Patent GB-569095-A (GB)
Title: Improvements relating to railway traffic controlling apparatus
IPC: B61L23/16
Filed: 1941-03-31
Abstract: 569,095. Railway signal systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. March 31, 1941, No. 4298. Convention date, Nov. 29, 1940. [Class 105] In a railway-traffic control system using coded current over either a track or a line circuit, the number of different signal indications which can be given is increased by the use of a polar relay distinctively responsive to code impulses of opposite polarity to control the reception of code impulses by a codefollowing relay responsive only to one polarity and controlling traffic governing apparatus. Thus, two signals can be given for each code frequency, according to polarity, and an additional " stop " signal with the track or line circuit shunted by train occupation, or de-energized. Fig. I shows a three-signal system for left-to-right traffic over insulated track sections. Section 1-11 has at its entrance end the signal S1, controlled by a polarized relay TRP bridging the track rails 1, 2, a code-following track relay TR and detecting relay H. Contacts 8, 9, 10 of relay TRP move to the right when positive code impulses (rail 1 positive with respect to rail 2) are received, and to the left for negative impulses (rail 2 positive with respect to rail 1), these contacts remaining in the position to which last moved until impulses of reversed polarity are received. Relay TR is operated only by direct current of one polarity, and is connected across the rails 1, 2 by pole-changing contacts 8, 9 so that it receives the code impulses in the right direction for energization irrespective of the polarity of the impulses in the track circuit. Contacts 11, 12 of relay TR thus follow the code. Contact 11 connects one pole of a local source of direct current (not shown), alternately to opposite ends of the primary winding of a decoding transformer DT, a central tapping being connected to the opposite pole. Reversal of current in the primary winding thus produced induce impulses in the secondary winding and these, rectified by contact 12, are supplied to the slow-release, direct-current relay H which energizes and holds up its contact 13. This connects one pole of a local current source (not shown) through conductor 27, to contact 10 of relay TRP. Contact 10 completes the circuit through " clear " signal G, or " caution " signal Y according to the polarity of the track current. Relay H also has contacts 6, 7 which control the polarity of code current impulses supplied to the next section to the rear. Thus, at the exit end II of the section shown, code current is supplied to the rails 1, 2 from track battery TB over the contacts 6, 7 of relay H of the next section in advance, the positive side of the battery being connected to rail 1 or 2 according to whether contacts 6, 7 are picked up or released. This current is coded by contact 5 of a code transmitter CT at the desired frequency, an impulse being sent to the track through front contact 5. Back contact 5 serves to discharge storage potential from the rails in the intervals between the impulses. An impedance 17 is included in the circuit. In operation, with all track sections of the stretch unoccupied, the apparatus is in the condition shown,'all sections receiving positive impulses and their entrance signals showing " clear." When a train enters any section, relay TR of that 'section is shunted and releases, thus de-energizing relay H. Back contact 13 of that relay connects the local source to signal R, indicating " stop." Contacts 6, 7 of relay H release and reverse the polarity of code current supplied to the first section to the rear. Contacts 8, 9, 10 of relay TRP of that section move to the left and the associated relay H is maintained energized. The entrance signal indication Y for that section is thus energized over front contact 13 and left contact 10. Front contacts 6, 7, of said relay H, cause positive code impulses to be supplied to the second section to the rear, so that section, and consequently successive sections to the rear, are in the condition shown in Fig. 1, with " clear " entrance signals. The train is thus protected against following traffic. An application of the invention to a line wire system is described, the circuit arrangements of which are identical with those of Fig. 1 except that the rails 1, 2 of Fig. 1 are replaced by line wires co-extensive with the adjacent track section, and that, in order to initiate protection for the train, the track section has a normally energized track relay, contacts of which are included in the line wires. Thus, when the section becomes occupied, said contacts open and break the line wire circuit, de-energizing the associated relays TRP, TR, H, putting the entrance signal of the occupied section to stop and causing supply of negative code impulses to the line circuit associated with the next section to the rear. Fig. 3 shows the invention applied to a system giving five indications a, b, c, d, e, progressively more restrictive from " clear " indication a to " stop " indication e, by the use of two code frequencies. The Specification describes in detail the circuits and operation outlined below. Each TRP relay has contacts 32 ... 35, 43, 44, 47 additional to the contacts 8, 9, 10. Each H relay has contacts 41, 42 additional to contacts 6, 7, 13. Frequencies of 75 and 180 cycles per minute are selectively provided by contacts 75 of a code transmitter CT75 and 180 of a code transmitter CT180, one or other of these frequencies being supplied to a code repeating relay CR contact 5 of which effects the corresponding coding of the track current supplied from track battery TB. At the entrance end of each section an additional relay D is provided, fed from the primary of the decoding transformer DT through a decoding unit 180DU, so that relay D is energized only when 180 code is supplied. Relay D has contacts 36 ... 40, 46. Which of the two code transmitters CT75 or CT180 shall drive the relay CR at the exit end of the section depends on the positions of contacts 40-44 of relays D, H, TRP at the entrance of the next section in advance, whilst the polarity of the code depends on the positions of contacts 6-7, 32-39 of the same relays. As shown, in normal condition with the track sections unoccupied, 180 code is supplied to relay CR over contacts 180, right-hand contact 44 and front contacts 41, 40, and positive 180 code is supplied to the track from battery TB over front contacts 36, 37. Positive 180 code is also supplied when relays H, TRP are in the condition shown, and relay D is released, the circuit being over front contacts 6, 7, right-hand contacts 32, 33, and back contacts 36, 37, the circuit of relay CR in this case being over contact 180, 42 and back contact 40. Negative 180 code is supplied when advance relay D is released, companion relay H is picked up, and contacts of companion relay TRP are in left-hand position. Positive 75 code is supplied when advance relays D, H are picked up, and contacts of companion relay TRP occupy left-hand position. Negative 75 code is supplied when both advance relays D, H are released and contacts of companion relay TRP are in either of their two positions. Normally, all sections are in the condition shown in Fig. 3, with positive 180 code track current, entrance relays D, H picked up, entrance relay TRP contacts in right-hand position, and " clear " 'indication a energized over contacts 13, 46, 10. When a section becomes occupied, entrance relays D, H release, and " stop " indication e is given over back contact 13. At the same time, negative 75 code is supplied to the track of the first section to the rear, the entrance relays of that section responding to give approach signal d and cause supply of negative 180 code to the next section to the rear. In response, entrance relays of that section cause " approach slow " indication c to be given, and positive 75 code to be supplied to the next section to the rear. Entrance relays of that section respond to give " approach restricting " indication b and cause positive 180 code to be supplied to the next section to the rear, the entrance signal of that section showing " clear " indication a. Positive 180 code is thus repeated in all further sections to the rear, with corresponding " clear " signals. It is pointed out that, since relay TR is energized only by current of one predetermined polarity, protection is given in the event of pole-changing contacts 8, 9 of associated relay TRP failing to take up a position corresponding with the polarity of the coded track current, because the consequent non-response of relay TR causes release of relay H, with consequent '' stop " signal indication..