US2354052A - Railway traffic controlling apparatus - Google Patents

Description

July 18, 1944. J. .M. PELlKAN RAILWAY TRAFFIC CONTROLLING APPARATUS 2 Sheets-Shet 2 Filed Aug. 26, 1942 Q HISATTUH/VJT:

RH U Lu SQNN .L mw NNMN kWN MWEE Patented July 18, 1944 RAILWAY TRAFFIC CONTROLLING APPARATUS John M. Pclikan, Chicago, 111., assignor to The Union Switch and Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application August 26, 1942, Serial No. 456,174

6 Claims.

My invention relates to railway traffic controlling apparatus for governing the movement of traflic over stretches of single track through which tralfic moves in both directions, and in its specific embodiment, to the provision of an improved absolute permissive block signaling system in which the signals for both directions are controlled by circuits employing but two line wires which may be energized at one end or the other by current of normal or reverse polarity to provide three position control of the signals, and in which the direction of traflic is manually governed from a central point by means of a centralized traflic control system.

My invention is an improvement upon that disclosed in an application for Letters Patent of the United States, Serial No. 412,627, filed September 27, 1941, by Henry S. Young, for Railway trafiic controlling apparatus.

The object of my invention is the provision of a single track signalin system of relatively low cost employing two-wire reversible line circuits in which hand throw'switches may be used in lieu of the usual power operated track switches, and in which the necessary number of track sections is reduced by the use of track circuits of the continuous code type for controlling the line circuits, the inherent efficiency and freedom from interference of track circuits of this type making it possible to use track circuits which are much longer than can be reliably operated when steady energy track circuits are used.

My invention includes the provision of novel means for the control of a block indicator for visually indicating at the control ofiice when a train moving in either direction occupies any portion of the single track stretch, and for the control of a direction locking relay associated with the block indicator for interlocking the signal control circuits associated with the levers for the opposing head block signals governing traflic movements into the single track stretch, so as to prevent interference with train movements in the event of improper manipulation of the levers.

In accordance with this feature of my invention, the track circuits for the single track stretch, exclusive of the switch. sections at the ends of the stretch, are arranged so that they all extend in the same direction, and they are normally controlled in cascade by coded current of the same frequency, such as 180 cycles per minute, to which frequency a block relay at one end of the stretch is selectively responsive. When any such track section is occupied, however. a different frequency, such as 120 cycles per minute, is supplied to the sections following the occupied section, to which frequency the block relay i non-responsive. Each such track section is provided with a code detecting relay responsive to either code frequency, which serves as a track repeating relay in place of the usual track relay for controlling the signal circuits.

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

Referring to the accompanying drawings, Figs. 1A and 13, arranged with Fig. 1A to the left and Fig. 1B, constitute a diagrammatic view showing trackway apparatus embodying one form of my invention applied to the portion of a single track railroad located between and including the ends of two adjacent passing sidings, to which sidings access may be had by reversing the hand throw switches ISW and SSW, respectively. Fig, 1A also shows the control ofiice apparatus including the signal control levers together with an illuminated track diagram of the stretch of track and associated apparatus for effecting the control and supervision of train movements over the single track block. 7

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

In order to simplify the drawings and to enable the circuits to be more readily traced, I have herein identified each switch and signal by a number and each relay by a letter or combination of letters with a numerical prefix identifying the switch or signal with which the relay is associated. Instead of showing the sources of cur rent'for energizing all of the various circuits, I have in most instances shown only the terminals of the sources, these being identified by the reference characters B and C, referring to the power supply or positive and the common return or negative terminals, respectively.

The track plan extending across the top of the drawings represents a stretch of railway track constituting a typical single track block to which my invention is applied in the manner illustrated by the circuits below the diagram. The block extends from the head block signal ZRA or ZRB, depending upon the position of switch ISW, to the opposing head block signal 4LA or 4LB, depending upon the position of switch 3SW, and is divided into track sections T by the usual insulated joints. Each track section T is provided with a track circuit having a current source 5 connected across the track rails at one end and a track relay TR connected across the track rails at its opposite end.

The track relays I'I'R. and 3TB for the relatively short detector or switch sections at the opposite ends of the block are continuously energized, while the track relays HTR, iZTR, I3TP. and MTR for the intervening single track sections are of the code following type and the current supplied by the sources 5 for each of these sections except section lilT is periodically interrupted by the contacts of a continuously operat ing code transmitter IZBCT or IS JCT. These code transmitters may be, for example, of the 7 type shown in Letters Patent of the United States No. 1,858,876, granted May 17, 1932, to P. N. Bossart, for Coding apparatus, and it is to be understood that each device CT when connected to the terminals 13 and C of a local source of current, as shown, operates its contacts repeat edly at the rate of 120 or 180 times per minute, respectively. Sections HT and NET taken together constitute a cut section, the code following relay IZTR of section liZT serving as the code transmitter for section I3T. Each of the code following relays HTR, lSTR and l-ATR have two contacts, the upper one supplying impulses of alternately opposite polarity to the primary of a decoding transformer 6, and the lower contact rectifying the code frequency impulses delivered by the secondary of the transformer 8 to operate a code detecting relay TP.

The circuits for the relays TP correspond tothose for the code detecting relay H in Letters Patent of the United States No. 2,237,788, granted April 8, 1941, to F. H. Nicholson et al., for Railway trafiic controlling apparatus, and arranged so that the relays TP are steadily energized in response to either 120 or 180 code operation of the associated relays TR but are nonresponsive to foreign alternating current, for reasons explained in that patent.

The track relays |3TR and MTR also control block relays BR through the medium of decoding units IBGDU connected to the corresponding decoding transformers 6. The decoding circuits are substantially similar to those shown'for relay K3 in Letters Patent of the United States No. 1,773,472, granted August 19, 1930, to P. N. Bossart, for Railway traflic controlling apparatus, and include tuned circuits and rectifiers which provide a high degree of selectivity for reasons explained in the patent, so that the relays BR are steadily energized in response to 180 code operation only of the associated relays TR.

By reference to the track plan it will be seen that each of the code detecting relays TP functions like an ordinary track reiay such as ETR to indicate the condition of occupancy of the corresponding section, relay ISTP indicating the condition of the two sections i2? and 63T. Terminal B of the local source of current is connected to the transformer 6 associated with relay MTR over a front contact of relay 3TH; consequently relay MTP responds to the code operation of relay l lTR only when relay 3T1 is picked up, and therefore indicates the condition of the tWo sections MT and ST. When relay il'IP is picked up, indicating that section HT is unoccupied, the code frequency supplied to section lZT and consequently to section 531, is changed from 120 to 180 cycles per minute, thereby energizing relay I3BR if these sections are unoccupied. This eflects a corresponding change in the code frequency supplied to section WI to thereby energize relay MBR provided sections MT and 3T are both unoccupied. The energization of relay MBR therefore indicates that the entire block, with the exception of section ii. is unoccupied.

The coded track circuit system thus not only serves the purpose of the usual track circuits in the control of the signals in accordance with traific conditions, but provides in addition the equivalent of a tramc locking circuit extending substantially the full length of the block, inasmuch as it serves to indicate the presence of a train in any of the intermediate track sections of the single track stretch or in section 3T by the deenergization of the block relay MBR.

Inasmuch as in systems of the type shown herein only one direction of traffic can be set up at a time, intermediate signals are not required for providing head-on protection as in systems in which two head block signals may be passed at clear by opposing trains at the same time, and inthe single track block chosen to illustrate my invention only two intermediate signals are providecl, namely, the signals 5 i and I4, constituting distant signals for the leaving signals 2L and 4R, although additional intermediate signals may readily be provided and the single track block may also include a greater or lesser number of track sections, depending upon traflic requirements and upon the distance between the passing sidings.

The territory illustrated may be extended through either passing siding to the entrance to an adjacent single track block, merely by placing Fig. 1A at the right of Fig. 1B. When so arranged, the track plan illustrates the opposite ends of a block extending from signal 4R to the right through track sections ST and IT to an opposing signal such as signal 2L, but located in the next single track block to the right of that described above, but since the circuits for controlling the opposing signals GR and 2L form no part of the present invention they have not been shown herein, suitable circuits being well known. For example, these signals may be controlled by circuits similar to those for signals R2 and L4 shown in Letters Patent of the United States No. 2,282,841, granted May 12, 1942 to H. S. Young, for Railway traffic controlling apparatus.

It will be understood that each of the head block signals is controlled automatically by the track relays in accordance with traffic conditions in advance, and is also subject to manual control from the central office illustrated in Fig. 1A. through the medium of a centralized traflic control system.

The communication system connecting the oifice with the various field locations may-be of any suitable type, and as shown herein it is to be understood to be of the impulse code type such. as that shown in Letters Patent of the United States No. 2,229,249, granted January 21, 1941, to Lloyd V. Lewis, for Remote control systems. In this system, communication is established intermittently between the control office and various 7 held stations over a single pair of line Wires extending from the office through each station corresponding to the location of a head block signal such as those shown in Figs. 1A and 1B of the present disclosure, in the manner illustrated in Fig. 10 of the Lewis patent. Direct wire control may also be used, and as illustrative of either form, these communication channels of the impulse code system which are directly involved in the operation of the apparatus of my invention are shown herein as direct wire connections extending from the office to the two field stations at the opposite ends of the block. These include the control channels over which signal control relays ERI-IS and LI-IS are energized in response to movement of the signal levers 2SG and 6S8: to the right and left, respectively, to establish the corresponding traific direction and to efiect the clearing of the respective head block signals ZRA and 4LA. They also include two indication channels over which the track indication relays iTK and BTK are energized to indicate the occupancy of the respective switch sections IT and 3T; two channels'over which the signal in response to the release of relays ZRGP and 4LGP, respectively, the latter relay being released when the corresponding signals are cleared, and they also include a channel'over which a block indication relay BK is picked up in response to the release of relay I 4BR, indicating the occupancy of'the main portion of the single track block, exclusive of section IT. The ofiice apparatus also includes a direction locking relay 2-4LP, of the stick polar type, as in the'system of the above-mentioned Young patent, and a normally energized indication storing stick relay j I TKS governed jointly by relays ITK and BK.

The signal circuits are of the two wire reversible line circuit type corresponding generally to those disclosed in Letters Patent of the United States No. 2,112,945, granted April 5,1938, to L. B. Yarbrough, for Railway trafilc controlling apparatus. That is to say, the signals for both directions are controlled over a system of cascadeconnected line circuits energized at one end or the other in accordance with the traffic direction established by the manually governed relays ZRHS and JLHS. Thus signal ZRA is governed by a line relay ZRHR, which is controlled at times by a relay I2HR, at the location of signal ll, over a circuit including the line wires and 26 and front contacts of relays ITR and HTP reflecting the condition of track sections IT and HT. This line circuit serves at other "times for the control of the mechanism HG of signal ll. Relay l2I-IR, in turn, is controlled at times by relay MHP, at the location of signal J4, over a circuit including line wires 3| and 32, and contacts of relay |3TP which reflect the condition of track sections IZT and l3T, the same line Wires providing a circuit at other times over which relay HHP, governed by mechanism HG, controls the line relay I3HR. Relay HP is governed by the mechanism M3 for signal M, which in turn is controlled at times over line wires 2? and 28 and contacts of relay MTP reflecting the condition of track sections MT and 3T, the same line wires providing a circuit at other times over which relay I3HR, at the location of signal I 4, controls the line relay 4LHR which governs signal -LA. The directional control, as shown, is arranged as in the corresponding circuits of the above-mentioned Young application by the provision of the traffic direction relays ZRFR and 4LFR and the directional stick relays 2RFS and lLFS for controlling the direction of energization of the cascade connected line circuits in place of direct control by the code controlled relays LRHS and 4LI-IS, as employed by Yarbrough. The control effected by these directional relays is such that as soon as the establishment of either traffic direction is completed by the energization of the line relay ZRHR at one end or of relay flLHR at the other end, the code con-.

trolled relay ZRHS or lLl-IS at the entrance end is free to be picked up or released as required to control the adjacent signal without interrupting the continuity of the line circuit, and the established trafiic direction is maintained by keeping the code controlled relay dLHS or ZRI-IS at the exit end deenergized. Furthermore, slow acting polarized line relays HR take the place of the signal mechanisms G in the circuits at locations where the intermediate signals are omitted, and

also at the ends of the block where they control the head block signals. Each intermediate signal mechanism is provided with the usual slow acting repeating relay HP and-a directional stick relay S for setting up the circuits for permissive following train movements. Relay I IS is controlled by the adjacent track repeating relay IITP in the usual manner, but no such relay is available at the location of relay MS, and for the control of that relay a floating track relay MATR of the code following type is connected across the track rails at the battery end o'f'section HT. Relay MATR responds periodically to the coded current from theassociated source 5 and holds a slow acting repeating relay I4ATP picked up, relay HATP releasing when a train passes signal l4 toefiect the directional energization' of relay MS in the usual manner.

The line circuits as shown are in the condition in which they are left following a train movement from left to right through the block. The directional relay 4LFR is energized over back contacts I, 8 and 9 of relays 4LHS, 4LFS and 4LHR, and

connects terminals B and C to the adjacent line circuit at the right-hand end, over contacts of a pole changer relay 4R-PC and an approach locking relay ALAS, which function like the corresponding relays shown in Yarbrough, and the circuit is completed over line wires 21 and 28 through mechanism MG over front contacts of relays 4LFR and MTP, and back contacts of relay ISHR. Relay lR-PC is deenergized, signal 4R being at stop, and consequently mechanism MG is energized in the reverse direction to cause signal M to indicate caution, and to energize relay MHP, the latter relay connecting terminals B and C to the right-hand end of the circuit comprising the next section of the line circuit systerm, which circuit is completed through relay I2HR. over front contacts of relay I3TP, line wires 3! and 37. and back contacts of relays III-1P and HS. Relay I2HR is energized in the normal direction and completes a circuit comprising the third section of the line circuit system through relay 2RHR over the normal polar and neutral front contacts of relay I2HR, line wires 25 and 26, front contacts of relays IITP and I'I'R, and

back contacts of relay ZRFR. Relay ZRHR is therefore energized in the normal direction and holds the circuit for relay ZRFR open at contact Ill. The circuits for controlling signal ZRA, shown only in part, include front contacts 4| and ll! of relays ZRI-IS and ZRFR and are now open at contact 4|. The circuits for controlling signal ZRB are also open. it being understood that these include contacts 4| and I2 and also other contacts. not shown, which are closed only when switch lSW has been reversed bythe train crew.

I shall now assume that the apparatus is in the condition shown and that the operator moves levers ZSG and GSG to the right, with the object of clearing signals 2RA, l4 and 4R for a train trolling a suitable indication lamp, not shown.

It will also be understood that signal 4R will be caused to indicate caution or clear in response to the movement of lever 4R to the right,

I so that relay 4R-PC will be picked up and signal I4 will indicate proceed.

The energization of relay ZRHK locks relay 2-4LP normal by opening contact I5 in its reverse energizing circuit which includes left-hand v contact I5 of lever 48G. Signal 2RA now cannot be put to stop by the operation of any lever other than its control lever ZSG, as, for example, by a movement of lever ISG to the left, nor can the intermediate signal I4 now be put to stop by a movement of lever 48G to the left. The line circuit system comprising the circuits for controlling signals ZRA and I4 is completed over front contacts of relay ELFR, which relay is held energised over back contact I of relay lLHS, and relay ILHS is held released because its circuit, which includes wire 33 and left-hand contact ll of lever 48G, is open at contact 44 in its normal position, and relay 24LP is non-responsive to a movement of lever 48G to the left clue to the fact that contact I 5 is open.

When the train governed by signal ERA enters the first track section IT of the block, relay ITR releases, opening the line circuit to release relay ZRHR, thereby putting signal 2RA to stop and consequently reenergizing relay ZRGP.

The dropping of relay ITR before the slow acting relay ZRHR releases completes a pick-up circuit at contact 4? for the directional stick relay 2RFS, which relay picks up and is held energized after relay ZRHR releases. over a stick circuit includingback contact I8 of relay ZRI-IR, opening contact IS in the circuit for relay ZRFR before contact II] of relay RHR closes.

At the office, relay ITK picks up to light the OS lamp IE and the block indication lamp BE in response to the release of relay ITR, and relay 2RHK becomes deenergized in response to the reenergization of relay ZRGP. Relay ZRHK is made slow to release so that when relay I TK picks up, terminal B is disconnected from the stick circuit for relay ITKS for a time sufiicient to effect the release of relay I TKS, and when relay I'IKS releases, a second circuit for the block indication lamp BE, over back contacts of relays 2RHK and ITKS is completed. It will be seen that the circuit for reversing relay 24LP is now open at contacts 29 and 2I of relays ITK and ITKS so that the direction locking is still effective.

When the advancing train enters section IIT the code operation of relay IITR ceases, releasing relay IITP, and the dropping of contact 22 of relay IITP causes 120 code to be supplied to section IZT. This 120 code is repeated by relay IZTR, and supplied from the associated source 5 over wires 34 and 35 to the track rails of section I3T with the result that relay I3TR is operated at the 120 code rate to maintain relay I3TP energized, but relay I3BR releases to cause 120 code to be supplied to section MT. Relay I4BR therefore releases to pick up the office relay BK over wire 36 thereby indicating the presence of the train in that portion of the stretchwhich is at the right of section IT. Relay BK maintains lamp BE lighted, and by opening back contact 23 holds relay 2QLP locked normal until the train vacates the last track section 3T of the block.

The indication codes transmitted by the. communication system for controlling relays I'I'K and BK are transmitted from different stations, and if this system is of the impulse code type, they are not only transmitted at different times but the delivery of one or the other may be delayed clue to the use of the communication line ill circuit by other stations, and it may happen that if a train governed by signal'ZRA passes the corresponding station and occupies section IT for a relatively short'time, a second code will be received at the office from that station to announce the departure of the train from section IT, therebyreleasing relay ITK, before the indication is received from the station at the exit end of the block announcing the movement of the train into section IIT. Relay ITKS serves as an indication storing relay to maintain the block indication and direction locking during this interval, that is, if it should happen that relays ITK and BK are both released While there is a train in the block. Relay ITKS releases when the train first enters section IT, as already explained, and is picked up by relay BK in response to the receipt of the indication from the second station that the train has entered another portion of the stretch, upon the closing of front contact 23.

As the train passes signal I4, the track relays I IATR and I4TR will be shunted, stopping their code operation so that relay MATP will release to pick up the directional stick relay MS, and then mechanism MG and relay MI-IP will release in response to the release of relay I4TP by relay I ITR, relay I4HP completing the usual stick circuit to hold relay HIS energized. When the train vacates section I3T, relay IZI-IR will become energized in the reverse direction over the front contacts of relay MS, and in turn will cause relay ZRHR to become energized in the reverse direction, causing signal 2RA to indicate caution, provided relay ZRHS is still energized. Relay ERHR releases relay ZRF'S, closing back contact I9 after contact I0 opens, so that relay ZRFR is held released and cannot be picked up by releasing relay ZRHS.

When the train enters section 3T, relay STR releases, energizing the ofiice indication relay 3IK over wire 31, and consequently the OS lamp 3TE becomes lighted. When the train vacates section MT, the code operation of relay I ITR will be resumed, and When it vacates section 3T, relay 3TB. picks up to release relay 3'IK and thereby extinguish lamp STE, and to supply current to the decoding transformer 6 associated with re- 1ay MTR, whereupon relays I IBR and MTP pick up. Relay MTP restores the line circuits to the condition shown in the drawings, and relay MBR releases relay BK, extinguishing lamp BE and rendering relay 24LP again responsive to signal lever operation.

I shall next assume that the apparatus is in the condition shown and that the operator moves levers ZSG and 48G to the left, with the object of clearing signals 4LA, II and 2L for a train movement through the block from right to left.

The movement of lever lSG to the left completes the reverse energizing circuit for relay 2-4LP at contact I6, whereupon relay 24LP operates its contact 44 to the right, completing a circuit at contacts 44 and I! over wire 33 to pick up relay lLI-IS. Relay ILHS, by opening contact I releases relay ILFS, deenergizing the line circuit system and-connecting relay ILHR thereto at its right-hand end. Mechanism. I IG, and relays ItI-IP, IZHR and ZRHR release, and relay 2RFR picks up over back contacts I0, 4| and I9 of relay ZRHR, ZRHS and ZRFS and connects sively, relay 4LHR opening contact 9 in the circuit for relay ALFR and completing the circuit for clearing signal 4LA. It will be understood that signal 2L will be caused to indicate caution or clear in response to the movement of lever 2SG to the left, and that consequently signal II will indicate proceed. The clearing of signal 4LA releases relay 4LGP, initiating an indication code to pick up the office indication relay 4LHK over wire 38, thereby opening back contact 24 to lock relay 2--4LP reversed. Signals lLA and H now cannot be put to stop by a movement of lever ZSG to the right, relay ZRFR being held energized over back contact 4! of relay 2RHS, the circuit for which is open at contact 44 in its reverse position. Relay 2--4LP now does not respond to a movement of lever ZSG to the right because its normal energizing circuit is open at contact 24.

When the train governed by signal 4LA enters the first track section of the block, in this case section 3T, relay 3TR releases, deenergizing transformer 6 associated with relay M'IR to cause the release of relays MBK and MTP. Relay l 4TP opens the line circuit to release relay 4LHR, thereby putting signal ALA to stop and consequently reenergizing relay 2RGP.

The dropping of relay 3TB. before relay 4LHR releases completes a pick-up circuit for relay fiLFS, which relay picks up and is held energized over its stick circuit to maintain relay 4LFR released by opening contact 8 before contact 9 closes.

The release of relay 3TB. also initiate an indicaticn code, energizing relay 3TK over wire 31 to light the OS lamp 3E, also releasing relay iLi-IK and energizing relay BK, thereby lighting lamp BE and opening contact 23 in the circuit for relay 24LP before contact 24 closes. In this instance it is obvious that since the block indication is transmitted in the first code along with the OS indication the operation of a storing relay. such a the relay ITKS above described is not required, that relay being held energized over a back contact of relay ZRHK. l

As the advancing train passes through th block, the successive release of the track repeating relays TP and of relay lTR controls the signal circuits in a manner similar to that already described. Lamp IE will become lighted by the energization of relay ITK in response to the *OS indication code announcing the movement of the train into section IT, lamp BE remaining lighted and the direction locking remaining effective until codes are received from both stations, to release relays ITK and BK, respectively.

It will be clear from the foregoing that the operator is able to send codes at will for energizing relay 2RHS or 4LHS to effect the clearing of the associated head block signal ZRA or 4LA for a train movement in the direction of traffic already set up, but that to reverse the direction of traflic, the block indicator must indicate that the block is unoccupied in response to indications received from the two stations at opposite ends of the block, and the lever locking relay 2-4LP must be operated in the required directionprior to the transmission of the code for clearing the signals. It follows that the signals which have been cleared cannot be interfered with by an inadvertent attempt to clear an opposing signal.

Although I have herein shown and described only one formof railway traific controlling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended 1 claim is:

1. In a block signaling system for railways, a stretch of track divided into track sections, a track circuit for each track section having a track relay, head block signals for governing traffic movements into the stretch in opposite directions, a manually controlled relay for each signal, a system of cascade connected line circuits for controlling the signals, each line circuit extending the length of one or more track sections and including contacts controlled by the track relays which are closed only when the corresponding track sections are unoccupied, means controlled by back contacts of each manually controlled relay for supplying current to the adjacent end of the line circuit system to effect the energization of said line circuits in cascade to thereby prepare a circuit for the opposing signal at the other end of the stretch, means comprising front contacts of each manually controlled relay for controlling the associated signal in aecordance with the condition of energization of said line circuit system when supplied with current at its opposite end, a block relay near one end of the stretch, means including the track relays for connecting said track circuits in cascade and for transmitting distinctive currents over the track rails section by section to the location of said block relay only when all the block sections are unoccupied, means controlled by the track relays and selectively responsive to said distinctive currents for energizing said block relay, direction locking means effective when in one condition to prevent the energization of one manually controlled relay and when in another condition to prevent the energization of the other manually controlled relay, and means preventing a change in the condition of said direction locking means except when said block relay is energized.

2. In a block signaling system for railways, a stretch of track divided into track sections, a track circuit for each track section having a track relay and a source of current, a code transmitter for each track circuit for periodically interrupting the current supplied thereto at a predetermined rate, a code detecting relay for each section which assumes its energized position in response to the periodic operation of the associated track relay, head block signals for governing traffic movements into the stretch in opposite directions, a manually controlled relay for each signal, a system of cascade connected line circuits extending the length of the stretch for controlling the signals said line circuits including front contacts of the code detecting relays for the adjacent track sections, means controlled by back contacts of each manually controlled relay for supplying current to the adjacent end of the line circuit system to effect the cascade energization of a plurality of said line circuits to thereby prepare a circuit for the opposing signal at the other end of the stretch, means comprising front contacts of each manually controlled relay for controlling the associated signal in accordance with the condition of energization of said line circuit system when supplied with current 'at its opposite end, a block relay near one end of the stretch responsive to the periodic operation of the adjacent track relay at a rate different from said predetermined rate, mean eifective when the code detecting relay for a track section near the other end of the stretch is energized for periodically interrupting the current supplied to the remaining track circuits section by section in cascade at a rate to which said block relay is responsive to effect the energization thereof only in the event all of said track sections are unoccupied, direction locking means effective when in one condition to prevent the energization of one manually controlled relay and when in another condition to prevent the energization of the other manually controlled relay, and means preventing a change in the condition of said direction locking means except when said block relay is energized.

3. In a block signaling system for railways, a stretch of track divided into track sections, a track circuit for each track section having a track relay, head block signals for governing traffic movements into the stretch in opposite directions, a system of cascade connected line circuits for controlling said signals, said line circuits including contacts controlled by the adjacent track relays which are closed when the corresponding track sections are unoccupied, means at each end of the block for supplying current to the line circuit system at that end to effect the energization of said line circuits in cascade to thereby prepare a circuit for the head block signal at the other end of the stretch, means for completing said prepared circuit to effect the clearing of such head block signal when all the track sections are unoccupied, and also when one or more of the track sections are occupied by a train moving in the direction governed by such signal to permit a following train to enter the stretch, a block relay near one end of the stretch, means controlled by the track relays for energizing said track circuits in cascade and for transmitting distinctive currents over the track rails section by section to the location of said block relay only when all the track sections are occupied, means selectively responsive to said distinctive currents for energizing said block relay, and

,a visual indicator for indicating the presence of a train in the stretch located at a central oflice and controlled by said block relay.

4. In an absolute permissive block signal system, a stretch of railway track divided into block sections and provided with coded track circuits a plurality of which are arranged to be controlled in cascade, a code detecting relay at one end of each such track circuit responsive to coded current supplied to the other end thereof, alinecircuit system extending from the entrance to the exit end of said stretch including a line circuit corresponding to each block section each said line circuit including front contacts of the code detecting relay or relays responsive to the condition of the corresponding portion of track, a three position signal for governing the movement of traiiic into each block section in a given direction, an electroresponsive device for controlling each signal adapted to be energized over the line circuit for the block section in advance thereof, means at the exit end, of the stretch for supplying current of normal or reverse polarity to the line circuit which extends to that end of the stretch, means at each intermediate signal location for supplying current of normal relative polarity to the line circuit extending to the rear thereof only when the electroresponsive device at that location is energized, and for supplying curiii rent of reverse relative polarity to that line circuit only when such electroresponsive device is deenergized by a train in the corresponding block section moving in said given direction, manually operable means at a control office for at times disconnecting the supply of current of normal or reverse relative polarity from the line circuit near the exit end of the stretch, a block relay at one end of the stretch, means for constantly supplying coded current to that one of said track circuits which is nearest the other end of the stretch, means dependent upon the energizedor deenergized condition of the code detecting relay for said one track circuit for supplying coded current of one frequency or another, to which the code detecting relays are responsive, to each remaining track circuit in said stretch, cascade means effective only when coded current of said one frequency is received over the track circuit nearest said one end of the stretch for energizing said block relay, and means at said office remotely controlled by said block relay for preventing the disconnection of said source of current from the line circuit at the exit end of the stretch unless the block relay is energized.

5. Trafiic locking means for a stretch of single track over which traffic may move in either direction comprising, in combination, a detector track circuit at each end of the stretch having a track relay, a block relay at one end of the stretch, means for transmitting current over the track rails of the intervening portion of said stretch to energize said block relay, said means being effective only when the track relay adjacent said block relay is picked up, two indication relays located at a central ofilce, means for controlling one indication relay to indicate the condition of said block relay, means for controlling the other indication relay to indicate the condition of the track relay at the other end of the stretch, direction locking means at said office for governing the direction of traffic movements into said stretch, and circuits controlled jointly by the two indication relays for controlling said direction locking means to prevent the reversal of trafiic direction except when the entire stretch is unoccupied.

6. In a centralized traific control system, an office and two stations, a stretch of single track extending between said stations, a detector track circuit at each end of the stretch having a track relay at the adjacent station, a block relay at one station, means for transmitting rail currents over the portion of track included between said detector sections to energize said block relay but only if the track relay at said one station is energized, a block indication relay at said ofiice controlled by the block relay, two track indication relays at the office one controlled by each track relay, a track diagram representing said stretch of track having track indication lamps for illuminating the detector track portions at the ends of the stretch and a block indication lamp for illuminating the intervening track, a circuit controlled by each track indication relay for energizing the associated track indication lamp when the corresponding detector section is occupied, and circuits controlled by the block indication relay and one track indication relay for energizing the block indication lamp when any portion of the stretch is occupied.

JOHN M. PELIKAN.

CERTIFICATE OF CORRECTION.

Patent No. 2,55L;.,O52. July 18, 19M.

JOHN M. PELIKAN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 6, sec- 0nd column, lines 1'? and 18, claim it, for "stretch, cascade means" read stretch, in cascade, means-;. and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of September, A. D. 19%.

Leslie Frazer (Seal) Acting Commissioner of Patents.

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