US2248321A - Railway traffic controlling apparatus - Google Patents

Description

July 8, 1941. E. M. ALLEN RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Sept. 27. 1939 2 SheetsSheet 1 l VENTOR Allen Earl HIS ATTORNEY 2 Sheets-Sheet 2 M. ALLEN- Filed Sept. 27, 1939 RAILWAY TRAFFIC CONTROLLING APPARATUS ENG Nkm

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OGOQ July 8, 1941.

HIS ATTORNEY Patented July 8, 1941 RAILWAY TRAFFIC CONTROLLING APPARATUS Earl M. Allen, Swissvale, PaQ, assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 27, 1939, Serial No. 296,835

16 Claims.

My invention relates to railway traffic controlling apparatus, and more particularly to apparatus for use in railway ,blocl; signaling systems for governing trafiic movements in both directions over stretches of single track of the type in which the direction of trafiic movements is governed from a centralofiice by means of a suitable communication system, and in which the railway signals are controlled in accordance with trackway conditions without the use of line wires, as in the system of my Patent No. 2,053,888, issued September 8, 1936.

One object of the present invention resides in the provision, in a system of this character, of improved arrangements for controlling the signals by means of coded or periodically interrupted current supplied to the track rails. Another object resides in the provision of improved means for the directional control of the signals. Other objects and features of my invention will be'pointed out as the description proceeds.

I shall first describe one form of apparatus embodying my invention, and shall then point out the novel features'thereof in claims.

Referring to the accompanying drawings, Figs. 1A and 1B taken together, with Fig. 1A at the left, constitute a diagrammatic representation of my invention as applied to a stretch of single track railway extending between the passing tracks at the ends of the stretch. The reference characters I and la designate the track rails, which are divided in the usual manner by insulated jointsZ to form trackfsections. Each track section is identified by the reference character T with distinguishing prefix.

The signals for governing traffic movements through the'single track stretch embodying the apparatus of my invention, in the direction from left to right, include the headblock signal 6 and theintermediate signals 8- and 12'; and those for governing traffic movements in the opposite direction include the headblock signal l3 and the intermediate signal I. The track sections 8-9T and Iii-HT taken together constitute a cutsection as shown, but the apparatus at the junction of these sections may be arranged like that at the junction of sections 6-1T and 8-9T for controlling two additional signals 9 and I0, and, similarly, the additional signal I! may be provided, if required; a variety of arrangements being shown herein in order to more clearly illustrate my invention. The sections of track to the left of signal 6 and to the right of signal [3 in practice would also preferably be equipped with the apparatus of my invention, but for simplicity these sections are shown as provided with ordinary track circuits comprising the track batteries 3 and the track relays 3TB. and ITR, respectively, and only the signals L4 and R2 and their control relays L lI-IR and RZHR are shown.

Each section of the single track stretch has two track circuits, one for each direction, both of which include the track rails of the section. For example, when the direction for train movements from right to left is established the track circuit for section (i-lT includes battery 3 adjacent signal 6 and the track relay 'ITR adjacent signal 1; when the direction from left to right is established the track circuit for this section includes battery 3 adjacent signal I and the track relay 6TB adjacent signal 6.

The current delivered to the track sections of the singletrack stretch by the batteries 3 is periodically interrupted, or coded, at different rates, to effect the desired control of the signals. This is accomplished by the provision, at each wayside signal location, of two code transmitters ISOCT and 'IECT. These may be of any suitable type, such, for example, as that shown in the Bossart Patent No. 1,858,876, issued May 1'7, 1932, for Coding apparatus. It is to be understood that the contacts of these code transmitters close 180 times per minute and '75 times per minute, respectively, in such a manner as to produce interrupted current having substantially equal on and off periods in the track circuits. The track relays'lifIR, 'i'I'R and other similar relays for the single track stretch are of the code following type such as are shown in the Blosser Patent No. 2,014,015, issued September 10, 1935, for Railway trafiic controlling apparatus. Each code following track relay at a signal location controls two slow acting relays such as the relays 'IHR and 'lI-IZ, similar to relays A and H of the Blosser patent, both of which, as explained in the patent, remain picked up as long as the track relay is being operated by or code. For example, relay 'IHZ releases if relay 'ITR is steadily energized, and relays 'IHR and lHZ release successively if relay 'lTRi is steadily deenergized.

Each code following track relay at a signal location also controls a relay DR through the medium of a transformer and decoding unit I8BDU so that relay DR responds to the 180 code only. The relays DR correspond to relay F of the Blosser patent, and the decoding units IBODU include resonant circuit elements and rectifiers as explained in detail in that patent.

The signals as shown are of the color light type, and it will be readily apparent that the relays HZ and DR function in such a manner that when 180 code is supplied to the track rails at one end of a section, both relays HZ and DR will be energized to light the lamp G for the signal governing traffic movements into that section from the opposite end to cause the signal to indicate proceed; that when 75 code is supplied to the track rails relay HZ will be energized and relay DR deenergized, and that then the lamp Y will be lighted to cause the signal to indicate caution, and finally, if the track relay is steadily energized or cleenergized, both relays l-lZ and DR will release to light the lamp R to cause the signal to indicate stop.

The apparatus at each intermediate signal location also includes a directional stick relay SR for purposes hereinafter pointed out.

The relays 4FR and ZFR adjacent the ends of the stretch are manually controlled traffic relays for governing the direction of trafic movements through the stretch. The communication system by means of which the operator at the control oflice may govern these relays may be of any suitable type, but preferably this is of the selective or code type, in which communication is established intermittently by means of impulse codes transmitted over a single pair of line wires to the various field stations, as shown, for example, in the British Patent No. 415,787, which corresponds to the United. States application Serial No. 660,785, filed March 23, 1932, for

emote control systems, by Lloyd V. Lewis. Direct wire control may also be used, and as illustrative of either form, dotted line connections are shown extending from a traffic lever F at the central ofiloe to relays QFR and 2P3.

For an understanding of the present invention it is deemed sufficient to point out that the traffic direction from right to left is established by movinglever F to the left to energize relay QFR, and that the trafficdirection from left to right is established by moving lever F to the right to energize relay ZFR. Each relay FR is provided with a slow release stick repeater relay FS for a purpose which will be explained hereinafter. It is to be undertsood that the communication system may also be used to manually govthe leaving signals L4 and R2 and for controlling the track switches in advance of these signals, and further, that itmay be used to prevent the manual reversal of trafiic in, the single track stretch except under proper conditions, as illustrated, for example, in my Patent No. 2,102,- 988, issued December 21, 1937, but since these features form no part of the present invention they have not been shown herein.

I shall now describe the operation of the apparatus of my invention in detail, first assuming that all relays except the code transmitters are dcenergized, and that the operator moves lever F to the left, thereby energizing relay 4FR to, set up the traffic direction from right to left. When relay dFR picks up, the code repeating relay L ICP is intermittently energized by 75 code over a circult which may be traced from one terminal B of a suitable source of current, contact M of the code transmitter ISCT adjacent signal L4, back contact l5 of the signal relay L lI-IR, front contact E6 of relay 4FR, the winding of relay L 4CP to the other terminal C of the source. Contact I I of relay LQCP is therefore operated repeatedly to deliver the 75 code from battery 3 to the track rails of section B-IT, to intermittently energize the code following track relay ITR. This track relay first energizes relay l'I-IR and then energizes relay 'IHZ over circuits which, as is apparent from the drawings, include back contacts l8 and !9 of relays BSR and BHZ associated with the opposing signal 8, and the front and back contacts 20, respectively, of relay 'lTR. Each time relay ITR picks up it energizes relay 'ISR over a branch circuit including front contacts 2! and 22 of relays 'ITR and II-IZ, and each time relay (TR releases it holds relay 'ISR energized over the stick circuit including front contact 23 of relay 'ISR, and back contact 2| of relay ITR. Relay ISR is slightly slow acting so as to bridge the relative short transfer time of the front and back contacts 2i, and therefore remains pickedup as long as relay ITR is operated by code, and also when section G-TT is occupied by a train so as to hold relay 1TB in its deenergi'zed position. Relay ISR, by closing its front contact 24, prevents the energization of track relay BTR, and by opening its back contact 25 disconnects terminal B from the circuits for relays BHR, 8HZ and BSR.

Vthen relays IHZ and. 'ISR pick up, a circuit is closed intermittently from terminal B over contact 26 of the code transmitter l 800T at the location of signal 1, front contacts 21, 28 and 29 of relays ISR, IHZ and II-IR through the winding of a code repeater relay 1GP to terminal C. Relay TOP responds accordingly and delivers 180 code over its front contact 3|] to the track rails of secto relay 'lHR and therefore remains picked up "and at contact 32 shunts the track relay IDTR.

Relay 9TH, by the operation of its contact 33 delivers 180 code to the track rails of the next section 19-4 IT to operate track relay HTR. Re-

lay HTR functions in the same manner as relay 9TB, that is, by the operation of contact 34 it energizes a slow release relay IITP, shunting relay IZTR. at contact 35, and by the operation of contact 35 relay IITR repeats the 180 code to the track rails of the following section l2-l3T to operate track relay I3TR.

Relay I3TR, by the operation of its contact 31, effects the energization of relays I3HR and I3HZ, and since relay I3TR, is operated by 180 code, relay ISDR, also becomes energized, causing signal l3 to indicate proceed.

The apparatus now occupies the position shown in the drawings.

I shall next assume that the operator clears signal L4 by means of the communication system, so that rela L4HR becomes energized to deliver 180 code to relay L4CP over its front contact [5. Relay 'ITR therefore operates in accordance with 180 code instead of 75 code and relay IDR 1 consequently becomes energized, causing signal 1 to indicate proceed.

I shall next assume that with signals l3, 1 and L4 at clear, a train moves from right to left through the stretch. The track relays I3TR,

. l ITR, and 9TB. will be successively shunted and will remain deenergized in the rear of the train, causing signal 13 to indicate stop. When the train enters section 641, relay lTR becomes steadilydeenergized and a circuit is closed over contact 38 of the code transmitter 15CT at the location of signal 1, front contact 39 of relay ISR- and back contact 29 of relay 'IHR to operate relay EC? in accordance with the 75 code and when the train vacates section 8-9'1 this code is supplied to the track rails of the sections in the rear of the train to cause signal I3 to indicate caution. Assuming that signal L4 returns to the stop position when the train enters section 3T, it will be seen that the release of relay L lHR at this time reestablishes the 75 code circuit alreadydescribed for relay LGCP, and when the train vacates section 6-1T this code is again supplied to the track rails of that section to cause signal I to indicate caution and signal I3 will again indicate clear, as shown in the drawings.

I shall next assume that the operator cancels the established traffic direction by moving lever F to the. center position to release relay 4FR as soon as he has been informed by means of the communication system that signal L4 has returned to its stop position.

Relay AFS, which picked up over contact 40 when relay 4FR first became energized, is now held'energized over a stick circuit including its own front contact 4 I and back contact 42 of track relay 3TB. It is to be understood that relay 3TR is now deenergized because the train which has just put signal L4 to stop still occupies section 3T. Relay LACP ,now becomes steadily energized over back contact 16 of relay 4FR and front contact 43 of relay 4FS, and when section 6-11 is vacated, battery 3 is connected steadily to the rails of section B-lT over front contact [1, so that relay 'ITR is steadily energized from the time section 6-71 is vacated until after section 3T is vacated, which time is suflicient to effect the successive release of relays 'lHZ and ISR. The release of relay 'lI-IZ also completes a circuit from terminal B over its back contact 28 to effect the steady energization of relay TCP and of the next track relay HTR in the rear of signal 1.

, When the layout includes signal ll, it is to be understood that a stick relay IISR, not shown, but which is similar to 'ISR, is provided at the location of signal ll. Relay HSR would be released. in response to the steady energizationof the track relay I iTR under this condition, and in a similar manner the stick relay for any other intermediate signal in the rear of signal H for governing traffic movements from right to left is released.

When the train leaves section 3T, relay'3TR becomes reenergized and releases relay AFS, whereupon relays LACP' and HR release. Relay 'lHZ picks up, releasing relay 1UP, and then relays ll-IR and 'iI-IZ release successively, and, finally, relays I3TR, I3HR and I3HZ release. The circuit for the traflic relay ZFR for the opposite direction includes back contacts 44 and '45 of relays l3I-IZ and IBHR, It will be seen, therefore, that the operator isnot able to pick up relay ZFR to reverse the trafiic direction until all the track circuits for the previously established direction have been deenergized.

It may happen that the operator releases relay lF-R when section ST is not occupied, and in order to insure the release of each of the energized relays SR under this condition, relay IFS is arranged to have a relatively long release period which is considerably in excess of that provided for the relays HZ. It will be seen, therefore, that in any case the stick relays SR become energized when the trafiic direction is first established and that these relays maintain the es,- tablished traffic direction irrespective of trafiic conditions, and that this direction must be cancelled manually by applying steady current to the track rails at the left-hand end of the stretch before the opposite direction of trafiic can be established.

I shall next assume that the operator energizes relay ZFR to set up the traffic direction from left toright. The apparatus for the two directions is similar and consequently a detailed description appears unnecessary. It has already been explained that relay ZFR may be energized when relays I3HZ and ISHR are released. Relay 2FR when energized completes circuits for sup.- plying '75 code to the right-hand end of section I2-i3T to which relay IZTR responds, causing relay I'ZCP to deliver code to section Iii-I iT to which relay iOTR responds. Relay IB'IR delivers this code to section 8-91 to operate relay 8TR, and .the relays controlled by relay BTR cause 180 code to be delivered to section B-IT to which relay BTR responds. Consequently, signals 6 and 8 indicate clear and signal l2 indicates caution, and when signal R2 is cleared the indication of signal i2 changes from caution to clear. The stick relays BSR and IZSR are now energized over back contacts of relays 'iSR and HT? respectively to provide the proper control for the signals in the rear of a train moving from left to right through the stretch, and it will be seen that this direction of traffic is maintained until it is cancelled manually by applying steady current to the track rails at the right-hand end of the stretch, in the manner already explained in connection with the operation of the apparatus for governing trafiic movements in the opposite direction.

In systems employing direct current coded track circuits of the type herein shown and described, it has been found desirable to shunt the track rails during-the intervals when the battery is disconnected in order to more quickly discharge any energy stored in the track circuit so as to'eliminate the code distortion which otherwise might result. One manner in which this result may be accomplished for single direction running/only is shown in Nicholson Patent No. 2,127,134, issued August 16, 1938, for Railway track circuit apparatus. This method is not applicable to reversible track circuits as employed herein, but I have devised several means by which the desired result may be obtained and which are selective as-to direction in accordance with the requirements of my invention. Thus, at outsections, a slow acting relay such as the relay STP controlled by a front contact of the corresponding track relay 9TR is provided, and relay 9T? has a contact 32 for shunting the track circuit. Relay QTP is made sufficiently slow in releasing so that it holds contact 32 closed during the off? periods of the code delivered by relay BTR. The additional relay TP required at a location where a suitable relay is provided for some other purpose, for example, at intermediate signal locations, a front contact of the relay HR, which is controlled in the same manner as relayHTP, may be used to shunt the adjoining track circuit. As an alternative, 2. front contact of the directional stick relay SR may be used, as illustrated by contact 24 of relay 'ISR which shunts the track circuit during the oif periods of the code delivered by relay 'ICP. That is, contact 24 may be either a contact of relay 1SR,J as shown, or may be a contact of the slow release relay ll-1R, as explained above. At the head-block locations a front contact of the traffic relay may be used, as illustrated by contact 46 of relay AFR which shunts the track circuit during the off periods of the code delivered by relay L4CP.

-Alth0.ugh my,, invention as hereinbefore described relatesprimarily to the operation of Wayside signals, it is to be understood that cab signals may also be used, with or without intermediate wayside signals, merely by superimposing coded alternating currents upon the direct current track circuits in the manner shown in the hereinbefore mentioned B-losser patent. It is clear that the operation of the direction selecting apparatus of my invention as hereinbefore described is such that coded track circuit energy may be rendered available at that end of each track section occupied by a train which is in advance of the train, and that my apparatus is consequently suitable for the control of cab signals of the usual continuous inductive type and that when so used it permits trafiic movements in either direction as desired.

. Although I have herein shown and described but one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention Having thus described my invention, what I claim is:

1. In combination, a stretch of single track railway divided into track sections, a track relay at each end of each section, signals at the ends of the stretch for governing trafiic movements in opposite directions into said stretch, two track circuits for each section each including the same track rails but arranged in opposite directions to control different track relays, direction selecting means selectively controlled from a central oifice for supplying periodically interrupted current to the track rails at one end of the stretch or the other to energize one track circuit for that section which is at the corresponding end of the stretch, means controlled wholly over the track rails comprising the track relays at the junctions of adjoining sections for supplying periodically interrupted current to the track rails for successively energizing the corresponding track circuit for each remaining section of the stretch in turn, and means including the track relay at the other end of the stretch and requiring the energization of the track circuit for one direction for each section by periodically interrupted current to clear the signal for the corresponding direction.

2. In combination, a stretch of single track railway divided into track sections, signals at the ends of the stretch for governing trafilc movements in opposite directions into said stretch, direction selecting means manually controlled from a central office for supplying periodically interrupted current to the track rails at one end of the stretch or the other, a track relay at each end of each section responsive to periodically interrupted current supplied to the track rails at the opposite end of such section, means controlled by each track relay located at the junction of two sections for supplying periodically interrupted current to the track rails at the adjacent end of the adjoining section, and means at each end of the stretch selectively responsive to the periodic operation of the adjacent track relay for clearing the signal at the same end of the stretch.

3. In combination, a stretch of single track railway divided into track sections, signals at the ends of said sections for governing traflic move ments through said stretch in opposite directions, direction selecting means manually controlled from a central ofiice for supplying periodically interrupted current tothe track rails at one end of the. stretch or the other, a track relay at each end of each section responsive to periodically interrupted current supplied to the track rails at the opposite end of such section, means controlled by each track relay located at the junction of two sections for supplying periodically interrupted current to the track rails at the adjacent end'of the adjoining section, means for governing therate of interruption of said currents in accoradnce with trafific conditions, and means controlled by eachctrack relay for governing the indications of the adjacent signal according to the rate of interruption of the current supplied to such relay.

4. In combination, a stretch of single track railway divided into track sections, signals at the ends of said track sections for governing trafiic movements through the stretch in both directions, track relays at the ends of the track sections, a track circuit for each'direction for each track section,each including the track rails of the section and a different track relay, direction selecting means manually controlled from a central office for supplying periodically interrupted current to the track rails at one end of the stretch or the other, means controlled wholly over the track'rails comprising the track relays at the junctions of adjoining sections for supplying periodically interrupted current to the track rails to successively energize the track circuit for the corresponding direction for each remaining track section of the stretch in turn, means controlled by trafiic conditions for controlling the rate of interruption of the currents supplied to said track circuits, and means controlled by each track relay at the end of the stretch for causing the adacent signal to indicate proceed or caution in accordance with the rate of interruption of the current supplied to that track circuit for the corresponding direction which is directly in advance of such signal provided such track circuit is not occupied.

5. In combination, a stretch of single track railway divided into track sections, signals at the ends of the stretch for governing traflic movements in opposite directions into said stretch, track relays at the ends of the track sections, two track circuits for each section each including the same track rails but arranged in opposite directions to include different track relays, a manually controlled trafiic relay at each end of the stretch, means controlled by each traflic relay when energized for supplying periodically interrupted current to the track rails at the adjacent end of the stretch to energize one track circuit for that section which is at that end of the stretch, means controlled wholly over the track rails comprising the track relays at the junctions of adjoining sections for supplying periodically interrupted current to the track rails for successively energizing the corresponding track circuit for each remaining section of the stretch in turn, and means including the track relay at the other end of the stretch and requiring-the energization of the track circuit for one direction for each section by periodically interrupted current to clear the signal for the corresponding direction.

6. In combination, a stretch of single track railway divided into track sections, a track relay at each end of each track section controlled over the track rails of the section, signals at the ends of the stretch for governing trafiic movements into the stretch in opposite directions, a traflic relay at each end of the stretch manually controlled from a central ofiice, means controlled by each trafiic relay when energized for supplying periodically interrupted current to the track rails at the adjacent end of the first track section at that end of the stretch, means controlled by each track relay at the junction of two sections dependent solely upon the operation of that relay by'current in the track rails of the correspond- 7. In combination, a stretch of single track railway divided into track sections, a track relay at each end of each track section controlled over the track rails of the section, signals at the ends of the stretch for. governing trafiic movements into the stretch in opposite directions, a trafic ,relay at each end of the stretch manually contrack relay at the junction of two sections dependent solely upon the operation of that relay by current in the track rails of the corresponding section for supplying periodically interrupted current to the adjacent end of the next succeeding track section in said stretch, means responsive only to periodically interrupted current and controlled by the track relay at the end of the stretch remote from said energized traflic relay for clearing the signal at that end of the stretch, and means associated with each signal for preventing the energization of the traffic relay at the same end of the stretch unless such signal is at stop.

8. In combination, a stretch of single track railway divided into track sections, signals at the ends ofsaid sections for governing traffic movements in both directions, a track relay at each end; of each track section controlled over the track rails of the section, a manually controlled traflic relay at each end of the stretch, means controlled by each trafiic relay for supplying pevriodically interrupted current to the track rails at theadjacent end of the stretch to energize the track'relay at the remote end of the first track section of the stretch, means controlled by each track relay at the junction of two sections dependent solely upon the operation of that relay by current in the track rails of the corresponding section for supplying periodically interrupted current to the adjacent end of the next succeeding track section in said stretch, means controlled by traffic conditions for controlling the rate of interruption of the current supplied to said track sections, and means selectively responsive to periodically interrupted current for causing each signal to indicate proceed or caution in accordance with the rate of interruption of the current supplied to that track section which is directly in advance of that signal provided such track section is not occupied.

9. In combination, a stretch of single track railway divided into track sections, two track circuits for each section having track relays at opposite ends of the section, signals at the ends of the sections for governing trailic movements in opposite directions, a manually controlled traffic relay at each end of the stretch; means controlled by each traffic relay when energized for supplying periodically interrupted current to the track rails at the adjacent end of the first track section at that end of the stretch for intermittently energizing the track relay at the remote end of said section, means responsive to the intermittent energization of, each track relay located at the end of a section adjoining another section to supply periodically interrupted current to the track rails at the adjacent end of said other section, and means selectively responsive to the intermittent energization of each track relay for controlling the adjacent signal to permit a train movement into the corresponding track section provided such section is not occupied. I

10. In combination, a stretch of singletrack railwaydivided into track sections, signals at the ends of saidsections for governing tramc move- ;ments in opposite directions, a manually controlled traflic relay at each end of the stretch,

means controlled by each traffic relay when energized to supply periodically interrupted current to the track rails at that end of the stretch for establishing the direction for traific movements through the stretch, a directional relay for each intermediate signal in the stretch controlled over back contacts of the directional relay for the opposing signal at the same location, means responsive to periodically interrupted current in the track rails of the section in advance of each signal for energizing the directional relay associated with such signal, means for maintaining each such relay energized as long as said traffic relay remains energized irrespective of the condition of said advance section, means controlled by each energized directional relay for supplying periodically interrupted current to the track rails of the next section in the rear for the corresponding direction, and means controlled by periodically interrupted currents in the trackrails for controlling said signals.

11. Incombination, a stretch of single track railway divided into track sections, signals at the ends of said sections for governing trailic movements in both directions, each said signal being arranged to indicate stop except when the track sectioninadvance is supplied with periodically interrupted current,.a directional relay for each intermediate signal in saidv stretch, a trafiic relay for each direction including one at each end of the stretch, manually controlled means for energizing each traffic relay effective only when the signal at the same end of the stretch is at stop, means' controlled byeach traffic relay when enerdependent upon the occupied or unoccupied condition of said advance section to the track rails of the next section in the rear, and means responsive to periodically interrupted current in the" track rails in advance of a signal for causing such signal to indicate proceed or caution depending upon the rate of interruption of said current.

12. In combination, a stretch of single track railway divided into track sections, a traflic relay at each end of the stretch, means controlled by each trafific relay when energized to supply current of a given character to the track rails for establishing the direction for trafiic movements through the stretch, directional relays for each direction at the junctions of adjoining sections, circuits for each directional relay controlled over back contacts of the other directional relay at the same location, means for energizing each directional relay in response to current transmitted over the track rails in a given direction, means controlled by each energized directional relay for supplying current of said given character to the track rails of the next section in the rear in said given direction, means rendered effective when said traffic relay is released for temporarily supplying current of a different character to the track rails, and means controlled by said current of said different character in the track for releasing each energized directional relay.

13. In combination, a stretch of single track railway divided into track sections, a trafiic relay at each end of the stretch, means controlled by each traflic relay when energized to supply periodically interrupted current to the track rails at the adjacent end of the stretch for establishing the direction for trafiic movements through the stretch, a directional relay for each direction located at the junction of adjacent sections within said stretch, circuits for each directional relay controlled over back contacts of the other directional relay at the same location, a track relay associated with each directional relay responsive to periodically interrupted current received over the track rails, means controlled by said track relays for energizing the directional relays for one direction or the other depending upon which traffic relay is energized, means controlled by each energized directional relay for supplying periodically interrupted current to the rails of the next track section in the rear in a corresponding direction, means for maintaining said directional relays energized irrespective of whether or not said periodically interrupted current is supplied to the track rails and requiring a steady current in the track rails to effect their release, and means operating when the energized traflic relay is released for supplyling current steadily to the track rails for a time sufficient to release said directional relays.

14. In combination, a stretch of single track railway comprising two track sections, a code following track relay for each section connected across the track rails of its section only when the track relay for the other section is deenergized, means for supplying periodically interrupted coded current to the track rails at one end of the stretch or the other to intermittently energize one track relay or the other, a second relay for each section having a front contact arranged to shunt the winding of the track relay for the other section to render such relay nonresponsive to current in the track rails, and means eifective when the track relay for either section is intermittently energized to maintain the second relay for the same section in its energized position.

15. In combination, a stretch of single track railway comprising two track sections, a code repeating relay for each section, a track relay for each section connected across the track rails of its section over back contacts of the code repeating relay for the other section, a source of current connected across the track rails of each section over front contacts of the code repeating relay for the same section, means for supplying periodically interrupted current to the track rails at one end of the stretch or the other to intermittently energize one track relay or the other, means responsive to the intermittent energization of each track relay for intermittently energizing the code repeating relay for the other section, an auxiliary relay for each section which remains picked up as long as the track relay for that section is intermittently energized, and means for shunting the winding of each track relay to prevent its response to current in the track rails when the other track relay is being operated, comprising a front contact of the auxiliary relay for the other section.

16. In combination, a first and a second track section, a track relay for the first section connected across the track rails of the first section, a source of current connected across the track rails of the second section over a contact closed intermittently in response to the intermittent energization of said track relay, means for supplying periodically interrupted current to the track rails of said first section to intermittently energize said track relay, an auxiliary relay which remains picked up as long asthe track relay for said first section is intermittently energized, a track relay for said second section arranged to be connected to the track rails of said second section whenever said source is disconnected from the track rails, and means for shunting the wind. ing of the track relay for said second section to prevent its response to current in the track rails when the track relay for the first section is being operated, comprising a front contact of said auxiliary relay.

' EARL M. ALLEN.

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