US2184543A - Approach control apparatus for railway signaling systems - Google Patents

Description

Dec. 26, 1939. H. G. BLOSSER 2,184,543

APPROACH CONTROL APPARATUS FOR RAILWAY SIGNALING SYSTEMS Filed Oct. 13, 1958 HIS ATTORNEY Patented Dec. 26, 1939 UNITE STATES APPRDACH CONTROL APPARATUS FOR RAILWAY SIGNALING SYSTEMS Herman G. Blosser, Pittsburgh, Pa., assignor to The Union Switch & Signal Company. Swissvale, Pa, a corporation of Pennsylvania Application October 13, 1938, Serial No. 234,814

9 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 improve certain features of an approach control without line wire scheme wherein the rails of each unoccupied signal block length of track transmit code step pulses of auxiliary energy forwardly from theblock entrance to eifect the energization of a slow release approach relay at the block exit.

A more specific object is to supply the referred to pulses of auxiliary energy to the entrance end of each track circuit in a simplified manner nwhich avoids interference with the normal code following operation of the signaling system track relay at that location.

Another object is to provide improved means for receiving these pulses at the exit end of the track circuit and for energizing the associated slow release approach relay in step with them.

In practicing my invention I attain the above and other objects and advantages by supplying the auxiliary energy during the off code periods from a direct current entrance end source which is poled in reversed relation to the coded signal control energy (normal polarity) which is recurrently impressed upon the rails by the usual track battery at the section exit; by connecting the exit end approach relay with the section rails through a rectifier which is poled to pass reversed polarity energy but not normal polarity energy; and by rendering the entrance end track relay of the signaling system responsive only to' normal polarity energy.

I shalldescribe several forms of approach control apparatus embodying my invention and. shall then point out the novel features thereof in claims. These illustrative embodiments are disclosed in the accompanying drawing in which:

Fig. l is a diagrammatic representation of a section of railway track which is equipped with one preferred form of my improved approach control apparatus;

Fig. 2 is a partial representation of the entrance end facilities of Fig. 1 arranged in a modified manner;

Fig. 3 is a similar partial representation of a modified form of exit end facilities which are usable with the approach control scheme of Fig. 1;

and

Fig. 4 is a diagrammatic showing of the apparatus of the earlier figures applied to control highway crossing signals without the aid of line wires. 7

In the several views of the drawing like reference characters designate corresponding parts.

Referring first to Fig. 1, the improved approach system of automatic block signaling for a railway track i2 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 is divided into the customarysuccessive sections by insulated rail joints 3 and the rails of each section form a part of a track circuit to which coded signal 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 following track relay which is installed at the entrance end of the-section and operated by energy received from the rails thereof; character TB 9. track battery or other direct current source provided at the section exit for the purpose of supplying these rails with the relay operating energy just 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 uards the entrance of each of the track blocks and which is controlled by the associated track relay TR through the medium of decoding apparatus H]. I

An automatic block signaling system of the referred to coded track circuit type operates without the aid of line wires and in representative 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 CR at one or another of the usual plurality of distinctive I code rates. Selection among these rates (which in a typical three indication system may consist of 80 and 180 energy pulses per minute) is made in accordance with advance traflic conditions by the decoding apparatus l0 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 minusf.

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, only one such function is approach controlled and this consists in lighting the wayside signal Se.

For governing the approach lighting function above stated, the approach relay AR is provided with a contact 9 over the back point of which the signal lighting circuits are carried. As will become apparent as the description proceeds, this or companion contacts of the relay AR also may be utilized to approach control signaling functions other than or in addition to the one just named. Typically, one such further function may consist in supplying the rails of the track section to the rear of the approach lighted signal with coded alternating current energy which is suitable for the control of train carried cab signals (not shown).

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 in association with the signal block DE of Fig. 1, this apparatus comprises: (1) entrance end facilities which supply the rails of that block with auxiliary energy having distinctive polarity characteristics and (2) exit end facilities which receive this auxiliary energy from the rails and transmit it to the operating winding of the approach relay AR.

As represented at location D, my improved entrance end facilities comprise: a battery or other source of auxiliary direct current energy AB; a circuit controlled over a back contact E2 of the track relay for connecting this auxiliary battery in energy supplying relation with the track rails during each off period of the received signal control code; and means, shown in the form of a rectifier M, for preventing the track relay from being falsely picked up by the auxiliary energy which the rails periodically receive.

For a purpose to be made more evident presently, this auxiliary or entrance end battery AB is poled in opposition to the exit end track battery TB. That is, while battery TB supplies the rails with what will be termed normal polarity energy (rail I positive with respect to rail 2) battery AB is arranged to supply the rails with what will be termed reversed polarity energy (rail 2 positive with respect to rail l). Under the action of the rectifier M the operating winding of the track relay TR receives current due only to the normal polarity track circuit energy and in this manner the relay is rendered unresponsive to the reversed polarity energy which the rails receive during the off code periods. Alternatively, of course, the track relay TR might be made of a polarized design which is incapable of picking up even though reverse flowing current does pass through its Winding. In that event, obviously, the rectifier I4 will not be required.

In the form shown at location E in Fig. 1, the cooperating exit end facilities include: a. circuit which at all times connects the winding of the approach relay AR in energy receiving relation with the track section rails I and 2; a rectifier IS included in this circuit and poled to block the flow of normal polarity current from the track battery TB but to permit passage of reversed polarity energy which is received over the rails from the entrance end auxiliary battery AB; and means for making this relay AR sumciently slow releasing to bridge the intervals between successive connections of the auxiliary battery AB with the track rails.

The delay producing means last named may, of course, take any suitable form, such as a snubbing impedance (not shown), bridged across the winding terminals or internal design cxpedients (again not shown) incorporated in the relay. Regardless of how obtained, the period of release delay for relay AR is made sufficiently long to bridge the spacing between consecutive off periods of the lowest pulse rate code which contact 5 of the signaling system device CR produces. Such a relation is necessary for the reason that the auxiliary energy from battery AB is transmitted to the approach relay AR only during the off code periods just referred to.

In operation of the complete approach control system 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 coding device CR is in the uppermost or on code period position, the track battery TB picks up the track relay TR by transmitting norm-a1 polarity current over a circuit which may be traced from the positive terminal of the battery through a current limiting impedance ll, front contact 5 of device CR, conductor. l8, track rail l, conductor l9, rectifier 14, the winding of track relay TR, conductor 20, track rail 2 and conductor 2| back to the negative terminal of battery TB.

Each time that the coding contact 5 occupies the lowermost or off code period position, the track relay TR releases in the usual manner and contact l2 thereof connects the auxiliary battery AB in energy supplying relation with the rails and causes it to circulate reversed polarity current through the operating winding of the approach relay AR at the section exit. The circuit over which, this auxiliary current fiows may be traced from the positive terminal of the battery AB through conductor 23, a current limiting impedance 24, conductor 20, track rail 2, conductor 2|, rectifier IS, the winding of relay AR, conductor [8, track rail I, conductors l9 and 25, and back contact l2 of .relay TR back to the negative terminal of battery AB.

In the manner just explained the operating winding of the approach relay AR is energized in step with each off period of the signal control code as long as the track section DE remains vacant. Because of its slow releasing characteristics, the relay now holds contact 9 continuously picked up and thereby maintains the lighting circuits of the wayside signal Se disconnected from their energizing source. In consequence, the approach controlled signaling function just named is continued inactive as long as the track section remains vacant.

In the event, now, that a train comes into the section DE, the usual shunting action of its wheels and axles cuts oii the transmission over the rails l and 2 of energy from battery TB to relay TR and also of energy from the auxiliary battery AB at the section entrance to the approach relay AR at the section exit. Now continuously deenergized, this approach relay releases and contact 9 thereof completes the energizing circuit for the signal Se. In consequence, that signal lights the particular lamp selected by the decoding equipment If].

As soon as the rear of the departing train clears location E, the track circuit again transmits coded direct current energy from the normal polarity source TB to the track relay TR at location D, auxiliary battery AB again supplies the track rails with reversed polarity energy during the off periods of the signal control code, these rails transmit this auxiliary energy forwardly to location E and the there located approach relay AR once more receives the recurring pulses of this energy over the rectifier 15. In again picking up in response to these pulses, contact 9 of relay AR, restores the associated wayside signal Se to its normally inactive state.

From the foregoing it will be seen that I have provided an exceedingly simple arrangement wherein the entrance end track relay TR responds only to the normal polarity energy from the exit end track battery TB andthe exit end approach relay AR responds only to the reversed polarity energy from the entrance end auxiliary battery AB. This selective action is made possible by the polarity selective characteristics which the rectifiers l4 and Hi respwtively impart to the relays TR and AR. Accordingly, it will be evident that without interfering with the desired operation of the approach control system (wherein the track and auxiliary batteries TB and AB are oppositely poled with respect to the track circuit rails I and 2) the polarity selective characteristics of the two relays TR, and AR may be secured in any other desired manner, as by designing the relays themselves to have polarity selective characteristics. In that event, both of the rectifiers could be dispensed with.

Referring now to Fig. 2, I have there represented a somewhat modified form of entrance end facilities which may be used in place of the apparatus represented at D in Fig. 1. These are generally equivalent to the corresponding facilities earlier described and in considering them it I will be helpful to assume that the conductors l9 and 2!! of Fig. 2 are joined at location D with the track rails I and 2 of Fig. 1 which extend forwardly to location E of the same figure where they are connected withthe exit end facilities of which the track battery TB and the approach relay AR form a part.

The modified facilities of Fig. 2 differ, however, from those of Fig. l in that the aux liary battery AB is at all times connected in energy supplying relation with the track rails l and 2 instead of being so connected only when contact l2 (Fig. 1) of relay TB is released. This means that the reversed polarity voltage of battery AB is at all times impressed upon the rail supply circuit instead of only during the off periods of the received signal control code.

The operation of an approach control system employing the simplified entrance end facilities of Fig. 2 is basically the same as that already explained in detail in connection with the earlier described complete system of Fig. 1, and diifers therefrom only in the respect that during the on periods of the received signal control code all of the potential of battery AB must be absorbed in the current limiting impedance 24 in order that sumcient of thenormal'polarity potential from battery TB may appear between the rails to pick up the track relay TR.

For this reason it is desirable when employing the simplified arrangement of Fig. 2 to proportion the element 24 to have a somewhat greater value of impedance than does the element I! which is included in the track battery circuit at the section exit. To the same end, it may also sometimes be desirable to choose the potential of the auxiliary battery AB to be substantially less than that of the signaling system track battery TB. For example, while battery TB will ordinarily be made up of two, three or even four primary cells, battery AB may consist of only a single one of such cells.

Referring now toFig. 3, I have there represented a modified form of exit end facilities which may be used in place of the apparatus represented at location E in Fig. 1. These modified facilities are generally equivalent to the corresponding facilities earlier described and in considering them it will be helpful to assume that the conductors l8 and 2| of Fig. 3 are joined at location E with the track rails l and. 2 of Fig. 1 which extend rearwardly to location D of the same figure where they are connected with the track relay TR and the auxiliary battery AB.

The modified facilities of Fig. 3 differ from those shown in Fig. 1 in that the static rectifier it in the winding supply circuitof the approach relay AR is replaced by carrying this circuit over the back. point of the coding contact 5 of device OR by way of a conductor 21. In this modified arrangement, that coding contact 5 connects the Winding of the approach relay in energy receiving relation with the track rails l and 2 only during the off periods of the signal control code which device CR produces. This action of the contact 5 thus is in effect a rectifying one in that it connects the winding of relay AR with the track rails only when the reversed polarity energy from the entrance end auxiJiary battery AB is received from those rails over conductors l8 and 2| and not when the rails are being supplied with normal polarity energy from the track battery TB.

In operation of the exit end facilities of Fig. 3, each time, under vacant conditions of the track section (see D-E of Fig. 1), that contact 5 of the coding relay CR is in the uppermost or on period position the track battery TB supplies the rails with energy for pickingup the track relay TR (see location D of Fig. 1) in the same manner as in Fig. 1. Each time, likewise, that coding contact 5 occupies the lowermost or off period position, the winding of relay AB. is connected in energy receiving relation with the rails and has impressed thereon a pulse of auxiliary energy from the battery AB (again see location D of Fig. 1). Accordingly, this relay AR operates in the same manner as when the winding supply circuit therefor includes the static rectifier as shown at It in Fig. 1. That is, the relay is maintained picked up by recurring pulses of auxiliary energy received from the entrance end battery AB as long as the section D-E remains vacant and is released when a train comes into the section and by-passes the rails I and 2 through its wheelsand axles.

It is immaterial whether the entrance end facilities which cooperate with the exit end facilities of Fig. 3 are of the type shown at location D in Fig. 1 or of the modified or simplified character represented in Fig. 2. In either instance the winding of the approach relay AR. is connected in energy receiving relation with the rails only during the 01f code periods when the reversed polarity potential from the auxiliary battery AB is available in these rails 'for circulating current through the relay winding.

The same comment also applies, as has been seen, to the exit end facilities shown at location E in Fig. 1 which are suitable for use either with the entrance end facilities shown at location D of the same figure or with the simplified facilities represented in Fig. 2. In the latter case, the relay AR still receives energy in recurring pulse form for the reason that even though the entrance end battery AB is continuously connected with the track rails, the reversed polarity voltage thereof is bucked down or overcome by the normal polarity and predominating voltage of the track battery TB during each on period of the signal control code.

Referring to Fig. 4, I have there shown the modified entrance end facilities of Fig. 2 and the modified exit end facilities of Fig. 3 combined into a system wherein the operation of a highway crossing signal XS is controlled without the aid of line wires. This signal guards a highway 39 which crosses the railway track I-2 at point Da. This point marks the usual cut or division of the main signal block length of track of which location D marks the entrance into two sections, the second of which has its entrance at the cut location Da. The exit end of this second section corresponds to location E of Fig. 1 and is provided with the usual signaling system facilities, shown as including a track battery TB and a coding device CR, which supply the rails with coded signal control energy.

For repeating this energy around the cut section joints 3 use is made of a code following track relay TRa which operates a contact corresponding to member 5 of Figs. 1 and 3. Each time that relay TRa picks up in response to a pulse of energy received from the forward section rails, this contact 5 connects the rear section rails with a track battery TB and each time that the relay TRa releases, the same contact connects the winding of a signal control relay ARa in energy receiving relation with the rear section rails. The operating circuit of the highway crossing protective signal XS is completed whenever a contact 9 of this signal control relay occupies the released position.

With the exception of the fact that the coding relay shown at GR in Fig. 3 is replaced by the code repeating relay TRa, the facilities represented at the cut section location Da in Fig. 4 are a duplicate of those shown in Fig. 3. They cooperate with the entrance end facilities represented at location D to maintain the crossing signal XS inactive as long as the section DDa remains vacant and to place this signal in operation when a train comes into the section of track just named. As will be evident, these entrance end facilities of Fig. 4 now shown as being a duplicate of those represented in Fig. 2 may if desired be replaced by the corresponding facilities represented at location D in Fig. 1 and a similar comment applies to the rear section exit end facilities shown at out location Dct. Instead of being a duplicate of those represented in Fig. 3 these may include the static rectifier arranged as at I5 in Fig. 1.

In operation of the highway crossing control system of Fig. 4, coded energy received from the rails of the section ahead of location Da by the code following relay TRa is repeated into the rails of the section to the rear of the named location battery TB is connected in energy supplying relation with the rear section rails and each time that the contact 5 is released this track battery connection is interrupted. As long as the rear section remains vacant, this coded energy is received and responded to by the track relay TR at location D and the auxiliary battery AB at that location is effective during the olf periods of the received signal control code to supply the rails with reversed polarity energy which is circulated through the winding of the slow release signal control relay ARa.

Under the influence of these recurring pulses of auxiliary energy the named relay maintains contact 9 continuously picked up and thus keeps the crossing protective signal XS inactive. As already intimated, the signal control relay has slow releasing characteristics which correspond to those already explained in connection with the approach relay AR of the earlier figure.

Upon entry of the train into the rear track section, the shunting action of its wheels and axles deprives the signal control relay ARa of this auxiliary energy and contact 9 thereof accordingly releases. In so doing it completes for the crossing signal XS an operating circuit which is shown as extending from the positive terminal of a suitable supply source through back contact 9, conductor 3i and the signal operating mechanism back to the negative terminal of the supply source. Thus energized, the signal becomes active in the usual manner to warn the users of highway 39 that a train is approaching the intersection.

When the rear of the forwardly moving train clears the cut section location Da the rails I and 2 thereof once more become effective for transmitting reversed polarity energy from the auxiliary battery AB forwardly to the winding of the signal control relay ARa. The circuit over which this winding current is supplied may be traced from the positive terminal of auxiliary battery AB through conductor 23, impedance 26. conductor 20, track rail 2, conductor 2!, the winding of relay ARa, conductor 21, back contact 5 of relay TR conductor 18, track rail and conductors l9 and 25 back to the negative terminal of battery AB.

Under the influence of this energy relay ARa picks up contact 9 and thus discontinues the operation of the crossing protective signal XS. As long as any part of the train remains in the section ahead of cut location Da, repeater relay TRa is continuously released and contact 5 thereof connects the winding of relay ARa continuously across the rails of the rear track section. Under this condition, the energy received by this winding is continuous. This is because battery AB at the entrance end is continuously connected in energy supplying relation with the rails. That relation holds true even when the entrance end facilities are of the character represented at location D in Fig. 1 as including back contact i2 of the track relay TR in the auxiliary battery circuit. In that case, the absence of energy from the track battery TB at location Da (contact 5 of relay TRa continuously released) allows contact l2 of relay TR. at location D to occupy the released position.

When the rear of the train clears the exit end of the forward section, coded signal control energy is again received by the code following relay TRa at out location Da and contact 5 of that re- .lay once more becomes active to cause coded energy from battery TB to be supplied to the periods of the signal control code. Because of its slow releasing characteristics, however, it still maintains contact 9 continuously picked up under the influence of the recurring pulses of auxiliary energy received from entrance end bat-- tery AB.

If desired, as already pointed out, the arrangement now represented in Fig. 4 wherein the winding of relay ARo; is connected with the rear section rails over the back point of coding contact 5 may be replaced by one corresponding to that shown at location E in Fig. 1 wherein the winding of the relay AR is at all times connected With the track rails by way of a circuit which includes a specially poled static rectifier 16. Such a change will not alter the explained operation of the hi hway crossing control system for the reason that rectifier it blocks off all energy from the track battery TB and permits passage of reversed polarity energy only from the entrance end auxiliary battery AB.

From the foregoing it will be seen that I-have provided improved facilities for systems of approach control wherein use is made of forwardly fed pulses of auxiliary energy supplied to the track circuit at the entrance end of the section.

As these facilities are entirely a function of the track circuit and apparatus which is directly associated therewith, they are independent of the coding and decoding apparatus of the coded signaling system with which they are combined and hence they are usable with signaling systems which employ a Wide variety of different types and forms of such apparatus. Moreover while I have explained my invention in applications wherein the lights of a wayside signal and the operation of a highway crossing signal are approach controlled, it will be understood that other comparable functions may also be provided for instead of or in addition to the illustrative ones just named.

Although I have herein shown and described only a few forms of approach control apparatus embodying my invention, it will be 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. 4

Having thus described my invention, what I claim is:

1. In combination with a section of railway track, a first source of direct current energy, coding means for periodically connecting said first source with the rails of said section in a manner to supply recurring pulses of normal polarity energy thereto, a second source of direct current energy, a circuit over which said second source supplies reversed polarity energy to said rails during the intervals which separate said recurring pulses of normal polarity energy, a traffic governing relay designed to respond to said reversed polarity energy, a continuously completed.

circuit over which the operating winding of said relay is connected in energy receiving relation with said rails, a static type rectifier included in said circuit for conditioning it to pass said reversed polarity energy but not said normal polarity energy whereby said relay winding is energized only from said second source when said section is vacant and is continuously deenergized when the section becomes occupied, and traflic governing apparatus controlled by said relay and rendered active. only when that relay. becomes continuously deenergized. I

2. In combination with a section of railway track, a first source of direct current energy, coding means for'periodically connecting said first source with the rails of said section in a manner to supply recurring pulses of normal polarity energy thereto, a second source of direct current energy, a circuit over which said-second fic controlling apparatus governed by said ap-.

, roach relay and rendered active when that relay becomes-released in response to the entry of a train into said section. V

3. In combination with a section of railway track, a source of direct current energy at the exit end of said section, coding means for periodically connecting said exit end source with the rails of said section in a manner to supply recurring pulses of. normal polarity energy thereto, a code following track relay at the entrance end of said section connected with said rails and designed to be picked up by each pulse of said normal polarity energy which is received therefrom, a source of direct current energy also at said section entrance, a circuit completed whenever said track relay is released for connecting said entrance. end source with said section rails in a manner to supply reversed polarity energy thereto, a trafiic governing relay at said section exit uninterruptedly connected to receive said reversed polarity energy from said rails and being capable of responding to that received. energy, a static type rectifier included in the said rail-totrack-relay connectionfor preventing said reversed polarity energy from being transmitted tosaid track relay, a static type rectifier included in said rail-to-trafiic governing relay connection for preventing said normal polarity energy from being transmitted to said trafiic governing relay, whereby that relay is energized only from said entrance end source when said section is vacant and is continuously deenergized when the section becomes occupied, and traflic governing apparatus controlled by said trafi'ic governing'relay and rendered active only when that relay becomes continuously deenergized.

4. In combination with a section of railway track, means at the section exitfor supplying the rails of the section with coded direct current track circuit energy which is of normal polarity, a code following track relay at the section entrance connected to receive said coded energy from said rails, means for rendering said track relay responsive to that received normal polarity energy but not to reversed polarity energy, means controlled by said track relay and effective during the off periods of the received track circuit code for supplying said rails with auxiliary direct current energy which is of reversed polarity, a traffic governing relay positioned at the section exit and being capable of responding to said auxiliary energy, a continuously completed circuit over which the operating winding of said trafiic governing relay is connected in energy receiving relation with said rails, a static type rectifier serially included in said circuit and poled to pass energy of said reversed polarity only whereby said relay winding receives only said auxiliary energy when said track section is vacant and becomes continuously deenergized when said section is occupied, and trafiic governing apparatus controlled by said traffic governing relay and rendered active under continuously deenergized conditions only of that relay.

5. In combination with a section of railway track, means at the section exit for supplying the rails of the section with coded direct current track circuit energy which is of normal polarity, a code following track relay at the section entrance connected to receive said coded energy from said rails, means for rendering said track relay responsive to that received normal polarity energy but not to reversed polarity energy, means controlled by said track relay and effective during the off periods of the received track circuit code for supplying said rails with auxiliary direct current energy which is of reversed polarity, an approach relay at the section exit having a slowness of release which is sufficient to bridge the spacing between said ofi code periods, a continuously completed circuit over which the operating winding of said approach relay is connected in energy receiving relation with said rails, a static type rectifier included in said circuit and poled to pass energy of said reversed polarity only whereby said approach relay receives only said auxiliary energy when said section is vacant and is continuously deenergized when the section becomes occupied, and trafiic controlling apparatus governed by said approach relay and rendered active only when that relay becomes released.

6. In combination with a section of railway track, a source of direct current energy at the exit end of said section, coding means for periodically connecting said source with the rails of said section in a manner to supply recurring pulses of normal polarity energy thereto, means for supplying reversed polarity direct current energy to said rails during the periods which separate said recurring pulses of normal polarity energy, a traffic governing relay located at said section exit and being capable of responding to said reversed polarity energy, a circuit which continuously connects the operating winding of said relay in energy receiving relation with said rails, a static type rectifier serially included in said circuit for conditioning it to pass current which results from said reversed polarity energy but not from said normal polarity energy, whereby said trafiic governing relay receives only said reversed polarity energy when said section is vacant and is continuously deenergized when the section becomes occupied, and traffic governing apparatus controlled by said relay and rendered active under continuously deenergized conditions only of that relay.

7. 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 traific conditions, means at the exit end of said rear section for supplying the rails of that section with coded direct current track circuit energy which is of normal polarity, an approach relay also positioned at said rear section exit and having a slowness of release which is sufficient to bridge the intervals between consecutive off periods of said track circuit code, means governed by said approach relay for supplying energizing current to said forward section signal when and only when that relay is released, a source of direct current energy at the entrance end of said rear section, a circuit over which said source supplies reversed polarity energy to said rear section rails during the said ofi periods of said track circuit code, a continuously completed circuit over which the operating winding of said approach relay is connected in energy receiving relation with the said rails of the rear section, and a static type rectifier included in said circuit for permitting said approach relay to receive energy of said reversed polarity only whereby that relay is energized from and held picked up by said entrance opposite polarity, a rectifier included in said connection to prevent reversedpolarity energy from being transmitted to said relay, a source of auxiliary direct current energy also at said section entrance, a circuit including an impedance by which said auxiliary source is continuously connected with said rails and over which that source supplies reversed polarity energy to those rails during the intervals which separate the said recurring pulses of normal polarity energy that are present in the rails at the said section entrance, a trafiic controlling relay installed at the section exit and operated by the said reversed polarity auxiliary energy that is there received from said rails, and traffic governing apparatus controlled by said exit end relay and maintained inactive as long as said operation of that relay continues.

9. In combination with a section of railway track, a first source of direct current energy, coding means for periodically connecting said first source with the rails of said section in a manner to supply recurring pulses of normal polarity energy thereto, a second source of direct current energy at the entrance end of said section, a circuit which continuously connects said second source with said section rails in a manner to supply reversed polarity energy thereto, an impedance included in said circuit for completely absorbing the voltage of said second source and a portion of the opposing voltage of said first source during each of the recurring periods that said normal polarity energy is received at the said section entrance whereby said reversed polarity energy is present in the rails only during the intervals which separate the said received pulses of normal polarity energy, a trafiic controlling relay installed at the section exit and, operated by the said reversed polarity auxiliary energy that is there received from said rails, and trafiic governing apparatus controlled by said exit end relay and maintained inactive as long as said operation of that relay continues.

HERMAN G. BLOSSER.

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