Patent GB-249485-A (GB)
Title: Improvements in and relating to track braking apparatus for railways and the like
IPC: B61K7/08
Filed: 1926-02-11
Abstract: 249,485. Westinghouse Brake & Saxby Signal Co., Ltd., (Assignees of Coleman, J. P.). March 18, 1925, [Convention date]. Arresting-grips on permanent way; fluid-pressure. - In poweractuated braking apparatus for railway and like vehicles and comprising devices located on the track and adapted to engage the wheels or other part of a vehicle, the supply of power is automatically controlled, by a device responsive to the speed of the vehicle approaching the apparatus and a control device responsive to the weight of the vehicle may also be provided. The braking pressure is controlled in accordance with the time occupied by the vehicle in passing over a predetermined section of track before the vehicle reaches the braking apparatus which may be mounted on a platform adapted to be depressed by the vehicle, the extent of the depression also controlling the brake pressure. As shown, the platform 4 is mounted on spring supported levers 32, 32a in a pit 3 and carries rail-sections 2, 2a at each side of which are arranged brake-bars 5, 6 connected by linkage to pistons 36, 36a in brake cylinders 7, 7a so that outward movement of the pistons causes the brake bars to move towards the rails. At the right hand side of the platform is arranged a track circuit consisting of railsections 2, 2a insulated at 8, a battery 34 and a relay R which is de-energized when the vehicle enters this section of the track resulting in closure of an electric circuit comprising contacts 15, 16, a motor M, battery or other electric supply 14, and connections 18, 19, 20. The motor drives a centrifugal governor C connected to a lever 13 which is pivoted at 13a and controls a variable impedance As in a circuit consisting of an electromagnet 39, connection 24, battery &c. 14, contacts 15, 16, connections 18, 21, lever 13, connection 22, lever 10, variable impedance Aw and connection 23. The impedance Aw is controlled by the lever 10 and rod 11 connected to one of the platform supporting levers 32. Pressure fluid is supplied to the brake cylinders for brake application through pipes 35, 26 under the control of a valve device V<R> controlled by the electromagnet 39, and for brake release through the pipe 27 and valve VR controlled by an electromagnet 50 which, when energized, connects pipe 27 to pipe 35. The valve device VA comprises an armature 38 controlled by the electromagnet 39 and connected to a. diaphragm 40 which engages a floating lever 44 carrying inlet and exhaust valves 41, 42 controlling the pressure in a chamber 43 which is in connection through the valve 41 with the pipe 35. The chamber 43 is connected by a pipe 46 with a cylinder 47 containing a piston 48 the stem of which carries a small piston valve adapted to cover or uncover a leakage groove 52 which permits communication between the pipe 26 and an exhaust port 54. Depression of the diaphragm builds up pressure in the chamber 43 causing the piston 48 to move downwardly so that the groove 52 is covered and the stem of the piston 48 depresses the stem of the application valve 49 putting the pipes 35, 26 in communication. The strength of the current controls the pressure in the chamber 43 and the position of the piston 48 and consequently the application pressure in the cylinders 7, 7a. The amount of the impedance As included in the application control circuit depends on the speed which is attained by the motor M which varies in accordance with the time taken by the vehicle to pass over the insulated track-section and therefore with the speed of the vehicle, The parts being so designed that the impedance varies inversely as the square of the speed of the vehicle. The amount of the impedance Aw in circuit decreases with the weight. The strength of current and brake pressure therefore are increased as the weight and speed increase. While the vehicle is on the platform the contact 12 operated by the rod 10 is held open so that the relay R is deenergized until the vehicle leaves the platform when the relay R is re-energized and the brake release valve is opened to the pressure pipe 35, the application valve being simultaneously closed. As the motor continues to run when the vehicle is on the platform, means comprising a toothed sector 28, pawl 29 and link 30 connected to the lever 10, are provided to lock the arm 13 and prevent any further increase in the impedance As after the vehicle has entered the platform.