US2571834A - Railway signal control system - Google Patents

Description

Oct. 16, 1951 w. H. CLAUS 2,571,834

RAILWAY SIGNAL CONTROL SYSTEM Filed Sept 25; 1947 2 SHEETS'-SHEET l H15 ATTORNEY W. H. CLAUS RAILWAY SIGNAL CONTROL SYSTEM 2 SHEETS-SHEET 2 l l I ll W BY QN NR m w R S m m Q Q m w m g J 1L" n mhw m w n n It. n flu M u i l m NJ w% mn R a w Oct. 16, 1951 Filed Sept. 25, 1947 Patented Oct. 16, 1951 RAILWAY SIGNAL CONTROL SYSTEM William H. Claus, Downers Grove, 111., assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania Application September 25, 1947, Serial No. 776,089

Claims.

My invention relates to a railway signal control system, and particularly to a railway signal control system for signals for governing trafiic movements in opposite directions over a stretch of single track railway.

In a railway signaling system for a stretch of single track railway which is provided with passing sidings spaced along the single track, two pairs of head block signals, each comprising an entering and a leaving signal, are commonly employed for each passing siding for governing traffic movements in opposite directions, and are placed one pair adjacent each end of each passing siding. One or more pairs of intermediate signals for governing traific movements in opposite directions are also commonly employed between consecutive passing sidings. Protection for opposing trafiic movements between passing sidings is obtained by suitable arrangement of the intermediate signals, or by overlapping controls for the opposing leaving head block signals.

One feature of my invention is the provision of speed controlled means for modifying or for rendering ineffective the overlap control for a leaving head block signal if a train approaches the opposing leaving head block signal slowly enough.

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

The accompanying drawings, Figs. 1a and lb, when placed end to end with Fig. 1a on the left, constitute a diagrammatic view showing one form of apparatus embodying my invention, in which a stretch of single track railway is provided with passing sidings spaced along the stretch, and in which two pairs of head block signals are employed for each passing siding and are placed one adjacent each end of each passing siding, and one pair of intermediate signals is employed between passing sidings for governing traffic movements in opposite directions; and also in which speed controlled apparatus is provided for modifying or for rendering ineffective the overlap control for each leaving head block signal if a train approaches the opposing leaving head block signal slowly enough.

Similar reference characters refer to similar parts in each of the drawings.

In each of the drawings, the contacts operated by the various relays are identified by numbers, each such number having a distinguishing prefix from which it is separated by a dash when the associated contact is shown apart from the relay by which it is operated. The prefix for each of these contact numbers comprises the reference character for the respective relay by which the associated contact is operated. For example, contact 5H-l8 shown at the extreme right hand end of Fig. 1a is identified by the number I8 separated by a dash from the prefix 5H which is the reference character for relay 5H by which this contact is operated.

Referring further to the drawings, one end which I shall assume is the west end, of a stretch of single track railway designated by the reference character U, is shown in Fig. 111 provided with a passing siding X, and the east end of the stretch is shown in Fig. lb provided with a second passing siding Z. The east end of passing siding X is connected with track U by a switch w. The west end of passing siding Z is similarly connected with the main track U by a second switch aw. In order to simplify the drawings, each track comprising two parallel series of track rails is represented by a single line.

Track U is divided by insulated joints, designated by the reference character [0, into sections a-b, 12-0, 0-11, de, ef, fg, g--h, hk, Icm, and mn. Sections 17-0 and -m will be referred to as timing sections, and sections c-d and h--k will be referred to as overlap sections. Each of the track sections is provided with a track circuit including a suitable source of current, such as a battery I I, connected across the rails adjacent one end of the section, and a track relay, designated by the reference character TR with a distinguishing prefix, connected across the rails adjacent the opposite end of the section.

Adjacent each end of each of the passing sidings is a pair of head block signals for governing traffic movements in opposite directions. Signals 0, 3, 6 and 9 which govern traflic movements away from the passing sidings are known as leaving signals, whereas signals I, 2, I and 8 which govern traffic movements toward the passing sidings are known as entering signals. One pair of intermediate signals 4 and 5 governs trailic movements in opposite directions between passing sidings. Signals I, 3, 5, I and 9 govern eastbound traffic movements, and signals 0, 2, 4, 6 and 8 govern westbound traffic movements. The signals may be of any suitable design, such, for example, as the color light type shown in the drawings, each of which comprises a green lamp G, a yellow lamp Y and a red lamp R.

Each of the signals is controlled by a polarized signal relay H having a numerical prefix which is the same as the reference character for its signal. Each of the signal relays H has a slow release neutral armature, and therefore its front contacts remain closed while its polar contacts are moving between their extreme positions. The

G, Y and R lamps of each signal are lighted by circuits which are controlled by the associated signal relay, and which are similar to the circuits shown for signal 3.

A time element relay AlTE, shown in Fig. la, is controlled to close its front contact if the timing section b-c is occupied by an eastbound train a measured period of time before the train enters the overlap section c-d. A second time element relay ZTE is controlled to close its front contact if a speed controlled stick relay is is in the deenergized condition at the time an eastbound train enters overlap section c-d. Other first and second time element relays, designated by the reference characters A8TE and lTE, ref spectively, shown in Fig. lb, are controlled similarly to relays AI'IE and ZTE, respectively.

Each of the time element relays may be of any suitable design, such, for example, as the code stepping type shown in the drawings, and which comprises a control elem-ent r and a code stepping element p. The stepping elements p formlays Al TE and 2TB are controlled by .a back contact of a code transmitting relay 'ICT, and the stepping elements p for relays and lTE are controlled by a back contact of .a second .code transmitting relay BCT.

The code stepping time element relays may be of a type such as the time element device TE which is described and claimed in Letters Patent of the United States No. 2,279,117, granted to Arthur W. Fisher, on April Ti, 1942, for Control Apparatus. A description of the time element device TE is given in that patent on page 2, .column 2, line 67, to page 3, column 1, line 72.

The code stepping element p of the time element relays in the present application corresponds to the stepping magnet 35 of the time element device TE in the Fisher patent referred to. The control element t of the time element relays in the present application corresponds to the clutch magnet 36 in the Fisher patent.

Back contacts 13 and d8 of relay A-ETE, for example, in the present application, correspond to checking contacts Iii-El a and 5"358a described in the Fisher patent on page 3, column 1, lines 36-43, and on page 4, column '2, lines 4-13, which open immediately when operation of the time element device is started. As stated in the patent, such contacts are checking contacts, included in the signal control circuits for checking that the time element device returns to its full normal position when it is deenergized, by preventing the signals from being cleared unless these contacts are closed.

Contact 65 of relay AlTE, for example, in the present application, corresponds to time contact 38-3811 described in the Fish-er patent on page 3, column 1, lines 43-48. Contact $5 of relay AiTE therefore closes, upon the lapse of a measured period of time after relay Ai'lE becomes energized.

A speed responsive stick relay iS is associated with timing section b-c and overlap section cd and is controlled to become energized when a the front contact of either one of the time element relays AITE and 2TE is closed while overlap track section relay 2TB is deenergized. Stick relay IS has also a third pick-up circuit which includes a back contact of relay 3TB, and has a fourth pick-up circuit which is controlled by a contact which is operated in conjunction with switch to so as to be normally open, but which becomes closed when switch w is moved to its r verse position. Relay iS has a stick circuit which ii i) is controlled by a back contact of track relay 2TB for overlap section cd.

A second speed responsive stick relay, designated by the reference character 8S, is associated with timingsection Icm and with overlap section 'h--Fc, and is controlled similarly to relay ES.

A directional stick relay 55, associated with signal 5, is controlled in a well-known manner to become energized when an eastbound train enters section ef while a front contact of relay 5H is closed, and to then remain energized by circuits controlled by back contacts of relays 5TB, and 5H. A repeater relay ESP is controlled by a Lf-ront contact of relay 5TB and by a back contact of relay 55. A second directional stick relay 4S and a second repeater relay 55?, shown in Fig. lb, for west bound traffic movements, are controlled similarly to relays 5S and'ESP, respectively.

Having described, in general, the arrangement and control of the apparatus shown by the accompanying drawings, I .shall now describe, in detail, its operation.

As shown in the drawings, all parts of the .apparatus are in their normal condition, that is switches 11; and mo are in their normal position; each signal is displaying a green or clear indication; all track sections are unoccupied, and hence all track relays are energized; each signal relay H is energized by current of normal polarity; each code transmitter CT is deenerg-ized; the control element 1 of each time element relay TE is deenergized, and its code stepping element p is constantly energized; each or the stick relays is, 3$, 5S and 855 is dee-nergized; and each of the repeater relays Q8? and ESP is energized.

The circuit for energizing relay 2H by current of normal polarity, only a portion of which is shown, includes a contact 52 of relay 2TB, contact iii of relay AiTE, and contact it of relay 2TB. The circuit for relay TH is closed similarly to the circuit just described for relay Relay SH is energized by current of normal polarity in a circuit passing from terminal B of a suitable source of current shown as a battery Q at the left-hand end of Fig. a, through contact 551-58, back point of contact ES-9, contact 4SP-Ei3, contact 25 of relay 5TB, contact 22 of relay 3TB, and the winding of relay (iii to terminal C of battery Q. Relay 8H is energized by current of normal polarity in a circuit which is similar to the circuit just traced for relay 3H.

With relay 3H energized by current of normal polarity, green lamp G of its signal 3 is lighted by a circuit passing from terminal EB of a suitable source of lighting current, through the front point of contact of relay 3H, contact ii of relay 3H closed in the normal position, and lamp G of signal 3 to terminal EN of the same source of lighting current.

Relay 5H is energized by current of normal polarity in a circuit passing from terminal B, through the front point of contact '28 of relay lI-I, contact 29 of relay lTR, contact 3! of relay BTR, contact 32 of relay 4TB, contact 33 of relay 5TB, and the winding of relay 5H to terminal C. Relay lH is energized by current of normal polarity in a circuit which is similar to that just traced for relay 5H.

Relay EH is energized by current of normal polarity in a circuit passing from terminal B, through the front point of contact 45 of relay 3H, contact 46 of relay is, contact .1 of relay 2TE, contact 48 of relay AITE, contact 49 of relay 3TR, contact 50 of relay ZTR, contact 5i of relay AITR, contact 52 of relay ITR, and the winding of relay II-I to terminal C. Relay 8H is energized by current of normal polarity in a circuit which is similar to the circuit just traced for relay IH. 5

Green lamps G of the signals l, 2, 4, 5, 5, 'l, and 8 are lighted by circuits which are similar to the circuit previously traced for signal 3.

Since code transmitter ICT is deenergized, the stepping elements p of relays AITE and ZTE are constantly energized by current passing from terminal B, through contact 42 of code transmitter l CT, and the stepping elements p of relays AI'IE and ZTE in multiple, to terminal C. The stepping elements 10 of relays A8'I'E and 'ITE are energized similarly'to the stepping elements p of relays AITE and ZTE.

Relay 5SP is energized by a circuit passing from terminal B, through the front point of contact 43 of relay 5TR, contact 53-44, and the winding of relay 58F to terminal C. I

I shall assume that, with apparatus embodying my invention as shown in the drawings thus in the normal condition, an eastbound train approaches signal I and deenergizes relay 2H, causing green lamp G of signal 2 to be extinguished, and red lamp R of this signal to be lighted for indicating stop. With relay 2H deenergized, relay 4H will now be energized by current of reverse polarity in a circuit which is the same as the circuit previously described for this relay except that it includes terminal N of battery Q, and the back point of contact 34 of relay 2H, instead of terminal B of battery Q and the front point of contact 34 of relay 2H. With relay 4H energized by current of reverse polarity, green lamp G of signal 4 will be extinguished, and yellow lamp Y of this signal will be lighted by a circuit which is similar to a circuit which will be traced for signal 3.

When the eastbound train enters sections a-b, relay lH will become deenergized, thereby extinguishing lamp G of signal I and lighting red lamp R of this signal by acircuit which is similar to a circuit which will be traced for signal 3.

When the train enters section b-c, code transmitter ICT will become energized by a circuit passing from terminal B, through contact 6| of relay Al TR, and code transmitter ICT to terminal C. With code transmitter ICT energized, stepping element p of relays AITE and ZTE will be periodically energized by the circuit previously traced for these relays. A circuit is now also closed for energizing the control element t of relay AITE, this circuit passing from terminal B, through the front point of contact 63 of relay ZTR, contact Al'I'R-54, and the control element t of relay AlTE to terminal C.

I shall assume further that the speed of the train, while it is moving through section 22-0,

is so high that there is not sufficient time for relay AITE to close its front contact before the train enters section cd, thereby deenergizing relay 2TR which then opens its contact 63 at the front point and thereby deenergizes control element t of relay AITE. With the control element t of relay AITE deenergized, its front contact remains open, and therefore stick relay IS doe not at this time become energized.

Contact IS-36 and contact 35 of relay ZTR in the circuits for relay 4H are therefore now both open, causing relay 4H to become deener-" gized. With relay 4H deenergized, yellow-lamp Y of signal 4 will now be extinguished and its red lamp R will be lighted. When relay 4H becomes deenergized, its contact 4H-23 opens the circuit for relay 6H, causing relay 6H to be deenergized, which in turn causes lamp G of signal 6 to be extinguished and lamp R of this signal to be lighted.

With relay 6H deenergized, relay 8H will now be energized by current of reverse polarity in a circuit which is the same as the circuit previously described for this relay except that it includes terminal N and the back point of contact 53 of relay 6H instead of terminal B and. the front point of contact 53 of relay 6H. Green lamp G of signal 8 is therefore now extinguished and its yellow lamp Y is lighted.

With relays ZTR and IS deenergized, a circuit is closed for energizing control element 12 of time element relay ZTE, this circuit passing from terminal B, through the back point of contact 53 of relay ZTR, back point of contact 51 of relay IS, and control element t of time element relay 2TE to terminal C.

I shall now assume further that the speed of the-train while it is moving through section c--d is still so high that there is not sufiicient time for relay ZTE to close its front contact before the train enters section de. Contact lS-36 therefore remains open until after the train enters section de, and hence relay 4H remains deenergized and signal 4 continues to indicate stop.

When the train enters section de, relay IS becomes energized .by its third pick-up circuit, passing from terminal B, through contact 68 of relay 3TR, and the winding of relay IS to terminal C. Contact 31 of relay 3TR i now open in the circuits for relay 4H, and therefore relay 4H remains deenergized although contact 18-36 is now closed. With relay 3TR now deenergized, its contact 22 opens the circuit for relay 3H, and therefore relay 3H becomes deenergized and extinguishes lamp G of signal 3, and completes a circuit for lighting lamp ,R of this signal, this circuit passing from terminal EB, through the back point of contact 40 of relay 3H, and lamp R of signal 3 to terminal EN.

When the train enters section e-f, relay 58 becomes energized by its pick-up circuit passing from terminal B, through the back point of contact 43 of relay 5TB, front point of contact 10 of relay 5H, and the winding of relay 5S to terminal C. Relay 5S thereupon completes a stick circuit passing from terminal B, through the back point of contact 43 of relay 5TB, contact H of relay 5S, and the winding of relay 58 to terminal C. Upon the lapse of a further brief period of time, a second stick circuit is closed for relay 58, this circuit passing from terminal B, through the back point of contact 10 of relay 5H, contact ll of relay 5S, and the winding of relay 58 to terminal C.

With relay 5TB deenergized, its contact 43 is now open at the front point, and hence relay 5SP is deenergized. On account of relay 5H being deenergized, its contact 40 will open, at its front point, the circuit for lamp G of signal 5, and red lamp R of signal 5 will then be lighted by a circuit including the back point of contact 40 of relay 5H.

When the train enters section f-g, relay 4TB. becomes deenergized, causing relay 48F to become deenergized by the opening of contact 43 of relay 4TR at its front point.

When the train leaves section ,fg, relay 3H becomes energized by current of reverse polarity in a. circuit which is the same as the circuit previously described for this relay except that it includes the front point of contact 53-!!! and terminal N, instead of the back point of contact 5Sl9 in series with contact Eli-I3 and terminal B. With relay 3H now energized by current of reverse polarity, lamp R of signal 3 will be extinguished, and lamp Y will be lighted by a circuit passing from terminal EB, through the front point of contact 69 of relay 3H, contact ll of relay 3H closed in the reverse position, and lamp Y of signal 3 to terminal EN. With relay 3H now energized, relay III will become energized by current of normal polarity in the circuit previously described for this relay, causing signal I to again display the green indication.

When the train enters section gh, relay 6TB. becomes deenergized, causing the circuit for relay 8H to be opened at contact 51 of relay BTR, and therefore signal 8 will now display the red indication. The first circuit for energizing relay BS is now closed, passing from terminal B, through contact 68 of relay 6TB, and the winding of relay as to terminal C.

Contact 88-33 is therefore now closed, so that when the train leaves section g-h, relay 5H becomes energized by current of reverse polarity in a circuit including contact ES-35 and the back point of contact 28 of relay 7H and terminal N, instead of contact 23 of relay l'TR and the front point of contact 28 of relay ill and terminal B in the circuit previously traced for this relay.

With relay 5H thus energized by current of reverse polarity, red lamp R of signal 5 is extinguished and yellow lamp Y of this signal becomes lighted. With relay 5H energized, the second stick circuit traced for relay SS is opened at the back point of contact E of relay H, causing relay 58 to become deenergized. Relay 58, upon becoming deenergized, again completes a circuit for energizing relay 5GP, as previously traced.

While the train is on section hk, the stick circuit for relay BS is closed, this circuit passing from terminal B, through the back point of contact 63 of relay lTR, front point of contact 67 of relay 8S, and the winding of relay 88 to terminal C.

When the train leaves section hic, relay 83 becomes deenergized so that contacts 88-30 becomes opened, but contact 29 of relay 1TB is now closed and therefore relay 5H continues energized by current of reverse polarity until the train has proceeded far enough to permit relay II-I to become energized.

I shall next assume that all parts of the apparatus are again. in the normal condition, and that an eastbound train again moves through section bc too rapidly for relay AITE to close its front contact before the train enters section c-d. Relays 4H and 5H will therefore become deenergized, causing signals 4 and 5 to indicate stop, as previously described.

I shall now assume further, however, that the train slows down in section c-d, preparing to stop at signal 3. Relay ZTE therefore now closes its contact 66, thereby completing a second pick-up circuit for relay IS, this circuit passing from terminal B, through the back point of contact 63 of relay ZTR, contact E55 of relay 2TE, and the winding of relay IS to terminal C. Relay IS, upon becoming energized, closes its own stick circuit which is the same as the pick-up circuit just ;traced for this relay except that it includes the front point of contact 61 of relay IS instead of contact 66 of relayZTE.

With relay IS energized, relay 3H becomes energized by current of reverse polarity in a circuit which i the same as the circuit previously described for energizing relay 4H by current of reverse polarity except that it includes contact 13-36 instead of contact 35 of relay ZTR. Signal 4 therefore now displays the yellow indication. With relay EH energized, relay 61-1 is now energized by current of normal polarity in its circuit previously described, and therefore green lamp G of signal 6 is now lighted for displaying the clear indication.

It follows that, if an eastbound train moves through section 17-0 at too high a speed, signals 4 and 6 are controlled to display the stop indication when the train enters section c-d, but if the train then slows down or stops before passing signal 3, signal 4 is controlled to display the yellow indication and signal 6 is controlled to display the green indication before the train leaves section cd.

I shall now assume that all parts of the apparatus are again in the normal position, and that an eastbound train moves slowly through section b--c. Relay AITE therefore closes its contact before the train enters section c-d, and relay I S therefore becomes energized, when the train enters section c-d, by a pick-up circuit passing from terminal B, through the back point of contact 63 of relay ZTR, contact 65 of relay-AITE, and the winding of relay IS to terminal C. Contact lS-36 is therefore now closed in multiple with contact 35 of relay ZTR, so that when the train enters section c-d, relay 4H continues to be energized by current of reverse polarity, and relay 6H remains energized by current of normal polarity, so that signal 4 continues to display the yellow indication and signal 6 continues to display the green indication.

I have described the operation of the apparatus for a few typical traflic movements. It is believed that, in view of this description, the operation of the apparatus for any other possible traflic movement will be readily understood by reference to the drawings.

Although I have shown a speed controlled overlap arrangement for only traffic movements between sidings X and Z, it is to be understood that a similar arrangement can be similarly pro vided for traffic movements between siding X and the next siding west of siding X, and that a similar arrangement can also be provided for traffic movements between siding Z and the next siding east of siding Z. In such an arrangement for controlling signals between siding X and the next siding West of siding X, section ab would serve as an overlap section and section b-c would serve as a timing section. Similarly, for controlling signals between siding Z and the next siding east of siding Z, section k-m would serve as a, timing section and section m-n would serve as an overlap section.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that variouschanges 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 control system for signals for a stretch of railway track, including a first signal adjacent one end of said stretch for governing traffic movements in a given direction over said stretch, and including a second signal adjacent the opposite end of said stretch for governing traflic movements in the opposite direction over the same track, the combination comprising, an overlap track section in the rear of each of said signals, a track circuit for each of said sections each including a track relay, time element means for each of said overlap track sections each controlled by a back contact of the track relay for its overlap track section, control means for said first signal including a front contact of the track relay for the overlap section in the rear of said second signal, control means for said second signal including a front contact of the track relay for the overlap section in the rear of said first signal, a stick relay for each of said overlap track sections, a pick-up and a stick circuit for each of said stick relays each controlled by a back contact of the track relay for the associated overlap track section and each of said pick-up circuits also controlled by a contact of the time element means for the associated overlap track section upon the lapse of a measured period of time after such time element means becomes energized, and a front contact of each of said stick relays connected in multiple with the said front contact of the track relay for the associated overlap track section in the said control means for said first or said second signal.

2. In a control system for signals for a stretch of single track railway which is provided with passing siding spaced along said stretch, including two pairs of head block signals for each passing siding placed one pair adjacent each end of each passing siding for governing traffic movements in opposite directions, and including one or more pairs of intermediate signals between consecutive passing sidings for governing traflic I movements in opposite directions, the combination comprising, an overlap track section and a timing track section in the rear of each head block signal known as a leaving signal which governs trafiic movements away from its passing siding, a time element device for each of said timing track sections each having a front contact and each arranged to close its front contact after a train has occupied its timing section a measured period of time, a stick relay for each of said a overlap track sections, a pick-up and a stick circuit for each of said stick relays each controlled by a contact which is closed if the associated overlap track section is occupied and each of said pick-up circuits also controlled by the front contact of the time element device for the timing track section which is adjacent the associated overlap track section, and control means for each leaving signal each including a front contact of the stick relay for the overlap track section in the rear of the next opposing leaving signal in multiple with a contact which is closed if the overlap track section in the rear of the next opposing leaving signal is unoccupied.

3. In combination, a stretch of railway track, a signal adjacent one end of said stretch for governing traffic movements in a given direction over said track, a second signal adjacent the opposite end of said stretch for governing traffic movements in the opposite direction over said track, a timing track section in the rear of said first signal, an overlap track section between said timing section and said first signal, a track circuit for each of said sections each including a track relay, a time element relay, a control circuit for said time element relay controlled by the track relay for said timing section in its deenergized condition and by a front contact of the track relay for said overlap section, a stick relay, a pick-up and a stick circuit for said stick relay each controlled by the track relay for said overlap section in its deenergized condition and said pick-up circuit also controlled by a front contact of said time element relay, a second pick-up circuit for said stick relay energized in response to occupancy of a portion of said track adjacent said first signal by a train between said first and second signals, and a control circuit for said second signal controlled by a front contact of the track relay for said overlap section in multiple with a front contact of said stick relay.

4. In combination, a stretch of railway track, a signal adjacent one end of said stretch for governing trafiic movements in a given direction over said track, a second signal adjacent the opposite end of said stretch for governing trafi'ic movements in the opposite direction over said track, a timing track section in the rear of said first signal, an overlaptrack section between said timing section and said first signal, a time element relay, a control circuit for said time element relay energized if said timing section is occupied while said overlap section is unoccupied, a stick relay, a pick-up and' a stick circuit for said stick relay each controlled by a contact which is closed if said overlap section is occupied and said pick-up circuit also controlled by a front contact of said time element relay, and a control circuit for said second signal controlled by a front contact of said stick relay in multiple with a contact which is closed if said overlap section is unoccupied.

5. In combination, a stretch of railway track, a signal adjacent one end of said stretch for governing trafi'ic movements in a given direction over said track, a second signal adjacent the opposite end of said stretch for governing trafiic movements in the opposite direction over said track, a timing track section in the rear of said first signal, an overlap track section between said timing section and said first signal, a time element relay, a control circuit for said time element relay energized if said timing section is occupied while said overlap section is unoccupied, a stick relay, a pick-up and a stick circuit for said stick relay each controlled by a contact which is closed if said overlap section is occupied and said pick-up circuit also controlled by a front contact of said time element relay, a second time element relay, a control circuit for said second time element relay energized if said stick relay is deenergized while said overlap section is occupied, a second pick-up circuit for said stick relay controlled by a front contact of said second time element relay while said overlap section is occupied, and a control circuit for said second signal controlled by a front contact of said stick relay in multiple with a contact which is closed I if said overlap section is unoccupied.

WILLIAM H. CLAUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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