15 at high speeds and high pressure reductions but this piston is held inoperative by a spring with low pressure reductions and is held entirely out of action at low speeds by pressure fluid supplied beneath it from the reservoir 4 by the governor. In this system the pivot 38 of lever 37 is adjusted only by the load.