US2763452A - Two wire-four indication railway signal control system - Google Patents

Description

Spf. m, 1956 A. HOOGERHYDE V TWO WIRE-FOUR INDICATION RAILWAY SIGNAL CONTROL SYSTEM Filed Sept. 27. 1951 MNNN kaq INVENTOR.

-Arzbm" Hoagerbgde BY LU -k. 61rd.

HIS ATTORNEY United States Patent TWO WIRE-FOUR INDICATION RAILWAY SIGNAL CONTROL SYSTEM Arthur Hoogerhyde, Verona, Pa., assignor to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application September 27, 1951, Serial No. 248,491

6 Claims. (Cl. 246-46) Name of Signal Signal Indication Signal Indication Aspect Proceed Green. Proceed, preparing to stop at next s Yellow. Stop Red.

If the spacing between consecutive signals provides in- SUIfiClEl'lt braking distance, that is, if a brake application other than an emergency application, when initiated at a given signal which is displaying an approach indication, on a train which is traveling at maximum speed, cannot stop the train at or before it reaches the next signal in advance which is displaying a stop indication, a restrictive indication should also be provided at one or more signals before the train reaches the signal which is displaying an approach indication.

If a restrictive indication is provided at one signal before a train arrives at a signal which is displaying an approach indication, the signaling system is known as a three-block four-indication signaling system. In threeblock four-indication signaling systems previously devised, embodying color light signals, the aspects and indications displayed by each signal are as shown in the following tabulation:

Name of Signal Indication Signal Indication Signal Aspect Clear Proceed Green.

Advance approach. Proceed, preparing to stop Two steady yellow at 2d signal in advance. lights, or one flashing yellow light.

Approach Proceed,preparingtostop One steady yellow at next signal. light. Stop Stop Red.

Name of Signal Indication Signal Indication Signal Aspect Clear Proceed Green. Advance approach Proceed, preparingtostop Two steady yellow at 2d signal in advance. lights, one above the other. Approach Proceed, preparingtostop One steady yellow at next signal. light. Stop Stop Red.

"ice

A feature of my invention for accomplishing this object is the provision of means embodying two biased neutral relays energized over a two-wire coded line circuit for effecting operation of a signal to display the four different indications specified in the last preceding tabulation.

Another feature of my invention for accomplishing this object is the provision of a decoding relay which is controlled to be slow releasing at times, for controlling, in part, the lighting of one of the yellow lamps of the signal while the signal is displaying two yell-ow lights, and for preventing a momentary lighting of a green lamp of a signal when a train passes the signal while it is displaying two yellow lights.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing one form of apparatus embodying my invention, in which two biased neutral relays for controlling a signal such, for example, as a distant signal for a home signal of an interlocking plant, are connected in series with each other but in opposed relation so that one of the biased neutral relays will close its front contacts in response to current of a given polarity passing through these relays, and the other biased neutral relay will close its front contacts in response to current of the opposite polarity; and in which steady current of normal or reverse polarity is supplied to these relays according as the home signal referred to is controlled to display a clear or a stop indication, respectively, and coded current of reverse p0- larity is supplied to these relays when the home signal is controlled to display an approach indication.

Similar reference characters refer to similar parts in the drawing.

Referring to the drawing, a stretch of single track railway is shown divided by insulated joints 5 into sections BZT, AZT, 1T, ZRT and ST. Each of these sections is provided with a track circuit including a suitable source of current, such, for example, as a battery 6 connected across the rails adjacent one end of the section, and a track relay, designated by the reference character R, with a distinguishing prefix, which is the same as the reference character for the corresponding section, connected across the rails adjacent the opposite end of the section. In order to simplify the drawing, each track, comprising two parallel series of track rails, is represented by a single line.

A track switch, designated by the reference character 1, is located in section IT. A switch contact, designated by the reference character 28, is operated in conjunction with switch 1, and is arranged to be closed when switch 1 is in its normal position and to become opened when switch 1 is moved to the reverse position.

I shall assume that traflic movements toward the right, as shown in the drawing, are eastbound, whereas traffic movements toward the left, as shown in the drawing, are westbound. An eastbound home signal comprises an upper unit, designated by the reference character ZRA, and a lower unit, designated by the reference character ZRB, for directing traffic movements over switch 1 in the normal position, as shown in the drawing, or in the reverse position, respectively. Westbound home signals, designated by the reference characters 2LA and ZLB, govern traflic movements over switch 1 in the normal and the reverse position, respectively. Operation of switch 1 and signals ZRA-ZRB, 2LA and ZLB may be effected manually from an interlocking plant, if traffic conditions are suitable.

An eastbound signal, designtated by the reference charmeans in accordance with traffic conditions east of signal 38.

An eastboundsignal, designated by the reference char:

3 acter 4S,.is-located in the rear of, and serves as a distant signal for, signal 2RA2RB.

As shown in the drawing, each of the signals is of the color light type, having green, yellow and red lamps, designated by the reference characters G, Y and R, respectively, for providing various signal'a'spects'.

I shall also assume that the distance between signal 2R:A- 2RB and signal 35 is less than braking distance, so that when signal unit 2RA is displaying the approach indication, while signal 35 is displaying the stop indication, a restrictive indication, such for example as an advance approach indication, should be displayed by signal 45.

Sections BZT and AZT constitute a block, which I shall designate a first block, sections IT and 2RT constitute a block which I shall designate a second block, and section 3T constitutes a block which I shall designate a third block. I shall refer to signals 45, ZRA-ZRB and 38 as first, second, andthird signals, respectively.

Signal 3Sflis lighted through a front contact 7 of relay 3TR and is controlled by well known means indicated at42 to display either of two proceed indications, namely, the' clear and the approach indication, as selected by traffic conditions in advance of section 3T, Means for selecting the clear and approach indications of signal 3S by traflic conditions in advance of section 3T are not shown in detail in the accompanying drawing, because such means are well known in the railway signaling art, and do not constitute a part of my invention. One such means is shown in Fig, 3 of the drawings in Letters Patent of the United States No. 1,888,706, granted November 22, 1932, to H. A. Thompson for Train Signaling System, and comprises the front and back points of a contact of a relay, designated by the reference character 2HD, in the lighting circuits for a signal designated by the reference character 28. Another such means is shown in Fig. 1a of the drawings in Letters Patent of the United States No. 2,586,458, granted February 19, 1952, to C. W. Failor for Railway Traffic Controlling Apparatus, and comprises normal and reverse polar contacts 25 of the track relay 41TR in the lighting circuits for the signal designated by the reference character 41W.

Signal unit ZRA is controlled by a home control relay, designated by the reference character ZRAHR, and by a distant control relay, designated by the reference character ZRAHDR, to display two proceed indications, namely, the clear and the approach indication, and also the stop indication. Relay ZRAHR is in turn controlled by track relays lTR and 2RTR, by a front contact 29 of relay ZRAHDR, by switch contact 28, and by a contact 26 of a signal. lever, designated by the reference character 2V.

Lever 2V has a normal position, designated by the reference character n, and two control positions, designated by the reference characters f and r. Contact 26 of lever 2V is normally open, but becomes closed when lever 2V is moved to the r position.

Relay ZRAHDR is controlled by a circuit which includes pole-changing contacts 31 and 32 of relay 3TR, so that relay ZRAHDR will be energized by current of normal polarity when contacts 31 and 32 are closed at their front points, and relay ZRAHDR will be energized by current of reverse polarity when contacts 31 and 32 are closed at their back points.

Atsignal control repeater relay, designated by the reference" character ZRAHPR, is controlled by a front contact 34 of relay ZRAHR, and by a normal polar contact 33 of relay 2RAHDR, and is therefore energized only when relay ZRAHR is energized and when relay ZRAHDR is energized by current of normal polarity for controlling signal. unit 2RA to display a clear indication.

A- coding device, shown as a relay, is designated by the reference character ZFR. Relay ZFR is controlled by a back contact 39 of relay ZRA-HPR and by a front contact 40 of relay ZRAHR. Relay 2FR is designed to operate at a relatively slow code rate for opening its contact 17 i on theorder of 40 times per minute. Contact 17 ofrelay which I shall assume is of normal polarity and which flows in the direction indicated by the arrow in the symbol for relay 4BR, is passed through the' windings of these relays. Relay 4HR closes its front contacts when current of reverse polarity flowing in the direction by the arrow in the symbol for relay 4HR passes through these relays. When track relays BZTR, A2TR and ITR are energized, and relay ZRAHPR is deenergized, relays 4HR and 4DR are energized by steady current of reverse polarity or by coded current of reverse polarity according as relay ZRAHR is deenergized or energized. Relays 4HR and 4BR are energized by steady current of normal polarity while relays B2TR, A2TR, lTR and ZRAHPR are all energized.

A home and distant control repeater relay, designated by the reference character HDPR, is controlled by the front and back points of contacts 18 and 19 of relays 4HR and 4DR, respectively, so that relay I-IDPR is energized When either one of the relays 4HR and 4BR is energized while the other of these two relays is deenergized, but relay HDPR is deenergized when relays 4HR and 4DR are both deenergized or both energized. Relay I-IDPR is rendered slow releasing by a capacitor d and'a resistor 1 connected in series with each other across the control winding of relay HDPR. Relay HDPR will therefore retain its front contacts closed while relays 4HR and 4DR are being energized by coded current.

Decoding relays, designated by the reference characters BTP' and CDR, are controlled by a front contact 35 of relay HDPR, and by the front and back points of a contact 36 of relay 4HR. Relay BTP is made slow releasing by a capacitor d and a resistor t connected in multiple with its control winding. Relay CDR is also made slow releasing by a capacitor d and a resistor 1 connected in multiple with its control winding only while relay BTP is energized.

Signal 4S is controlled by relays HDPR, 4BR, 4HR and CDR to display three proceed indications, namely, the clear, the advance approach, and the approach indication, aswell as a stop indication. The clear, advance approach, and approach indications are displayedby the steady green, two yellow lamps, one above the other,v

and a single yellow lamp, respectively, of signal 45.

The various control and operating circuits shown in the accompanying drawing may be supplied with energizing current from any suitable source such, for example, as abattery, designated by the reference char acter Q, having terminals 13 and N.

Having described, in general, the arrangement of the various parts of apparatus embodying my invention, I shall now describe the circuits and operation in detail.

As shown in the drawing, all parts of the apparatus are in the normal condition, that is, the stretch of track shown is unoccupied, and therefore all track relays are energized; switch I is in the normal position; signal lever 2V is in its normal or n position; each of the signals 2RA2RB, ZLA and ZLB is displaying the stop' indication; signal 38 is displaying the clear proceed indication; signal is displaying the approach proceed indication; relay ZRAHDR is energized by current of normal polarity; relays 4HR and 4BR are energized by steady current of reverse polarity; relay HDPR is energiz'ed by steady current; and relays ZRAHR, ZFR, ZRAHPR, CDR and BTP are deenergized.

Only a portion of the lighting circuit for signal 35 is shown, including, the front point of contact 7 of relay 3TR, but it is assumed that traflic conditions in advance of Signal 38 are such that the circuit for lamp G of signal 38 is selected so that lamp of signal 38 is lighted by its circuit which includes the front point of contact '7 of relay 3TR.

The circuit by which lamp R of signal unit ZRA is lighted passes from terminal B, through the back point of contact 8 of relay ZRAHR, and lamp R of signal unit 2RA to terminal N.

The circuit by which relays 4HR and 4DR are energized by steady current of reverse polarity passes from terminal B, through the back point of contact 15' of relay ZRAHPR, windings of relays 4DR and 4HR, contacts 14, 13 and 12 of relays BZTR, AZTR and lTR, respectively, back point of contact 11 of relay ZRAHPR, back point of contact 16 of relay ZRAHR, and a resistor rt to terminal N.

With relays 4HR and 4DR energized by current of reverse polarity, to which relay 4HR responds by closing its contact 13 at the front point and relay 4DR responds by retaining its contact 1? closed at the back point, relay HDPR is energized by a circuit passing from terminal B, through the front point of contact 18 of relay 4HR, back point of contact 19 of relay 4DR, and the winding of relay HDPR in multiple with a resistor t and a capacitor d to terminal N.

With relays HDPR and 4HR energized, and with relay 4DR deenergized, the approach aspect of signal 48 is displayed, comprising only the upper yellow lamp Y, the circuit for this lamp passing from terminal B, through the front point of contact 20 of relay HDPR, front point of contact 22 of relay 4HR, back point of contact 21 of relay 4DR, and upper lamp Y of signal 45 to terminal N.

I shall assume that, with apparatus arranged as shown in the drawing, a leverman or dispatcher moves lever 2V to its r position to elfect the control of lamp G of signal unit ZRA to display a proceed indication for an eastbound train.

Relay ZRAHR will therefore be energized by a circuit passing from terminal B, through contact 26 of lever 2V, contact 27 of relay ZRTR, contact 2? of switch 1, contact 29 of relay ZRAHDR, contact 36 of relay lTR, and the winding of relay ZRAHR to terminal N. With relay 3TR energized, relay ZRAHDR is energized by current of normal polarity passing from terminal B, through the front point of contact 31 of relay 3TR, winding of relay ZRAHDR, and the front point of contact 32 of relay 3TR to terminal N. With relay ZRAHR energized, and with relay ZRAHDR energized by current of normal polarity, lamp G of signal unit 2RA will be lighted by a circuit passing from terminal B, through the front point of contact 8 of relay ZRAHR, polar contact of relay ZRAHDR closed in the normal or lefthand position, as shown in the drawing, and lamp G of signal unit ZRA to terminal N.

Also, with relay ZRAHR energized, and with relay ZRAHDR energized by current of normal polarity, relay ZRAHPR will be energized by a circuit passing from terminal B, through contact 33 of relay ZRAHDR, contact 34 of relay 2RAHR, and the winding of relay ZRAHPR to terminal N. With relay ZRAHPR energized, relays 4HR and 4DR are now energized by current of normal polarity passing from terminal B, through the front point of contact 11 of relay ZRAHPR, contacts 12, 13 and 14 of relays lTR, AZTR and B2TR, respectively, windings of relays 4HR and 4DR, front point of contact of relay ZRAHPR, and resistor It to terminal N.

With relays 4HR and 4DR now energized by current of normal polarity, so that the contacts of relay 4HR are closed at their back points and the contacts of relay 4DR are closed at their front points, relay HDPR will be energized by a circuit passing from terminal B, through the back point of contact 18 of relay 4HR, front point of 6 contact 19 of relay 4DR, and the winding of relay HDPR in multiple with a resistor t and a capacitor d to terminal N. With relay HDPR energized, and with relay 4HR deenergized, relay BTP will now be energized by a circuit passing from terminal B, through contact 35 of relay HDPR, back point of contact 36 of relay 4HR, and the winding of relay BTP in multiple with a resistor t and a capacitor d to terminal N.

With relays HDPR and 4DR energized and with relay 4HR deenergized, lamp G of signal 48 will now be lighted by current passing from terminal B, through the front point of contact 20 of relay HDPR, front point of contact 21 of relay 4DR, back point of contact 22 of relay 4HR, contact 23 of relay CDR, and lamp G of signal 48 to terminal N.

When an eastbound train now enters section B21, deenergizing relay B2TR, contact 14 of relay BZTR will open the circuit for relays 4HR and 4DR, causing these relays to be deenergized. With relays 4HR and 4DR deenergized, relays HDPR and BTP will in turn also be deenergized. Lamp R of signal 48 will now be lighted by a circuit passing from terminal B, through the back point of contact 20 of relay HDPR, and lamp R of signal 48 to terminal N.

When the eastbound train enters section AZT, deenergizing relay AZTR, contact 13 of relay A2TR will open the circuit for relays 4HR and 4DR at a second point, and when the eastbound train enters section 1T, deenergizing relay 1TR, contact 12 of relay lTR will open the circuit for relays 4HR and 4DR at a third point.

The train, upon entering section 1T, also eifects deenergization of relay ZRAHR by the opening of contact 30 of relay ITR. Relay ZRAHPR then. becomes deenergized by the opening of contact 34 of relay 2RAHR. With relay ZRAHR deenergized, lamp R of signal unit 2RA will again be lighted by its circuit previously traced.

When the eastbound train enters section ZRT, deenergizing relay ZRTR, contact 27 of relay ZRTR will open the circuit for relay 2RAHR at a second point.

When the eastbound train enters section 3T, deenergizing relay 3TR, the circuit for lamp G of signal 38 will be opened at the front point of contact 7 of relay 3TR, and the circuit for lamp R of this signal will be closed passing from terminal B, through the back point of contact 7 of relay STR, and lamp R of signal 38 to terminal N.

When the eastbound train leaves section 1T, relays 4HR and 4DR will again be energized by current of reverse polarity in the circuit previously traced. With relays 4HR and HDPR again energized, as previously described, upper lamp Y of signal 45 will again be lighted.

When the eastbound train leaves section ZRT, if, while the train is on section 3T, lever 2V is in its r position for controlling signal unit 2RA for a second eastbound train, relay 2RAHR will again be energized, as previously described. With the train on section 3T, relay ZRAHDR will now be energized by current of reverse polarity in a circuit which is the same as the circuit previously traced for this relay except that it includes the back points of contacts 31 and 32 of relay 3TR instead of the front points of these contacts. With relay ZRAHR now energized and relay ZRAHDR energized by current of reverse polarity, yellow lamp Y of signal unit ZRA will be lighted by a circuit passing from terminal B, through the front point of contact 8 of relay ZRAHR, polar contact 10 of relay ZRAHDR closed in the reverse position, and lamp Y of signal unit ZRA to terminal N.

With relay ZRAHDR energized by current of reverse polarity, its contact 33 will be moved to the: reverse position, so that relay 2RAHPR will now be deenergized although contact 34 of relay ZRAHR is closed. With relay ZRAHPR deenergized, and with relay ZRAHR energized, the coding relay ZFR will be energized by its circuit passing from terminal B, through contact 39 of relay ZRAHPR, contact 40 of relay ZRAHR, and the winding of relay ZFR to terminal N.

WithrelaysZRAI-IR and 2F R now energized'while relay 2RAHPR- is deenergizcd, relays 4HR and 4DR- will be energized by coded current of reverse polarity passing from terminal B, through the back point of contact of relay ZRAHPR, windings of relays 4BR and 4HR, contacts 14, 13 and 12 of relays BZTR, AZTR and lTR, respectively, back point of contact 11 of relay ZRAHPR, front point of contact 16 of relay ZRAHR, and contact 17 of relay ZFR to terminal N. In order to improve the operation of relays ll-IR and 4BR While energized by coded current, the resistor it is omitted from the circuit by which relays 4HR and 4BR are energized by the coded current of reverse polarity.

With relays 4HR and 4DR energized by coded current of reverse polarity, relay HDPR will now be energized by coded current in the circuit previously traced passing from terminal B, through the front point of contact 13 of relay SHR, and the back point of contact 19 of relay 4BR. During'the periods when contact 36 of relay 4HR- is closed atits back point, relay BTP will be energized by its circuit previously traced. Relay BTP, on account of being rendered slow releasing by resistor t and capacitor d in multiple with its control winding, will retain its front contacts 37 and 38 closed during the cleenergized periods of relay BTP while contact 36 of relay 4HR is closed at its front point.

Relay CDR will therefore be periodically energized by current passing from terminal B, through contact 35 of relay HDPR, front point of contact 36 of relay 4HR, contact 37 of relay BTP, and the winding of relay CDR to terminal N. At the same time, capacitor d will be charged by a circuit which is the same as the circuit just traced for relay CDR as far as the front point of contact 36 of relay 4l-IR, and then passes through the front point of contact 38 of relay BTP, and resistor t and capacitor d to terminal N.

With relays HDPR and CDR now energized while relay ADR- is deenergized, both yellow lamps Y of signal 45 will be lighted, the circuit for the upper lamp passing from terminal B, through the front point of contact 20 of relay HDPR, contact 24 of relay CDR, back point of contact 21 of relay 413R, and upper lamp Y to terminal N. The circuit by which the lower lamp Y of signal 45 is lighted is the same as that just traced for the upper lamp Y except that it includes also contact 25 of relay CDR.

if a second train should now enter section BZT, effecting deenergizaticn of relay 4HR, relay BTP would be kept energized, for a brief period of time, by its circuit which includes contact of relay HDPR and the back point of contact 36 of relay 4HR. With contacts 37 and 38 ofrelay BTP closed at their front points, capacitor d would discharge through the winding of relay CDR, making'relay CDR slow in releasing. Relay ODR would therefore retain its contact 23 open for a brief period of time, thereby preventing momentary lighting of lamp G of signal 48 before the front point of contact 29 of relay HDPR opens.

When the first eastbound train leaves section 3T, lamp Y of signal 35 will first be lighted, as selected by traffic conditions in advance, by a circuit including the front point of contact '7 of relay STR. If lever 2V is still in its r position, relay ZRAHR Will again be energized, and relay ZRAHDR Will be energized by current of normal polarity, as previously described, so that lamp G of signal unit 211A will be lighted, and relay ZRAHPR will again be energized. If the second eastbound train has not yet entered section B21 relays 4HR and 4DR will again be energized by current of normal polarity, aspreviously described, so that lamp G of signal will again be lighted.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein Within the. scope of the appended claims" Without departing from the spirit and scope of my invention;

Having thus described my invention, what I claim is:

1. In a two line wire, four indication railway signal control system for a stretch of railway track comprising a first and a second and also a third block arranged in that order, including a first and a second and a third signal for governing traffic movements in a given direction over said first and second and third blocks respectively, including third control means for controlling said third sig+ nal to indicate proceed or stop, and including second control means for controlling said second signal to display a clear or an approach indication according as said third signal is controlled to indicate proceed or stop respectively, the combination comprising, two biased neutral home and distant control relays connected in series with each other but in opposed relation so that said distant control relay will close its front contacts in response only to current of normal polarity and said home control relay will close its front contacts in response only to current of reverse polarity, means including said second control means for effecting energization of said home and distantcontrol relays by steady current of normal or reverse polarity according as said second signal is controlled to display a clear or a stop indication respectively, means including said second control means for effecting energization of. said home and distant control relays by coded current of reverse polarity if said second signal is controlled to display an approach indication, a home and distant control repeater relay, means controlled by said home and distant control relays when energized by current of normal or reverse polarity for energizing said home and distant control repeater relay, a first and a second decoding relay, means controlled by'a front contact of said home and distant control repeater relay and by a back contact of said home control relay for energizing said first decoding relay, means including front contacts of said home control relay and said first decoding relay for energizing said second decoding relay, and means controlled by said home and distant control relays and by said home and distant control repeater relay and also by said second decoding relay for controlling said first signal to display a clear indication and an advance approach indication and also an approach indication as well as a stop indication.

2. In a two line wire, four indication railway signal control system for a stretch of railway track comprising a first and a second and also a third block arranged in that order, including a first and a second and a third signal for governing traflic movements in a given direction over said first and second and third blocks respectively, including third control means for controlling said third signal to indicate proceed or stop, and including second control means for controlling said second signal to display a clear or an approach indication according as said third signal is controlled to indicate proceed or stop respectively, the combination comprising, two biased neutral home and distant control relays connected in series with each other but in opposed relation so that said distant control relay will close its front contacts inresponse only to current of normal polarity'and said home control relay will close its front contacts in response only to current of reverse polarity, means including said second control means for effecting energization' of said home and distant control relays by steady current of normal or reverse polarity according as said second signal is controlled to display a clear or a stop indication respectively, means including said second control means for effecting energization of said home and distant control relays by coded current of reverse polarity if said second signal is controlled-to display an approach indication, a home and distant control repeater relay, means controlled by saidhome and distant control relays when energized by cur rent ofnormal or reverse polarity for energizingfisaid home and distant control repeater relay, a first and a second decoding relay, means controlled by a front contact of said home and distant control repeater relay and by a back contact of said home control relay for energizing said first decoding relay, means including front contacts of said home control relay and said first decoding relay for energizing said second decoding relay, means including front contacts of said distant control relay and said home and distant control repeater relay and back contacts of said home control relay and said second decoding relay for lighting a green lamp of said first signal, means including front contacts of said home control relay and said home and distant control repeater relay and a back contact of said distant control relay for lighting a first yellow lamp of said first signal, and means including front contacts of said home and distant control repeater relay and said second decoding relay and a back contact of said distant control relay for lighting said first yellow lamp and also a second yellow lamp of said first signal.

3. In a two line wire, four indication railway signal control system for a stretch of railway track comprising a first and a second and also a third block arranged in that order, including a first and a second and a third signal for governing traffic movements in a given direction over said first and second and third blocks respectively, including third control means for controlling said third signal to indicate proceed or stop, and including second control means for controlling said second signal to display a clear or an approach indication according as said third signal is controlled to indicate proceed or stop respectively, the combination comprising, two biased neutral home and distant control relays connected in series with each other but in opposed relation so that said distant control relay will close its front contacts in response only to current of normal polarity and said home control relay will close its front contacts in response only to current of reverse polarity, means including said second control means for effecting energization of said home and distant control relays by steady current of normal or reverse polarity according as said second signal is controlled to display a clear or a stop indication, respectively, means including said second control means for eifecting energization of said home and distant control relays by coded current of reverse polarity if said second signal is controlled to display an approach indication, a first and a second decoding relay, means controlled by said home and distant control relays when energized by coded current of reverse polarity for energizing said first decoding relay during the off periods of said coded current and for energizing said second decoding relay through a front contact of said first decoding relay while said coded current is flowing, and means controlled by said home and distant control relays and by said second decoding relay for lighting a green lamp of said first signal through means including a front contact of said distant control relay and for lighting a first yellow lamp of said first signal through means including a front contact of said home control relay and also for lighting said first yellow lamp and a second yellow lamp of said first signal through means including a front contact of said second decoding relay.

4. In combination, a stretch of railway track divided into a first and a second block, a first color light signal embodying a green lamp and two yellow lamps and also a red lamp for governing traffic movements in a given direction onto said first block, a second color light signal embodying a green lamp and a yellow lamp and also a red lamp for governing traific movements in said given direction from said first block onto said second block, control means for said second signal, means including trailic responsive means controlled by traffic conditions on said track in advance of said second signal for controlling said control means for said second signal, means including said control means for selectively lighting said green or said yellow or said red lamp of said second signal in accordance with tratfic conditions in advance of said second signal, two biased neutral home and distant control relays connected in series with each other but in opposed relation so that said distant control relay will close its front contacts in response only to current of normal polarity and said home control relay will close its front contacts in response only to current of reverse polarity supplied to the windings of said relays, means for supplying steady current of normal or reverse polarity to the windings of said relays according as the green or the red lamp of said second signal is controlled by said control means to be lighted, means including a flasher relay for supplying coded current of reverse polarity to the windings of said relays when the yellow lamp of said second signal is controlled by said control means to be lighted, and means controlled by said home and distant control relays when energized by steady current of normal or reverse polarity for steadily lighting the green or only one yellow lamp respectively of said first signal and when energized by coded current of reverse polarity for steadily lighting the two yellow lamps of said first signal.

5. In combination, a stretch of railway track divided into a first and a second block, a color light signal embodying a green lamp and two yellow lamps and also a red lamp for governing traffic movements in a given direction onto said first block, a second signal operable to display a clear or an approach as Well as a stop indication for governing traffic movements in said given direction from said first block onto said second block, control means for said second signal, means controlled by said control means for selectively operating said second signal to display a clear or an approach or a stop indication, a first and a second biased neutral relay connected in series with each other but in opposed relation so that said first relay will close its front contacts in response only to current of normal polarity and said second relay will close its front contacts in response only to current of reverse polarity supplied to the windings of said relays, means for supplying steady current of normal or reverse polarity to the windings of said relays according as said second signal is controlled by said control means to display the clear or the stop indication respectively, means including a flasher relay for supplying coded current of reverse polarity to the windings of said relays if said second signal is controlled by said control means to display the approach indication, and means controlled by said first and second code following relays when energized by steady current of normal or reverse polarity for steadily lighting the green or only one yellow lamp respectively of said color light signal and when energized by coded current of reverse polarity for steadily lighting the two yellow lamps of said color light signal.

6. In combination, a stretch of railway track divided into a first and a second block, a color light signal embodying a green lamp and two yellow lamps and also a red lamp for governing traflic movements in a given direction onto said first block, a second signal operable to display a clear or an approach as well as a stop indication for governing traific movements in said given direction from said first block onto said second block, control means for said second signal, means controlled by said control means for selectively operating said second signal to display a clear or an approach or a stop indication, a first and a second biased neutral relay connected in series with each other but in opposed relation to that said first relay will close its front contacts in response only to current of normal polarity and said second relay will close its front contacts in response only to current of reverse polarity supplied to the windings of said relays, means for supplying steady current of normal or reverse polarity to the windings of said relays according as said second signal is controlled by said control means to display the clear or the stop indication respectively, means for supplying coded current of reverse polarity to the windings of said relays if said second signal is controlled by said controlrneans to display the approach indication, a slow releasing. home and distant control repeater relay, means controlled by said-homeand distant control relays when energized by current of. normal or reverse polarity for energizing said home and distant control repeater relay, a slow releasing first decoding relay, a second decoding relay, means including a front contact of said home and distant control repeater relay and a back contact of said home control relay for energizing said first decoding relay, means including front contacts of. said home control relay and said first decoding relay for energizing said second decoding relay, means for rendering said second decoding relay slow releasing if said second decoding relay becomes deenergized while said front contact of said first decoding relay is closed, means including front contacts of. said distant control relay and said home and distant control repeater relay and back contacts of said home control relay and said second decoding relay for lighting a green lamp of said first signal, means including front contacts of said home controlrelay and said home and distant control repeater relay and a back contact of 12 said distant control relay for lighting a first yellow lamp of said first signal, and means including front contacts of said home and distant control repeater relay and said second decoding relay and a back contact of said distant control relay for lighting said first yellow lamp and also a second yellow lamp of said first signal.

References'Cited in the file of this patent UNITED STATES PATENTS 2,103,016 Pflasterer' Dec. 21, 1937 2,107,679 Kemmerer Feb. 8, 1938 2,107,680 Crago Feb. 8, 1938 2,130,470 Pflasterer Sept. 20, 1938 2,153,668 Kemmerer Apr. 11, 1939 2,168,816 Young Aug. 8, 1939 2,168,817 Pilasterer Aug. 8, 1939 2,547,664 Rost Apr. 3, 1951 2,638,536 Tizzard May 12, 1953 2,654,831 Willing et al. Oct. 6, 1953 2,692,942 Young Oct. 26, 1954

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