US2176605A - Approach control apparatus for railway signaling systems - Google Patents

Description

' 0d. 17, 1939. H. G. B'LOSSER APPROACH CONTROL APPARATUS FOI I RAILWAY SIGNALING SYSTEMS Filed Aug. 4, 1938 INVENTOR fieima'niBlossen Patented Oct. 17, 1939 UNITED STATES P AT E N "-l' 0 FjFiE-E APPROACH CONTROL APPARATUS FOR RAILWAY SIGNALING SYSTEMS Application August 4, 1938, Serial No. 223,076

23 Claims.

My invention relates to approach control apparatus for use in railway signaling systems of the coded track circuit class and it has special reference to the employment of such apparatus for approach controlling various signaling functions without the use of line wires.

Generally stated, the object of my invention is to provide a new and simplified method for approach controlling coded signaling systems without the use of line wires.

A more specific object is to restrict the apparatus required by the approach control facilities to the exit end only of each of the signaling system track circuits.

Another object is to lower the cost and reduce the quantity of this apparatus and to simplify its application to coded track circuits of standard type.

An additional object is'to extend the length of the track circuit which may be approach controlled by the novel non-line wire facilities which are disclosed herein.

A further object is to compensate these facilities for variations in track ballast resistance and in track battery voltage.

A still further object isto accomplish the above without interfering with the normal operation of the coded signaling system with which the facilities are used.

In practicing my invention I attain the above and other objects and advantages'by providing the exit end of each track circuit with a code following detector relay which locally controls the energization of a 510W release approach relay by which various signaling functions may be governed. This detector relay receives acomponent of the coded energy which is supplied to the trackcircuit rails'for' signal controlling purposes and it'is arranged toreriderthe approach governed:functions active'only when that component has the relatively extreme value which accompanies a by-passing ofthe named rails by the wheels and axles of a-train.

.I' shall describe a'few forms ofapproach control apparatus I embodying my invention, and shall then point out the novel'features thereof in claims. These illustrative'embodiments are disclosed in the accompanyingdrawing in which:

:Fig. 1 is -a=diagrammatic representation of a section of railway track which is equipped with one preferred form of the approach control apparatus of my invention;

Fig. :2 is a diagrammatic View of cutsection facilities which are suitable for use with the approach control scheme of Fig. 1;

Fig. 3 is a diagrammatic showing of a form of my improved approach control apparatus in which the code following detector relay is energized by the current component rather than the voltage component of thecoded track cir- 5 cuit ener y; and

Fig. 4 is a similar showing of a third form of my improved approach controlapparatus which compensates for variations in track ballast resistance and in track battery voltage.

In the several views of the drawing like reference characters designate corresponding parts. Referring first to Fig. 1, the improved approach control apparatus of my invention .is there disclosed in association with a coded track circuit system of automatic block signaling for a'railway track l-2 over which it will be assumed that traffic moves in the single direction indicated by the arrow, or from left to right in the diagram. The protected stretch of' this track v20 is divided into the customary successive sections by-insulated rail joints 3 and the rails of each section form a part of a track circuit to which codedsignal control energy is supplied in customary manner.

'In this View of Fig, 1, reference characters D and E respectively designate the entrance and the exit ends of one of these track sections which is illustratively shown as being a full signal -block'in length; character TR designates a. code ,30

following track relay which is installed at the entrance end of the section and operated by energy received from the rails thereof; character TB a track battery or other direct current source provided at the section exit for the pur- 35 pose of supplying these rails with the relay operating energyjust referred to; character CR a coding device having a contact 5 which codes .this energy by periodically interrupting the rail supply circuit; and character S the usual wayside signal which guards the entrance of each of ;the track blocks and which is controlled by the associated track relay TR through the medium of decoding apparatus ill. I

An automatic block signaling system of the referred to coded track circuit type operates without the aid of line wires and in representa tive form it includes all of the elements above named. Such a system further comprises the customary facilities (not shown) for continuously operating each of the exit end relays GB at one or another of theusual plurality of distinctive code rates. Selection among these rates (which in a typical three indication system may consist of '75 and 180 energy pulses per minute) is made in accordance with advance traffic conditions by the decoding apparatus l functioning in customary manner.

This decoding apparatus (details not shown) is controlled in the usual fashion by the associated track relay TR and it performs the further function of selectively setting up a lighting circuit for one or another of the lamps (G, Y and R in the typical three indication system above referred to) of the wayside signal at the same location. In the arrangement represented these signal lamps derive energizing current from a power source which is designated by the terminals plus and minus.

For applications in which train carried cab signals (not shown) also are to be controlled, the representative coded signaling facilities may still further comprise means at the exit end of the track circuit for additionally supplying the rails thereof with coded alternating current energy. In the form shown at location E in Fig. 1, such means include a track'transformer TT having a secondary winding which is connected with the track rails over coding contact of device CR during each energy 01f period of the signal control code from battery TB. At proper times the primary winding of this transformer is energized over a conductor 1 from a suitable alternating current source designated by the terminals- B and C.

In order that certain functions of the signaling system may be rendered active only upon the approach of a train, the apparatus installed at each of the signal locations D, E, etc., is supplemented by an approach relay AR which is arranged to maintain the referred to functions inactive at all times except when the section of track to the rear of the location becomes occupied. In the illustrative arrangement which is shown at location E in Fig. 1, these approach controlled functions consist in lighting the wayside signal Se (normally dark) and in supplying the rails of the track section to the rear of that signal with coded alternating current energy for cab signal control.

The former function is governed by a contact 9 of the approach relay AR and the latter by a companion contact H thereof. Either of these functions may, of course, be controlled individually by the approach relay and it will be apparent, moreover, that signaling functions other than or in addition to those just named may likewise be governed by the same relay.

When applied to coded signaling systems of the conventional character just considered, the improved approach control apparatus herein disclosed renders the relay AR at each signal location responsive to the approach of a train and does this, moreover, without the use of control line wires. In the form shown at location E in Fig. 1, this apparatus comprises a detector relay KR which is connected in energy receiving relation with the rails of section DE, a circuit controlled by a contact l3 of that relay for energizing the approach relay AR from a local source designated by the terminals plus and minus, and means for making the approach relay suinciently slow releasing to bridge the intervals between recurrent responses of the detector relay.

This detector relay KR is of the code following type and its operating winding is bridged directly across the track rails l and 2 (in the manner disclosed and claimed in a copending application Serial No. 220,015 filed July 19, 1938, by Crawford E. Staples) to receive all potential d fierences appearing therebetween. The relay has special response characteristics which enable it to pick up each time that coding contact 5 connects the rails across the battery TB when the track section DE is vacant but yet which prevent it from responding to these on code peri ods when a train comes into the section and bypasses the rails. Under that condition the major portion of the track battery voltage appears not across the rails l and 2 and the parallel connected winding of relay KR but rather in the form of a potential drop across a current limiting impedance l4. Moreover, this detector relay responds only to direct current energy (from battery TB) and cannot be picked up by alternating current energy such as may, under certain conditions, be received from source B-C by way of the transformer TT.

For energizing the approach relay AR in step with the responses of the detector relay, the arrangement of Fig. 1 makes use of a circuit for connecting the approach relay winding directly across the local power source terminals plus and minus each time that contact l3 of relay KR is picked up. This arrangement may, if desired, be replaced by one of those represented in Figs. 2 and 4 as involving an interposed transformer AT. In each of those modified arrangements the contact l3 of relay KR controls a connection of the primary winding of the transformer with the direct current source while a second contact N5 of the same relay acts to rectify the current which the secondary winding of the transformer supplies to the winding of relay AR when the detector relay is following a trackway code.

For delaying the release of the approach relay AR and thereby enabling it to remain continuously picked up as long as its winding receives energizing pulses which are in step with recur- I rent periods of any of the signal control codes which device CR produces, use may, of course, be made of any suitable means such as a snubbing impedance (not shown) bridged across the winding terminals or internal design expedients incorporated in the relay. Because of their wellknown character, the drawing makes no attempt to represent any such means.

In operation of the complete approach control scheme of Fig. 1, the track rails I and 2 of section DE act in the usual manner to transmit energy from one end of the section to the other as long as the section remains unoccupied. Each time, under such conditions, that contact 5 of the continuously operating coding device CR is in the lowermost or on code period position the track battery TB picks-up the entrance end track relay TR in the usual manner and each time that the coding contact occupies the uppermost or ofi code period position, the track relay is permitted to release. The direct current potential of these recurring pulses of signal control energy is also received by the exit end detector relay KR over a circuit which may be traced from the positive terminal of battery TB, through impedance l4, back contact 5 of device CR, conductors I! and I8, the winding of relay KR, and conductors l9 and 20 back to the negative terminal of the track battery.

As long as the track section DE remains vacant, the referred to potential appearing between the rails I and 2 during each on period of the signal control code is substantially the full terminal Voltage of the supply battery TB andissufliciently high to cause the detector relay KR to pick-upits contact l3 upon the occasion and for the duration of each of these on periods. In consequence, the operating winding of the approach relay AR is energizedin step with each on period over a circuit which extends from the positive supply terminal through front contact it of relay KR, conductor 2!, and the relay winding back to the negative supply terminal.

Because of its slow releasing characteristics the approach relay AR now holds its contacts 9 and ii continuously picked up and thereby maintains, the lighting circuits of the wayside signal Se disconnected from their energizing source and the primary of transformer TT disconnected from'the alternating current source B-C. In this manner the approach controlled signaling functions just named are continued inactive as long as thetrack section D-E- remains vacant.

In the event, now, that a traincomes into the section D-E, the usual shunting action of its wheels and axles so reduces the potential appearing between the rails l and 2 that the detector relay KR is no longer able to respond to the pulses of trackway energy supplied from track battery TB. It accordingly releases and contact is thereof causes the operating winding of the approach relay AR continuously to be deenergized. That relay now releases and contacts 9 and ii thereof connect the wayside signal Se with its lighting source and the primary of track transformer TT with the alternating current source B-C.

In consequence the named'wayside signal lights the particular lamp selected by the decoding equipment ill and transformer TT supplies the track rails with a pulse of alternating current energy from source BC each time that the contact of coding device CR occupies its uppermost position. As has been mentioned, this energy is suitable for the control of train carried cab signals. The circuit over which it is supplied may be traced from the right terminal of the secondary winding of transformer TT through conductor 23, front contact 5 of device CR, conductors I! and it, track rail the wheels and axles (not shown) of the train, rail 2, and conductors i9, Zil and 2- 5 back to the left terminal of the track transformer secondary.

The approach relay AR remains released until the rear of the departing train clears the exit end of the track section DE at which time the potential appearing between the track rails again rises to the relatively high value necessary to effect code following operation by the detector relay KR. When this happens contact 53 of that relay restores the recurrent energization to the operating winding of relay AR and it, in turn, again picks up contacts 9 and H to restore the wayside signal Se and the track transformer T1 to their normal inactive condition.

One very practical advantage of my just described approach control facilities is that they include provision for counteracting the undesirable effects of track storage energy. As is known, such energy tends to accumulate in the rails and ballast of each of the signaling system track circuits as a result of the repeated application thereto of the direct current code pulses from the track battery TB. Unless counteracted the potential appearing between the rails l and 2 because of this energy may, over a period of time, build up to a value which becomes sufficient even to prevent the signaling system track relay TR at the section entrance from releasing during the off periods of the signal control code.

The counteracting provision mentioned above takes'the form of a discharge path which is set up between the track rails I and 2 during each off period of the direct current signal control code. This path is completed over coding contact 5 when in its uppermost position and it includes the secondary winding of the transformer TT. Through that winding the track storage potential discharges during each off code period by way of a circuit which extends from rail 5 through conductors i8 and El, front contact 5 of device CR, conductor 23, the secondary of transformer TT and conductors 24, 26 and is back to rail 2.

This shunting action reduces to a comparatively low value the potential which remains between the track rails following each disconnection of the direct current source TB therefrom. For lowering the impedance of the secondary winding of transformer T1 and hence increasing its effectiveness as a discharge path, the contact H of the approach relay AR may, as shown in Figs. 1 and 4, be arranged to short circuit the primary winding of the transformer whenever the approach relay is picked up. Whenever the track section D-E is unoccupied, this primary shunting path is completed from the right terminal of the primary of transformer'TT through conductor 7, front contact H of relay AR and conductor back to the left terminal of the transformer primary.

In addition to assuring proper code following operation on the part of the signaling system track relay TR at the section entrance, the just described connection of the transformer TT across the track rails during the off code periods also assures that the code following detector relay KR at the section exit will be deenergized sufficiently to release promptly at the beginning of each of these off periods. For the detector relay the referred to energy discharge path may be traced from the right terminal of the relay winding through conductors I8 and !1, front contact 5 of device CR, conductor 23, the secondary winding of transformer TT, and conductors 24, 20 and i9 back to the left terminal of the relay Winding.

This off period discharging action com bined with the use of a direct current code to operate the detector relay KR assures a high sensitivity of the apparatus to train shunting. As compared with alternating current code the named use of direct. current trackway energy (from battery TB) offers a special advantage in that the impedance of the track rails l and 2 is much lower to direct current than to alternating current and hence the shunting effect of a train coming into the entering end (as D in Fig. 1) of the track circuit becomes correspondingly more pronounced with the direct current code.

Moreover, the herein disclosed use of a detector device KR of the code following type directly contributes to the positiveness of this same. shunting action since the effectiveness of the shunt is now determined by a failure of the relay to pick up rather than by a failure of the relay to release. As is known, the minimum pick-up voltage of commercially available relays issubstantially higher than the minimum release voltage and in consequence the introduction of'code operation results in a definite improvement which is evidenced by increased operating. margins as well as increased track circuit lengths over which the approach control can be exercised.

Referring now to Fig. 2, I have there represented cut section facilities which are suitable for use with the approach control scheme of Fig. 1. These facilities are required when because of excessive length or for any other reason it becomes necessary to subdivide the main signal block length of track into two or more track circuits. In Fig, 2 one location of such a subdivision is designated by character Da and to facilitate explanation it will be assumed that this particular location is constituted by interposing insulated rail joints 3 between the limits D and E of the signal block of Fig. l.

The facilities of Fig. 2 are arranged to perform two functions. First, they repeat the coded direct current trackway energy received from the forward section around the joints 3 and into the rails of the section to the rear of cut section location Da and second, they additionally supply the rear section rails with coded alternating current energy suitable for cab signal control whenever a train comes into that rear section.

Aiding in the first named function is a code following track relay TR which is operated by energy received from the forward section rail and which carries a coding contact over which a track battery TB is connected in energy supplying relation with the rear section rails each time that the coding contact occupies its lowermost position. Under that condition, the rear section rails receive a pulse of direct current energy over a circuit which extends from the positive terminal of battery TB through an impedance it, back contact 5 of relay TR, conductors El and I8, the rear section rails I and 2, and conductors i9 and 20 back to the negative terminal of the track battery.

Each time that relay TR responds to a pulse of energy received from the forward section rails it picks up contact 5 and interrupts the circuit just traced. In this manner it will be seen that each off period of the direct current trackway code in the forward section rails produces an on period of corresponding energy supplied to the rear section rails and similarly each on period of the forward section code results in an ofi period in the rear section repeated code.

Aiding in the second named function of the cut section facilities of Fig. 2 is a code following detector relay KR which is bridged across the rear section rails as in Fig. 1, a slow release approach relay AR which is energized in step with each response of the detector relay over a circuit which includes an interposed transformer AT, and a track transformer TT which is connected with an alternating current source B-C whenever relay AR is released.

As long as the rear track section remains vacant, relay KR responds to the direct current energy pulses which are supplied over coding Contact 5 from battery TB at location Da and following each of these responses contact l3 thereof completes the direct current exciting circuit for the before mentioned interposed transformer AT. Each of these completions causes to be induced in the secondary winding of this transformer a pulse of voltage which by way of back contact l5 of relay KR circulates a pulse of current through the operating winding of relay AR. In this manner relay AR is recurrently energized as long as relay KR continues to follow code and thereby caused to hold its contact ll continuously picked up to maintain transformer TT in the normally inactive condition.

In the event that a train enters the track section to the rear of location Da, the shunting action of its wheels and axles reduces the rail potential to the extent that relay KR no longer follows the direct current code. In continuously releasing, contacts l4 and I5 thereof discontinue the supply of recurring energy pulses to the relay AR. That relay, in turn, now releases contact I! and connects transformer TT with the alternating current source BC.

Each time, now, that the coding contact 5 of relay TR is in the uppermost position the secondary winding of this transformer supplies the rear section rails with a pulse of alternating current energy which is suitable for controlling train carried cab signals. This action continues until the rear of the departing train has cleared the insulated joints 3 at the location of the cut section.

When that happens the continued shunting by the train of the forward section rails causes relay TR to maintain contact 5 continuously released or that steady or uncoded direct current energy continues to be impressed upon the rear section rails and the operating winding of relay KR. Relay KR now holds its contacts continuously picked up but because of the nature of the circuit which includes transformer AT the operating winding of the approach relay AR still remains continuously deenergized.

When the rear of the departing train clears the exit end of the forward section relay CR at the cut section location again follows code as does the associated relay KR and the recurring energization is restored to the approach relay AR with the result that track transformer TT again becomes inactive.

Referring to Fig. 3, I have there represented the exit end location E only of a track section which is equipped with a second form of the improved approach control facilities of my invention. Comparing the diagram of Fig. 3 with that of Fig. 1, it will be seen that the two are generally similar but that whereas the operating winding of the code following detector relay KR is bridged across the track rails I and 2 in Fig. 1 the operating winding of a corresponding code following detector relay KRI of Fig. 3 is serially included in the circuit through which the coded signal control energy is supplied to the rails 1 and 2 of the track section to the rear of location E. In addition, it will be seen that contacts 9 and I l of the slow release approach relay AR are in Fig. 3 arranged to render the associated wayside signal Se and track transformer TT active when the approach relay is picked up rather than when it is released as in Fig. 1.

All of these differences are accounted for by the fact that in the system of Fig. 3 the code following detector relay KRl is energized by the current component of the coded trackway energy rather than by the voltage component thereof as in Fig. 1. In many respects, however, the two systems are similar. That is, the relay KR! of Fig. 3 is responsive only to unidirectional current (from battery TB) and not to alternating current (from source B-C) and also it requires. that the intensity of this current be greater than a given minimum value before the relay will pick up its contact it.

In operation of the approach control scheme of Fig. 3 the continuously operating contact 5 of coding device CR periodically connects the track rails I and-2 with the direct current track battery TB over a circuit which extends from the positive terminal of that battery through current limiting-impedance I4, back contact of device CR, conductor I1, the operating winding of detector relay KRI, conductor [8, the track rails l and 2, and conductor l9 back to the negative terminal-of the track battery. As long as the track section to the rear of location E remains vacant, the magnitude of this rail current is below the minimum required to pick up relay KB! and in consequence the contact M of that relay remains released continuously to deenergize the approach relay AR. That relay, in turn, also remains released and the contacts 9 and l i thereof maintain the wayside signal Sc and the associated track transformer TT in their normally inactive condition.

In the event, now, that a train enters the referred to track section, the shunting action of its wheels and axles establishes a low resistance path between the track rails and in consequence the coded energy from track battery TB has a current component of a substantially elevated value. Under the influence of this increased current relay KRI picks up upon the occasion and for the duration of each of the on periods of the direct current code.

Contact l3 of that relay now periodically com pletes the energizing circuit for the approach relay AR and it, in turn, picks up its contacts 9 and l l thereby connecting the wayside signal Se with its source of lighting current and the associated track transformer TT with the alternating current terminals B and C. In this manner the entry of a train into the track section to the rear of location E lights the signal Se and supplies the rails of the track section with coded alternating current (over a circuit which includes conductor .23 and front contact-5 of device CR.) suitable for cab signal control.

The conditions just described continue until the rear of the departing train-clears location E at which time the rail supply current drops to a value below the pick-up intensity for the detector relay KRI. In continuously occupying the re leased position, that relay deenergizes the ap-. proach relay AR which in turn drops out and restores signal Se and the associated track trans?v formerTT to their normally inactive condition.

Referring now to Fig. 4, I have there represented a third form of the improvements of my invention again applied to the exit end E of a signal block length of railway track 1-42, This arrangement of Fig. 4 combines features of both of the schemesof .Figs. 1 and 3 and offers the practical advantage of extending the length of the track circuit which maybe approach controlled by the novel method herein disclosed.

In it use is made of a code following detector relay KRZ having a pair of differentially related operating windings 26 and 21. Winding 26 is bridged across the rails of the associated track :section over a circuit which includes conductors i8, 28 and I9 while Winding 2'! is serially included in the circuit (including conductors II and i8) over which the rails receive coded signal control energy from the track battery TB.

This detector relay KRZ of Fig. 4 is provided with contacts l3 and it which when periodically operated cause the transformer AT to transmit from a direct current exciting source recurrent pulses of pick-up energy to the operating-winding of the slow release approach relay AR. That relay, in turn-controls (by meansof contacts 9 and I I) energizing circuits for the wayside signal Se and the associated track transformer TT. As in the earlier figures, this track transformer cooperates with coding contact 5 of device CR in supplying the rear section rails with coded alternating current energy suitable for cab signal control.

In the particular form represented in Fig. 4

these direct and alternating current rail supply circuits differ slightly from those shown in Figs. 1, 2 and 3 in that the direct current supply circuit is completed when contact 5 is in the uppermost position and the alternating current circuit when that contact is in the lowermost position. It will be seen, however, that each arrangement is the operative equivalent of the other and hence the two are interchangeable in all of the embodiments of my invention herein disclosed.

Likewise, the energizing circuits for the approach relay AR are in Fig. 4 shown in a more elaborate form than in Fig. 2 and Figs. 1 and 3. As has been pointed out, these also are equivalents and have interchangeable possibilities in all of the embodiments of my invention which are herein disclosed.

Considering further the windings of the detector relay KR2, in a particular installation the number of turns of these two windings 26 and 21! will be so chosen that the magnetic flux produced by one of them substantially-predominates that produced by the other. That is, with reference to the track circuit the detector relay may be either a seriesoperating relay with a parallel compensating winding (in which event the winding 21 will be the predominating one) or it may be a parallel operated relay with a series compensating winding (in which event winding 26 will be the predominating one).

In either case the relay works on the resultant flux of the two opposing windings. As will be evident presently, this arrangement minimizes the effect of fluctuations in the voltage of the track battery TB and variations in the ballast resistance between track rails l and 2 and it thus makes possible a satisfactory operation of the approach control facilities on longer track circuits than is possible with either of the arrangements of Figs. '1 and 3. Under conditions of actual service the named fluctuations cannot, of course, be avoided and both, moreover, frequently are subject to comparatively wide limits of variation. Thus, the ballast resistance of a given track circuit is considerably higher when the road bed is dry than when the bed is wet. Likewise, the terminal voltage of a given track battery is conditioned upon a number of fractors including temperature, length of service, state of change and the like.

In the parallel winding arrangement of Fig. 1 there is a practical limit to the length of track circuit and minimum ballast resistance which can satisfactorily be worked. For example, it is found that circuits up to approximately 4,500 feet in length and having a ballast resistance of down to 3 ohms per thousand feet present no operating difliculties. Beyond these limits, however, difiiculty sometimes is experienced for the reason that it becomes impossible to detect at the leaving end of the block the diiference between an unoccupied wet or low ballast track circuit with a low track battery voltage and an occupied dry or high ballast track circuit with a high track battery voltage.

In the case of the series winding arrangement of Fig, 3 a comparable practical limit can be shown to exist. Here the maximum operable length of track circuit is reached when it becomes impossible to detect at the leaving end of the block the difference between an unoccupied wet or low ballast track circuit with a high battery voltage and an occupied dry or high ballast track circuit with a low battery voltage.

As will be seen from the foregoing, the effect of battery voltage fluctuation is opposite in the two cases. That is in the Fig. 1 system the limitations imposed by a low voltage of the track battery TB are comparable to those imposed by a high voltage of that battery in the Fig. 3 system, and vice versa. Consequently, where a substantial battery voltage fluctuation does exist a detector relay Working on the resultant flux of a series winding and an opposing parallel winding will minimize the effect of the battery voltage fiuctuation and make possible the satisfactory operation of a longer track circuit.

It is upon this principle that the improvements of the two winding relay KHZ of Fig. 4 are based. Since the flux created by each of the two windings 28 and 27 varies with the current circulated therethrough, the dilference in these fluxes or the resultant flux which is available for relay operation will also have a variation which generally is proportionate to the magnitude of the voltage of track battery TB. However, because of the difierential or subtractive relation of the two windings this flux will differ in a direction favoring extended track circuit lengths under given battery voltage and track ballast conditions from that which would appear in either a simple series (Fig. 3) or simple parallel (Fig. 1)

relay under like conditions.

As has been pointed out, the named benefit may be obtained when the detector relay KRZ is either a series operated device with a parallel compensating winding or a parallel operating device with a series compensating winding. For purposes of explanation it will be assumed that the device KRZ shown in Fig. 4 is of the latter type and that the normal ampere turns of the series winding 27 are of the order of only 50 per cent of the normal ampere turns of the parallel winding 25.

In operation of the approach control system of Fig. 4, each time that the continuously operating coding contact 5 of device CR is in the uppermost position, the rails I and 2 of the track section to the rear of location E are supplied with a pulse of direct current energy over a circuit which may be traced from the positive terminal of the battery TB through current limiting impedance 14, front contact 5 of device CR, conductor I7, the series winding 2'! of the relay KR2, conductor l8, the track rails l and 2, and conductors l9 and 28 back to the negative terminal of battery TB. Each pulse of rail voltage thus supplied is also impressed upon the parallel winding 26 of relay KRZ over a circuit which extends from the positive terminal of battery TB, through impedance 14, front contact 5 of device CR, conductor H, the series winding 21, conductor ill, the parallel winding 28, and conductor 28 back to the negative terminal of the track battery.

Since this parallel winding 26 predominates, each of these direct current pulses picks up relay KRZ as long as the track section to the rear of location E remains vacant. Contacts l3 and [5 of that relay now operate to cause transformer AT to supply the operating winding of the approach relay AR with recurring pulses of current which hold contacts 9 and l I of the relay in the pickedup position shown thereby to maintain inactivethe wayside signal Se and the associated track transformer TT.

When, now, a train comes into the track section under consideration, the shunting action of its wheels and axles reduces the voltage impressed upon the parallel winding 26 of relay KR2 and causes that relay continuously to release. This releasing action takes place in spite of the attendant increase in current which is circulated through the opposing series compensating winding 27. Thus deenergized at contacts i3 and I5 of relay KRZ, the approach relay AR now releases and contact 9 thereof completes the lighting circuit for the selected lamp of the wayside signal Se while contact ll connects the primary winding of transformer TT with the alternating current source B-C.

In this manner the named wayside signal becomes active and transformer TT supplies coded alternating current energy suitable for cab signal control to the track rails over a circuit which may be traced from the lower terminal of the transformer secondary through conductor 3|, back contact 5 of device CR, conductor ll, series winding 27 of relay KRZ, conductor IS, the track rails l and 2, and conductor I9 back to the upper terminal of the transformer secondary. As has already been pointed out relay KR2 is responsive only to direct current and as a result is does not pick up when subjected to the alternating current energization just referred to. Instead it remains continuously released until the rear of the departing train has cleared location E.

When that happens the Voltage appearing between the track rails l and 2 again rises to a relatively high value, detector relay KRZ responds to the individual pulses thereof, the relay AR once more is periodically nergized and contacts 9 and l l thereof return to the picked-up position in which they cause signal Se and the associated track transformer TI to return to their normally inactive condition.

In situations in which it is desired to modify the detector relay KR2 to the extent that it operates as a series relay with a parallel compensating winding, then the magnetizing eifect of series winding 21 will be chosen substantially to pre-= dominate that of the parallel winding 26. In such a situation the relay will respond only when a train comes into the track section and with the particular circuits represented in Fig. 4 it will then cause the approach relay AR to pick up.

In order that the desired approach functions may be effected the contacts 9 and l I of this relay may be modified in the manner shown in Fig. 3. When so modified the wayside signal Se and the associated track transformer TT will be rendered active when the relay is picked up instead of when it is released as in the systems of Figs. 1 and 4.

It will be understood that approach control functions other than those shown may readily be effected by the improved facilities of my invention. Instead, therefore, of controlling either or both of the wayside signals and track transformer devices S and TT, the slow releasing approach relay AR of any of the systems herein disclosed may be arranged to approach control highway crossing signals or approaches to interlockings or to perform any of numerous functions for which control by an approach relay is appropriate. 7

From the foregoing it will be seen that I have provided a new and simplified method for approach controlling various functions of coded signaling systems without the use of line wires. Since this method employs approach control facilities at the exit end only of each of the signal block lengths of track rather than at both ends as in comparable systems known to the prior art, both the cost and the quantity of the apparatus required by these facilities are substantially re duced.

As has been seen, this apparatus takes the form of .a relatively inexpensive code following detector relay KB and simple circuits governed thereby for locally energizing. the operating winding of a slow releaseapproach relay AR. Be-.

cause of its extreme simplicity the apparatus may readily be applied to existing coded track circuits of standard type and when used in conjunction therewith it does not interfere with the normal operation of the coded signaling system of which the circuits form a part.

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

Having thus described my invention, what I claim is:

1. In a system for approach controlling a signaling function without the use of line wires, the combination with a section of track to the rails of which coded energy is continuously supplied of a code following detector relay connected to receive a component of said coded .rail energy and being adapted to respond when and only when said component has the relatively high value which accompanies a predetermined trafiic condition of the section, a slow release approach relay energized in step with the responses of said detector relay, and traffic controlling apparatus governed by said approach relay.

2. In a signaling system which includes a sec tion of track to the rails of which coded energy is continuously supplied, the combination of a code following detector relay connected to receive a component of said coded rail energy and being adapted to respond when and only when said component has the relatively high value which accompanies a predetermined traffic condition of said section, a slow release approach relay energized in step with the responses of said detector relay, and trafiic controlling apparatus governed by said approach relay.

3. In a railway signaling system which includes a section of track to the rails of which coded signal control energy is continuously supplied and at the exit end of which a slow release approach relay is provided, the combination of means for maintaining said approach relay picked up under predetermined traffic conditions of said section and released at all other times comprising a code following detector relay also located at the exit end of the section, a circuit for impressing a component of said coded rail energy upon the operating winding of said detector relay, and means for energizing said approach relay in step with the detector relay responses.

4. In combination with a section of railway track, a source of trackway energy, a continuously operating coding contact which recurrently connects said source to the rails of said section, a code following detector relay having an operating windingconnected to receive a component of said coded rail energy and being adapted to respond when and only when said component has the relatively high value which accompanies a predetermined trafiic condition of said section, a slow release approach relay, and means for energizing said approach relay in step with each of the detector relay responses.

'5. In a system for approach controlling a signaling function without the use of line wires, the combination with a section of track to the rails of which coded energy is continuously supplied of a code following detector relay having an operating winding bridged across said rails and being adapted to respond only when the potential appearing between said rails is of the relatively high value which accompanies a vacant condition of the section, a slow release approach relay energized in step with the responses of said detector relay, and traffic controlling apparatus governed by said approach relay.

6. In combination with a section of railway track which forms a part of a signaling system of the continuously coded track circuit class, approach control apparatus comprising a code following detector relay having an operating winding bridged across the rails of said section and being adapted to respond when and only when the potential appearing between said rails is of the relatively high value which accompanies a vacant condition of the section, and a slow release approach relay energized in step with the responses of said detector relay.

'7. In combination, a section of railway track which forms a part of a signaling system of the continuously coded track circuit class, a slow release approach relay at the exit end of the section, similarly located traffic controlling ap paratus governed by said relay, and means for maintaining said approach relay picked up when the section is vacant and released when the section is occupied comprising a code following detector relay bridged across the rails of the section-and being adapted to respond only when the potential appearing between said rails is of the relatively high value which accompanies a vacant condition of the section, and a circuit over which said approach relay is energized in step with the responses of said detector relay.

8. In a signaling system which includes a section of track to the rails of which coded energy is continuously supplied, the combination of a code following detector relay bridged across said rails and adapted to respond to the potential appearing therebetweenwhen and only when that potential has the relatively high value which accompanies a vacant condition of the section, a slow release approach relay energized in step with the responses of said detector relay, and trafiic controlling apparatus governed by said approach relay.

9. In combination with a section of railway track, a source of trackway energy, a continuously operating coding contact which recurrently connects said source to the rails of said section, a code following detector relay bridged across said rails and adapted to respond to the potential appearing therebetween when and only when that potential has the relatively high value which accompanies a vacant condition of the section, a slow release approach relay, and means for energizing said approach relay in step with the responses of said detector relay.

10'. In combination with adjoining forward and rear sections of railway track, a signal positioned at-the entrance of said forward section and controlled in accordance with advance traffic conditions, a source of trackway energy, a continuously operating coding contact, a circuit recurrently completed by said contact for connecting said source to the rails of said rear track section, a code following detector relay bridged across said rear section rails and adapted to respond to potential appearing therebetween when and only when that potential has the relatively high value which accompanies a vacant condition of the rear track section, a slow release approach relay energized in step with the responses of said detector relay, and means governed by said approach relay for supplying energizing current to said signal when and only when that relay is released.

11. In combination with a section of railway track, direct current and alternating current sources of trackway energy, a continuously operating coding contact, a circuit completed by said contact when in one position for connecting said direct current source to the rails of said section, a circuit set up by said contact when in another position for supplying said rails with energy from said alternating current source, a code following detector relay bridged across said rails and responsive to direct current potential appearing therebetween when and only when that potential has the relatively high value which accompanies a vacant condition of the track section, and a slow release approach relay energized in step with the responses of said detector relay and arranged to render said alternating current rail supply circuit inactive at all times except when that relay is released.

12. In combination with a section of railway track, a direct current source of trackway energy, a track transformer, a continuously operating coding contact which repeatedly connects the rails of said section first to said direct current source and then to the secondary winding of said track transformer, a code following detector relay bridged across said rails and responsive to direct current potential appearing therebetween when and only when that potential has the relatively high value which accompanies a vacant condition of the track section, and a slow release relay energized in step with the responses of said detector relay and arranged to short circuit the primary winding of said track transformer at all times except when that relay is released.

13. In a system for approach controlling a signaling function without the use of line wires, the combination with a section of track to the rails of which coded current is continuously supplied of a code following detector relay having an operating winding serially included in the circuit through which said coded current is transmitted to the rails and being adapted to respond when and only when that current rises to the relatively high value which accompanies the presence of rolling stock within the section, a slow release approach relayenergized in step with the responses of said detector relay, and traflic controllin apparatus governed by said approach relay.

14. In combination with a section of railway track which forms a part of a signaling system of the continuously coded track circuit class, approach control apparatus comprising a code following detector relay having an operating winding serially included in the circuit through which the rails of said section receive coded current and being adapted to respond when and only when rolling stock interconnects said rails and thereby elevates'the value of said coded rail current, and a slow release approach relay energized in step with the responses of said detector relay.

15. In combination, a section of railway track which forms a part of a signaling system of the continuously coded track circuit class, a slow release approach relay at the exit end of the section, similarly located traflic controlling appara tus governed by said relay, and means for maintaining said approach relay picked up when the section is occupied and released when the section is vacant comprising a code following detector relay having an operating winding which is serially included in the circuit through which the rails of said section receive coded current and being adapted to respond when and only when that current rises to the relatively high value which accompanies the presence of rolling stock within the section, and a circuit over which said approach relay is energized in step with the responses of said detector relay.

16. In a signaling system which includes a section of railway track and a circuit through which coded current is continuously supplied to the rails of said section, the combination of a code following detector relay which obtains operating energy from a serial connection with said rail supply circuit and which is adapted to respond when and only when said coded rail current rises to the relatively high value which accompanies the presence of rolling stock within the section, and a slow release approach relay energized in step with the responses of said detector relay.

17. In combination with a section of railway track, a source of trackway current, a continuously operating coding contact, a circuit through which said contact recurrently connects said source to the rails of said section, a code following detector relay having an operating winding serially included in said rail supply circuit and being adapted to respond when and only when the rail current rises to the relatively high value which accompanies the presence of rolling stock within the section, a slow release approach relay, and means for energizing said approach relay in step with the responses of said detector relay.

18. In a system for approach controlling a signaling function without the use of line wires, the combination with a sectionv of track to the rails of which coded energy is continuously supplied of a code following detector relay having a pair of differentially related windings one of which is bridged across the rails of said section and the other of which is included in the circuit from which said rails receive the coded signal control energy, a slow release approach relay energized in step with the responses of said detector relay, and traffic controlling apparatus governed by said approach relay.

19. In combination with a section of railway track which is included in a signaling system of the coded track circuit class, approach control apparatus comprising a code following detector relay having a pair of differentially related Windings one of which is bridged across the rails of said section and the other of which is serially included in the circuit from which said rails receive the coded signal control energy, and a slow release approach relay energized in step with the responses of said detector relay.

20. In combination, a section of railway track which forms a part of a signaling system of the continuously coded track circuit class, a slow release approach relay at the exit end of the section, similarly located trafiic controlling apparatus governed by said relay, and means for maintaining said approach relay picked up under predetermined traffic conditions of the section and released at all other times comprising a code following detector relay having a pair of differentially related windings one of which is bridged across the rails of said section and the other of which is serially included in the circuit from which said rails receive the coded signal control energy, and a circuit over which said approach relay is energized in step with the responses of said detector relay.

21. In a signaling system which includes a section of railway track and a circuit through which coded energy is continuously supplied to the rails of said section, the combination of a code following detector relay having a pair of differentially related windings one of which is serially included in said rail supply circuit and the other of which is bridged across said section rails, a slow release approach relay energized in step with the responses of said detector relay, and traffic controlling apparatus governed by said approach relay.

22. In combination with a section of railway track, a source of trackway energy, a continuously operating coding contact, a circuit through which said contact recurrently connects said source to the rails of said section, a code following detector relay having a pair of differentially related windings one of which is serially included in said circuit and the other of which is energized by the potential appearing between said section rails, a slow release approach relay, and means for energizing said approach relay in step with the responses of said detector relay.

23. In combination with a section of railway track, direct current and alternating current sources of trackway energy, a continuously operating coding contact, a circuit completed by said contact when in one position for connecting the rails of said section to said direct current source, a circuit set up by said contact when in another position for supplying said rails with energy from said alternating current source, a code following detector relay having a pair of difierentially related direct current windings one of which is serially included in said direct current rail supply circuit and the other of which is bridged across said section rails to receive the potential appearing therebetween, and a slow release approach relay energized in step with the responses of said detector relay and arranged to render said alternating current rail supply circuit inactive at all times except when said approach relay is released.

HERMAN G. BLOSSER.

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