Patent GB-570039-A (GB)
Title: Improvements relating to railway signal systems
IPC: B61L23/16
Filed: 1942-03-06
Abstract: 570,039. Railway signalling systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. March 6, 1942, No. 2953. Convention date, March 8, 1941. [Class 105] In an automatic permissive block signalling system, particularly for controlling traffic in both directions over a single-track stretch between passing sidings, each insulated section of the track provides two track circuits fed respectively with current of master-code and feed-back or detector-code type. The code used is of frequency type having approximately equal on and off periods. As described the system uses two frequencies of 75 and 180 cycles per minute for controlling three-indication track signals but may beadapted to use more frequencies, for example three frequencies of 75, 120 and 180 for a three-block four-indication signal system. In operation master code is fed towards an oncoming train irrespective of the direction of train movement and feed-back code in the opposite direction. The arrangements described operate track signals to prevent opposing traffic movements but permit following movements, at usual following distance, in the established direction. The code current may, however, be utilized, by known means not described, to operate cab signals or stop the train. Fig. 1a shows, in normal condition with track section unoccupied, the equipment for location II at the junction between sections A, B of the track, similar equipment being provided for location III, Fig. 1b, at the junction between sections B and C. Track signals SE II and SE III control east-bound (left to right) traffic, and signals SW II, SW III control west-bound traffic. The right end of each track section is bridged by winding 5 of a transformer TTE described as normally supplying master code current towards one left end to control eastbound traffic. The code frequency is determined by one of two coders 75CT,-180CT. As shown, contact 180a of coder 180CT is included, together with front contact 17 of relay HE associated. with the next section to the right, in the circuit of a code following-relay CP contact. 7 of which controls the circuit from source BX, CX through the primary winding 6 of transformer TTE so that 180 master code is normally supplied to the track. When contact 7 releases it closes the circuit of winding 6 through a fullwave rectifier, the output of which, due to feedback code as described below, energizes a codefollowing track relay TRA. Contact 32 of relay CP closes an auxiliary stick circuit over contacts 30, 31 so that relay TRA holds up until relay CP picks up. Relay TRA is associated in known way with transformer DTW and decoding relays HW, DW, the former responding to code of any frequency and the latter being connected through a decoding unit 180DU so that it responds only to 180-cycle frequency. Normally, however, relay DW does not function owing to its circuit being open at contact 16 of a relay HE referred to below. Normally, therefore, relays DW, HW function to detect feed-back energization of the track irrespective of frequency. The left end of each section is bridged by winding 8 of a transformer TTW, the primary winding 9 of which is connected intermittingly to a source BK, CK by contact 10 of a code-following relay RC. When contact 10 is released it closes the circuit of winding 9 through a full-wave rectifier, the output of which supplies a code-following track relay TR which is associated with transformer DTE and decoding relays HE, DE. Relay HE is responsive to all frequencies and relay DE is connected through a decoding unit 180DU to respond only to 180-cycle frequency. The circuit of relay DE is, unlike that of relay DW, permanently closed so that relay DE is always ready to function. The equipment also includes directional relays ES, WS which respectively pick up in the usual way when the associated track section is entered by east-bound or westbound traffic. Normally, relay RC follows the frequency of relay CP as described below, and the contacts 7, 10 operate so that the picked-up period of each coincides with the release period of the -other. Thus, as shown, contact 7 is picked up so that transformer TTE is supplying master code to the track, and this code current traverses winding 8 of transformer TTW. As contact 10 is now released, master code energy is operating relay TR, which thus normally follows master code current so that, together with its associated relays HE, DE (the contacts of which control the indication circuits of signals SEII, SE 111) it is ready for control of eastbound traffic. When contact 10 picks up and contact 7 releases, energy from source BK, CK supplies transformer TTW to send feed-back code to the right. The feed-back code current traverses, the winding 5 of the transformer TTE at the right of the section and rectified current of feed-back code frequency operates relay TRA to control west-bound traffic. Normally, relays DW are released and west-bound signals stand at approach (Y) whilst relays HE, DE are picked up and east-bound signals stand at stop (R) Device RC is supplied from secondary winding 21 of a transformer 20 when the associated relays HE, ES are respectively picked up and released, to close front contact 22 and back contact 23. The circuit of primary winding 24 of transformer 20 is closed in series with winding 25 of transformer DTE when relay HW associated with the next section to the left is picked up to close front contact 26 as shown, or alternatively, when relay HW is released to close back contact 26 and the associated relay WS is 'picked up to close front contact 27. Current in windings 24, 25 is controlled by contact 28 of relay TR, and relay RC is designed to respond only to the polarity of current supplied from winding 21 when contact 28 releases. Thus during the " off " period of relay TR contact 10 picks up to break circuit of relay TR and connect source BK, CK to winding 9 of transformer TTW, supplying feed-back code impulses through transformer TTE to relay TRA. Under some circumstances, however, device RC is energized from a direct current source under coder control to supply master code from source BK, CK through transformer TTW to the track section. Thus, with relay TR continuously de-energized so that relay HE is released current passes from positive over contact 180 of coder 180CT, front contact 34, back contacts 22, 23, winding RC to negative. Alternatively, if relay HW is released and associated relay WS picked up, current passes from positive over contact 75 of coder 75CT, front contact 35, back contacts 34, 22, 23, winding RC to negative. Master code supplied in this way to section B at location II is followed by relay TRA at location III. The operation of the system for east-bound traffic is as follows. When an east-bound train enters section A, relay TRA of that section (location II) is shtmted, relay HW released, causing signal SW II (for west-bound traffic) to indicate " stop ", whilst contact 26 opens to de-energize transformer 20, so that device RC is de-energized and supply of feed-back code to section B stops. Relay TRA at location III is thus de-energized and relay HW releases, putting signal SW III to stop, 'and contacts 26 opens, so that the process just described for section B is applied to section C and so on in succession for all sections to the right. De-energization of relay TRA at a location does not affect the supply of master code controlled by device CP at that location. Thus, generally, all sections of the stretch to the right of an occupied section are deprived of feed-back code and their signals for west-bound traffic indicate "stop", but are still supplied with master code and their signals for east-bound traffic remain at " clear ". The master code supplied to the occupied section (A) is available for operation of a " clear " cab signal. When the train enters section B, relay TR of that section is shunted, relays HE, DE release, and signal SE II indicates " stop ". East-bound relay ES is picked up. Device CP at location II is then operated at 75 code rate, its circuit being from positive, over contact 75a of coder 75CT, front contact 18, back contact 17, winding CP to negative. Master code of 75 rate is thus supplied to section A. Similarly, when the train enters section C relay TR of that section is shunted, signal SE III indicates " stop " and 75 master code is supplied to section 13, so that when section B is vacated, relay TR of that section (location II) operates at 75 rate and detecting relay HE picks up, relay DE remaining released. Signal SE II is thus operated to its " approach " indication. Relay ES at location II also releases. Pick-up of contact 17 and opening of contact 18 replaces the 75 rate of operation of relay CP by 180 rate, so that the normal 180 master code is restored in section A. Closure of contacts 22, 23 causes device RC to operate at 75 rate since relay TR is following the 75 master code in section B. The feed-back 75 code thus fed to section B is followed by relay TRA at location III, where relay HW picks up so that signal. SW III indicates " approach ", and contact 26 closes the primary circuit of transformer 20. When section C is vacated, it is supplied with 75 master code, relay HE picks up, putting signal SE III to " approach " and, with release of relay ES, 180 master code is supplied to section B. Relay TR at location II follows this code, so that relays HE, DE pick up and signal SE II displays its normal " clear " indication. The Specification also traces in detail the progress of a west-bound train. Briefly, assuming the train to occupy section C, relay TR (location III) is shunted, releasing relay HE, putting east-bound signals SE III to " stop " and, at contact -17, de-energizing device CP, so that the normal supply of 180 master code to section B is discontinued, with consequent release of relay TR at location II, where similar action occurs, putting signal SE II to " stop ". Contact 16, lo