US2914663A - Highway crossing signaling system having high sensitivity to train shunts - Google Patents

Description

Nov. 24, 1959 G. o. FERM ETAL 2,914,663

HIGHWAY CROSSING SIGNALING SYSTEM HAVING HIGH SENSITIVITY T0 TRAIN SHUNTS Filed Feb. 24. 1956 EDT IMPULSE-4 TRANSFORMER TO XG OPERATING APPARATUS INVENTORS G.O.FERM AND BY M.A. SCHEG THEIR ATTORNEY HIGHWAY CROSSING SIGNALING SYSTEM HAV- ING HIGH SENSITIVITY T TRAIN .SHUNTS Glenn 0. Ferm, Gates, and Marcian A. Scheg, Rochester, N.Y., assignors to General Railway Signal Company, Rochester, N.Y.

Application February 24, 1956, Serial No. 567,597

5 Claims. (Cl. 246-130) This invention relates to railway signaling systems for the protection of highway crossings, and relates more particularly to crossing warning systems which are actuated in response to the shunting of detector track circuits by trains.

In crossing warning systems which are operated by the shunting of detector track circuits, the reliability of the system is dependent upon the sensitivity of such detector track circuits to train shunts of all types. The inability of track circuits to detect the presence of a train either initially or continuously can'result in the failure of signaling operations while trains are approaching and/or occupying the highway crossing. The modern use of high-speed lightweight trains raises a problem is that the sensitivity of detector track circuits of the type usually used in general practice is not great enough to provide continous positive detection of such trains, since these trains provide higher wheel-to-rail contact resistance than that provided by the heavier standard trains.

A further consideration common to all crossing warning systems is the condition of the rails of the track section which includes the highway crossing. Poor shunting sensitivity is common to such sections because of dirt, sand or other susbtances which are depositedby highway traflic and which accumulate on the rail surfaces.

In view of the preceding considerations, the present invention provides means for improving the operating sensitivities of detector track circuits, such means being applicable both to new. and to existing installations. More specifically, the present invention proposesithe [ICC and because of the relatively short length of standard crossing track sections, the installation of high voltage use of auxiliary detector track circuits having high shunting sensitivity to cooperate with standard approach track circuits in a manner such .that the auxiliary circuits are capable of detecting trains which might not benormally detected by the standard approach circuits. The detector track circuits may be of a high voltage type or of the impulse track circuit type which are sensitive to highresistance train shunts. The detector track circuitsare used to insure the response of theassociatedstandard approach track circuits to approaching trains regardless.

tions.

of the ability of such trains to provide positive shunts in 1- the standard approach track circuits. Since the track sections included in such-detector track circuits can be relatively short in length, the addition of detector track circuits to existing installationsis structurally and economically feasible. f

In order to insure continuous detection of trains appreaching a highway crossing, the present invention further proposes the use of lock-out circuit means to prevent the picking up of shunted or deenergized approach track relays until an approaching train has vacated the associated approach track sections and has passed the highway crossing. The present invention furtherproposes the use of a high-sensitivity detector track circuit at the highway crossing. This track circuit can-be of the high voltage type;

ing up of the crossing track relay during intervals ofpoor shunting, or loss of shunt, until a passing train is detected as having reachedv the exit side of the crossing section.

In using detector track sections in advance of approach track sections, conditions can arise in which a train may completely pass the crossing, but fail toshunt theapproach track circuit at the leaving end. During time 'intervals when the approachtrack section alone is occupied,

a momentary loss of shunt could result in the clearing out of the warning circuits, followed by the reactivation of the circuits when a shunt is reestablished. Under such. conditions, warning signals could be left in operation after the departure of the train. To preclude the response of approach track relays to momentary los'ses'of shunt, the pldsfillt invention includes circuit means for rendering the approach track relays non-responsive to energies which would normally energize such track relays whenever the detected train is receding fromthe highway crossing. The pick-up characteristics of the approach track relays are, in other words, rendered selective-' ly sensitive to the magnitude of operating voltages, and such selections are made through the use of directional stick relays. More specifically, it is proposed that directional stick relays which are selectively energized to-indicate directionsof train movement be used to qualify the pick-up circuits for the approach track relays" ina manner such that an approach track relay is rendered responsive to normal energization when a train is approaching the crossing through the approach track section and is rendered responsiveonly to a higher level of energization when an occupying train is receding from the crossmg. I I v Since interdependent lock-out circuits are proposed for both the crossing and approach track relays, means must be provided .to prevent the mutual locking out of such track relays under abnormal 'op'erating conditions.- The present invention includes timing relay means which is actuated in response to thedetection 10f an approach' ing train. The timing means is capable of measuring a time interval which is normally suflicient for a train to completely pass through the various detector track sec Upon the completion of a timing operation; circuit means are established-to permit the restoration of the crossing and approach track relays to their normal energized states, provided that such relays are not shunted in any manner. I f

In view of the preceding considerations, an object of this invention is to provide auxiliary detector track cir cuit means having high shunting sensitivity for insuring the detection of trains approaching a highway crossing. Another object of this invention is to provide lock-out circuit means for preventing the picking up of shunted approach wtrack relays whenever the associated approach track circuit means having high shunting sensitivity and including lock-out circuit means responsive tooperations of the approach track circuits forpreventing the picking up of the crossing track relay whilethe crossingrtr'ack section is occupied by trains which produce poor shunts;

A further object of this invention is to provide tint Patented Nov. 24, 1959,

In addition to irnproving means for restoring the various approach and crossing track circuits to their normal states whenever abnormal conditions occur which might result in the locking up the track circuit .system. Y

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying. drawings, and in part pointed. out as the description of the invention progresses.

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 drawings 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 are illustrated in a conventional manner, and symbols are used to indicate connections to the terminals of batteries, or other sources of electric current, instead of showing all of the wiring connections to these terminals.

The symbols (-1-) 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.

Apparatus In the accompanying drawings, a stretch of railway track is shown intersected by a highway H. The stretch of track is dividedinto a central or crossing track section XT, two approach track sections ET and WT, and two approach detector track sections EDT and WDT. The various track sections are electrically insulated from each other by insulated joints 4. Crossing. warning protection is given by warning signals XG which are located on each side ofthe stretch of trackalong the highway H.

The west approach. detector track section WDT is included in a track circuit comprising a battery 8, a relay WDTR and two variable limiting resistors 9 and. 10. The winding of relay WDTR. is connected to one rail through either its stick contact 11 or front contact 12 of a repeater relay WDTBP. Thus, relay WDTR is actually a stick relay for reasons tobe described later. The track circuit is a high voltage circuit, in that the voltage applied to the rails by the battery 8 is of a greater magnitude than that normally supplied for ordinary types of track circuits. The track circuit is adjusted by the resistors V 9 and in the usual manner to provide a track circuit shunting sensitivity which is high enough to detect lightweight trains which'provide high-resistance shunts.

g The east approach detector track section EDT has an associated track circuit which is shown to be of the impulse type. A track circuit of this type is described in detail in the co-pending application Ser. No. 454,956 of M. A. Scheg, dated September 9, 1954, now U.S. Patent 2,859,335, granted November 4, 1958; and relying on that application for a complete description of track circuit operations, the present description will be confined to former, and the directions of magnetic flux produced by current in the two windings are in opposition. When the track circuit is shunted by a train, the winding 20 of the impulse transformer is shunted, while the current produced by the train shunt rises sharply in the winding 14 of the impulse transformer. The resulting change in magnetic flux induces a voltage across a secondary winding 20, and this induced voltage is applied to the winding of the impulse relay IR through rectifiers 21 and 21a. Relay IR is assumed to be a polar relay, and it can be noted that one terminal of the winding of the relay IR is connected to a center tap provided in the winding 20, while the other terminal of the relay winding is connected through the rectifiers 21 and 21a to the extremities of the Winding 20. In this manner, relay IR is energized by energy of a particular polarity regardless of the polarities of voltage induced in the secondary winding of the transformer. A capacitor 22 can be connected across the secondary winding 20 to reduce the effects of initial sharp peaks of induced voltage applied across either rectifier, thereby protecting the rectifiers against inverse voltages.

When relay IR is energized by a pulse of induced voltage, it is desirable to maintain the picked-up condition of the relay for a time interval sufiicient to operate a repeater relay EDTP. Therefore, slow-release characteristies are provided in the present disclosure by means of a resistor-capacitor unit 23 connected in parallel with the winding of relay IR.

Under ideal shunting conditions, the occupancy of the track section EDT results in the deenergization of the track relay EDTR and the concurrent energization of the impulse relay IR. Back contact 24 of relay IR and front contact 25 of relay EDTR both open to deenergize a repeater relay EDTP. relay EDTP is deenergized either by a normal shunt across the track rails or by a momentary detected shunt which results in the operation of the impulse track relay. Relay EDTP is normally energized through its stick contact 26, and can also be energized through front contact 27 of a repeater relay EDTBP, The function of the two energizing circuits will be described later in detail;

The track repeater relay EDTP cannot be energized until the impulse relay IR is again actuated to close its front contact 17 to pick up relay EDTR. Since this cannot occur until an occupying train vacates the track section EDT, relay EDTP will remain deeuergized, thereby detecting track occupancy conditions. The description of an impulse track circuit is given primarily to illustrate analternate means for detecting poor shunting cars. Inactual practice either a high-volt age track circuit of the type described for the west approach detector track "section WDT or an impulse track circuit can be used, but the type of track circuit to be used need not be limited to the two examples shown.

Each of the approachdetector track relays-WDTR and EDTP have slow-acting back repeater relays WDTBP and EDTBP, respectively. Back contacts 28 and 29 of a general description of the circuit elements and their operations. The track circuit apparatus includes a battery 13 and a limiting resistor 13a which are connected to the rails of the track section through a Winding 14 V of an impulse transformer. A track relay'EDTR is connected to the rails at the other end of the track section by a circuit which can be traced from the upper rail through wire 15, either front contact 16 of relay EDTR or front contact 17 of an impulse relay IR, the winding of relay EDTR and a wire 18 to. the lower, rail. A second winding 19 of the impulse transformer is connected in parallel with the winding of relay EDTR. When the track section is unoccupied,.current flows. from the battery through the windings. 14. and. 19 of the impulse transrelay WDTR and-EDTP, respectively, act to energize or deenergizethe associated back repeater relays.

The high-voltage detectortrack circuits are used to insure the response of trackcircuits associated with the track sectionsW'I and ET to poor-shunting trains. In the present disclosure, this is accomplished by opening the track circuits associated with the approach track sections at the battery ends. More specifically, under normal conditions the approach tracksection WT is energized by a battery 30 which is connected at one terminal to the lower. rail by a wire.31 andis connected at the other terminalto the upper rail by a circuit including front contact 32 ofirelay WDTRand two resistors 33 and 34. It is evident that a shunting of relay WDTR results in the disconnecting of the battery 30 from the rails by the opening of front contact 32 ofrelay WDTR. A second circuit for. applyingenergy: tothe rails of track section In this manner, the

includes the battery 30 and a second battery'36 which can be connected to the rails through front contact 37 of relay WDTBP, front contact 38 of relay WDTR, and

the resistor 34. This circuit is effective momentarily when a train vacates the track section WDT to cause the energization of relay WDTR which closes its front contact 38 before the slow-acting repeater relay WDTPB can releaseits front contact 37. This operation will be described later in greater detail.

It can be seen that a similar energizing circuit is associated with the approach track section ET, and it is con trolled by the relays EDTP and EDTBP.

The track circuit associated with the approach track section WT includes a track relay WTR which is normally connected to the rails of the track section through a resistor 39, front contact 40 of relay WTR, and'a wire 41. Obviously; the circuit described for energizing relay WTR is a stick circuit. Therefore, relay WTR when deenergized must be dependent on particular pick-up circuit means for restoring the relay to its picked-up condition.

WTR whenever the track section WT is vacated. One pick-up circuit includes the resistor 39, a resistor 42, front contact 43 of a directional stick relay WBS, front contact 44 of thecrossing track relay XTR, and wire- 41. The remaining two pick-up circuitsboth include front contact 44 of relay XTR and include, respectively, front contact 45 of a timing repeater relay TESP and front contact 46 of a directional stick relay EBS. Without describing the various pick-up circuits'specifically, it can be noted that relay WTR can be energized only when the crossing track relay XTR is energized and either directional stick or timing circuit means are operated.

The approach track relay ETR is provided with similar pick-up and stick circuit means. The stick circuit for relay ETR includes a resistor 47, front contact 48 of relay ETR and a wire 48a. The pick-up circuits for relay ETR all include front contact 49 of the crossing relay XT R, and the respective pick-up circuits include, respectively, front contact Sil of relay WBS, front contact 51 of relay TESP, and front contact 52 of relay EBS which is connected in series with a resistor 53. e

' The crossing track section XI has an associated track circuit which is energized by a battery 54 through a limit-' ing resistor 55. The battery 54 is a high-volta-ge source comparable to those described for the detector track sections. The crossing track relay XTR is normally energized through a stick circuit which includes a limiting resistor 56 and a front contact 57 of relay XTR. -Relay XTR is provided with a plurality of pick-up circuits; One pick-up circuit arrangement includes contacts 58 and 59 of the respective approach track relays ETR and WTR, while the remaining pick-up circuit includesfront contact 60 of the timing repeater relay -T ESP. It is evidentthat pick-up operations of relay XTR are possible only'in response to operations of the approach track relays orto the completion of timing operations which will be described. The high-sensitivity track circuits employed in conjunction with the track sections XT and WT are, as described, of a type in which the supply voltage is higher than that normally employed in track circuits in general. Shunting resistance is dependent on the wheel-to-rail contact resistance encountered, and often such resistance is jhigh because of the condition of the Wheel and rail surfaces. Often such high contactresistance is caused by surface layers of dirt, grease, etc. A higher interrail potential is one effective means for overcoming the contact resist ance and, thereby, increasing the effectiveness of a shunt.

Two directional stick relays EBS and WBS are provided to indicate the directions of movementof trains passing through the stretch of track. The eastbound directional stick relay EBS has a pick-up circuit which includes'back contact 61 of relay WTR, back contact 62. of relay XT R, front contact 63 of relay ETR, back contact 64 of relay A plurality of pick-up circuits are provided for restoring relay' W38, and the winding of relay EBS. Stick circuits for relay EBS are provided through its stick contact 65 and either back contact 63 of relay ETR or back contacts 61 and 62 of relays WTR and XTR, respectively. The pickup circuit for the westbound directional stick relay WBS includes back contact 63 of relay ETR, back contact 62v of relay XTR, front contact 61 of relay WTR, back contact 66 of relay EBS and the winding of relay WBS. Relay WBS can be energized by stick circuits which in-' clude its front contact 67 and either back contact 61.of

relay WTR or back contacts 62 and 63, respectively, of

relays XTR'and ETR. -Without describing the operation of the directional stick relays in detail, it can be noted that a particular directional stick relay is energized whenever an approach track relay and the crossing track relay are concurrently deenergized, and energization is maintained until a train causing such pick-up operations vaby a circuit including front contacts 68, 69 and 70 of' relays WTR, XT R, and ETR, respectively. From this it can be seen that initially relay XR can be deenergized by the shunting of any of the approach and crossing track circuits. Front contacts 71 and 72 of the directional stick relays WBS and E88, respectively, are provided inthe pick-up circuit for relay XR to operate relay XR" under particular conditions of track occupancy which will be described. Whenever relay XR is deenergized, it closes its back'contact 73 to energize the operating circuits (not shown) for the crossing warning signals X6; and itlis' assumed that such control circuits can be of any of a number of well-known types.

In order to provide circuit means for restoring the various track circuits to normal under unusual operating conditions, a timing relay TE is provided. Although the timing relay can be of any of a number of types, it is assumed in the present disclosure that relay TE is of a well-known thermal type. More specifically, relay TE is assumed'to include a bimetallic contact member which is caused to bend in accordancewith temperature. This Well-known type of contact member is made of two attached strips of dissimilar metals which have different thermal coefficients of expansion. Thus, under varying conditions of heating the metallic strips expand or con: tract at different'rates causing the contact member to bend. In the circuit drawing the bimetallic contact mem-' her is shown as a front contact 77 which is located in close proximity to the relay Winding, or heating element. Contact 77 is assumed to be fully open when the winding isdeenergized, and is assumed to'bend to its closed positions in response to heat produced in the relay winding when energy is applied to the winding. A check contact The timing relay TE can be energized by'a circuit iricluding either back contact 74 of relay [WTR or back contact 75 of relay ETR, the winding of relay TE, and back contact 76 of a stick relay TES. 'Thus,-when an approach track section ET or WT is occupied energy is applied to relay TE, and the resulting heat produced in the winding of relay TE causes contact 77 to 'move toward its closed position. This movement of contact 77 causes contact 79 to move from its closed position at the same time. V j Q The stick relay TES is provided todetect operations of relay TE which result in the closing of contact 77 of relay TE. When relay TE is energized for a time interval long enough to result in the closingof contact 77, relay TES becomes energized by a circuit including either back contact 74 or 75 of relays WTR and ETR, respectively, contact 77 of relay TE, the winding of relay TES and back contact 78 of a repeater relay TESP. When relay TES opens its back. contact 76 and closes its front contact 76"relay TE ismomenta'rily deenergized. Front contact 76 establishes an alternate energizing circuit for relay TE and establishes a stick circuit for relay TES. While front contacts 76 and. 77 of the respective relays TES and. TE are both closed the winding of relay TE is shunted, and this shunt circuit combination is in series with the winding of relay TES. Thus, the current in relay winding TE decreases, and the heat produced by the winding of relay TE decreases accordingly, resulting in the opening of contact 77. When contact 77 of relay TE opens, the windings of relays TE and TES are connected inseries through front contact 76 of relay TES.

' The resistance of the winding of relay TES, however, is

high enough to maintain the level of current low in this series circuit so that insufiicient heat is produced by the winding of relay TE to affect contact 77, and contact 77 moves to its fully open normal position, while contact 79 of relay TE moves to its normally closed position.

In view of the operation of the relays TE and TES, a timing operation begins with the energization of relay TE and ends with the reclosing of back contact 79 of relay TE. When back contact 79 closes, the repeater relay TESP is energized by a circuit including front contact 80 of relay TES. Relay T ESP opens its back contact 78 in the energizing circuits for relay TES, causing relay TES tobe deenergized. In order to insure that the pick-up circuit for relay TESP is closed long enough to cause the relay to pick up its armature relay TES is made slow-acting in releasing its armature, as previously described. When relay TES releases its armature, front contact 80 of relay TES then opens to deenergize relay TESP. Thus, relay TESP is energized momentarily at the end of each timing operation and causes the deenergization of relay TES. If either contact 74 of relay WTR or contact 75 of relay E'ER is closed at the end of one timing operation, the closing. of back contact 76 of relay TES closes the previously described initial energizing circuit for relay TE to start another timing operation.

Relay TESP, during periods of energization, acts in the previously described pick-up circuits for the approach and crossing track relays. The function of the relay TESP in establishing pick-up circuits for these track relays can best be described when a more specific description of circuit operation is given. It should be noted that relay TESP is made slow-acting in releasing its armature so that contacts of relay TESP in approach and crossing track circuits are closed long enough to per mit circuit operations.

Operation In. describing the operation of the present circuits it initially and described later.

7 It will be assumed that. an eastbound train advances into and through the stretch of track, and it is assumed that the length of the train is such that all of the track sections can be occupied by the train at one time.

When the train enters the west approach detector track section WDT a shunt is produced in the associated detector track circuit. Since, as described, the approach detector. track circuit is. of a high voltage type, adjusted to be responsive to high-resistance shunts, the range of shunt detection. is greater than the range of standard track circuits encountered in general practice. Therefore, even under poor shuntingconditions the detector track, circuit. can be expected. to respond, at least momentarily, to a train shunt. Thus, relay WDTR is shunted and releases its armature, resulting in the opening of front contacts 11, 32 and 38 and the subsequent closing of back contact 28.

The opening of front contact 32 of relay WDTR deenergizes the west approach track relay WTR, since front contact 32 of relay WDTR disconnects one terminal of the battery 30 from the upper rail of the approach track section WT. Since relay WTR is normally energized by a stick circuit including its front contact 40, relay WTR cannot be reenergized until energy is again supplied to the rails and until one of the previously described pick-up circuits closes. Thus, any effective shunting of relay WDTR results in the deenergization of the approach track relay WTR, and the continued deenergization of relay WTR is not dependent upon the ability of a train to produce effective shunts in the approach track section WT.

In addition to disconnecting the battery 30 from the track section WT, relay WDTR also precludes the connecting of the batteries 30 and 36, in series, to the track rails. Specifically, front contact 38 of relay WDTR is open before front contact 37 of the repeater relay WDTBP closes in response to the energization of relay WDTBP by the closing of back contact 28 of relay WDTR.

It should be noted here that whenever relay WDTR is again energized it opens its back contact 28 to deenergize relay WDTBP. Since relay WDTBP is slow-acting in releasing its armature, front contacts 32 and 38 of relay WDTR close before front contact 37 of relay WDTBP opens. Thus, for a moment the batteries 30 and 36 are connected in series in the track circuit associated with the approach track section WT, and a pulse of higher voltage is, applied to this track circuit momentarily. However, no pick-up circuit is closed at this time to permit relay WTR to respond to the high voltage pulse. The utility of the application of a high voltage pulse is particularly related to operations resulting from trains leaving the stretch of track and will be further described later.

When the train advances into the approach track section WT, no further circuit operations occur because relay WTR is already deenergized. It must be noted at this time that the approach track circuit including relay WTR is a standard track circuit, responsive to train shunts falling within a normal range of resistance. This track circuit can be reasonably assumed to be responsive, at least momentarily, to poor shunts. Therefore, even a momentary effective shunt which can be detected by the approach track circuit results in the sustained deen ergization of relay WTR until a pick-up circuit is closed for that relay. The combination of the approach track circuit and the adjoining high-sensitivity approach detector track circuit thereby insures the deenergization of the approach track relay WTR as an eastbound train enters the stretch of track.

The deenergization of relay WTR results in the opening of front contact 68 of relay WTR in the normal energizing circuit for the crossing relay XR. Relay XR releases its armature and closes its back contact 73, thereby activating the operating apparatus for the crossing warning signals XG.

When the train advances into the crossing track section XT the train shunt produced in the crossing track circuit results in the deenergization of relay XTR. Since this track circuit is also of the high-voltage type, adjusted to respond to high-resistance train shunts, the susceptibility of relay XT R to shunting is high. The detection of even a momentary shunt by relay XT R is sufiicient to sustain the deenergization of the relay because relay XTR is normally energized through its stick contact 57. Thus, one of the pick-up circuits for relay XTR must be closed before the relay can again be energized.

The deenergizationof relay XTR results in. the energization of the eastbound directional stick relay EBS through the pick-up circuit including back contact 61 of relay WTR, back contact 62 of relay XTR, front contact 63 of relay ETR, and back contact 64 of relay WBS. A stick circuit including back contacts 61 and 62 of relays WTR and XTR, respectively, and front contact 65 of relay EBS then closes to hold relay EBS energized.

' As the train advances into approach track section ET it may or may not be capable of effectively shunting relay ETR. If relay ETR is shunted, at least momentarily, it will openits stick contact 48 and become dependent on its pick-up circuits for subsequent reenergization. If the traincannot efiectively shunt relay ETR, the subsequent entrance of the train into the approach detector track section EDT can be expected to result in the deenergization of relays EDTP and ETR. More specifically, the combination of track circuits associated with track sections ET and EDT is comparable to that associated with track sections WT and WDT. Although, for illustration ofalternate types of high-sensitivity track circuits, thetrack circuit for track section EDT has been assumed to be of the impulse type, operations of this track circuit result in operations of relay EDTP which selectively connect or disconnect track batteries in the track circuit for track section ET.

Assuming that the train is capable of shunting relay ETR, at least momentarily, relay ETR releases its armature; The crossing over of the movable contact spring of contact 63 of relay ETR opens the pick-up circuit for relay EBS and subsequently closes to provide another stick circuit for relay EBS.

l Assuming at this point that all of. the track sections are :occupied by the train, the condition of the various track circuits should be reviewed. Relays WDTR, XTR andEDTR are deenergized because of the. shunting action of the train. Relays WTR andETR are deenergized, regardless of effective shunting, because their respecti"e pick-up circuits are opened by front contacts 44 and 49, respectively, of relay XTR; and furthermore, their respective energy supply batteries are disconnected by contacts of relays WDTR and EDTP, respectively.

9 When the train vacates track section WDT, relay WDTR picks up, closing its front contacts 32 and 38 to apply high voltage to the rails of track section -WT, as previously described, through front contact 37 of the slow-release'WDTBP. When relay WDTBP opens its front contact 37, the energy supplied to track section WT reverts to normal, being supplied by battery 30 through front contact 32. of relay WDTR. Relay WTR cannot, however, be picked up until the train vacates track sections WT and XT. As soon as'track section XT is vacated, removing the train shunt from relay XTR, relay XTRis energized through back contacts 58 and 59 of relays'ETR and WTR, respectively. Stick contact 57 of relay XTR closes to restore the normal "energizing circuit .for relay XTR. Relay WTR becomes energized as soon as front contact 44 of relay XTR closes. The pick-up circuit efifective at this time includes front contact 46 of relay EBS as well asfront contact 44 of relay XTR. The normal energizing circuit for relay WTR: is' closed by the stick contact 40,,of relay WTR;

,nA pick-up circuit for relay XR is now closed through front-contacts 68, 69 and 72' of relays WTR, XT R and BBS, respectively. Relay XR picks up and opens its back contact 73, thereby stopping operations of the warnsignalsXG. Thus, signaling operations cease when the. train vacates the crossing. I I

When the train vacates track section ET, no circuit ll rations occur. When track section EDT is vacated, i removal ofthe shunt produces 'a pulse of energy in the secondary winding of the impulse transformer, as previously described, resulting in the momentary energizationof the impulse relay IR. The closing pr. front contact 17 of relay IR permits the picking up of the track 10 relay EDTR which, in turn, closes its stick contact 16 to restore its normal energizing circuit. The repeater relay EDTP is then energized as soon as the impulse relay IR releases its armature to close back contact 24. The slow-acting repeater relay EDTBP is deenergized, but retains its armature long enough to permit the momentaryapplication of a pulse of high-voltage energy to the rails of track section ET. This results in the pickingup of relay ETR through its pick-up circuit including front contact 49 of relay XTR, front contact 52 of relay EBS and the resistor 53. Relay ETR closes its stick contact 48 and is maintained energized by its normal energy supply battery after relay EDTBP releases to cut off the highvoltage pulse.

The picking up of relay ETR results in the opening of the stick circuit for relay EBS at back contact 63 of relay' ETR. The deenergization of relay EBS returns'the circuits to their normal operating status.v It can be noted here that relay EBS (and W138) is of the slow-release type to insure the continuous energization of relay XR. Specifically, front contact 72 of relay EBS must remain closedunt'il'front contact 70 of relay ETR closes; otherwise' momentary undesirable operations of the crossing signals could result.

Returning to the conditions under which relay ETR became energized when the train vacated the detector track section EDT, the pick-up circuit available for energizing relay ETR included the resistor 53. This'resistor is adjusted to be capable of preventing the picking up of relay ETR by normal energization, but permits the pick-' ing up'of relay ETR in response to the momentary pulse of high-voltage energy produced when track section EDT is vacated. Theutility of this circuit arrangement can be seen in considering conditions underwhich a short eastbound train advances into the track section ET and is' completely contained within the limits of that track section. The condition of the circuits under such conditions is dependent upon whether or not-the train is, or has been, capable of effectively shunting relay ETR. Since relay WTR- cannot be picked up until relayXTR picks up, and since relay XTR cannot pick up unless both relays WTR and ETR are dropped away, the clear ingup of the track circuits previously shunted by the train is dependent upon the deenergization of relay ETR. Assuming that the train does effectively shunt relay ETR, relay ETR drops awaypermitting the energization of relaysXTR and WTRin sequence. A pick-up circuit is now available for relay'ET-R and includes the resistor 53along with front contacts 52 and 49 of therespective relays -EBS and XI R. If the shunt produced by the train should become poor,-or lost completely, relay ETR will not be picked up by its normal energy supply which is available Whenever track section EDT is unoccupied.

. If such operations were permitted, a momentary; loss of shunt could cause r'elay ETR to pickup, resulting-in the deenergization-of relay EBS iwhichj'at this point, vis held energized by itsstickcircuit through back contact 63 of relay-ETR. Asubsequentdeenergization of relay ETR; upon a reestablishing of the effective train shunt would result in, the deenergization of relay -XR; specifically; front contact 17 0" of relay ETR and front contact'72 of relay BBS would open the, energizing circuits for relay XR. 'Thus', the momentary loss of shunt could cause the reactivation of the warning signals XG, and signaling of high-voltage energy in the pick-up" circuit for relay- ETR.

In view of the foregoing description, it can be pointed out that during the time when relay ETR can be'energizedby high-voltage energy through the biasing resistor 53, the approach track circuit is essentially a high-voltage circuit comparable to those associated with track sections WDT and XT; and this circuit is arranged to be sensitive to high-resistance shunts. Therefore, if the front of a train should produce an effective shunt followed by a momentary loss of shunt when entering track section EDT from track section ET, relay ETR is not responsive to the resulting high-voltage energy pulse because relay ETR is etfectively connected into a circuit having high shunting sensitivity at the time, and the shunt produced by the remainder of the train in track section ET will be detected.

A westbound train moving through the stretch of track will produce similar circuit operations. The track relays EDTP and ETR are dropped away in sequence, and warning signaling operations are initiated by the opening of front contact 70 of relay ETR in the energizing circuit for relay XR. The subsequent shunting of relay XTR results in the energization of the westbound directional stick relay WBS which, in turn, conditions the pickup circuits for relays ETR and WTR. The later shunting of relay WTR conditions the pick-up circuit for relay XTR so that relay XTR will pick up when the train vacates track section XT. At this time relay ETR can be energized by its normal energy source through front contact 50 of relay WBS, while relay WTR can be energized only by high-voltage energy through the biasing resistor 42 and front contact 43 of relay WBS. As previously pointed out, the biasing resistors 42 and 53 are selectively inserted in the pick-up circuits for re lays WTR and ETR, respectively, in order to prevent energizations of relays WTR and ETR which result from losses of shunt. Since the biasing resistors are either inserted or by-passed by selective operations of the directional stick relays EBS and WBS, it is essential that concurrent energizations of relays EBS and WBS be prevented. Thus, as described, the pick-up circuit for relay EBS includes back contact 64 of relay WBS, while back contact 66 of relay EBS is included in the pick-up circuit for relay WBS. This cross-checking in the pick-up circuits for relays EBS and WBS insures the prevention of concurrent energizations of these relays under any-conditions which might conceivably arise.

Having described circuit operations resulting from the passing of a train through the stretch of track, various specific operating features can be pointed out in detail.

The arrangement of the approach detector track sections and approach track sections is such that a train entering the stretch of track is required to produce at' able of deenergizing either relay WDTR or WTR, and

such a shunt will cause relay WTR to drop away and initiate warning signaling operations. Since relay WTR is normally energized by a stick circuit it cannot be again picked up until a pick-up circuit is closed. Excluding the timing means, no pick-up circuit is available to relay WTR until the directional stick relay EBS is energized; and no directional stick relay can be energized until the crossing track relay XTR is'effectively shunted. Therefore, the system will cause safe conditions to prevail even if the eastbound train does not produce a single effective shunt in passing through track sections XT, ET and EDT. Unless relay XTR is shunted, relay EBS cannot be picked up; and unless relay EBS picks up in response to the eastbound train, relay WTR cannot have a closed pick-up circuit. Similarly, a westbound train which effectively operates the impulse track circuit or shunts relay ETR, causes the deenergization of relay ETR, re-

'dition especially when visibility is poor.

The arrangement of the track circuit associated with the crossing track section has particular utility in the present system. As previously described, relay XTR is normally energized by a stick circuit. Once deenergized, relay XTR cannot be picked up again until both of the track relays ETR and WTR are either energized or deenergized (ex eluding timing circuit operations). If the crossing track circuit were arranged to be similar to that associated with track section WDT, the possibility would arise that a short train, engine, or railway car could shunt relay XTR when occupying only the extremities of the track section. In other words, deposits accumulated on the rail surfaces at the highway could prevent effective shunting in the highway sector. Thus, 'an eastbound train could produce an effective shunt upon entering the crossing track section, but would fail to shunt upon entering the highway sector. If the crossing track relay XTR were capable of responding to such operations, and since track section WT would have been vacated, relay XTR would first drop away causing relay EBS to pick up. Relay WTR could then pick up when relay XT R is picked up in response to the loss of shunt. The crossing relay XR would then be energized, causing the cessation of warning signaling operations. Thus, a short train, engine or railway car could occupy the crossing undetected, this being an unsafe con- On the other hand, if the short train proceeded through the crossing, again shunting relay XTR at the east end of the crossing track section, the warning signaling operations would be again initiated. .The present circuit arrangement preeludes the assumed unsafe cessation of warning signal operations because if relay XTR is once shunted it cannot pick up again until the train is detected by the dropping away of relay ETR. Thus, relay WTR is held deenergized by relay XTR, and relay XTR is held deenergized by relay ETR until relay ETR becomes deenergized. Obviously, if the train has advanced far enough to shunt relay ETR it must also occupy an extremity of track section XT where shunting conditions are good.

' In view of the preceding, the approach and crossing track circuits are arranged to cooperate so that lock-out means are provided to prevent unsafe energizations of the associated track relays under conditions of poor shunting;

As stated earlier, the west approach detector track circuit is arranged so that the associated track relay WDTR is normally energized through its stick contact 11 and can be picked up only when front contact 12 of the associated repeater relay WDTBP is closed. Relay WDTBP is energized when relay WDTR is deenergized, closing back contact 28. It is essential that relay WDTBP be picked up in response to the shunting of relay WDTR so that front contacts 38 and 37, respectively, of relays WDTR and WDTBP are closed for an interval to deliver a' high voltage energy pulse for restoring the approach track relay WTR. If the picking up of relay WDTR were not dependent uponthe picked up condition of relay WDTBP conditions could arise wherein a brief shunting of relay WDTR might not'result in the energizationof relay WDTBP, and such brief shunting intervals can exist when a short train (or a single car) passes through the track'section WDT at a high speed. Thus, the present circuit arrangements enforces a complete cycle of operation by relay WDTR and WDTBP in response to any effective shunting of relay WDTR.

. Similarly, the relays EDTP and EDTBP associated with the east approach detector track section are operatedin a like manner, relay EDTP being normally energized by'a stick circuit and being subjected to pick up energization only if relay EDTBP is energized.

Attention can now be given to the function of the tim ingcircuit means. As described previously, the thermal element of the timing'relay TE is energized whenever an approachtrack relay WTR or'ETR is deenergized. .The subsequent heating causes 'back' contact 79 of relayTE to' open and causes 'front"conta'ct"77 of relay TE to close. Relay TES is energized when contact 77 of relay TE closes, and the subsequent alteration of the circuit arrangement results in both the shunting of the heating element and the addition of the winding of relay TES in series with the shunted heating element. The resulting cooling causes contact 77 of relay TE to open. Subsequently, back contact 79 of relay TE closes to energize relay TESP, and back contact 78 of relay TESP opens to deenergize relay TES. The deenergization of relay TES results in the deenergization of relay TESP by the opening of front contact 80 of relay TES. When back contact 76 of relay TES again closes, the timing operation can be repeated if one or the other (or both) of the approach track relays WTR and ETR is deenergized.

The timing cycle is adjusted to be slightly longer in duration than the time normally required for a train to pass completely through the stretch of track at a normal speed.

Whenever relay TESP is picked up, its front contacts 45 and 51 close in pick-up circuits for relays WTR and ETR, respectively, thereby rendering these relays dependent only on the condition of the crossing track relay XT R. The conditions of the directional stick relays EBS and WBS are thereby rendered immaterial to the picking up of relays WTR and ETR. Front contact 60 of relay TESP provides a pick-up circuit for relay XTR which excludes contact of the approach track relays ETR and WTR. Since relay TESP is energized only briefly at the end of each timing cycle, it is made slow-acting so that its front contacts are closed long enough to permit operations of the track relays.

Assume that an eastboun". train enters the stretch of track and causes the deenergization of relay WTR. Assume further that before reaching the crossing track section XT the train stops, reverses its direction of movement, and leaves the stretch of track. The deenergization of relay WTR causes the deenergization of relay XR and the energization of the timing relay TE. Warning signal and timing operations are thereby initiated and continue as long as relay WTR is deenergized. The departure of the train cannot cause relay WTR to pick up because no pick-up circuit is closed. When the timing operation progresses far enough to cause the energization of relay TESP, however, front contact 45 of relay TESP closes to establish a pick-up circuit for relay WTR. The resulting picking up of relay WTR restores the circuits to normal, cutting oif signaling and timing operations.

If an eastbound train advances into the crossing section XT before reversing its direction of movement and departing from the stretch of track, timing and signaling operations are efiected as soon as relay WTR drops away. Since relay XTR is also assumed to drop away, relay EBS is energized to close its contact 46 in one pick-up circuit for relay WTR. However, neither relay XTR nor WTR can be energized when the train departs. Relay XTR cannot be picked up because back contact 59 of relay WTR is closed while back contact 58 of relay ETR is not closed; and while relay XTR is deenergized the pick-up circuits for relay WTR are opened by front contact 44 of relay XTR. Relays XTR and WTR are thereby mutually locked out. When relay TESP becomes energized near the end of a timing cycle, its front contacts 45 and 60 close in pickup circuits for relays WTR and XTR, respectively. Relay XTR picks up, closing its front contact 44 in the pick-up circuits for relay WTR, .and the opening of back contact 62 of relay XTR deenergizes relay EBS. If the train has vacated track sections WT and WDT before relays TESP and/or EBS release their 14 armatures, the closing of frontcontact 44 of relay XTR will pick up relay WTR; otherwise relay WT R will remain deenergized and initiate another timing cycle. Timing cycles will be repeated until relay WTR can be picked up.

Similar conditions to those described above for trains reversing directions of movement ,canjbe'produced by accidental shunts or open circuits which cause either the deenergization of relay WTR or the deenergization of relays WTR and XTR. It is further evident that similar operations result from comparable deenergizations of either relay ETR or relays ETR and XTR.

In view of all of the preceding descriptions of circuit operations, it is evident that the present invention provides highway crossing protection means having a high integrity of operation. The present system offers improved means for insuring both the detection of trains and the safe operation of warning signaling means when such trains are incapable of producing continuous effective shuntings of the various track circuits.

Since the problem of track circuit operation in response to poor shunts is not confined by any means to highway crossing systems, the circuit arrangements disclosed herein have general utility in other signaling systems as well.

Having described a highway crossing signaling system as one specific embodiment of the present invention, it is desired to be understood that this form is 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 alterationsmay 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 we claim is:

1. A control system comprising a highway crossing signal, a stretch of railway track extending across a highway, crossing means for registering the presence of a train in a short section of track traversed by the highway, intermediate approach means for registering the presence of a train on approach sections of track adjacent to each end of the section of track over which the highway crosses, distant approach means for registering the presence of a train on the track adjacent the far end of each approach section, each said intermediate approach means including a relay energized by a stick circuit including its own front contact and a contact controlled by the distant approach means and energized by a pick-up circuit controlled by the crossing means, said crossing means including a relay normally energized over its front contact or in parallel therewith either both front contacts or both back contacts of the relays of the two intermediate approach sections, and circuit means controlled by the crossing means and the intermediate approach means for controlling said crossing signal.

2. A control system according to claim 1 wherein the crossing means includes directional means for sensing the direction of train movement as Well as the presence of the train in passage through the short section of track traversed by the highway, and means controlled by said directional means for further controlling said crossing signal. v i

3. A control system according to claim 1 wherein said distant approach means includes a distant approach track circuit having a track relay for registering the presence of a train.

4. A control system according to claim 1 wherein said relays are track relays which are energized in respective track circuits for registering the presence of a train.

5. A control system according to claim 1 wherein timing means is provided for timing an interval after deenergization of said relay of either of said intermediate approach means, and circuit means is rendered eflfective by said timing means at the end of said interval for energizing the relay of said crossing means provided no train 15 is registered as being present in said short section of track traversed by the highway.

References Cited in the file of this patent UNITED STATES PATENTS 2,027,216 Young 12111.7, 1936

Images