Patent GB-571112-A (GB)
Title: Improvements relating to railway track circuit apparatus
IPC: B61L1/18
Filed: 1942-10-20
Abstract: 571,112. Railway signalling track-circuit systems. TOMLINSON, A. V. (Union Switch & Signal Co.). Oct. 20, 1942, No. 14683. [Class 105] [Also in Group XXXVII] In a track-circuit system for railway signalling, the track relay is designed to adjust its pick-up and release energy levels automatically to compensate for slow variations in the trackcircuit current due to variations in ballast resistance, maintaining the open or closed condition of its contacts (as the case may be) during such variations, the contacts, however, being operated by sudden variations when the track section becomes occupied or vacated. This result is obtained by using a relatively heavy.. armature 10 pivoted at 12, with contact extension 19, in co-operation with a relatively light and slow moving pivoted member 11 having a contact extension 20. Figs. 1-3 show different forms of the invention in each of which a relay winding 7 on core 6 is bridged across the rails 1, 1a at one end of an insulated track section DE, a source of current 4 being bridged across the other end through resistor 5. The parts are thus shown in the normally energized condition with the track-section vacant, and contacts 19, 20 closed, these contacts being shown as controlling the circuit of a repeater relay TP supplied from source terminals B, C. Relay TP has a contact 22 controlling signals, locks, &c. (not shown) in the usual way, and also has a pivoted armature the movements of which take part in controlling the track circuit arrangements. In Fig. 1 the armature 10 is biased away from core 6 towards a back stop 14 by spring 13. Member 11, pivoted at 15 and.having a counterweight 18, forms the armature of a second winding 9 on a core 8 and is biased towards back stop 17 by spring 16. The stops 14, 17 are positioned so that when winding 7 is de-energized and members 10, 11 rest against the stops, contacts 19, 20 are open. As shown, member 10 occupies a position depending on the strength of current in winding 7, and, by engagement of contacts 19, 20 has moved member 11 to a corresponding position. With slow variations in current through winding 7 armature 10 makes corresponding slow movements which member 11 is able to follow, keeping contacts 19, 20 closed. Relay TP is thus kept energized and its make-before-break contact 23 engaging contact 24 connects winding 7 across the track in series with resistor 26 having a resistance equal to that of winding 9, the circuit of which is broken at contacts 23, 25. With sudden decrease of current in winding 7 armature 10 drops more quickly than member 11 can follow, thus opening contacts 19, 20 to de-energize relay TP. Contact 23 drops, first closing with contact 25 to connect Winding 9 in series with winding 7 and then breaking contact at 24 to cut out resistor 26. If the train shunt is of low resistance, armatures 10, 11 may rest against their back stops, but if the train shunt is of high resistance any current flowing through the relay passes through both windings and causes armatures 10, 11 to take up corresponding positions with contacts 19, 20 still open. Any slow variations in the current also causes corresponding variations in the positions of both armatures, thus maintaining contacts 19, 20 open whilst the track section is occupied. Sudden increase of current when the track section is again vacated causes armature 10 to pick up more quickly than armature 11, thus closing contacts 19, 20 to energize relay TP and restore the device to the normal condition shown. In Fig. 2, winding 9 is omitted, and member 11 is connected with armature 10 by a spring 30 and with armature 32 of relay TP by a spring 31 under tension whilst armature 32 is picked up. In the track vacant condition shown, armature 10 occupies a position depending on the strength of current through winding 6 in series with resistor 33, and has moved member 11 to a corresponding position, contacts 19, 20 being closed, relay TP energized, and contact 34 of relay TP open. The parts are proportioned so that member 11 follows movement of armature 10 due, to slow variations of current. When the track becomes occupied, armature 10 and member 11 rest against the back-stop 14, 17 with contacts 19, 20 open, relay TP being deenergized and contact 34 closed, to shunt resistor 33. Armature 32 releases to remove tension from spring 31. When the track is vacated, the. initial current through winding 6 is stronger than normal owing to the shunting of resistor 33, and ammature 10 picks up to restore the conditions shown In the modified arrangement of Fig. 3, member 11 is supported on a knife-edge 40, is connected to armature 32 of relay TP by spring 31, and is gravity biased in counter-clockwise direction. A compression spring 41 between members.10, 11 is effective to hold contacts 19, 20 apart when armature 32 is released to decrease the tension of spring 31, but not when armature 32 is picked up as shown. In t'he-normally energized condition armature 10 is positioned according to the, strength of current. in winding 6 and contacts 19, 20 remain closed during small variations of current. When the track-section is occupied armature 10 releases quickly to open contacts 19, 20. Relay TP de-energizes and releases armature 32 to decrease the tension in spring 31. With low resistance train shunt members 10, 11 rest against their back-stops with contacts 19, 20 open. With high-resistance train, shunt the current through winding 6 may lift armature 10 more or less and slow variations in its position impart corresponding movements, to member 11, spring 41 holding contacts 19, 20. open. When the section is vacated, armature 10 picks up quickly to close contacts 19, 20 and restore the parts to the normal energized condition shown.