GB563588A - Improvements relating to fluid pressure braking apparatus for vehicles - Google Patents

Abstract

563,588. Fluid-pressure brakes. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd., KERSHAW, A. G., and SIMMONS, A. W. Nov. 19, 1942, No. 16369. [Class 103 (i)] In a fluid-pressure &c. brake system for coupled vehicles in which control of the brakes on a trailer vehicle is effected from a tractor vehicle by a brake pipe, the pressure supplied to the brake pipe is normally maintained at a value higher than the standard value and the control valve on the tractor is adapted when operated, initially to reduce the pressure to the standard value while the control valve on the trailer vehicle is so constructed as to be unaffected by this reduction but to be responsive to variations in the brake pipe pressure below the standard value, to effect an application and release of the trailer brakes. Minor brake pipe variations during running do not, therefore, affect undesired application of the brakes and a pressure higher than the standard value is established in the auxiliary reservoir on the trailer. The control valve on the tractor comprises a manually-operated lever 9 one arm 12 of which operates exhaust and supply valves 4, 5 for the tractor brake cylinder connected at 1, through a spring 8 beaTing on a piston 7 which is subject to the cylinder pressure and which carries a tubular part 6 forming the seat of the valve 4. The main reservoir is connected by passage 2, filter 20 and passages 22 to chambers containing the supply valve 5 and the supply valve 15 of the trailer brake pipe 18 the pressure in which is controlled by the arm 14 of the lever 9. For this purpose, the arm 14 engages the casing 28 of a spring 27 which normally bears on a piston 24 subject to the pressure in the brake pipe. An extension of the piston forms the seat of the brake pipe exhaust valve 16 the stem of which operates the supply valve 15. A second spring 30 bears on the piston 24 and on a casing 31 connected at 33 to the casing 28. Normally the parts are in the position shown with the supply valve 15 open so that the brake pipe pressure is maintained at a value dependent on the spring 27. Operation of the lever 9 effects an application of the tractor brake and its initial movement relieves the piston 24 of the pressure of the spring 27 so that the brake pipe pressure falls to the standard value determined by the spring 30 and further movement of the lever by reducing the pressure of spring 30 effects a corresponding further reduction of the pipe pressure. The control valve on the trailer, comprises in one form, Fig. 6, a piston 36 subject to the pressure of springs 38, 49 and to the pressure in chamber 39 connected by passages 40, 43 to the control pipe. The spring 49 bears on the piston 36 through a plate 48 and through a rod 47 slidable in this piston on a differential piston 77, 78 the upper face of which is connected to the atmosphere at 54. A chamber 56 connected to the chamber 79 below the piston area 77 is arranged to be connected either to atmosphere through the piston or to a supply chamber 66 by exhaust and supply valves 60, 62 operated by the piston. The chamber 66 is connected to the auxiliary reservoir by a port 67 and is supplied from the control pipe through a non-return valve 68. When the trailer is loaded a cock 82 is turned to the position shown in Figs. 8, 11 so that the chamber 56 and thus the chamber 79 is connected to the trailer brake cylinder through passages 74, 72, 73, 57 while the chamber 80 below the piston area 78 is connected to atmosphere by passages 81, 85, only the piston area 77 being thus effective. The piston 36 normally abuts on the spring casing 45 but when the control pipe pressure is reduced below the standard value by operation of the tractor control valve, this piston, with the pistons 77, 78, is moved downwards by the springs 38, 49 thus seating the exhaust valve 60 and opening the supply valve 62. When the brake cylinder pressure acting in chamber 79 has risen to a corresponding value the pistons move upwards sufficiently to re-close the valve 62. When the cylinder pressure acting on the piston 77 reaches a value equal to the pressure of the spring 49, further reduction of the pipe pressure is ineffective further to increase the cylinder pressure. If the trailer is unloaded, the cock 82 is turned to a position in which while the passages 73, 74 are still connected, the passage 81 is connected to the passages 73 and 74 through passages 83, 84 so that piston chambers 79, 80 are both connected to the brake cylinder the pressure in which for a given control pipe pressure reduction is thus reduced. The cock may also be turned to a third position in which the cylinder passage 73 is connected by passages 83, 84, 75 to the control pipe to release the brake on an uncoupled trailer. The brake may be re-applied by returning the cock. Simpler forms of the trailer valve are described in which a piston with a single lower pressure area replaces the piston 77, 78 and in which the cock 82 is dispensed with.