US2235525A - Railway traffic controlling apparatus - Google Patents

Description

March 18, 19 1- .1. w. LIVINGSTON RAILWAY TRAFFIC CONTKOLLING APPARATUS Filed Sept. 7, 1939 w WE 0 5 .III .6. F W m Om m 1 5 M w 1--- 9 w m. a m Tm My. a 2 5T 5 2 Z J V n a Z J 4 5- 5. 8 2 -J T. 4 6 WW 2 1 a 5 Z 2 40 IF w l T 2 1 2 3 5 r f 5 2 4 P B w 8 2 ,4 I 2 1 Ha 3 6 0 5 J l w H16 ATTORNEY Patented Mar. 18, 1941 umreo STATES RAILWAY TRAFFIC CON TROLLING APPARATUS John W. Livingston, Forest Hills, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 7, 1939, serial No. 293,783

7 Claims.

My invention relates to railway traffic controlling apparatus, and has particular reference to the organization of such apparatus into railway traffic controlling systems of the class in Which control of a railway trafiic controlling device is established by trailic conditions in a selected stretch of track independently of track circuits.

It has heretofore been proposed to govern traffic controlled relays by trafiic conditions in a stretch of track independently of track circuits through the medium of a light source and a light responsive device arranged to co-operate therewith in such manner as to be responsive to trafiic conditions in the stretch. Such light responsive devices generally control electronic tubes, which function as amplifiers for the associated devices and control one or more relays of'the usual tractive armature type. An object of my invention is the provision of novel and improved means whereby the electronic tubes may be employed as relays in systems of the above type, thereby avoiding the use of relays of the tractive armature type.

Another object is to provide novel and improved means for selectively controlling a control device in accordance with the control established by trafiic conditions upon relays of the electronic type.

A further object is the provision of means which provides a railway traffic controlling device with a detector track section having the shortest practicable dimensions.

An additional object is the provision of novel and improved means to enable a control lever to control a railway traffic controlling device to a position of correspondence under certain traffic conditions adjacent the device, but to remove the lever from control of the device under other traffic conditions.

Another object is to provide novel and improved means to at times automatically hold the control device in a position of non-correspondence with the control lever.

A further object is to provide novel and improved means in systems of the above type for displaying an indication when and only when the position of the control device corresponds with the position of the lever.

Other objects and advantages of my invention will appear as the description proceeds.

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

The accompanying drawing is a diagrammatic view showing a preferred form of apparatus embodying my invention as applied to the control of a railway trafiic controlling switch.

Referring to the drawing, the reference character W designates a two-position railway traflic controlling device associated with a stretch of railway track X. Device W, as shown, may be a railway track switch movable between a normal position and a reverse position by means of a suitable switch mechanism, designated by the reference character SM. Mechanism SM is illustrated diagrammatically as direct acting switch movement having a pneumatic motor, but it is contemplated that other types of motors, as for example an electric motor, may be employed if desired.

Switch mechanism SM has associated therewith a normal valve magnet NV and a reverse valve magnet RV, it being understood that When normal magnet NV is energized, switch W is operated to its corresponding normal position, and that when reverse magnet RV is energized, the switch then is operated to its corresponding reverse position.

The reference character J designates a switch circuit controller operatively connected in the usual manner with switch W. Circuit controller J comprises six movable contact members I, 2, 3, 4, 5 and 6, each movable between a normal position and a reverse position. Contact membersl to 5, inclusive, of controller J are con-- trolled by the position of switch W in such manner as to be operated to their normal positions (in which they-are illustrated in the drawing) at the mid-stroke position of the switch when the switch is being operated to its normal position, and are operated to their reverse positions at the mid-stroke position of the switch when the switch is being operated to its reverse position, In the normal positions of contact members l-5, the members engage fixed contact members I, B, 9, l and II, respectively, to form contacts 1-4, 2-8, 3-9, 4-40 and 5l i. In the reverse positions of members 1-5, fixed contact members l2, l3, I4, l5 and I6, respectively, are engaged by contact fingers l-5 to form contacts ll2, 2l3, 3-14, l l5 and 5-l6.

Movable contact member 6 of controller J is controlled by the position of switch W in such manner that member 6 is operated to its normal position to engage a fixed contact member I! and form contact 6ll when and only when the switch occupies its full normal position, and member 6 is operated to its reverse position 'to engage a fixed contact member l8 to form con-- tact 6l8 when and only when the switch occupies its full reverse position.

The reference character E designates a manually operable two-position control lever, which may, for example, be a switch control lever of an interlocking machine. Lever E i operable be tween a normal position N and a reverse position R, and is provided with contacts I9, 20, 2| and 22, which are selectively closed in accordance with the position of the lever, the positions in which the contacts are closed being designated in the drawing by the reference characters designating the position of the lever. For example, contacts I9 and 2| of lever Ei each bear the reference character N, indicating that contacts I9 and 2i are closed when and only when lever E is in its normal position N. Similarly, contacts 22 and 22 of lever E each bear the reference character R, indicating that contacts 20 and 22 are closed when and only when the lever is in its reverse position R.

Associated with lever E are two indication lamps KN and KR, the function of which will be made clear presently.

Lever E and controller J cooperate to control suitable static relay means for controlling the operation of switch W. As herein shown, the relay means comprises two electronic tubes TI and T2, one tube Tl of which is controlled under certain traffic conditions adjacent switch W to be conducting and thereby enable switch lever E and switch circuit controller J to cooperate in controlling the operation of switch mechanism SM to cause the switch to be moved to its position of correspondence with the lever. The other tube T2 is controlled to its conducting condition by other traific conditions adjacent the switch to prevent switch mechanism SM from operating switch W to its position of correspondence with the lever in the event that non-agreement exists between the switch and the lever under the latter traffic conditions. Tubes Ti and T2, as shown, are threeelement tubes each having two main electrodes, an anode or plate 23 and a cathode or filament 2'4, and a control grid 25 sealed within an envelope 26. Preferably, the envelope 26 of each tube TI and T2 is filled with a suitable medium, such as neon gas, which forms a conducting path between the two main electrodes when and only when the potentialbetween these electrodes exceeds a value which depends upon the relative potential of the grid with rspect to one of the electrodes. Tubes Ti and T2 further are characterized by the fact that for a given plate potential, each tube is caused to operate and pass current only when its anode is positive with respect to its cathode.

The above-mentioned control of tubes TI and T2 by trafiic conditions adjacent switch W is established by means of light-responsive devices, designated by the reference characters P with suitably distinguishing sufiixes, and their associated sources of light, which are designated by the reference characters S with suitably distinguishing sufiixes. As shown, two sources S (which preferably are constantly illuminated electric lamps) are located spaced apart along the stretch of track X adjacent switch W, each source directing its beam of light across the rails of the stretch to thereby define a detector track section for the switch. Source Si preferably is positioned to project its beam over the heel of switch W. Located on the other side of the track in the path of the beam of source SI is a reflecting prism, designated by the reference character H with a suitably distinguishing suffix, which splits into two parts the beam of source SI, and projects one part of the beam or the other to one or the other of two light-responsive devices PI and P2 associated with source SI.

Source S2 is located in advance of the points of switch W, and is positioned to project its beam across stretch X so that, in the event that an operation of the switch has been initiated just prior to the beam of source S2 being interrupted by a railway car moving toward the switch, complete movement of the switch will be efiected prior to the car arriving at the switch points. In the following description, it will be assumed that the beam of source S2 is arranged to be projected across track X approximately ten feet in advance of the switch points, and that the distance between the two beams of sources SI and S2 is less than the length of the shortest car to be operated over the switch. Located on the other side of stretch X in the path of the beam of source S2 is a prism H2 which splits the beam of source S2 into two parts and projects one part of the beam or the other to one or the other of two lightresponsive devices P3 and P4 associated with source S2.

The light-responsive devices P preferably are photo-electric cells of the type characterized by the fact that when illuminated or actuated by light rays, the cells have relatively little resistance, but that when non-illuminated or dark, the resistance of the cells increases and becomes relatively large. As will be made clear presently,

photo-cells PI and P3 are included in series in a grid circuit for tube Tl in such manner that when a potential of a given magnitude is applied across the two electrodes of tube Tl, the tube is conditioned to be conducting when and only when cells PI and P3 are both actuated or illuminated. Photo-cells P2 and P4 are included in series in a grid circuit for tube T2 in such manner that when a potential of a given magnitude is impressed across the two electrodes of tube T2, the tube is conditioned to be conducting when and only when at least one of the cells is unactuated or nonilluminated.

Having thus described the apparatus embodying my invention, I shall now explain its operation and at the same time shall trace in detail the circuit connections of the system.

I shall first assume that the apparatus is in 4 its normal condition, as illustrated in the drawing, when switch W and lever E are both in corresponding normal positions and the stretch of track intermediate the two beams of sources S is unoccupied. In this condition of the apparatus, cells PI and P2 are actuated by the beam of source S! and cells P3 and P4 are actuated by the beam of source S2. Valve magnet NV of mechanism SM is energized over a normal circuit which may be traced from one terminal of a suitable source of periodically varying current, such as a source of alternating current indicated as an alternator and designated in the drawing by the reference character G, through wire 28, wire 29, the winding of normal valve magnet NV, wire 30, normal contact 4-40 of controller J, wire 3!, lever contact 2|, and wire 32 to the other terminal of alternator G. Indication lamp KN also is energized and displays an illuminated indication to signify that the switch W and lever E are in corresponding normal positions. An energizing circuit for lamp KN may be traced from one terminal of alternator G through wire 28, wire 33, normal contact ll-G of controller J, wire 34, the filament of lamp KN, wire 35, lever contact l9,

and wire 36 to the other terminal of alternator G.

With the apparatus in its normal condition above described, switch W may be moved to its reverse position by operating lever E to its reverse position. In this event, lever contact I9 is opened to open the previously traced circuit of indication lamp KN, which accordingly becomes dark to indicate that switch W and lever E are out of correspondence. Lever contact 2| also is opened upon movement of lever E, thereby opening the previously traced energizing circuit for normal valve magnet NV, which accordingly becomes deenergized. However, with the switch control lever in its reverse position, a circuit including the Winding of reverse valve magnet RV of mechanism SM is established through tube TI. This circuit passes from one terminal of alternator G through wire 28, wire 31, the winding of reverse valve magnet RV, wire 49, wire 38, normal contact 5-H of controller J, wire 39, filament 24 of tube TI, intervening tube space, plate 23 of tube Tl, wire 40, normal contact 3-9 of controller J, wire 4|, wire 42, lever contact 22, and wire 32 to the other terminal of alternator G. The above circuit impresses across the plate and filament of tube Tl an electromotive force having a magnitude selected to be below that efiective to break down the tube medium. However, cells PI and P3 are connected in series across the filament 24 and grid 25 of tube Tl over a circuit which may be traced from filament 24 of tube Tl through wire 39, wire 43, photocell Pl, wire 44, photo-cell P3 and wire 45 to grid 25 of tubeTl, and in addition, a grid resistor 48 and a condenser 41 are connected across plate 23 and grid 25 of tube Tl, as is readily apparent from an inspection of the drawing. The values of resistor 46 and condenser 41 are so selected that, when alternator G impresses its electromotive force across plate 23 and filament 24 of tube TI, the tube is caused to be conducting when and only when a low resistance path is established across the grid and filament of the tube. Photo-cells PI and P3, which are connected across the grid and filament by the circuit traced above, establish such low resistance path due to thefact that each of the two photocellsis actuated by light rays from its associated source. Tube Tl accordingly is caused to operate and pass current during each half cycle of alternatingcurrent that its, plate 23 is positive with respect to its filament, and consequently, reverse valve magnet RV is supplied with half-wave or rectified current during the period tube TI is controlled to its operating condition, The energization of magnet RV causes mechanism SM to operate switch W to its reverse position. Upon operation of the switch from its normal position, normal contact l|6 of controller J is opened, and when switch W reaches its mid-stroke position, normal contacts I-'|, 2-8, 39, 4-lll and 5H of controller J are opened, and reverse contacts l-l2, 2-l3, 3-", 1-45 and 5I5 are closed. The opening of normal contacts 39 and 5H of controller J opens the previously tracedcircuit of tube Tl, with the result that tube TI is restored to its normal non-operating condition. However, reverse valve magnet RV is maintained energized over a circuit passing from one terminal of alternator G through wire 28, wire 31, the winding of valve magnet RV, wire 49, wire 38, reverse contact 5-l6 of controller J, wire 42, lever contact 22 and wire 32 to the other terminal of alternator G, and switch W is operated 'to its full reverse position.

" When the switch reaches its full reverse position, a circuit then is established for indicator KR, which becomes energized to display its illuminated indication signifying that the switch and control lever are in corresponding reverse positions. A circuit for energizing indicator KR may be traced from one terminal of alternator G through wire 48, lever contact 20, the filament of lamp KR, wire 34, reverse contact 6-I8 of controller J, wire 49, wire 38, reverse contact 5-[6 of controller J, wire 42, lever contact 22, and wire 32 to the other terminal of alternator G.

To restore switch W to its normalposition, lever E is first operated to its normal position, thereby opening lever contacts and 22 to open the last traced circuit for valve magnet RV and the previously traced circuit for indication lamp KR, which lamp then becomes dark to indicate that lever E and switch W are out of correspondence. The closing of lever contact 2| establishes a circuit which includes valve magnet NV for applying the electromotive force of alternator G across tube TI. This circuit extends from one terminal of alternator G through wire 28, wire 29, the winding of valve magnet NV, wire 30, reverse contact 4--l5 of controller J, wire 39, filament 24 of tube TI, intervening tube space, plate 23 of tube Tl, wire 40, reverse contact 3l4 of controller J, wire 50, wire 3|, lever contact 2!, and wire 32 to the other terminal of alternator G. Tube TI is conditioned to be operating in response to the electromotive force applied by the above circuit by virtue of the action of photo-cells PI and P3 (which are in their illuminated condition) establishing a low resistance path across the filament and grid of tube TI, and consequently, valve magnet NV is supplied with half-wave current during the halfcycle periods that the plate of tube TI is positive with respect to the filament. The energization of magnet NV controls mechanism SM to cause switch W to move to its normal position. Upon the switch moving from its reverse position, reverse contact B-I8 of controller J opens, and when the switch reaches its mid position, reverse contacts ll2, 2-l3, 3-l4, 4-15 and 5-46 are opened and normal contacts l-l, 28, 3-9, 4--l0, and 5-H are closed. The opening of reverse contacts 3l4-and 4-|5 opens the circuit previously traced for tube Tl, with the result that tube Tl no longer operates. The normal circuit hereinbefore traced for valve magnet NV, however, is now completed so that operation of the switch is maintained until it reaches its full normal position. In the full normal position of the switch, normal contact 6l1 of controller J closes to complete the previously traced energizing circuit for indicator KN, which becomes illuminated to indicate that switch W and lever E are in corresponding normal positions.

From the foregoing, it is readily apparent that when the beams of both sources SI and S2 are uninterrupted, the light-sensitive devices PI and P3 function to condition tube TI to be conducting when alternator G impresses its electromotive force across the tube electrodes. It is further apparent that, under the above conditions,

the electromotive force of alternator G is applied across the tube electrodes of tube Tl whenever lever E and switch W are out of correspondence. It follows, therefore, that when lever E and switch W are out of correspondence, control lever E and switch circuit controller J cooperate to connect across the electrodes of tube Tl in series with the source of energy the particular one of the two valve magnets NV and RV that, when energized, controls switch mechanism SM to move the switch to its position of correspondence with lever E.

I shall now assume that during the interval that a railway car operating in the stretch of track interrupts one or both of the beams of sources SI and S2, switch W and lever E are operated to a position out of correspondence with each other. For example, I shall assume that with switch W in its normal position and a car interrupting the beam of source S2, lever E then is moved to its reverse position. Under the above condition, indication lamp KN becomes da-rlc due to the opening of lever contact I9 to indicate that the switch and switch control lever are out of agreement. Also, a circuit is established for connecting the normal valve magnet NV across the two electrodes of tube T2 in circuit with the source of energy. This circuit may be traced from one terminal of alternator G through wire 28, wire 29, the winding of normal valve magnet NV, Wire 30, normal switch contact 4-43, wire 3|, wire 5|, normal contact I-l of controller J, wire 52, the filament 24 of tube T2, intervening tube space, plate 23 of tube T2, wire 53, normal contact 28 of controller J, wire M, wire 42, lever contact 22, and wire 32 to the other terminal of alternator G. Pho-tocells P2 and P4 are connected in series across plate 23 and grid 25 of tube T2 over a circuit path which may be traced from grid 25 of tube T2 through wire 54, photocell P l, wire 55, photo-cell P2 and wire 56 to plate 23 of tube T2, .and in addition, a grid resistor 51 and a condenser 58 are connected across the filament 24 and grid 25 of tube T2. The values of resistor 51 and condenser 58 are selected to condition the tube to be conducting in response to the electromotive force applied across its two electrodes by alternator G only in the event that a low resistance path is not established across the plate and grid of the tube. Such low resistance path is provided by cells P2 and P5 when both cells are actuated, but whenever one (or both) of the cells is unactuated, the low resistance path is removed and tube T2 becomes conducting. Under the above condition, therefore, that is, with cell P4 unactuated due to a car interrupting the beam of source S2, tube T2 is conditioned to be conducting since the high resistance of cell P4 causes tube T2 to operate and pass current in response to the electnomotive force applied across its electrodes by alternator G, and tube T2 passes current during the intervals that its plate is positive with respect to its filament. Normal valve magnet NV interposed in circuit across the electrodes of tube T2 accordingly is energized by the half-wave or rectified current passed by the tube to maintain switch W in its normal position out of correspondence with reverse position of lever E. The tube T2 remains conducting during the interval that the car interrupts either or both of the beams of the sources SI and S2.

When the car vacates the detector track section as defined by the beams of sources SI and S2, then the low resistance path is established through actuated cells P2 and P4 to establish a negative grid bias on grid 25 of tube T2, and as a result tube T2 is controlled to its non-conducting condition. With photo-cells PI and P3 now actuated, tube TI is controlled to its conducting condition by virtue of the positive grid If, under the last assumed conditions (lever I E and switch W in corresponding reverse positions), the detector track section is entered by a car in such manner as to trail the switch, the apparatus then functions to hold the switch in its trailed position out of correspondence with the lever. That is to say, if the beam of source SI is interrupted by the car entering the detector track section, tube T2 is conditioned to be conducting and tube TI is conditioned to be non-conducting. Under the above condition, when switch W is moved past its mid position in response to the trailing car, the circuit previously traced for tube T2 and including normal valve magnet NV is completed, whereupon normal valve magnet NV becomes energized to hold switch W in its trailed normal position out of correspondence with lever E during the interval that the car is on the detector track section defined by the beams of sources SI and S2. When the detector section is vacated, however, tube T2 becomes non-conducting and tube TI becomes conducting to control switch W to its reverse position in correspondence with the position of switch lever E, in substantially the same manner as was pointed out in detail hereinbefore in connection with the movement of lever E to a non-corresponding position when the detector section is occupied.

In similar fashion, if lever E and switch W are in corresponding reverse positions and the detector section is occupied, a movement of the lever to its normal position out of correspondence with the position of switch W control-s tube T2 to cause mechanism SM to hold the switch in its non-corresponding reverse position. This is effected by virtue of the circuit which extends from one terminal of alternator G through wire 28, wire 31, the winding of reverse valve magnet RV, wire 49, wire 38, reverse contact 5I6 of controller J, Wire 42, wire 59, reverse contact I-I2 of controller J, wire 52, the filament 24 of tube T2, intervening tube space, plate 23 of tube T2, wire 53, reverse contact 2-I3 of controller J, wire 60, wire 3I, lever 2|, and wire 32 to the other terminal of alternator G. When, however, 1

the detector section becomes vacated, then tube T2 is controlled to its non-conducting condition and tube TI is controlled to its conducting condition, whereupon normal valve magnet NV becomes energized over its previously traced circuit including the two electrodes of tube TI, to cause mechanism SM to move switch W to its normal position in agreement with the position of lever E.

In the event that switch W and lever E are in their respective normal positions, and the switch is trailed by a car to interrupt first the beam of source SI and then the beam of source S2, then thelast traced circuit for tube T2 is established whereby switch W is held in its reverse position (to which it is moved by the trailing car) out of correspondence with lever E until the detector section becomes vacated, in which latter event the switch is restored to its normal position in agreement with the position of lever E, as pointed out hereinbefore,

From the foregoing, it is readily apparent that when switch W and lever E are caused to be out detector section is occupied, the apparatus func-' tions to hold or look the'switch in its non-corresponding position until such time as the section becomes vacated. This results from the fact that tube T2 is conditioned to be conducting when the detector section is occupied and that lever E.and switch circuit controller J cooperate to connect across the electrodes of tube T2 in series with the source of energy the particular one of the two valve magnets NV and RV which when energized holds the switch in its non-corresponding position. When the section becomes vacated so that tube T2 is controlled to its non-conducting condition and tube Tl is controlled to be conducting, lever E and controller J then function to connect across the electrodes of tube Tl in series with the source of energy the particular one of the two valve magnets NV and RV which when energized controls the switch mechanism to move the switch to its position of correspondence with the lever. It can be seen from the foregoing that tubes TI and T2 function as traflic controlled relays, in that under certain traflic conditions in the detector section, the tubes are controlled to enable lever E to govern the operation of mechanism SM in such manner that switch W is always controlled to a position of correspondence with lever E, but that under other tramc conditions in the detector section, the tubes then are controlled so that if the switch and control lever are out of correspondence, switch mechanism SM is controlled to cause the switch to be held in its noncorresponding position.

It should be pointed out that tralfic controlled relays controlled independently of track circuits are-particularly advantageous for use in controlling the operation of a trafiic controlling switch in freight classification yards. This results from the fact that when relays are controlled by means other than track circuits, the detector track section can be shortened to a distance only a little greater than the shortest car operated over the switch, whereas when track circuit control is employed, the track circuit is of necessity at least as long as the distance between the trucks of the longest car operated over the switch. It can be seen, therefore, that since switching yard apparatus is operated most efficiently and economically when the headway between successive cars is the shortest possible, use of photo-cell controlled relays enables the shortest practicable detector section to be employed, thereby enabling the switching apparatus to operate at its highest efliciency.

It should further be pointed out that use of the usual tractive armature type relays is avoided by apparatus embodying my invention, since the amplifying tubes generally used in connection with photo-cells to establish control of relays are replaced by grid-glow tubes controlled by the photo-cells to function as circuit breakers. It follows, therefore, that apparatus embodying my invention provides novel and improved systems requiring a minimum of apparatus which 1) provides control of the switch movement to operate the switch to its position of correspondence with the switch lever when the detector section is unoccupied, (2) prevents operation of the switch in response to a lever movement when the section is occupied, (3) automatically holds the switch to its trailed position during the intervals the section is occupied, regardless of the position of the switch control lever, and (4) restores a trailed switch to its position of correspondence with the control lever when the section becomes unoccupied.

Although I have herein shown and described only one form of railway traflic controlling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim; is:

1. In combination with a stretch of railway track provided with a two-position railway traffic controlling device operatively connected with an operating mechanism for selective operation to each of its two positions, said device having a circuit controller provided with contacts selectively controlled in accordance with the position of said device, a manually operable two-position control lever, means for projecting beams of light across said stretch of track for defining a track section adjacent said device, two electronic tubes, means responsive to said beams of light for controlling one of said tubes to be conducting when and only when at least one of said beams of light is intercepted and for controlling the other of said tubes to be conducting when and only when none of said beams is intercepted, and circuit means controlled by said control lever and by said circuit controller and including said two electronic tubes for controlling said operating mechanism in such manner that when none of said beams is intercepted said control device is operated to a position of correspondence with said lever upon movement of the lever and when at least one of said beams is intercepted said control device is held in a position out of correspondence with said lever upon movement of the lever. V

2. In combination, a stretch of railway track, a detector track section for said stretch defined at each end by a source of light and a lightresponsive device cooperating therewith in such manner asto be responsive to trafiic in said stretch, a two-position trafiic controlling device positioned adjacent said section, a circuit controller operatively connected with said device, operating means for selectively operating said control device to each of its two positions, two electronic tubes, means controlled by said light-responsive devices for conditioning one of said tubes to be conducting when and only when said section is unoccupied and for conditioning the other of said tubes to be conducting when and only when said section is occupied, a twoposition manually operable control lever, and control means governed by said control lever and said circuit controller as well as by the particular one of said two tubes conditioned to be conducting for controlling said operating means in such manner that said traffic controlling device is operated to a position of correspondence with said lever when said section is unoccupied and is held in its last-operated position regardless of the position of said control lever when said section is occupied.

3. In combination, a stretch of railway track provided with a railway track switch, a switch mechanism operatively connected with said switch and having a normal magnet and a reverse magnet for operating said switch to its corresponding normal position and reverse position, a switch control lever having a normal position and a reverse position, two electronic tubes, means responsive to trafiic conditions in a given zone of said stretch adjacent said switch for conditioning one of said tubes to be conducting when and only when said zone is unoccupied and for conditioning the other of said tubes to be conducting when and only when said zone is occupied, means controlled by the position ofsaid switch for connecting the non-corresponding magnet of said mechanism in circuit with said one tube and for connecting the corresponding magnet of said mechanism in circuit with said other tube, and means efiective when said switch and said lever are out of agreement as to position for connecting a source of current to said tubes for controlling to its operating condition that tube conditioned by traffic conditions in said zone to be conducting, whereby non-agreement of the switch and switch lever when said zone is unoccupied causes said switch movement to operate the switch to its position of agreement with said switch lever but non-agreement of the switch and switch lever when said zone is occupied causes said switch movement to hold said switch at its position out of agreement with said lever.

4. In combination with a section of railway track provided with a railway track switch operatively connected with an operating mechanism for selective operation to each of its two positions, a circuit controller operatively connected with said switch, a manually operable twoposition switch control lever, two electronic tubes, means responsive to trafiic conditions in said section for conditioning one or the other of said two tubes to be conducting according as said section is or is not occupied, and circuit means controlled by said control lever and said circuit controller and including said two tubes for controlling the operation of said operating mechanism, whereby when said other tube is conducting said switch is operated to a position of correspondence with said lever but when said one tube is conducting said switch is held in its lastoperated position regardless of the position of said control lever.

5. The combination with a railway track switch located in a stretch of railway track and operated by a switch mechanism] to a position of correspondence with a manually operable switch lever having a normal position and a reverse position, said switch having a circuit controller provided with contacts selectively controlled in accordance with the position of said switch, of two electronic tubes, means responsive to trailic conditions in a given zone of said stretch adjacent said switch for conditioning one or the other of said two tubes to be conducting according as said given zone of track is or is not occupied, a source of energy, means controlled by said lever and said circuit controller and efiective when said lever is out of correspondence with said switch for connecting said source across said two tubes, and means operated by the current passed by the particular tube controlled by the traific conditions in said given zone of track to be conducting for controlling the operation of said switch mechanism in such manner that if said one tube is conducting said switch is held in its position out of correspondence with the lever but if said other tube is conducting said switch is moved to its position of correspondence with the lever.

6. The combination with a stretch of railway track provided with a railway track switch operated by a switch mechanism to a position of corespondence with a manually operable switch lever having a normal position and a reverse position, said switch having a circuit controller provided with contacts selectively controlled in accordance with the position of said switch, of a track section for said stretch defined at each end by a source of light and a light-responsive device cooperating therewith in such manner as to be responsive to traflio in said stretch, two electronic tubes, means controlled by said lightresponsive devices for conditioning one or the other of said tubes to be conducting according as said section is or is not occupied, a source of energy, means controlled by said lever and said circuit controller and efiective when said lever is out of correspondence with said switch for connecting said source across said two tubes, and means operated by the current passed by the particular tube controlled by the traiiic conditions adjacent the switch to be conducting for controlling the operation of said switch mechanism in such manner that if said one tube is conducting said switch is held in its position out of correspondence with the lever but if said other tube is conducting said switch is moved to its position of correspondence with the lever.

7. The combination with a switch control lever having normal and reverse positions and a railway track switch located in a stretch of track and having corresponding normal and reverse positions, said switch having a circuit controller provided with contacts selectively closed in accordance with the position of said switch, of two electronic tubes, means controlled by traffic conditions in a zone of said stretch adjacent said switch for controlling one or the other of said two tubes to be conducting according as said zone is or is not occupied, a source of energy, circuit means controlled by said lever and by said circuit controller and efiective when and only when said lever and said switch are out of correspondence for connecting said source across said two tubes, switch operating means for reversibly operating said switch, and means controlled by the current passed by the particular tube selected by trafiic conditions in said zone to be conducting for operating said switch op erating means in such manner that if said one tube is conducting said switch is held in its position out of correspondence with said lever but if said other tube is conducting said switch is moved to its position of correspondence with said lever.

JOHN W. LIVINGSTON.

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