Patent GB-366531-A (GB)
Title: Improvements in or relating to compressed air brake devices
IPC: B60T17/10
Filed: 1930-11-03
Abstract: 366,531. Fluid - pressure brakes. HOLMBERGS MEKANISKA VERKSTADS AKTIEBOLAG, C., 10, Bangatan, Lund, Sweden. Nov. 3, 1930, No. 33017. Convention date, July 14. [Class 103 (i).] The piston of a two-chamber compressed air brake carries a single-chamber cylinder which is first supplied in applying the brakes, to engage the brake shoes quickly with the wheels. As described in Specification 275,401, [Class 103 (i), Brakes &c.], the working chamber of the two-chamber cylinder, that is, the chamber which is not vented in the application of the brakes, is normally at atmospheric pressure and is connected to charged reservoir during brake application. This chamber is in permanent communication with the single-chambercylinder. To adjust the maximum braking pressure according to the load, the function chamber of , the two-chamber cylinder may be vented in brake application either to atmosphere or to a closed chamber, as described in Specification 348,529. The piston -63- of the twochamber cylinder 46 has a tubular rod 48<1> which forms the single-chamber cylinder, the piston 55 of which is connected to the brakes by rod 61. A supply and exhaust pipe 60 projects into a space in the piston 55 which is connected by a restricted passage to the working chamber 50 of the cylinder 46. The piston 63 is adapted to be clutched to the piston 55 by a toggle device carried by the pistonrod 48<1> and. comprising a spring-urged lever 57<1> the upper end of which abuts against a projection on the cylinder in the released position and thus disengages a pawl 57 from a rack on the rod of the piston 55. The valve device 3 parts of which are similar to a Westinghouse triple valve has the main piston connected by springs 14 to a slide valve 15 which is held by a spring stop 17 in both its release and application positions. The valve device comprises also a piston slide valve 13 co-operating with a further piston 44. The train-pipe 1 is connected through passage 4 with the valve chamber 11, and with the parts in the normal position shown, to the auxiliary reservoir 25 through grooves 26 and valve chamber 24 and to the function chamber 30 of the cylinder 46 by passages 28, 29 ; the working chamber 50 of the cylinder 46 and the chamber of the singlechamber cylinder 48<1> are connected to atmosphere by passages 60, 20, 22 ; chamber 42 of the valve is connected to passage 29 and the end chamber to chamber 24 by passage 45; an annular area 38 of the piston 13 is connected by passages 39, 40 to passage 20 and thus to atmosphere ; the valve 13 is thus held in the position shown by train-pipe pressure in chamber 11. For an unloaded wagon, the cock 37 connects a venting chamber 33 for the function chamber 30 to a passage 32 and this passage is, on release, vented to atmosphere as shown by passages 31, 35. If, to apply the brakes lightly, the train-pipe pressure is reduced by about half an atmosphere, the piston 11 moves the valve 15 to the right, connecting the reservoir 25 by passages 24, 20, 60 to the space in brake piston 55 which then quickly engages the brake shoes with the wheels. The movement of the valve 15 also exposes the upper face of the valve piston 10 to. the pressure in reservoir 25 so that this piston opens the valve 9 and the trainpipe 1 is vented through a non-return valve and passages 20 to the chamber of piston 55 until upon equalization of the pressure on the two faces of the piston 10 through port 23, the valves and piston are returned by springs. The pressure fluid supplied by pipe 60 to the chamber of piston 55 gradually equalizes through the restricted passage into the chamber 50 of the piston 63 so that the fluid pressures on the two sides of the piston 63 are at this stage substantially equal but by reason of the difference in the effective area of the two sides, the piston 63 is advanced sufficiently to effect the engagement of the pawl 57 with the rack on the piston 55. The annular area 38 of the piston valve 13 being now connected by passage 40 to the reservoir 25 this valve moves sufficiently to close the passage 28 and thus cut off the function chamber 30 of piston 63 from the train-pipe. If the train-pipe pressure is further reduced, the pistons 13, 44 move further to the left, uncovering the port 32 to the chamber 42 so that the function chamber 30 vents into the chamber 33 and a difference of fluid pressure is thus established on the two sides of the twochamber brake piston 63, which thus becomes effective. When the pressure in the chambers 30, 42 has fallen to a value corresponding to the fall in train-pipe pressure the pistons 13, 44 return sufficiently to close the port 32. The maximum braking pressure is reached when the pressure in chamber 30 has equalized with that in chamber 33. For a loaded vehicle, however, the cock 37 is turned to connect the port 32 to atmosphere, and the pressure in the chamber 30 can thus be fully reduced to that of the atmosphere by a fall of train-pipe pressure from 5 atm. to about 3.3 atm. The release of the brakes may also be graduated by raising the train-pipe pressure in stages, the chamber 30 being correspondingly recharged at each stage through the port 28 and the chamber 33 being partly discharged through passages 31, 35 so that the same maximum brake cylinder pressure is obtained if the brakes are re-applied after a partial release.