Patent GB-1206893-A (GB)
Title: Fluid pressure distribuiton system for controlling fluid pressure brakes
IPC: B60T15/18
Filed: 1968-06-20
Abstract: 1,206,893. Railway brake system. COMPAGNIA ITALIANA WESTINGHOUSE FRENI E SEGNALI. 20 June, 1968 [21 June, 1967], No. 29346/68. Heading F2F. In a fluid pressure braking system for railway vehicles in which the brake cylinder 21, Fig. 1, is connected to an auxiliary fluid pressure reservoir 22 or to exhaust 5, for applying or releasing the brakes respectively, by movement of a pressure control device 3 in dependence on the difference in pressure of that in the brake control line 24 and a control pressure, a changeover valve 15 is provided whereby the system can operate to provide gradual brake release or direct brake release, in the former mode the control pressure being that in a control reservoir 23 and the device 3 is further biased towards its brake release position and in the latter mode the control pressure is that in the auxiliary reservoir 22. Operation in gradual brake release mode:- With the changeover valve 15 as shown, Fig. 1, the cylinder is connected either via bore 39 in the stem 3 to exhaust 40 or with movement of the stem upwards to close the bore 39 against valve 7 and open valve 6, to reservoir 22. The stem 3 is provided with two pistons 1, 2 and, in this mode, the chambers 45, 4, above and below piston 2, are connected to the brake cylinder and exhaust, respectively, and the chambers 25, 37, above and below piston 1, are connected to the brake pipe and reservoir 23, which after being changed is isolated from the rest of the system so that the pressure therein is maintained substantially constant. Thus during brake application and release the piston moves to its equilibrium position with both valves 6, 7 closed when the brake pipe pressure in chamber 25 and the brake cylinder pressure in chamber 45 are in equilibrium. This has the effect that during brake release the pressure in the brake cylinder is decreased in dependence on the pressure in the brake pipe. Operation of direct discharge brake release mode.-With the changeover valve 15, as shown in Fig. 2, the reservoir 23 is disconnected from the system and the chambers 45, 4 are both connected to exhaust and chambers 37, 25 to the reservoir 22 and brake pipe, respectively. To apply the brake when a pressure supply is applied to the brake pipe, the cylinder 21 is connected to the reservoir 22 until the reservoir pressure has dropped until it is substantially equal to the pressure in the brake pipe. At brake release when the brake pipe is connected to vacuum the stem 3 moves down to connect the cylinder to exhaust, which connection will be continued until the brake pipe is again connected to a pressure supply, because equilibrium of the piston 1 is no longer obtainable. In both modes, prior to operation of the brakes or after brakes release, when the piston has moved down to its lowest position, the reservoir 22, and in the gradual release mode, the reservoir 23, are both connected to the brake pipe to be charged therefrom. Changeover valve.-The valve may be manually operable, Figs. 1, 2, electromagnetically operable, Figs. 3, 4 (not shown) or electropneumatically, Figs. 5, 6 (not shown).