Patent GB-367073-A (GB)
Title: Improvements in or relating to vacuum brake cylinders
IPC: B60T15/06
Filed: 1930-12-03
Abstract: 367,073. Fluid - pressure brakes. VACUUM BRAKE CO., Ltd. and STEVENS, W. C. I., 3, Old Queen Street, London. Dec. 3, 1930, Nos. 36477/30 and 4871/31. [Class 103 (i).] Automatic vacuum brake apparatus comprises a pair of pistons in a common cylinder, one of which after a predetermined movement during which it takes up the brake shoe clearance at a low leverage, opens a passage to admit air to the second piston which then applies additional pressure to the shoes at a higher leverage. The first piston may open a venting valve for the cylinder to effect a quick partial application of the brakes and there may be further valves adapted to connect the chambers on the two sides of the pistons, to accelerate the release of the brakes. The second piston may be rendered inoperative. In the construction shown, the cylinder 2 is divided by a partition 7 into chambers A, B containing the pistons 3, 4. A vacuum chamber is connected to the chamber A at 42. The piston 3 is connected to the brakes by lever 21 pivoted at 22. Piston 4 is connected to the lever 21 at a higher leverage by lever 12, rods 16, 24 and a one-way clutch comprising a member 19 pivoted to the rod 16 and normally held from engagement with the toothed rod 24 by resting against a stop 28. An alternative clutch comprises links 55, 58, Fig. 4, pivoted together at 59, and at their upper and lower ends to the cylinder and to the rod 16, respectively. The links are toothed at 56, 60 to grip the rod 24. A fixed tubular member 8 serves as a guide for the piston 4 and piston rod 5. The train-pipe 30 is constantly connected by passages 31, 33, 34 to the outer side of piston 3 and communicates bv a ball-valve 45, passage 36 and port 35 with the chamber A and thence by passages 43, 44 with the chamber B. Passage 38 from the outer side of piston 4 is connected to passage 36. The chambers on both sides of both pistons are thus normally exhausted. Air admitted to the train-pipe to apply the brakes, first passes to the outer side of piston 3 which moves to take up the clearance of the brake shoes and then uncovers the port 35 to admit air also to the outer side of piston 4 the movement of which engages the clutch member 19 with the rod 24 and thus applies additional pressure to the brake shoes at a higher leverage.. The piston 4 canbe rendered inoperative, for instance, on an unloaded vehicle, by turning a cock 37 whereby passages 38 and 44 are disconnected respectively from passages 36, 43 and are connected together. The quick-application and release valve device comprises a spring-pressed valve 72, a spring- pressed piston valve 80, an air chamber 88 connected to chamber 90, and chambers 87, 82 connected to ports 34, 35 and the vacuum chamber V which is constantly connected to the cylinder chamber A at 42. The initial movement of piston 3 in applying the brakes, opens the valve 72 by the lever 79 and air from chamber 88 thus flows therefrom to the outer side of the piston 3. At the same time, the depression of the piston 80 due to the rise of pressure in chamber 87 closes the port 83 so that connection of the vacuum chamber V with the outside of the piston 3 when it passes the port 35 is prevented. When however in releasing the brakes, the pressure is reduced in chamber 87 sufficiently to enable the spring to raise the piston 80 communication is established between the outerside of the piston 3 and the vacuum chamber through the port 35 thus quickening the release of the brakes.