Patent GB-812629-A (GB)
Title: Improvements in electric apparatus for railway signalling
IPC: B61L23/16
Filed: 1956-01-12
Abstract: 812,629. Railway track and cab signalling systems. TELECOMMUNICATIONS RADIOELECTRIQUES ET TELEPHONIQUES T.R.T. Jan. 12, 1956 [Jan. 17, 1955; Feb. 24, 1955; Aug. 3, 1955], No. 1113/56. Class 105. In a railway track circuit signalling system having successive electrically insulated track sections, each section having at least one electrically controlled multi- (preferably light) aspect track signal, a transceiver is associated with each sectional junction and comprises a combination of a pulse generator which feeds the cyclically generated pulses to the train approaching section with the phase of the pulses characteristic of the action and a receiver which receives the pulses from the train receding section and causes the generator of the train approaching section to repeat the pulses received so that each receiver receives a series of time phased pulses each representing an unoccupied receding section, said receiver also controlling the track signal of its associated receding section in accordance with the location of receding trains as indicated by the absence from the series of pulses, of a pulse due to the short circuit of a receding section by train occupation. The cyclically generated pulse of a generator is phased, e.g. by triggering means, and the generators of all the sections are synchronized by a common generator or a single pulse generator may be used for all the sections with a distributing means feeding the several sections through means determining the appropriate phase. The receivers determine the phase relationships between the pulses received. An engine may be provided with known means for detecting the magnetic field set up by the current flowing through its front axle and for actuating an indicator which is located in the driver's cab and adapted to give " stop," " caution " and " line-free " indications. Thus, for no pulses received, a " stop " indication results, and for one pulse per cycle, which means that the next section in advance to the one occupied by the engine, is occupied, a " caution " signal results in the driver's cab. Two or more pulses received means that the next two or more sections in advance are clear and a " line clear " signal results in the driver's cab. Using threeaspect signals at the beginning of each section, it is sufficient for each receiver of a section numbered x to be able to ascertain that the signal corresponding to section (x+ 1) or (x+ 2) is absent, in order to give the " stop " and " caution " signals. The receiver of a section compares the phase of the pulse emitted by that section generator and the phases of the pulses corresponding to the next two receding sections. The same apparatus may be used for both directions of traffic on a single track by means of change-over switches operated, e.g. by relays, which commute the connections between each of the transceivers and those in the two adjacent sections (Fig. 3, not shown) so that the pulses are always transmitted in the opposite direction to train travel. The changeover may also be effected by electric discharge tubes or crystal rectifiers. The change-over may be effected by remote control means from stations at the ends of the line as by the transmission of a distinctive pulse on a carrier frequency f 0  (which need not be repeated) selected by filters and applied to the relays to cause them to change over. The same end station then transmits a continuous sequence of timing pulses of a carrier frequency f<SP>1</SP> different from f 0  and are received by all the transceivers over a cable and each repeats or transmits into the associated track section circuit a corresponding pulse on a carrier frequency f2, properly phased to identify that section, as by an apparatus as shown in Fig. 5, so that when no train is present the pulse series on the rails comprises the timing pulses intercalated with the section characterizing phased pulses. If a train is in, say, the third section from the start, then the receiver at the start end would receive all the timing pulses and the phased pulses of all the sections before the third, i.e. the first and second counting in the direction of train travel. By comparison of the characterizing pulses with the timing pulses the missing pulses can be ascertained and hence the section in which the train is located. Also the pulses from the advance sections may be received by a magnetic detector on the train itself from which pulses received the occupied or vacant state of the track ahead can be ascertained. In Fig. 5 assuming a transceiver for the sectional junction a5, a filter for carrier frequency f2 connected between points VAv on the receding track section A4, selects the section characterizing pulses and passes them through amplifier 2 to the approaching track section A5 represented by the point VAm. A filter 3 for passing carrier frequency f1 selects the time pulses from the cable k and passes them to a counter 4 having five stages 4a-4e so that it counts a series of five timing pulses. Since only the three sections ahead are of interest for a threeaspect signal, the first timing pulse received controlling the stage 4a is employed to restore the apparatus to its normal at-rest condition. The second stage 4b controls an electronic switch or gate 5. This stage is operated by the second time pulse followed by the second section characterizing pulse which is applied to the gate 5 and passes through to actuate a delayed release relay 6, preferably electromagnetic. In like manner, the third and fourth section characterizing pulses pass through the gates 7 and 9 to operate relays 8 and 10 respectively, the timing pulses opening one gate and blocking the preceding one. The release delay of the relays enable them to be held between successive pulse cycles so that if the appropriate pulse becomes absent from the pulse series, the relay will release. The fourth pulse passing through the gate 9 is also applied, preferably through a filter 12 to the cable k for communication of the information represented thereby to the end stations. The fifth counter stage 4e controls the generator 13 which generates the characterizing pulse for the section and injects it into that track section following the fifth timing signal which operated the stage 4e. The succeeding timing pulses have no effect on the counter 4. Contacts of the relays 6, 8, 10 depending upon whether they are operated or not close circuits for operating the usual red, yellow and green lights. In the case of a junction breakdown, or of a broken rail the track signals are put at the " stop " aspect. The timing pulses passing through the filter 3 on carrier frequency f are applied to the approaching section VAm (or A5) through a repeater stage 14 to operate an indicator at the terminal starting station. Fig. 6 shows a single line for traffic in both directions and divided up into insulated sections c1-c4, &c. in whch the series of phased section characterizing pulses are transmitted in both directions, and these pulses are repeated, employing different carrier frequencies of, say, in the range 500-6,000 c/s. from section to section by " markers " M1, M2, M3, comprising transceivers with two-way repeater devices, coupled to the two ends of the sections on either side of a junction through balanced transformers T1, T2, T3 which do not transmit the signals from section to section directly. Motive power carried by the rails may be passed on from section to section through connections Z between the two transformer windings connected across the rails at a junction. All the markers are synchronized by means of a line L to which phased pulses are applied on a carrier frequency of e.g. 4,000 c/s. from a governor device R, and are retransmitted to the rails preferably on a different carrier frequency, e.g. between 500 and 2,000 c/s. The appropriate phased pulse from the line L is segregated at each sectional junction from the train of pulses in the line by means, e.g. of a counter device having n counter stages, n being the number of the section, in combination with a triggering device adapted to actuate a changeover device at the end of n pulses, to render the generator of the marker momentarily operative. The governor R also provides a synchronizing pulse signal with a carrier frequency, e.g. of 6000 c/s. and the end of this pulse constitutes the starting point from which the counters associated with the markers M1, M2, M3, &c. begin to count the pulses from the line L. The received pulses from the rails in any section marker are used to provide a track signal indication accordingly as in the signal devices D1, D2, D3 for traffic to the left and in the signal devices D<SP>1</SP>1, D<SP>1</SP>2, D<SP>1</SP>3 for traffic to the right. The synchronizing pulse may also be transmitted over a channel other than the rails and line L, such as the overhead conductor H of an electric traction system, and is received into an engine cab through the trolley V, for use in combination with the pulses picked up from the track or front axle of the train. In the cab a counting device Q1, Fig. 8, is associated with pulse generator J1 of the pulse recurrence frequency, and is triggered into action by the synchronizing pulse. The counting device Q1 thereupon counts the pulses generated until the instant at which the first coinciding section characterizing pulse arrives from the rails and this gives an indication of the occupied section in advance. To this end the termination of the synchronizing pulse operates a change-over relay m<SP>1</SP> to trigger the generator J<SP>1</SP> which feeds the pulses into two counters Q, Q<SP>1</SP> through a gate g<SP>1</SP>. As soon as the first of the identifying pulses (C1-C2) arrive from the rails it changes over a relay m which blocks the gate g<SP>1</SP> and thereafter only the track pulses c6 ... c2 go into the counter Q<SP>1</SP>. A rectifying element r keeps the track pu