US2135499A - Railway track circuit - Google Patents

Description

Nov. 8, 1938. o. s. FIELD RAILWAY TRACK CIRCUIT Filed June 21, 1935 ATTORNEY Patented Nov. 8, 1938 STATES PATENT. OF

RAILWAY TRACK CIRCUIT Oscar S. Field, Rochester; N'. Y., assignor to General Railway Signal Company, Rochester,

A Application June 21, 1935," Serial No. 27,737

13 Claims.

terythrough the track rails in series, but when a train" shuntj is applied to the track rails, the increase .in'current at the battery end of the circuit flowing through the included resistance must reduce the voltage at the relay end sufficiently torelease thetrack relay armature. The ballast between the rails of the track section however varies considerably in resistance according to weather conditions, thereby forming an interrail'shuntwhich may vary the interrail voltage sufficiently to at times prevent proper track circuit, operation. In other words, when the track circuit current is adjusted to provide proper operation under any one condition of the track ballast, a'decrease in ballast resistance may decrease the interrail voltage sufficiently to prevent the attraction of the track relay armature upon the removal of a train shunt, or an increase in ballast resistance may increase the interrail voltage sufiicientlyto producea dangerous condition by preventing the release of thearmature when the train shuntis applied. 7

It then becomes desirable to employ a means for maintaining a constant interrail voltage when thetrack section is unoccupied regardless of f ballast resistance changes, but to allow changes in interrail voltage caused by the application or removal of a train shunt. In my prior application se'r. No. 25,472 filed June '7, 1935, I have provided such a regulating me'anscomprising a motor means for actuating a variable resistorin series with the track battery, which motor means is controlled by a relay connected across the track rails, the control relay being more sensitive than the track relay thereby responding to interrail voltage changes which occur in increments or decrements too small to operate' the track relay, and being caused by changes in ballast resistance which occur slowly, these increments or decrements are compensated for before they can cumulatively amount to a change suiiiciently to cause operation of the track relay. The application of a train shunt in this arrangement causes a reduction in interrail voltage which abruptly amounts to a much greater change than is permitted to occur in response to ballast resistance changes, and consequently the motor driven variable resistor does not start to compensate for this abrupt decrease in voltage before the armature of the control relay has been operated beyond its position taken in response to decrements in ballast resistance, and the armature of the control relay in this extreme position is arranged to prevent operation of the motor driven variable resistor while a train shunt exists across the track rails.

The increased reliability of detecting a train shunt provided by the above regulating means however is dependent upon the proper operation of certain apparatus employed. In other words, theoperation of the motor driven variable resistor to prevent an increase in ballast resistance from increasing the interrail voltage to a value preventing reliable release of the track relay armature is dependent upon the proper response of the control relay to this increased voltage, which response may be prevented by an open Winding, loose connection or the like. Likewise, the, compensation for an increase in interrail voltage caused by an increase in ballast resistance even when properly detected by the control relay is dependent on the proper operation of the motordriven variable resistor which operation may be prevented by a failure of the motor windings, mechanical driving means or the like. Consequently, it will be clear that when a track circuit regulating means is relied upon to provide proper track circuit operation by automatically changing the characteristics of a track circuit in response to ballast resistance changes, a failure of the apparatus employed in this regulating means may under certain conditions result in an unsafe condition.

This application is an improvement upon the invention disclosed in my prior application Ser. No. 25,472 filed June 7,1935, and no claim is made in this application to subject matter shown and claimed in said prior application.

' In view of the above and other considerations, it is proposed in accordance with the present invention 'to' provide an improved means for maintaining a constant voltage between the rails of a track section when unoccupied by a train regardless of changes in interrail ballast resistance, and for allowing changes in interrail voltage caused by the application or removal of a train shunt. It is further proposed to provide means in such a track-circuit voltage regulating means operating in response to the failure of any of the apparatusemployed to effect regulation to provide and to retain a condition in the track circuit which results in restricted but from the adjacent track by insulating joints 2 to form a conventional insulated track section.- A center-tapped track battery B is connected'acros's the right hand end of this track section, that is, the extreme terminal of battery B is connected through a variable resistor R to the right hand end of the lower track rail I, while the extreme terminal is connected through a manually variable resistor 3, such as usually employed in track circuits, to. the right hand end of the upper rail 1. A primary secondary track relay combination such asshown in my. prior application Ser. No. 711,397, filed Feb. 15, 1934, is shown associated with the left hand end I of this track section, this arrangement being illustrated as a means forprovidlng improved track circuit operation although it" is =under'stoodthat a single track relay .mayof course'be employed in the usual manner." r

In this primary-secondary relay combination, the magnetomotive" force required to attract the armature of a primary track relay PTfrom its released position issupplied by the normal track circuit current flowing through all of its windings, but after thearmature of relay PT has been attracted, a secondary relay'ST (which controls signal circuits and the like by contacts such as l) is picked up through a front contact 4, thereby substituting a substantially equivalent resistor 5 for a portion of the winding of relay PT by a make-before-break contact 6, thus reducing the magnetomotive force'o'ifrelayv PT to a value just suflicient to reliably retain its armature in an' attracted position. '.In this manner,v a track relay combination may be arranged to drop away at nearly the same interrailvolta'ge that is sufficient to cause its picking up, and consequently it will be clear that when the interrail voltage of the track section is maintained at a'valuepermitting proper picking up of the combination, a rather slight reduction in interrailvoltage can cause its release in response to a train shunt.

A means for operating the variable resistor R at the right hand end of the track section has herein been illustrated as a conventional permanent magnet direct current motor including an armature A and a'permanent magnet III, or of course any other suitable motor means could be employed, such, as a series or shunt field direct current motor, the permanent magnet fieldbeing considered preferably inviewof saving the energy required to magnetize an electro-magnetic field. The armature A of this'motor is illustrated as connected through a suitable reduction gearing means comprising a worm. gear H attached to the shaft of armature A and driving a sector gear l2 attached to theshaft of an arm I43 arranged to contact in a suitable manner with various portions of the resistance-wire R.

A means for controlling the energization and the direction of current'in the armature A is provided by a control relay C, and a check relay K is also provided to check the continuity of the windings of the controlrelay C. A winding around'the other leg of thecore of relay K, and

likewise windings l8 and I!) are connected across the track rails I. The windings I 6 and I8 are "s0 arranged on the core of relay C that the interrail potential causes current to flow therethrough which produces cumulative flux values which normally provide an upward tractive force on a pivoted armature 20 associated therewith, but the windings Hand [9 on relay K are so arranged that this same current normally produces opposing flux values in the core thus producing substantially no tractive force on a similar, pivoted armature 22 associatedtherewith,

A lower compression spring 24 isj'arranged to exert'an upward biasing force on armature 20 which is adjusted by a screw 25 to substantially oppose the normal gravitational bias on armature 20, and an upper spring 26 is also provided to exert a downward biasing force on armature 20 which is adjustable by a screw 21 toequally oppose a predetermined upward magnetic attraction of the armature 20. The track circuit is adjusted by positioning the manually variable resistor 3 so that an interrail voltage exists when the track section is unoccupied which is found to provide reliable track circuit operation, and this interrail voltage provides a definite upward attraction of the armature 20 of the control relay C, which upward attraction obviously has a substantially constant relation to the degree of energization of the track relay combination at the other end of the track section.

The downward biasing force of, spring 26 is then adjusted by screw 21 so that the upward magnetic attraction of armature 20 produced by this normal interrail voltage is balanced by the biasing. force of spring 26 so that amovable contact 28 attached to the armature 20 by an insulating block 29 is positioned midway between a pivoted front contact 30 and a pivoted back contact..3l. The pivoted contactsv 30 and 3| are each biased inwardly by compression springs 32 and 33 respectively to contact with inner fixed contacts 34 and 35 respectively, this contacting force being adjustable by screws 36 for varyingthe biasing force of springs 32 and 33. A movable contact finger 39 is attached to the armature 22 of relay K by insulating connecting means lo, and the armature 22, being normally released as previoulydescribed, engages the movable contactj39 with a back fixed contact 4|.

' In describing .the op'erationof the present invention, it will first be considered that the resistance of the ballast between therails l increases s'othat the interrail leakage current decreases. This decreases the current flowing through resistances 3 and R and slightly reduces the voltage drop therethrough which obviously raises the interrail voltage of: the track circuit and likewise the energization of windings l6 and I8 of relay C. The relay C is adjusted to respond to a much smaller change in interrail voltage than can possibly causeoperation of the primary-secondary track relay combination; and consequently this gradual decrease in interrail leakage current soon causes a sufiicient increase in interrail voltage to upset the rather delicate balance on the armature 20' and operate the movable contact 28'into engagement with the pivoted front contact 30. The biasing force onthe pivoted contact 30 exerted by spring 32 however is adjusted so that the engagement of the movable contact 28 therewith caused by this slight increase in interrail voltage does not havesufiicient force to disengage front contact30 from the fixed contact 34.

A circuit is now completed for applying one polarity of energization to the armature A which maybe traced from the or extreme right hand terminal of battery B, through the pivoted front contact 30 engaged by the movable contact 28', and upwardly through armature A to the center terminal of battery B. This upward direction of current through armature A is in a proper direction to cause rotation of the resistor arm I4 in a clockwise direction which shunts out a smaller portion of the resistance wire R through a circuit including the movable contact 39 of relay K engaging the fixed back contact 4| and the fixed back contact 34 engaged by the pivoted front contact 30' of relay C. In this manner, the resistance in series with the track battery to the track rails is increased by one direction of operation of the armature A, which continues until the interrail voltage has been reduced to its normally adjusted value, thereby restoring the energization of the control relay C to a value which balances the forces on armature 20 and positions the movable contact 2 8 midway between the front and back contacts 30 and'3l.

- "The above operation of the control relay C and the motor driven variable resistor obviously continues in an intermittent manner as long as the ballast resistance continues to increase, thereby maintaining a substantially constant interrail voltage,-the only change in the interrail voltage beingthat which 'is required to cause an unbalance of theiforces on armature 20, which as previously described is'much smaller than the change required to cause operation of the track relay means;

Now considering that the resistance of the comparatively dry ballast decreases, it will be clear that an increased ballast leakage current occurs which flows'through the increased resistance inserted into the track circuit by the variable resistor R. A slight reduction in the interrail potential then occurs which reduces the energization of windings I6 and I8 of relay C to again upset the rather delicate balance of forces acting on armature 29 and in this case cause the movable contact 28 to engage the pivoted back contact 3|. Likewise, the movable contact 28 does not engage the pivoted back contact 3I with sufficient force to overcome the biasing. force of spring 33 so that the pivoted back contact 3| is not disengaged from the fixed contact 35. This completes a circuit for applying a different polarity of energization to armature A which may be traced from the center tap of battery B, downwardly through armature .A, through movable contact 28 of relay C engaging the pivoted back contact 3|, and through fixed contact 35 to the or extreme left hand terminal of battery B.

In this case, current flows downwardly through armature'A thereby causing a reverse direction of rotation which moves" the variable resistor arm I 4 in a counter-clockwise direction to shunt out a greater portion of the resistance wire R. This rotation of the armature A continues until the variable resistor arm I4 is moved in a counterclockwise direction toa position which decreases the resistance of the track circuit sufificiently to restore thenormally adjusted interrail voltage, thereby restoring the balance of the forces acting on armature 20 of-the control relay C and again positioning the movable contact 28 midway between the front and back contacts 30 and 3|.

This operation of the control relay C and the motor driven variable resistor also continues intermittently as long as the ballast resistance continues to decrease, thereby maintaining the interrail voltage substantially constant except for the small changes necessary to cause release of the armature 20 of the control relay, which as described is much smaller than can possibly cause the release of the track relay means.

It is of course understood that a regulating means of the present type should not operate when a 'train is occupying the associated track section, as such operation might compensate for the reduction in interrail voltage effected by the train shunt and prevent the release of the track relay, thereby defeating the purpose of the track circuit. In thepresent arrangement, the entrance of a train into the associated track section shunts the track rails I to cause an abnormal increase in the current flowing through resistances R and 3, thereby providing an abnormal voltage drop which reduces the energization of windings I6 and I8 of the control relay C to a much greater degree than the rather slight reduction in energization permitted by the regulator in response to an increase in ballast leakage current.

This greater degree of reduction in the energization of windings I6 and I8 caused by the train shunt greatly reduces the normal magnetic attraction of armature 20, thus allowing the force of spring 26 to exert a downward force on the pivoted back contact 3I through the movable contact 28 which overcomes the force of spring 33 and disengages the pivoted back contact 3| from the fixed contact 35. The ener'gizing circuit for armature A is thus opened at contacts 3I-35 which prevents operation of the motor driven variableresistor to restore the normal interrail voltage, and consequently the armature 20 of relay C remains in its extreme lower position and the interrail voltage remains at a reduced value which releases the track relay combination as long as the train shunt exists on the track section.

The present system then differentiates between a reduction in interrail voltage due to increased ballast leakage current from a reduction due to a train shunt in a manner to prevent the operation of the motor driven variable resistor as long as the train shunt exists on the track circuit. In other words, the application of a train shunt causes a reduction in interrail voltage which abruptly amounts to a much greater change than is permitted to occur in response to ballast'resistance changes, and consequently the motor driven variable resistor does not start to'compensate for this abrupt decrease in voltage before the armature of the control relay C has been operated downwardly with a force sufficient to disengage contact 3| from contact 35 and prevent energization of the armature A.

It will now be clear that when the apparatus of the present system thus far described is operating properly, a constant voltage is maintained between the rails of the track section whenunoccupied by a train regardless of changes in interrail ballast resistance, but a reduction in interrail voltage is permitted which occurs abruptly such as caused by the application of a train shunt. The present system also maintains .the interrail voltage at the proper adjusted value regardless of gradual changes in the terminal voltage of the track battery B such as may be caused by improper charging, abnormal loads or the like. In other words, the adjustment of the biasing forcesof springs 24 and 26 on the armature 20 provides a definite standard unaffected by variable conditions of the track circuit, to

' which standard the interrail voltage or the energizationof .vvindings l6 and I8 is related, thereby permitting any gradual change in interrail voltage regardless of its cause to effect operationof the regulating means. It is further obvious that this definite standard to which the interrail voltage is related also determines a fixed point at which the action of the regulating means is stopped, thereby preventing the hunting or overrunning operation which is inherent to some regulator-operation. t In the present system, any change in interrail voltage results in a corresponding change in current in windings l1 and I 9 of the check relay K,.but such current changes do not affect the normal released position of armature 22. In

other words, the windings I! and I9 being in parallel circuits will receive equalcurrent values,

and being oppositely arranged will produce neutralizing flux values regardless of the interrail voltage as long as these parallel circuits which include windings .l6 and I8 of relay C are intact.

However, considering now that either winding IE or winding I8 of relay C becomes open circuited, such as by a broken wire or loose connection, thereby reducing the flux value in the control relay C to such an extent that the armature 2B is released in the same manner as during the application of a train shunt, that is, the movable contact 28 is operated downwardly and may be operated with suflicient force to disengage contact M from contact 35. Under this condition, either winding l8 or l6 alone could notiproperly detect a change in ballast resistance in a manner to cause operation of the motor driven variable resistor and compensate therefor. Consequently, a continued increase in ballast resistance might cumulatively amount to an increase in interrail voltage which would'be sufficient to prevent reliable detection'of a train shunt by the track relay'combination.

-In-the present'arrangement, however, the failure-of either winding IE or l8 of the control relay C at the same time de-energizes the associated winding I! or 19 of the check relay K so that the flux produced by the Winding remaining energized is no longer opposed by the flux of the other winding, thereby picking up armature 22 of relay K. The picking up'of armature 22 opens the circuit shunting out a portion of the resistance wire R by disengaging the movable contact 39 from the fixed back contact 4|, thereby inserting the total value of resistance B into the track'circuit which reduces the track circuit current to a value precluding the possibility of a failure of the track relay combination to respond to-a train shunt. I

It will likewise be clear that in the eventthe failure of either winding "5 or l8 of the control relay C does not result inthe disengagement of the pivoted back contact 3| from the fixed contact 35 to prevent operation of the armature A, a dangerous condition would result from the following operation of the motor driven variable resistor to decrease the resistance insertedinto the track circuitfthereby also abnormally: increasing, the interrail. voltage. In otherwords, the check relay K prevents any dangerous condition from obtaining in the track circuit due to a, failure ,ofyeitherwinding I6 or winding l8 of the controlrelay C by causing the insertion of a maximumvresistance value which may result in a condition-r providing more restricted train: movements, but which obviates the possibility of afailureof the-track relay combination to detect the presence of a train in a track section. In this connectionit should be'noted that the windings [B -l1 and l8|9 are individually connectedto the track circuit lead-in Wires, so that a single break cannot open both pairs of windings unless the break occurs in the track circuit itself. I, g a g It may now be seen that although the armature ofrelay K is attractedin'response to the de-energization of one or the other of the windings l6 and I8 of relay C, it will not be attracted, in response to the de-energization of both windings. The two windings l6 and I8 however-haveino portion of their energizing circuits'in common which is not a part. of the track circuit, and consequently it is very remote that both ofthese windings could become de-energized simultaneously and leave the track circuit intact. However, if one of the windings of relayC fails andpicks up relay K, it may be advisable to mechanically retain the armature 22 in its picked up position in order to guard against its subsequent release by the failure of the remaining winding of relay C before the defective one hasbeen replaced.

A manually'releasable latch 44 may be provided for this purpose which is biased by a spring 45 to retain the armature 22 in an attracted position thereby holding contacts 39,- open.

In usingthis latch arrangement in the present system, it is assumedthat-incase of a failure of a windingof relayC, the track relay combination will either,be immediately released or will not pick up upon the departure of'a train from the track section, and consequently, attention will be called to. thefact that an abnormal condition exists at this track section, thereby allowing the defective circuit to be corrected andv the system restored to itsproper operating condition by manually releasing the latch 44.

A meanscis also provided in the present system for preventinga dangerous condition from obtaining in thetrack circuit due to a'failure of the'motor drivenvariable resistance to properly reduce theinterrail voltage in; response to I a decrease in ballast leakage current or the like.

For example, considering that-an increase in the interrail voltage occurs, due for example to an increase in ballast resistance, the armature 20 of the control relay C is moved upwardly into engagement with the pivoted front contact '30 thereby normally operating'the motor driven resistance to -a position compensating for this voltage .increase, but however, if the variable resistor does not respond forsome reasons such as a failure of a motor Winding or the like, the increase in interrail voltage might cumulatively amount to a value which would prevent proper trac k circuit operation.

However, before the interrail voltage has reached such a value, the armature 20 of the control relay C is attracted upwardly, with sufficient force to overcome the force of spring .32 and disengage the pivoted front contact 30'from the fixed contact 34, thereby opening the circuit shunting out a portion of the resistance wire R.

In: this manner, the total value of resistance R is inserted into the track circuit in the same manner as during the attraction of armature 22 of the check relay K, thus resulting in an abnormally low interrail voltage which may provide a restricted traffic condition by releasing the track relay combination, but which prevents an abnormally high interrail voltage from ob- 10 taining which would prevent the detection of a train shunt. I

It is also considered expedient to provide a means for mechanically retaining this circuit open at contacts 30--34 when a failure of the motor driven variable resistor occurs, as otherwise a subsequent train shunt would reduce the energization of the control relay to a degree allowing contact 30 to again engage contact 34, thereby defeating the purpose of this check contact arrangement. Consequently, a similar manually releasable latch 48 has been provided which is biased by a spring 49 to retain the pivoted front contact 30 inits upper position, thereby mechanically holding contacts 30-34 open. Likewise it is considered that this abnormally low track circuit current will either immediately release the track relay combination or prevent its picking up when the track section becomes unoccupied,thereby calling attention to the fact that an abnormal. condition exists and allowing the cause of the failure of the motor driven variable resistorto be corrected and the system restored to normal by the manual release of the latch 48.

A track circuit regulating means has thus been provided wherein a simple and efiicient permanent magnet motor means has been employed to operate a variable resistor included in the track circuit, the operation of this motor being normally governed by a control relay which is provided with two windings, each winding being energized by separate parallel circuits connected across the rails of the track section and each circuit including a winding of a check relay. A change in current in the windings of the con- .trol relay causes a corresponding operation of the control relay armature while the windings of the check relay are so arranged that a change in current does not affect the check relay armature as long as both the windings of the control and check relays are intact.

In this manner, the control relay which is more sensitive than the track relay is able to detect changes in interrail voltage which are too small to cause operation of the track relay, and the control relay is arranged to accordingly cause operation of the motor driven variable resistor to compensate for these small changes in interrail voltage. Inasmuch as changes in interrail voltage caused by ballast resistance changes occur slowly, the motor driven variable resistor is able to compensate for the ballast resistance changes in increments or decrements of interrail voltage detected by the control relay before they can cumulatively amount to a change suflicient to afiect the track relay. I

The present system thereby maintains a substantially constant interrail voltage while the track section is unoccupied regardless of ballast resistance changes, but upon'the entrance of a train into the track section, a reduction in interrail voltage occurs which abruptly amounts to a much greater change than is permitted to occur in response to ballast resistance changes, and con' sequently the motor driven variable resistor does not start to compensate for this abrupt decrease in voltage before the armature of the control relay has been operated beyond its position taken in response to a decrease in ballast resistance. The control relay in this position is arranged to open the control circuit for the motor driven variable resistor, thereby preventing compensation for the reduction in interrail voltage caused by the train shunt, and of course the armature remains in this position until the train departs from the track section to restore the system to its normal condition.

. The control relay in the present system is also provided with a check contact means which is operated and mechanically retained in response to the occurrence of an abnormally high interrail voltage, and in the present system, this contact is arranged to remove a shunt around a portion of the variable resistor, but obviously a separate resistor could be provided in the track circuit for this purpose. In other words, a check means is provided which responds to an excessive interrail voltage such as may be caused by a failure of the motor driven variable resistor to properly increase the track circuit resistance, and this check means is arranged to prevent an unsafe track circuit condition by inserting an increased resistance value.

The check relay is provided to likewise prevent an unsafe track circuit condition from arising due to a failure of a winding of the control relay, that is this check relay as previously mentioned does not normally attract its armature, but in the event one of the windings of the control relay fails or becomes open, the armature of the check relay is attracted and mechanically retained which also removes a shunt around a portion of the variable resistor, but likewise a separate resistor could also be provided in the track circuit for this purpose. The check relay thereby prevents an abnormally high interrail voltage from being applied to the track circuit either by unwarranted operation of the motor operated variable resistor caused by the reduced magnetism of the control relay or by an increased ballast resistance which cannot be detected by the impaired sensitivity of the control relay.

The above rather specific description of one form of the present invention is given solely by the way of example, and is not intended, in any manner whatsoever, in a limiting sense. It is to be understood that various modifications, adaptations and alterations may be applied to meet the requirements of practice without in any manner departing from the spirit or scope of the present invention except as limited by the appended claims.

What I claim is:

1. In a track circuit, an insulated track section, a source of energy for the track section, a resistor in series with the source of energy to the track section, a motor driven arm contacting with various portions of the resistor, a control relay having two windings connected in multiple across I the track section, a check relay having two opposing windings one in series with one of the windings of the control relay and the other in series with the other winding of said control relay, said check relay acting to attract its armature when ever its two windings are not equally energized, a circuit connecting the motor driven arm to one extreme end of the resistor through a back con-. tact'of the check relay and a contact on the control relay, said contact being opened only in response to current in the windings of the control relay above a predetermined value, contacts on thecontrol relay forcontrolling operation of'the.

motor driven arm in accordance with relatively slight changes in current in the windings: of the control relay, and contact means on the control relay preventing operation of the motor driven arm in responseto current in the windings of the control relay below a predetermined value.

2. In a track circuit including a track relay energized by current flowing from a track battery through the' rails of a track section in series, a resistor in series with the track circuit, a power operated arm contacting with various portions of the resistor, a control relay having two windings connected in multiple across the track section and governing operation of the power operatedarm inaccordance with relatively slight changes in interrail voltage, a check relay responsive to the integrity of the windings of said .control' relay, and a shunt circuit connecting the power-operated arm with one end of the resistor through a contact ofthe checkwrelay and a: contact of the control relay operated by anexcessiverinterrail voltage. 1

3. In'a track circuit, insulated track section, a source of energy fOI'IthGQtIaCK circuit, a power operated variable resistor in the track circuit, a control relay having windings energized in accordance with the interrail potentialof the track circuit and governing operation of the power operated variable resistor, a, check relay responsive to the integrity of the control relay windings, means controlled: by thezcheck relay for increasing the resistance of the track" circuit upona failure of the windings of thecontrol relay, and means controlled by thecontrol relay for increasing the resistance of'the track circuitupon an excessive interrail potential.

4. In a track circuit: includinga track relay; means energized by currentlfrom a track bat-,

tery flowing through? therails of a track section in series, a power-actuated variable: resistor in the track circuit," a control relay controlling the actuation of the variable resistor-in accordance with an increase or a decrease in interrail'ivoltage between predetermined limitsof variation, means on the control relay for preventin'g actuation" of the variable resistor in response to;a1decrease in interrail potential beyond saidzpredetermined" limits of variation, andmeans .onith'e controli relay for causin'g'a. maximum resistance to be inserted into the track circuit in responseto an increase in interrail potential beyond's'aid pre-' determined limits of variation.

5.. Ina track circuit voltage regulating means, a control relay having an energizing circuit-responsive to the track circuit voltage, a power the energizing circuitior the control relay, said check relay upon attraction of its armature inserting the maximum resistance of said resistor in the track circuit, and-a manually releasable latch means for holding thearmature of-the check relay in its attractedposition.

'7. In a track circuit voltage regulating means,

aiicontrolrelay' responsive to-theitrack circuit voltage, a variable resistance in series with the source supplying voltage across the track rails of the track circuit and operated to different positionsby the control relay to maintain a substantially constant voltage across the track rails, contact means on the control relay operated in response to an excessive track circuit voltage, a manually releasablelatch means'for holdingv the contact means in its operated position, and means controlled by said contact means for including all of said variable resistance in the track circuit feed independently of the' operated position. of said variable resistance; 7

8. In atrack circuit voltage regulating means, a control relay having an energizing ci rcuitre sponsive to the inter-rail voltage of the track: circuit, a power-operated regulator governed by sai'dcontrol relay so as to maintain a substantially constant inter-rail voltage upon gradual changes in the resistance of the-track circuit, a check relay included in series with said control relay in such a manner asto be actuated upon a' break in the energizing circuit/ 0f said control relay and rendered efiectiveupon such actuation for inserting apredetermined resistance insai'd trackcircuit, and means includi'ng, a contact ofsaid control relay whichis actuated upon the presence of an excessive voltage across the track circuit for causing said predetermined resistanceto be inserted in said track circuit, whereby the failure of eithersaid control relay'ci'rcuit or an excessive voltage across the track circuit results in" the insertion of a predeterminedresistance in said track circuit.

9; In a track'circuit forrailroads, an insulated track section having a source" of energy con nected across the rails at one end of the section and a track relay connected acrossthe rails'at the other end of the section; a power-operated variableresistor included in" series with the source of energy atthe' end-of said track section at'which said source is located,la control relay having'windings energized-in accordance with the inter rail potential of the track circuit and effective to govern the power-operation of said variable resistor so as to maintain a substantially constant inter-rail potential upon gradual changes in the ballast resistance of the track circuit, and a check relay arranged to attract its armature upon a failure of theenergizing circuit fo'r the control relay, said check relay being ef-" fective upon the" attraction ofits armature for inserting a predeterminedresistance in the track circuit;

1'0'. I n a track eircuitfor railroads in 'combin'a tionwith an insulated section of track and'a source of' energy for supplying currentto the track at one end of the section foren'ergiz'ing a track relay connected to the track at the opposite end of said section, a variable resistor in series with said source ofenergy, electrically operable means for actuating said resistor to varyconnected across the track rail'sand-havingan armature cooperating with the windings of-said electrically operable means closed by said front contact foractuating said variable resistor to in- 7 its resistance, a control relay having windings crease the resistance insaid'track circuit and to said predetermined value, another contact operated by excessive current in said control relay such as would occur if the variable resistor fails to insert added resistance in the track circuit, said another contact when operated under such conditions causing a predetermined resistance to be inserted in said track circuit independently of said electrically operable means for actuating said variable resistor.

11. In a track circuit for railroads having the usual trackrelay connected across the rails of an insulated track section at one end and having a source of current connected across the track rails at the other end of such section, a power-operated variable resistor included in series with said source of energy connected to the track rails, control means responsive to gradual changes in the inter-rail voltage for governing the power operation of the variable resistor to increase or decrease the resistance in the track circuit to obtain a substantially uniform inter-rail voltage with varying ballast leakage conditions, and means operated upon the energization of said control means by an excessive inter-rail voltage such as may exist in the event that the poweroperated resistor fails to respond to said control means, for including a predetermined resistance in series with said source of energy independently of the existing condition of said variable resistor, said means being maintained in its operated condition until manually restored.

12. In a track circuit for railroads having the usual track relay and source of current connected across the track rails of an insulated track section, a variable resistor in series with said source of current at the end of the track circuit at which said source is located, power operating means for actuating said resistor to increase or decrease its resistance, a control relay responsive to variations in the inter-rail voltage of said track circuit and having a movable armature, spring means for biasing said armature towards its retracted position with such force that such armature assumes a neutral position for a predetermined inter-rail voltage, means rendered effective upon the movement of said armature from its neutral position by an increase or decrease in inter-rail voltage above or below said predetermined inter-rail voltage for governing the operation of said power operating means to cause either an increase or a decrease in the resistance of said resistor as the case may be until said armature is restored to its neutral position, contact means responsive to a relatively quick and large movement of said armature as caused by the shunting of the track circuit by a train for preventing operation of said power means, and other contact means responsive to a relatively quick and large movement of said armature as may be caused by the failure of said power operating means to insert added resistances in said track circuit for permanently preventing operation of said power operating means until such other contact means is manually restored.

13. In a track circuit for railroads having the usual track relay and source of current, a variable resistor connected in series with the source of current at the end of the track circuit at which said source is located, power-operated means for actuating said variable resistor and having an operating circuit for increasing its resistance and another operating circuit for decreasing its. resistance for regulating the voltage impressed across the track rails, a control relay having its windings responsive to the voltage applied to the track rails and having an armature biased to a retracted position with such a force as to assume an intermediate neutral position when its windings are energized with a predetermined value of current, two front contacts on said control relay one of which is opened by a small movement of said armature fromv a neutral position and the other of which is opened by a relatively larger movement of said armature from a neutral position with said one front contact governing the operating circuit for said power operating means to cause an increase in the resistance of said resistor and said other front contact eifective when operated for preventing the operation of said power operating means, and two back contacts on said control relay one of which is closed by a small movement of said armature towards its retracted position and the other of which is opened by a relatively larger movement of said armature towards a retracted position with said one back contact gov: erning the operating circuit of said power-operated means to cause a decrease in the resistance of said resistor and the other back contact eifective when operated to prevent the operation of said power-operated means, whereby gradual changes in the inter-rail potential are governed by the operation of said variable resistor to maintain the inter-rail potential substantially constant, and whereby relatively sudden and large changes in inter-rail potential are effective to prevent the operation of said variable resistor from its last operated position.

OSCAR S. FIELD.

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