Railway signalling system
United States Patent [1 1 Birkin [111 3,876,171 [451 Apr. s, 1975 RAILWAY SIGNALLING SYSTEM [75] Inventor: Michael S. Birkin, London, England [73] Assignee: British Railways Board, London,  
 England [22] Filed: Mar. 15, 1973 [211 App]. No.: 341,664  
 OTHER PUBLICATIONS Davies et 211., Bournemouth Line Cab Signalling, Railway Gazette, July 18, 1969, pp. 545, 546, 549.  
 Primary Examiner-Robert S. Ward, Jr.  
 Assistant E.\&#39;aminerReinhard J. Eisenzopf Attorney, Agent, or Firm&#39;-&#39;Pol1ock, Philpitt &amp; Vande Sande [57] ABSTRACT A railway signalling system comprises a permanent magnet positioned on a railway track at a point preceding a multi-aspect signal, an electro-inductor and an antenna positioned adjacent the magnet, means for energizing the electro-inductor with a dc supply and the antenna with high frequency signal in dependence upon the current aspect of the signal. A detector is carried by a railway vehicle for detecting the fields produced by the magnet, electro-inductor and antenna and provides a warning to a driver of the train corresponding to the current aspect of said signal.  
 5 Claims, 5 Drawing Figures PMENTEUAF 75 876, l 71 sziznlqgs FIGI.  
 KBELL /7 3 FIGZ. 77  
 AWN/76 ACKNOWLEDGE [BUTTONS /B.F? FILTER DETECTOR\ I J N 23 pd 4p Pd 1 LOGIC UNITJ l5 Q; 22  
 W x i J DETECTOR SELECTOR RELAY saw 2 or &#39;3 mQE RAILWAY SIGNALLING SYSTEM The present invention relates to an improved railway signalling system of the kind in which train borne indicators provide an automatic warning of the signal aspect to the driver of the train. The indicators are controlled by devices located between the rails of the track.  
  According to the present invention there is provided a railway signalling system comprising a permanent magnet positioned on a railway track at a point preceding a multi-aspect signal, an electro-inductor and an-antenna means positioned adjacent said magnet, means for energizing said electro-inductor with a dc. supply and said antenna means with high frequency signal in dependence upon the current aspect of the signal, detector means carried by a railway vehicle fordetecting the fields produced by said magnet, electro-inductor and antenna means and to provide a warning to a driver of the train corresponding to the current aspect of said signal.  
  A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:  
  FIG. 1 is a plan view of a length of railway track in which the track mounted transmitting portion of a signalling system is positioned between the rails.  
  FIG. 2 is a schematic diagram of the detection and cab signalling equipment carried by the train.  
  FIGS. 3 and 4 are circuit diagrams of two possible arrangements of the electro-inductor and a track coil mounted on the railway track.  
  FIG. 5 is a circuit diagram of an alternative embodiment for the track mounted antenna.  
  As shown in FIG. 1, a permanent magnet and an electro-inductor 11 are laid between the rails 12 of a railway track. This combination ofa permanent magnet and an electro-inductor forms the basis of a known railway automatic warning system. Colour light railway signals commonly have four aspects, namely one green, two yellow and one red. The green aspect alone is lit to indicate that the line ahead is clear, and in this situation the electro-inductor is not energized by a suitable d.c. source. Detecting equipment carried by a train detects the magnetic fields of both the permanent magnet and the electro-inductor and when the latter is energized and its field is detected, equipment carried by the train automatically registers that a signal with a green aspect is being approached and consequently no braking action is required by the driver.  
  When however the two cautionary aspects, single or double yellow or the red stop aspect is lit, the electromagnet is not energized. The detecting equipment carried by the train registers this fact and operates an appropriate warning indicator on the train and unless appropriate action is taken by the driver, operates the train brakes.  
  In addition in the arrangement according to the present invention a loop antenna 13 of suitable size and of one or more turns is laid between the rails 12 adjacent the magnet and electro-inductor. I  
  The electro-inductor 11 is fed from a rectified a.c. supply and the antenna 13 is fed from an appropriate transmitter as will be described below, and the two elements can be energized or not as required as will be described.  
  A train passing along the rails 12 of the track in the direction of the arrow A, carries detecting equipment for detecting the fields produced by each of the three elements 10, 11 and 13. The table below shows how each of the two elements 11 and 13 is energized in dependence&#39; upon the aspect of the signal being approached by the train.  
 Signal Aspect Permanent Elcctro- Antenna magnet inductor Red energized Yellow energized Double Yellow energized energized Green energized v energized 5th aspect energized energized energized aspects indicate the safe maximum speed at which the train should be driven.  
 Depending upon which combination of energized/not energized states of the three elements exists, the detect-&#39; ing equipment activates an appropriate warning in the drivers cab which in certain cases must be acknowledged by the driver.  
 For use with other signalling systems, the equipment could be used to give suitable indication such as numerical indication of speed permitted. I  
  For a green aspect, the train equipment detects first the permanent magnet 10 and then the energized-electro inductor 11, the antenna 13 being unenergized. For a double yellow aspect the train equipment detects first the permanent magnet-10, then the antenna 13 which&#39; is energized with an HR, carrier, the electro inductor 11 being unenergized.  
  For yellow and red aspectsneither the electro tor 11 or the antenna 13 is energized.  
  A detector 14 carried by the train detects the presence of the permanent magnet 10 and actuates a logic unit 15 which operates a display, alarm and acknowl edgment unit. The detection of the presence of a permanent magnet sets the logic unit 15 into a state such that if neither an energized electro-inductor 11 nor an energized antenna 13 are detected within a certain time interval, an audible warning sounds on a horn 1 6. The driver may acknowledge the warning by pressing an acknowledgment button 17 which is illuminated by the unit 15, which will cause the horn 16 to cease; if the driver doesv not do this, the train brakes will be automatically applied.  
  If an energized electro-inductor 11 is also detected by the detector l4within the stated time interval, indicatingagreen signal aspect, a further signal is sent to the logic unit 15 which causes a bell 18 to ring briefly and the logic unit 15 is reset. No acknowledgment action by the driver is necessary.  
  If a receiving aerial 19 carried by the train detects a carrier signal from the energized track loop antenna 13 within the stated time interval, in place of a detection induc- 3 bythe detector 14 of an energized electro-inductor, this signal is fed to a selector relay 20 via a band-pass filter 2i, amplifier 22 ahd detector 23, causing relay contacts 24 to switch over and connect an acknowledgrnentbutton 25 to the logic unit lSQThe logic unit 5 causes&#39;a&#39;n audible warning to sound on the horn 16 and the driver must acknowledge this warning of a double yellow aspect by means of the press button 25 which is illuminated by unit 15, otherwise the brakes will be automatically applied. The relay &#39;is reset by a signalfrom the logic unit 15 when the detector 14 detects the presence of the next permanent magnet 10, causing the logic unit 15 to again be connected to the acknowledgment button 17.  
 &#39; l &#39;or&#39;a-train fitted to&#39;receive the 5th aspect, the display unit is more complex than that shown in FIG. 2, and ineludes a facility for the acknowledgment and display of agreen aspect. The logic unit 15 would require enhancing also, so that a second time interval is available, if bothithe permanent magnet 10 and electro inductor 11 have been detected, within which the presence ofa carrier signalfr om the loop antenna 13 may be detected in order that the train equipment might differentiate betweenthe green and 5th aspect conditions.  
  .ElGSg and 4 show alternative feed circuits for the electro-inductor l1 and the antenna 13. In FIG. 3, the electro-inductor 11 is fed by a cable 26 directly from a rectifiedac. supply, a relay switch 27 being included in,-th e, cable 26 which is closed wherever the inductor ll is. to bev energized. Similarly the antenna 13 is fed with a signal from an oscillator 28, for example a signal of 68 KHz frequency, by way of a cable 29. A relay sw;i,tch ,30,,is includedin the cable 29.  
  1&#39;ll&#39; -E,lG;&#39;4,&#39; anarrangement is shown in which a common cable 31 is employed in place of the two separate cables 26 and 29 shown in FIG. 3. In this arrangement, a capacitor 32 connected in parallel with the coil of the elecitro-indu&#39;ctor -1l; ensures that the high frequency signa&#39;l&#39;from the oscillator 28 does not affect the electroinductor-r&#39;similarly a capacitor 33 in series with the an ten&#39;na&#39; .13, prevents the dc. signal from --the electroinductor supply from passing through the antennar13.  
  FIGS illustrates an alternative arrangement in which a carrier signal gen&#39;erator34 consisting of a power supplyirni-t &#39;35 on oscillator 36 and a power amplifier 37 is&#39; p os&#39;iti oned closely adjacent to the antenna 13, being coupled to it via a matching transformer 38. In this way the use of&#39;lon&#39;g lengths of high quality feed cablebetween the carrier generator 34 and the antenna 13 is a&#39;v&#39;oidedfflhe a;c. supply to the carrier generator 34 passes along a feed cable 39 and is switched by&#39;means of&#39;a relay contact 40, whi&#39;chcon&#39;tact is arranged to be closedwh&#39;en&#34; the signal aspect &#39;is&#39; double yellow, and when it isdesiredftoexhibitthe 5th aspect.&#34; v  
  Similarly relay contacts 27 in the supply leads 26 for the electro inductor l1 closeto &#34;energize the electro l inductor 11 when the signal aspect is green and when it is desired to exhibit the 5th aspect.  
  Asian alternative to using a loop antenna 13 in the arrange ent s hown in FIG. 5, a ferrite rod antenna of known&#39;eonstruction can be employed to transmitth&#39;e carrier signal to the pick-up coil 19.  
  As a further alternative, a frame antenna, which may be of prin td circuit constructiom could be used. This frame antenna could, be incor&#39;poratedinto&#39; the structure of the housing forthe generatorunit 34.  
 The 5th aspect referred to in the Specification in which both the electro-inductor 11 and the antenna 13 are energized, is intended for use with very high speed trains in order to extend the signalling range. Very high speed trains clearly require a considerably longer distance in&#39;which to brake from maximum speed&#39;to rest than do trains whose maximum speed is considerably less. The 5th signal aspect is intended for use in such situations, to indicate to the driver of a very highspeed train that&#39;it is safefor&#39;the train to travel at its maximum speed since the track ahead is clear for at least the necessarymaximum braking distance.  
 lclaim:  
 1. A railway signalling system comprising:  
 a permanent magnet positioned on a railway track at a-point preceding a multi-aspect signal,  
 an electro-induc&#39;tor and&#39;an antenna&#39;means positioned in sequence directly following said magnet in the intended direction of movement of a train along said track,  
 means for energising said electro-inductor with a die.  
  supply and said antenna means with a high frequency signal in dependence upon the present aspect of the signal, detector means carried by a railway vehicle for detecting the fields produced by said magnet, by said electro-inductor and by said antenna means to provide a warning to adriver of the train corresponding to the present aspect of saidsignal, said detector means including a first and second in- .ductive pick-upcoil, said first pickup coil being adapted to detect the static magnetic field produced by the permanent magnetand by said electro-inductor, and said second pick-up coil being adapted to detect the high frequency alternating V magnetic field produced by said antenna, I said first coil being connected by way of a logic unit to a first and second alarm means, first acknowledgement means for said second alarm means, saidsecond coil being connected to a relay coil whose contacts connect said logic unit to a second alternative acknowledgment means for said second alarm means, said logic unit in response to detection by said first pick-up coil of a signal from said permanent magnet along actuating said second alarm means to thereby require the train driver to operate said firstacknowledgment means to prevent automatic application of the train brakes, said logic unit in response to detection by said first pickup coil of a signal from said permanent magnet followed subsequently by detection by said second pick-up coil of a signal from said antenna means controlling said relay unit to operate and thereby controlsaid logic unit to actuate said second alarm means to thereby require the driver to operate the secondacknowledgment means to prevent automaticapplic ation of the train brakes and detection by said first pick-up coil of a signal from said per- I manent magnet followed subsequently by a signal from said electro-in&#39;du&#39;ctor controlling said logic unit-to actuate said first alarmmeans, which requires no acknowledgment action by the driver.  
 2&#34;. A signalling system as-claimed in claim wherein a single feed cable .is used to connect said electroinductoritosaid d.c. supp&#39;ly&#39; and&#39;said antenna means to said high frequency signal source, and wherein a first filter is connected to said electro-inductor to block said said antenna means is in the form of a closed loop of one or more turns.  
 5. A signalling system as claimed in claim 1 wherein 5 said antenna means is in the form of a ferrite rod.  
  UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,876, 171 DATED April 8, 1975 INVENTOR(S) Michael S. Birkin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:  
 Foreign Applicatiofi Priority Data March 17, 1972 Great Britain. 12642/72 Sigrted and sealed this 10th day of June 1975.  
 (SEAL) Attest: v  
  C. MARSHALL DANN RUTH C. MASON Commissioner of Patents and Trademarks Attesting Officer