Patent GB-572894-A (GB)
Title: Improvements relating to railway track circuit apparatus
IPC: B61L23/16
Filed: 1942-10-19
Abstract: 572,894. Railway traffic-control track-circuit relays. TOMLINSON, A. V. (Union Switch & Signal Co.). Oct. 19, 1942, No. 14612. [Class 105] A track relay for railway track-circuit traffic control, in order to give relatively slow pick-up and quick release characteristics and to obtain from a single relay structure the functional advantages of a primary-secondary relay combination, has an operating winding connected across the track rails in the usual way, and a second winding coupled to the track circuit and controlled so as to oppose the attractive action of the operating winding on the relay armature during, pick-up operation. A make-beforebreak contact operated by the relay armature may be used to control the energy level created by the operating winding. Fig. 1 shows an insulated track section DE with the usual track battery TB and resistor 3 connected across the rails at one end and the track relay TR across the rails at the other end. The operating winding 5 on a cora 5 serves, when energized, to attract armature 7, operating contacts 12, 13, 14. Normally, part only of winding 6 is connected across the rails through front contact 15, contact 12, and resistance 17, this part being just sufficient to ensure armature 7 being held up under low-resistance ballast conditions, so that the ready release occurs when the section becomes occupied. When armature 7 is released the whole of winding 6 is connected across the track through back contact 16 and contact 12, the latter being bifurcated to make before break and prevent the circuit of winding 6 from being broken. A second winding 11 on a core with pole-piece 10 serves, when energized, to attract armature 8 in opposition to the attraction of winding 6 on armature 7, armatures 7, 8 being rigidly connected by a non-magnetic member 9, the combination being pivoted at 4, and biased (as by gravity) to the position in which armature 8 rests on pole-piece 10. Winding 11 is in series with a winding 18 on core 5 and its circuit is normally open at contact 13. When the track section becomes occupied armature 7 is released, resistor 17 is cut out of circuit at contact 15, and the whole of winding 6 is connected across the track but is shunted until the section becomes vacated, whereupon winding 6 becomes energized, and during the building up of current therein the current induced in winding 18 energizes winding 11 to attract. armature 8. Pick-up of armature 7 is thus retarded until the flux in core 5 reaches a steady state, the pick-up restoring the parts to the normal condition shown. The Specification describes two modifications in which winding 18 is replaced by the secondary winding of a transformer in series with winding 6 and contact 12, the primary winding being in series with winding 11. In one of these modifications the arrangement is otherwise similar to, and functions in the same way as, the arrangement of Fig. 1. In the other modification, Fig. 4, the arrangement is for use in a system in which the polarity of track current from battery TB is reversible by pole-changing contacts 26, 27. Relay TR is polarized and has at least one polar contact 29, armature 7 and its associated contacts being neutral. The primary winding 23 of the transformer 22 is in series with winding 6. Contact 13 of Fig. 1 is omitted and the secondary winding 24 is permanently in series with winding 11, the core of which has two pole-piece extensions 30, 10. The arrangement is such that when polarity reversal occurs at contacts 26, 27 and the track is unoccupied, contact 29 is moved to right or left as the case may be, but current induced in windings 24, 11 maintains armature 8 in contact with extension 30 and so prevents release of armature 7 by polarity reversals. When the track becomes occupied armatures 7, 8 are released, and when the track is again vacated winding 11 is energized during the building up of energy in winding 6, to hold armature 8 in contact with extension 10 and thus retard pick-up of armature 7. In another modification winding 18 and contact 13 are omitted, and winding 11 is permanently connected across the track in series with a condenser (which may be electrolytic) and in parallel with winding 6 and contact 12, the arrangement being in other respects as shown in Fig. 1. The condenser is normally charged but is discharged by train-shunt when the track becomes occupied, without affecting release of armature 7. As winding 6 is reenergized when the track is vacated, the condenser is recharged, the charging current flowing through winding 11 to hold armature 8 and retard pick-up.