Patent GB-571241-A (GB)
Title: Improvements relating to railway signalling systems
IPC: B61L23/16
Filed: 1942-03-13
Abstract: 571,241. Railway signalling systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. March 13, 1942, No. 3341. Convention date, March 27, 1941. [Class 105] In a track circuit system for controlling one-way railway traffic master and feed-back frequency-code impulses of opposite polarity are supplied to insulated track sections and both codes pass through an entrance track relay and an exit detector relay in series. The system provides, inter alia, against wrong operation by current due to energy stored in the track or by certain relays closing one contact before another is opened. As shown in Fig. 1 a code-following track relay TR bridging the rails 1, 2 at the entrance end of the section is associated with an impulse relay IR the contact 12 of which alternately connects relay TR to the track directly and through a battery IB in series with a resistance 21. Contacts 15, 16 of relay TR control circuits of a transformer DT having a secondary winding 17 supplying current impulses to relay IR, and another secondary winding supplying current impulses to an auxiliary relay H of slow release type so that the relay remains picked up so long as the impulses are supplied thereto. This relay may control the supply of energy to the next track-section in the rear, and control the signal, not shown, at the entrance to its own section. Transformer DT is supplied from direct current source terminals B, C the latter being centrally connected to the primary winding which is thus energized alternately in opposite senses bv closure of front and back contacts 15, the impulses supplied to relay IR being alternately of opposite polarities. Relay IR is, however, of biased polar type and picks up. only in response to current of one polarity, as, also, does relay TR. At the exit end of the section the rails are bridged by a detector relay KR associated with a code relay CR operated at any one of a number of frequencies by known coders, not shown. Contact 10 of relay CR alternately connects relay KR to the rails directly and through a battery TB in series with resistance 14. Relay KR is of polarized type the contacts 18, 19 of which remain in the position to which they were last moved until the relay is energized by current of opposite polarity. These contacts control the circuits of a transformer KT which supplies a current impulse to an approach relay AR each time contacts 18, 19 close. Relay AR is of slow release type to remain picked up so long as impulses are supplied thereto and may be used to control signals in the next section ahead or for other purposes. The positive poles of batteries TB, IB are both connected to rail 1 so that the master code and feed-back code current impulses respectively supplied thereby are of opposite polarities, and both these code currents flow through relays TR, KR in series. Relay TR picks up only in response to impulses of master-code polarity, relay IR picks up only by the impulse sent to it when relay TR releases, whilst contacts 18, 19 are moved to the left by master code and to the right by feed-back code. Thus when contact 10 picks up battery TB supplies an impulse which picks up relay TR thus sending impulses to relays H, IR, the former picking up and the latter remaining released. Contacts 18, 19 are also moved to the left sending an impulse which picks up relay AR. When contact 10 releases, contacts 15, 16 release and send impulses which respectively pick up relay IR and keep relay H picked up. Closure of front contact 12 causes battery IB to send a feed-back current which leaves relay TR released but moves contacts 18, 19 to the right, thus sending an impulse to keep relay AR picked up. When contact 10 again picks up the above process is repeated and this continues so long as the track is unoccupied. When a train occupies the section relay TR is and remains released but master code current continues to flow through relay KR so that contacts 18, 19 more to and remain in left-hand position. Thus current impulses to relays H, AR cease and these relays release. Should current continue to flow due to energy stored in the track, this current flows in the same direction as that supplied by the battery so that no improper relay operation occurs. In the event of either of the contacts 10, 12 touching a front and back contact simultaneously the battery TB, or IB is merely short-circuited through its resistance 14 or 21 so that no energizing current is supplied to relays KR, TR. The relay CR may have an additional contact such as contact 11, Fig. 6 which short-circuits the detecting relay when master code is being sent. Relay IR may have a similar contact for short-circuiting the track relay during transmission of feed-back code. This short-circuiting of the relays lessens circuit resistance so that the arrangement may be used with longer track sections. A modification is described in which transformer KT is omitted and contact 18 directly controls the circuit of relay AR and in a further modification the polarized relay KR is replaced by a relay similar to relay TR which picks up with one polarity of current and releases with opposite polarity or on being deenergized. Fig. 6 shows another form in which the detector relay KRA picks up only with one polarity of current and has an additional hold-up winding closed over backcontact 26 of relay CR and front contact 27 of relay KRA. As shown, a second contact 25 controls relay AR, but this contact may be omitted and relay AR inserted between contacts 26, 27 so that it is controlled by contact 27. Alternating current code may be supplied to the track to control train-carried signals in known way, and Fig. 6 shows an arrangement for this purpose in which the secondary winding of a transformer TT is included in series with the battery TB, the primary winding being energized from an A.C. source BX, CX.