Patent GB-633044-A (GB)
Title: Improvements relating to fluid pressure braking apparatus for railway and like vehicles
IPC: B60T8/18
Filed: 1948-01-09
Abstract: 633,044. Fluid-pressure brakes. WESTINGHOUSE BRAKE & SIGNAL CO. Jan. 9, 1948. No. 713. Convention date, March 20, 1947. [Class 103 (i)] An automatic fluid-pressure braking system for railway vehicles, of the type having the usual triple valve 1, brake-pipe 2, auxiliary reservoir 3, emergency reservoir 4, brake cylinder pressure retaining valve device 5 and a brake cylinder 6 having a main pressure chamber 18 and a second or compensating pressure chamber 24 so that the degree of brake application is governed by the difference in pressure between the two chambers, is characterized in that the pressure set up in the compensating chamber 24 is at all times proportional to the pressure set up in the main chamber 18, that proportion being determined in accordance with the load carried by the vehicle. The variation of pressure in chamber 24 with load is brought about by a relay valve device 8 in combination with an adjusting mechanism 9 that is associated with an unsprung part of the vehicle truck 138. Briefly the operation of the device 8 provides that on each occasion that pressure is supplied through pipe 2 for normally charging the auxiliary and emergency reservoirs 3 and 4, a piston 99 and rod 100 are operated to move the plate 137 of the adjusting mechanism 9 into contact with the unsprung member 138. Such movement, which is proportional to the deflection of the vehicle's springs by the loading, being used to produce through a pivoted lever 107, a corresponding displacement of a rod 74 carrying a fulcrum for a balance lever 73 so as to vary the leverage between two members 40 and 44 responsive respectively to the pressures in the brake cylinder chambers 18 and 24. Since this operation takes place only each time the reservoirs are charged and the plate 137 is at other times held clear of the member 138, the pressure in brake cylinder 24 is not subject to the usual deflections of the springing system due to irregularities in the track. The initial setting of the apparatus, when the reservoirs are being charged through the brake-pipe 2, takes place as follows. Fluid-pressure is supplied from the pipe 2 through pipe 158 and passage 157, choke passage 156, and passage 155 to a chamber 154 containing a slide valve 160. Fluid also flows from passage 157, past checkvalves 172, 173, choke passage 176, passages 177 and pipe 62 to a load reservoir 7 combined with the auxiliary and emergency reservoirs in a unitary assembly. Until the pressure of pipe 2 acting in chamber 154 reaches a certain pressure, such as 40 pounds per square inch, the slidevalve 160 remains in the cut in position shown, and fluid flows by passages 169, 165 to a checkvalve chamber 94 and a tuning reservoir 166, and also by passage 153 to a chamber 92 below a diaphragm 90 arranged to operate by lever 85 a plunger 84 for locking the position of the rod 74. When the pressure acting in chamber 92 reaches about 10 pounds per square inch the diaphragm 90 deflects to unlock the plunger 84 by movement downwards which also presses open the check-valve 93. Fluid from chamber 94 may then flow by passage 103 to the piston chambers 102 and 78. When the pressure in chamber 102 has increased sufficiently to overcome spring 104, rod 100 rocks the lever 114 clockwise about pivot 115 so that the cam surface 117 moves anticlockwise the bell-crank 119, 126 so as to draw up the plate 137 into engagement with the unsprung member 138, further movement of piston 99 being then prevented. The cam element is provided with a surface 123 that may be adjusted in relation to the stiffness of springing on any particular vehicle so as to obtain the required movement of rod 74. Thus for various degrees of loading of the vehicle, between empty and full load, the vehicle body will assume corresponding positions with respect to the unsprung part 138, these positions producing through the action of surface 111 on rod 100 abutting against lever 107, corresponding positions of the rod 74 and its fulcrum 64 below the balance lever 41. Pressure in slide-valve chamber 154, acting also in chamber 152 on the right of diaphragm 143 in the cut-out unit 142, deflects the diaphragm 143 sufficiently against spring 149 to bring member 150 into contact with spacer element 145. Further increase of pressure to about 40 pounds per square inch in chamber 154 then overcomes the spring pressure on the right of diaphragm 144 so that it is deflected to the right and slidevalve 160 is moved correspondingly to its cutout position. In this cut-out position chamber 92 below the latch diaphragm 90 is exhausted to atmosphere through a passage 164. The spring 91 then moves lever 85 to lock the plunger 84 in the teeth of rod 44, thus fixing the position of the fulcrum 64. In this position also, the passage 165 is put in communication with passage 103 so that the tuning reservoir 166 and the piston chamber 102 are together exhausted through a choke passage 171 and the port 164 to atmosphere. The choke passage 171 and the timing reservoir 166 are of such a size as to ensure that sufficient pressure is maintained in the piston chambers 78 and 102 to keep the rod 74 in contact with the lever 107 and the plate 137 in contact with the member 138, at least until after the plunger 84 has locked the rod 74 in its adjusted position. After the cut-out valve device 142 has operated as described above, the brake pipe pressure continues increasing up to its normal maximum and charges the load reservoir 7 through checkvalves 172 and 173. When the apparatus is fully charged and ready for operation, a brake application is initiated in the normal way by a reduction in the pressure of the brake-pipe 2. The pressure applied to chamber 18 of the brake cylinder by the pipe 11 leading from the triple valve 1 is also applied by pipe 35 and passage 34 to chamber 33 above diaphragm 31. This tends to move member 40 down so as to rock the lever 41 about its fulcrum and so raise member 44 against spring 50 and to open supply valve 59. This enables fluid to pass from the load reservoir 7, by pipe 62, passage 61, valve 59, passage 38 and pipe 27 to the brake cylinder compensating chamber 24. Fluid from the load reservoir 7 passing through choke passage 37 however later builds up pressure above diaphragm 32, thus tending to close the valve 59. The pressure finally attained in the chamber 49 and therefore also in chamber 24 of the brake cylinder depends on the position of the fulcrum 64 which is varied in accordance with the loaded condition of the vehicle as described. It is arranged that when the vehicle is fully loaded, the fulcrum 64 is located directly below the member 40 so that the lever 41 is not rocked and the valve 59 remains shut under the action of springs 50 and 63 so that no fluid is supplied to chamber 24 to reduce the full braking load resulting from the full pressure in chamber 18. In the event of some pressure remaining in chamber 24 from a previous brake application, this may escape by pipe 27, passage 38, chamber 49, valve 53, passage 51, chamber 52 and port 55 to atmosphere.