GB205520A - A distributor for fluid-pressure brakes - Google Patents

Abstract

205,520. Bozic, D. Oct. 16, 1922, [Convention date]. Fluid-pressure. - Relates to an air distributor for fluid-pressure brakes and comprises means whereby (1) the braking effort on each vehicle is varied in accordance with the load, (2) the braking effort is increased in systems working under high pressure, e.g. on high-speed vehicles, (3) in highspeed vehicles the initial braking pressure is automatically diminished with reduction of speed to prevent skidding of the wheels, (4) the brakes may be released by hand, (5) an accelerator is brought into action during emergency braking. (1) The distributing piston 2 is located between chambers 6, 15 and its stem 9 is internally bored to receive a second piston 10, subject on its underside to atmospheric pressure through the channel 13 and having a stem 11 which bears on one arm of a lever 4 pivoted at 5 to a slide 64 which is moved progressively to the left with increase in load by a stem 54 mounted on the axle-box 55 and adapted, when the springs 550 are deflected under load, to bear on one arm 56 of a lever 57 fulcrumed at 58, whereby the arm 59 is lowered and the arm 63 of a bell-crank lever moves the slide to the left. During normal running of the vehicle pressure air from the train-pipe passes to the chamber 6 by the passages 8, 7, and by the passages 20, 19, 18 and past the needle valve 22 to the chamber 15, so that the pressures on each side of the diaphragm 14 are equalized. Air also passes to the auxiliary reservoir by the passage 34, past the ball valve 33, and by the passage 32. The ports being in the positions shown, the brake cylinder exhausts through the passages 36, 28 and 29. To apply the brakes, the train-pipe pressure is reduced, when the diaphragm 17 closes the valve 22, and the diaphragm 14 is flexed downwardly by the excess of pressure in the chamber 15, whereby the stem 11 of the piston 10 acting through the lever 4 raises the piston 3 to close the exhaust valve 30 and open the valve 31, so that air from the auxiliary reservoir passes into the brake cylinder until the pressure in the chamber 28 balances the braking effort transmitted to the piston 3 by its stem 27, when equilibrium is established with both valves 30 and 31 closed. The braking pressure is thus dependent on the braking effort for a given reduction in train-pipe pressure and this effort is increased with the load by the automatic movement of the fulcrum 5 of the lever 4. Variation of braking pressure due to inequalities of the track is prevented, since during braking the slide 64 is under sufficient pressure to prevent the bell-crank from operating it. (2) The slide 64 is connected through a rod 67 to a piston 66, which with low working pressures follows the movements of the slide due to loading. At its right-hand side, the piston is in communication through a passage 70 either with the train-pipe, the auxiliary reservoir or the chamber 15, so that when high-working pressures are employed it overcomes the resistance of a spring 68 and moves to the leit, carrying the slide with it and displacing the fulcrum 5 so that a greater braking effort is transmitted to the rod 27. (3) The brake blocks 49 are suspended by links 48 from a lever 45, which may pivot about either of two fulcra 52, 53 and is normally urged downwards by a spring 46 or a weight 47. When the pressure between the blocks and the wheels for either direction of rotation is such that skidding is imminent, the frictional drag on the shoes rocks the lever 45 about one or other of its pivots to raise the stem 44 cf a valve 43, whereby the brake cylinder exhausts to atmosphere, the auxiliary reservoir being temporarily cut off by the closing of the valve 35. This exhaustion proceeds until the lever 45 falls into its normal position. (4) The brakes may be manually released by opening the valve 22 by means of the handle 24, so that the pressures in the chambers 6, 15 equalize and the spring 16 returns the pistons 2, 10 to normal position. (5) The accelerator for emergency braking comprises a piston 74 mounted between chambers 73, 75, the stem of which carries a valve 77 normally closing a passage 78 leading to atmosphere or to the brake cylinder. During normal braking air passes from the chamber 73 by the passage 72 and leaks from the chamber 75 so that the pressures equalize, but an abrupt reduction in train-pipe pressure results in excess pressure in the chamber 75, so that the piston 74 rises and the train-pipe exhausts through the port 78 until the piston reaches its highest position, when the inertia. of the valve 80 opens it against the pressure of the spring 79 and the resulting equalization of the pressures in the two chambers 73, 75 causes the piston 74 to fall to close the valve 77. The passage 72 may be replaced by an axial boring in the valve 80 and its stem, when the chamber 73 communicates with the train-pipe through the passages 82, 83. Specification 175,271 is referred to.