Patent GB-291115-A (GB)
Title: Improvements in or relating to train control systems
IPC: B61L3/12
Filed: 1928-05-25
Abstract: 291,115. Associated Telephone & Telegraph Co., (Assignees of Hudd. A. E.). May 27, 1927, [Convention date]. Fluid-pressure.-The driver's brake valve is operated by a piston in a cylinder to which air is supplied when a pipe 3, Fig. 2, and reservoir B supplied through a needle valve 4 are exhausted under control of an electromagnet EP and a valve 6. At a caution or danger signal the driver may acknowledge the warning within a predetermined time and reset the valve 6 but cannot reset after a second operation within a given time interval. If no acknowledgement is made, the brakes are applied and can only be removed after the train has stopped completely. The track apparatus, Fig. 5, comprises two pairs of magnets at each signal spaced apart a predetermined distance. The first magnet of each pair passed by a. train is a permanent magnet P which initiates a brake application and the second is an electromagnet E1, E2 the condition of which depends upon traffic conditions and which, when energized restores the train apparatus. The track magnets co-act with the receiver relay having an armature 45 and pick-up brushes which pass over the poles of the track magnets as described in Specification 278,730. At each permanent magnet P, the armature 45 is moved from the position shown, so as to open the circuit over wire 48 to the magnet EP and the battery. The armature 29 falls and allows valve 6 to open and contact 22 to fall to open the circuit to lamp G and close that of lamp R. At a. clear or caution signal the first electromagnet E1 a few feet beyond the first permanent magnet is energized and the armature 45 is reset and magnet EP re-energized to restore the valve 6 and the lamp signals. The whistle W is not sounded, since there is insufficient time for the charging of chamber E to the required pressure. At a clear signal the above operations are repeated at the second pair of track magnets. At a caution signal the second electromagnet E2, is de-energized and the armature 45 remains reversed and magnet EP de-energized and lamp R alight. The pressure in reservoir B is reduced through valve 6 and chamber E and whistle W is sounded. Unless the driver uses the acknowledging plunger AP the pressure in reservoir B will be so far reduced that the valve controlling the driver's valve piston will open and the brakes will be applied. If the plunger AP is depressed, valve 26 is opened and reservoir C, and chambers 16, 15, are exhausted at a greater rate than they are supplied from the main reservoir connection MR through a restricted orifice 17. Valve 28 is released on collapse of diaphragm 27 and a momentary rush of air passes from chamber D through pipe 14 to lift the disc 15 and close for a short time only, the contact 13 in the circuit 34 of the resetting coil 39 of armature 45, which restores magnet EP. The valve 6 is thus re-set but the lamp R remains active since the plunger AP moves the spring 23 clear of the contact arm 22 which is therefore only reset on energization of the magnet EP when a clear signal is passed. A second closure of contacts 13 is not possible until pressure has been again built-up in reservoir C which requires about 20 seconds. Hence if a stop signal is passed at a speed higher than that at which the distance between the two pairs of track magnets is covered in less than 20 seconds, the driver is unable to prevent the brake application resulting from reduction of pressure in the reservoir B. The brake application can only be annulled after the train has come to a standstill. The abovedescribed resetting circuit includes the switch PS, which is closed by air pressure in the reservoir B, and is opened when the brakes are applied. A second resetting circuit is from battery over contacts 40 which are normally open but are closed when maximum air pressure of the main reservoir is supplied from pipe 20 through valve 19 which is opened by operation of the acknowledging plunger AP. The piston 41 is connected to a stop-detector SD as described in Specification 285,804 which comprises a spherical valve element 46 forced by moderate air pressure into engagement with a train wheel and unseated by the rotation of that wheel so as to allow escape of air and prevent the necessary rise of pressure on the piston 41 to close the resetting circuit so long as the train is moving. The receiver relay is mounted on the locomotive by bolts, one of which BB is turned out of cast iron and is, therefore, very brittle. This bolt is included in the circuit of the magnet EP and the resetting coils 39. If the receiver relay structure meets an obstacle and is displaced so as to be rendered useless the brittle bolt will be fractured and a brake application will follow. Specification 300,244 is referred to.