US2135498A - Railway track circuit - Google Patents

Description

O S. FEELD Nov. 8, 1938.

RAILWAY TRACK CIRCUIT Original F iled June '7,

3 Sheets Sheet l 9 M k j 6 HQ. NS 2% & ww wm h H on o N N 3. I y m m .1 M mm m Y W% ov f U B M B W N E N m Q k NM. WV NV MG MK Fm. N. @Vmr NN F Mk ON. N ON J lu BLJH A W Nov. 8, 1938. o. s FIELD 2,135,493

RAILWAY TRACK CIRCUIT Original Filed June 7, 1935 3 Sheets-Sheet 2 s I cl \l m E q, If I .1 m A e [-59 m .L I]

5 ENVENTOR I a). 5, M,

BY w AZ M I ATTORNEY RAILWAY TRACK CIRCUI T Original Filed June 7, 1935 5 Sheets-Sheec 3 FIG-.5

Tolerabia Train ShunT Resismn 4;

40 Track BailasT ResisTame INVENTOR Patented Nov. 8, 1938 PATENT OFFICE RAILWAY TRACK cmcUrr Oscar S. Field, Rochester, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application June 7, 1935, Serial No. 25,472 Renewed March 2, 1938 14 Claims.

This invention relates to railway track circuits and more particularly to means for maintaining a substantially constant energization of a. track relay associated with a track circuit regardless of changes in inter-rail leakage current due to changes in track ballast resistance and also regardless of changes in potential of the source. of energy for the track circuit. This application is an improvement over my prior application Ser. No. 722,934 filed April 28, 1934, and the common invention between these applications is claimed in said prior application.

In a normally energized track circuit, a track relay is maintained energized when the track section is unoccupied by current flowing from a track battery through the track rails in series,

and it is desirable to adjust this track circuit current to a value which reliably attracts the armature of the track relay, and yet which is sum- 2O ciently low to permit a train offering a maximum oi rail shunting resistance to reduce the energization of the track relay to a degree which reliably releases its armature. However it is found that when the track circuit current is adjusted to a value permitting proper operation under average condition of track ballast, the increased interrail leakage current caused by wet ballast may prevent attraction of the relay armature or the decreased leakage current caused by dry ballast may prevent the release of the relay armature in response to a train shunt. It is also found that abnormal loads, improper charging or the like may cause variations in the voltage of the track battery which act in a like manner to prevent proper track circuit operation.

In view of the above and other considerations, it is proposed in accordance with the present invention to provide means which operates automatically to maintain a substantially constant 4 track relay energization regardless 01' changes in inter-rail leakage current while the track section is unoccupied. It is further proposed to automatically distinguish the increments or decrements of inter-rail potential obtaining during an 45 unoccupied condition of the track section from the more intense or abrupt changes in track relay energization, whereby to allow changes in energization oi the track relay in response to the application and removal of a train shunt and to prevent operation of the automatic regulating means throughout the time in which a train shunt exists on the track section.

Other objects of the present invention include the provision of apparatus in a track circuit reg- 55 ulating means having novel structural features of rugged and simple design providing greater eiliciency, sensitivity and reliability of operation and which are arranged for convenient manual adjustment to permit a greater flexibility of application. 5 Still other objects, purposes and characteristic features of thepresent invention will appear as the description thereof progresses, during which references will be made, to the accompanying drawings, in which:- 10

Fig. 1 shows in a diagrammatic and conventional manner a preferred form of the present invention as applied to a conventional railway track circuit with certain parts of the apparatus shown in section and other parts illustrated in 15 an exploded relation to their structural supports.

Fig. 2 is a sectional elevational view of a portion of a device shown in Fig. 1.

Fig. 3 shows in a wholly diagrammatic manner a modiflediform of the present invention also applied to the conventional railway track circuit.

Fig. 4 shows in a diagrammatic manner a modiflcation which may be made in either the track circuit of Fig. 1 or Fig. 3.

Fig. 5 is a graphic illustration of the operating 25 characteristics of typical track circuits employing the present invention and compared to the usual characteristics of conventional track circuits.

Referring to Fig. 1 of the drawings, a section or 30 track rails 4 is shown divided from the adjacent trackby insulating joints 5 to form aconventional insulated track section. A track relay TB of the type usually employed to control block signals is shown connected across one end of this 5 track section and is normally energized from a suitable source of energy such as a storage bat tery B provided at the other end of the track section. A manually adjustable resistor 6 is, employed in series with the battery B in accordance with the usual practice, and in the present arrangement, a resistor R is also included in series with battery B, which resistance R is provided with a movablearm 1 arranged to shunt out var'ious portions thereof as will later be described in detail.

In the present system, the resistance inserted intothe track circuit by the resistorR is automatically varied by an electro-magnetic means, under the control of a relay which is diagrammatically illustrated as comprising a magnetic core l0 actuating a pivoted armature II, the core Ill carrying windings I! connected across the track rails I as shown. A movable contact I4 is attached to the armature II by an insulating 5 biasing force on the armature ii in opposition to the biasing force of spring i4, and the force of spring i4 is likewise manually adjustable by a screw IS.

The track circuit is adjusted by positioning the manually variable resistor 4 so that a desired energization of track relay TR is produced which obviously causes a definite upward attraction of armature H which has a substantially constant relation to the degree of energization of the track relay inasmuch as the windings i2 are virtually in multiple with the track relay TR. The biasing forces of springs i4 and i4 are then adjusted so that the contact I4 is positioned mid-way between an upper adjustable fixed contact 24 and a lower fixed contact 2|. In other words, the control relay is adjusted so that the force exerted by spring it plus the gravitational bias of armature counter-balances the upward force of spring plus the upward magnetic attraction of armature II when a predetermined current fiows in windings i2.

The lower fixed contact 2| cooperating with the movable contact i4 is illustrated as a pivoted arm biased upwardly by a compression spring 22 to engage a fixed contact 24, the compression spring 22 being adjustable by a screw 23. This arrangement permits the upward biasing force of spring 22 to be so adjusted that a slight decrease in the energization of windings l2 causes a slight downward movement of armature II which engages contact l4 with-the pivoted contact arm 2|, but the force of this downward movement of contact I4 is not sufficient to disengage the arm 2| from the contact 24. However when the energization of the windings i2 is abruptly decreased, such as is effected by a train shunt, the downward force of armature H is sufiicient to move the pivoted contact 2| out of engagement with the fixed contact 24.

The electro-magnetic means employed in the present system to actuate the arm I of the variable resistor R comprises three vertical parallel magnetic cores 21, 2| and 24 which extend through an insulating top plate 44 with their lower ends terminating in enlarged pole faces and having respective nuts 4| threaded thereon, whereby they are clamped on the top plate 20. The upper ends of the cores 21, 24 and 24 are jointed by a magnetic strip 22 clamped thereto by bolts 44, and the two outer cores 2'! and 2| are provided with windings I4 and 44 respectively which are selectively energized in accordance with the position of contact i4 01 the control relay as will be fully described hereinafter.

The pole race at the end of the center core 24 is shaped to present a concave lower surface which is separated by a small air-gap from a solid magnetic cyiinder 4| removably attached to a shaft 4| by means not shown herein. e shaft 4| is rotatably carried by a non-magnetic anger member 42 which is suitably attached to the top plate 3|, which member 42 is shown in Pig. 2 but has been omitted from Fig. 1. One end of the shaft 4| carries a pinion gear 44 suitably attached thereto as shown in Fig. 2 and indicated by dotted lines in Fig. 1, which pinion operates a sector 44 riveted to a shaft 41, the shaft 41 being rotatably carried by a downwardly extending arm 44 which may be integral with the hanger member 42.

Two armatures 44 and 44 are arranged as shown in Pig. 1 to magnetically coact with the cylinder 4| and the pole faces of cores 2! and 2| respectively. These armatures are each shaped .to present a fiat upper horizontal surface coacting with their respective pole faces while a downwardly extending portion is shaped to conform with the curvature of opposite sides oi the cylinder 44, and the extreme lower ends of the armature 54 and 54 are pivotably attached to side members 4| and 42 by pivot pins 44. The side members 4| and 42 are rotatably carried on the shaft 4| at opposite ends of the cylinder 4|, and horizontal extending ends thereof (one end being broken away in Fig. l) carry cross rods 4| extending beneath the horizontal portion of each of the arrnatures 54 and 5|, which cross rod 44 carries an upwardly extending screw 44 threaded therethrough whereby to adjustably limit the downward travel of armature 44 and 54.

The side armature carrying members 4| and 42 are biased to a center position by two oppositely disposed spring strips I4 carried by the hanger member 42 and shaped to normally engage opposite sides of a centering pin 12 fixed to the hanger member 42, to extend downwardly to also engage opposite sides of an operating pin 12 attached to the armature carrying member 4| and extending through a clearance slot in the hanger member 42. Two downwardly extending contact fingers I4 and 14 are clamped to the hanger member 42 by screws H which also hold the centering springs 14, the fingers 15 and 14 being insulated therefrom by insulating spacers l1 and 14. The contact finger 14 is provided with a contact which is engaged by the end of a contact screw threaded through the contact finger 15 when the armature carrying member 4| is in its center position. The lower ends of the centering springs I4 carry insulating blocks I9 suitably attached thereto which engage contact fingers I4 or 14 to separate contacts 44 and 4| when either of the springs N are moved away from the centering pin 12 by a clockwise or counter-clockwise rotation of the armature carrying member 4| about shaft 4|.

The armatures 44 and II are each provided with an inwardly extending metal strip 44-held thereto by screws 44, the strip 4| of armature 44 being arranged to coact with notches in a peripheralring "held in an annular groove in one end of the cylinder 4|, while the strip 44 of armature 54 is arranged to coact with a second ring 44 similarly held on the other end of the cylinder 44 and having teeth oppositely arranged totheteethofthefirstring. 7

It may now be seen that energization of the winding 24 around the core 21 produces a fiux therein which fiows through the center 'core 2|, through the magnetic cylinder 44 and through armature 54, thereby first attracting the lower portion of armature 44 toward the cylinder 4!] to engage the strip 44 with the teeth or the associated ring 44 and then attracting the outer end of armature 5| upwardly toward the pole face of core 21 which rotates the cylinder 40 in a clockwise direction. It 'will also be clear that the energization of winding 44 will in a similar manner first attract armature 4| toward the cylinder 4| thereby engaging its strip 44 with the teeth of the ring on the other side of the cylinder 44 and the following upward travel of the outer end of armature II causes a rotation of the cylinder 45 in a counter-clockwise direction. During the return travel 01 armatures l5 and 55, the initial movement is away irom the cylinder 45 thereby withdrawing the strip 55 from the teeth of the associated ring 55 so that the following downward movement does not rotate the cylinder 45. I

During the above operation either armature 58 or 59, the' pin 18 is operated either to the left or to the right which disengages contact 85 from contact 8| as previously described which opens a common portion of the energizing circult for both coil 35.and coil 35 as will be obvious from the circuit arrangement shown in Fig. 1. In order to permit the armatures 58 and 59 to complete their travel after the energization of their associated coils is thus interrupted, a. sleeve 14 of non-magnetic current conducting material is provided around the center core 28 which acts in the usual manner to retard any change in flux value therethrough. It will then be clear that after the energizing circuit for coils 85 or 35 is interrupted by the initial movement of armature 58 or 59, the flux value in the magnetic structure decreases slowly and continues to attract the armature which, together with the momentum imparted to the armature during the energization of its associated coil, is effective to complete its upward travel.

When the attracted armature has completed its upward travel, the flux in the magnetic circuit has decreased to a value permitting the associated biasing spring 15 toreturn the armature assembly to its center position. It is of course obvious that the energizing circuit for coil 85 or 85 is again completed through contacts 55 and II before the armature assembly reaches its center position, but the sleeve 14 is again effective to retard the building up of, a flux in the magnetic structure to a value which is sufllcient to overcome the biasing force of springs 15 until the armature assembly has reached-a center pomtion.

It may now be seen that the energization of either coil 35 or attracts the associated armature upwardly whereupon a common portion of the energizing circuit for both coils is interrupted allowing the attracted armature to return to its original position [after which it is again attracted and released as before, and this operation of one oi the armatures 58 or 55 continues as long as coil 55 or 56 is selected and energized by its external control circuit. In other words, the energization of coil 35 causes an oscillating motion of armature 58 which imparts intermittent rotation to cylinder 45 in a clockwise direction, while the energization of coil 35 causes an oscillation of armature 55 which imparts intermittent rotation to cylinder 45 in a counter-clockwise direction.

The specific contact arrangement illustrated for the purpose of causing oscillatory motion of the armature assembly has been selected merely because of its simplicity, and it is desired to be understood that other contact arrangements may be employed. For example, a contact arrangement having an asymemtric operation may be provided to maintain the coil energizing circuit closed during the major part of the upward armature travel but to hold the circuit open during the major part of the return travel.

The arm I which coacts with the resistance wire R is shown in Fig. 2 as made up of two spring strips having the upper ends thereof separated to form a bifurcation contacting with opposite sides of the resistance wire R which may be wound around a suitable insulating strip 58 having an oval cross section as illustrated. The ends or the resistance wire it are anchored to terminal screws 55, and the insulating strip 55 is mounted beneath the top plate 55 by suitable brackets 54. I'he lower end of the arm 1 is suitably attached to an insulating member 45 which is in turn mounted upon the sector 45 by screws 55 and spacers II. It will then be clear that a clockwise rotation of cylinder 45 as effected by energization of winding 35 rotates the sector 45 in a counter-clockwise direction through pinion gear 43, thereby moving the arm 1 nearer to the left-hand end of resistance-wire R, and conversely a counter-clockwise rotation of cylinder 45 as efiected by the energization of winding 35 rotates the sector 45 in a clockwise direction to move the arm 1 nearer to the right-hand end of the resistance wire R.

It is found expedient for reasons later to be brought out to adjust the variable components of the present track circuit to provide proper operation under the wettest condition of the track ballast which is expected to obtain on the particular track circuit. In other words, when the interrail leakage current is at substantially its maximum value, these adjustments may be made by positioning the arm I' of the present resistance adjusting means near the right-hand end of resistance wire R, such as the position shown in Fig. 1, thereby shunting the major part of resistance R from the track circuit, and adjusting the manually variable resistor 5 so that a proper voltage is obtained across the track rails 4.

The proper inter-rail voltage must of course be a predetermined value which reliably picks up and retains the armature oi the track relay TR when the track section is unoccupied and yet which permits a train offering a maximum rail shunting resistance to eflect the release of the relay armature. The previously described adjustment of the control relay is now made so that with this proper inter-rail voltage across windings I2, the armature'li assumes an intermediate position wherein contact i4 is midway between contacts 25 and ii.

In order to describe the operation of the automatic regulating means, it will'flrst be considered that the ballast resistance increases due for example to the drying of the ballast between the track rails 4 so that the inter-rail leakage current decreases. This decreases the current flowduces the voltage drop therethrough which raises the inter-rail voltage oi the track circuit and likewise the energization of windings i2. This de-' crease in inter-rail leakage current occurs of course rather slowly but the increase in energization of windings I! caused thereby soon reaches a sufllcient value to upset the rather delicate adjustment of armature ii, that is a slight increase in the magnetic attraction of armature il plus the biasing' force of spring i5 is sufilcient to overcome the force of spring i8 thereby operating contact i4 into engagement with fixed contact 25. The winding 35 of the resistance actuating means is nowenergized over a circuit from the lower terminal of a suitable battery i5, through con- 55, through contacts 85 and 8i and back to the upper terminal of battery is.

The energization oi! winding 35 causes oscillation of armature 58 in the manner previously de-.

tact l4 engaging contact 25, through the winding.

50 ing through resistances 5 and R and slightly reof armature ill continues until the resistance inserted into the track circuit by the variable resistor R is increased to a value which reduces the inter-rail potential to its originally adjusted proper value. This proper value oi energization of windings I! obviously restores the balance of the forces acting on armature ll so that contact ll again assumes its center position which de-energizes winding 35 to stop the operation of arm I Now considering that the conductance of the comparatively dry ballast is increased by rain or the like, it will be clear that an increased ballast leakage current occurs which fiows through the increased resistance inserted into the track circuit by variable resistor R. A slight reduction in the inter-rail potential then occurs which reduces the energization of windings I2 to a degree allowing the biasing spring is to overcome the reduced magnetic attraction of armature ll plus the force of spring It and thereby cause a movement of the contact ll into engagement with contact 2|. In this case, the armature II is responding to a rather small decrement in the energization of windings l2 and the downward force of contact H is not sufiiclent to disengage the pivoted back contact II from the fixed contact 24, and an energizing circuit for winding II is completed from the lower terminal of battery It through contacts ll, 2| and 2, through the winding 36, through contacts "I and BI to the upper terminal of battery It.

This energization of winding II now causes armature 59 to oscillate as previously described which rotates the cylinder 40 in a counter-clockwise direction, thereby moving the arm I back toward the right hand end of resistance R to decrease the resistance inserted thereby into the track circuit. This oscillation of armature 58 also continues until the resistance has been sufilciently lowered to raise the inter-rail potential to its originally adjusted value thereby restoring the balance of forces acting on armature l I so that contact I4 is returned to its center position to de-energize winding I8 and stop the operation of arm I.

In the present system, the value of the resistance inserted into the track circuit by the variable resistor R may be changed much more rapidly than changes in ballast leakage current can possibly occur, and consequently the regulating means will not operate continuously during any very definite change in ballast leakage current, but rather the regulation will occur in short cycles during the total continuous change in ballast resistance. In other words, the time required for a degree of ballast change to occur which is sufilcient to move the control relay armature H out of its center position is considerably longer than the time required thereafter to actuate the resistance arm I to a new position which compensates for this change, and consequently the regulating means never allows ballast changes to cause an increase or a decrease in the energization of windings I! which exceeds that required to Just engage contact I with either contact 20 or II.

It may now be seen that the present track circuit regulating means maintains a constant inter-rail voltage, aside from the small waves of voltage change necessary to efiect the control of the regulator, regardless of changes in interrail leakage current. The degree of voltage change necessary to initiate operation of the means compensating for such change is determined by the sensitivity of the control relay, and

it seems that the waves caused thereby in the otherwise constant voltage are not detrimental as long as their magnitude does not approach the degree 0! change necessary to cause operation or the track relay.

The system shown'in Fig. 1 also maintains the inter-rail 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 force of springs It and II on the armature Ii provides a definite standard unatiected by variable conditions of the track circuit, to which standard the inter-rail voltage or the energization of windings I2 is related thereby permitting any gradual change in inter-rail voltage regardless of its cause to effect operation of the regulating means. It is further obvious that this definite standard to which the inter-rail 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 most regulator operation.

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 inter-rail voltage ei'lected by the train shunt and hold the armature oi the track relay in its energized position thereby defeating the purpose of the track circuit. In the present arrangement, the entrance of a train into the associated track section shunts the track rails l to cause an abnormal increase in voltage drop through resistances l and R and a consequent decrease in voltage drop through windings it, which reduces the energization of windings I! 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 energization of windings I! caused by the train shunt greatly reduces the normal attraction of armature H thus allowing the force of spring I. to exert a downward force on the pivoted contact 2| through contact II which overcomes the force of spring 2! thereby disengaging contact II from contact 24.

In this manner, it will be obvious that the present system differentiates between a reduction in inter-rail voltage due to increased ballast leakage current from a reduction due to a train shunt in a manner to prevent the energization of winding ll oi the regulating means as long as the train shunt exists on the track circuit. In other words, the downward force of armature II is determined by the degree of reduction in the energization of windings I 2, and as previously described, the reduction in energization of windings I 2 due to increased ballast leakage current occurs so slowly that the regulator is able to prevent a reduction in excess of that required to just engage contact I4 with contact 2|, but the abrupt reduction in energization of windings l2 due to a train shunt distinguishes therefrom by causing an excessive downward force of armsture II which is effective to move contact 2| downwardly and open the energizing circuit for winding 80 before the regulator can effectively operate.

In the modified form or the present invention shown in Fig. 3, the track circuit is illustrated in substantially the same form as in Fig. 1, that is,

a track battery 3 normally supplies current through the manually variable resistor and the automatically variable resistor R to the track rails 4 and energizes the same track relay TR.

magnetic resistance changing means in Fig. 3,

however, comprises a control relay including a polarizing magnetic structure illustrated as a general U-shaped permanent magnet 83, or oi course a continuously energized electro-magnet could be used as well. The lower end of a soft iron armature I4 is coupled magnetically and pivotably attached to the center of the permanently magnetized structure 80, while the upper end of armature 44 extends between inwardly extending poles N and S at the upper end of the structure 83. A winding 85 is arranged around the armature 84 and connected across the track rails 4 while a second winding l6 also around the armature I4 is connected in multiple with the manually variable resistor 6 and the automatically variable resistor R through a second manually adjustable series resistor 81 as shown.

,The track circuit is adjusted in Fig. 3 in the same general manner as in Fig. i, that is, under the wettest ballast condition, the resistance arm I is positioned to the righthand end or resistance wire R to insert a minimum resistance into the track circuit, and the manually variable resistor I is adjusted to provide the proper inter-rail voltage which is found to provide reliable track circuit operation. The windings 85 and 88 are oppositely wound around the armature 44, and with this proper inter-rail voltage across winding ll,

the manually variable resistor 81 is adjusted so that the energization of winding it produces a flux which neutralizes the flux produced by winding ll. 1

Twocompression springs 88 and I! are provided on opposite sides of the upper end of armature 04, which springs are individually adjusted by respective screws u so that when the energization oi windings II and I. are balanced to provide equal and opposite flux values, the armature I4 is positioned midway between the poles N and S or the permanently magnetized structure It. With the armature 84 in this position, a contact 9| attached to the upper end.thereoi by insulating connectors 92 is positioned midway between a fixed contact 03 and a pivoted contact !4, the contact 84 being arranged in a similar manner to contact 2| in Fig. 1, that is, a compression spring ll adjustable by screw 80 biases contact 94 against a fixed contact 91.

Considering now that the ballast leakagecurrent decreases in Fig. 3, it will be clear that the voltage drop through resistances 8 and R decreases thereby slightly decreasing the energization of winding 88 while the inter-rail voltage and the energization of winding 45 slightly increases. thereby upsetting the flux balance in armature 44 and allowing the predominating energization of winding ll to produce a flux attracting the armature l4 toward pole N of the nagnetic structure II. This operation of armaure '4 engages contact Ii with contact I; which :ompletes an obvious energizing circuit for windng 44 thereby causing oscillation oi. armature II and moving arm I toward the leit hand end 0! resistance wire it in the same general manner as described in connection with Fig. 1. This oscillation of armature ll continues until the resistance inserted into thetrack circuit by resistance R has been increased to a value which reduces the inter-rail voltage to its normally adjusted value, thereby restoring the balance between the energization of windings 85 and 86 which returns contact 9! to its center position and stops move ment of arm I.

An increase in ballast leakage current however causes an increased voltage drop through resistances 8 and R which increases the energization of winding 84 but decreases the energlzation of winding 85, due to a decrease in the inter-rail voltage of the track circuit. This unbalances the energizationof windings 85 and 86 and the predominance of winding 86 now-produces a flux in the opposite direction than the flux previously considered during the predomi nance of winding 85, so that in this case, armature i4 is attracted toward pole S of the magnetic structure". The contact 0| now engages contact 04 which completes an obvious energizing.

circuit for winding" which causes oscillation of armature I! and moves the arm I back toward the right hand end oi resistance wire R. Likewise this oscillation of armature II continues until'the resistance inserted into the track circuit by resistor R has been decreased to a value which increases the inter-rail voltage to its normal adjusted value, thereby restoring the balance between the energization of windings l5 and l! to return armature 44 to its center position and stop the movement of arm I.

The action of the re ulating means in response to a train shunt on rails 4 in Fig. 3 is very similar to that described in connection with Fig. 1, that is, the present regulating means prevents the occurrence of a decrease in inter-rail voltage in response to ballast changes which exceeds that required to produce the rather small unbalance in the energization otfwindings N and I8 necessary to just move contact Oi into engagementwith contact 04, but theabrupt increase in voltage drop through" resistances I and R caused by a train shunt produces an abnormally high degree of energisatio'n of winding 08 and an abnormally low degree of energiaation of winding 85. This produces'such an unbalance in the energization of windings I and I! that contact 9| forces contact M away from contact I! and prevents operation oi the resistance changing means as long as the train shunt exists onthe track circuit.

It will now be clear that each of the illustrated forms of the present invention operates to compensate for small increments or decrements in inter-rail voltage which are due to changes in ballast resistance. but distinguishes therefrom the abrupt decrease in inter-rail voltage caused by a train shunt in a manner to prevent compensation for the voltage decrease across the track rails caused by a train shunt. In this manner, a substantially constant energization of the track relay is maintained when the track section is unoccupied so that the decrease in inter-rail voltage caused by a train shunt, which is prevented from causing operation oi the voltage regulating means, can reliably effect the release of the armature of the track relay regardless oi ballast conditions;

In making the manual adjustments oi the track circuit, it was previously stated that these adusualtypeoitraokcirouit.

' Fig. 4, the

"attracted. a secondary relay 8'! iustments should ballast conditions ance inserted into matically variable resistor ments areproperiymsdeundertheabove tions so that reliable track drcuit niltaitisioundthatbytheuseoithe regulating means, a great tactor oi safety in responseoithetrackrelaytoatrainshunt provided as the ballast dries out. In other words, when the track rails are shimted by a train, the voltage drop from rail to rail acrou shuntmustbesolowavaluethat rile Proportional increase in resistance of a track shuntandstillprovidethelowvoltagedroptherc-. across whichisrecmiredinordertoreleasethe armature of the track relay. Therefore, it reliable response oi the track relay is obtained during the wettest ballast condition, an even greater assurance of reliable response is provided by the sents the relaflon oi the maximum resistancewhichlstqdropa afar gi s riiiiialii i i ae trackcircuittodetectatrainshimtdecreasesas, theballastdrieaoutascomparedtotheincreased reliability provided by the present system.

trectthe armatureotaprimaryrelayPltrom itsreleasedpositionissuppliedbythenormal trackcircuiteurrentflowingthtoillhallofits windingabutatter thearmatureoirelayl'lis isrleked &

masses through a front contact II which substitutes a substantially equivalent resistance Ill tor a portionoithewindingoirelayP'rbyamakebeiore-break contact OI. thereby supplying a reducedmagnetornotiveiorcewhichismflicientto .retain the armature of relayP'Iin its attracted position.

ibis track relay combination shown in Hg. 4 maybe arrangcdtodropawayatnearlythesame energizing voltage that is suiiicient to pick up its armature and consequently, it will be clear that when the normal inter-rail voltage is properly adjusted. a rather slight reduction in interrailvoltagecancausearesponseoithisrelay mmbinatlon. Consequently when the arrangement shown in Hg. 4 is employed in combination with the present voltage regulating means shown in Fig. 1 and Fig. 2, the shunting sensitivity is still further improved so that the relation oi the maximumtrainahuntruistancewhichisable todroptherelaycombinationini'ig.4tovarious trackballastreaistance valuesisrepresentedby curveBinl'igt. Theadvantageoiemploying.

the voltage regulating means of the present invention in combination with the track relay arrangement oi Pig. 4 is graphically illustrated in Fig.5bytheoomparisonotthiscurve8witha dotted curve B which represents the shunting sensitivity of a primary-secondary track relay combination in a conventional track circuit without the present automatic voltage regulating meana In describing the praent invention, attention has only been directed to the illustrated embodiments thereof, without attempting to point out the various alternate or optional features of construction, or the diiierent organizations or combinations that may be employed. For example, the specinc oscillating armature meam illustrated for moving the resistance arm in either oitwodirectionsisonlyonetypeolmotormeans which may be used to'advantagein the present system,anditistobeunderstoodthattheeontrolmeansshownineitherl'ig.lorl'ig.3may beucedlnaveryobviousmannertoselectively control the operation and the direction oi rotationotasmalleiectricmotoroitheusualtype connectedthroughsuitablegearstomovethe armlotthevariableresistornintherequired direction.

Inotherwordatheparticularembodimentso! I the present invention have been selected to lacilitateinthediaclosurethereoiratherthanto limit the number of iorms which it may assume.

What I claim is:-

l. In combination; a track circuit including a section of railway track, a track relay, asonrce otenergyandavariablereaistorallconnecledin series; a control relay energised in constant proportion to the energinatlon oi the tract relay; biasing means adjusted to hold the armature o! the control relay in a definite center position at a predetermined degree or inter-rail voltage; an

actuating means for the variable resistor distinctively controlled by relatively small movements 0! the control relay armature in each direction from said center position; and means [operated by a greater movement 0! the control relay armature in one direction from said center positim [or preventing operation of the variable resistor ni's track circuit having a section of track rails, a track relay, a source of energy and a variable resistor all connected in series; the comv bination oi; a reversible electric actuating means 1 means for the variable resistor; a control relay connected across the track rails; biasing means centearing the armature or the control relay when a predetermined voltage exists across the track rails: control contact means arranged to selectively control the direction of operation of the electric actuating means in accordance with the direction 0! a relatively slight movement of the control relay armature irorn said center position;

and a contact means arranged to prevent operation oi the electric actuating means by the movement of the armature of the control relay a relatively larger distance from said center position.

3. In a track circuit having an insulated track section, a track battery and a variable resistor I all connected in series; the combination of; an electro-magnetic actuating means for the variable resistor; a polarized control relay having'an armature biased to a center position: a first winding connected across the rails of the track section and arranged to actuate the armature oi the polarized relay in one direction; a second winding connected across the variable resistor and arranged to actuate the armature of the polarized relay in another direction, said armature responding to its bias and the energization of said windings to assume its center position it a predetermined inter-rall voltage exists, contact means distinctively operated by relatively slight 80 movements oi the armature of the polarized relay in either direction from its center position in response to variations in ballast resistance to cause operation oi the variable resistor actuating means to increase or decrease the resistance of said resistor to restore said armature to said center position: and means operated by a relatively large movement of the armature of the polarized relay in response to shunting oi the track circuit by a train for preventing the contact means from causing operation of the variable resistor actuating means.-

4. In a track circuit, an insulated track section, a track relay connected across one end of" the track section, a track battery connected across the other end of the track section, a variable resistor in series with the track batteryto the track section, a polarized relay. having one winding connected across the rails of thetrack section and an oppositely arranged second wind- ,1

ing connected across the variable resistor, an armature on the polarized relay biased to a center position and operable in either direction therefrom by a predominance in the energization of one or the other oi said windings, an electro-' magnetic actuating means for the variable resistor distinctively controlled in accordance with a relatively, small movement of said armature in either direction from said center position in response to changes in ballast resistance, and means 00 operated by a larger movement of said armature from said center position in response to shunting of the track circuit by a train for preventing operation of the actuating means.

5. In a track circuit, an insulated track sec- \than, a source 01' energy connected across one end of the track section, a primary track relay connected across the other end of the track section, a secondary track relay controlled by the primary track relay, means operated by the secondary 7o track relay for regulating the magnetomotive force of the primary relay,-a rheostat connected in series with the source of energy, electro-magnetic operating means for the rheostat, a control relay connected across the track section, a first contact means on the control relayior controlnected acrosssthefitracklmilt ling the electro-magn'etic operating means in accordance with smaller changes in energization oi the track section than can cause operation oi the primary track relay, and a second contact means" on th' control ,zreiayw-l iorpreventing operation or v s the m amstins aia tsb i i to a cnangeinrenersizatlon 0M track sect j'ii which=-can:causc-'operation ,th rimar tr 1:" Q relay,

6. In rack-:ciscuitgto r tion Wlthi.-8.!l'2:i1h5li1flti1 source o'i' lenergy ionsupplying relay throughathe railswoi' said, resistor miseries-With. said. source trically operableiineansiior a tua tor to varyq its gresistance, a out 1 re ture moved from; tion by a gradual decrease in inter oi the track circuitibelovnaf lpnadet, as caused byvvariationarin ballast armature beingtimovedrzfizonwruch; N eutrai ticn in the other: direction yi miincreasein in rail VOItaQG IbOVGFJ'SUAhYL' YHlIG "0 33 9 operating withtsaid armaturm ation of saidatel'eetrioallyia 7. In a track circuitsior raumssinsvlneitne" usual track relama'nfl-asourne oi.-:. acurrent;.; ,con;-

, nected across the tract: railsna yariablerresiston in series with saidisouroeil'ois-currentlin thelcon nections between sachz-source landrthettracktrails; power means iomactuating: said; tesistorjgtoginr l0 crease or decreaseits resistancet a r-control re a responsive to variations w-theizintcr -rail zvoltage of said track circuit- "d iringl a-gmovableqarmature, spring rneani zior wiriasingrsaidsarmature toward its retracted "flositionxwith such-force that "it said armature assumes a neutral position {or a predetermined inter railfyoltageiwmeans rendered elective upon movement -:oi:,:said armatureg from its neutral'positlon by arr'increase ornecreasein the inter-rail voltage rahovefzia'nd lbelowr-rtflldw. i determined value iomgoverningwthei-operation oi said power means to causeseith'enanaincreaseiorwa decrease in the resistanclioi 'saidiresistortaszthe case may be until saidarmature is .restoredito the g neutral position, and means? responsive tosaxelasg tively quick and large movementlot s'aid-aarmature caused by the shunting ot,athestrackicircuitby;a train for preventing .operatiom Ofslf881d -;-,-;power means and a change ofsaldnraakton from ti e, condition existing at the shuntgis" so applied.

8. In a track circuit for railroadsxhaving' the usual track relay and souroeoi". currentzav variable resistor in the connectiohs-zbetweenilsaid source and the track rails for regulating ithe inter railgs voltage produced by said 'sourcelunderedlfleitnt ballast conditions, a power -idevice operahle $.01! crease or decrease the resistance:of-saidwresistor at a relatively slow rate, andrcontrolcmcanafor governing the operation oisaidapoweridevice com 7o prising, a winding connected across the, track rails,

a spring biased movable elementtmovahle in; one direction or the other from aneutralspos'ltionrby an increase or decrease in the 'currentrinqsaid.

winding above or below a predeterminedvalue in response to an increase or decrease in the particular inter-rail voltage which provides the proper operating current ior the track relay. contact means co-operating with said movable element to cause operation oi said power device and increase or decrease the resistance of said resistor as the case may be until said movable element is restored to its neutral position, and contact means co-operating with said movable element and responsive to a relatively and sudden large movement thereof caused by theshunting of the track circuit by a train for preventing operation of said power device and a change of said resistor existing when a train enters the track circuit.

9. In a track circuit for railroads having the usual track relay and source of current, a poweroperated variable resistance at the iced end of the track circuit in series with said source for regulating the voltage impressed across the track rails from said source, said variable resistance having an operating circuit for an increase in its resistance and another operating circuit for a decrease, a control relay having its winding contrack rails at the feed end of armature biased to a neutral position which it assumes for a predetermined said winding, front and back contacts associated with said armature and respectively closed by its movement from its neutral point in one direction or the other for energizing one or the other of said operating circuits to actuate said variable resistance to increase or decrease its resistance as the case may be to restore said armature to its neutral point, and contact means opened by a relatively quick and large movement of said armsture toward its retracted position such as would be produced by the shunting oi the track circuit by a train for breaking both of said operating circuits and preventing operation of said resistance device.

10. In a track circuit ior railroads, in combination with a source of current ior supplying voltage to the track circuit, a variable resistor included in series with said source for regulating the voltage impressed across the track rails from said source, said resistor having an element movable in opposite directions to increase or decrease its resistance, a power device for actuating said element of said resistor, operating circuits for said power device one for each direction of movement of said element, and control means for said power device comprising, a control relay of the tractive armature type having its winding connected across the track rails at the feed end of the track circuit, adjustable spring means tending to move the armature or said relay in opposite directions from the neutral point at which said armature is positioned when a current of a predetermined value flows in said winding, front and back contacts actuated by the movement of said armature from its neutral position for energizing one or the other of said operating circuits to cause a change in the resistance of said resistor to restore the predetermined value of current in said winding, and contact means operated by a relatively sudden ahd large movement of said armature from its neutral position in response to the shunting oi the track circuit by a. train for opening both of said operating circuits to prevent a change in said resistor when a train enters the track circuit.

11. In a track circuit (or railroads. a poweroperated variable resistance in series with the lating the voltage impressed the track circuit,

in the condition circuit for reguacross the track rails from said source, a control relay oi the tractive armature type having its winding connected across the track rails at the feed end oi an adjustable spring acting to move the armature oi said relay toward its retracted position, said armature in response to the iorce exerted by said spring and an energizing source of current for the track current of a predetermined value in said winding assuming a neutral position, front and back contacts closed by movement 01 said armature irom its neutral position in response to changes in ballast resistance ior governing the operation of said variable resistance to increase or decrease its resistance as required to bring the current said predetermined value, yleldable biasing means opposing movement oi said armature irom its attracted posltion beyond the point at which said back contact is closed, and contact means operated by the movement of said armature in opposition to said biasing means and in response to a large decrease of current in said winding as would be caused by the shunting oi the track circuit by a train for rendering the closing 01 said back contact ineffective to govern said variable resistance.

12. In a track circuit for railroads having the usual track relay and source of current, a poweroperated variable resistance device ior regulating the voltage impressed across the track rails from said source, a control relay oi the tractive armature type having its winding connected across the adjustable springs acting upon the armature 0! said relay in opposite directions, said armature in response to the forces exerted by said springs and an energizing current of a predetermined value in said winding assuming a neutral position, a front contact closed by attraction of said armature from its neutral position by an increase in said energizing current for said predetermined value, a spring biased movable back contact closed by a small movement of said armature irom its neutral position toward its retracted position in response to a decrease in the energizing current through said winding for causing operation of said resista ce device to decrease its resistance until the current through said winding is restored to said predetermined value, and means associated with said back contact and responsive to a movement thereof in response to a sudden and large decrease in said energizing current as would be caused by the shunting of the track circuit by a train for rendering the closing of said back contact ineflective to govern the operation 0! said resistance device.

13. In a track circuit for railroads, a regulating device for maintaining substantially constant inter-rail voltage at the feed end of the track circuit irrespective of variations in ballast resistance comprising, a power-operated variable resistance device having operating circuits acting when respectively energised to increase or decrease the resistance of said device gradually, as control relay connected across the track rails at the feed end of the track circuit and including an armature spring biased to a neutral position when a predetermined inter-rail voltage exists, a contact finger carried by said armature for engaging a front contact to close one of said operating circuits when said armature is attracted beyond said neutral position in response to an II inter-rail voltage greater than said predetermined value. a pivoted back contact engaged by said contact finger to close the other of said operating circuits when said armature moves beyond its neutral position in response to a decrease in said inter-rail voltage, an adjustable ilxed contact engaging and limiting the movement of said pivoted back contact to a position out of engagement with said contact arm when said armature is in its neutral position, a spring pressing said pivoted back contact against said fixed contact with a predetermined pressure, said pivoted back contact being moved out of engagement with said fixed contact by movement of said armature in response to a sudden and large decrease in inter-rail voltage as would be caused by the shunting oi the track circuit for opening said other operating circuit controlled by said back contact.

14. In a track circuit. an insulated track section, a source of energy (or the track section, a

variable resistor connected in series with the source of energy to the track section, a magnetic rotor operably connected to the variable resistor, electro-magnetic step-by-step means for selectively imparting intermittent rotation 01' said rotor in either direction, electro-responsive means connected directly across the track rails and responsive to gradual changes in the inter-rail potential for controlling said electro-magnetic means to adjust said variable resistor to maintain a substantially constant potential across the track rails to compensate for gradual changes in inter-rail resistance, and a contact operated by said electro-responsive means and opened upon a sudden drop in said inter-rail potential due to the entrance of a train into said track section for preventing operation of said electromagnetic means and adjustment of said variable resistor during the presence of a train in said track section.

OSCAR B. FIELD.

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