Patent GB-348529-A (GB)
Title: Improvements in compressed air brakes for obtaining a variable braking effect
IPC: B60T8/18
Filed: 1930-02-10
Abstract: 348,529. Fluid - pressure brakes. ARMSTRONG, J. J. V., 12, Church Street, Liverpool.-(Holmbergs Mekaniska Verkstads Aktiebolag, C.; 12, Bungatan, Lund, Sweden.) Feb. 10, 1930, No. 4401. [A Specification was laid open to inspection under Sect. 91 of the Acts, Feb. 24, 1930]. [Class 103 (i).] To limit the braking pressure according to the load in compressed air vehicle brakes that are applied by reducing the pressure of the air on one side of the piston, this air is vented into one or more chambers which may be put into service either by hand or automatically by the vertical displacement of the vehicle body on the springs. The apparatus shown is of the kind described in Specifications 275,401 and 307,644, [both in Class 103 (i), Brakes &c.], comprising a single chamber cylinder 1 for bringing the brake shoes into engagement with the wheels and a two-chamber cylinder 2 for applying the main pressure. Control is effected by the valve mechanism shown, connected to the train-pipe 7 whereby normally the chambers 42, 43 of the cylinders 2, 1 respectively are open to atmosphere by the channels 44, 45, slide valve 41, passage 46, and throttling member 60; the auxiliary reservoir 8 is charged from the train-pipe 7 through the groove 48 past the piston 40 of the slide valve and channel 50 ; the chamber 5 of the cylinder 2 is charged from the train-pipe 7 through the port 55 and channel 56. By means of a cock 14 the upper side of the slide valve piston 10 is connected to the train-pipe 7, the lower side of the piston 11 is connected by channels 59 to the reservoir 8 and the chamber between the pistons is connected to the chamber 5 of the cylinder 2 by channels 58, 56. By means of a cock 14, the channel 13 connected to the valve port 12 may be connected to one or more chambers 26, 27 or as shown to an atmosphere port 20. The channel 13 is normally connected to atmosphere by the valve port 37. A train-pipe venting chamber 9 normally vented to atmosphere by channel 52, slide valve 41, and channel 46 permanently communicates by passage 53 with an annular area of the piston 10. When the train-pipe pressure is reduced to apply the brakes, the slide valve 41 is released from the detent 49 by the piston 40 and connects the reservoir 8 by passages 50, 45 to the chamber 43 of the cylinder 1 and to the chamber 42 of the cylinder 2. The train-pipe is at the same time vented to the chamber 9 and also to the annular area of the piston 10 thereby equalizing the pressures on the two sides of this piston so that it is raised by the spring 54 cutting off the chamber 5 of the cylinder 2 from the train-pipe and venting it to the chambers 26, 27 if these are in service, by channels 56, 58, 13 and the cock 14. The piston 3 is thus rendered effective and is coupled to the piston 1<1> by the device 4. When the pressure in the chamber 5 acting beneath the piston 10 has fallen sufficiently, the piston is returned to a neutral position by the train-pipe pressure. An initial pressure sufficient to effect a light application of the brakes is thus obtained. If the train-pipe pressure is further reduced the piston 10 and with it the piston 11 acted upon by the auxiliary reservoir pressure through the channel 59 again rises to connect the cylinder chamber 5 to the chambers 26, 27 until the pressures acting on the two pistons 10, 11 are in equilibrium. The pressure in chamber 5 may thus be gradually reduced until it is limited by equalization with that in the chambers 26, 27 or it may be reduced to atmospheric pressure if, as shown, the channel 13 is connected to the atmosphere port 20. Similarly, upon raising the train-pipe pressure the pressure in the chamber 5 may be gradually increased and when the trainpipe pressure reaches the normal value, the valve piston 40 returns to connect the cylinder chamber 43 to atmosphere. The rise and fall of pressure in the chambers 5, 43 respectively may be adjustably retarded by throttling members 57, 60. The exhaust port 37 for the chambers 26, 27 may also be adjustably throttled. In order that the maximum fall of pressure in the cylinder chamber 5 may be reached with the same fall of train-pipe pressure, irrespective as to whether any or none of the chambers 26, 27 are in service the piston 11 may be formed as shown in Fig. 3 so that either or both the areas 11<1>, 11<11> may be connected to the auxiliary reservoir by means of a cock 61. The cock 14 may be adjusted automatically according to the vehicle load, by the movement of the body on the springs through mechanical, fluid pressure or electrical means. The invention may be applied to combined single and two-chamber brakes of the kind in which the function chamber of the twochamber cylinder is vented first to the singlechamber cylinder and then to atmosphere, means being provided whereby the function chamber instead of being vented to atmosphere may when desired be vented as described above to obtain braking pressures suitable to various load values.