US2362156A - Coded track circuit signaling system - Google Patents

Description

Nov. 7, 1944. N. D PRESTON.

CODED TRACK CIRCUIT sIGNALI'Nq SYSTEM Filed Sept. 29,1942 2 Sheet-Sheet 2 39 @BgPIAWL milmbig a 2 Sheets-Sheet 1 244- N. D.'PRES TON CODED TRACK CIRCUI'I' SIGNALING SYSTEM File d Sept. 29, 1942 Nov. 7,

Patented Nov. 7, 1944 CODED TRACK CIRCUIT SIGNALING SYSTEM Neil D. Preston, Rochester, N. Y., assignor to General Railway Signal Company,

Rochester,

Application September 29, 1942, Serial No. 460,107

15 Claims.

This invention relates to coded track circuit signaling systems for railways, and more particularly relates to coded track circuit highway crossing control for use in an automatic block signaland in those signaling systems employing coded track circuits, it is also desirable to provide for the automatic control of the highway crossing signals by coded track circuits Without the use of line-wires.

One of the objects of the present invention is to provide coded track circuit approach control for highway crossing signals insuch a manner that the highway crossing signals cease operation as soon as a train passes the crossing by reason by distinctive control of the approach track section as exercised at the highway crossing. This object is accomplished by distinctively energizing the approach section when the train passes the highway crossing from an energy source located at the crossing; and this distinctive energization is effected insuch a manner that the wayside signal for following trains is still held at stop. Furthermore, the system is so organized that this distinctive energization of the approach section is readily'removed as soon as the train passes out of the control limits of the associated block, and thereby permits the transmission of the usual coded track circuit impulses through such approach section.

More specifically, the system of the present invention is characterized by the use of a shunt track relay for governing the highway crossing signal, which shunt track relay is connected across the approach track section for the crossing signal, and is energized at times by code pulses at code rates suitable for controlling the indications of the wayside signal governing train movement into the stretch of track including the crossing, and is energized at other times behind a train by a distinctive energization to, thereby stop operation of the-crossing signal Without clearing said highway crossing signal I In one form of the invention, thisdistinctive energization is the application of code pulses of a distinctive code rate to which the decoding apparatus at the wayside signal will not respond; in another form of the invention, the distinctive energization is of the same coderate as used for the control of the Wayside signal, but the code pulses are of a different polarity to which the decoding apparatus will not respond; and in still another form of the invention, the distinctive energization of the approach track section is a steady energization which effects the energization of the shunt track relay while the decoding apparatus at the wayside signal assumes a stop condition in the absence of coded impulses.

Although one purpose of the invention is to provide highway crossing protection which is particularly suitable to double track signaling systems wherein the direction of traffic is normally in one direction, it is'also an object of the invention to provide such automatic highway crossing control in a manner which is also adaptable in its broadest aspects to various other coded track circuit signaling systems including those for single track, railroads.

Various other objects, characteristic features and attributes of the invention will be pointed out and also become apparent, as the specific embodiments of the invention are hereinafter described and explained; and the combinations of functions and structural organizations constituting the invention will be 'set forth in the appended claims.

In describing the invention in detail, reference will be made to the accompanying drawings, in which certain specific embodiments of the invention have beenillustr'ated in a simplified and diagrammatic manner, more with the object of facilitating an explanation and understanding of the nature and mode of operation of the system, rather than to show in detail the construction and arrangement of parts preferably employed in practice, and in which Fig. 1 illustrates one embodiment of the invention as applied to a typical stretch of track included in a double track railroad and having an intersecting highway;

Fig. 2 illustrates one modified form of the invention; and Fig. 3 illustrates another modified form of the invention.

'The various relays, contacts and other parts have been illustrated in these drawings in a conventional manner; and to simplify the illustration of the circuits, connections to the opposite terminals of the battery or other suitable sources of current for energizing the local circuits have been represented by the symbols and associated with arrow tails and heads respectively. A system of this type inherently involves similarity and duplication of relays and like parts for the different signal locations; and for the sake of simplicity various relays common to the various signal locations are assigned the same letter reference characters with prefix numerals corresponding to the associated signal.

One arrangement for providing automatic control of highway crossing signals in a coded track circuit signalling system for train movements normally in one direction over a stretch of track is shown in Fig. 1. Although the normal direction of traffic is to the east as indicated by the proach track section of such length that the protective device is set into operation upon the approach of a train within a reasonable clearance time prior to the arrival of that train at the crossing, and the length of such an approach track section is usually in the order 2,000 feet for the generally accepted clearance time of 20 seconds for the usual maximum speed of trains. This of course is varied in accordance with the maximum speed of the trains over the particular railroad to be provided with highway crossing protection.

Either in the case of a single track railroad, where a train may approach the highway cross ing from either direction or in the case of a double track railroad where under certain emergency conditions trafiic may approach the highway crossing from either direction, there is an approach track section provided on each side of the crossing; equivalent means is governed by these approach track sections to cause operation of the protective highway crossing device at the crossing when an approach track section is occupied by a train traveling toward the crossing but acts to render such protective device inactive when the train is travelling away from the crossing. Thus, in the diagrammatic illustrations of the system of the present invention, it has been assumed that the highway crossing is located an appropriate control distance from the location of the signals 2 and 3, so that each track section ZAT and 2BT separated by insulated joints I will be sufiicient length approach sections for traffic in either direction.

In some cases, the length of the stretch of track between two succeeding block signals is so great as to require cut sections, and in such cases the approach sections for the crossing are correlated to the remainder of the stretch be tween two signals by suitable repeating means. Although the disclosure does not show such an arrangement, it is believed that it will be readily apparent how the principles of the present invention may be applied to such a situation after the detailed discussion of the disclosure of the present invention.

In the arrangement of Fig. 1, a highway crossing is located intermediate of signals 2 and 3 for governing trafiic in a particular direction along one track of a double track railroad. Suitable insulated joints ID are located at the highway crossing so as to provide an approach track section ZAT for the highway crossing as well as a receding track section ZBT for reasons above mentioned.

and an interlocked relay orv A code transmitting relay ZBCTP is controlled through contact I l of the relay 3H for the signal 3 so as to apply a 180 or a 120 code to the receding track section ZBT in accordance with the indications of the signal 3 and trafiic conditions in advance. More specifically, when signal 3 is at stop with relay 3H deenergized, a 120 code is applied; but with signal 3 displaying a caution or clear indication, a 180 code is applied by relay ZBCTP. At the highway crossing, a track relay ZBTR. responds to each of the code impulses applied to the receding track section ZBT, and when this track relay follows a regular 180 or 120 code it causes a slow-acting repeater relay ZB'IP to remain picked up by reason of its intermittent energizations through front contact l2. It is of course understood that this relay EBTP is sufficiently slow-acting to remain picked up during the deenergized periods between the successive code impulses but will drop away whenever the relay 2BTR, remains deenergized for a longer time.

The reception of a regular code by the relay ZBTR and the picked up condition of the relay 2BTP allows such code to be repeated into the approach track section ZAT by the control ofthe transmitter relay ZACTP through front contact E3 of relay ZBTP and front contact Id of relay ZBTR.

The code pulses thus applied to the approach section 2AT are received at the signal 2 by the track relay ZATR and are decoded by any suitable decoding means. As shown, this decoding means comprises, a decoding transformer having its primary energized in opposite directions alternately as the track contact l5 of the track relay ZATR operates to its opposite positions;

. and the secondary of this decoding transformer feeds to two tuned circuits each having a fullwave rectifier for supplying its respective relay 2H or 2D. The tuned circuits are so organized that the home relay 2H responds only to a code rate, while the relay D responds only to a code rate. It should be noted that the track relay ZATR may be of the neutral type or may be of the two-position biased polar type as indicated in Fig. 2.

When both relays 2D and 2H are deenergized, the signal 2 is caused to display a red indication by reason of a circuit including back contacts 16 and I! of the relays 2D and 2H respectively supplying energy to the red lamp R of signal 2. When the relay 2H is picked up by the reception of a 120 code, the relay 2D is deenergized so that a circuit through back contact i6 and front contact I! supplies energy to the yellow lamp Y of the signal 2 so that it displays a caution indication. On the other hand, when a 180 code rate is received, the relay 2D is picked up and the relay 21-1 is dropped away. Thus, front contact l6 of relay 2D supplies energy directly to the green lamp G of the signal 2.

Although the relation of this portion of the signaling system to the remaining portion of the coded track circuit signaling system has not been shown in detail, it is to be understood that the relays 2H and 2D control the application of coded impulses to the track section in the rear of signal 2, so that trains may proceed over the entire system with the usual three-indication signaling.

The application of any code rate to the approach track section 2AT by the transmitting relay ZACTP causes the intermittent energization of the shunt track relay ZAXR so that it The track repeating relay ZBTP and the shunt track repeating relay ZAXRP respectively control the opposite windings of a highway crossing interlocking relay XR. by contacts I9 and. 20,

whichin turn effects the control of a suitable highway crossing signal through back contacts 2| and 22.,

Let us now consider the operation of the system when a train passes the signal 2. The entrance of the train into the approach track section ZAT of course shunts the track relay 2ATR and causes it to remain deenergized irrespective of the code transmission by the transmitter relay ZACTP. This causes the signal 2 to indicate stop. The entrance of such train also causes the shunt track relay ZAXR to remain dropped away so that its repeater relay ZAXRP also drops away and acts through the interlocking relay to cause the proper operation of the highway crossing signal.

It will of course be appreciated that the track relays 2A'I'R and ZAEHQ. remain deenergizedafer once dropping away, because there is insufficient potential across the track rails of the track section ZAT to again pick them up while a train is present. This is because of the usual actingin a track circuit where the train shunt causes such a current flow from the battery through its series resistor that the potential drop therein reduces the potential across the track rails sufflciently to prevent such track relays 2ATR and ZAXR from being picked up although the transmitter relay 2ACTP continues its operation.

When the train proceeds into the receding track section 213T, it of course stops the operation of the track relay ZBTR and causes its repeater relay ZBTP to drop away. This closes the back contact l3 of relay ZBTP and connects the transmitter relay ZACTP to the highway crossing coding contacts 150T. This operation of the code transmitter relay 2ACTP at the '75 code rate acts through its contact 25 to intermittently connect the track battery 26 through the variable resistor 21 across the approach track section 2AT at the '75 code rate. However, it will be appreciated that the shunt track relay zAXR does not follow such code because the train is assumed to still be in the approach track section 2AT causing such a potential drop in the variable resistor Zlthat this shunt track relay cannot respond.

When the train fully enters the track section ZBT and vacates the track section 2AT, the application of this '75 code to the approach track section 2AT causes the operation of the code following track relay ZATR and the shunt track relay 2AXR in the usual way. This immediate operation of the relay ZAXR causes its repeater relay zAXRP to be picked up and remain picked, thereby reenergizing the initially deenergized winding of the interlocking relay. This stops the operation of the highway crossing signal because the deenergization of its other winding by the opening of front contact E9 of the repeater relay ZBTP subsequent to the opening of front contact 20 of relay ZAXRP does not allow the right hand armature of the interlocking relay to close its back contacts due to the mechanical interlocking in the relay. In other words, the particular winding of the interlocking relay which is deiii energized first is allowed to haveits associated armature close its back contacts, but the subsequently deenergized winding is not allowed to have its armature close its back contacts until after both windings have been reenergized. Thus, the passage of the trainpast the highway crossing causes the crossing signal to cease its operation.

The application of this crossing code of the 75 code rate (as chosen for the present embodiment), does not cause the signal 2 to clear because the home relay ZI-I is responsive only to the code rate and the distant relay 2D is responsive only to the code rate. In other words, this form of the invention contemplates the application of a distinctive code of any suitable rate at the highway crossing which code will effect energization of the shunt track relay EAXR but will not cause the clearing of the way side traffic signal 2. If another train should en ter the track section ZAT under hand signaling conditions or otherwise, the shunt track relay ZAXR would be shunted by such train and be caused to remain deenergized, thus causing the crossing signal to be energized for such a follow in": train movement.

However, assuming that there is no following section 2BT by the code transmitting relay ZBCTP which. code operates the track relay ZBTR, causing the repeater relay 2BTP to be picked up removing the highway crossing code of the 75 code rate immediately retransmitting the 120 code rate into the track section ZAT. This 120 code rate continues to operate the shunt track relay ZAXR and cause its repeater relay ZA-XRP to remain picked up, and also acts through the code following track relay ZATR to energize the home relay 21-1 to cause signal 2 to indicate caution for any following train.

It is of course obvious that asthe first train progresses and the home relay 3H is picked up, the 180 code rate will be re-applied to the track section ZBT and then repeated into the track section 2AT for energizing the distant relay 2D and causing signal 2 to indicate clear. In this way, it is seen that means is provided for applying a code rate to the crossing approach section at the highway crossing which acts to remove the crossing signal from operation as the train passes the insulated joints at the crossing without effecting the clearing of the signal in the rear until a regular signal clearing code is received from the exit end of the receding track section. It will also be noted that the use of the interlocking relay, as shown, provides that should a train make a back-up movement past the signal 3 in a West-bound direction into the track section ZBT (under normal conditions shown), the relay ZBTP would drop away opening front contact l9 to cleenergize the right hand winding of the interlocking relay XR to close back contact 2: to set the crossing signal into operation. Thus, the form of the present invention as shown in Fig. 1 provides the usual highway crossing protection for double track railroads by the use of the principles of the present invention.

With reference to Fig. 2, the principles of the invention are also applied to the stretch of track between signals 2 and 3 in a modified form. This is a modification of Fig. 1 in which the application of the highway crossing code in the rear of a train having just passed the crossing causes the crossing signal to be removed from operation but does not clear the wayside signal 2 in the rear, because such code is of reversed polarity that cannot operate the polarized track relay 2ATR In this modified form of Fig. 2, the various devices corresponding to Fig. 1 have been given the same reference characters and only those devices and circuits differing from Fig. 1 have been given distinctive reference characters so as to more clearly bring out the features of this Fig. 2.

More specifically, it can be seen that the transmitting relay ZBCTP normally causes a 180 code to be applied to the receding track section 2BT because it is connected through front contact II to coding contacts IBUCT, but if relay 31-1 is deenergized due to traific conditions, back contact H is closed connecting transmitter relay 2BCTP to coding contacts CT. The application of either a 180 or a 75 code to the receding track section 2BT causes the operation of the track relay ZBTR which in turn maintains its repeater relay 2BT? picked up so that the impulses of the selected code may be repeated into the approach track section 2AT by the transmitting relay ZACTP having a circuit including front contact 13 of relay 2BTP and front contact M of relay '2BTR. In this Fig. 2, the track repeater relay ZBTP is shown shunted by rectifier unit 30 so as' to make it slightly move slow in releasing because of the use of the '75 code for the low code rate.

The code on the approach track section 2AT is received by the track relay 2ATR which track relay is of the two-position polarized type with the polar contacts biased to a normal position, and thus differs from the track relay in Fig. 1 where it is optional whether or not the track relay should be of the neutral or the polar type, but in this form of the invention it is essential that the track relay be responsive to only a particular polarity as'will be presently described. The track relay 2ATl=t acts through a decoding transformer and a tuned circuit to control the distant relay 2D in accordance with a 180 code the same as in Fig. 1; but the home relay 2H is connected through the decoding transformer and a rectifying contact 23 on the track relay ZATR in a manner well known in the art so that this home relay 2H responds to the reception of code impulses of the 75 or the 180 code rate.

Thus, the reception of the 180 code causes both the home and distant relays 2H and 2D to be picked up completing a circuit from through front contacts 28 and 29 of these relays respectively to energize the green lamp G of the signal 2. If the '75 code rate is being received, then only the home relay 2H is picked up so that a circuit is closed from through front contact 28 and back contact 29 to energize the yellow lamp Y of signal 2. If no code is being received, then both of the relays 2D and 2H are dropped away, and back contact 28 of home relay 2H applies energy directly to the red lamp R of signal 2.

The application of the 180 code or the '75 code to the approach track section 2AT is also repeated by the shunt track relay 2AXR, and its operation acts to maintain its repeater relay ZAXRP energized the same as described in connection with Fig. 1.

When a train accepts the signal 2 and passes into the approach section 2AT, the track relays 2ATR and ZAXR remain deenergized so that th home and distant relays 2H and 2D drop away to cause the signal 2 to display a stop indication, and also to release the'repeater relay ZAXRP and deenergize the right hand winding of the interlocking relay XR to set the crossing signal into operation.

When the train passes into the receding track section 2BT, the track relay 2BTR is caused to remain dropped away which releases its repeater 2BTP closing back contact l3 to connect the code transmitting relay 2ACTP to the highway crossing coding contact 150T. At the same time, back contacts 3| and 32 are closed so as to cause the code impulses applied to the approach track section 2AT from the track battery 26 to be of reversed polarity. These impulses of reversed polarity at the 75 code rate of course causes the operation of the shunt track relay 2AXR which is repeated by th relay ZAXRP to close front contact 20 to reenergize the interlocking relay and cause the crossing signal to cease its operation. These impulses of reverse polarity are also received at the signal location 2 but are not repeated by the track relay EATR because it is so connected to the track circuit that such impulses merely cause its contacts to be forced more strongly to their biased positions. Thus, the signal 2 is held at stop although code impulses are applied to the approach track section to cause the highway crossing signal to cease its operation in the rear of the train as it passed the insulated joints ID at the crossing. If a following train should enter the approach section 2AT while section 2BT is occupied, then the crossing signal would again be set into operation, because such following train would shunt the track relay ZAXR. and hold it in a dropped away position. This would happen only under special conditions, such as switching train movements or the like.

When the train passes the signal 3 (neglecting any following train), it is of course obvious that the relay 3H is deenergized closing back contact if to connect the code transmitting relay ZBCTP to the coding contacts T. This applies impulses to the track section 2BT which are repeated by the track relay ZBTR into the track section 2AT by reason of the circuit for relay 2ACTP including front contact [3 of relay 2BTP and front contact M of relay ZBTR. It is obvious that, the picking up of the relay 2BTP in response to these impulses, closes front contacts 3i and 32 to restore the polarity of these impulses applied to the approach track section 2AT back to the normal polarity, so that they will be repeated by the track relay ZATR Such operation of the code following track relay 2ATR of course causes the energization of the relay 2H in the usual Way to cause the signal 2 to display a caution indication in the usual manner.

When the train progresses sufliciently along the railroad as to allow the signal 3 to display caution or clear, the relay 3H will of course be energized by a proper code or othercontrol restoring the code to the track section 2BT, which in turn is repeated into the track section EAT to cause the signal 2 to display a clear indication. These 180 codeimpulses in the track section ZAT cause the continued energization of the shunt track relay ZAXR so as to maintain the crossing signal in an at-rest condition. The interlocking relay is provided in this Fig. 2 the same as in Fig. 1, so as to provide highway crossing protection in the event that a train is travelling under train orders against the nor mal direction of trailc. With reference to Fig. 3, another modified form of the invention is shown, and the various devices of this Fig. 3 have been given the same reference characters as in Fig. 2 because the same devices are used in this form of the invention.

Withreference to Fig. 3, it will be seen that codes are applied to the receding track section ZBT at the signal 3 the same as described in con nection with Fig. 2 and these codes are repeated into the approach track section 2A'I' so as to be received at the signal 2. For convenience, this Fig. 3 shows the same decoding apparatus as shown in Fig. 2, but it is to be understood that the decoding apparatus shown in Fig. 1 might also be used and the codes selected accordingly.

At the highway crossing, the battery 26 .and

. variable resistor 21 is connected the same as .in

Fig. 1 so that the contact 25 of the code transmitter relay ZACTP connects them directly across the track rails when it is closed.

The distinction between this form of the invention and the forms shown in Figs. 1 and 2 is that steady energy is applied to the transmitter relay ZACTP while back contact I3 of the relay ZBTP is closed instead of connecting this transmitter relay ZACTP to highway crossing coding contacts. In other words, when a train has passed over the approach track section 2AT. into the receding track section ZBT, steady energy is applied to the approach track section which acts to steadily energize the shunt track relay ZAXR closing front contact l8 to energize its repeater relay ZAXRP and in turn close front contact 20 to reenergize the left hand winding of the interlocking relay XR to return the crossing signal to rest. This steady energization of the approach track section behind the train, energizes the track relay ZATR. to its actuated position in which it remains, and because of this, the relays 2D and 2H remain dropped away as they require coding operation of the track relay ZATR in order to energize them as previously described.

If a following train should enter the approach section ZAT while the receding section ZBT is occupied, then the shunt track relay ZAXR would drop away and through the control previously described for the other forms set the crossing signal into operation. i

When the train moves out of the receding track section (neglecting any following train), a code is again restored to that section ZBT and These several forms of highway crossing control illustrate that th broad principle of the invention relating to the application of a distinctive energization to the approach track section in the rear of a train to remove the crossing signal from operation while holding the wayside trafiic signal at stop, may take numerous forms and still come within the scope of the invention. In the present disclosure, this principle has been particularly applied to a signaling organization of coded track circuits for a stretch of double track railroad, but it is appreciated that th principles of thisinvention may be applied to single track railroads and to various types. of coded track circuit signaling systems. For an example of such an application of the invention to a single track railroad, reference should be made to my co-pendin-g application filed of even date herewith and entitled Coded track circuit signaling systems.

is pointed out to emphasize the broad application of the present invention of highway crossing control.

Various other modifications and adaptations not illustrated or described may be made in the construction and arrangement of parts and cirrepeated into the approach track section ZAT as described in connection with the other forms of the invention. In this way, the application of steady energy to the approach track section in the rear of a train acts to cause the crossing signal to cease its operation although holding the wayside traffic signal at stop until the train has passed out of the associated block to restore clear coding conditions.

In each of the forms of the invention, the interlocking relay XR. has been shown so as to provide highway crossing protection in the event that a train is travelling in a direction opposite to the normal direction of traffic. In such a case, the entrance of a west-bound train into the track section ZBT, would cause the cessation of code and the release of the relay 2BTP opening front contact l9 and causing the deenergization of the right hand winding of the interlocking relay XR to close back contact 2| and set the crossing signal into operation. As soon as such west-bound train passes into the approach track section ZAT, it is obvious that code is restored. in the receding track section ZBT to cuits illustrated without departing from the invention; and it is to be understood that the specific embodiments and modification of the invention illustrated are merelytypical and illustrative of the principles and mode of operation of the invention.

What I claim is:

1. In a coded track circuit signaling system pro-f viding approach control for highway crossing signals,a stretch of railway track having an entering signal and divided into an approach track section and a receding track section on the opposite sides of an intersecting highway, driven code transmitting means associated with the exit end of said receding track section for applying driven code pulses to the rails of said receding track section at different selected rates in accordance with trafiic conditions in advance, means at said highway crossing responsive to said driven codes and acting to repeat such codes into said approach track section, decoding means at said entering signal responsive to said driven codes of said selected rates only for controlling the proceed indications of said entering signal, means at said highway crossing including a shunt track relay responsive to the application of driven. code pulses of any rate to said approach track section section, such means acting without clearing said entering signal because of the difference in the code rates.

2. In a coded track circuit signaling system providing approach control for highway crossing signals, a stretch of railway track having enter ing and leaving signals, said stretch being divided into an approach track section and a receding. track section at the point of intersection of a highway crossing, driven code transmitting means associated with said leaving signal for applying codes of difierent selected rates to the rails of said receding track section in accordance with trafiic conditions in advance of said leaving signal, means at said highway crossing for repeating said driven codes of selected rates from said receding track section into said approach track I section, decoding means at said entering signal responsive only to said driven codes of said selected rates for controlling the indications of said entering signal, means at said highway crossing responsive to the presence of a train in said receding track section for applying a driven code to said approach track section of a rate other than said selected rates, whereby such code does not. effect the clearing of said entering signal, a shunt track relay at said highway crossing connected across the rails of said approach section and responsive to the application of driven codes of any rate to said approach section but maintained dropped away .by the presence of a train in said approach section, and a highway crossing signal set into operation whenever said shunt track relay remains dropped away.

31 In a coded track circuit signaling system pro- 'viding approach control for highway crossing signals, a stretch of railway track divided into an approach track section and a receding track section at the point of intersection of the railroad with a highway and having a signal at the entrance to said stretch for governing train movements thereover, a crossing signal associated with the highway crossing, means for transmitting driven code impulses of selected rates over the rails of said sections toward the entrance end of the stretch in accordance with traffic conditions in advance, driven code responsive means rendered operative by said driven codes only for governing the clear indications of said signal at,

the entrance to said stretch, a shunt track relay at the highway crossing connected across the rails of said approach track section, said shunt track relay being responsive to the presence of any code impulses in the associated approach track section only if that track section is not occupied for preventing operation of said highway crossing signal, whereby said highway crossing signal is normally inactive and is set into operation upon the entrance of a train into said stretch, and means at the highway crossing for applying distinctive code impulses across the rails of the approach track section while a train is in the receding track section to cause the energization of said shunt track relay, said distinctive impulses being ineffective to cause operation of said driven code responsive means to govern the clearing of said signal at the entrance to the stretch, whereby the highway crossing signal may be caused to cease its operation in the rear of a passing train without causing the clear control for said entering signal. 1

4. In a coded track circuit control system for highway crossing signals, a stretch of railway track intersected by a highway crossing and divided into approach and receding track sections by insulated joints at the crossing, an entering signal governing train movement into said stretch and over said approach and receding track sec-tions in that order, means associated with the stretch of track for transmitting caution and clear code impulses of normal polarity from the'exit end to'the entrance end thereof in accordance with traflic conditions in advance, a highway crossing signal for warning traflic on the highway, means at the highway crossing for applying code impulses of reverse polarity to said approach section while a train is in the receding section, meansat the, highway crossing responsive to the energization of the approach section by code impulses of either polarity for maintaining said crossing signal inactive but responsive to the shunting of the rails of said approach section by a train for setting the crossing signal into operation, and decoding means at the entrance end of the stretch responsive to the code impulses of normal polarity to control the entering signal to display caution or clear indications but being unresponsive to code impulses of said reverse polarity.

5. In a coded track circuit signaling system providing approach control for highway crossing signals, a stretch of track divided into an approach section and a receding section at the point of intersection of a railroad with a highway, a crossing signal at the highway crossing, a wayside signal at the entrance to said stretch of track for governing train movement thereover, means associated with the stretch of track and acting to transmit different codes over the rails of the stretch from the exit end toward the entrance end, means at said highway crossing for steadily energizing said approach section while a train is in said receding section, means at the highway crossing connected across the rails of the approach section and responsive both to said codes and said steady energization of the approach section to maintain the crossing signal inactive but acting to set the crossing signal into effective operation upon the entrance of a train into the approach section when it is energized either by code impulses or steady energy, and means located at the entrance endiof the stretch and connected to the rails thereof acting to clear said enterin signal in response to the reception of code impulses but acting to hold said signal at stop in the absence of code impulses and during the steady energization of the approach section.

6. In a coded track circuit control system for highway crossing signals, a stretch of railway track intersected by a highway crossing and divided into approach and receding track sections by insulated joints at the crossing, an enter-- ing signal governing train movements into the stretch of track and over said approach and receding track sections in that order, means associated with said stretch of track for transmitting different coded impulses over the rails of the stretch from the exit end to the entrance end in accordance with trafiic conditions in advance, means at said highway crossing for distinctively energizing said approach section while a train is in the receding section, a highway crossing signal, means at the highway crossing connected to the rails of the approach section and responsive both to said coded impulses and to' said distinctive energization to maintain the highway crossing signal inactive but acting to set such crossing signal intooperation upon the shunting the rails of said approach section by a train, and decoding means at the entrance end of the stretch acting in response to said different coded impulses to control the entering signal to indicate caution or clear but acting in the absence of said coded impulses and in the presence of said' distinctive energization of the approach section to hold said entering signal at stop.

'I. In a coded track circuit control system for, highway crossing signals, a stretch of railway track intersected by a highway crossing and divided into approach and receding track sections by insulated joints at the crossing, an entering signal governing train movement into said stretch of track, means associated with the exit end of the stretch for transmitting code impulses over the rails, of the stretch toward the entrance end to govern the clear indications of said enter ing signal, means at said highway crossing for distinctively energizing said approach section of the stretch while a train is in the receding section, a highway crossing signal, a shunt track relay connected across the rails of, the approach section at the highway crossing and, responsive both to said: code impulses. and, said distinctive energi'zation of the approachsection to maintain the highway crossing signal} inactive but acting to, set such crossing signal into operation upon the entrance, of a train into the stretch, and decoding means at the entrance end of the stretch responsive to said code impulses to control the clear indicationsof said entering signal but being ineffective to clear said. entering signal inresponse to. the distinctive energization of the approach 7 section.

8,. In a coded track circuit control system for highway crossing, signals. a stretch of railway track intersected by a highway crossing and divided into an approach and receding track sections by insulated joints at the crossing, a wayside signal governing train movements in said stretch and over said approach: and receding. track sections in that order, means associated withthe-stretch of track for transmitting caution" and clear code impulses from the exit end .to the entrance en'd thereof in accordance with traffic conditionsin advance for controlling the indications of" said wayside signal, ahighway crossing signal for warning trafiic on: the highway, control. means for. said highway crossing signal including a relay connected across the rails "of said-approach track section adjacent said highway crossing and normally controlled by said code impulses for maintaining said highway crossing signal inactive'but acting upon the entrance of a train into the stretch to set said cross- 1 ing signal into operation, and means for energizing said approach section'in a distinctive manner to govern said control means to stop operation of'said crossing signal and holding said Wayside signal at stop while a train is in said receding section.

9. In a system for the control of highway crossing protective devices in a coded track circuit block signaling system, the combination with a highway crossing located at an intermediate point in a block between an entering signal and a leaving signal governing train movement in the same direction, an approach track section and a receding track section on opposite sides of insulated joints at said crossing, coding means for applying signal control code pulses across the track rails of said approach track section at its exit end adjacent said crossing for governing the indications of said entering signal in accordance with the character of coding in said receding track section, a shunt track relay connected across the track rails. of saidv approach track section at the same exit end and normally ener giz'edintermittently by the signal control code pulses applied to said approach track section, said shunt track relay being shunted and maintained denergized by thepresence of a train in said approach track section spite oi the operation of said coding means, a protective device for said highway crossing governed by said shunt track rela and effective while that track relay is maintained deenergized, and means responsive to the eluding acode following track'relay-for'governing presence of a train in the receding track section for energizing said approach track. section at its exit end distinctively from said signal control code pulses tocause energization of said shunt track relay when said approach track section becomes vacated to: stop operation of the protective device while keeping the entering signal at stop.

10. In a coded track circuit control: system for highway crossing signals, a stretch of track intersected by a highway crossing and having an approach track section and receding track section on opposite sides of insulated joints at the crossing, code transmitting means associated with the exit end of each of said track sections for normally transmitting signal control code pulses over the track rails of said track sections in the same direction, a shunt track relay connected across the track rails at the exit end of said approach track section and normally energized by said signal control code pulses at said exit end only if said approach t-raclr section isnot occupied by a train, a highway crossing signal; means rendering said crossing signal ineffective while said shunt track relay is energized, and means responsive to the cessation of the signal control code-pulsesin said receding track section for steadily energizing the track rails of said approach track'section.

11. In a system for controlling highway cross= ing signals in a coded track circuit automatic block signal system, thecombination with a'blo'ck between two signals governing train movement in the same direction intersected bya. highway crossing and having an approach track section at one side-of the crossing over which-trains in the normal direction of traffic governed by said signals move toward said crossing, means inthe indication of said signals in response to the intermittent energization only of said track relay by signal control code pulses, code transmitting means'normally applying signal control code pulses across the track rails of said approach track section at its exit end adjacent the crossing for governing the control of the indications of the signalgoverningtraih movement into said block, a shunt track relay connected across the track rails at the'same exit end of'said approach track section and-normally energized by said signal control code pulses only if saidtrack section is not occupied, a protective device for the highway crossing, means for rendering said protective device ineffective while said shunt track relay is energized, and means responsive to the presence of a train in said block beyond said crossing for steadily energizing track rails of said approach track section and thereby cause energization of said shunt track relay to stop operation of said protective device without clearing the signal for the entrance end of said block when a passing train vacates said approach track section.

12. In a system for the control of highway crossing signals in acoded track circuit automatic block signal system, the combination with a block intersected by a highway crossing and including an approach track section at one side of said crossing, a signal governing train movement into said block and over said approach track section toward said highway crossing, code transmitting means normally applying across the track rails of said approach track section at its exit end adjacent the crossing signal control code pulses of different rates in accordance with traffic conditions, means responsive to the presence of a train in said block beyond said approach track section for governing said code transmitting means to cause steady energization of the track rails of said approach track section, and a shunt track relay connected across the track rails of said approach track section at its exit end and responsive to signal control pulses or said steady energization, a highway crossing protective device, and means including a slow release repeater relay governed by said shunt track relay for causing operation of said protective device while said approach track section is occupied.

13. In a control system for highway crossing signals for an automatic block signal system, the combination with a highway crossing having an approach track section and a receding track section on opposite sides of insulated joints at the crossing, code transmitting means associated with the exit end of each of said track sections for normally transmitting code pulses in the same direction over the track rails of said track section, a code following track relay associated with each entrance end of each track section, a shunt track relay connected across the track rails of said approach track section at its exit end and responsive to the energization of the track rails of said approach track section only if that track section is not occupied, decoding means associated with the code following track relay for the receding track section for governing the code transmitting means for the approach track section to provide code pulses in accordance with trafiic conditions when said receding section is not occupied and a steady energization of said approach track section when said receding track section is occupied, a highway crossing protective device, and means controlled by said shunt track relay and by said code following track relay for said receding track section for causing operation of said protective device while either of said track sections is occupied by a train approaching the crossing.

14. In a coded track circuit signaling system providing approach control for highway crossing signals, a stretch of railway track having an entering signal and divided into an approach track section and a receding track section on opposite sides of an intersecting highway, a crossing signal associated with the highway crossing, code transmitting means for the exit end of each of said track sections for transmitting driven code signal control impulses of selected rates over the rails of said sections toward their entrance ends, decoding means at the entrance of said approach track section for governing the indications of said entering signal only in response to said driven codes of said selected rates, a shunt track relay at the highway crossing connected across the rails at the code transmitting end of the approach track section over which train approach the crossing, said shunt track relay being responsive to the presence of driven code impulses of any rate to maintain inactive said highway crossing signal, and means for governing said code transmitting means at the highway crossing to apply code impulses of a different code rate across the rails of the approach track section in the absence of the reception of signal control code impulses at the highway crossing over the rails of the receding track section, whereby the highway crossing signal may be caused to cease its operation in the rear of a passing train by the application of code impulses at the crossing without causing a clear control for signals governing approaching trafiic.

15. In a system for the control of highway crossing signals in a coded track circuit automatic block signaling system, the combination with a highway crossing located at an intermediate point in the block between an entering signal and a leaving signal governing train movement in the same direction, an approach track section and a receding tracksection on opposite sides of insulated joints at said crossing, code transmitting means associated with the exit end of said receding track section for applying distinctive signal controlcodes across the rails thereof in accordance with traffic conditions in advance, coding means for applying signal control code pulses of normal polarity across the track rails of said approach track section at its exit end adjacent said crossing in accordance with the distinctive codes in said receding track section, a highway crossing protective device associated with said crossing, a shunt track relay connected across the track rails of said approach track section at the same exit end and normally energized intermittently by code pulses of either applied to said approach track section, said shunt track relay being maintained deenergized by the presence of a train in said approach track section in spite of the operation of said coding means, means at the highway crossing for setting said protective device into operation when said shunt track relay is maintained deenergized, and means at the highway crossing acting upon said coding means to apply code impulses of the reverse polarity in the absence of the reception of code impulses over said receding track section, and decoding means associated with said entering signalat the entrance to the stretch and responsive to signal control code impulses of said normal polarity only for governing the indications of such entering signal but acting to hold said signal at stop in the absence of code impulses and during the reception of code impulses of said reverse polarity.

NEIL D. PRESTON.

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