US2520858A - Railway traffic controlling apparatus - Google Patents

Description

5 Sheets-Sheet 1 C. B. SHIELDS INVENTOR. Clzaflles B. Shel/3M5: Z

FUND" RAILWAY TRAFFIC CONTROLLING APPARATUS Aug. 29, 1950 Filed May 27, 1946 C. B. SHIELDS RAILWAY TRAFFIC CONTROLLING APPARATUS Aug. 29, 1950 5 Sheets-Sheet 2 Filed May 27, 1946 QTJ Ll ,r J 3 54in w w 8 IUI Q a H swww M INVENTOR.

e rs Ubaples B. Shields:

H15 dTZOHNFY Aug. 29, 1950 c. B. SHIELDS RAILWAY TRAFFIC CONTROLLING APPARATUS 5 Sheets-Sheet 5 Filed May 27, 1946 INVENTOR.

B. Shields.

Aug. 29, 1950 c. B. SHIELDS RAILWAY TRAFFIC CONTROLLING APPARATUS 5 Sheets-Sheet 4 Filed May 27, 1946 g- 1950 c. B. SHIELDS 2,520,858

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed May 27, 1946 5 Sheets-Sheet 5 INVENTOR.

H [S 47 'TORNE 'Y Patented Aug. 29, 1950.

RAILWAY TRAFFIC CONTROLLING APPARATUS Charles B. Shields, Penn Township, Allegheny County, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application May 27, 1946, Serial No. 672,395

12 Claims.

My invention relates to railway trafiic controlling apparatus for governing the movement of traffic over stretches of single track over which traffic moves in two directions. More particularly, my invention relates to an improved absolute permissive block signaling system employing cascade connected reversible track circuits of the continuous code type, for use in a centralized trafiic control system in which the trafiic direction is set up and the head block signals are i is interrupted when the controlling track section cleared by manual control from a central office by means of an intermittently operated communication system, while the intermediate signals, which are controlled solely by the track circuits, are cleared automatically in one direction or the other in accordance with the direction of energization Of the track circuit system.

In an absolute permissive block signaling system, such as is herein disclosed, directional stick relays are provided in connection with the intermediate signals, each of which is normally arranged to become energized when a train passes the associated signal at clear or caution, and when energized prepares a circuit for energizing the next signal in the rear, governing traffic movements in the same direction, to permit that signal to indicate caution as soon as the block section in advance is vacated by a train. I

The principal object of my invention isthe provision of improved means for controlling these directional stick relays by the track relays of a coded track circuit system, so that each directional stick relay becomes energized when the code operation of the associated track relay ceases due to a train entering the corresponding track section in the established direction, but not when the operation of the track relay is discontinued due to an opposing train overrunning a head block signal nor when the track circuit systemis manually deenergized in preparation for reversing the direction of traffic.

A feature of my invention isthe provision of means for terminating the supply of coded track circuit current to the rails of each section having a track relay which controls a directional stick l relay, by a period of steady energization during which a code detector relay governing the signal is released without operating the directional stick relay, whereby the directional stick relay is selece tively energized or not, depending upon whether the track relay remains released when its periodic operation ceases, as is the case when the controlling track section is'occupied, or whether it remains steadily energized for a time, as is the case if the'supplyof coded current to thetrack rails is not occupied.

Other objects and features of my invention will be pointed out as the description proceeds.

I shall 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, 1B, 1C and 1D, placed side by side in the order listed illustrate the track plan and wayside circuits for a typical single track block embodying the apparatus of my invention. The block shown includes three sections, over which opposing traffic movements are governed by the entering head block signals ZRA and 2R3, Fig. 1A, and by the similar signals 4LA and 4LB of Fig. 1D. Figs. 2 and 3 show two forms of cut section apparatus which may be interposed between any two of the drawings illustrating the single track block. It is to be understood that such apparatus is required for any block section the length of which exceeds the permissible length of a single coded track circuit. Fig. .4 shows circuits for the control of an outlying hand throw track switch W, this View being arranged to be interposed between Figs. 13 andlC. Figs. 1A and 1D also show different portions of the circuits for the leaving signals ZLA and ZLB and the similar signals 4RA and lRB. These signals also constitute the entering signals for a typical block comprisingthe main track of the double track stretch including the passing track, the circuits for which may be viewed in their entirety by placing Fig. 1A at the right of Fig. 1D.

Similar reference characters refer to similar parts in each of the views.

To simplify the circuit drawings, only the terminals of the local sources of current for energizing the relays are shown, these being designated by the referenc characters B and C, respectively. Each track switch and railway signal is identified by a number identifying its location, the signal designations also including the sufiix L or R to indicate the corresponding direction of trafiic movements to the left or right, respective ly. Each relay is identified by a characteristic letter or combination of letters, prefixed by the designation of the switch or signal with which it is associated. The track relays TB in each of the views, and also the approach relays AR of Figs. 1B and 1C by which the lamps of the intermediate signals are caused to be lighted upon the ap proach of a train, are code following relays of the biased polar type, such as shown for example in Letters Patent of the United StatesNo. 2,057,605,

issued October 13, 1936 to Herman G. Blosser. The polarity responsive feature is designated by an arrow on the relay winding, and it is to be understood that each such relay is normally biased to its released position and assumes its energized position only when currentflows from the plus terminal of the track battery through-its winding in the direction of the arrow. Relay 6LTR of Fig. 1B, for example, is picked up by current received over the track rails only when the plus terminal of the source TB at the left hand end of the section, shown in Fig. 1A, is connected to the lower track raiLand is noneresponsive to current supplied through its winding to the track rails by the battery 'IB at the righthand end of the section. Relay BRAR, which is connected through a resistor across theterminals of relay GLTR when the contacts of relay BLC T ar closed, responds to the current supplied by the battery TB at the same location, but only when this is increased bythe "presence .of atrain within the approach lighting limits for signal GB. The periodically operatingcontacts of the code following relays are distinguished-from those of other quick acting relays by horizontal dotted lines indicating their closed positions. .The contacts of slow acting relays are identifiedin. the conventional manner by vertical arrows thereon. Itis to be understood that the slow acting relays havingcondensers associatedtherewith have release periods of about five seconds. V

-Ea'ch-of the block signals as shown, is of the well-known searchlight type having a three-posihon-mechanism identified by the reference character-G prefixed by the designation of the corres'ponding signal. It is to be understood that the signal mechanisms, and also the polar. neutral relays 2LI-ID and lRHD are so polarized that they close their left-hand 'contactswhen terminal B is applied to the left-hand terminals of their wind- 2,229,249, issued January 21, 1941, to Lloyd V.

Lewis, for Remote Control Systems, or more'particularly, is a modification thereof described in a publication entitled Centralized Traific I Control system -Time Code Scheme, Manual-No. 506- published by the Union Switch and Signal 'Co.,

Swissvale, Pennsylvania. For'an understanding of my invention, it will suffice to point outthat the remote control system has a field station at the end of each block which is connected with a control ofiice by a line circuit over which codes are transmitted in either direction for selective communication between the office and the different stations, one at 'a time. The control codes transmitted tothe stations serve to operate a group of control relays of the stick polar type, in accordance with the positions of control levers at the ofii'ce. Four such control relays are shown herein at each station, and as shown in Fig. 1A these comprise a trafiic relay for each direction, such as relay ZLFS or ZRFS, whichgovern the direction of traffic movements in the blocks'exinvention relates to wayside tending in opposite directions from the station, by cooperation with similar relays 4RFS and lLFS at the opposite ends of the respectiveblocks, shown in Fig. 1D, and also include two signal control relays, such as the relays ZRHS and ZLHS or lRHS and ALHS, by which the clearing of the correspondingly designated entering signals is made subject to manual control from the ofiice. Each trafiic relay LFS or RFS when in its normal position as shown, with its left-hand contacts closed, designates its location as the em trance end of its block, in which position the trafiic relay enables the adjacent entering head block signal to be cleared under proper conditions, in response to the reversal of the associated signal control relay ZRl-IS or ZLI-IS. Each traflic relaywhen reversed, with its right-hand contacts closed, designates its location as the exit end of the block. In this position the traflic relay supplies energy to the sign'al circuits for the block to enable the "signals which govern traffic movements toward its location to beclear'ed.

The trackway system includes continuous track circuits for all main track. The detector sections at the ends of the block each have a conventional "track circuit "including a track grel'ay', such as relay ITR, which is normally energized bya track battery as shown. The remaining'track circuits of the single track block are of the reversible coded type, connected in cascade when the block includes two or more sections, and provide means for controlling the sig nals for both directions to provide three indications and for also indicating at either end whether or not the block is occupied, without line wires. "Since the block which includes the main track of the double track portion is relatively short, this is moreconveriiently controlled b'y 'th'e provision of a conventional track circuit having a normally energized track relay LETR which controls the signals by means of a twowire reversible line circuit system comprising theline wires 2| and '22,"as shown, this arrangemerit corresponding to that disclosed in an application for Letters Patent of 'the Unitd'Stat'es, Serial bio/539,619, filed June 10, 1945i, by John C. 'Law, for Railway Traflic "Controlling Apparatus, now Patent No. 2,404,303, issued July "16, 1946.

The present invention relates inor'e particularly to the coded track circuit' apparatus, and is ah'impr'ovei'ne'nt upon "that disclosed 'inlan "application for Letters Patentof the United States, Serial No. 596,470Qfi1ed May2'9y1945, by"I-Ienry S. Young, for Railway Traffic Controlling Apparatus. In the system of this Young'application,'the coded track circuitsare normally de energized and are setup by manual control by reversing the traffic relay at theexit end of the block for. the desired direction of traffic movement, and then reversingthe signal control relayifor theentering signal/at the other end of the block. Thissystemis .also so arranged that when a train vacates the block and ani'ndication of that fact has been transmitted. to the oflice, the operated traflic relay is restored automatically to normal, and the wayside circuits thereby restored to their normal deenergized condition. This'mode of operation may be employed in connection with the track circuits of my invention, or they may be left energized until a'reversal of the trafiic direction is required to provide a normally energized system. It is also to be understood that theremote co'ntrolsystem preferably includes means for preventing the op;

eration of the traffic and signal control relays except under the proper traflic conditions, so that a signal cannot be put to stop by the operation of any lever other than its control lever, one arrangement suitable for this purpose being disclosed in the above mentioned Young application.

In the coded track circuit system as disclosed herein, the coded currents are generated by code transmitters of the pendulum type designated l8llCT, IZEJCT and 150T, which when energized operate their contacts periodically at a rate of 180, 120 or 75 times per minute, respectively, to periodically operate the transmitter relay such as relay ZRCT, by which the coded current of the selected frequency is supplied to the track rails.

Each code following track relay, such as relay ZRTR, is provided with a slow release, front contact repeater, such as the relay 2RTF, which remains picked up as long as the track relay is responding to coded current. The code responsive apparatus at the different signal locations is substantially similar and its operation will be understood from a description of that of Fig. 1A, where it will be seen that the closing of front contact a of relay ZRTR. when its code operation begins energizes relay IRTF, and the closing of front contact a. of relay 2RTF prepares a circuit over which a code following repeating relay 2RTP is energized each time the track relay ZRTR releases. The closing of contact b of relay 2RTF energizes the primary winding of a decoding transformer 2DT over contact a. of relay ZRTP, transformer ZDT being thereby supplied with current which alternates in direction at the code rate, inducing current in its lower winding which is rectified by the operation of contact b of relay ZRTP to energize a slow acting code detector relay ZRH, which thus responds selectively to the code operation of relay ZRTR. Transformer ZDT also supplies code frequency currents to resonant decoding units IZDDU and IBBDU, which it is to be understood are of the type disclosed in Letters Patent of the United States No. 1,773,472, issued August 19, 1930, to Paul N. Bossart, for Railway Traffic Controlling Apparatus, whereby the decoding relays 2RD and ZRK are selectively energized when the code operation of relay ZRTR is at the rate of 120 or 180 times per minute, respectively.

The circuits for controlling the track switches IW and 3W which lead to the passing tracks at the ends of the single track block have been omitted in order to simplify the drawings, and it will be understood that when switch IW is locked in its normal position as shown, a normal switch repeating relay INWP is energized, and when switch IW is locked in reverse, a reverse switch repeating relay IRWP is energized, over the contacts N and R respectively, of a circuit controller actuated by switch IW. These relays serve to select the signal mechanism 2RAG or ZRBG for energization, in accordance with the position of the track switch, the selected signal indicating caution when the code detector relay 2RH is energized, or indicating proceed in the event relay 2RD or ZRK is also energized. When either signal mschanism has been energized in the manner hereinafter described, a normally energized indicating relay ZRGP is released by the opening of contacts controlled by the signal mechanism, and relay ZRGP opens a contact in the circuit for an approach locking stick relay ZRAS associated therewith. Relay ZRAS provides the usual time and approach locking required in connection with the'operationof:'signa1s 2RA and ZRB, having a front contact d in the circuit for the transmitter relay 2RTC and a front contact 0 in the circuits for the mechanisms ZLAG and 2LBG for signals ZLA and ZLB governing opposing traffic movements, and a back contact 0 in the circuits for the mechanisms for the associated signals 2RA and'2RB. -Relay ZRAS is released to complete the mechanism circuit to permit the selected signal to be cleared by the provision of a block repeating relay ZRBP which becomes energized in response to the reversal of the signal control relay ZRHS but only if the required traffic direction is established and a route is available.

The circuits for controlling the opposing signals 2LA and 2L3 are generally similar to those for signals ZRA and 2R3 except that they are controlled by the polar neutral relay ZLHD instead of by code responsive relays, and mechanism ZLBG is operable only to its caution position, in View of the fact that movements into the side track are limited to slow speed. I

The operation of the system is generally similar for both directions of traffic movement and the circuits of Fig. 1D, therefore, are similar to those of-Fig. 1A, except that they are oppositely directed. Likewise the apparatus at the two intermediate signal locations of Figs. 13 and 1C is similar, but oppositely directed. In these views, but one set of decoding apparatus is used, this being arranged for either direction of operation depending'upon which of the track relays is operated, and in addition, a pair of directional stick relays, such as the relays 2RS and 2L8, is provided for controlling the energization of the track circuit system as required for the following train movements in either direction.

The mode of operation of the coded track circuit system will now be described under difierent assumed conditions by tracing the circuits in detail, starting with the apparatus in its normal deenergized condition, as shown, and assuming first that the central ofiice operator reverses the trafiic relay ZRFS, Fig. 1A, and also reverses the signal control relay ALI-1S, Fig. 1D, for, a train movement from right to left. Since signal 2LA is at stop, its repeating relay ZLAPC is released, in which case the reversal of relay ZRFS completes circuits from terminal B at its contact a over back contact a of relay ZLAPC to set the code transmitter I5CT into operation, and from terminal B at contact b of relay 3RFS, front contact b of a repeating relay lTP of the detector track relay [TR and front contact I) of an approach locking relay ZRAS to pick up a relay ZRAF, which in turn energizes a slow release repeating relay ERAFP, completing a, branch of the circuit just traced over back contact I) of relay ZLAPC, contacts a of the code transmitter 150T and of relays ERAF and ZRAFP and a connector X through relay ZRTC to terminal C, whereby relay ZRCT is caused to supply current interrupted at the code rate to the track rails, to which the code following track relay ELTR of Fig. 1B responds. In Fig. 1B, relay SLTF is energized over the circuit from terminal B at back contact d'of adirectional stick relay BBB and front contact a of relay GLTR, and prepares a circuit for the code following repeating relay STP over back contact a of relay SLTR, front contact a of relay BLTF and back contact a of relay BRTF through relay GTP to terminal C, so that relay BTP operates at the same rate as relay ZRCT.

stick relay GLS through the winding of trans- 7 The closing of front contact b of relay 'BL'IF supplies current over contact a of relay BTP to the primary winding of the decoding transformer EDT and also sets the associated code transmitter IBDCT into operation, and the periodic operation of relay ETP causes the code detector relay 6H to become energized over contact I) of relay B'I'P. A slow release repeating relay BHP is ener ized over front contact b of relay 6H, and a circuit is closed from terminal B at contact a Of relay 6H over back contact a. of a decodin relay 6D, back contact of relay GRTF, front contact 0 of relay SLTF through mechanism BLG to terminal C at back contact I) of relay 6D. Mechan sm BLG is therefore energized to condition signal 6L to indicate caution, completing a circuit from terminal B at its front contact Y over contact b of the code transmitter IBOCT, front contact e of relay 6H, back contact 12 of a directional mitting relay SRCT over back contact 0 of relay BRS to terminal C at the back contacts of mechanism BRG. Relay BRCT therefore operates to supply current interrupted at the '180 code rate to the track rails of the section in the rear of signal 6L, to which the track relay 8LTR of Fig. lC'responds. In Fig. 10, due to the operation of relay 8LTR. at the 180 code rate, relay BLTF becomes energized to cause relay BLTR to operate relay STP at the same rate and to supply current to the decoding transformer 8DI' whereby the code detector relay BH, its repeater relay BHP, and the decoding relay 8D are energized and mechanism SLG is energized over the front contacts of relays 8H and BDto condition signal 7 8L to indicate proceed. The code transmitter IBIJCT of Fig. 1C is set into operation by current supplied from terminal B at front contact b of relay BLTF over back contact b of relayBRTF and front contact 0 of relay 8D, and operates the transmitter relay BRCT at the 180 code rate over the circuit from terminal B at front contact G of mechanism BLG, contacta of the code transmitter IBOCT, front'contact cl of relay 8).), front contact of relay 8H, back contact bet a direc tlonal stick relay 'BLS through the winding of relay SRCT over backcontact-c of a directional Stick relay BRS to terminal C at the back contacts of mechanism 8RG.

Relay 8RCT therefore supplies current interrupted at the 180 code rate to the track rails of the section in the rear of signal 8L, to which-the track relay iL'IR of Fig. 1D responds. In Fig. 1D, due to the operation of relay 4L'IRat the,

180 code rate, relay 4LTF becomes energized to -mal, relay 4LI-I- energizes the block repeating re lay ALBP over the circuit from terminal B at the normal contact b of relay 4LFS, contact a of relay ALI-I, the normal contact a ofrelay dRHS, contact b of the detector section track relay 3TB,

back contact a of relay 3RWP, front contact a of. relay 3NW?, reverse contact a of relayALI-IS through relay lL BP to terminal C.

Relay 4LBP when energized, releases theapproach locking relay JSLAS by opening its ,normal- 'ly closed stick circuit which extends from terminal B over back contact a, of relay 4LBP, back ontact c of the signal repeating relay ALAPC and front contacts a of relays ALGP and 4LAS through the winding of relay 4LAS to terminal C and relay GLAS upon releasing completes a circuit for mechanism ALAG extending from terminal B at front contact a. of relay 4LBP over front contact 0 of relay ERAS, back contact 0 of a time element relay 3TE'R, back contact 0 of relay ALAS, front contacts 17 of relays 41K and SNWP, through the winding of mechanism QLAG and over back contact b of relay 3RWP, front contact a of relay 4LK and front contact 19 of relay 4LBP to terminal '0. Signal ALA is thereby caused to display its proceed indication and the operation of contact G of mechanism lLAG causes relay ALGP to release and relay QLAPC to become energized.

By placin Fig. 1A at the right of Fig. 1D, it will be seen that if the trafiic relay ARFS and the signal control relay ZLHS are reversed by the operator, current will b supplied to relay ZLHD under proper'trafiic conditions as reflected by relay *S'I'R and relays SEAS and 3'1? or relay v .tRWP, over the contacts a and b of relays GLAPQ and ARFS. the line wires 2! and 22 and the mor mal contacts a and :b of relay ELFS t p r te relay QLHD to reverse if relay 4LAPC is released and .to normal if relay 4LAPC is energized, and that-the closing of the front contact a. of relay ZLHD will complete a circuit from terminal B over contacts a of relays iRl-IS, iNWP and IRVVP, contact b of relay ETE and over thereverse contact a of relay 2LHS to energize the block repeating' relay ZLBRthereby releasing relay ,ZLAS and energizing mechanism ZLAG, so that si nal 2LA in the rear ofsignal LA will indicate caution when signal tlLA indicates stop and will indicate proceed when signal QLA indicates caution or proceed. Y

The caution control circuit for mechanism dLAG, closed when relay ZLI-ID is energized reverse. may be traced from terminal B at front contact a of relay lLBP over front contact e of relay ERAS, back contacts 0 of relays lTER, ZLAS and IRWP, front contact 0 of relay I'NWPpreverse contact c and front contactb of relay ZLHD,

- the winding of relay 2LAG, reverse contact (1 of relay ELI-ID toterininal C at contact b of relay ZLBP; The proceed control circuit for mechanism QLAGis similar, except that it includes the normal or left-hand contacts d and c of relay extended by energizing relay ZLAPC only' when signal ZLA indicates proceed. 'Relay ZLAPC when energized causes the transmitter relay ZERCT to operate at the codegrate instead of at the 75 code rate for the control of relay fiLTR of Fig. 1B, and it follows that when signal ZLA indicates proceed relay 6D will be energized along with relay 61-1 to reverse the polarity of the current supplied to mechanism ELG so that signal GL will also indicate proceed.

The movement of a train through the sin le track block will now be traced, assuming that signals ZLA, tL, 8L and lLA have been conditioned to indicate proceed .as above described.

Signal ALA is put to stop by the release .of relays 3TB and-dhBP whenthe train enters the detector section 3T, and it is to be understood that the signal control relay ALI-IS is restored automatically to normal and an indication of the occupancy of section 31' is transmitted to the con aczasss 9 trol ofiice as described in the manual hereinbefore referred to. Relay 4LGP becomes energized, the closing of its contact 0. allowing relay iLAS to pick up over back contact of the track relay 3TR to reestablish its stick circuit.

When the train enters the first coded track circuit of the block, the operation of relay fiLTR ceases, and relays iLTF, liLH and iKrelease. Due to the shunting effect of the wheels and axles of the train, the current supplied to the rails by relay 8RCT increases as the train approaches signal 8L until the series connected approach relay fiLAR begins to respond, thereby energizin the slow release repeating relay SLAP, which by closing its contact a completes a circuit for the lamp of signal 81. to cause this signal to display its proceed indication. The closing of contact b of relay SLAP decreases the value of resistance in series with relay BLAH and thereby stabilizes its operation to prevent the flickering of the signal lamp which might otherwise occur when relay SLAR first starts to operate, in the event the current supplied at that time is insuflicient for reliable operation.

As the train passes signal 8L, the code operation of relay 8LTR ceases with the relay in its released position, deenergizing relay 8LTF, but relay BTP is held steadily energized for a period of several seconds corresponding to the release period of relay SLTF, during which relays 8H and 8]) release. Relay 8H deenergizes relay BHP, and for the release period of relay 8H? a circuit for the directional stick relay 8L8 is completed from terminal B over front contacts 41 of relays sLTF and BTP, front contact I: of relay BI-IP, back contact d of relay 8H, the winding of relay 8L8, back contact 0 of relay 8R8 to terminal C at the back contacts of mechanism 8RG. Relay BLS picks up, completing a stick circuit including its own front contact a and back contact (1 of relay 8H over which relay 8LS is held picked up until relay 81-1 is again energized, and by closing its front contact d, relay BLS sets the code transmitter 150T into operation. The release of relay 8H also deenergizes mechanism 8LG, causing signal 8L to indicate stop, and then relay 8LTF releases to discontinue the operation of the code transmitter ISGCT. Relay BRCT continues to operate, but at the 75 code rate, being now energized over front contact b of relay BLS and contact a of the code transmitter 150T.

When the train vacates the section in the rear of signal 8L, relay BLAR ceases to operate, and after several seconds relay BLAP releases to extinguish the lamp for signal 8L. Relay 4LTR responds to the '75 code supplied to the track rails, energizing relays 4LTF and 4LH, so that, if relay 4LHS has been reversed again by the operator to enable a following train to enter the stretch, relay 4LBP picks up and mechanism 4LAG will be energized over the back contacts of relays ALD and 411K to cause signal 4LA to indicate caution.

As the train passes signal 6L, similar operations occur, signal 6L is restored to stop and relay BLS becomes energized, and 75 code is supplied by relay BRCT to the rails of the section in the rear, and when the train vacates this section, relay BLTR responds to the '75 code to energize relays BLTF' and 8H. Relay 8LS is released by relay 8H, and relay 8LTF completes a circuit from terminal B at its front contact b over back contact b of relay SRTF and back contact c of relay 8D to set the code transmitter IZOCT into operation, so that relay 8RCT operated, at the code rate, over the branch of its circuit which includes contact a of the code transmitter IZUCT and back contact d of relay 8D. Accordingly, in Fig. 1D, relay 4LD becomes energized along with relay 4H, so that if mechanism 4LAG is energized, the polarity of the current supplied thereto is reversed to change its indication from caution to proceed:

As the train passes signal 2LA, relays ITR, ITP and 2LBP release, restoring signal 2LA to stop. The opening of contact 17 of relay ITP releases relays ZRAF and ZRAFP and stops the code operation of relay ZRCT so that relay BLTR remains released after the train vacates the section in the rear of signal 2LA. Relay ZLAPC releases, setting the associated code transmitter 15CT into operation in place of transmitter ISOCT. When the train vacates section IT, relays ITR, ITP, ZRAF and ZRAFP are reenergized and relay 2RCT supplies 75 code to the section in the rear, the operation of relay BLTR at that rate energizing relays GLTF and 6H, thereby energizing mechanism GLG to condition signal 6L to indicate caution, and releasing relay 6L5. Relay BRCT is then caused to operate at the code rate and the operation of relay BLTR, at that rate energizes relay 8D along with relay 8H, reversing the polarity supplied to mechanism BLG to change the indication of signal 8L from caution to proceed. The code transmitter I80CT of Fig, 1C is energized over front contact 0 of relay 8D and relay 8RCT supplies 180 code to the section in the rear of signal 8L and the operation of relay 4LTR at that rate energizes relay 4LK in place of relay 4LD to maintain signal 4LA at proceed. In addition, relay 4LK completes a circuit over its contact 0 and a wire l4 by which the code communication system may be caused to light a lamp BKE at the control oflice, as show diagrammatically in Fig. 1D, the lighting of which indicates to the operator that the entire block is vacant and that the traflic relay ZRFS may properly be restored to normal.

Assuming next that after the signals for the relay BLTR, is held energized for the same period; During this period relay 6T]? remains steadily released and is then reenergized, releasing again at the end of the release period of relay SLTF. The release of relays 6H and BHP occurs during the first of these periods, and therefore occurs wherifront contact 0 of relay 6TP is open, consequently relay BLS does not become energized When, as in this case, the code operation of the track relay is terminated by a relatively long period during which the track relay is steadily energized.

As soon as relay 6H releases, the code operation of relay BRCT [ceases and during the remainder of the period of steady energization of relay GLTR relay BRCT is held energized over the circuit from terminal B at contact d of relay BLTF over back contact 0 of relay BTP, back contact e of relay 6H and back contact b of rea L5- by relay GRC'I holds the track relay BLTR. steadily energized for a prolonged interval with the same effect as when relay GLTR. is steadily energized, that is, relay BLTR. is held energized following the termination of its code operation for a time sufiicient to cause the release of relays 8H and SH? without energizing relay BLS.

Since the track section controlled by relay SRCT does not have a directional stick relay at its entrance end, it is not necessary to terminate the code operation of that relay by a period of steady energization. This, however, would be provided in the event the block included amadditional intermediate signal, located in the rear of signal BL, by connecting back contact d of relay BTP to back contact f of relay 8H, as shown by a dotted line in Fig. 10.

It will be' seen therefore that the directional stick relays, such as relayBLS and BLS, are energized when the code operation of the associated track relay ceases due to a train entering the corresponding track section, but are not energized if the code operation of the track relay ceases when the section is not occupied as manifested by the steady energization of the track relay.

One advantage of this arrangement is that it allows all of the opposing signals in the block to assume the stop position in case a train overruns the entering head block signal at the exit end of the block.

This will be clear from the foregoing description since'the effect of a train overrunning signal ZRA when signals 6L, BL and 4LA are at clear is to open contact b of relay iTP, thereby releasing relay ZRAF and thereby terminating the code operation of relay ZRCT with a period of steady energization, the same as when contact I) of relay ZRFS is opened by the operator 'as above described. g

It may be that some of the coded track sections are too long for reliable track circuit operation, in which case the track circuit is divided into two sections by insulated joints and the cut secv 1 tion apparatus of Fig. 2 ready mentioned.

In Fig. 2 the track relay LTR, or RTR for each section when energized supplies current to the rails of the other section, as will be obvious from the drawing. The length of block to which this form of repeater is applicable is limited by the code distortion which may occur due to variations in ballast resistance with weather conditions, the on periods of the code tending to .be prolonged when the track relays are over-energized, and to be shortened when they are under-energized. This may be compensated for to a large extent and the permissible length of block further increased by back contact coding, as illustrated in Fig. 3, in which the transmitting relays LCT and RCT are energized over back contacts of the or 3 is interposed as alcontrolling track relays, like relay STP in Fig.

1B. In order to obtain equivalent protection in the event of a broken down insulated joint, the plus terminals are connected to the same rail of the adjoining sections in Fig. 2, and to the opposite rails in Fig. 3. Thus Fig. 2 as shown may be interposed between Figs. 1B and' 10, but requires the plus terminals to be connected to the lower rail when interposed between Figs. 1A and.

1B orbetween Figs. 10 and 1D. Fig. 3, on the 12 sections in Fig. 10, which in turn requires a reversal of the connections to the rails of the lefthand section in Fig. 1D.

It is to be noted that the apparatus of Fig. 3 repeats the coded current received from either section into the other section with a reversal of phase, each 'on period being repeated as an OK period, and vice versa. In Fig. 3, if relay LTR remains released when the reception of coded current from the rails of the left-hand section ceases, it is obvious that relay RCT' will be held energized to supply current steadily to the rails of the right-hand section, for the release period of relay LTF. The cut section apparatus of Fig. 3 therefore constitutes an alternative means for preventing the energization of the directional stick relays and when this is used, the apparatus at the signal locations for that purpose as hereinbefore described is not needed, and in fact, if used, its effect would be nullified by the phase reversal due to the apparatus of Fig. 3.

It follows therefore that if Fig. 3 is interposed between Figs. 13- and 1C, the branch circuit for relay SRCT including back contact 0 of relay 6TP l and back contact e of relay 6H should be omitted so that when relay 6H releases the code operation of relay GRCT terminates without a period of steady energization. Consequently, in Fig. 3, relay LOT remains released and holds relay RCT picked up to maintain relay BLTR, energized until relays SH and 8HP release.

When Fig. 3 is interposed between Figs. 1A and 1B, relays ZRAF and 2RAFP may be omitted. The alternative circuit for relay ZRCT for use under this condition may be shown by placing the connector X in its upper position, in which the contacts a. of relays 2RAF and ZRAFP are removed from the circuit so that relay 2RCT will remain released following the opening of contact b of relay ITP or 2RFS.

This alternative circuit is also used when the single track block contains no intermediate signals, as illustrated by placing Fig. 1D directly at the right of Fig. 1A.

It will be understood that when a block section is of sufficient length to require two sets of the cut section apparatus of Fig. 3, the reversal of the phase of the coded current produced by the first set is nullified by the second set, and the alternative arrangements mentioned are not used.

The circuits of my invention also include special provisions for the control of an outlying hand throw switch W, as shown in Fig. 4. It will be assumed that switch W is located in the intermediate section of the block and that Fig. 4 is interposed between Figs. 1B and 1C.

Fig. 4 includes a set of cut section apparatus by means of which a short releasing section T, having 'a normally energized track relay TB, is interposed between two sections of the coded track circuit system.

The operating mechanism for switch W is equipped with an electric lock, which may be of the type shown in'Letters Patent of the United States No. 1,126,834, issued February 2, 1915, to Neubert et al., for Electric Switch Locks. This serves to lock the operating lever 8 for the switch in its normal position by a latch attached to a segment 25 and held in looking position by the bail 50 of a padlock, and also by a locking dog 21 attached to the armature of a lock magnet WLM. The locked condition of switch W in its normal position is made manifest in the circuits for Signals =53. and BL which govern traffic movements over the switch by the provision of an indication relay NWP. This relay is normally energized over a circuit which includes the normally closed contact of a push button PB, a contact 26 which is closed when the locking dog 21 is in a position to engage segment 25, and a contact N closed by switch W when locked in its normal position. When the track relay LTR, is responding to code, its operation is repeated by relay RCT, the circuit for which extends from terminal B at front contact a of relay TR over front contacts a of relays LTR and NWP through relay RCT to terminal C. Relay LCT is controlled over front contact a of relay RTR by a similar circuit including front contacts I) of relavs TR and NWP.

It will be seen that the transmitter relays RCT and LCT in Fig. 4 repeat the coded currents without change of phase, as in Fig. 2, their circuits differing from those for the transmitter relays of Fig. 3 in this respect.

To unlock switch W for a movement into the side track, the train must occupy section T to release relay TR and the padlock must be removed by the train crew and the segment 25 moved to the position in which it is stopped by the locking dog 21, thereby closing a circuit from terminal B at back contact a of relay TR through magnet WLM to terminal C over contacts 46--41. The energization of magnet WLM opens contact 26 to release relay NWP, and lifts the locking dog 21 to permit segment 25 to be moved to full reverse position in which lever B is free to be operated to reverse the switch.

For movements out of the side track, cooperation with the central ofiice operator is required, it being necessary for him to reverse the trafiic relays ZRFS and iLFS so as to supply coded current to the track circuit system at both ends.

It will be assumed that the system is already set up for traflic movements from right to left as hereinbefore described, so that the traffic relay ZRFS is reversed and relay -4LFS is normal, with the signal control relay 4LHS in its normal position to hold signals ALA and lLB at stop. The reversal of relay ALFS disables the circuits for signals 4LA and ALB and sets the transmitter relay 4LCT into operation at the 15 code rate, its circuits being similar to those for relay 2RCT already described, The'padlock bail 5B is removed by the train crew and segment 25 is moved to its intermediate position thereby energizing a slow release relay NWPR over contacts 46-41 and a contact 0 of relay NWP, The :push button PE is pressed by a member of the train crew, thereby releasing relay NWP, and in turn releasing relay NWPR after a release period during which relay RCT is held steadily energized over the circuit from terminal B at front contact b of relay LTF over front contact a of relay NWPR and back contact d of relay NWP. Relay RCT then releases, but relay LTR continues to operate and the closing of back contact a of relay NWP causes the slow release relay LTF to become energized, its circuit extending from terminal 13 over front contacts a of relays TR and L'I'R and back contact a of relay NWP through relay LTF to terminal C, and the slow release relay LTB is energized over the back contact a of relay LTR and the front contacts a of relay LTF and TR.

If relay ALFS is reversed by the operator before relay NWP is released by the train crew, relay 8RCT of Fig. 1C and relay 4LCT of Fig. 1Dv will both be in operation for a time, at'dif v ferent rates, and current will be supplied over the track rails by relay 4LCT to pick up relay BRTR. at irregular intervals whenever relay BRCT releases and relay 4LCT is picked up. The slow release relay BRTF'Will therefore become energized, and since relay BLTF is also energized, relay 81? will remain released, deenergizin relay BTP, transformer BDT and mechanism 8LG, and releasing relays 8H and 8HP without operating the directional stick relay 8LS. The release of relay 8H and mechanism 8LG stops the code operation of relay 8RCT, which relay then remains released and allows relay 8RTR to respond properly to the code transmitted by relay 4LCT. Signal 8R, however, is held at stop and relay BLTR is prevented from operating until relay BLTR ceases to operate and thereby releases relay 8LTF.

If on the other hand, relay NWP is released by the train crew before the operator reverses relay ALFS, relay BLTR ceases to operate and releases relays 8H and 8I-IP and restores signal8L to stop without energizing relay 8LS, due to the period of steady energization of relay BLTR provided by relay NWPR. as above described.

In either case, the code operation of relay BRTR, due to the reversal of relay lLFS, together with the release of relay 8LTF, due to the release of relay NWP, conditions signal 8R to indicate caution and to operate relay BLTR at the code rate to which relay RTR of Fig. 4 responds and thereby energizes the slow release relays RTF and RTB over circuits similar to those traced above for relays LTF and LTB. When relays RTB and LTB are both energized, a circuit is closed over their contacts a to energize magnet WLP to unlock the switch.

It will be understood that after the train entering the block via switch W occupies the main track and has fully passed the switch, switch W is restored to normal and locked in that position to energize relay NWP, and the central office operator will restore relay 4LFS to normal when he has been advised by the train crew that this has been done.

In the foregoing it has been assumed that the energization of relay LTB to unlock the switch is due to the operation of relay LTR at the 180 code rate, indicating that the entire portion of the block at the left of switch W is vacant. Relay LTB may also be energized by the operation of relay LTR at the '75 code rate, indicating that the block is occupied by a train 'beyond signal 6L moving away from the switch. Switch W may therefore be reversed to permit a train to follow another train through the block as soon as the first train is entirely past the first signal beyond the switch. Likewise, signal 4LA or 4LB may be cleared under similar conditions, provided relay NWP has been reenergized.

In the foregoing, the operation of the apparatus has been considered principally with reference to traific movements from right to left, with the track switches IW and 3W in their normal positions. Since the circuits for the two directions are similar, it is deemed unnecessary to describe their operation in detail, for traffic movements from left to right, nor to describe the operation involving the clearing of signals ZRB and 4LB for movements out of the passing tracks, thecircuits for which are similar to those for signal 4LA as described in detail herein.

Although I have herein shown and described only one form of railway trafiic controlling ap paratus embodying my invention together with several modifications of portions thereof as, applied to different situations, 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 claimis:

1. In combination, a, stretch of single track railway comprising two adjoining track sections, a track relay for one section connected across the rails of its section, a directional stick relay, a code detector relay selectively responsiv to the periodic operation of said track relay, a slow release repeating relay for said code detector relay, means at the remote end of said one section for supplying periodically interrupted current to the track rails thereof to operate said track relay to indicate the unoccupied condition of said one section, a pick-up circuit for said directional stick relay including a back contact of said code detector relay and a contact which closes each time the track relay is released, said circuit also including a front contact of said repeating relay, a stick circuit for said directional stick relay including its own front contact and a back contact of said code detector relay, and means controlled by said directional stick relay when energized for supplying periodically interruptedcurrent to the rails of the other of said adjoining track sections.

2. In combination, a stretch of single track railway comprising two adjoining track sections, a track relay for one section connected across the rails of its section, a directional stick relaya code detector relay selectively responsive to the periodic operation of said track relay, a slow release repeating relay for said code detector relay, meansat the remote end of said one section for supplying periodically interrupted current to the track rails thereof to operate said track relay to indicatethe unoccupied condition of said one sec tion, a pick-up circuit for said directional stick relay including a back contact of said code detector relay and a contact which closes each time the track relay is released, said circuit also including a front contact of said repeating relay, a stick circuit for said directional stick relay including it own front contact and a back contact of said code detector relay, means acting whenever the supply of periodically interrupted current to th rails of said one section is discontinued for supplying steady current to said rails for a time suficient to effect the release of the code detector relay and of its repeating relay while the track relay is held energized to prevent the closing of the pick-up circuit for said directional stick relay, and means controlled by said directional stick relay when energized for supplying periodically interrupted current to the track rails of the other of said adjoining track sections. I

3. In combination, a stretch of single track railway comprising two adjoining track sections, a cod following track relay connected across the rails of one of said sections, means at the remote end of said one section for supplying coded current to the track rails thereof to operate said track relay, a code detector relay which assumes its energized position in response to the code operation of said track relay, a slow release repeating relay controlled by a front contact of said code detector relay, a directional stick relay, a pick-up circuit for said directional stick relayincluding a front contact of said repeating relay and a contact which closes each time the track relay releases and arranged to be completed only when said code detector relay is releas d by the continued deenergization of said track relay, a stick circuit arranged to hold said directional stick relay energized until said code detector relay is again energized, and means controlled by said directional stick relay when energized for supplying coded current to the rails of the other of said adjoining track sections.

4. In combination, a stretch of single track railway comprising two adjoining track sections, a code following track relay connected across the rails of one of said sections, means at the remote end of said one section for supplying coded current to the track rails thereof to operate said track relay, a code detector relay which assumes its energized position in response to the code operation of said track relay, a slow release repeating relay controlled by a front contact of said code detector relay, a directional stick r lay, a pick-up circuit for said directional stick relay including a front contact of said repeating relay and a contact which closes each time the track relay releases and arranged to be completed only when said code detector relay is released by the continued deenergization of said track relay, a stick circuit arranged to hold said directional stick relay energized until said code detector relay isagain energized, means elfective whenever the supply of coded current to the rails of said one section is discontinued for supplying steady current thereto to hold the track relay energized for a time sufficient to cause said code detector relay and its repeating relay to release before said track relay is released, whereby said directional stick relay is caused to be energized wh n the track relay remains released due to a train entering said one section but not if the code operation of said track relay ceases while said one section is unoccupied, and means controlled by said directional stick relay when energized for supplying coded current to th track rails of the other of said adjoining track sections.

7 5. In combination, a stretch of single track railway comprising two adjoining track sections, a code following track relay connected across the rails of one of said sections, means at the remote end of said one section for supplying coded current to the track rails thereof to operate said track relay, a code detector relay which assumes its energized position in response to the code operation of said track relay, a slow release repeating relay controlled by a front contact of said code detector relay, a directional stick relay, a pick-up circuit for said directional stick relay including a front contact of said repeating relay and a contact which closes each time the track relay releases and arranged to be completed only when said code detector relay is released by the continued deenergization of said track relay, 2. stick circuit arranged to hold said directional stick relay energized until said code detector relay is again energized, means controlled by said directional stick relay when energized for supplying coded current to the rails of said other track section, and means for rendering the energization of said directional stick relay dependent upon whether th release of said code detector relay is due to a train entering said one section or is due to the termination of the supply of coded current to the rails thereof, comprising means for supplying steady current to the rails of said one section following the termination of the supply of coded current for a time suflicient to release said code detector relay and its repeating relay before said track relayis released.

6. In. combination, a stretch of railway track divided into track sections, means effective only when the end section of said stretch is unoccupied for supplying coded current to the track rails of a second section adjoining said end section, a code following track relay at the remote end of the second section responsive to said coded current, a directional stick relay associated with said track relay effective when energized to supply coded current to the track rails of a third section adjoining said second section, a code detector relay which assumes its energized position in response to the continued code operation of said track relay, a slow release repeating relay controlled by front contacts of said code, detector relay, a pick-up circuit for the directional stick relay including a contact closed when the track relay releases and a front contact of said repeating relay and adapted to be closed in response to the release of said code detector relay when the code operation of said track relay ceases due to the movement of a train from the third section to the second section, a stick circuit for maintaining said directional stick relay energized until said code detector relay is again energized, and means for preventing the energization of said directional stick relay when the code operation of said track relay ceases due to the occupancy of said end section by an opposing train, comprising means rendered effective when the supply of coded current to the rails of the second section is terminated by the occupancy of said end section for supplying steady current to the rails of said second section to hold the track relay energized until the code detector relay and its repeating relay are released.

7. In combination, a stretch of railway track divided into track sections, means effective only when the end section of said stretch is unoccupied for supplying coded current to the track rails of, a second section adjoining said end section, a code following track relay at the remote end of the second section responsive to said coded current, a directional stick relay associated with said track relay effective when energized to supply coded current to the track rails of a third section adjoining said second section, a code detector relay which assumes its energized position in response to the continued code operation of said track relay, a slow release repeating relay controlled by front contacts of said code detector relay, a pick-up circuit for the directional stick relay including a contact closed when the track relay releases, a back contact of said code detector relay and a front contact of said repeating relay and adapted to be closed momentarily in response to the release of said code detector relay, provided the track relay remains in its released position when the code operation of said track relay ceases, and means rendering the energization of said directional relay dependent upon whether said code detector relay is released due to a train entering said second section from said third section or is due to an opposing train entering said end section, comprising means controlled by a train entering said end section for supplying steady current to the track rails of said second section to terminate the code operation of the track relay by holding such relay steadily energized until the code detector relay and its repeating relay have released.

8. In combination, a stretch of single track railway divided into reversible track sections each having a, track relay at each end, signals: at the ends of said sections for governing traflic movements through said stretch in opposite directions, a code detector relay for each signal for controlling the signal, means for selectively energizing each code detector relay in response to the operation of an adjacent track relay by periodically interrupted current in the rails of the section in advance of the corresponding signal, a manually controllable trafiic relay at each end of the stretch, means controlled by said trafiic relays and by the code detector relays for the intermediate signals in said stretch for supplying periodically interrupted current to the track rails of the sections to energize said track relays in cascade by periodically interrupted current as required to establish either direction for traflic movements through the stretch, a directional stick relay for each intermediate signal, a pick-up circuit for each directional stick relay closed when the reception of current over the track rails at the location thereof ceases and the code detector relay for the associated signal is released, due to the continued deenergization of the associated track relay, a stick circuit for holding each directional stick relay picked up until the associated code detector relay is again energized, means controlled by each directional stick relay when energized for supplying periodically interrupted current to the track rails for the track section in the rear of the signal with which such stick relay is associated, means associated with each directional relay for preventing its energization in response to therelease of the code detector relay for the associated signal due to the continued energization of the associated track relay by steady current supplied over the track rails in advance of such signal, and means at each end of the stretch for temporarily supplying steady current to the track rails of said sections in cascade whenever the supply of interrupted current to the track rails at thatend is discontinued, for a time sufficient to effect the release of said code detector relays without energizing any of said directional relays.

9. In combination, a stretch of single track railway comprising two adjoining track sections, a code following track relay for each section connected aClOSs the track rails thereof, means at the remote end of each section for supplying coded current to the track rails to operate the track relay for that section, a slow release repeating relay for each track relay, a code detector relay which assumes its energized position in response to the code operation of either track relay, a slow release repeating relay controlled by a front contact of said code detector relay, a directional stick relay for each track relay, a pick-up circuit for each directional stick relay including a back contact of the other directional relay, front contacts of the repeating relays for the associated track relay and for said code detector relay and arranged to be closed when said code detector relay releases in response to the steady deenergization of said track relay, a stick circuit arranged to hold the energized directional stick relay picked up until said code detector relay is again energized, means controlled by each directional stick relay when energized for supplying coded current to the rails of the other section, and means for rendering the energization of each directional stick relay dependent upon whether or not the release of the code detector relay is due to the occupancy of the corresponding track section, comprising means at the remote end of each section acting whenever the supply of coded current to the track rails thereof is discontinued for supplying stead-yourrent to said rails to hold the corresponding track relay energized for a time sumcient to release said code detector relayand its repeating relay.

10 :In combination, ,a stretch of single track railway comprising two adjoining track sections, code iollowing track relays "connected across the rails :of said sections, that .for one section being located at'the junction of said sections and that for the other section at the remote end of such section, means 'atthe remote end of said one section .for supplying coded current to the rails thereof to operate the track relay thereof,a code detector relay which assumes its energized positioninresponse to thecode-operati'ono-f the'track relay for said one section, a slow release repeating relay for said code detector relay, adirectional stick relay, a pick-up circuit for said'directional stick relay including a front contact of said repeating relay and arranged to be closed if said code detector relay releases while said track relay occupies its released position, a stick cir- 'cuit arranged to hold said directional stick relay 1.

energized until said code detector relay is again energized, means effective when said code detecitor relay is energized .for supplying current coded at a given rate and when said directional stick relay is energized for supplying current coded at a different rate, to the track rails of said other section, means forrendering the energization of said directional stick relay dependent upon Whether the release of said code detector relay is due'to a train entering said one section or is due to the termination of the supply of coded current to the rails thereof, comprising. means for supplying steady current to the rails of said one section following the termination of the supply of coded current for a time suilicient to release said code detector relay and its repeating relay before the track relay for said one section is released, and means rendered eifective upon the releaseof said code detector relay while the track relay for said one'section is energized for supplyingisteady current to the track rails of the other ,sectionras long as said track relay remains energized. 1

1-1. In combination, a stretch of single track railway divided into track sections, signals at the ends .of said sections for governing traffic movements in both directions, each such signal being arranged to indicate stop except when the track section in advance is supplied with periodically interrupted current, a directional stick relay for each intermediate signalin said stretch, manually controllable means for supplying periodically interrupted current to the track rails at one end ofthe stretch ,or the other to designate the direction for traffic movement in the stretch, code detector means at each signal location selectively responsive to periodically interrupted current received :over the track rails from either track section for supplying current periodically interrupted at a given rate to the track rails of the other see- -'tion atthatlocation, whereby said track sections are energized in cascade when the stretch is unoccupied, means for energizing each directional stick relay in response to the release of the associated code detector means when current ceases toibe received over the track rails at-that location, meansior maintaining such relay energized until such code detector means again indicates the reception of periodically interrupted current, means for rendering the energization of each directional stick relay dependent upon whether or not the corresponding track section is occupied comprising means for supplying steady current to the railsv of said section to which such relay is nonresponsive for a time following the termination of the supply of interrupted current thereto, sufficient to effect the release of said code detector means without energizing said relay, means controlled by each directional stick relay for supplying'current to the rails of the adjoining track section interrupted at a rate difierent from that supplied thereto when the associated code detector means is energized, 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 dependent 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 traffio relay when operated for supplying periodically interrupted current to the track rails for establishing the direction for trafiic movements through the stretch, a directional stick relay ,for each direction at each junction of two sections in said stretch, a pick-up circuit for each directional stick relay including a back contact of the other directional stick relay at thesame location and arranged to be closed when periodically interrupted current ceases to be received over the track rails at that location from'the corresponding direction, provided the reception of such current is terminated by a prolonged intervalduring which no current is received, a stick circuit for maintaining each energized directional stick relay picked up until interrupted current is again received at its location in the corresponding direction, means efieotive when the operated traffic relay is restored to normal and the supply of interrupted current. is thereby discontinued for supplying steady current to the track rails for a time to prevent the energization of such directional stick relays, means at each junction of two sections for supplying periodically interrupted or steady current to the rails of either section as long as such current is being received over the vtrackrails of the other section at thatlooation, and means controlled by the directional stick relay for either section when energized for supplying periodically interrupted current to the track rails of the other section at the same location.

CHARLES B. SHIELDS.

No references cited.

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