US2817011A - Block signal system for railroad - Google Patents

Description

Dec. 17, 1957 Filed Dec. :50, 1954 M. A. SCHEG BLOCK SIGNAL SYSTEM FOR RAILROAD 6 Sheets-Sheet 1 IN V EN TOR.

M. A. SCHEG BY HIS ATTORNEY Dec. 17, 1957 M. A. SCHEG BLOCK SIGNAL SYSTEM FOR RAILROAD 6 Sheets-Sheet 2 Filed Dec. 30, 1954 INVENTOR. M.A. SCHEG HIS ATTORNEY M. A. SCHEG BLOCK SIGNAL SYSTEM FOR RAILROAD Dec. 17, 1957 Filed Dec. 30, 1954 6TB SLR 6 SheetsSheet 3 INVENTOR.

.M.A. SCHEG HIS ATTORNEY Dec. 17, 1957 M. A. SCHEG 2,817,011

BLOCK SIGNAL SYSTEM FOR RAILROAD Filed Dec. 50, 1954 6 Sheets-Sheet 4 IN VEN TOR.

BY MA, SCHEG FQMW HIS ATTORNEY Dec. 17, 1957 M. A. SCHEG 2,817,011v

BLOCK SIGNAL SYSTEM FOR RAILROAD Filed Dec. :50, 1954 e Shets-Sheet s (\l yf)\ INVENTOR. M.A. SCHEG (D r BY HIS ATTORNEY Dec. 17, 1957 M. A. SCHEG 2,817,

' BLOCK SIGNAL SYSTEM FOR RAILROAD Filed Dec. 30, 1954 6 Sheets-Sheet 6 GT5 SLR E 9 N 2 I P fla -1 (D I L l I A m :t 3 5 m 5 y- :0 f)

I II) lcc T o l (D w Y 1D 0 L m INVENTOR.

I N 53, N -M. A.SCHEG o BY 7 W HIS ATTORNEY United States Patent BLOCK SIGNAL SYSTEM FOR RAILROAD Marcian A. Scheg, Rochester, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application December 30, 1954, Serial No. 478,585

15 Claims. (Cl. 246-41) This invention relates to block signaling systems for railroads, and more particularly pertains to the provision of such a system with track circuits which are immune to temporary losses of train shunt.

The usual block signaling system is based upon the use of conventional track circuits including a track relay con nected across the track rails at one end of a track section with a source of direct current and a series limiting resistor connected across the track rails at the other end of the section. Normally the track relay is energized; but when a train enters the track section and shunts the rails, the current in the track relay is reduced to a low value causing it to drop away. When the train leaves the track section, the track relay again picks up.

When a block signaling system uses the conventional track circuits, it relies upon the continuous effectiveness of a train to shunt the track rails and maintain the track relay continuously dropped away. Although this organization is effective for the usual heavy weight equipment type trains, it becomes unpredictable when light weight equipment is employed. This is because the light weight equipment travelling at high speeds does not provide a continuous shunting effect but rather one that varies. However, it has been found that the light weight equipment provides intermittent track shunts, one of which usually is sufficient to cause the initial release of a track relay upon the entrance of a train into a section.

In addition, the light weight equipment may at times be required to use considerable sanding in order to come to a stop. Thus, the train or car has in efiect rolled upon a sand rug where no electrical shunting effect is present. With the conventional track circuit organization, this latter condition results in the clearing of the signals in spite of the presence of a train.

With the above considerations in mind, it is proposed to provide a block signaling system based upon the use of track circuits which are immune to the above variable conditions so that the block signaling system will be just as effective for light weight equipment as for the regular heavy weight equipment.

Generally speaking, and without making any attempt to define the exact nature of the invention, it is proposed to provide a track circuit organization which has a socalled stick effect so that the entrance of a train which produces an initial shunting efiect results in the track circuit giving an occupied indication regardless of either an intermittent or a continuous loss of shunt thereafter; and this stick effect is removed and the track relay restored only after the train has actually passed out of such section and into the next successive track section as there registered by the dropping away of the track relay for that section.

It is proposed to provide the stick effect by the manner in which a regular track relay is connected to the track rails forming the track circuit in combination with a restoring organization which is operative over the track 2,81 7,01 l Patented Dec. 17, 1957 rails to restore the track relay when the train has passed into an adjoining section.

A further proposal is to correlate the restoring organization with the track relay in the next adjoining section in such a way that the track relay of the next adjoining section must have responded to the presence of a train before a restoration pulse can be given to the track relay in the rear.

More specifically, it is proposed to provide a track relay connected to the track rails of a track section through its own front contact in a way to provide a stick effect, but with such front contact shunted by a resistor which will allow pick-up current to flow through the track relay when the potential across the track rails is raised to a value substantially above the normal value. A regular battery source and limiting resistor are connected directly across the rails at the other end of the section. In addition, a second source is provided which is momentarily connected'in series with the first source when a train leaves the section provided the adjoining section indicates the presence of a train. This momentary additional energization is provided by the use of a regular approach relay and a slow release repeating relay. In this way restoration is accomplished over the track rails by the use of simple apparatus and well known principles.

It will be observed that since the track relay is released by a train shunt but is picked up by additional or increased inter-rail potential, the regular characteristics of a track relay having a drop away value about fifty percent of its pick-up value permits this diiferential be tween values to be utilized in connection with the stick feature. This is accomplished by having the track circuit normally adjusted to provide a potential across the rails which brings the track relay current close to its release value under the most adverse normal conditions. This makes the track relay more sensitive to a train shunt than if its normal value of current were well above the pick-up value.

Thus, it can be seen that the present invention, among other things, proposes to take advantage of the usual characteristic of tractive type relays in providing the features of control contemplated in accordance with the present invention.

In a modified form of the present invention, it is proposed that the track relay be made sensitive by having the selection of its main and auxiliary windings dependent upon the operation of the approach relay of the preceding track section. While a train is occupying an approach section, only the main winding of the track relay of the advance section are connected across the track rails. It is also possible to have the interrail potential of the track circuit adjusted to a value just slightly above the release value of the track relay when only the main winding is connected across the track rails. This increases the sensitivity of the track relay to the entrance of a train into the track section, but when the train leaves the section the track relay can pick up because both the main and auxiliary windings are connected across the track rails, assuming that there is no train approaching such section. This, of course, assumes that the proper release conditions are present at the exit end of the track section. This arrangement provides that the track relay of this form has the same sensitivity as that shown in the main form of the invention; but this modified form has the additional advantage that restoration of a track relay can be effected locally by energy over the track rails from the regular track battery. Such local restoration can be accomplished either by manual manipulations or by a train backing out of a section under conditions described in greater detail hereinafter.

In a modified form of the present invention, it is proposed that the track relay be made sensitive by having the selection of its main and auxiliary windings dependent upon operation of the approach relay of the preceding track section. It is possible to have the relay sensitized for the entrance of a train by having the interrail potential of the track circuit adjusted to a value just slightly above the release value of the track relay. During this condition and while the train is approaching only the main winding is connected across the track rails, but when the train enters the track section and wholly leaves the track section to the rear, then the auxiliary winding is also connected into the circuit which makes it possible for the relay to pick up when the train leaves the section, assuming of course a proper release. This arrangement provides the same sensitivity of the track relay as that shown in the main form of the present invention; but this modified form permits the restoration of the track relay by energy over the rails from the regular track battery in the event a train backs out of that section.

Other objects, purposes and characteristic features of the present invention will in part be obvious from the accompanying drawings and will in part be more specifically described hereinafter.

In describing the invention in detail, reference will be made to the accompanying drawings in which like reference characters designate corresponding parts throughout the several views, and in which:

Figs. 1A, 1B and 10, when placed end to end, illustrate a stretch of track signalled for traflic in one direction with the features of the present invention embodied therein; and

Figs. 2A, 2B and 2C, when placed end to end, illustrate a modified form of the invention for a stretch of track signalled for traffic in one direction with certain auxiliary added features not shown in the main and preferred form of the invention mentioned above.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawing having been made more with the purpose of making it easy to understand the principles and mode of operation, than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts, sources of energy and other devices have been illustrated in a conventional symbolic manner.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries, or other sources of direct current; and the circuits with which these symbols are used, always have current flowing in the same direction. The symbols (B+) and (B) indicate connections to the opposite terminals of a suitable battery, or other direct current source which has a central or intermediate tap designated (C); and the circuits with which these symobls are used, may have current flowing in one direction or the other depending upon the particular terminal used in combination with the intermediate tap (C). In this particular case, certain of these symbols (13+), (B) and (C) are used in connection with line circuits in which the polarized line has been shown, but the common line has not been shown but is to be assumed as a part of the designated connection to (C).

With reference to the drawings of Figs. 1A, lB and 1C, a stretch of track having rails 1 is shown as having a plurality of track sections separated from each other by the usual insulated joints. These track sections have apparatus associated therewith organized to embody the present invention. The organization of the first and last track sections is slightly different than that provided for the intermediate track sections, which is necessary in order to provide for the proper approach and exit of trains into a stretch of track signalled in accordance with the present invention; but the intermediate track sections may be duplicated any number of times depending upon the number of track sections required for the length of the stretch of track being signalled. Thus, the intermediate sections are assumed to be typical of the various track sections found in a relatively long stretch of track.

The track sections shown have been designated 2T, 3T, 4T, ST and 6T. The track section ST is shown as including a turnout switch STS to connect the main track with a spur track section, such as section 8T. The stretch of track shown illustrates the use of three aspect signals which have been designated as signals 2, 3 and 5. Signal 6 is a two aspect signal. It is noted that there are two track sections 3T and 4T located between the signals 3 and 5; and that each of these track sections have their apparatus organized the same as any of the other intermediate track sections.

Each of the track sections is provided with a track relay TR which has been given a distinctive preceding numeral corresponding to the track section with which it is used. For example, the track section 21 is provided with a track relay 2TR. These track relays T are preferably connected to the track rails at the entering end of the section, while at the exit end of the section a track battery TB is connected in series with a limiting resistor LR across the track rails.

Associated with the leaving end of each track section, except the last, is a suitable approach relay AR. These approach relays AR may be of any suitable type, but for convenience they have respectively been shown as being connected in multiple with the limiting resistor LR for the corresponding section. Under normal conditions, each approach relay AR is dropped away, but when a train enters its track section and causes an increased current flow through the limiting resistor LR, the approach relay AR at the exit end is picked up. For this reason, these relays AR may be conveniently termed series approach relays; but it is to he understood that shunt type approach relays, that are connected across the rails and are normally picked up, may be employed if desired.

Each of the approach relays AR is provided with a slow releasing repeater relay ARP, which picks up whenever its corresponding approach relay AR is picked up. This relay ARP has such slow releasing characteristics as to remain picked up for a predetermined time after the associated approach relay AR has been released. The length of this predetermined time will be discussed hereinafter in connection with the operation of the system.

The signals 2, 3, 5 and 6 are shown as being of the color light type; but it should be understood that any other suitable type of signal may be employed, if desired, such, for example, as Searchlight signals. The respective lamps for these signals have been shown adjacent their circuits rather than carrying their circuits to the symbols themselves for the purpose of simplifying the drawing. The different signal lamps designated as R, Y and G for identifying the different aspects of red, yellow and green, of each signal, are shown as selected by a suitable home-distant relay HD associated with that signal.

The home-distant relays HD are controlled over suitable polarized line circuits which include contacts of all the track relays of the associated sections between signals. In circuits of this kind, it is desirable that changes in polarity do not afiect momentary flashes of the signal nor cause a wave of successive deenergizations of the line circuits to the rear of a train. Although various expedients may be employed, one convenient way to accomplish this is to provide that the HD relays are of the type known as retained-neutral type relays, such, for example, as shown in the prior patent to J. E. Willing Patent No. 1,969,055 dated August 7, 1934.

It should also be noted that the leaving end of each track section except the first and the last, are provided with additional sources of energy use-d for the restoration of the track circuit organization after the passage of a train. For convenience, these additional sources of energy have been shown as batteries conveniently designated RB. These batteries RB used for restoration purposes may be of any suitable type, but since they are employed for very short periods of time and only intermittently, they may preferably be some form of primary battery source.

The track relays for the first and last sections of the stretch of track are shown as being of the primary-secondary type track relay organization. Such a track relay organization has been disclosed in the prior patent to O. S. Field Patent No. 1,942,141 dated January 2, 1934. This organization includes a track relay TR which, when picked up, also energizes its secondary slow release repeater relay SR which in turn shifts the energization of the relay to only one of its windings. This means that the holding effect then present on the relay armature is just above its release value. This makes the relay sensitive to the shunting effect of a train. When the track relay is shunted by a train and its armature releases, the secondary relay SR is also deenergized and releases its contacts. This shifts the circuit for the track relay TR to include both of its windings. Thus, when the train leaves the track section, the energization from the regular track battery is sufficient to cause the relay to be picked up. This arrangement makes it so that the track relay has its pick-up and drop-away values brought relatively close together.

The other track relays TR used for intermediate track sections are any suitable type of track relay connected into the circuit in a manner to have particular regard to its pick-up and release characteristics. Relays of this type generally have a drop-away value which is around fifty to sixty percent of the pick-up value; and this difference in release and pick-up values is taken advantage of in this particular form of the invention as will be apparent as the description progresses.

In the form of the invention shown in Figs. 1A, 1B and 1C, the replacement of a rail section or bonding in any one of the track sections results in the deenergization of the track relay for that section, which cannot be restored without the manual act of an authorized person. For this reason, each track section is provided with a reset button PB adjacent the relay end of its section. This reset button PB also permits a section to be restored if a train should back out of a section.

In connection with the turnout track switch 5T8, suit able switch box contacts or point detector contacts SPD are associated with the switch points in a way to be normally closed in the position shown when the track switch STS is in a position for main line movement; but, when the switch STS is moved to a position for turnout traffic, the contacts are moved to the dotted line positions. Associated with these point detector contacts SPD is a slow repeater relay SSR together with an associated battery 5B. The associated limiting resistor 24 may or may not be required depending upon the circumstances of practice; but in the form shown it prevents battery SE from being shorted by the make-before-break contact 66.

The present disclosure shows the invention embodied in two different forms; the structure of the first form having been discused above in connection with Figs. 1A, 1B and 10, While the structure of the second form will now be discussed in connection with Figs. 2A, 2B and 2C. The apparatus used in both forms is very similar, but for the sake of definiteness in the disclosure the entire structure of the second form will be discussed with particular emphasis on the differences over the first form. The same reference characters employed in Fig. 1 will be used in Fig. 2; but, where the apparatus is modified,

the reference characters will be made distinctive by the use of a succeeding numeral 2.

With reference to the drawings of Figs. 2A, 2B and 2C, a stretch of track having rails 1 is shown as having a plurality of track sections separated from each other by the usual insulated joints. Each of these track sections has apparatus associated therewith organized to embody the invention and adapted to cooperate with the apparatus of adjoining sections. The organization of the first and last track sections is slightly diiferent than that provided for the intermediate track sections. The first track section has a track relay of the primary-secondary type; whereas, the last track section has a track relay controlled the same as disclosed in connection with the intermediate track sections. Neither the first nor the last section is provided with an additional restoration track battery as is provided for the intermediate track sections. The intermediate track sections may be duplicated any number of times depending upon the number of track sections required for the stretch of track being signalled, so that these intermediate sections may be assumed to be typical of all such intermediate sections as found in a relatively long stretch of railroad track.

The track sections have been designated as 2T, 3T, ST and 6T, the same as in connection with Fig. l. The track section 5T also has been shown as including the turnout track switch ST S to connect the main track with a spur track including track section 8T. The stretch of track is shown as having signals 2, 3, 5 and 6 of the color light type, although it is to be understood that any other suitable type of signal may be employed, if desired, such, for example, as searchlight signals. The respective lamps for these signals have been shown adjacent their respective circuits rather than carrying their wires to the symbols themselves.

The signals are controlled by home-distant relays HD which are respectively controlled over suitable polarized line circuits each of which includes contacts of all the track relays for the sections of track over which the associated signal governs traific. These HD relays may be of any suitable type, but in order to prevent certain undesirable actuations during the changes in polarity, it is preferable to provide some type of retained neutral relay, such for example, as shown in the prior patent to J. E. Willing, Patent No. 1,969,055, dated August 7, 1934.

Each of the intermediate track sections is provided with the usual track battery TB, limiting resistor LR, and approach relay AR. Each approach relay AR is provided with a slow repeating relay ARP. These relays are associated with the track section along with the restoring battery RB in the same way as described in connection with Fig. 1. In addition, each track relay TR is shown as having two windings, and the approach relay of the next adjoining section is shown as having a contact which selects these two windings in a way to make these relays more sensitive to train shunt the same as described in connection with the primary-secondary relay combination. This preselection of the track relay control to render it sensitive upon the entrance of a train is maintained until the associated approach relay and its repeater have indicated that the train has fully left the one section and entered the other section. This gives a prolonged time of sensitivity for the track relay which more positively assures that it will be responsive to the entrance of the train for reasons later discussed.

In addition, this form of the invention provides that a restoration or pick-up circuit is controlled by the approach relay and its repeater relay for the track relay of the adjoining track section in advance to facilitate the restoration of the circuits when a train backs out of a section. It might be noted here that this restoration does not occur immediately upon the movement of a train out of a section because of a peculiarity of the organization of the circuits. Sometimes two sections are restored at a time for reasons later discussed. Since this facility is provided,

then the selected adjustment of the track circuits is such that the regular track battery TB is capable of picking up a track relay when this back up restoring circuit is closed. Actually, the interrail potential is adjusted to be close to the release value of the relay, because at such time that the track relay is to be released by a train-shunt, the approach relay has rendered the track relay wholly dependent upon current through its main winding; but, when the track relay is to be picked up, the approach relay has rendered the track relay dependent upon the current flowing through both of its windings. For this reason, it is apparent that the approach control of a track relay is desirable if the releasing facility for back-up moves is provided.

It is believed that the nature of the invention, its advantages and characteristic features can be best understood with further description being set forth from the standpoint of operation.

OPERATION (First form) The block signaling system of Figs. 1A, 1B and 1C is of the normally energized type with approach lighting for the signals except in the case of the entering signal 2 which is steadily illuminated. It is assumed that all track relays are in normally energized positions, which the track relay 2TR and 6TR will automatically assume when there is no train present in their respective sections, but the other track relays such as 3TR, 4TR, STR must be restored to such normally energized positions either by the passage of the train or the actuation of their respective reset buttons 3PB, 4PB and SPB. The track relays ZTR and 6TR energize their respective repeater relays ZSR and 65R through obvious circuits including respectively the contacts and 26.

Since all the track relays are energized, then all of the home-distant relays HD are energized. More specifically, the home-distant relay 6HD is energized from (B+), through a circuit including front contact 27 of relay 65R, windings of relay 6HD, to the mid tap of the battery over common return Wire C. With this relay 6HD picked up, a circuit is closed for energizing relay 5HD from (B+), through a circuit including front contact 28 of relay 6HD, line wire 29, front contact 43 of push button SPB, front contact 30 of relay STR, windings of relay SHD, to the mid tap of the battery over common return wire C. This completes an energizing circuit for the relay 3HD from (B+), through a circuit including front contact 31 of relay SHD, line wire 32, front contact 44 of push button 4PB, front contact 33 of relay 4TR, line wire 34, front contact 45 of push button 3PB, front contact 35 of relay 3TR, windings of relay 3HD, to the mid tap of the battery over the common return wire C. This completes an energizing circuit for the relay 2HD from (B+), through a circuit including front contact 36 of relay 3HD, line wire 37, front contact 38 of relay 28R, winding of relay ZHD, to the mid tap of the battery over the common return wire (C).

The relay ZHD closes a circuit for the signal 2 from through front contact 40 of relay 2HD, polar contact 41 in a left-hand position, lamp G, to Thus, signal 2 is normally illuminated to display a green aspect. The other signals are normally dark, but are illuminated upon the approach of a train as will be described later.

Each track relay, as above mentioned, is normally picked up. For example, the relay 3TR is picked up which closes a front contact 42 to shunt the pick up resistor 3PR. The track relay 3TR is thus energized over the track rails from the track battery 3TB in series with the limiting resistor 3LR.

The adjustment of the track circuit is such that the normal interrail potential provides a current through the track relay 3TR which is above its release or drop away value, but which may or may not be above the pick up value of the track relay. This normal interrail potential is prQ- vided by .the track battery 3TB connected in series with the limiting resistor 3LR across the rails of the section ST. The limiting resistor 3LR is provided to give a potential drop in the interrail potential when a train enters the section, and also to prevent excessive current flow from the battery while the section is thus occupied. Since the actual critical adjustments of the track circuit are provided by the resistor 3R, the limiting resistor SLR may be of a fixed value suitably selected for the length of track circuit involved. For example, this limiting resistor 3LR may have a value in the order of one or two ohms.

The resistor 3R is adjusted so that the normal interrail potential will provide sutficient current through the track relay 3TR to maintain it picked up, but yet be as close to the drop away value of the relay as suitable margins will permit. The ballast conditions will of course vary due to dilferent weather conditions so that the interrail potential will vary over a range that has two extremes. The low extreme of interrail potential will be near the release value of the track relay including resistor 3R in series, but the high extreme of interrail potential may or may not be above the pick up value of the track relay 3TR with resistor 3R in series.

When the track relay 3TR is released and its front contact 42 is opened, then the resistor SPR is included in the circuit. The interrail potential required to pick up the track relay 3TR under this condition must be of a value considerably above the range of interrail potentials which may exist due to varying ballast conditions. In any event, the regular track battery 3TB cannot provide such an interrail potential; and such restoring or picking up interrail potential is provided only by the addition of the potential of the restoring battery SRB to the regular track battery 3TB. In one organization, the resistor 3R had a value in the order of ten ohms, while the resistor 3 PR had a value in the order of forty ohms. In this organization, the track relay had a winding in the order of four ohms.

From this description, it will be seen that the drop away value of the relay 3TR with resistor 3R in series is of significance, and that the pick up value of the relay with the resistors SR and 3PR in series is also of significance; but the pick up value of the relay alone without the resistors 3R and 3PR in the circuit is not of particular significance for regular operation. However, it might be mentioned here that the shunting of the resistors 3R and SPR by the push button 3PB will cause the track relay 3TR to pick up in response to the regular interrail potential supplied from the track battery 3TP. This will be discussed in detail later. The above description with regard to the adjustment of the track circuit for section 31 is to be considered as typical, since similar conditions will be established in each of the other intermediate track sections.

Let us assume that a train is given orders to travel over the stretch of track. It approaches signal 2 which displays a green proceed aspect as above pointed out. This, of course, assumes that there is no other train in the stretch.

As the train enters the track section 2T, it shunts the track relay 2TR and causes it to release opening front contact 25 which in turn releases the slow acting repeater secondary relay ZSR. This opens front contact 38 and releases the home-distant relay ZI-ID, which in turn deenergizes the green lamp G and energizes the red lamp R of signal 2 through back contact 40.

The entrance of the train into the section 2T is assumed to provide a train-shunt which is adequate to release the track relay 2TR, and it is also assumed that it is adequate to maintain it released even though the secondary relay shifts its make-before-break contact to a back point to include both windings of the track relay ZTR in the circuit.

The train-shunt across the rails of section 2T will increase the current through the limiting resistor ZLR,

and thus provide a potential drop across it which is sufficient to pick up the approach relay 2AR. In some cases where the track sections are extremely long, and the ballast conditions are extremely variable, it will not be possible for the train-shunt to immediately pick up the approach relay ZAR, but it will effect such energization when the train has moved into the section a sufiicient distance. In any event, it is desirable that the approach relay 2AR be picked up well in advance of the signal 3 so that the engineer of the train will receive an indication from the signal 3 as he approaches it. It should also be noted in this connection that when the conditions of the track section are such that the approach relay does not immediately pick up upon the entrance of the trains into the section, changes in ballast conditions as from dry to wet conditions will change the actual point at which a train must be in the section before the approach relay will be picked up.

The picking up of the approach relay 2AR closes its front contact 51 and energizes the relay 2ARP. This closes front contact 52 which completes a circuit from through a circuit including front contact 52 of relay ZARP, front contact 53 of relay 3HD, polar contact 54 of relay 3HD in a left-hand position, green lamp G of signal 3, to In this way, the signal 3 is approach lighted.

The train approaching signal 3 at clear accepts its indication and proceeds into the track section 3T. This train-shunt of the section 3T causes the track relay 3TR to be released opening front contacts 35 and 42. The opening of contact 35 releases the relay SHD so that back contact 53 is closed preparing signal 3 for displaying a red or stop aspect should another train enter section 2T while the train is in the section 3T.

Let us assume that this train in passing into the section 3T Wholly leaves the section 2T which allows the track relay 2TR to be picked up by energy from the track battery 2TB through both of the windings in series, since back contact 56 is closed. The picking up of the track relay 2TR picks up the relay 2SR closing front contact 38 which allows the relay ZHD to be picked up by energy from (B-), through back contact 36 of relay 3HD. This actuates the polar contacts of the relay 2HD to the right so that the yellow lamp Y is energized from through a circuit including front contact 40 of relay 2I-ID, polar contact 41 of relay 2HD in a right-hand position, lamp Y of signal 2, to

The release of the track relay 3TR opening front contact 42 inserts the resistor 3PR in series with the track relay connection across the track rails. This means that there must be additional potential across the track rails in order to provide suflicient current through the relay to cause its armature to pick up. It is clear that if the train has a variable train-shunt, even to the extent of wholly failing to shunt the section 3T, such loss of train shunt will not allow the track relay 3TR to pick up because there is insufiicient potential across the train rails as supplied by the track battery 3TB to pick up the track relay 3TR through the resistance 3PR. If this loss of train-shunt, or variation therein, occurs before the approach relay 3AR is picked up, it is apparent that there is no resulting relay action, and the track relay 3TR remains steadily dropped away holding the relay 3HD steadily deenergized causing the signal 3 to be steadily at stop.

In the event that the approach relay 3AR is picked up when the variation in the train-shunt takes place, it is apparent that the relay SAR will be released. Before considering what happens under this circumstance let us consider more specifically how the approach relay 3AR is connected into the circuit organization.

Referring to Fig. 1B, the approach relay 3AR is connected across the limiting resistor 3LR in series with an adjustable resistor 55 and back contact 56 of relay 3ARP. When the approach relay 3AR is picked up, it closes its front stick contact 57 which shunts the back contact 56 of relay 3ARP so that the picking up of relay 3ARP by reason of the disclosure of front contact 58 does not deenergize the relay 3AR. The adjustable resistor is provided so that the relay 3AR may be adjusted to respond to proper values of potential drop across the limiting resistor 3LR dependent upon the actual circumstances of practice; but after once adjusted, it does not have a functional significance in the operation of a circuit.

Let us assume that the train is in the section 3T, as above discussed, and that the approach relay 3AR has been picked up but the train-shunt is lost causing the relay 3AR to drop away. Since the relay 3ARP is picked up, opening back contact 56, it prevents the relay 3AR from being again picked up, even though a train-shunt is restored, until the relay 3ARP again releases. However, whenthe relay 3ARP releases, relay 3AR again picks up and closes front contact 57. Even though the train-shunt may be repeatedly removed and several sequential operations of these two relays, the releasing energy cannot be placed across the track rails of the section 3T because of open front contact 60 of track relay 4TR.

As above briefly mentioned, the train in moving through the section 3T may temporarily lose a train-shunt but this is not permanent since the train is moving. Also, the closer the train approaches the battery end of the section, the more elfective it is to pick up the relay 3AR and steadily hold it up. This is because the train-shunt becomes more effective for drawing additional current from the battery 3TB through the limiting resistor 3LR. For this reason, when the train is ready to enter the track section 4T, it is well assured that the approach relay 3AR and its repeater 3ARP are both picked up.

The entrance of the train into the section 4T causes the track relay 4TR to release opening its front contact 33 to maintain the relay 3HD deenergized even though the track relay 3TR is restored. This deenergization of the track relay 4TR also closes back contact 60 preparatory for a restoration operation when the train wholly leaves the track section 3T. This is indicated by the deenergization of the relay 3AR when the axles of the train are wholly out of the track section 3T. The restoration circuit is closed following the release of the relay 3AR and during the releasing period of the repeating relay 3ARP. This circuit is closed from the negative terminal of the releasing battery 3RB through front contact 61 of relay 3ARP, back contact 60 of relay 4TR, and back contact 57 of relay 3AR, to the lower track rail.

This restoration circuit connects both the batteries 3TB and SRB in series across the track rails, but this application of increased potential across the track rails is not applied to the approach relay 3AR because during the time that front contact 61 is closed the back contact 56 is open. Thus, the relay SAR is wholly disconnected from the circuit during the application of this increased potential across the track rails. Also, it will be noted that the increased potential may result in added current flow through the limiting resistor 3LR dependent upon the relative potentials of the two batteries 3TB and 3RB and also the resistance of the lead connections and trainshunt values. Whether the current through 3LR is increased or decreased due to the cancellation of currents which may occur under some circumstances, the particular condition is momentary and does not affect the actual functioning of the system since it lasts for only the limited release time of the slow release of the relay 3ARP.

During the application of this increased potential across the track rails with no train in the track section 3T, there is sutficient current flow through the resistor 3R, the track relay 3TR, and resistor 3PR, to allow the track relay 3TR to pick up. As soon as it closes front contact 42, it shunts the resistor 3PR assuring that the track relay 3TR remains picked up at the termination of the increased potential applied for restoration purposes. Since the track relay 4TR must be released closing back contact 60 before restoration potential can be applied, there is no chance that the relay 3TR can be picked up to close contact 35 before contact 33 is open. In this way, the signal 3 is held at Stop" throughout the time that the train is in the sections 3T and 4T between signals 3 and 5. The action of the train in section 4T with regard to the relays 4TR and 4AR is exactly the same as described for section 3T and will not be repeated.

Let us assume that the train enters the section ST and releases the track relay 5TR. This places the signal 5 at stop by deenergizing the relay SHD at open front contact 30. When the train wholly enters the section 5T leaving the section 4T, the restoration circuit is closed from the negative terminal of battery 4RB through front contact 62 of relay 4ARP, back contact 63 of relay STR, back contact 64 of relay 4AR to the track rails. In this way, the track relay 4TR is restored by the application of the increased interrail potential. Since this takes place, the energy from (B) is supplied to the relay 3HD to prepare the signal 3 for displaying a caution aspect in the event a train approaches such signal. The picking up of the relay 3HD closes front contact 36 to apply potential from (B+) to the relay 2HD to cause it to display a green or proceed aspect.

lt is noted that there is an insulated joint 65 in the track section 5T which is shunted through back contact 66 of relay SSR and point detector contact 67. Due to this shunting circuit, the track circuit for section 5T operates the same as any of the other sections so long as the track switch STS is in the normal main line position. The operation for a turnout train movement will be discussed later. Thus, the train passes through the section ST and enters the section 6T. This causes the track relay 6TR to be released to deenergize relay 6HD and place signal 6 at stop. When the train has wholly left the section ET the restoration circuit is closed from the negative terminal of battery SRB, through front contact 70 of relay SARI, back contact 71 of relay 65R, back contact 72 of relay SAR, to the rail section 5T. This restoration circuit causes the picking up of the track relay STR to allow the relay SHD to be energized from (B-) through back contact 28. This causes signal 5 to display a caution or yellow aspect. Also, the picking up of relay SHD closes front contact 31 to apply (B+) to the relay SHD which, of course, will cause the signal 3 to display a green or proceed aspect upon the approach of a following train. The train in passing through the section 6T is assumed to maintain the track relay 6TR released,

and this track section may be a section of an interlocking plant or may be the approach section to a home signal of an interlocking plant so that the train is assumed to leave the stretch of track when it has left the section 6T. This permits the track relay 6T R to be picked up and in turn energize the relay 6HD so that signal 6 can give a proceed or green indication. In the event that there is a home signal at the exit or leaving end of the track section 6T, polarized control will be provided for the relay 6HD so that it will provide a caution approach signal for the home signal.

In this way, a train in passing through the stretch of track at relatively high speeds is assured of a positive protection regardless of momentary or temporary losses of train-shunt. Expressing the result in a ditferent way, it can be said that each train is checked into a section by the dropping of the track relay for that section; but it is not checked out of that section until it has been checked into the next section in advance. For this reason, the failure of a train to properly check out of a section results in the leaving of the signal at the entrance to that section in a stop condition. This provides a check on all track circuits. In other words, the failure of a train to provide an adequate shunt for a section results in the failure of that train to properly check into a section during a predetermined restoration time so that a stop signal is left to the rear of the section which it is just leaving. In prior systems, track circuits have been arranged to leave stop signals in the event the track relay failed to pick up either due to an inadequate track battery, very poor ballast conditions, or a broken rail; but there was no check upon the failure of a track relay to release due to either an inadequate train-shunt or an over energization of the track relay due to ballast conditions or improper adjustment of the limiting resistor. The present system checks a track circuit from all of these standpoints, so that the recurrent reporting of a particular signal erroneously at stop will advise the signalman that there is something wrong with the associated track circuit.

Turnout track switch In the event that an eastbound train entering section 5T desires to operate the track switch 5TS to the reverse position to permit the train to enter the track section 8T, the trainman throws the track switch STS to a reverse position. This causes the point detector contacts SPD to open contact 67 and close contact 75. This energizes the relay 58R through an obvious circuit picking up front contact 66. The opening of back contact 66 as well as the opening of contact 67 assures that no energy can be supplied over the rails to the track relays 5TR regardless of a loss of shunt by reason of the insulated joint 65.

However, when the train has entered the track section 81 fully clearing the fouling point for the turnout switch 5TS, the trainman can restore such switch to its normal position closing contact 67. The opening of contact 75 releases the relay 55?. but its contact 66 does not drop for a predetermined time thereafter. Thus, the battery 5B is inserted for a limited time through front contact 66 in series with the battery 5TB. This places an increased potential across the track rails which acts to restore the track relay STR even though the train did not leave the section at its regular leaving point of signal 6.

When a train enters the single track stretch moving to the left from track section 8T over the track switch STS in a reverse position, it will occupy the track section 5T to a point where it entirely clears the switch STS allowing it to be restored to a normal main line position. If such train did not have to pass the signal 5 in a reverse direction, then the train may proceed in an eastbound direction (to the right) over the track switch STS in a normal position without having to obtain a clear signal 5. However, on some railroads, if the switch is close to the signal it is required that the train proceed to the left until it has passed the signal 5 and then receive a clear indication from signal 5 before it proceeds to the right. In the latter case, the train should be in approach to the signal 5 before the track switch 5TR is restored so that the closure of contact 67 while the relay 53K is releasing, will apply restoring energy to pick up the relay STR and allow the signal 5 to clear.

On the other hand, if the train has not passed to the left of signal 5, then it can proceed in a right-hand normal direction over the stretch receiving the first signal indication at signal 6. It is of course understood that the track switch has been restored to normal while the train was occupying section 5T so that the restoration energy applied to the track section 51 is unlikely to cause the picking up of the track relay STR. In any event, should the track relay STR be momentarily picked up, as soon as the train moves to improve its shunting characteristics, the track relay STR will immediately drop out especially when the amount of energy is applied to the track section is returned to normal following the restoration energization by the movement of track switch STS to a normal position. Such restoration energy with a train coming into the stretch from the tracksection ST is of little importance and in most cases not required; but this provision for the application of restoration energy upon movement of the switch is made for train movements out of the single track stretch into the track section 8T.

As the train moves to the right and passes signal 6 a proper restoration pulse from battery SRB will be applied through front contact 70 of relay SARP, back contact 71 of relay 68R, back contact 72 of relay SAR to the track rails. This restoration energy will cause the picking up of the track relay STR and the operation of the system in the same manner as previously described.

In some cases, where the signal is relatively close to the turnout track STS, it will be necessary for the train to move to the left until it is wholly past the signal 5. In such an instance, it will be necessary for the trainman to actuate the restoration button SPB adjacent the signal 5. This causes the resistor SPR to be shunted and allows the regular track battery 5TB to properly energize the relay STR so that it will pick up. This picking up of the track relay STR permits the signal 5 to clear so that the train can then proceed in the normal eastbound direction under the regular signal indications.

Special restoration conditions There are certain occasions when the track rails of a section must be replaced by the track maintenance department. Under such circumstances the track relay for that section is released, and it is necessary for the foreman of the crew or some authorized person such as the signal maintainer to come to that section and actuate the restoration button PB at the signal location at the entrance thereto.

Also, in the case of double track signaling there are times When one track is not available, and it is necessary to run trains on the other track in the reverse direction under train order employing what is known as manual blocking. Under such circumstances, the passage of a train will cause all of the track relays through the stretch to be released, and they will not be automatically restored in the usual way.

More specifically, the restoration push button SPB is associated with the track relay 3TR and has a back contact 80 and a front contact 45. These contacts are suitable spring biased to their normal positions shown. Similarly, track relay 4TR is provided with the restoration push button 4PB having contacts 81 and 44; and track relay STR is provided with the restoration push button SPB having contacts 82 and 43.

Let us assume, for example, that a train has moved through the stretch to the left and has deenergized each of the track relays in turn. When the train moves out of the section 5T it causes the approach relay SAR to be released which is in turn repeated by its repeater relay SARP. This does not apply the restoration energy because of open back contact 72, since the track relay 6TR automatically picks up when the train left the section 6T. Thus, the track relay STR is left in a deenergized condition.

The train in passing through the section 4T in the reverse direction of course picks up the relay 4AR and its repeater 4ARP as well as releasing the track relay 4TR. Thus, when the train wholly enters the section 3T so as to allow the release of the approach relay 4AR and its repeater relay 4ARP, the restoration energy is applied to the track section 4T through front contact 62 of relay 4ARP, back contact 63 of relay STR and back contact 64 of relay 4AR. This added potential from the restoration battery 4RB causes the track relay 4TR to be picked up at which time it closes front contact 65 to shunt the resistor 4PR. Thus, the track relay 4TR remains picked up.

When the train leaves the section 3T by wholly entering the track section 2T, the dropping away of the approach relay 3AR and its repeater 3ARP cannot close the restoration circuit because of open back contact 60 of relay 4TR. For this reason, the track relay STR is left deenergized.

From this description, it is apparent that a train travel ling in the reverse direction leaves every other track section with its track relay locked down and the alternate sections with their track relays picked up. In any event, there are circumstances which may at one time or another require the track relays for the intermediate sections to be restored and their respective restoration push buttons PB are employed for this purpose.

Referring to Fig. 1A, it will be observe-d that the operation of the push button SPB closes back contact and shunts both the resistors 3R and 3PR. This removal of resistance from the circuit including the windings of the track relay 3TR in effect places this relay directly across the track rails. Under these circumstances, the track battery 3TB is supplying sufiicient interrail potential to cause the track relay 3TR to pick up. Since the closure of back contact 80 removes the stick efiect for the loss-of-shunt protection, it is desirable to protect this contact from being erroneously held down. To do this, the front contact 45 of button 3PB is included in the circuit for the relay 3HD. Thus, when the push button SPB is operated to allow the track relay 3TR to be restored, the signal 3 is held at stop by reason of the deenergized condition of the home-distant relay 3HD. Should the restoration spring be broken, or some other erroneous conditions be present, this holding of the signal 3 at stop would betray the fact that the push button 3PB had not properly restored. Similar operations and functioning of each of the other restoration push buttons accomplishes the same result; and for the circumstances being considered, this requires the operation of push button SPB. However, it should be noted that in the case of the stretch of track between signals 3 and 5, there is a plurality of track sections. In the particular illustration selected, the track relay 4TR is automatically restored, but it should be understood that there are some circumstances under which the track relays of all the sections between two signals may be released and for this reason the individual manual restoration of each of the track relays may be required.

OPERATION (Second form) The block signaling system of Figs. 2A, 2B and 2C is of the normally energized type with approach lighting for the signals except in the case of the entering signal 2 which is steadily illuminated. It should perhaps be noted again that all devices of this second form corresponding to the same devices in the first form are provided with the same reference characters; but for those devices which are different, the reference characters have been made distinctive by the addition of a succeeding numeral 2.

All of the track relays are shown normally energized, since all of the track sections are unoccupied and have been set in normal conditions. The track relays ZTR and 6TR2 will automatically assume such energized conditions when no train is present in their respective sections, but the other track relays such as 3TR2, 4TR2, and 5TR2 must be initially set in their normally energized or picked up conditions by a manual operation of an associated push button PB for each track relay.

Since all of the track relays TR are normally energized or picked up, then all of the home-distant relays HD are energized. These circuits are exactly the same as shown in the first form, so that they have been given the same reference characters and will not be pointed out in detail. Likewise, the signal 2 is normally energized and displays its green aspect as previously described.

The other signals are normally dark, but they are illuminated upon the approach of a train as will be described later.

Each track relay, as above mentioned, is normally picked up. For example, the track relay 2TR is energized from the track battery 2TB over the track rails of section 2T in series with the limiting resistor ZLR. This circuit also includes front contact 50 of relay 28R which is in turn energized through front contact 25 of relay 2TR. The resistor 2R is preferably included in series with the track relay 2TR, so as to provide that the relay end of the track circuit has a higher resistance than the battery end. This resistor 2R provides that the current through the track relay ZTR (while no train is present) is more uniform regardless of changes in the track ballast conditions. For this reason, a similar resistor is preferably included in series with each of the track relays.

As previously explained, the track relay 2TR is of the primary-secondary type so that the entrance of a train-shunt causes the track relay to readily release opening front contact 25 which in turn releases the slow acting repeater relay 28R. This opens front contact 38 and releases the home-distant relay 2HD, which in turn deenergizes the green lamp G and energizes the red lamp R of signal 2 through back contact 40. The entrance of the train into the section 2T is assumed to provide a train-shunt which is adequate to release the track relay ZTR and to maintain it released even though the secondary relay 25R shifts its make-before-break contact 50 to a back point to include both windings of the track relay 2TR in the circuit.

The train-shunt across the rails of section 2T will increase the current through the limiting resistor 2LR and thus provide a potential drop across it which is sufficient to pick up the approach relay 2AR2. It is, of course, understood that the resistor included in series with the relay 2AR2 is adjusted so as to provide for the response of this relay over the proper range. It is assumed that the relay 2AR2 picks up when the train enters the track section 2T, but should the section be very long, it is assumed that relay ZARZ picks up when the train is well in advance of the signal 3 so that the engineer will receive an adequate indication from the signal 3 as he approaches it. The picking up of the relay 2AR2 closes from contact 51 which energizes its repeater relay 2ARP through an obvious circuit. The closure of front contact 52 of relay ZARP applies energy to the lamps of the Signal 3 in accordance with the existing condition of the relay 3HD in a manner previously described.

The relay 2AR2 dilfers from the approach relay ZAR of Fig. 1A in that it is provided with a make-before-break contact 101 which is shifted to its upper position when this relay is picked up. This means that the track relay 3TR2 is connected across the track rails to include only its upper winding in series with the resistor SR and the front contact 42 which shunts the associated resistor 3PR. In this way, the track relay 3TR2 is made dependent only upon the holding winding and the degree of flux in the relay is close to the drop away value. This renders the relay 2 TR2 sensitive to a train-shunt in the same way that the relay ZSR renders the track relay ZTR sensitive to a train-shunt.

It may be appropriate to here point out that the track circuit for section ST is adjusted in this form of the invention by selecting the proper value of resistor 3R to permit the track battery 3TB to pick up the track relay 3TR2 when both of its windings are connected in series through back contact 101 but with the resistor 3PR excluded from the circuit. When the front contact 101 is picked up to include only the upper winding of the track relay 3TR2, then the magnetic flux in the relay is reduced to a value just slightly above the drop away value for the relay. In other words, a particular value of pick up energy for the relay is not much above the drop away value for the relay when only the upper winding is included. The adjustment of the resistor SR is then made so that the normal interrail potential will provide suflicient current through the track relay to maintain it picked up with front contact 101 closed with a suitable margin to assure that this condition always exists. The ballast conditions will, of course, vary due to different weather conditions so that the interrail potential will also vary over a range that has two extremes or limits. The lower limit of the interrail potential will in this form of the invention be above the pick up value of the relay with both windings included in series with the proper adjustment of the resistor 3R; and the higher extreme or limit of the interrail potential will also be of a value greater than the pick up of the relay including both windings and resistor 3R. Thus, it will be obvious that whenever the track relay 3TR2 is released opening front contact 42, the resistor 3PR will be additionally included, so that the pick up value for the relay 3TR2 with this resistor included will require an interrail potential substantially higher than the upper limit of the range of interrail potentials supplied by the battery 3TB under any of the varying ballast conditions. Thus, the restoration potential must be applied by including the battery 3RB in order to pick up the relay 3TR2 with the resistor 3PR in its circuit. With this arrangement a loss of a train-shunt will not result in the picking u of the track relay 3TR2, but under certain circumstances the shunting of the resistor 3PR will allow the track relay 3TR2 to pick up without the additional restoration energy. For these reasons, the track circuit is rendered very sensitive to a train-shunt, and this applies to each of the intermediate track sections in a manner which will be apparent by analogy.

The train approaching signal 3 at clear accepts its indication and proceeds into the track section 3T. This trainshunting of the section 3T causes the track relay 3TR2 to release opening front contacts 35 and 42. The opening of front contact 35 releases the relay 3HD causing the signal 3 to display a stop or red indication. Also, the opening of front contact 42 removes the shunt around the resistor 3PR, so that the track relay 3TR2 cannot again pick up until restoration conditions are established. In other words, this resistor 3PR is of such a value that the loss or removal of the train-shunt will not effect the picking up of the track relay 3TR2 by the interrail potential due to the track battery 3TB. This is true regardless of whether the train has just entered the track section 3T and the relay 2AR2 is picked up due to the rear of the train still being in the section 2T or whether the train is wholly in the track section 3T and the relay 2AR2 is released. In this connection, the holding current which is required to flow through the upper winding of relay 3TR2 is just slightly lower than the pick up current required to flow through both of the windings of this relay when back contact 101 is closed. Thus, the value of this resistor SPR only needs to be sufficiently large to prevent the pick up current to flow through the track relay over the range of values of interrail potential for the various ballast conditions. Of course, there must be a sufiicient margin to provide for safe operation. It is because of the insertion of this resistor 3PR that the track relay 3TR2 is protected against picking up erroneously during temporary losses of train-shunt while a train is passing through the section 3T.

When this train wholly passes into the section 3T and allows the approach relay 2AR2 to release, a temporary circuit is established through back contact 102 of relay 2AR2 and front contact 103 of relay 2ARP. This shunt circuit across the resistor 3PR is closed during the release time of relay ZARP, so that it is relatively short. During this shunting of the relay 3TR2 there is no protection against the loss of shunt with the train in section 3T. But assuming that the train-shunt during this short interval of time is effective, the track relay 3TR2 is not picked up. Even if the train-shunt should be variable and ineffective to hold. the track relay 3TR2 down during; this short interval, it is assumedthat the variable shunt effect of the train as it is moving through the section 3T would be effective. to again release. the track relay 3TR2v the same. as it had when the. train entered the section. Once the repeating relay ZARP has released and opened front contact 103, and the: track relay 3TR2 is in a released condition, then the temporary loss of a train-shunt is ineffective to allow the track relay 3TR2 to be. picked up.

As the train passes into and through the track section 3T, the: approach. relay 3AR2 isv picked up. by the increased potential drop across the limiting resistor 3LR through a circuit including back. contact 56 as previously described for relay 3AR of. Fig. 1B. This. closes front. contact 58 and energizes the relay 3ARP through an obvious circuit. The picking up of relay 3AR2 closes front contact 104 and shifts the connections of track relay 4TR2 from its pick up to itsholding circuit connections. This renders the track relay 4TR2 sensitive to a train-shunt as. previously described.

Let us assume that the train enters the track section 4T andshunts the track relay 4TR2 to cause its release. This opens the front contact 33 so that the relay 3HD is maintained deenergized. even though the track relay 3TR2 is picked up as the train wholly occupies the section 4T. More specifically, as the train leaves the section 3T, the approach relay 3AR2 is released so that restoration poten tial is placed across the track section 3T through a circuit including back contact 57 of relay 3AR2, back contact 60 of. relay 4TR2, and front contact 61 of relay SARP. The closure of this circuit connects the restoration battery SRB in series with the regular track battery 3TB to apply in creased potential across the rails of section 3T. This increased potential. causes sufiicient current to flow through the protective resistor SPR and the two windings of relay 3TR2 in series with back contact 101 and resistor 3R to cause this track relay to. pick up. It is noted that this restoration potential cannot be applied to the rails of section 31 unless the track relay 4TR2 is released closing back contact 60. In this way, the train which has just left the section 3T mustpositively check into the section 4T before itis checked out of the section 3T.

While the train is in the section 4T, the track relay 4TR2 cannot be. picked up even though it is conditioned for pick up by the closure of back contact 104. This is because of the open condition of front contact 65 and the consequent. unshunted condition of the resistor 4PR. Thus, the loss of a train-shunt in section 4T does not result in the undesired picking up of the track relay 4TR2. It should be noted that, when the train leaves the section 3T, there is a momentary shunting of the resistor 4PR through back contacts 105 of relay 3AR2 and front contact 106 of relay SARP. Since this circuit includes front contact 106 it is closed only during the release time of relay 3ARP, so that the protection of section 4T against the loss of a train-shunt is effective at all times except during this temporary period.

The train proceeds through the section 4T and the pick ing up of the approach relay 4AR2 of course causes the lighting of the signal 5 in a manner easily understood by analogy as previous description. The track relay STRZZ is sensitized for the entrance of the train into the section 5T;v

, Similarly, the entrance of the train into the section 5T causes-the. release of the approach relay 4AR2. which acts to apply temporary restoration energy to the track rails of section 4T. The. train passes through the section ST and acts on the approach relay 5AR2 in a similar manner to approach light the signal 6 and sensitize the track relay 6TR2. It is believed unnecessary to further describe the conditions of the circuits as the train passes through the stretch of track. It will be appreciated that. the train is checked into and out of each track section in turn, the checking into one section being required before. the train cancheck out of the preceding section.

From this description, is, will be appreciated that this second form of Figs. 2A through 2C provides the same characteristic operation described in connection with the first form of Figs. 1A through 1C. This second form is particularly characterized by the fact that the approach relay for one section sensitizes the track relay for the section in advance. Another feature provided by this form, is the provision for trains travelling in the reverse direction, i. e., means is provided to cause the restoration of the track sections in turn as the train is travelling in the reverse direction.

For example, should a train proceed from the turnout switch STS in the reverse direction, it is apparent that the opening of contact 67 would release the track relay 5TR2 which would result in the inclusion of the resistor fi'PR because of the open condition of contact 66. Since the train is located between the turnout switch STS and signal 5, the manual restoration of the switch STS cannot effect the pick up of the track relay ETRZ. When the train proceeds in the reverse direction past signal 5 into the section 4T, it is obvious that the release of the approach relay SARZ cannot apply restoration potential to the section 5T because of open contact 73 of track relay 6TR2. Thus, if no added means were provided, the track relay 5TR2 would be maintained released as the train proceeds to the left through the stretch. This would be true of each of the track sections so that should the train proceed all the way through the stretch, all of the track relays would be locked down, so to speak, and all of the signals would be held at stop, except the entering and leaving signals.

This form of the invention, however, takes care of this situation since the picking up and release of the approach relays acts to provide a temporary release circuit for each of the adjoining track relays. For example, when the train has passed from section 5T into the section 4T, the approach relay 4AR2 and its repeater 4ARP are picked up. Then as the train enters the track section ST and leaves the section 4T the approach relay 4AR2 is released and closes a circuit through back contact 107 of relay 4AR2 and front contact 108 of relay 4ARP. This temporarily shunts the resistor SPR, so that the interrail potential provided by the track battery 5TB can cause the picking up of the relay 5TR2. This is a temporary circuit and as soon as the relay 4ARP releases front contact 108 is opened and the track relay STRZ is then in condition to be released should a shunt occur across the track rails of section 5.

As the train moves from section 4T into section 3T the approach relay 3AR2 is, of course, picked up and the track relay 3TR2 is released. But the train has to move from section 3T to section 2T before the relay SARZ is released to provide a release circuit for the track relay 4TR2 through back contact and front contact 106. In this way, each track section in turn is released as the train travels in the reverse direction but it is released only after the train has left the next adjoining section.

Special restoration conditions There are certain occasions when the track rails of a section must be repaired or replaced by the track maintenance department. It is readily apparent that the removal of a rail in a section causes the release of the track relay for that section; and the mere replacement of the rail and reestablishment of the track circuit by bonding the rails and the like does not cause the restoration of the track relay to its normal condition. It is necessary for some authorized person, such as the signal maintainer, to come to that section and actuate a push button associated with the track relay at the entrance to the section in order to restore the track circuit to its normal condition.

For example, let us assume that areplacement of rail or bonding in the track section 3T has caused the release of the track relay 3TR2, and for this reason front contact 42 is open. The restoration of the track circuit does not cause sufficient current to flow through the two windings of the track relay 3TR2 in series because the resistor 3PR is included in the circuit. However, the maintainer can actuate the push button 3PR2 which shunts this resistor 3PR and allows the existing interrail potential to produce sufiicient current through the track relay 3TR2 to cause it to pick up and close front contact 42.

A similar push button PB2 is associated with each of the track relays in a similar way. This arrangement is believed to be safe without checking the operation of the button, because the track circuit is still subject to its normal conditions and the presence of a train can be detected in the usual way. The only thing that the push button, such as 3PB2 accomplishes, is the temporary elimination of the stick feature of the associated track relay. This means that the protection for losses of trainshunt is removed while the push button is operated; but this push button is assumed to be of the self restoring type and can be operated only by an authorized person. If further protection is desired, to check that the push button is restored, a front contact on such button may be included in the circuit for the associated home-distant relay HD in a manner similar to that shown in Figs. 1A, 1B and 1C. More specifically, a front contact on the push button 3PB could be included in the wire 34 leading to the relay 3HD. This has not been shown in the drawings for the sake of simplicity.

Summary Two forms or embodiments of the present invention have been shown each of which accomplishes the basic principles of the present invention wherein a train must be checked into one section before it is checked out of the preceding section. These forms also register a section as being occupied regardless of temporary losses of shunt while a train is travelling through such section. In this way, the present invention protects against the characteristics of light weight equipment wherein the shunting effects are not wholly predictable, but will be present with a good shunt and then perhaps temporarily lose the trainshunt effect.

Both forms of the invention provide for manually operable means to initially set the track relays and to provide for their restoration under special conditions such as rail replacement and various abnormal train movements.

The present invention also provides track circuits which are particularly sensitive to train-shunts and which are particularly adapted to provide the check in and check out feature over the track rails without additional line wire.

The provision of approach lighting by suitable approach relays together with the releasing of a track section being dependent upon the control of such approach relays provides an indication to the engineer of a train passing through a section as to whether or not his train is providing an adequate train-shunt insofar as the approach relay is concerned.

Having described two forms of a block signaling system as specific embodiments of the present invention, it is desired to be understood that these forms are selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modifications, adaptations, and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention.

What I claim is:

1. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a source of energy, a limiting resistor, circuit means connecting said source and said limiting resistor in series across the rails at one end of said section, a track relay connected across the rails at the other end of said section through its own front contact to provide a stick circuit .normally energizing said track relay from said source over F 20 said track rails, a resistor of relatively high value compared to the resistance of said track relay for shunting said front contact of said track relay, whereby said track relay is released in response to a train-shunt and cannot be reenergized by the interrail potential supplied by said source even though no train-shunt is present, circuit means associated with said source at said one end of said section and including a control relay actuated in response to the presence and absence of a train-shunt in said section, and restoring circuit means governed by said control relay for causing an increased interrail potential across the rails for a limited time, whereby the interrail potential is sufficient to cause a pick up current value to flow through said track relay and its associated resistor to cause such relay to be picked up.

2. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a source of energy, a limiting resistor, circuit means connecting said source and said limiting resistor in series across the rails at one end of said section, a track relay having front contacts, circuit means connecting said track relay in series with one of its front contacts across the rails at the other end of said section, whereby said track relay is normally held in a picked up condition by energy from said source but is released when the rails of said section are shunted, train presence detecting means at said one end of said section acted upon in response to a train leaving said section, circuit means controlled by said train detecting means for applying distinctive energy to said rails when a train leaves said section, and circuit means at the other end of said section effective to cause said track relay to be actuated in response to said distinctive energy to close its front contacts.

3. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a first source of energy, a limiting resistor, circuit means connecting said first source of energy and said limiting resistor in series across the rails at one end of said section, a track relay having front contacts, circuit means connecting said track relay in series with one of its front contacts across the rails at the other end of said section, whereby said track relay is normally held in a picked up condition by energy from said source but is dropped away when the rails of said section are shunted by a train, train presence detecting means at said one end of said section acted upon in response to a train leaving said section, a second source of energy, circuit means controlled by said train detecting means for connecting said second source of energy in series with said first source for applying an increased potential to said track rails when a train leaves said section, and circuit means at the other end of said section effective to cause said track relay to be actuated to a picked up condition in response to said increased potential across said track rails.

4. In a track circuit organization for railroads, a plurality of sections of track each having its rails insulated from the adjoining sections, a source of energy and a limiting resistor for the exit end of each section, circuit means for the exit end of each section for connecting the source of energy and limiting resistor for that end in series across the track rails, a track relay for the entrance end of each section having front contacts, circuit means connecting said track relay in series with one of its front contact across the rails at the entrance end to its section, whereby each of said track relays is normally held in a picked up condition by energy from its source but is released when the rails of that section are shunted by a train, a train presence detecting means at the exit end of each section rendered active in response to a train leaving said section, a second source of energy for the exit end of each section, and circuit means for the exit end of each section controlled by said train detecting means for that section for connecting said second source for that section in series with its associated first source to increase the potentials over the track rails of that section for a limited time when a train: leaves said section; providing the track relay for the next adjoining section isreleased, and circuitmeansassociated with each track relay effective to cause that track relay to be restored to a picked up condition in response to the increased potentialacross the track railsot its section.

5. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, afirstsource of energy, a limiting resistor, circuit means connecting said firstv source of energy and said limiting resistor in series across the rails at one end of said section, atrack relay having front contacts, circuit meansconnecting said track relay in series with one of its own frontcontacts across the rails at the other end of said section,a pick up resistor connected across said front contact of said track relay included in its stick circuit, whereby said; track relay is normally held in a picked upcondition by energy from said first source but is releasedwhen the trackarails of said section are shunted by a train and remain released until: an increased potential is applied to therails of said section, a second source of. energy, train presence detecting means at said one end of said section rendered active in response to a train leaving said section, circuit means controlled by said train detecting means for connecting, said second source in series with said first source across the rails of said section for a limited time after said train presence detecting means has been actuated by a train leaving said section, whereby increased potential is applied to the rails of said section to efiect the picking up of said section at the other end of said section and manually operable means for at times shuntingsaid pickup resistor.

6. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a first source of energy, a limiting resistor, circuit means connecting said first source and said limiting resistor in series across the rails at one end of said section, a track relay having front contacts, circuit means connecting said track relay in series with one of its own front contacts across the rails of the other end of said section, a pick up resistor connected in multiple with said front contacts said front contact of said relay included in said stick circuit, an approach relay connected in multiple across said limiting resistor at saidone end of said section, a second source of energy, and circuit means controlled by said approach relay for connecting said second source of energy in series with said first source across the rails of said section for a limited time following the release of said approach relay when a train leaves said section, whereby said track relay is normally held in a picked up condition by energy from said first source but is released when the rails of said section become shunted and remains released until an increased potential is applied across said rails sufiicient to provide pick up energy for said relay through said pick up resistor.

7. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining section, a first source of energy, a limiting resistor, circuit means connecting said first source and said limiting resistor in series across the rails at one end of said section, a track relay at the other end of said section connected through a stick circuit across the track rails, an approach relay connected in multiple across said limiting resistor, a second source of energy, circuit means controlled by said approach relay for connecting said second source in series with said first source across the track rails for a limited time upon the release of said approach relay when a train leaves said section, and circuit means preventing said approach relay from responding to said increased potential across the track rails, and circuit means associated with said track relay for rendering it responsive to said increased potential across said track rails.

8. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a first source of energy and a limiting resistor connected in series across the rails at one end oi said section a track relay having front. contacts, an adjustable. resistor, circuit. means connecting said track relay inseries with: said adjustableresistor and one of its own front contacts across thev track rails at the other end of said section; saidladjustab le resistor being, of. a value several times the resistance of. said limiting resistor and being adjusted to provide: normalenergy through said relay slightly above its drop away value, a pick. up resistor connected. across. front. contacts included in said relay circuit,- train presence detecting means at said one end of. said section acted upon in response to a train leaving said section, a second source of energy, circuit means. controlled" by said train detecting means for connecting said secondsource of energy in series with said first source across the rails of. said section for a limited time when a train leaves said section, whereby said track relay while normally picked up is maintained in such condition by energy near itsrel'ease value to render the relay sensitive to a train-shunt, but whereby said track relay when released requires a substantial increase in potential across said track rails which is supplied for a limited time upon the leavingof a train fromsaid section to establish normal pickedup conditions for said track relay.

' 9. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a first source of energy and a limiting resistor connected in series across the rails of said section at one end, a track relay connected across the track rails of said section at its other end through a stick circuit including one of its own front contacts, a pick up resistor connected to shunt the stick contact of said track relay, an approach relay, aslow acting repeater relay controlled by said approach relay, circuit means connecting said approach relay in series with a back contact of said repeater relay across said limiting resistor, said circuit means including a front contact on said approach relay for shunting said back contact of said repeater relay, a second source of energy, and: circuit means connecting said second source of energy in series with said first source of energy and a back contact of said approach relay and a front contact of said repeater relay across the track rails to provide an increased potential across the track rails for a limited time.

10. In a track circuit organization for railroads, a stretch of track divided into a plurality of track sections each having its rails insulated from the adjoining sections, a source of energy and a limiting resistor connected in series across the rails at the exit end of each of said sections, a track relay connected across the track rails at the entrance end of each of said sections and normally energized to a picked up position from the source of energy at the exit end of its section but released from its normally picked up position by a train shunt manitesting occupancy of its section and remaining in its released condition until restored to a picked up position by an energization increased above that which is normally provided by said source at the exit end of its section, and means at the exit end of each section actuated in response to the leaving of a train from that section and requiring said track relay for the next adjoining track section in advance to be released for increasing the interrail potential of its section for a limited time only above that potential that is normally provided by said source of energy for its section, whereby the track relay for its section is caused to be restored to its normally picked up position.

11. In a track circuit organization for railroads, a stretch of track divided into a plurality of track sections each having its rails insulated from the adjoining sections, a source of energy and a limiting resistor connected in series across the rails at the exit end of each of said sections, a track relay having front contacts provided for each of said sections, circuit means connecting each track relay across the rails at theentrance end of its section 1 and including its own front contact in such circuit means,

a resistor connected across the front contact of each of said track relays to provide a circuit for that track relay when it is released which circuit is of such high resistance as to prevent the associated track relay from picking up in response to potential provided by said source of energy connected across the track rails at the exit end of that section but permitting an additional potential across the track rails to provide adequate current through the track relay to cause it to pick up, and means at the exit end of each section actuated in response to the leaving of a train from that section and requiring. said track relay for the next adjoining track section in advance to'be released for increasing the interrail potential of that section for a limited time above the potential normally provided by said source of energy for that section, whereby the track relay for each section is caused to be restored to its normal picked up position only after a train has left that section and caused the release of the'track relay next in advance. p

12. In a track. circuit organization for railroads, a stretch of track divided into a plurality of track sections each having its rails insulated from the adjoining sections, a source of energy and a limiting resistor connected in series across the rails at the exit end of each of said sections, a track relay for each of said sections and each such track relay having front contacts, circuit means con- .necting each track relay across the track rails at the entrance end of its section through a circuit including at least one of its own front contacts, a pick-up resistor connected across the front contact of each of said track relays to provide a pick-up circuit for that track relay when it is released which pick-up circuit is of sufiiciently high resistance to prevent the associated track relay from picking up in response to energy from said source at the exit end of that section but permitting an additional potential across the track rails to provide adequate pick up energy through the track relay, and means at the exit end of each section rendered momentarily active in response to a train leaving that section for increasing the interrail potential of such section only if the track relay for the next adjoining section in advance is released, and circuit means associated with each track section responsive to the leaving of a train from that section for momentarily shunting said pick-up resistor for the track relay of the next adjoining section in advance.

13. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a source of energy and a limiting resistor connectedin series across the rails at one end of said section, a track relay connected across the track rails of said section at its other end and characterized by having characteristics that if once released will remain released until otherwise acted upon whereby the shunting of the track rails by a train releases said track relay which remains released regardless of the presence of such train shunt, means at said one end of said track section for applying energy to the track rails to act upon said track relay a 24 for causing it to be restored to a picked up condition, said means being effective only for a limited time as a train leaves that end of said section, and other means at 'the other end of said section adjacent said track relay fo'r'acting upon said track "relay to restore it to a picked up condition dependent upon conditions in the adjoining track section.

14. In a track circuit organization for railroads, a stretch of track divided into a plurality of track sections each having its rails insulated from the adjoining sections, a source of energy and a limiting resistor connected in series across the rails at the exit end of each of said sections, a track relay connected across the track rails at the entrance end of each of said sections and normally energized to a picked up position from said source of energy at the exit end of that section but released from its normally picked up position by a train shunt manifesting occupancy of that sectionand remaining in its released position until restored to a picked up position by an increased energiz ation above that which is normally provided by said source at the exit end of that section, an approach control relay associated with the exit end of each section and actuated by the presence of a train shunt approaching the exit end of its section, a slow-acting repeater relay associated with each approach control relay, circuit means for each section governed by the approach control relay and repeater relay for that section for increasing the interrail potential of its section only for a limited time and only if the track relay for the section in advance is released, a signal at the entrance to each section for governing the entrance of trafiic into that section, and circuit means for causing each signal to display the proper aspect only if the approach control and repeater relays for the exit end of the adjoining section are actuated.v p

15. Ina track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a source of energy and a limiting resistor connected in series across the rails at one end of said section, an electroresponsive means connected'across the track rails of said section at its other end and including a stick relay with characteristics that if once released will remain released until otherwise acted upon whereby the shunting of the track rails by a train releases said stick relay which remains released regardless of the presence of such train shunt, means at said one end of said track section for applying distinctive energy to the track rails to act upon said stick relay for causing it to be restored to a picked up condition, said means being effective only for a limited time as a train leaves that end of 'said section, and dependent upon the occupied condition of the next adjoining track section.

References Cited in the file of this patent UNITED STATES PATENTS 2,176,612 Pflasterer- Oct. 17, 1939 2,187,225 Dower et al Jan. 16, 1940 2,311,034 'Dodd Feb. 16, 1943

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