US2269292A

US2269292A - Railway traffic controlling apparatus

Info

Publication number: US2269292A
Application number: US348423A
Authority: US
Inventors: Crawford E Staples
Original assignee: Union Switch and Signal Inc
Current assignee: Hitachi Rail STS USA Inc
Priority date: 1940-07-30
Filing date: 1940-07-30
Publication date: 1942-01-06
Anticipated expiration: 1959-01-06

Description

Jan. 6, 194-2.

c'. E. STAPLES 2,269,292

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed July 30,-1940 5 Sheets-Sheet 1 INVENTOR HIS A'TTORNEY Jan. 6, 1942.

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Patented Jan. 6, 1942 UNITED STATES PATENT. OFFICE Appl ca ion J uly 30, 4:0,1Ser a No. .3i rl23.

'13 Glaims.

My inven ion relates to railway trafi o coir trolling apparatus, and more particularly to apparatus for railway si al systems using coded energy of the time code typ Signal systems usin ooded enej y having a cy l c pattern consistin of on on and one off" period of preselected durations have been pro posed. A plura ity of diiiferent codes, re pro vided y selecting different absolute and relati durations ior the on and. off periods. In such im ode systems the d coding means is mad ing sensitivity and low ower consumption, 1

Accordingly, a feature, of my. invention is the provision of novel and improved apparatus for providing a signal system with a plurality of different time codes which have a uniform on period and ofi periods of difierent lengths ordurations. A further feature of my invention is, the provision of novel and improved apparatus for a time code signal system wherewith recurrent impulses of direct current arranged in different codes are used with the di-fiierent codes differently constituted by separating the successive impulses of direct current by intervals of different lengths,

the length of the interval being predetermined and distinctive for each code.

Another feature of my invention is the provision of novel and improved decoding means for a signal system of the type here contemplated.

Again a featureof my invention is the provision of novel means for creating'different time code patterns. I i 91 Again a feature of'my invention is the provision of novel and improved apparatus for a fourblock five-indication signal system for railways and which apparatus may readily be modified to 'Di' idde a three-blockiour indication signal sys-' '01" a two-block threeiindication signal systent with additional codes available for special control purposes.

The above ieatures of my invention as well f other advantages which will-become apparentas the specification progressesare attained by us of a code. transmit ing means" operative to a divide in o di fe ent code pat erns whic "have a uniform on period and differentlengths of off periods the il pe iods b in preferably va ied in s eps of equ increments .of time. Th i to sa the oil p r od of each cod is ma up o a p eselected number of the pr determined unit or time. To effect uch .oode pat erns th ode transm tin means includes one or m conta t m mbers operative to open and cl s a circuit at di ferent recurrent intervals, hi h intervals are tim spa ed by o e or more un of time of prede e mi d du ation, Thu the difl'lerentcodes hear .a predetermin d relationsh p with respect to each other. .As stated o h e fo e, th on period or all the v d s s e abl uni orm. For exam le, a motor pe a d ode. transmitter may he provided wi c proportioned o yclical y ope ate r sp ct v c tact members to effect the fierent o patte ns. or scillating code trans it rs dju e for pr de ermined osc ation p ds m y b u ed.-

In one .form, of the inventi n a sing tuned oscillator efiects several different code patterns through the m d um o .a hain of r lay Th .ciropits for the relay hai are rr e so that the relays are con ecutively ope a i a. cyclic ma ner a lon v a the o c l at r is act v h last re ay o the re ay c ai when operat d eith interrupts. or closes a circuit by which current is supp ed to transm ttin circu th as track circuit of a railway track section. Hence current is periodically supplied to such track cird t at in erva s spaced a t a co g t h nuinber of relays .of the relay chain used to form the cyclicoperation. Since the relays are consecutiyely operated one, relay each half cycle of the oscillator, the oil period between successive on periods of the track circuit current is made up or .a predetermined number of half cycles of the oscillatorand hence is made up of a predetermined number of units of time Which unit of time is equal, to, a half cycle operation of the oscillator. The odd numbered relays of v the relay chain are controlled by traffic conditions in such a manner that the odd numbered relay at which the cycllcoperation of the relay chain 'is started is different for each of the different tralfic conditions with the result that the number of relays to be consecutively operated before the last relay is operated to supply current to the track circuit is different for eachof the difierent trafiic conditions. In this manner the ofi period of the coded track circuit current .is made up of a distinctive number of time units chain is substantially the same under all conditions, the on period of the different codes is uniform. It follows that each of the different traffic conditions is reflected by a different code pattern of the track circuit current, all the codes having the same on period but with off periods of different lengths.

When recurrent impulses of direct current are used the contact member of the coding transmitting means, such as the last relay of the relay chain, interrupts a circuit by which direct current is supplied to the winding of a reactor having a magnetic core in which magnetic energy is stored when current flows in the reactor winding. Another winding, or a portion of this same winding of the reactor is connected across the rails of the track section. The parts are so proportioned that when the reactor circuit is closed and direct current flows in the reactor winding the magnetic energy builds up in the core relatively slow and little or no electromotive force is induced in the winding connected across the track rails but that when the reactor circuit is interrupted the magnetic energy stored in the reactor core dies away rapidly and a relatively large electromotive force is induced in the winding connected across the track rails and an effective current impulse flows in the track circuit. Since the circuit characteristics of the track circuit remain the same for all traffic conditions except for ballast conditions, the impulses of direct current are substantially uniform in duration for all of the different traffic conditions, but the interval between successive impulses of current is varied according to the manner in which the code transmitting means is controlled by traffic conditions. Consequently, the impulses of direct current supplied to the track circuit are formed into different codes which distinguish from each other by the different duration or length of the intervals between successive impulses.

A code following track relay is connected to receive energy from the transmitting or track circuit and is operated to one position when energized during each on period of the coded current and is operated to a second position when deenergized during each off period of the coded current. To detect the character of the coded current I preferably provide a group or series of code following repeater relays which are arranged to be sequentially energized over first and second position contacts of the code following relay. Each such repeater relay is proportioned for a predetermined slow release period, the slow release period being preferably the same for all the repeater relays and made of a duration that bears a predetermined relation with respect to the unit of time used in determining the off period of the different codes. In this way the repeater relays are cyclically operated in a specific manner for each of the different codes. That is to say, the number of repeater relays operated and the cyclic operation thereof depend upon the duration of the off period of the coded current because of the definite relationship between the slow release periods of the repeater relays and the duration of the off periods of the code in respect to a predetermined unit of time.

The repeater relays together with the code following track relay govern slow acting decoding relays according to the cyclic operation of the repeater relays and hence such decoding relays are selectively controlled according to the different code patterns of the coded track circuit current. The decoding relays are used in turn to selectively govern the operating circuits of a signal capable of displaying a distinctive indication for each one of the different codes. The decoding relays associated with one track circuit are also used to selectively determine the code pattern of the current supplied to the track circuit for the section next in the rear.

I shall describe two forms of apparatus embodying my invention and shall then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing one form of apparatus embodying my invention when used for a four-block five-indication signal system for railways. Fig. 2 is a diagrammatic View showing a second form of apparatus embodying my invention when used for a four-block five-indication system for railways. Figs. 3a, 3b, 3c and 3d are diagrams illustrating the operation of the relays of the receiving apparatus of Fig. 1 in response to four different codes. Fig. 4 is a tabulation of the positions of the several relays of the receiving apparatus of Fig. 1 under the four different codes, together with the signal aspect effected and the code transmitted in response to the respective position of the decoding relays. Fig. 5 is a diagram illustrating a first, a second, a third and a fourth code pattern that may be effected by the apparatus of Fig. 2.

In each of the several views like reference characters are used to designate similar parts.

It is to be understood of course that my invention is not limited to a four-block five-indication signal system for railways and this one use serves to illustrate the many places where apparatus embodying my invention is useful.

Referring to Fig. 1, the reference characters la and lb designate the track rails of a stretch of railway over which traffic normally moves in the direction indicated by an arrow and which rails are formed by the usual insulated rail joints into consecutive sections of which sections only one section WX and the adjoining ends of the two adjacent sections are shown for the sake of simplicity, since these are sufficient for a full understanding of my invention. Each track section is provided with a track circuit of which the track circuit of section WX is typical of all. The track circuit of section WX includes a source of coded current connected across the rails at the exit end X of the section, and a code following track relay connected across the rails at the entrance end W. The means for supplying coded current to the track circuit of section WX includes a reactor TX and a battery XB, together with codetransmitting apparatus associated with the section next in advance'and to be referred to hereinafter. Reactor TX comprises a winding 10 mounted on a magnetizable core II. A portion of winding I 0 is connected across the rails of section WX over wires l2 and I3 and the full winding I0 is connected to battery XB over a reactor circuit controlled by the code transmitting apparatus for the section next in advance of section WX in a manner to later appear, the circuit being periodically interrupted to form different code patterns in response to different trafiic conditions. When the reactor circuit is closed direct current flows from battery XB to winding ID to energize that windingand cause magnetic flux to be stored in magnetic core I I; When the reactor circuit is intervan 8 8.

rupted, the flowv of current ceases and the magnetic flux dies away. The parts are so propornected across'the. rails and a current impulse of relatively large magnitude is caused to fiowin the track circuit. The duration of this current impulse is relatively short and is determined by the circuit characteristics of the track circuit. Hence different codes for the track circuit current of section WX can be effected by varying the interval between the recurrent interruptions of the reactor circuit, the on period, that is, the duration of the current impulse being substantially uniform under all codes. A condenser [4 may be connected across winding it of reactor TX to improve the operation.

At the upper' left-hand portion of Fig. 1 is shown a reactor TW having a portion of its winding 15 connected over wires l6 and H to the rails of the section next in the rear of section WX for supplying current to the track circuit of the section next in the rear. Winding l of reactor TW is connected to a track batteryWB over a reactor circuit controlled by code transhermit] iscperated to alternately engage and disengage a'contact lMa to effect a second code pattern which consists of an on period the same as that of the first code pattern and an off pev riod of three. units of time in length. In like manner, contact member I02 is operated to alternately engage and disengage a contact [02a to 3 effect a third code pattern having an on period the same as that of the first and second code patterns and an off period of two units of time in length, and contact member |03-.is operated to engage a contact 103a to effect a fourth code pattern having an on period the same as the other three code patterns and an ofi period of one unit of time, in length.

Under a first trafiic condition of section W relays H, D and DD of the decoding means, to be fully described hereinafter, are all released and a reactor circuit can be traced from battery WB over contact IUD-H1011 of codetransmitter CT, back contact 33 of relay H, winding [5 of reactor TW and to battery WB. Current flowing in windmitting means associated with the track section WX. In other words, impulses of direct current are supplied to the track circuit of the section next in the rear through reactor TW controlled by apparatus associated with section WX in the same manner current impulses are supplied to the, track circuit of section WX through reactor TX under the control of the code transmitting apparatus of the section next in ad- Hence a description of the code transmitting apparatus associated with section WX for coding, the current supplied to the track circuit for the section next in the rear will serve to describe the apparatus and manner wherein current impulses are supplied to the track circuit of section WX.

The coding transmitting means may take different forms, there being several well known to the art. In Fig. 1 a code. transmitter CT of the 'motor operated type is provided with four .code

contact members I00, Hil, I02 and I03, each of which contact members is cam operated at a distinctive operation cycleaslong as the motor element 164 of. the code transmitter is supplied with current from any convenient source, such stantially four such units of time in duration.

That is to say current flows (on period) for an interval not greater than. one predetermined unit of time whil the interval between successive impulses of current (off period) is substantially four such units of time in length. Contact meming I 5 of the reactor causes magnetic flux to be built up in magnetic core 23 of the reactor. When contact HID-l0fla is opened the flow of current ceases in winding l5 and the magnetic flux of core 23 dies away. The reactor and track circuits are so proportioned as to their time constants that'the magnetic flux builds-up in core 23 relatively slow and little or no electromotive force is inductively applied to the track circuit from windrapidly and an electromotive force of relatively high voltage is induced in winding [5, causing an effective impulse of direct current to be supplied to the associated track circuit; The duration of such-impulse of direct current is relatively short and is determined by the track circuit characteristics, and furthermore the duration of such impulse is not greater than the assumed unit of time. It follows that under the first traflic condition of section WX the track circuit current of the section next in the rear of section W- x is coded according to a first code pattern wherein an impulse of current of a duration not greater than one predetermined unit of time flows during each on period and the off period of the code is substantially four such units of time in length.

Under a second trafiic condition of section WX, relay H is picked up and relays D and DD are released, and the reactor circuit includes contact 0-l-l'0|a of coder CT, back contact 30 of relayD and front contact 48 of relay H. When contact I'M-40m is closed, current flows in winding 15 and magnetic flux is stored in core 23 and when contact l0ll0la is interrupted an effective impulse of current is supplied to the associated track circuit. The current impulse is of the same duration as before and the off period of the code is of three units of time in duration due to the operation cycle of contact member lll l of coder CT.

Under a third traffic condition of section W--'X. relays H and D are picked up and relay DD is released and the reactor circuit. includes contactlll2-l02a of coder CT, back contact 21 of relay DD and

front contacts

49 and 48 of relays D .and H, respectively. Again magnetic flux is built up in core 23 of reactor TW when the reactor circuit isc losed at contact NIL-M212, and an :eitective current impulse is supplied to the respective track circuit when contact I02|02a is opened and the magnetic flux in core 23 dies away. Under this third code the current impulse is of the same duration as before and the off period consists oftwo units of time in length due to the cyclic operation of contact member I02.

Under a fourth traffic condition of section WX relays H, D and DD are all picked up and the reactor circuit includes contact Ill3|03a of coder CT and

front contacts

50, 49 and 4B of DD, D and 1-1, respectively. Each time. contact lfl3lll3a is opened and the current flowing in reactor winding I5 is interrupted an effective current impulse is supplied to the associated track circuit, the current impulse being of the same duration as in the previous codes but the off period being of one unit of time in length. It is to be seen that each of the four different trafiic conditions of section WX is reflected by current impulses of four different code patterns, being supplied to the track circuit of the section next in the rear of section WX, the current impulses being of the same duration for all codes while the off periods are of different lengths based upon the operation cycle of the o different contact members of the code transmitter.

As will appear hereinafter, relays H, D and DD are all released to effect the first or approach code pattern of the track circuit for the section next in the rear when section WX is occupied. Relay H is energized and relays D and DD are released to effect the second approach slow code pattern for the track circuit current impulses for the section next in the rear when section WX is unoccupied and. the section next in advance is occupied. Relays H and D are picked up and relay DD is released to effect the third or approach medium code when section WX and the section next in advance are unoccupied and the second section in advance of section WX is occupied. Again, relays H, D and DD are all picked up to effect the fourth or clear code when section WX and the first two sections in advance are all unoccupied.

A code following track relay CF has an operating winding 54 connected across the rails of section WX over

wires

55 and 56 for operation of the relay in response to the coded track circuit current, the arrangement being such that contact members 5'! and 58 of relay CF are raised to engage

front contacts

59 and 60, respectively, when current flows in the track circuit and winding 5A is energized, and

contact members

51 and 58 are released to engage respective back contacts SI and 62 when no current flows in the track circuit and winding 54 is deenergized. To improve the operation of relay CF and slightly prolong the period its front contacts are closed in response to an impulse of track circuit current, a condenser 63 is preferably charged over back contact 5l.6l of the relay and is connected to a lower winding 64 of the relay over front contact Ell-59 to prolong the energization of the relay by the discharge of condenser 63. It is clear, however, that condenser 63 and the winding 64 of relay CF may not be needed and may be omitted.

Code following relay CF operates a series of three code following repeater relays TPI, TP2 and TF3, each of which is provided with a slow release period, preferably of the order of two units of time as used to determine the off period of the different codes. These three repeater relays, together with code following relay CF govern four decoding relays H, D, DD and DDD in accordance with the code of th track circuit current, relay H serving as a code detecting or check relay. The decoding relays control the operating circuits of a wayside signal WS for governing traffic through section WX, signal WS being of any one of the standard types of wayside signals and here shown as a color light signal capable of displaying five different signal aspects. Relays H, D and DD are also used to govern the code pattern for the track circuit current for the section next in the rear of section WX in the matter explained hereinbefore. It is believed that the manner of controlling repeater relays TPI, TPZ and TF3, together with the manner of controlling the decoding relays can best be understood from a description of the operation of the apparatus in respect to the different trafiic conditions.

Assuming first that section WX is occupied causing the track relay CF to be shunted and inactive, the repeater relays TPI, TH and TF3 are inactive and relays H, D, DD and DDD are deenergized and released as indicated at the first column at the left in Fig. 4. Under this condition of the relays, two signal operating circuits are formed, one suchcircuit including terminal B, back contact 65 of relay H, lamp R of a top group of lamps of signal WS and terminal C; and the other circuit including terminal B, back contact 66 of relay D, lamp R of a lower group of lamps of signal WS and terminal C; and signal WS is caused to display a red light over a red light for a stop signal indication. As explained hereinbefore, current of the first code is transmitted to the track circuit for the section next in the rear when the three relays H, D and DD are released.

Assuming next that the train in section WX advances to the right to vacate section WX and occupy the section next in advance, the track circuit current of section WX is coded at the first code, it being recalled that the code transmitting means for the section next in advance controls the current supplied from battery XB to winding IU of reactor TX in the same manner the code transmitting means of section WX controls the supply of current of battery WB to winding l5 of reactor TW. When current of the first code is supplied to the track circuit of section WX, relay CF is correspondingly operated, the interval relay CF is retained picked up being slightly greater than the duration of the current impulse and substantially one unit of time due to the action of condenser 63 and the lower winding 64 of relay CF. The operation of code following relay CF is diagrammatically illustrated by the top curve in Fig. 3a, the raised portions of the curve indicating the periods the relay CF is picked up and the depressed portions of the curve indicating the periods the relay is released. Thus, when a section immediately in the rear of an occupied section as illustrated by the heavy line in the track diagram at the top of Fig. 3a is supplied with current of first code the associated code following track relay CF is picked up for substantially on unit of time and is released for substantially four units of time due to the off period of the code. Starting with repeater relays TPl, TF2 and TF3 released, on the first on period of code following relay CF current flows from terminal B over front contact 586ll of relay CF, back contact 61 of relay TP2 and winding of relay TPI to terminal C, and relay TPI is picked up. At the first off periodof code following relay CF, current flowsfrom terminal C over back contact 58*52' of relay CF, back contact 68 of relay TP3,.front contact 69 of relay TPI. and winding of relay TP2 to terminal C, and relay TP2 is picked up. Since the off period of the code is of the orderof four units of time and relays TPI and TPZ are provided with slow release periods substantially equal to two units of time, these relays are sequentially released during-this first off period so that at the next on period of code following relay CF and front contact 58-60 of the relay is closed, relay TPI is picked upas before to start v a new cyclic operation of the relays TPI and TPZ, relay TPZ being again picked up at the beginning of the second off period of the code fol.- lowing relay. With the two repeater relays TPI and TP2 thus cyclically operated in response to this first code, the third repeater relay TP3 re mains deenergized and released. When repeater relay TPI is picked up closing front contact 10, current is supplied to the primary winding ll of a transformer T2, the circuit also including back contact 12 of repeater relay TF3, as will be apparent from an inspection of Fig. 1. This surge of current in primary winding "of transformer T2 induces an electromotive force in secondary winding 14 of that transformer, which second ary winding is connected to the winding of relay a H through a rectifier 15. Hence relay H is effec supplied thereto, and hence remains picked up as long as the code following relay CF is operated at this first code. The decoding relays D, DD

and DDD remain deenergized and releasedunderthis first code.

Referring to'Fig. 3a, the operation of repeater relays TPI andTPZ', and code detecting .relay H in response to operation of relay CF at the first code is illustrated by the curves for the respective relays. The portions ofeach curve above the base line indicate the periods the relay is picked up, the portions of a curve on the base line indicate the periods the relay is released and the sloping portions of a curve indicate the periods of buildingup and decaying of the energization of the respective, relay. "For example, the curve for relay 'I'Pl indicates its energizes tion builds up quickly and relay TPI ,is'p'icked up when relay CF is picked up at the start of an on period, the energization of relay TPI ceaseswhen relay CF is released at the start of an off period andsuch energization slowly dies away in relay T191 and relay TPI is released at the end. of two units of time, the-slow release period provided for relay TPI. The curve for relay TPZ indicates that this relay is energized and picked up when relay CF is released because relay 'I'P-l is picked up. The energization of relay TB-2 ceases when relay TPI is released, and the energization of relay TPZthen dies away and relay TF2 ,is released at the end of two units of time after relay T1! is released 'or four units of time after-relay CF is released. In other words relay TP2 is released just prior torelay CF being picked up in response to the second'on period :of the code. Belay H is energized when relay TPI is'picked'up and its successive energizations occur frequently enough that its energization never fails. to the re lease value of relay The positions of the respective relays under the first code are illustrated at thesecond column from the left in Fig. 4. and as to be seen in Fig. 1, two signal operating circuits, are formed one including terminal B, front contact 16 of relay H, back contact 1'! of relay DD and lamp Y of the top, group 'of lamps of signal WS to terminal C; and the second circuit including terminal 13, back contact 66 of relay D and lamp R of the lower group of. lamps to terminal C; and Signal WS displays a yellow light over a red light for an approach signal indication. When relay H is picked up and relays D and DD are released the I current impulses supplied to the track circuit of the section next in the rear are coded by the second code pattern as described in detail heree inbefore.

Assuming the train advances another track section to the right, leaving section W-..-:X and the first section in advance unoccupied, the track circuit current impulses supplied to section WWX are coded at the second code pattern and code following relay CF is correspondingly operated. That is, the second unoccupied section to the rear of an occupied section as illustrated by the heavy line of the track diagram at the top of Fig. 3b is supplied with current of the secondccde and the operation of relay CF is that indicated by the top curve of Fig. 3b, it being noted that the off period of relay CF is now of three units of time in length. a

At the first on period of relay CF under the second code when front contact 58-60 is closed, repeater relay TPI ispicked up over the circuit including back contact 61 of relay TF2, and then at the first off period when back contact 53 62 of relay CF is closed, the second repeater relay TPZ is picked up over the circuit including back contact 68 of relay TP3' and front contact -69 of relay TPI. ,Since the .ofi period of this second code is of the order of three units of time, repeater relay TP2 as indicated by the respective curve of Fig. 3b, is not released until the end ,of the second on period so that whenfront contact 58-60 of relay :CF is closed at the second on period, current is supplied. from terminal B oyer front contact ail--60, front contact 18 of relay TF2 and winding of relay T1 3 to terminal C, and relay TP3 is picked up. .As indicated in Fig. 3b the repeater relays are sequentially released and are all released prior to the end of the second off period, so" that at the beginningof the thirdon' period the above cyclic operation of the repeater relays is again initiated. Relay H is effectively energized and picked up in respOnse to the operation of repeater relay TPI the same as explained in connection with the first code.

' During the second off period andbefore the third repeater relay TF3 is released, current is supplied from terminal B over back, contact 558-451 of relay CF, front contact 1.9 ofrelay TF3, back contact till of relay TPZ, back "contact 8| of'decoding relay DDD and winding of decoding relay D to terminal C, and relay 'D is energized and third column from the left in Fig. 4, and as shown in Fig. 1 the operating circuit for lamp Y of the top group of lamps is closed as before, and an operating circuit is completed at front contact 82 of relay D and back contact 83 of relay DDD for lamp Y of the lower group of lamps with the result that signal WS displays a yellow light over a yellow light for an approachslow signal indication. When relays H and D are picked up and relay DD is released, the current impulses supplied to the track circuit for the section next in the rear are coded according to the third code pattern effected by contact l0Z-|02a of coder CT as explained hereinbefore.

Again assuming the train advances another track section to the right, leaving section WX and the next two sections in advance unoccupied, the track circuit current impulses for section WX are coded at the third code pattern and code following relay CF is correspondingly operated. This time the traffic condition is illustrated by the track diagram at the top of Fig. 3c and the operation of relay CF is indicated diagrammatically by the top curve of Fig. 3c, it being noted that the off period of relay CF is now of substantially two units of time in length. On the first on period of this third code and contact 5860 of relay CF is closed, repeater relay TPI is picked up as in the previous codes and at the first ofi period and back contact TPZ is not released until the latter part of the second off period of relay CF and the third repeater relay TP3 is not released until the very end of the second off period, and consequently during the part of the second off period While both ys TF2 and TF3 are picked up, current flows from terminal B over back contact 5862 of relay CF,

front contacts

19 and 85 of relays TP3 and 'IPZ, respectively, and winding of relay DD to terminal C, and relay DD is energized and picked up. Beginning with the third on period of relay CF the repeater relays are cyclically operated as above with the result that each relay H, D and DD is again supplied with an energizing impulse, and each is retained picked up from one energizing impulse to the next due to its slow release characteristics. This condition of the relays is illustrated by the fourth column of Fig. 4. When relays H, D and DD are picked up a signal operating circuit is formed over front contact 16 of relay H and front contact 8'! of relay DD for the G lamp of the top group of lamps; and the previously traced circuit including front contact 82 of relay D and back contact 83 of relay DDD is still closed for lamp Y of the lower group of lamps so that signal WS now displays a green light over a yellow light for an approach-medium signal indication. Since relays H, D and DD are now picked up, the current impulses supplied to the track circuit of the section next in the rear are coded according to the fourth code pattern as effected by the contact member I93 of coder CT.

When the train moves to the right another track section, leaving section W-X and the next three sections in advance unoccupied, the fourth code is impressed upon the track circuit current impulses of section WX and relay- CF is correspondingly operated as indicated by the top curve of Fig. 3d, it being observed that the off period of the relay is now of one unit of time in length. At the first'on period of this fourth code, repeater relay TPI is picked up as in previous codes, and at the first off period, the second repeater TPZ is picked up and then at the beginning of the second on period the third 'repeater relay TP3 is picked up over the previously traced circuits. Relays H and DD are again supplied with energizing impulses and are picked up in a manner similar to that described in connection with the third code. Since repeater relay TPl is picked up the second time at the beginning of the third on period of this fourth code prior to the release of the third repeater e relay TF3, current flows from terminal B over front contact 10 of relay TPI, winding of relay DDD,front contact 84 of relay DD and front contact 13 of relay TP3 to terminal C, and decoding relay DDD is energized and picked up.

- When relay DDD is picked up to close front contact I06, relay D is energized over a simple circuit including front contact I86. From this point on the repeater relays are cyclically operated in the manner illustrated in Fig. 3d and the decoding relays are all energized and picked up the top group of lamps of signal WS is closed the same as under the third code, and a circuit is formed at front contact 82 of relay D and front contact 89 of relay DDD for lamp G of the lower group of lamps, and signal WS displays a green light over a green light for a clear signal indication. It is to be observed that sincerelays H, D and DD are picked up under the fourth code the same as under the third code, the fourth code pattern is still impressed upon the current impulses for the track circuit of the section next in the rear.

In the form of the invention disclosed in Fig. 2 the track section W-X is provided with apparatus substantially the same as that shown in Fig. 1, except for the code transmitting means and the circuit arrangement by which the repeater relays govern the decoding relays, and the apparatus of Fig. 2 is described only as required for a full understanding of the code transmitting means disclosed therein and the control of the decoding relays.

In Fig. 2 the code transmitting means includes a tuned oscillator OS and a chain of relays identified by the numerals I to 8, inclusive. The oscillator OS is preferably of the mechanically tuned relay type and is provided with a contact member I 9 which is operated at a predetermined frequency as long as the winding I8 of the oscillator is supplied with current from a convenient source, such as the battery whose terminals are indicated at B and C. Hence contact member I9 of oscillator OS is oscillated between

contacts

20 and 2| at a rate predetermined by the adjustment of the parts of the oscillator. As will shortly appear, oscillator OS is adjusted so that a half cycle period of its operation is used as the unit of time in determining the off period of the different code patterns.

;-Each of the'relays 1 to 8 of the relay chain is at least relays 3, and I are ofv the well-known construction such that the relay can be energized and picked up over a back contact of the relay. The relays are consecutively operated in a cyclic manner inresponse to the operation of oscillator OS to effect any one of four different code patterns. At the start it is to be pointed out that when the last relay 8 of the relay chain is released closing back contact 22 a circuit is completed by which battery W3 is connected to winding I5 of reactor TW and current flows in the winding I5 causing magnetic energy to be stored in the magnetic core 23 of the reactor. When the last relay is picked up opening back contact 22 the flow of current'in winding I5 ceases and the magnetic flux dies away to cause an effective impulse of current to be supplied to the track circuit in the manner already explained. Thus with the last relay 8 picked up at different intervals apart the impulses supplied to the track circu'it are spaced-according to the intervals between the successive operations-of relay 8.

Under the first traff c condition and relays H, D and DD are released, the relays I to 8, inclusive, of the relay chain are cyclically operated in response to operation'of oscillator OS and a corresponding first or approach code is impressed upon the track circuit current impulses for the section next in the rear. Assuming at the start'that relays I to 8 are all released, the first half cycle of oscillator OS closes contact I9-20 and current flows from terminal B of the source of current, over contact Iii-20, wire 24, back contacts 25 to 34, inclusive, of

relays

8, 1, DD, 6, 5, D, 4, 3, H and 2, respectively, winding of relay I and terminal C of the current source, and relay I is picked up. On the second half cycle of oscillator OS, connect, I9-2fl is opened to deenergize relay I and contact I9-2I is closed causing current to flow from terminal B over contact I9-2I, wire 35, front contact of relay I, prior to relay I releasing, and winding of relay 2to terminal C, and relay 2 is picked up. It is to be observed that subsequent to relay I releasing to open front contact 36, relay 2 is retained picked up over back contact 99 of relay 3 and front contact 90 of relay 2 until the end of the second half cycle of oscillator OS and contact I9-2I is opened. On the third half cycle of oscillator OS and contact I920 is closed for the second time current flows over the previous traced circuit up to backcontact 33 of relay H, thence over front contact 31 of relay 2 and winding of relay 3 to terminal C, and relay 3 is picked up before relay 2 is released. Relay 3 is then retained .picked up subsequent to the release of relay 2 for the remaining portion of the third half cycle over its own front contact 38. The fourth half cycle of oscillator OS closes contact I92I for the second time and current flows from terminal B over contact I9-2I, wire 35, back contact 39 of relay- 2, front contact of relay 3 prior to the release of relay. 3, and winding of relay 4 to terminal C, and relay 4 is picked up. Relay 4 is retained picked up subsequent to the release of relay 3 for the remaining portion of the fourth half cycle overback contact 9| of relay 5 and front contact 92 of relay 4. On the fifth half cycle of oscillator OS contact I320 is again closed and current flowsover the previously traced circuit up to back contact 33 of relay D, and thence over front contact M of relay 4 prior to the release of relay 4, and winding Orv-relay 5 to terminal 0, and'relay 5 is picked up and is then retained energized over its own front contact 42 for the remaining portion of this fifthhalf cycle subsequent to the release of relay 4. On the sixth half cycle of oscillator OS, contact I9ZI is closed, and current flows over terminal B, contact I9-2I, wire 35, back contact 43 of relay 4, front contact 44 of relay 5, prior to the release of relay 5, and winding of relay 5 to terminal C, and relay 6 is picked up and is then retained energized subsequent to the release of relay 5 over back contact 93 of relay 7 and front contact 94 of relay 6. On the seventh half cycle of oscillator OS and contact I 9- 25 is again closed current flows over the previously traced circuit up to'back contact 21 of relay DD, thence over front contact 45 of relay 6, prior to the release of relay 6, and winding of relay I to terminal 0, and relay 1 is picked up. Relay 1 is then retained energized subsequent to the release of relay 6 over its own front contact 5|. On the eighth half cycle of the oscillator OS and contact I9-2I is closed current is supplied to relay 3 over back contact 45 of relay 6 and front contact 41 of relay I, prior to the release .of relay I, and winding of relay 8 to terminal C, and relay 8 is picked up and then released subsequent to the release of relay I so that at the beginning of the ninth half cycle of oscillator OS the relays I to 8 are all deenergized and the above described cyclic operation of the relay chain is repeated. When relay 8 is picked up to open back contact 22 at the end of the cyclic operation of the relay chain, a current impulse is supplied to the track circuit in the manner previ- I ously explained.

Referring to Fig. 5, the top curve represents the operation of oscillator OS, the raised portion of thecurve designating the half cycle that contact I92Il is closed and the depressed portion of the curve designating the half cycle the contact l3--2I is closed. The second curve from the top represents the operation of the relay chain under this first code condition when relays H, D and DD are released, the raised portion of the curve designating the period during which relay 8 is picked up and an impulse of current is supplied to the associated track circuit. Under this first code it is to be noted that there are seven half cycle periods of oscillator OS between successive impulses of current. In other words the first code is one having off periods that are seven units of time in length.

Under the second traflic condition, relay H is picked up and relays D and DD are released.

Again assuming the relays I to 8 are at the start released and contact I920 of oscillator OS is closed causing current to flow from terminal B over the contact I92U, wire 24, back contacts 25 to 32, inclusive, and thence over frontcontact 48 of relay H and winding of relay 3 to terminal C and relay 3 is picked up and will remain picked up during the remaining portion of this first half cycle of oscillator OS over its own front contact 38. From this point on the

relays

4, 5, 6, I and 8 of the relay chain are consecutively operated in response to operation of oscillator OS in the manner previously explained. When the last relay 8 is picked up to open back contact 22, an impulse of current is 1 caused to flow in the associated track circuit.

Hence under this second traffic condition, the cyclic operation of the relay chain is started each time with relay 3 and the off period of the code is of 5 units of time in length. In Fig. 5 the third curve from the top represents the operation dition and the effective off period between successive impulses of current.

Under the third traflio condition of section W--X relays H and D are picked up and relay DD is released. Again assuming relays l to 8 are all released at the start and contact l9-25 oi oscillator OS is closed causing current to flow from terminal B over contact Iii-4E), wire 24, back contacts 25 to 29, inclusive, and thence over front contact 49 of relay D and winding of relay 5 to terminal C, and relay 5 is picked up and then retained energized over its own front contact 42 during this half cycle operation of oscillator OS. Relays 5 to 8, inclusive, are now operated consecutively in response to operation of oscillator OS and relay 8 when picked up to open back contact 22 causes an impulse of current to be supplied to the respective track circuit. Hence the cyclic operation of the relay chain is started at relay 5 under this third trafiic condition and there are only three units of time between successive impulses of current. In Fig. 5 the next to the bottom curve designates the operation of the relay chain and the code efiected thereby under this third traflic condition.

Under the fourth traflic condition of section W-X relays H, D and DD are all picked up. The picking up of relay DD to close front contact 50 causes the cyclic operation of the relay chain to start at relay 1 as will be readily understood by an inspection of Fig. 2 with the result that relays l and 8 only are cyclically operated and only one unit of time occurs between the successive impulses of current supplied to the respective track circuit by the picking up of relay 1 8. In other words under this fourth trafiic condition the 01f period of the code pattern is one unit of time in length. In Fig. 5, the lowest curve represents the operation of the relays and the code effected thereby under this fourth tramc condition.

A resistor 52 may be inserted between contactl920 of oscillator OS and terminal C of the current source and a resistor 53 may be inserted between contact til-2| at the terminal C to improve the operation of the relay chain.

In Fig. 2, the repeater relays TPI, TPZ and- TP3 are sequentially energized in response to operation of the code following relay CF for the different code patterns in substantially the same manner as explained in connection with Fig. 1, except in Fig. 2 the slow release periods for the repeater relays are based on the units of time used in determining the OK periods of the different codes and which units of time in Fig. 2 are predetermined by one-half cycle operation of the oscillator OS.

In Fig. 2 the control circuits for the decoding relays are modified somewhat from that of Fig. 1. Relay H of'Fig. 2 is controlled over contact 10 of repeater relay TPI and back contact I2 of repeater relay TP3 the same as in Fig. 1, except for the fact that the connection to the B and C terminals of the current source is reversed. Relay D of Fig. 2 is controlled over a front contact 95 of relay H and front contact 13 of relay TP3 as well as the back contact 95 of relay TP! and hence is picked up under the second, third and fourth codes the same as in Fig. 1. Relay DD of Fig. 2 is provided with a circuit the same as in Fig. 1, except for the fact that front contact 86 of relay H is interposed in the circuit to avoid possible false energization of this relay, and

of the relay chain under this second traffic conrelay DDD is provided with a control circuit the same as in Fig. 1.

In the light of the description of the operation of the apparatus of Fig. 1, it is clear that the apparatus of Fig. 2 will function in a similar manner to control the operating circuits of wayside signal WS and to control the code impressed upon the track circuit for the section in the rear in response toeach of the four diiferent traffic conditions of track section WX and a description of the operation of the apparatus of Fig. 2 is unnecessary.

While impulses of direct current coded at the four different code patterns are used in the forms of the invention here disclosed, it is apparent that alternating current can be used. For example, relay 8 of the code transmitting means of Fig. 2 instead of controlling the reactor circuit at back contact 22 to cause time spaced impulses of direct current to be supplied to the associated track circuit, can be provided with a front contact over which alternating current is supplied to the associated track circuit. Such on periods of alternating current would be uniform at all codes and would be of a duration not greater than the period relay 8 is picked up and which period is not greater than one-half cycle of the oscillator OS. That is to say under such conditions coded alternating current having an on period of substantially one unit of time is used. When coded alternating current is used the code following relay CF would be either an alternating current relay or would be a direct current relay receiving energy from the track circuit through the medium of the usual transformer-rectifier unit.

It is also clear that the apparatus can be used for a three-block four-indication signal system by omitting one coding element in the code transmitting means and by omitting one decoding relay from the receiving apparatus, or it can be used for a two-block three-indication system by omitting two coding elements and two decoding relays.

Although I have herein shown and described only two forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. Railway traflic controlling apparatus comprising in combination, a track section providedwith a track circuit, current supply means including a source of current and code transmitting means connected to said track circuit to supply coded current thereto, said code transmitting means including contact members arranged to eifect any one of a plurality of different code patterns having a substantially uniform on period and ofi periods of different lengths with the length of the off period for a code pattern made up of a preselected number of a predetermined unit of time, a code following relay receiving current from said track cir-' cuit operated to a first and a second position in response to the on and ofi periods of such coded current, a series of repeater relays each of which is provided with a slow release period bearing a preselected relationship to said unit of time, circuit means including a first and a second position contact of said code following relay to sequentially energize said repeater relays for operating such repeater relays at a'distinctive cycli'c" opthe code patterns and the slow release periods of said repeater relays as effected through said unit of time, and signaling means having a distinctive condition for each of said code patterns selectively controlled by said repeater relays in accordance with the cyclic operation at which they are operated.

2. Railway traffic controlling apparatus comprising in combination, a track section provided with a track circuit, current supply means including a source of current and code'trans mitting means connected to said-track circuit to supply coded current thereto, said code trans mitting means characterized by effecting any one of a plurality of different code patterns which" have a substantially uniform on period and off periods of different lengths and which lengths are made to differ from eachother by-each having a different number of a predetermined unit of time, a code following relay connectedto receivecurrent from said track circuit operatedto a first and a second position in response to the on and off periods of such codedcurrent, a series of repeater relays each provided with a given slow release period which is based upon said unit of time, circuit means including'first and secondposition contacts of said code following relay to cyclically operate said repeater relays in a manner predetermined for each of'said'code patterns because of the relationship between the off periods ofthe code patterns and the slow release periods of said repeater relays, and signaling means having a different condition for each of said code patterns selectively controlled by said repeater relays in accordance with the manner at which they are cyclically operated,

3. Railway traflic controlling apparatus comprising in combination, a track section provided with a track circuit, current supply means including a source of current and code transmitting means connected to said track circuit to supply coded current thereto, said code transmitting means characterized by effecting any one of a plurality of different code patterns which have a substantially uniform on period'and off periods of different lengths and which lengths are made to differ from each other byeach having a diiferent number of a predetermined unit of time, a code following relay connected to receive current from said track circuit operated to a first and asecond position in response to the on and off periods of such coded current, a series of repeater relays each provided with a slow release period which is equal to a preselected number. of said units of time, circuit means including first and second position contacts of said code following relay to cyclically operate said re-, peater relays in a manner predetermined for each of said code patterns because of the relationship between the off periods of the code patterns and the slow release periods of said repeater, relays, slow acting decodingrelays onefor each of said code patterns, circuit means including contacts of said repeater relays and said code following relay to selectively govern said decodingrelays according to the code pattern of the track circuitcurrent, and a signal having a different indication for each of said code patterns selectively gov-. erned by said decoding relays.

'4. Railway traffic controlling apparatus comprising'in combination, atrack section provided with a track circuit having a current supplymeans including a source of direct current connected to a winding mounted on a magnetizable core over coding contacts of a code transmitting means, said coding contacts effective when operated to periodically interrupt the'connection of the direct current source to said winding to cause recurrent impulses of direct current to flow in said track circuit, said code transmitting means effective to' operate said coding contacts to cause said connectionto be interrupted at any one of several different rates which are based upon a predetermined unit of time so that the interval between successive current impulses is predetermined according to a preselectednumber of such units of time, a codefollowing relay receiving current from said track circuit operated to a first position in response to a current impulse and to a second position in response to an interval between such current impulses, a series of repeater relays sequentially energized over contacts of saidcode following relay and each provided with a "slow releaseperiod equal to a preselected number of said units of time to operate such repeater relays in a manner predetermined by the length of the interval between successive current impulses of the track circuit, and signaling means having different conditions selectively governed by said repeater relays according to the manner at which they are operated.

5. Railway traffic controlling apparatus comprising in combination, a track circuit, current supply means including a source of direct current connected to a winding mounted on' a magneticcore and having a portion of such winding connected to "said track circuit, coding means including a contact interposed in the connection of said'direct current source to said winding and operative to recurrently interrupt such connection at any one of several different rates for supplying to said track circuit recurrent impulses of current of corresponding code rates, said coding means arranged to effect rates of an arithmetical progression to create intervals between successive current impulses that starting with the highest rate progressively increase in length by predetermined increments of time, a code following relay receiving current from said track circuit operated to a first and a second position in response to the on and off periods of such impulses of current, a series of repeater relays each provided witha slow release period predetermined in length to agree with said increment of time, circuit means including a first and a second position contact of said code following relay to sequentially energize said repeater relays to effect a distinctive cyclic operation for said repeater relays for each of said rates. signaling means having a different condition of each of saidrates, and circuit means including contacts of said repeater relays to establish the condition of said si naling means correspondingto the respective rate of the current impulses.

.6. Railway traffic controlling apparatus comprisingin combination, a track section having a track circuit. means including a current source and, a code transmitting means connected to said track circuit'tosupply thereto current coded at any one of a plurality of different code patterns which have the same on period and off periods different o ea h code pattern. said code transmitting means arranged in such a manner as to cause said off periods to differ from each other by the length of the off period of a code pattern being formed by a preselected number of units of time, traffic controlled means for selectively controlling said code transmitting means to cause the track circuit current to be coded at a preselected code pattern for each of a plurality of different traffic conditions, a code following relay receiving current from said track circuit operated to a first and a second position in response to the on and off periods of such coded current, a series of repeater relays each of which is provided with a slow release period based upon said unit of time, means including first and second position contacts of said code following relay to sequentially energize said repeater relays to cyclically operate the series of repeater relays at a distinctive cycle for each of said code patterns as determined by the relationship between the slow release periods of said repeater relays and the off periods of the code patterns, slow acting decoding relays one for each of said code patterns selectively controlled by said repeater relays, and a signal having a distinctive indicad tion for each of said different traffic conditions selectively governed by said decoding relays.

7. Railway traffic controlling apparatus comprising in combination, a track section having a track circuit, current supply means including a source of direct current connected to a winding mounted on a magnetizable core connected to said track circuit for supplying an impulse of direct current thereto when the connection of such current source to said winding is interrupted,

coding means operative to recurrently interrupt said connection at any one of several different rates with said rates differing from each other according to a predetermined unit of time, trafiic controlled means to govern said coding means to a ircuit Operated to a first and a second position v at a rate corresponding to the rate of said current impulses, a group of repeater relays each provided with a slow release period preselected in accordance with said unit of time, circuit means including first and second position contacts of said code following relay to periodically energize said repeater relays to cause such relays to be cyclically operated in a predetermined manner different for each rate of current impulses, slow" acting decoding relays energized over circuits including contacts of said repeater relays to pick up a different combination of the decoding relays for each rate of current impulses, and a signal having a different indication for each of said traffic conditions selectively governed by said decoding relays.

8. Railway trafiic controlling apparatus comprising in combination, a track section having a track circuit, current supply means includingv a source of direct current connected to a winding mounted on a magnetizable core connected to said track circuit for supplying an impulse of direct current thereto when the connection of such current source to said Winding is interrupted, coding means operative to interrupt said connection at any one of four different rates with said rates preselected to provide intervals between successive impulses that progressively increase in length by a preselected unit of time starting with the highest rate, traffic controlled means to condition said coding means to efi'ect a preselected one of said rates for each of four different trafiic conditions in advance of said section, a code following relay receiving current from said track circuit operated to a first and a second positional/3a rate po -responding to the rate of the, current impulses supplied to the track circuit, three repeater relays each proportioned for a slow release period having a preselected relationship with respect to said unit of time, circuit means including first and second position contacts of said code following relay to sequent combinations and its fifth indication when a par ticular one of said decoding relays is released.

9. Railway traffic controlling apparatus comprising in combination, a track section provided with a track circuit, means for supplying to said track circuit current coded at any one of four different code patterns which have a substantially uniform on period'andoff periods made different in length by being made up'of a different number of a preselected unit of time, a code following track relay receiving current from said track circuit operated-to a first and a second position in response to the on and off periods of such coded current; a first, a second and a third repeater relay each adjusted with a slow release period having a definite relationship with respect to said unit of time; a first circuit including a first position contact of said track relay and a back contact of said second relay to energize said first relay; a second circuit'including a second position contact of said track relay, a back contact of said third relay and a front'contact of said first relay to energize said second relay; a third circuit including a first position contact of said track relay and a front'contact of said second relay to energize said third'relay, decoding means operable to any one of four conditions selectively governed by said three repeater relays, and signaling circuits selectivelygoverned by said decoding means.

10. Railway traffic controlling apparatus comprising in combination, a track section provided with a track circuit, means for supplying to said track circuit current coded at any one of four dilferent code patterns which have a substantially uniform on-period and off periods made different in length by being made up of a different number of a preselected unit of time, a code following track relay receiving current from said track circuit operated to a first and a second position in response to the on and off periods'of such coded current; a first, a second and a third repeater relay each adjusted with a slow release period having a definite relationship with respect to said unit of time; a firstcircuit including a first position contact of said track relay and a back contact of "said "second relay to energize said, first relay; a second circuit including a second position contact of, said track relay, a back contact of said third relay and a front contact of said first relay to energize said second relay; a

third circuit including a first position contact of said track relay and a front contact of said second relay to energize saidthird relay, code detecting. means, including a transformer and checkrelaycontrolled over a front contact ofsaid first repeater relay to energize said check relay in response to operation of said first relay by any of said codes, three decoding relays controlled over contacts of said check relay and said repeater relays to energize a first one of the decoding relays in response to a second, third and fourth of said codes; to energize a second one of the decoding relays in response to the third and fourth codes and to energize a third one of the decoding relays in response to the fourth code; and a signal having five difierent indications selectively governed by said check relay and said three decoding relays.

11. Railway trafl'ic controlling apparatus comprising in combination, a track section provided with a track circuit, an oscillator having a contact member operated to a first and a second position in a preselected interval, a chain of relays, circuit means including said contact member to consecutively energize the relays of said relay chain to cyclically operate the relay chain and recurrently operate the last relay of such relay chain at intervals spaced apart according to the number of relays to be operated, means including a current source and a contact of said last relay to supply current to said track circuit when said last relay is operated, and a trailic controlled relay responsive to a given trafiic condition in advance of said section and having a contact interposed in said circuit means to determine the relay of the relay chain at which said cyclic operation is to start for impressing a code pattern upon the current supplied to the track circuit distinctive for said given traffic condition.

12. Railway traiiic controlling apparatus comprising in combination, a track section provided with a track circuit, current supply means including a source of direct current and a winding mounted on a magnetizable core connected to said track circuit to supply thereto an impulse of current when the connection of said direct current source to said winding is interrupted, an oscillator having a contact member operated at a predetermined frequency, a chain of relays, circuit means including said contact member to consecutively energize the relays of said relay chain when said contact member is operated to effect a cyclic operation of the relay chain the duration of which is governed by the i number of relays of the relay chain, the last relay of said relay chain provided with a contact for interrupting said connection of the direct current source to said winding when said last relay is operated to cause said current impulses to be spaced apart an interval governed by said relay chain, and a traffic controlled relay responsive to a given trafiic condition in advance of said section having a contact interposed in said circuit-means to determine the relay of the relay chain at which its cyclic operation is to start to form the current impulse into a code distinctive for said given traific condition.

13. Railway trafiic controlling apparatus comprising in combination, a track section provided with a track circuit, current supply means including a source of direct current and a winding mounted on a magnetizable core connected to said track circuit to supply thereto an impulse of current when the connection of said direct current source to said winding is interrupted, an oscillator having a contact member operated at a predetermined frequency, a chain of eight relays, a circuit means including said contact memher to consecutively energize and deenergize said eight relays in response to operation of said contact member to effect a cyclic operation of the relay chain, the eighth relay provided with a back contact interposed in the connection of said direct current source to said winding to cause the current impulses supplied to the track circuit to be spaced apart by an interval governed by the frequency of said contact member and the cyclic operation of said relay chain, three control relays responsive to three difierent traffic conditions in advance of said section; a first one of said control relays having a contact interposed in said circuit means to start the cyclic operation at the third relay of said relay chain,

3 a second one of said control relays having a contact interposed in said circuit means to start the cyclic operation at the fifth relay of the relay chain and the third one of said control relays having a contact interposed in said circonditions and a fourth code when the cyclic operation is started at the first relay of the relay chain.

CRAWFORD E. STAPLES.