US1710499A - Railway signaling - Google Patents

Description

April 23,1929, y 1 v, LEWIS y 1,710,499

RAILWAY SIGNALING original Filed oct. s, 1916 4 Sheef'sheeg 1.

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April 23, 1929. l.. v.v LEwls RAILWAY SIGNALING original Filed oct. s, 1916 4 sheets-sheet INVENTOR /M i N ...UE

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RAILWAY SIGNALING Org'i'nal Filed Oct, 5, 1916 4 Sheets-Sheet 3 FIG-[4 INVENTOR wlTNEssES April 23, 1929. 1 \ll. LEWIS RAILWAY SIGNALING 4 Sheets-Sheet original Filed oct. s, 191e Lilla m R R k A RR R. R

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Panarea Apr. 23,1929.

UNITED STATES PATENT. oEr-icE LLOYD V. LEWIS, OF EDGEWOOD BOROUGH, PENNSYLVANIA, ASSIGNOR TO UNION SWITCH & SIGN AL COMPANY, 0I SWISSVALE,

PENNSYLVANIA.

' RAILWAY sIGNALINa Application led October 3, 1916, Scrial'IN'o. 123,493. Renewed October 12, 1928.

My invention relates to railway signaling. I shall describe several forms of'apparatus and l circuits embodying my invention and then point out the novel features thereoflv 1n 5. claims.

-In the accompanying drawings Fig. 1 is a diagrammatic view showing one form and arrangement of trackway apparatus and circuits embodying my invention. Fig. 2 1s a diagrammatic view showing onel forml and arrangement of vehicle carried circuits and apparatus lembodying in y invention and adapted for use in connection with the trackway circuit-s shown in Fig.1. Fig. 3 is a r respectively.

" diagrammatic view showing a modification of the trackway apparatus and circuits shown in Fig. 1. Fig. 4 is a diagrammatic view showing a modification ofthe vehiclecarried apparatus and circuits shown in Fig. 2, the apparatus and circuitsbcing adapt-ed yfor use i-n connection with thc circuits shown in Fig. 3. Figs. '5 and 6 are diagrammatic views showing modifications of the trackway apparatus and circuits shown in Figs. 1 and 3 and also embodying my invention.

Similar reference ycharacters refer to similar parts in each ofthe several views.'

Referring first to Fig. 1, reference char.

acters 1 and 2 designate the track rails of a stretch of railway track A-B, which lrails are electrically continuous throughout the length of the stretcli.` G' and G' are generators of alternating signaling -currents of frequencies which I shall designate g and g',

y These frequencies are preferably higher than those now in commercial use, but lowen than the order of frequencies now in general use in wireless telegraph practice. The generators G and G 'are connected respectively to transmission lines N and N parallel to the railwayy track. .Current from line N is fed to the track rails at a by means of a transformer 6 connected to the line N by wires 3 and 4. The secondary circuit of this -transformer comprises a conresonance for. current of frequency g. The:

secondary coil of transformer 8 is connected in series Awith a condenser 9 to' the track rails 1 and 2, the condenser 9 having such capacity that when the railsare bridged by v a car or train a considerable distance from point a the secondary circuit of transformer 8 is-resonant atfrequency The above de,

The connection from line N to the track rails I at .o comprises similar a paratus, similarly adjusted to resonance or current of the same frequency g. Line N vis connected in similar manner to the track rails at points b and d, the connecting apparatus being ad- ]usted to resonance for the current from gen'l erator G. vThe points at which line N is connected to the track rails alternate with the points at which the line N is connected to the rails, as shown on the drawing, so that adjacent points of connection with the track rails are supplied with currents differing 1n frequency.

The signaling currents thus supplied to the rails 'flow along the rails to a railway the wheels and axles of the car or train. If

there i-s a car or train 'V on the track lbetween band c,.as shown on Fig.' 1, all currents that PENNSYLVANIA, A CORPORATION OF pedance to the iow of current from generare supplied to the Irails at points to the right' of the car or. train are short-circuited by the car axles, whereby they are prevented from owing' beyond the car or train into the rails to the left thereof. Similarly, the currents in the rails to the left of the car or train are short-circuited by the car axles so that they cannot flow into the rails on the right of the car 0r train.- v Each c ar or train is provided with control apparatus responsive' to the currents inthel trackrails immediately in advance of the car or train, which apparatus I shall now describe. Referring to Fig. 2, this control apparatus comprises a coil 10 fixed to the'v vvehicle V in front of the front axle and in inductive relation to the front axle and to the track rails 1' and 2 immediately in advance of such axle. A condenser 41'1 is connected in series with coil 10, the inductance of the'coil and the capacity of the condenser being of such relative values that the circuit formed by the condenser and the coil is resonantfor the mean of the frequencies g and g. When, therefore', current of either frequency is present in the t 'ack rails it will induce in circuit m alternating current of the corresponding frequency. Circuit a' is connected by wires 14 and 15 to the grid 16 and the filament 17 of a vacuum tube amplifier' P, a device now well known in the art. Briefly, described this amplifier comprises a vacuum bulb 18 enclosing a plate 20, the grid 16 and the filament 17 above referred to, which filament is constantly heated to .ineandescence by current from a battery 19. A continuous current is sent through the amplifier by means of a battery 21, the negative terminal of which is connected to the filament 17 and nthe positive terminal of which is connected to the plate 20, the circuit, which l shall designate y being in detail: from battery'21, through transformers T and T', wire 23, plate 20, filament 17, to battery 21. The grid 16 is interposed between plate 20 and filament 17, and when the voltage between the grid and the filament is caused to vary, the current in the circuit just traced fluctuates in accordance with the variations in the voltage. 1When an alternating voltage is impressed between grid 16v and filament 17, as for example, by current in circuit a", the current from battery 21 is caused to pulsate in harmony with the frequency of the alternating voltage in circuit the variations of the current in circuit y being of much greater-.magnitude than the amplitude of the current in circuit The inductance of the transformers T and T is balanced by a condenser 25 which has such capacity that the local circuit comprising the two transformers and the condenser in series is resonant at they mean of the fre'- quencies g and g.

The secondary circuits of transformers T and T comprise, respectively, relays S and S connected in series with condensers 26 and 26, the capacities of vwhich condensers are such that the circuits comprising relays S and S are respectively resonant at frequencies g and g. When, therefore, there is current of frequency g in circuit y the relay S is energized, and when there is current of frequency g. in circuit y the relay S is energized. As explained hereinbefore, the current in circuit y depends -upon the currents induced in circuit .fr by the signaling currents in track rails 1 and 2 in front of the car or train, henceit is clear that current in the track rails of frequency g causes energization of relay S and that current in the rails of frequency g causes energization of relay S". Relay S will not respond however to current of frequency g', and likewise relay S will not respond to current of frequency g; and to insure this selection the imanes two relays may be so constructed as to be selectively responsive to the currents to which they are intended to respond.v

Relays S and S may govern suitable signaling apparatus, or speed controlling apparatus, or both, on the vehicle, as I shall now describe. Reference characters LG, LY, and LR designate signal lamps comprised in acab signal F, which lamps indicate respectively, when illuminated, proceed, proceed with caution, and stop. The green lamp LG is illuminated only when both relays S and S are energized, theeircuit being: from battery 3G, through wire 31, front contact 32 of relay S, wire 33, front contact 34 of relay S, wire 35, green lamp Cr, Wires 36 and 37 to battery 30. The yellow lamp LY is illuminated when only one of the relays S or S is energized and the other is de-energized; when relayy S is the one' which is energized, the circuit for lamp LY is from battery 30, through wire 31, front contact 32 of relay S, wire 33, back contact 34 of relay S, wire 40, lamp LY, wires 36 and 37 to battery 30; when on the other hand relay S is the one which is energized, the circuit for lamp LY is from battery 30, through wire 31, back contact of relay S, wire 38, front contact 39 of relay S, wire 40, lamp LY, wires 36 and 37 to battery 30. When both relays S and S are de-energized, lam LR is illuminated by current in the following circuit: from battery 30, through wire 31, back contact of relay S, wire 38, back contact 39 of relay S, wire 41, lamp L, wires 36 and 37 to battery 30. It is clear from the foregoing, that when both relays S and S are energized, the cab signal gives` the proceed indication; when only one relay is energized, the signal gives the caution indication, and when both relays are de-energized, the signal gives the stop indication.

To enforce observance of these signals, suitable automatic vehicle governing means may be provided for use in connection with llt) relays S and S". In the form here shown this means comprises' a centrifugal device 44 operatively connected with an axle of the vehicle. This centrifugal device controls a magnet 42, which magnet governs a valve 43 in the fluid pressure brake. system of the vehicle, in such manner that the brakes are applied when the magnet is deenergized. The arms of the centrifugal device are connected at one end to a shaft 45 bearing a contact sleeve 45, so 4that the spread of the fly balls due to movement of the car or train causesthe cont-act sleeve 45a to move to the right. The contact sleeve -coacts with three'pairs of contact fingers 46 and 46a, 47 and 47, 48 and 48a, in such manner that all three pairs of contact fingers are bridged by the contact sleeve when Ythe speed of the car ortrain is low, as, for example, miles per hour and less. Above this speed the sleeve 45 is drawn out of' engagement with the rst pair of fingers 46 and 46a, remaining however, in engagement with the other two until the speed of the car orptrain reaches an intermediate value suoli as miles per hour. Above this includes the right hand pair of contact fingers 48 and 48, the circuit being' from battery 30, through front contact 50 of relay S, wire 51, front contact 52 of relay S, wire 53, contact finger 48, sleeve a, contact finger 48a, wire 54, magnet 42, Wires 55 and 37 to battery 30. When only one of the magnets S or S is energized, the circuit for magnet 42 includes the middle pairof contact fingers47 and 47; when rela S is energized and relay S de-energize the circuit is :troml battery '30 through front con- `tact of relay S, Wire 5,1, back contact 52 of relay S', Wlre 56, contact finger 47, contact sleeve 45a, contact finger 47, wire- 54, brake magnet 42, wires 55 and 37 to battery .30; when relay S is energized instead of relay S, the circuit is the same as traced above except that it passes through the back contact 50 of relay S, wire 57, and front contact 58 of relay S to wire. 56. When neither relay S nor S is energized, the circuit for magnet 42 includes the left hand pair of contact fingers 46 and 46a, the circuit in detail being from battery 3() through wire 59, contact finger 46, contact sleeve 45a, contact linger 46, wire 54, magnet 42, wires 55 and 37 to battery 30. y It is clear therefore, that when both relays AS and S are energized the speed of the car or train is limited only to 60 miles per hour. When,l 1owever, only one of these relays'. is energized, the speed limi't'is reduced to 30 miles per hour, .and when both relays S and S are de-energized, the speed is limited to 5 miles per hour. It is understood, however, that the apparatus herein shown for accomplishing this control of' the speed of the car or train by relays S and S is merely illustrative, and that any other suitable appara-v v tus may be employed in the practice of my invention.

-It will now be clear that when a car orl train equipped lwith the apparatus shown in F ig. 2 proceeds over track rails in which both signaling currents are flowing, the cab signal gives a proceed indication and the speed of the car or train is limited only 'to 6() miles per hour; when'the car or train proceeds over track rails in which only one of the signaling currents is fiowing, the cab signal indicates proceed with caution and the brake control apparatus limits the speed to 30 miles per hour; and when the car or train enters upon track rails in which neither of the signaling currents is flowing,

the cab signal changes to stop yand thel brake control apparatus limits the speed to 5 miles per hour or less.

From the above description ot'l apparatus the operation of the signaling system will be easily understood. For a brief explanation I shall assume that in Fig. 1 there is` a car or train V on the track between points b and c and that lanother car or train V approaching from the left, the latter car or train being equipped with the apparatus shown in Fig. 2. IWhile vehicle V is to the left of point a both signaling currents are present in the track rails in advance of the vehicle, so that the cabsignal indicates proceed and the speed of' the vehicle is limited only to 60 miles per hour, as I have previously described. When the vehicle passes beyond point however, only one of the signaling currents is present in the track rails, namely, current from generator G', consequently the cab signal changes its indication to caution and unless the speed has -been reduced to 30 miles per hour or less, the

ICS

until the vehicleV is, reached or the 'signal indication is changed. It the engineer fails to comply with this rule, the brakes will be applied automatically until the speed ofthe Ulf) train is less'than 5 milesvper hour. If now the first train V moves to the right beyond c, signaling current from generator G again fiows in the track rails in advance of the car or train V `so that the engineer of the latter train receives a proceed with cau'- tion signalin the cab. At the same time.

the speed limit imposed on the car or train is raised, allowing the car or train to proceed at a speed of 30 miles per hour.

Referring now toFig. 3, the signaling system here shown is similar to the system previously described, but it comprises four generators G',- G2, G3 and G4, generating currents of four distinct frequencies, which frequencies I shall designate g, g2, g3 and g4, respectively. In the. arrangement here shown, all of the generators are connected to one transmission line N, which line is connected to thetrack rails at a, b, c, etc.,

by means of intermediate circuits, each of which circuits is resonant for one of the frequencies of current in line N, so that only current. of the one frequency can enter the track rails at each of the said points of connection. For example, at point a the rails are supplied with current by a transformer 6T whose secondary is connected with the rails and whose primary is connected with the swfondary of another transformer 69, the primary of the latter being connected with the transmission line N. The circuit including the rails and the secondary of transformer 67 is tuned to resonance at frequency g by a condenser 68, and the circuit including the secondary of 69 and the primary of 67 is similarly tuned to the same frequency by a condenser 70. Tn this manner the rails are furnished at ai With current of frequency g', at b with current of frequency g2, etc., currents of the various frequencies being supplied to the track rails in rotation as indicated by letters g1, g2, etc. on

ythe drawing. lVhen, therefore, in Fig. 4

the cars or trains V and V areseparated by four or more track connections, the track rails in front of car or train V are energized by four signaling currents. When the second car or train V approaches the first car or train V until they are separated by only three track connections, the rails between them are energized by only three signaling currents. It is clear, therefore, that, as the car or train V approaches closer to car or train V, the track rails between the cars or trains carry fewer signaling currents, until the rails are completely de-energized as the second car or train V passes the last track connection behind vthe first car or train V. It may be said, therefore, that the number of signaling currents in the track rails in front of a car or train depends upon the distance to the next car or train'ahead.

Referring now to Fig. 4, the apparatus on the. ear or train for use in connection'with the trackway circuits shown in Fig. 3 is similar to the apparat-us shown in Fig. 2 previously described. The circuit is tuned to resonance at the mean of the four frequencies g', g2, g3 and g4. The circuit y, however, comprises in seriesthe primary windings of four transformers T, T2, T3, T4, having secondary circuits comprising cab relays'S. S2, S3 and S4, respectively, which circuits are adjusted to resonance for frequencies g', g2, g3 and g4, respectively. From the description of Fig. 2 it is clear that the relays S', S2, S3, and S4, respond respectively to signaling current in the track rails of the frequencies g', g2, g3 and g4.

These relays control, as in Fig. 2, af cab signal F, Whichas here shown comprises five lamps, the faces of which are marked respectively With numerals 60 45, 25, l() and 5, which numerals designate the permissible speed of the car or train in miles per hour. `When all of the cab relays are fle-energized, the lowest lamp, marked 5, is illuminated, indicating that the speed of the car or train must not exceed 5 miles per hour. .Vhen any one of the cab relays is energized, this lamp is extinguished and the next higher lamp is illuminated, indicating that the speed may be raised to l0 miles per hour. In this manner, as the number of energized relays increases, the speed limit indicated by the lamps is raised in steps to the maximum of miles per hour at which time all four relays are energized. These speed limits may be enforced, if desired, by a governor 44 controlling contacts in the circuits of the magnet 42, the control of these circuits being similar to the control shown in Fig. Q and explained hereinbefore.

The operation of this signaling syst-em is similar to the operation of the system shown in Figs. l and 2. Referring again to Fig. 3, it is apparent that the coil 10 on car or train V receives signaling currents of four frequencies as it approaches car or train V, until train V reaches the track connection `designated c. With four signaling currents in the track rails the four cab relays S', S2, S3 and St are energized so that the cab signal indicates the highest speed limit of miles an hour and the governor limits the speed of the car or train accordingly. However, as the car or tra-in V passes point c, the track rails in front of the car or train are energized by only three of the signaling currents, namely, those currents having frcquencies g4, g', and g2. As a result, the relay S3 inthe cab is der-energized, leaving only three of the cab relays closed, so that the signal G changes its speed limit indication to 45 miles per hour and the governor 44 becomes effective to enforce this speed limit as explained hereinbefore. As the car or train V proceeds still further and passes point d, signaling current of the frequency g4 is also shunted from the track rails in front of the ear or train so that relay S4 in the cab becomes cle-energized. Only relays S and S2 are now closed, so that the eab signal indicates a speed limit of 25 miles per hour and the governor becomes effective to enforce this speed limit. As the car or ytrain passes point e, signaling current of only one frequency, namely, g2 energizes the track rails in front of the car or train so that only relay S2 in the cab is energized, which results in a speed limit of 10 miles per hour. As the car or train passes point f, it enters upon fle-energized track rails so that none of the relays in the cab are closed and the cab signal changes its speed limit indication to 5 miles per hour, which limit is enforced bythe governor, as previously explained. Tt Will be seen that thisr signaling system differs' from the one previously described .while the caror train is running on this down grade I supply to the track rails of this section only two frequencies of sig.- naling currents so that only two of the cab relays can be energizedeven when there is no other car or train ahead, whereby the car or train is automatically prevented from 'assuming a higher speed than 25 miles per hour in the manner explained hereinbefore. As shown in Fig. .5, the frequencies g and g2 are notsupplied to the rails on the down grade, andthey are prevented from flowing into this Isection of the rails by lshunts 65 and 66 connected between the rails adjacent II. The shunt 65 comprises an inductance and a condenser resonant for frequency g', so that current of this frequency in the rails to the right of the shunt is short-circuited and prevented from flowing into the rails extending to the left of the shunt. In the same manner the current of frequency g2 lis prevented from` flowing past the shunt 66 which is resonant at frequency g2. When, therefore, a car or train equipped with sign al and speedcontrolapparatus, as shown and described in Fig. 4, approaches'the down grade extending from I to II, traveling in the direction of the arrow, the coil 10 thereon receives all four signaling currents upto the point designated lo so that the speed is limited only to miles per hour. After passing vthis point, however, the car or train short-circuits the current of frequency g' supplied at c so that this lcurrent cannot flow into the track rails preceding "the car or train. Current of frequencyg is not supplied to the track rails within the limits of the down gradesection, as previously mentioned, and cannot flow into these rails from the rails beyond the lower end of the grade because of the resonant shunt 65. The track rails in frontof the car or train are therefore energized only by signaling currents of frequencies g, g3 and g4, so that only three cab relays are energized and the speed limit is reduced to 45 miles per hour, as hereinbefore explained. As the car or train passes point 1, it shunts out current of frequency 'g2 from the trackrails ahead of4 `the car o r train so that the speed limit is automatically reduced to 25 miles .perhour, as hereinbefore explained. Signaling currents of frequencies g3 and gv4 are supplied tothe track ralls on fthe down grade, permitting the car. or -train to proceed down the grade at 25 miles per hour, unless there is another car or tram in advance, in which case the first-mentloned -car -or train must slow down rst-to 10 lmiles y is connected between the track rails.

per hour and then to 5 miles per hour in the manner which- I have explained hereinbefore. Assuming that the track is unoccupied. the car or train proceeds at 25`miles per hour to' the point at which the shrlllllt rails beyond this point are energized by current of frequency g supplied at 0 so thatA the speed limit is changed to 45 miles per hour. As the car or train passes shunt 66 it enters on track rails energized by signaling currents of all four frequencies, so that the speed limit is raised to 60 miles per hour permitting the car or train to resume normal speed.

.In similar manner a reduced speed limit may be imposed on cars or trains when passing over curves, switches or tunnels.

Referring now to Fig. 6, reference character Q designates a railway switch in a section of track IV-VI. When the switchis in its normal position, traiic passing over the switch in the direction of the arrow continues on the straight or high speed route, Whereas when the switch is in its reversed position, traiiic passing over the switch is diverted into a branch track 110, which I will term a medium speed route. For purposes of description `I shall assume that the maximum safe speed on the high speed route is' 60 miles per hour, whereas on the medium speedroute it is 25 miles per hour. Reference character K designates a signal stationed adjacent the trackway, which signal comprises two semaphore arms 108 and 104. These arms are fnormally in the horizontal position, indicating stop. When arm 104 is raised to the vertical position it indicates that switch Q, is normal, and when arm 103 is raised to the vertical position it indicates that switch Q is reversed.

I have omitted from the drawing the eircuits for the control of signal K, these circuits being irrelevant to my invention. It need here be mentioned only that a track circuit comprising the track rails from IV `and, VI enters into the controlof signal K through a track relay 106, the length of the track circuit being dened by insulated joints 112 in rail 2. The track circuit is supplied by atransformer 111 adjacent point VI l 'an alternator U. The indications of signal K are'repeated by a distant signal Ka located in the rear of signal K, the arms 101 and102 of signal Ka corresponding respectively to semaphores 104 and 103 of signal K. Signal Ka is also controlled by a track circuit extending from point III to point IV, which circuit comprises a track relay 107, energized also from the low frequency source U.

For the purpose of repeating the; indications of signal Ka and K in the cab of a car ortrain', and in order to automatically enforce observance of ,these signals, I provide my hereinbefore described high frequency signaling system suitably modified, as I shall now describe. The apparatus on the car or train may be the same as that shown in Fig. 4. 'Ihe transmission line'N energized by generators G, G2, G3 and G4, supplies signaling currents to thc track rails, in somewhat the same manner as in Fig. 3, ,the frequency supplied to the track rails being indicated by the same letters as before at each point of connection. It should here be noted that the insulated joints 112 in rail 2 prevent thc high frequency signaling currents supplied to the track rails within the insulated sections from flowing beyond the limits thereof. For example, with the arrangement of apparatus thus far described, current of frequency y supplied at 123vto the track rails in section III-IV canno-t flow to the rails extending to the left of point III because of joint 112 in rail 2. To pass this current around the said joint I provide a shunt 119 connected to the ends of rail 2 abutting said joint, which shunt is resonant for frequency g,so that currents of the other frequencies cannot flow through this shunt in appreciable quantities.

A car or train V traveling` in the direction of the arrow will receive at 120 current of frequency g as Well as currents of frequencies g2, g3 and gt, so that the car or train may proceed at 60 miles per hour. When the ear or train passes point 120 it will, however, receive only three of the said currents i. e. g', g and g3, unless the frequency g4 is supplied to the rails through a transformer 124, whose connection to the line L is controlled by the relay 107, the control being such that current flows to the transformer only when thesection III-IV is unoccupied. In similar manner current of frequency g3 is supplied to the said rails by a transformer 125, similarly controlled by relay 107. In this manner the car or train may proceed at full speed to the entrance of section III-IV except when said section is occupied, in which case the speed of the car or train is reduced automatically.

Assuming now that the section III- IV is unoccupied and that signal K at the entrance to the next section is at stop, 'the car or train on entering section III-IV receives only three signaling currents g', g'1v and g3 supplied to the track rails at 123, 120 and 127, so that the speed of the car or train is reduced to 45 miles per hour. As the car or train passes point 123 its speed is reduced to 25 miles per hour, at point 126 it is limited to 10 miles per hour, and at 127 it is limited to 5 miles per hour, all in the manner hereinbefore explained.

.VVhen, on the other hand, signal K indicates proceed at full speed, i. e. when semaphore arm 104 is in the vertical position, all four signaling currents are supplied to the rails of section III-IV adjacent point IV through transformers 130, 131, 132 and 133, respectively, which transformers are controlled through contacts 104, 104, 104, 104, governed by arm 104 of sig-v nal K, the contacts being closed or open according as blade 104 is horizontal or vertical'. In this manner the train receives all four signaling currents as it approaches signal K so that it may pass this signal at full speed, in accordance with the indication of the signal.

When, however, the signal K indicates proceed at medium speed, blade 103 being vertical and blade 104 horizontal, only currents of frequencies g and g2v are supplied to the track'rail's at point IV through transformers 130v and 131 governed by'contacts l 1032L and 103D, operated by signal blade 103. In this case the car or train receives all four frequencies of current only -up to point 126 in the section III-IV. .After passing this point only three currents are transmitted to the car or train and the speed is reduced to 45 miles per hour. .At 127 the speed is reduced to 25 miles per hour, thus insuring a safe medium speed when the car or train passes signal K.

The control of the car or train after it passes signal K is the same as hereinbefore described; in connection with Fig. 3; I have omitted the circuits and apparatus for the control thereof to avoid unnecessary complication of the drawing.

Although I have herein shown and described but several forms of apparatus and circuits 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. I

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

1. A stretch of railwa track, a plurality of sources'of current di ering in frequency connected to the rails of said track, and a shunt resonant at one of said frequencies connected between said rails for preventing flow of said current beyond said shunt.

2. In combination, a stretch` of railway track supplied with a plurality of signaling currents, a portion of said stretch being supplied with a lesser number of signaling currents, means for preventing currents not directly supplied to the said portion from entering said' portion at one end, and vehicle-carried controlling means responsive to said signaling currents.

3. In combination, a stretch of railway track comprising a portion necessitating a lower speed than the remainder of the stretch, means for supplying to said portion one or more signaling currents and for supplying to the remainder of the stretch a greater number of signaling currents, resonant means for preventing the signaling currents not directly supplied to the said portion ofthe stretch from entering said portion, and vehicle-carried governing means 5 responsive to the said signaling currents.

4. In combination, a stretch of railway track comprising a portion necessitating a lower speed than the remainder of the stretch, means for supplying to the track -10 rails of said portion one or more signaling currents and for supplying a greater number of signalin currents to the track rails of the remain er of the stretch, resonant shunts connected between said track rails for preventing the How of the signaling currents into Said portion and vehicle-carried governing means. responsive to the number of signaling currents supplied to the track rails in front of the vehicle.

In testimony whereof I aiix my signature.

LLOYD v. LEWIS.

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