US2357519A - Coded track circuit signaling system - Google Patents

Description

Sept. 5, 1944'. T, J, JUDGE 1 2,357,519

CODEI) :IRACK CIRCUIT SIGNALING SYSTEM Fil ed Sept. 7, 1942 8 Sheets-Sheet l W &5 W

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CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Sept. 7, 1942 8 Sheets-Sheet 6 IAR Sept. 5, 1944. T. J. JUDGE CODED TRACK CIRCUIT SIGNAL ING SYSTEM Filed Sept. 7, 1942 8 Sheets-Sheet 7 E5 um.

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8 Shets-Sheet 8 Filed Sept. 7,, 1942 an E ' tive track sections.

Patented Sept. 5, 1944 CODED TRACK CIRCUIT SIGNALmG SYSTEM Thomas J. Judge, Rochester, N. Y.,.assign or to General Railway Signal Company, Rochester,

Application September 7, 1942, Serial No. 457,545

21 Claims.

This invention relates to coded track circuit signaling systems for railroads, and it more particularly pertains to coded track circuit signaling systems for single track railroads used in com bination with centralized traffic control.

The system of this invention is to be considered in the nature of an improvement over my prior application Ser. No. 365,669 filed November 14, 1940. Similarly, the system of this invention is to be considered in the nature of an improvement over the prior application of N. D. Preston, Ser. No. 439,520 filed April 18, 1942, as well as his prior Patent No. 2,342,489 granted February 22, 1944, on the application Ser. No. 455,328 filed August 19, 1942. It is to be understood that no claim is made in this application to any subject matter disclosed in the above men-' tioned prior applications. I

The organization of the system provided by the present invention is such as to control the signals at the respective ends of passing sidings by the communication of distinctive signal controls from a control office tothe location of such signals, the indications of the signals being also governed in accordance with trafiic in advance by' distinctive automatic signal controls transmitted through the track rails by coded track circuits. The apparatus grouped at each end of each of the passing sidings constitutes a field station. Controls are transmitted through the track rails by driven and inverse codes, a driven code being formed of time spaced impulses having Another object of the present invention is to I follow up the abnormally long periods of energization for the various track sections by driven codes transmitted through the track rails for the direction of trafiic desired to be established, the

which they are applied to the track rails, While .an inverse code is formed of impulses transmitted during the oil periods of a driven code applied at the exit end of the track section, the rate of the inverse code being determined by the rate of the driven code transmitted from the opposite end of that track section.

An object of the present invention is to govern the direction of track circuit code transmission in a stretch of track between two field stations by a trafiic direction lever for such stretch at the control office, a change in the positionof such lever being effective to initiate the checking of the unoccupied condition of each of the track sections before removing the code formerly transmitted by code transmitters through such respec- Such condition is checked by the transmission in opposition "to the driven code being transmitted of an abnormally long impulse through the track rails of each of the the entrance endof the route according tothe transmission of such driven codes being rendered effective for the various track sections in the stretch successively, starting with the track section at the entrance end of the route according to the prior established direction of track circuit code transmission.

Another object of the present invention is to allow both directions of traffic to be established at the same time for the respective ends of a single stretch of track when such stretch is occupied by a train as would be desirable for backup train movements, the establishment of such directions being subject to the manual operation of the trafiic direction lever for such stretch of track at the control office.

Another object of the present invention is to provide suitable means for restoring directional control relays for the signal locations of a stretch of track in correspondence with each other after they have become out of correspondence as, for example, in connection with back-up train movements.

Another object of the present invention is to control traflic direction relays at the various. signal locations in such a manner as to cause them to be responsive to the reception of an abnormally long impulse transmitted through the track rails, but to be non-responsive to driven or inverse codes.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the in- Y vention progresses.

In describing the invention in detail, reference will be made to the accompanyingdrawings in 'which those parts having similar features and functions are designated throughout the several illustrations by like letter reference characters which are generally made distinctive by reason of preceding numerals indicativeof the location or signal with which such parts are associated, and in which:

Fig. 1 illustrates control oflice apparatus for the communication of traflic direction and switch and signal controls to the respective field stations; 1 v I 1 Figs. 2A through 2D when placed side by side respectively illustrate the circuits employed for the control of the signals of this embodiment of the present invention, and the circuits employed in connection with the governing of code transmission in the various track sections;

Fig. 3 illustrates the manner in which approach locking is employed in this embodiment of the present invention;

Fig. 4 illustrates how the power operation of a track switch is effected in accordance with switch controls communicated from the control office; and

Figs. 5A through 5K (letter I omitted) illustrate diagrammatically conditions of track circuit code transmission through the various track sections under typical operating conditions.

The illustrations employed in the disclosure of this embodiment of the present invention have been arranged to facilitate the disclosure of the present invention as to the mode of operation and principles involved in the system rather than for the purpose of illustrating the construction ,Figs. 5A through 5K (letter I omitted) are to be .considered as indicative of the indications of the signals rather than the type of signals employed, the signals employed in this embodiment of the present invention being of the color light type. The signal arms of the symbols are relatively heavy and light to indicate the respective illuminated or dark conditions of the signals.

In order to simplify the description of the present invention, a general reference is made from time to time to functions common to all parts of a similar character by use in the description of letter reference characters without their preceding numerals. It is to be understood that such a reference applies to any parts designated in the drawings by reference characters. that are similar except for preceding numerals associated therewith.

The trackway for which this embodiment of the present invention is provided comprises a main stretch of track (see Figs. 2A through 2D) divided into track sections, and having signals for governing traffic in both directions, such stretch of track having associated therewith at one end a passing siding A, and at the other end a passing siding B. The arrangement of the signals at each end of each of the passing sidings is provided in the usual manner to provide a short detector or OS track section for the track switch. The detector track section 'l8T, for example, is provided for the track switch 3W at the lefthand end of the passing siding B, and such track section has the usual type of steadily energized track circuit for the energiztion of the detector or OS track relay 1--8TR.. The power operation of the track switch 3W by remote control can be provided as disclosed in detail, for example,

in my prior application Ser. No. 365,669, dated November 14, 1949.

The signals at each of the field stations for governing passage of trains through the detector track section at such station are normally at stop and subject to manual control by an operator at the control office in any suitable manner such for example, as by the communication of controls by a coded centralized trafiic control system such as disclosed in the patent to Judge et al., No. 2,082,544, dated June 1, 1937. The entering signals 8A and 83 at the left-hand end of the passing siding B,for example, govern east bound trafilc (to the right) through the track section l-8T, and the head-block signals IA and 1B govern west bound traffic (to the left) through such track section. Similarly, the entering signals IA and. IB govern west-bound traffic over the switch 2W in normal or reverse positions respectively; and head- block signals 2A and 2B govern east-bound trafiic over the switch 2W in its normal and reverse positions respectively. The head-block signals are considered to be absolute signals, that is, a train must stop and stay when such signals indicate stop; While the other signals are assumed to be of the permissive type.

Intermediate signals are included between the passing sidings A and B, the signals 4 and B being provided for governing east bound traflic and the signals 3 and 5 being provided for governing west bound trafiic.

Although the signals illustrated are of the color light type having individual color lamp units for the display of respective green (for clear), yellow (for caution), and red (for danger or stop) indications, it is to be understood that other types of signals such as Searchlight, semaphore and position light signals could as well be employed.

* Each of the track sections in the stretch of track between the passing sidings A and B has a coded track circuit which includes a track battery and a code following track relay TR at each end of the track section. For the purpose of obtaining the best operating conditions of the code following track relays it is desirable that each relayhave a polar structure so arranged as to cause the relay contacts to be biased to a deenergized position from which they can be moved only upon energization of the relay windings with a particular polarity.

At each end of each of the track sections having a coded track circuit is a code transmitter relay CP which is operable when rendered active to transmit a or 75 driven code, and, for certain of the track sections such relay can be at times active for the transmission of an inverse code. For purposes of obtaining the most desired operating characteristics of each of the relays CP, particularly when such relay is used as an inverse code transmitter, the relay has a polar structure to provide the operating characteristics above described as being preferable for the code following track relays TR.

Relays FP andFBP are provided for the ends of the track sections having coded track circuits, the relays FP being energized during the on periods of codes received, and the relays FBP being energized during the off periods of the codes received in such a manner as to detect the coding condition of the track circuit with which they are associated. Each of the relays is sufilciently slow in dropping away to be maintained picked up when a code is being received.

East and west directional stick relays EFR. and WFR. respectively are provided for each of the intermediate signal locations, and for each of assure the field stations for maintaining'a direction of driven codetransmission in the track circuits to correspond with the position of the traific lever 2-7FL at the control office. The relays EFR and WFR for each of the intermediate signal locations are sufficiently slow in picking upto allow their picking up only in response to a prolonged impulse transmitted through an associated coded track circuit.

Associated with each end of each of the track sections having a coded track circuit are H and D relays which are sufliciently slow acting to cause them to be maintained picked up when a code is being received. Each of the D relays is energized through the medium of a decoding transformer and a tuned circuit in a manner generally employed in coded track circuits so as to cause such relay to be picked up only in response to a 180 code. Each of the relays H, however, is picked up in response to a 75 or a 180 code, but only if it is a driven code that is received.

The relays EFR and WFR associated with the field stations are similar to those provided for 'the intermediate signal locations except for the as code oscillators or motor driven coders to form the difierent code rates employed. For this embodiment of the present invention an oscillator I800 is provided for each of the signal locations for forming a 180 code, and an oscillator 150 is provided at each of the signal locations for forming a 75 code.

Each of the field stations has ofiice controlled relays for use in the manual control of the signals, a relay RGZ being provided for governing the clearing of signals for governing traffic to the right, and a relay LGZ being provided for'governing the clearing of signals for governing traffic to the left. A stop relay Bis associated with the relays RGZ and LGZ at each of the field stations to provide for the manual restoration to stop of a signal where a coded CTC communication system is employed for communication of signal controls from the control office to the respective field stations.

Associated with the control of the signals at each of the field stations are signal control relays AG and BG having their control circuits selected by correspondence relays NOR. and RCR in the usual manner. I

Having thus considered the structural organization of the system of this embodiment of the present invention a consideration will now be given to the mode of operation'of the system under various typical operating conditions which would be encountered in practice.

Operation 5A through 5K (letter I omitted) the generaloperating characteristics of the system and the utility of such characteristics.

bound traffic.

With reference to Fig. 5A, it will b noted that the conditions of code transmission are such as to transmit a driven code from left to right in each of the track sections having a coded track circuit,

and to transmit an inverse code from right to left in the track sections 23T and45T. The direction of driven code transmission is established to correspond with the position of the trafiic direction lever 2-'IFL (see Fig. 1) at the control ofiice, such lever. having been positioned for west Thus a relay WFR (see Figs. 2A through 2D) is picked up for each of the signal locations and the energized condition of such relay is effective to establish the direction ofcode transmission illustrated. The direction of driven code transmission is obviously established to clear signals for a west bound train, while the transmission of an inverse code in the track sections 2-3T and 4-5T is for the purpose of providing approach looking for the entering signal IA, and for establishing means to provide an approach indication. With these conditions of code transmission effective, the signal 3 is at caution because the signal in advance is at stop, and the signal 5 is clear because of the signal 3 being at caution. It will be noted that the relay 2H (see Fig. 2A) at the left-hand end of the stretch of track between the passing sidings A and B is deenergized under the conditions illustrated because of the deenergized condition of the relay 2EFR, and thus it would be impossible for an operator at the control oilice to cause the clearing of signal 2A or signal 23 for governing east bound traffic in accordance with the reception at the left-hand end of track section 23T of the inverse code. In other words, the relay 2H can be picked up only by a driven code, and therefore the signals 2A and 23 can be cleared only by the transmission of a driven code in the direction of said signals in the track section 23T.

A problem to be dealt with in the control of traflic direction relays is to provide a means to prevent the taking of a code away from a train if such train occupies the stretch of track between the passing sidings in an attempt to reverse the direction of driven code transmission. In order to prevent such a condition in this embodiment of the present invention it is provided that a code is removed from a track section upon achange in of the stretch of track used as an entrance point for the trafiic direction previously established. For example, if the direction previously established is for west bound trains as illustrated in Fig. 5A, and an operator attempts to reverse the direction of traffic by actuating his lever 21FL (see Fig. 1) to the right-hand position, a prolonged impulse is applied to the right-hand end of track section 6--'IT without having removed the driven code normally transmitted from left to right in that track section.

If thetrack section 6-'|T is unoccupied, the

reception of the prolonged impulse at the lefthand end of such section causes the cessation of the code transmitter relay 6GP for that end, thus establishing conditionswhich exist momentarily as illustrated in Fig. 5B in which a prolonged impulse is illustrated .as being transmitted from right to left in track section 6'|T to check the unoccupied condition of such section, and the reception of such impulse at the left-hand end of the track section'causes the removal of the 180 driven code which has been transmitted from left to right in the track section according to the diagram of Fig. 5A.

A function of the prolonged or clear-out impulse, other than to cause the cessation of code transmission in the prior established direction, is to condition the traffic direction relays for the newly established traific direction. Such conditioning is accomplished because the traffic direction relays are controlled in such a manner as to be responsive to a prolonged impulse as compared to their being non-responsive to code impulses of normal length. Thus, upon changing traific direction as assumed above, the reception of the prolonged impulse at the left-hand end of the track section 61T is effective to cause the picking up of the relay GEFR (see Fig. at the intermediate signal location at the left-hand end of the track section. The picking up or such trafiic direction relay causes the dropping away of the relay SWFR which has been energized according to the prior established direction, and the picking up of the relay BEFR is also efiective to initiate the transmission of a prolonged impulse through the adjacent track section 45T. In accordance with the reception of the prolonged impulse at the left-hand end of the track section 4--5T, the driven code which has been transmitted from left to right in that track section is removed as illustrated in Fig. C, and the traffic direction relays for the intermediate signal location at the left-hand end of the track section 45T are conditioned for the direction of traffic desired to be established. When such traific direction relays are conditioned, the transmission of a prolonged impulse in the track section 23T is initiated, and the reception at the left-hand end of the track section 23T of such prolonged impulse i effective to cause the removal of the code which has been transmitted through such section in accordance with the prior established direction of traffic. The reception of the prolonged or clear-out impulse at the left-hand end of the track section 23T is effective to condition the traific direction relays at that signal location in accordance with the desired traflic direction.

By the scanning of the track sections in the manner which has been described (starting with the entrance end for the previous direction of trafiic) there i no possibility of causing an intermediate signal to go to stop in advance of a train on account of removal of code upon changing direction because each track section is checked for occupancy before the direction of code transmission is reversed.

The length of the prolonged or clear-out impulse transmitted through the track section adjacent the entrance end of the stretch of track, according to the prior established traffic direction, is determined by a timing device at'such end to be of sufiicient length to insure the proper response of the traflic direction relays for the various signal locations in the stretch of track. It will be noted as the description progresses that the length of the prolonged impulse transmitted through the track section adjacent such entrance end should be determined dependent upon the number of track sections in the stretch, as the circuit organization is such that the prolonged impulse for each of the successive track sections is shortened in accordance with its remote relationship to the entrance end of the route according to the prior direction of traffic. Therefore, the prolonged impulse for the first track section must be of such a duration as to cause the prolonged impulse for the last track section of the single track stretch to be of sufficient length to insure the proper response of the trafiic direction relays for the extreme end of the single track stretch.

With'reference to Figs. 50' and 5D, it will be seen that these prolonged impulses are applied to the successive track sections in overlapping relationships to insure a proper repeat of the impulses into each of the sections throughout the stretch. The system is thus so organized that, when the prolonged or clear-out impulse is made of greater duration in the first track section, the clear-out pulse in each of the remaining track sections is similarly made of greater duration.

This is especially useful in cases where there may be a large number of successive track sections in the single track stretch and the duration of the prolonged or clear-out impulse for the first section must be of a substantial value, inasmuch as the timing for the clear-out pulse for the first section can be repeated to the other track sections without additional' timing devices for each of the intermediate signal locations. 7

Immediately at the end of the prolonged impulse transmitted from the entrance end of the route according to the prior direction of traffic, a driven code is applied by the transmitter which has transmitted such prolonged impulse as illustrated in Fig. 5D, ItWill be noted that the application of such driven code is in accordance with the termination of the prolonged impulse in the first track section rather than being in accordance with the complete scanning of the stretch of track by the transmission of the prolonged impulses in the respective track sections. Similarly, in each of the track sections, the termination of the prolonged impulse transmitted through such section defines the beginning of driven code transmission through that track section in the newly established direction until the conditions of code transmission are established throughout the entire stretch of track as illustrated, for example, in Fig. 5E for the desired traffic direction.

The conditions of code transmission in the various track sections upon passage of a train are illustrated in Figs. 5F through 5K, and it is believed that such conditions will be more readily understood from the description as it will be hereinafter set forth with respect to the specific circuit conditions involved upon the progress of a train.

The system provided by the present invention is particularly adapted to the control of intermediate signals for the provision of back-up train movements in that reversal in the direction of driven code transmission can be made effective in the rear of a train, and thereby provide control for signals governing a back-up train movement (see Fig. 5K). When a driven code is transmitted from each end of the stretch of track between the passing sidings as is the case when providing for a back-up train movement, or when an operator attempts to reverse the direction of traffic when a train is occupying the stretch of track between the passing sidings, it is necessary in order to establish one direction or the other for traific through the stretch for an operator to position his traific lever 21FL (see Fig. l) to correspond with the direction of traflic desired to be maintained and to press the cancel button 2-ICB for cancelling the opposing direction which has been established.

Normal conditions.The' conditions which are considered as normal are those conditions of the system in which the trackway is unoccupied by trains, the signals at the field stations are at stop, and the intermediate signals display proceed indications (see Fig 5A) for one direction of traffic or the other in correspondence with the position of the trafiic lever 2.1FL (see Fig. 1) at the control ofiice. At the control office the switch control levers SML are illustrated as being in their normal positions, and the signal control levers SGL are illustrated as being normally in center positions in correspondence with the stop indication dsplayed by the signals at the respective field stations. The indicator lamps on the control panel are normally extinguished to correspond with the unoccupied condition of the trackway, except for the trafiic direction indicator 2-1WFK which is illuminated in accordance with the direction of traflic established through the stretch of track between the passing sidings A and B, such direction being assumed to have last been established for the passage of west bound trains.

In that the manner in which the respective switch and signal and traflic direction controls are communicated from the control office to the respective field stations, and the manner in which the indications are communicated from the field stations to the control office has little bearing upon the present invention, for the purpose of simplification of the drawings, the communication of such controls has been merely indicated by dotted lines.-

system is operativeif the wires indicated as destined for stations Nos. 1 and '2 respectivel are connected directly to wires designated by similar reference characters shown associated with the respective field stations. It is no doubt preferable, however, in most cases where the control office is located some distance away from the field stations that line wires be saved by the use 7 of a code communication system for the communication of the controls such, for example, as is disclosed in the above mentioned Judge et a1. patent, or as shown in the patent to Hailes et al., No. 2,259,561, dated October'21, 1941.

In accordance with the direction of trafiic established for the passage of west bound trains, a traffic direction relay WFR at each of the signal locations is maintained picked up by a stick circuit closed at the back contact of the relay EFR for the opposite direction at that No. 1 location. For example, the relay ZWFR' (see Fig. 2A) at the field station No. 1 at the left-hand end of the stretch of track between the passing sidings A and B is maintained picked up by an obvious stick circuit closed at back contact 40 of relay ZEFR. By such stick circuit control of the relay ZWFR, it will be noted that such relay can be deenergized only upon the picking up of the relay ZEFR for changing the traffic direction, relay ZEFR being responsive only to the transmission of a prolonged impulse from right to left through the track section 2--3T.

In accordance with the energized condition of the relay ZWFR. under the conditions illustrated as normal, the relay 2GP is active for the transmission of a 75 driven code from left to right in the track section 2-3T because'of the energization for each on period of the oscillator 15C of It will be readily apparent that the arrangement of the circuits issuch that the a circuit extending from including front contact 4| of relay ZWFR, contact 42 of oscillator 150, back contact 43 of relay IAG, front contact 44 of relay ZTJ S, back contact 45 of relay 5 2TB, and winding of relay ZCP, to

The closure of front contact 46 of relay ZCP for each impulse of the driven code causes the energization of an obvious track circuit for the relay 3TB (see Fig. 2B) including back contact 41 of relay 3CP at the right-hand end of track section 23T. The pulsing of contact 48 of relay 3TR causes the repeater relay 3TP to follow the code, and the pulsing of contact of relay N r 3TP causes the relays 3FP and 3FBP to be maintained picked up. The relay 3FBP checks that a code is being received by the inclusion in its circuit of front contact 50 of relay 3FP, relay 3FP being energized by front contact 5l' of relay 3TP, and relay 3FBP being energized by back contact 5| of relay 3TP with relay 3FP picked up. The relay 3H is picked up in response to the 75 driven code by the energization for each impulse of that code of a circuit extending from (+),.including front contact 5| of relay 3TP, 2 front contact 52 of relay 3FBP,-front contact 53 of relay 3WFR, and winding of relay 3H, to The closure of front contact 54 of relay 3H allows the energization of the decoding transformer s 55, but the tuned circuit associated therewith 313 allows the picking up of the relay 3D only upon the reception of a 180 code. With the relay 3H picked up and the relay 3D dropped away, an

obvious circuit is closed by which the yellow lamp W of the intermediate signal 3 is energized at front contact 56 of relay 3WFR.

For approach control purposes the relay 3GP is active to transmit an inverse code from right to left in the track section 23T when traflic D V is established for the passage of west bound trains, such relay being picked up by the collapse of the flux in the transformer 51 at the end of each impulse of the driven code received. The primary winding of such transformer is energized for each impulse of the driven code received 4 5 at the right-hand end of track section 2-3T by a circuit extending from includingfront contact 48 of relay 3TR, front contact 58 of relay 3WF R, front contact 59 of relay 4FBP, and primary winding of transformer. 51, to It will to, be noted that the relay 3CP is active for the transmission of aninverse code only if front contact 59 of relay 4FBP is closed in accordance with the reception of an inverse code at the left-hand end of the track section 45T, thus providing efiectively an approach control portion of trackway including the track sections 23T and 45T. The relay 3GP, because of its polar structure, is

responsive only to the collapse of flux in the transformer 5'! by the energization of the secondary winding 60 of that transformer, the circuit including back contact 6| of relay 4EFR for the purpose of disconnecting thewinding from the relay 3CP when such relay is employed as -a driven code transmitter at a time when trafiic direction is established for the passage of east bound trains.

Because of the caution indication of the intermediate signal 3, a 180 driven code is transmitted from left to right through the track sec- 7 7 tion in the rear to cause the clear indication of signal 5. The relay 4GP is active for the transmission of such 180 driven code by the energiza-' tion for each impulse of such code of a circuit extending from including front contact 62 of relay 3WFR, contact 63 of oscillator C.

front contact 64 of relay 3H, front contact 65 of .relay SFBP, front contact 66 of relay 3FP, windaccordance with the closure of front contact 68 of relay 51-1, the decoding transformer 69 is effective to energize the tuned circuit for the relay 5D, and because of the 180 rate of the code, sufiicient energy flows in the circuit to cause the relay 5D to be picked up. Because of the energized condition of the relays 5D and 5H, the green lamp G of signal 5 is energized by a circuit closed at front contact of relay 5WFR.

The relay 5GP is active for the conditions under consideration for the transmission of an inverse code from right to left in the track section 4-5T in a manner similar to that which has been considered in the control of the relay 3GP for the transmisison of an inverse code in the track section 23T. The primary winding of the inverse code transformer H is energized for each impulse of the driven code received at the right-hand end of the track section'4--5T by a circuit extending from including front contact 12 of relay 5TB, front contact 13 of relay 5WFR, and primary winding of transformer II, to It will be noted from such circuit that inverse code transmission is effective in the track section 4-5T until such track section becomes occupied upon the passage of a west bound train.

In accordance with the clear indication of signal 5, the relay GOP is active to transmit a I80 driven code from left to right in the track section 6-1T by the energization for each on period of the oscillator IBOC of a circuit closed from including front contact 14 of relay 5WFR, contact l5 of oscillator 1800, front contact 16 of relay 5H, front contact ll of relay 5FBP, front contact 78 of relay 5FP, winding of relay GOP, and back contact 19 of relay BTR, to

At the right-hand end of the track section 6-1T, the reception of the 180 driven code causes the pulsing of contact 80 of relay 'ITR, and the relay 'ITP following the code causes the pulsing of contacts 8| and 82 to cause the relays IFP, 'IFBP, IT and 'lD'to be maintained picked up in a manner corresponding to that which has heretofore been specifically described for relays designated by similar letter reference characters. The energized condition of the relays 1H and ID does not cause the clearing of the signal.

1A or the signal '!B because of the manual control included in' the circuits for such signals It is believed to be readily apparent to those skilled in the art how the transmission of a control for the clearing of either of such s gnals becomes effective through the medium of an office controlled relay 'ILGZ, signal 1A or signal 1B being selected by the correspondence relays 3NCR and 3RCR in accordance with the position to which the track switch 3W is operated.

Having thus considered the conditions in which the system exists when traffic direction is established for the passage of West bound trains, consideration will now be given to the establishment of the opposite direction of traflic. Reversal in trafl'ic direction-To consider the conditions effective upon a reversal in the direction of trafiic, it will be assumed that an operator desires to establish a route for the passage of an east bound train. To initiate the establishment of such direction of traffic he actuates the traffic lever 21FL (see Fig. l) to its righthand position. The actuation of contact 83 of lever 2-'IFL to its right-hand position opens an obvious circuit including wire 21 by which the relay ZWFR (see Fig. 2A) has been energized, but such relay is maintained picked up by its stick circuit The closure of contact 83 of lever 2-'IFL in its right-hand position through wire 28 causes the picking up of the relay IEFR.

(see Fig. 2D) by the energization of an obvious the transmission of a prolonged impulse such impulse being terminated after a time by the picking up of relay 'ITJS as controlled by the slowpick-up relay ITJ in a manner presently to be described. The circuit by which the relay 'ICP is picked up extends from including front contact 85 of relay 'IEFR, back contact 86 of relay ITJS, back. contact 81 of relay 'ITR, and winding of relay 1GP, to The closure of front contact 88 of relay ICP causes the track relay 6TB (see Fig. 20) at the left-hand end of track section 6'IT to be picked up by the energization of an obvious circuit closed at back contact 89 of relay'GCP. The picking up of re- "lay GTR opens the circuit by which the relay -6CP has been active for the transmission of a driven code from left to right in the track section 6-'IT at back contact 19, and thereby establishes a circuit by which the relay GTR is energized continuously until the termination of the prolonged impulse transmitted from the right-hand end of the track section.

At the time the relay IEFR is picked up at the right-hand end of the track section 6-1T for initiating the transmission of the prolonged impulse, a circuit is closed for the energization of the relay 'ITJ (see Fig. 2D) which is provided for measuring the length of the prolonged impulse by its slow pick-up characteristics. Such circuit is closed from including back contact 98 of relay 'ICR, front contact 9| of relay IEFR, back contact 92 of relay ITJS, and winding of relay 'ITJ, to The slow operation of relay 'ITJ can be provided in any suitable manner, such, for example, as by the use of a motor driven time element relay such as that disclosed in the O. S. Field patent, No. 2,199,335, dated April 30, 1940. After the relay 'ITJ has completed its time of operation, the closure of front contact 93 of such relay causes the picking up of the relay 'ITJS, and the picking up of such relay establishes a stick circuit by which it is maintained energized extending from including back contact 90 of relay ICR, front contact 9| of relay IEFR, front contact 92 of relay ITJS, and winding of relay 'ITJS, to The opening of back contact 92 of relay 'ITJS in the circuit for relay ITJ causes the restoration of relay 'ITJ.

Upon the picking up of the relay 'ITJS, the prolonged impulse is terminated by the opening of back contact 86 in the circuit for relay 'ICP,

andthe closure of front contact 86 of relay ITJS provides for the relay 'ICP to be active for the transmission of a 75 driven code (assuming the signal 8A to be at stop). The relay 'ICP is active for the transmission of the 75 driven codeunder such conditions by the energization of a circuit for such relay for each on period of the oscillator 15C extending from including front contact 85 of relay TEFR, contact 94 of oscillator 150, back contact 96 of relay BAG, front contact 86 of relay 'ITJS, back contact 81 of relay ITR, and winding of relay 1GP, to It has therefore been described how the relay 'ICP is active for the transmission of a prolonged impulse followed by a driven code upon the picking up of the relay lEFR for changing the direction of traific.

At the left-hand end of the track ction 6--'IT, the reception of the prolonged impulse causes the relay GFP (see Fig. 20) to be picked up by the closure of front contact 9'! of relay ETP, but because of the sustained energization of the relay BTP, the circuit for the relay BFBP is'maintained open at back contact 9'! to prevent such relay from being picked up. Conditions are therefore established for the picking up of the relay SEF'R by the energization of the circuit extending from including front contact 98' of relay GFP, back contact 99 of relay tFBP, and winding of relay EEFR, to The picking up of such relay opens the stick circuit by which the relay BWFR has been maintained picked up at back contact I00 to cause the dropping away of such relay. When the relay E'WFR is dropped away, a stick circuit is closed at back contact IIII to maintain the relay BEFR picked up. It will be noted from the pick-up circuit just described for the relay BEFR, that the picking up'of the relay EFBP upon the reception of the newly applied driven code at the end of the prolonged period of energization will open the pick-up circuit for relay GEFR at back contact 99.

Upon the picking up of the relay GFBP in response to the driven code transmitted from right to left in the track section 6'lT following the prolonged impulse a circuit is closed for the energization of the relay 6H extending from including front contact 91 of relay GTP, front contact I02 of relay BFBP, front contact I03 of relay BEFR, and winding of relay 6H, to Upon the picking up of relay 6H, an obvious circuit is closed for the energization of the yellow lamp Y of signal 6; such circuit having energy applied at front contact I04 of relay SEFR.

At the time when the relay BEFR, is picked up, a circuit is closed for the energization of the relay ECP for the transmission of a prolonged impulse in the track section 45T. Such circuit extends from including front contact I05 of relay GEFR, back contact I06 of relay BFBP, front contact IB'I of relay BFP, winding of relay 5GP, and back contact I38 of relay 5TB, to described that the prolonged period of energization of the relay SC? is terminated by the picking up of the relay BFBP in response to the newly applied driven code in the track section 6'IT. The picking up of such relay opens the circuit for relay 5GP at back contact I86 and closes a circuit by which the relay 5GP becomes active for the transmission of a 180 driven code in the track section 4-5T. Such circuit extends from including front contact I95 of It will be noted from the circuit just relay BEFR, contact I09 of oscillator I806, front contact III) of relay 6H, front contact Hit of relay GFBP, front contact IIlI of relay BFP, winding of relay 5GP, and back contact I08 of relay 5TH, to

At the left-hand end of the track section 45T, the reception of the prolonged impulse transmitted through such track section causes the picking up of the relay 4EFR (see Fig. 2B) in a manner similar to that which has just been described in connection with the picking up of the relay BEFR, and the picking up of such relay causes the dropping away of the relay 3WFR by opening its stick circuit at back contact I I I. The dropping of relay 3WFR closes the stick circuit for relay IEFR at back contact II2 to-complete the change in the conditioning of the traflic direction relays for that intermediate signal location. Upon the closure of front contact II3 of relay 4FBP in response to the newly established driven code, the relay 4H, is picked up, and the closure of front contact I I4 of such relay renders the pulsing of contact H5 of relay 4TP effective to cause the relay 4D to be picked up in response to the 180 driven code transmitted from right to left in the track section 4--5T following the prolonged period of energization of the track circult. When these relays have been picked up, an obvious circuit is closed for the energization of the green lamp G of signal 4 at front contact H6 of relay GEFR.

Upon the picking up of the relay IEFR, a cir:

cult is closed for the energization of the relay 3GP for the transmission of a prolonged impulse in the track section 23T corresponding to that which has been described in connection with the energization of the relay 5GP for the transmission of a prolonged impulse in the track section 45T, the impulse transmitted by the relay 3GP being terminated by the picking up of the relay AFBP when the newly established code is received at the left-hand end of track section 45T. When such code is received the relay 41-1 is picked up, and thus the relay 3GP becomes active for the transmission of a 180 driven code from right to left in the track section 23T by the energization of a circuit extending from including front contact In of relay iEFR, contact I I8 of oscillator I C, front contact II9 of relay 4H, front contact I20 of relay AFBP, front contact I2I of relay 4FP, winding of relay 3GP, and back contact I22 of relay STR, to

At the left-hand end of track section 23T, the energization of the relay ZTR (see Fig. 2A) during the prolonged impulse causes the dropping away of the relay ZFBP because of the failure to close a circuit for such relay at back contact I23 of relay ZTP. A pick-up circuit is then established for the relay 2EFR extending from including front contact I24 of relay ZFP, back contact I25 of relay ZFBP, and winding of relay ZEFR, to to cause such relay to be picked up, and by theopening of its back contact 4-0 to cause the release of the relay ZWFR.

- The dropping away of the relay ZWFR completes the conditioning of the trafiic direction relays for the establishment of east bound traffic. The pick-up circuit for relay ZWFR is open because of the right-hand position to which the operator has been assumed to have operated the traffic direction lever '2'IFL (see Fig. 1) at the control office.

The relay 2H (see Fig. 2A) is picked up in accordance with the closure of front contact I26 of relay ZEFR when the newly established driven code is received at the left-hand end of the track section 23T. In accordance with the closure of front contact I2'I of relay 2H, the pulsing of contact I28 of relay 2T? is effective to cause the picking up of the relay 2D by the energization of its circuit tuned to the 180 rate. With the relays 2H and 2D picked up, it will be readily apparent that conditions are established whereby signal 2A or signal 2B can be cleared by manual control upon the positioning of the signal control lever belonging to such signals at the control ofiice.

It will be noted that there is no inverse code transmitter at the left-hand end of the track section 23T, and therefore there is no inverse code transmitted from left to right in such section. Thus the relays 3FP, 3FBP, 3H and 3D (see Fig. 2B) are deenergized for east bound traffic, and the opening of front contact 56 of relay 3WFR causes the signal 3 to be dark.

The closure of front contact I29 of relay IEFR in the circuit for the primary winding of the transformer I33 renders the relay 40? active for the transmission of an inverse code from left to right in the track section 45T. The primary winding of such transformer is energized for each driven code impulse received by the relay 4TR by a circuit closed from including front contact I30 of relay 4TH, front contact I29 of relay 4EFR, and primary winding of transformer I33, to The back contact I3I of relay 3WFR is closed to connect the secondary winding of the transformer I33 across the winding of the relay 4GP to render such relay active for the transmission of an inverse code.

The reception of the inverse code at the righthand end of the track section 45T causes the energization of the relays FP and 5FBP (see Fig. 2C), but the relays 5H and 5D are deenergized becaus of the opening of the circuit for relay 51-1 at front contact I32 of relay SFWR. Because of the reception of the inverse code at the right-hand end of track section 45T, the relay 6GP becomes active for the transmission of an inverse code from right to left in the track section B'IT. Such inverse code is transmitted because of the energization of the primary winding of the transformer I34 for each driven code impulse received by relay BTR, a circuit for the primary winding of the transformer being closed each time the relay 3TB is picked up from including front contact I35 of relay 6TB, front contact I36 of relay BEFR, front contact I31 of relay SFBP, and primary winding of transformer I34, to

At the right-hand end of the track section 6-'IT, the reception of the inverse code causes the relays 'IFP and 'IFBP (see Fig. 2D) to be picked up, but the relays TH and ID are dropped away because the circuit for relay IE is open at front contact I38 of relay 'IWFR. The maintaining of the relay 'IFP picked up by the inverse code closes an obvious circuit at front contact I39 to maintain the approach relay 8AR, energized, and the energized condition of the relay IFBP because of the reception of a code holds the pickup circuit opened for the relay IWFR at back contact I40. It will be noted that the relay 8AR has been held up by its stick circuit for the duration of the prolonged impulse transmitted from that end of the stretch of track. Such stick circuit is closed upon the picking up of relay IEFR and extends from including front contact I4I of relay 'IEFR, back contact I42 of relay ITJS, front contact I43 of relay 8AR, and winding of relay 8AR, to Back contact I42 of relay 'ITJS is opened upon the termination of a prolonged impulse transmitted from that end of the stretch. Thus by this arrangement, in combination with relatively slow acting characteristics of the relay, the relay 8AR is deenergized only when either track section 45T or 6--IT is occupied by an east bound train.

Passage of a train-To consider the mode of operation of the system upon passage of a train, it will be assumed that the conditions of the system are initially as illustrated in Fig. 5A and as described when considering the normal conditions of the system, with traffic direction established for the passage of west bound trains. It will be assumed that a west bound train approaches the signal IA at the left-hand end of the passing siding B (see Fig. 5F), and that an operator at the control oflice actuates the signal control lever 'I8SGL (see Fig. 1) to its lefthand position to cause the clearing of such signal.

With the lever 'I-8SGL in its left-hand position, a circuit is closed at contact I44 to apply energy to wire 32 for the communication of a control to the field for causing the picking up of the relay ILGZ (see Fig. 2D). If such relay is picked up by a code communication system, the energization of the wire 32 for its pick-up circuit is only momentary, and a stick circuit is established for the relay in a manner fully disclosed in my prior application, Ser. No. 365,669, filed November 14, 1940.

. Upon the picking up of the relay 'ILGZ, a circuit is closed to cause the picking up of relay 'IAG extending from including front contact I45 of relay 'I-8TR,, front contact I46 of relay 3NCR, back contact I41 of relay 3RCR, front contact I48 of relay 'ILGZ, front contact I49 of relay 'IWFR, front contact I50 of relay 1H, and winding of relay 'IAG, to The picking up of relay 'IAG, by the shifting of contact I5I causes the extinguishing of the red lamp R of signal IA, and causes the energization of the green lamp G of such signal in accordance with the energized condition of the relay ID.

Upon accepting the signal IA, the entrance of the train into the track section I-BT causes the restoration of the signal to stop in the usual manner, the relay 'ILGZ being dropped away because of the opening of its stick circuit if the signals are controlled as stick signals as disclosed in my above mentioned prior application.

When the train enters the stretch of track between the passing sidings A and B (see Fig. 5A), there is no APB tumble-down to be effected because such condition has already been taken care of by the directional stick relays for th intermediate signal locations, the opposing signals being not only conditioned to display stop indications, but being dark as selected by the directional control relays.

When the west bound train progresses to a point, however, where it enters the track section 4-5T (see Fig. 51-1), the shunting of such track section causes the dropping away of the relays 4FP and 4FBP (see Fig. 2B) which have been held up by the inverse code, and the opening of front contact 59 of relay 4FBP in the circuit for the primary winding of transformer 51 renders the relay 3GP inactive for the transmission of an inverse code from right to left in the track section 23T.

The cessation of the inverse code in the track section 23T causes the dropping away of the relays 2F? and ZFBP (see Fig. 2A), and the dropping away of the relay 2FP causes the approach control relay I AR to be dropped away upon the opening of front contact I52. The dropping away of relay IAR closes back contact I53 to provide for the application of energy to wire 2| for the illumination of the approach indicator lamp IAK (see Fig. l) at the control olfice. The dropping away of the relay IAR opens the approach locking contact I54 (see Fig. 3) in the controlof the approach locking relay IAS associated with signals IA and IB. By such arrangement it is provided that the changing of the position of the track switch 2W can be eifectcd only after a predetermined time interval if a route has al-' ready been established over the track switch. This Is in accordance with the usual desired mode of operation in providing approach locking, the time interval being required only when the approach section is occupied by a train as detected by the approach relay IAR.

When the track section 6"IT becomes unoccupied' in the rear of the train, the transmission of a '75 driven code by the relay GOP is effective to provide a caution indication for the passage of a following train, dependent of course upon the' manual control of the signals IA and 1B.-

The circuit by which relay 6GP is energized for each impulse of the 75 code extends from including front contact I I of relay 5WFR, contact l55of oscillator 150, back contact I56 of relay FSFBP, back contact 18 of relay 5FP, winding of relay 6GP, and back contact 19 of relay BTR, to It will be noted that the usual type'of directional stick relay generally employed at intermediate signal locations is notrequired to select the transmission of the code for a following train, because the transmission of such code is rendered effective by the directional stick relay 5WFR which is a trafiic direction relay that is unaffected by thepassage of trains, such relay being controlled only by prolonged periods of energization of the track circuitinitiated by manual control from the'control office.

For the purpose of simplification of the disclosure of the present invention, details have not been shown for the control of the relays ID and IH for the main'track section IT associated with the passing siding A; however, it is to be under-' stood that such relays can be controlled either bycoded track circuits, as indicated in the drawings, or by line wire control, in accordance with the condition of occupancy of the'track section IT and'in accordance with the indication of the next signal-in advance. For convenience in the disclosure, itis assumed that coded track circuit control is provided for the sidin sections IT and BT, and although no efiort has been made to disclose such coded control, it has been assumed'to be of the type shown in my prior application Ser. No. 455,922, filed August 24, 1942, so as to facilitate the showing of the contacts of certain relays, such as relays IH, ID, 8H, 8D, required in the control of the signals illustrated in the present disclosure. In other words, the Figs. 2D and 2A placed side by side in that order with coded track circuit apparatus provided for the siding section (thus formed),'the same as the coded track circuit apparatus shown for the siding section in my above mentioned application provides a complete system within the scope of this invention. In this way, the signals I and '8 are properly interlocked and means is provided to. govern the approach locking relays ZAS and 'IAS of Fig. 3. It is thus believed to be sufiicient for the purposes of the present disclosure to know that the relays IE and 8H, corresponding to simi lar I-I relays in my prior applicatiomare normally picked up; While the relays ID and 8D, corresponding to similar relays in my prior application, are normally dropped away. Also; the clearing of the signal IA would effect thejdro'pf ping away of the relay 8H; and similarly, the clearing of the signal 8A would cause the drop? ping away of the relay II-l. More specifically, with the relay IH picked up, then the signal IA maybe caused to indicate caution which effects the dropping away of the relay 8H and ultimatly the picking up of. the relay ID dependent upon the indication of the signal 1A. It is thus un'; derstood how the relays ID and II-I may both be picked up. l i

Assuming the relays ID and IHto' be picked up, an operator at the control oilice can cause the clearing of signal IA and thus cause, the transmission of a 180 driVen code from leftto right in the track section 2+3T for the clearing of signal 3, if the signal control lever I'-2SGL relay IAG extending from including front contact I 51 of relay I -2TR, front contact I58 of relay 2NCR, back contact I59 of relay ZRCR,

front contact I60 of relay I LGZ, front contact? I 6| of relay IH, and winding of relay IAG, to The shifting of contact I62 of relay IAG.v

causes the extinguishing of the red lampR of signal IA, and causes the energization of the green lamp G of such signal with the relay ID' picked up. I

The picking up of the relay IAG with the re-i. lay IH picked up, by the shifting of contact 43 changes the driven code transmitted from left to' right in track section 2 -3T from a code to a .180 code. The reception at the right-hand end of the track section of the code causes the picking up of the relay 3D (see Fig. 2B), and the picking up of such relay upon the shifting of contact I63 causes the extinguishing of the yel; low lamp Y of signal 3and the energization of the green lamp'G of such signal. I N

As the westbound train progresses further so as to leave the tracksection 45T unoccupied in the rear of the train (see Fig. 5J), a 75 driven code is transmitted-by the relay ICP in the'track section 4 5T in accordance with the closureqf back contacts I64 and 66' of relays 3FBP and- 3FF respectively. At theright-hand end of the tracksection 45T the conditions are restoredto normal except for the relay 5D (see Fig. 20)

which remains deenergized because of the 75 code being received, such relay in'its deenergized condition selecting the energization of the yellow lamp of signal 5. The picking up of relay 5H incombination with the picking up of, relays 5FBP and 5FP closes a circuit by' which therelay BCP is active for the transmission of a 180 driven code in the track section 6 '1T to'lrest'ore'the normal conditionsfor such track section.

Further progress of the westbound'train into' the track section IT allows restoration to stop of the signal IA, and, when the track section 2'-3T becomes unoccupied in the rear of the train, the; normal conditions of code, transmission are restored for such track sectionby the energization of circuits which have been described when considering the normal conditions of the system. The reception at the right-hand end of the track section 2-3T of the 75 code causes the restoration to normal conditions at the intermediate signals 3 and 4 to provide for the transmission of a 180 driven code in the track section 4-5T for causing the illumination of the green lamp of signal 5, thus completing the restoration to normal conditions after the passage of the train, as indicated in the diagram of Fig.

' Back-up train mooements.A desirable feature of the present invention lies in the provision for back-up train movements, particularly in that the intermediate signals are subject indirectly to manual control of an operator at the control office for making such back-up train movements possible. To consider specifically a typical condition, it will be assumed that a west bound train has occupied the track section 4.5T, and the track section 61T has become unoccnpied in the rear of the train (see Fig. 5H)

It has been described that under such conditions 3. '75 driven code is transmitted from left to right in the track section 6-'IT in accordance with the energized condition of the trafilc direction relay SWFR (see Fig. 2C) at the intermediate signal location. Because of the deenergized condition of the traffic direction relay BEFR, the signal 6 is dark in accordance with its circuit having been opened at front contact I04. Under such conditions it will be assumed that an operator desires to cause the train to proceed in the direction of the passing siding B. The conditions involving the reversal in the direction of trafiic in accordance with the regulations of the railroads as to the communication between the trainman and the operator at the control office would necessarily be complied with; but, the extinguishing of the approach indicator lamp 8AK (see Fig. l) on the control panel at the control oflice would indicate to the operator that the track section 6'|T were unoccupied in the rear of the train, and thus it would be possible to control the signal 6 for a back-up train movement.

To cause the signal 6 to display aproceed indication for a back-up train movement and set up conditions indicated in Fig. 5K, it will be assumed that anoperator actuates the lever 2-1FL on the control panel to the right-hand position for the establishment of east bound traffic. In accordance therewith, the contact 83 of the lever 2-1FL applies energy to wire 28 to cause the picking up of the relay 'IEFR (see Fig. 2D) at passing siding B. The picking up of such relay causes the dropping away of the relay 'IWFR by opening its stick circuit at back contact 84, and the dropping away of relay 'IWFR establishes a stick circuit for relay 'IEFR closed at back contact I65. It will be readily recognized that this is the beginning of a cycle of operation corresponding to that which has been described when considering the mode of operation of the system upon changing trafiic direction during which a prolonged impulse is transmitted in the track section 6-'IT, followed by the transmission of a 75 driven code (assuming signal 8A to be at stop).

The reception of the prolonged impulse at the left-hand end of. the track section B1T causes the picking up of the relay BEFR, and the dropping away of relay EWFR, and the relay 61-1 is picked up by the '75 driven code which follows the prolonged impulse. Upon the picking up of relay 6H, an obvious circuit is closed at front contact I66 for the energization of the yellow lamp of signal 6 to display a caution indication for a back-up train movement. Front contact I04 is closed because of the response of the relay GEFR to the long impulse transmitted through the track rails.

It is believed to be readily apparent that the signal 6 could be controlled to display a clear indication in accordance with the transmission of a 180 driven code from right to left in the track section 6-IT if the signal 8A were controlled to indicate proceed. It will be noted at this point that the system is adapted to allow the control of signals for back-up train movements either with or without controlling the signals at the ends of the stretch of track.

Correspondence of trajfic direction relays.- There are certain conditions when the traflic direction relays for the respective signal locations become out of correspondence with each other. One condition is that just described above where the control of signals for back-up train movements is provided. Under such conditions, when the stretch of track becomes unoccupied after passage of. a train, the trafiic direction relays for certain of the signal locations, particularly the locations for the extreme ends of the stretch of track, are out of correspondence; and therefore driven codes are transmitted through the respective end sections in the direction of the intermediate track section 45T.

Upon considering the circuits for the traffic direction relays EFR and WFR for the field stations at the ends of the stretch of track between the passing sidings A and B, it will be noted that a change in the condition of the trafiic direction relays can be accomplished only by the transmission of a prolonged impulse through the track rails. Thus, to restore the trafilc direction relays in correspondence for the establishment of a particular direction of trafiic, the traflic direction lever 2--1FL (see Fig. 1) at the control ofiice is positioned as desired, and the traific correspondence button 2'|CB is depressed. The depression of such button applies energy to contact I61 of lever 2'lFL, and if the lever is positioned for west bound trafiic, energy is applied to wire 26 for the communication of a control to cause themomentary energization of the relay ZCR. at the field station associated with passing-siding A.

The picking up of relay 20R, under such conditions, opens the stick circuit for relay ZTJ S at back contact I68 to cause such relay to be dropped away. The stick circuit by which the relay ZTJS has been energized corresponds to the stick circuit which has been described for relay ITJS at the opposite end of the stretch. With relay ZTJ S dropped away, a circuit is closed at back contact 44 to energize the relay 2GP for the transmission of a .prolonged impulse. Because of the relay 205. being only momentarily picked up, the closure of back contact I68 of such relay establishes a circuit for the slow pickup relay ZTJ for measuring the length of such prolonged impulse, such circuit corresponding to a circuit which has been described for relay lTJ at the opposite end of the stretch.

Upon the reception of the prolonged impulse at the right-hand end of track section 23T, the traiiic direction relays 3WFR and AEFR are reversal in trafiic direction, unless they are already in correspondence with the relays at the right-hand end of the stretch of track. After the traffic direction relays have been properly conditioned at the intermediate signal location of signals 3 and 4, a prolonged impulse, followed by a driven code is transmitted in the track section 4--5T, and in each other track section successively until the traffic direction relays for each of the signal locations are conditioned to correspond with the traffic direction relays at the lefthand end of the stretch of track.

Another condition under which a similar mode of operation would be required for the establishment of correspondence between the traffic direction relays would be a condition where an operator inadvertently moved the traffic direction lever 2-'IFL when the stretch of track between the passing sidings A and B were occupied by a train. Under such conditions, the system would attempt to change direction for each track section successively in the rear of the train, but at some point the prolonged impulse would lose out because of failure to transmit under the train. Thus, when the track section would become unoccupied after passage of the train, whether such train had reversed its direction or not, some of the trafiic direction relays for the stretch would be out of correspondence. It will be readily apparent that the remedy for such a'condition is to select the desired direction of traffic by the lever 2'IFL as has been described and depress the correspondence button 2'ICB.

Approach Zoclcing.The system according to the present invention is adapted by the use of inverse code to provide for approach control in connection with the signals governing entrance to the respective siding sections, such control extending for two track sections in the rear of such entering signals. As for the circuits involved in the control of the approach locking relays AS associated with the respec-' tive oifice controlled signals at the field stations, it is to be understood that various forms of control can be provided in accordance with the requirements of practice, such forms being wellknown to those familiar with the art.

One form is illustrated, for example, in Fig. 3

7 or signal IB would cause the dropping away of relay IM, and the dropping away of such relay would cause the release of the relay IAS because of the opening of front contact I69.

Upon the manual restoration of either signal IA or signal IE to stop before such signal has been accepted by a train, the relay IM becomes energized to close front contact I69 in the circuit of relay IAS, and the relay IAS can be picked up immediately if front contact I54 of the relay IAR is closed, such circuit extending from including front contact I69 of relay IM, front contact I 54 of relay IAR, and windin of relay IAS, to The relay IAR (see Fig. 2A), however, can be energized only if the track sections 2-3T and 45T are unoccupied by a west bound train. Thus, upon the entrance of a west bound train into the track section 4-5T, the inverse code would be removed from the track sections 4-51 and 2--3T, and the v 1-1- a removal of such code by causing the dropping the circuit for relay IAR at front contact I52, I

thus causing such relay to be dropped away. In accordance with the opening of the approach control restoration circuit for relay -I AS (see Fig. 3) at front contact I54 of relay IAR, the restoration of relay I AS could be effected only after a predetermined time measured by the thermal relay ITH, such thermal relay being energized by a circuit extending from including front contact I69 of relay IM, winding of thermal relay ITH, and back contact III) of relay IAS, to At the end of such predetermined time, the relay IAS would be picked up by a circuit extending from including front contact I69 of relay IM, contact I13 of thermal relay ITI-I closed in its operated position, and winding of relay IAS, to The picking up of the relay IAS under such conditions would open the circuit by which the thermal relay ITH is active at back contact I10, and closea normally energized stick circuit Which has been described. When the signal IA or IE is put to stop automatically upon passage of a train past such signal, the closure of back contact I14 of the OS track relay I2TR causes the immediate restoration of the relay IAS by the energization of an obvious circuit which is closed upon the restoration of the .relay IM to its normally ener gized position.

The approach locking relays in this'disclosure have their contacts including directly in the switch machine operating circuits as illustrated in Fig. 4, but it is to be understood that they could as well be included indirectly through the medium of a lock relay in accordance with the requirements of practice. It will be noted in Fig. 4 that the relay IAS, for example, has front contacts I11 and I18 included in the normal and reverse control circuits respectively of the switch machine ZSM for the power operation of the track switch 2W.

Having thus considered specifically the conditions with respect to the approach locking for a particular one of the manually controlled signals at a field station, it is to be understood that the conditions described are typical of those conditions associated with the approach locking provided for the other manually controlled signals disclosed in this embodiment of the present invention.

Indications.-The relays IAR" (see Fig. 2A) and BAR (see Fig. 2D) for the respective left and right-hand ends of the stretch of track between the passing sidings A and B are also employed in' the provision of approach indications at the control office, such relays being energized except when their respective approach sections are occupied by a train proceeding in either direction. Thus, the relay IAR, for example, beingdependent for its energization upon the reception of code transmitted from right to .left in the track sections I-5T and 23T, is dropped away whenever either of such track sections are occupied by a, train proceeding in the direction of the passing sidin A. In accordance with the deenergization of the relay IAR, the closure of back contact I53 applies energy to wire 2I for communication of a control to the control office for causing the energization of the indicator lamp IAK (see Fig. 1).

'If the track section 23T were occupied by an east bound train, the 'relay' 2FP would be dropped away, and the opening of front contact [52 under such conditionswould cause the closure of back contact I53 of relay IAR for the communication of a control over wire 2| to the control ofiice for the energization of the approach indication lamp IAK. If an east bound train were to proceed so as to cause the track section 2--3T to become unoccupied by the train; however, the transmission of a 75 code from right to left in the track section 2--3T as selected by the energization of the relay 4EFR (see Fig. 2B) to close front contact ill in the circuit for relay 3CP would cause the picking up of the relay ZFP (see Fig. 2A) at the left-hand end of the track section, and the picking up of that relay upon the closure of front contact I52 would cause the energization of the relay IAR for the extinguishing of the lamp IAK in accordance with the opening of back contact I53. It will therefore be seen that the indicator lamp IAK, for example, is illuminated whenever a west bound train occupies either track section 45T or track section 23T, but is illuminated upon the passage of an east bound train only when such train occupies the track section 2-3I A stick circuit is provided for the relay IAR and for the relay BAR to prevent the illumination of the respective approach indicator lamps IAK and BAK at the control ofiice momentarily upon the changin in traflic direction through the stretch of track between the passing sidings A and B. The manner in which such stick circuit is employed has been described in detail with respect to the control of the relay BAR when considering the mode of operation of the system with respect to reversal in the direction of traffic.

It will be noted in Fig. 1 that in addition to the approach indicator lamps, OS indicator lamps I2TK and l8TK are provided in the manner commonly employed in practice to indicate occupancy of the respective detector track sections.

The trafiic direction lamps 2-1WFK and 2-1EFK provided at the control ofilce for indicating the direction of traflic established in the stretch of track between the passing sidings are governed in accordance with the conditions of the traffic direction relays for the respective ends of the stretch of track between the passing sidings. Thus, the lamp z-JWFK is normally illuminated because of the closure of front contact I75 of relay 2WFR (see Fig. 2A) to apply energy to the wire for communication to the control office for the energization of that lamp. Upon changing trafiic direction, the operation of the lever 2-lFL to its right-hand position by an operator would cause the picking up of the relay 'IEFR (see Fig. 2D) in accordance with the application of energy to wire 28 in a manner which has been described, and the picking up of such relay would close front contact I16 to apply energy to wire 30 for the communication of a control to the control ofiice for the energization of the traffic direction lamp 2-1EFK (see Fig. 1). Under such conditions both trafiic direction lamps will be momentarily illuminated as the extinguishing of the lamp 2-1WFK is dependent upon the dropping away of the relay ZWFR to open its control circuit at front contact I15. The dropping away of the relay ZWFR upon changing the direction of traffic as above assumed, could be effected only after the transmission of an abnormally long impulse through the track sections of the stretch successively, starting at the right-hand end of the stretch, so as to cause the'picking up of the relay ZEFR. (see Fig. 2A), the picking up of which would be effective to open the stick circuit for the relay ZWFR at back contact 40 and cause the release of. that relay. The release of relay ZWFR would open front contact I15, and thereby cause the extinguishing of lamp 2--lWFK through the medium of a communication system.

From the mode of operation which has just been described with respect to the control of the traffic direction indicator lamps, it is believed to be readily apparent that the operator is kept well informed as to the condition of the trailic direction relays in the field under all conditions, even under conditions involving back-up train movements. When back-up train movements are involved, the energization of both indicator lamps 2-'IWFK and 21EFK at the control office indicates an out-of-correspondence condition of the traffic direction relays for the respective ends of the stretch of track, and in accordance with such indication, it is brought to the attention of the operator that he must depress the cancel button 2--1CB after the stretch of track has become unoccupied to cause the reestablishment of a single direction of traflic through the stretch as selected by the position of the traffic direction lever 2'IFL.

From the description as it has been set forth it is believed to be readily apparent that the system is symmetrical in its operation for both directions of traflic, and it is therefore to be understood that the apparatus and mode of operation described specifically with respect to one direction of trafiic are typical of similar conditions for the opposite direction of traffic.

Modifications-It is to be understood that the system can be modified from that which has been described in that the means for governing the trafiic direction relays manually can vary to considerable extent in accordance with the requirements of practice. In some cases it may be desirable to control the traffic direction relays at 0 the respective field stations by a code communication system such as shown, for example, in the patent to Judge et al., No. 2,082,544, dated June 1, 1937; by direct wire control, where the control ofiice is relatively close to the field stations; or by direct lever control of the manually controlled traffic direction relays for the respective field stations where an operator is present at each end of the stretch of track as could well be the case if the stretch of track were to extend through a tunnel, or over a bridge, with an interlocking plant at each end thereof. Under the last named condition, the track layout and the control of the signals at the respective field stations would necessarily be modified. The traflic direction relays upon control from the control office would be energized'directly from a trafiic control lever, and the back contact of the relay OR at each of the field stations would be replacedby a normally closed contact of a correspondence button CB. By such an arrangement it would be required that the operators'at the respective ends of the stretch of track communicate with each other by telephone in order to most eilectively control the direction of trafiic in order that their traflic direction levers could respectively be maintained on correspondence with each other.

Another manner in which the traflic control system provided by this invention can be modi-

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