US2215822A - Railway signaling apparatus - Google Patents

Description

Sept. 24, 1940. B QHAGAN 2,215,822

RAILWAY SIGNALING APPARATUS Filed Jun 27, 19:59

lNV NTOR Bernard Hagan.

HIS AT-TORNEY Patented Sept. 24, 1940 UNITED STATES PATENT OFFICE RAILWAY SIGNALING APPARATUS.

Bernard E- OHagan, Swissvale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., acorporation of Pennsylvania Application June 2'7, 1939,,Serial No. 281,373

12Claims. My invention relatesto. railway signaling apparatusand has particularreference to appara-l tus of the type employed. in railway signaling systems in which coded trackway energy is utihzed to. control: either or both" wayside signals and train-carried cab signals.

It hashitherto been proposed to employ relays l of the saturationtype as code following relays. in;

connection with signaling systems utilizingcoded trackway energy. I havefound that whensaturation type code following relays are so employed, the energy which is caused to be reproduced in the saturation relays inresponse to the coded trackway energy might not correspond to such trackway energy, due to the fact thatsaturation type relays have, as a generalrule, a residual output during the interval that the saturation relay is controlled, to have itsminimum output.

Thiscauses the saturation relays to have a rela 20;. tively lowamplification ratio, or in other words, the ratio of themaximum output of'such relays to their minimum output is relatively small. As

a result of the above condition, systems employing such relays might have somewhat limited 25. eflicienoy in operation. Accordingly, an object. of

my present invention is the provision of a novel and improvedtype of saturation relay having a relatively high amplification factor.

Another object is to'effect the improvement in 3m the amplifying, ratio of such relays by decreasing the minimum or residual-output of such relays.

A further objectis to effect the above reduction sented in thedrawing, apparatus embodying my invention is illustrated as being utilized at a cutsection location: in. a track section to cascade track circuit current from one subsection into 50,

this-manner is disclosed and? broadly claimed: in

. aco-pending applicationfor Letters Patent, Serial No. 280,731, filed on June 23, 1939, by Claude M. Hines, for Railway signaling. apparatus. as; Referring. to. the drawing; the. reference charthe next. The. use of a saturable transformer in.

(crem -s4 acter DR designates a novel and improved type of relay Of. what I shall term the saturation type. As. here shown, relay DR comprises a ladder shaped magnetizable core 3, having five parallel legs 4, 5, 6, 'l,and 8 connected. together at each end to form an integralv relay core structure. The central. leg 6 of the. core is provided with a primary. or local input -winding H constantly connected to a source of periodically varyingcurrent,.prefer'ably a source of alternating current. (such as a generator not shown in the drawing) having its terminals designated by the reference characters BX and CX, for setting up a primary flux in. core 3.. As is readily apparent from an inspection of the drawing, .the primary ilux set up by winding. H isprovidedwith twomagnetic circuits through the relay core, one circuit of which I. shall term amain circuit, andthe other circuit of. which I shall, term a leakage circuit. The main magnetic circuit of core 3 comprises the commonleg 6, the two core legs land 8 in paraIleLand the adjacent top and bottom portions of the. core. The leakage, magnetic circuit comprises the common leg 6, the two core legs 4 and. 5; in, parallel, and the adjoining top and bottom portionsof the core; Both circuits, therefore, have a common leg 6 of the coreand each circuit is provided with twowparallel paths. The relative. dimensions or cross sections of, the core elements forming the two magnetic circuits are selected and so proportioned that under no load conditions, the circuits have substantially equalreluctances so that the primary flux divides. equally between the two circuits.

The main, magnetic, circuit of core 3 is provided with asecondary winding l2 which comprises twocoils Na and [2b disposed respectively on the two parallel paths 1 and 8 of the main circuit, and which coils are connected in" series in such manner that any electromotive .forces inducedthereinin response to flux flowing in the same directions, in the legs are additive. The leakage magnetic circuit of core 3 is provided with two biasingcoils I3 and I4 disposed respec-. tively on the two parallel paths 4 and 5 of the circuit, eachof the coils. I3 and I 4being shortcircuited by an asymmetrical unit designated by the reference character |5-or l 6, as the case may be, whereby unidirectional current only is permitted to. flow inv the coils; The coils. I3 and M: are each effective normally to increase the reluctance ,of' its. associated path in the leakage circuit of the core, by supplying thereto unidirectional flux-in response to. the unidirectional cur-,- rent induced in. the. coils by the primary flux supplied from winding II. The coils i3 and I 4 and their associated asymmetrical units l5 and I6 are so arranged as to send flux through legs 4 and 5 in opposite directions, as indicated by the arrows shown in the diagram; or in other words, to act cumulatively to send flux around in a local magnetic circuit which includes the legs 4 and 5 and the adjoining top and bottom portions of the core.

With relay DR constructed and arranged in the manner thus far described, it is apparent that the increase in reluctance of the leakage circuit effected by the short circuited coils I3 and I4 normally causes the greater portion of the primary flux to be circulated through the main circuit whereby normally a relatively high electromotive force is induced in secondary winding i2.

Relay DR further is provided with a saturation winding I], which winding comprises four coils I'Ia, IIb, I10 and IId disposed respectively on legs 4, 5, I and 8 of the relay core 3. The pairs of coils Ho and I ll), which are disposed on the two parallel paths 4 and 5 of the leakage circuit, are connected in series in such manner that the resultant of the electromotive forces normally induced therein by the alternating primary flux is substantially zero, and the other pair of coils Ho and i111, which are disposed on the two parallel paths 1 and 8 of the main circuit, also are connected in series in such manner that the resultant of the electromotive forces normally induced therein by the alternating primary flux is substantially zero. The pairs of coils of the saturation winding disposed on the main and on the leakage circuits are connected in series across the terminals of a source of unidirectional current, such, for example, as a rectifier R, which rectifier has'its output terminals connected to winding I7 and has its input terminals connected to a source of alternating current. The polarity and magnitude of the current supplied from rectifier R to winding I! is such that when the winding is energized, the coils I10 and Hal act cumulatively to'send a saturating flux around in a local magnetic circuit comprising the two parallel paths 1 and 8 and the adjoiningtop and bottom portion of the core forming a portion of the main magnetic circuit, whereby the reluctance of that portion of the main circuit is increased to a value such as to substantially magnetically saturate that portion of the core. Under the above condition (winding I'I supplied with unidirectional current) the two coils Ho and Ilb act cumulatively to circulate a flux around in the local magnetic circuit formed in the leakage circuit by the legs 4 and 5, in opposition to the flux circulated therein by biasing coils I3 and I4, whereby the two Opposing fluxes tend to neutralize each other so that as a result the normal reluctance of the leakage circuit is decreased. It can be seen, therefore, that when winding I! is supplied with unidirectional current of the above mentioned polarity and magnitude, the primary flux then is caused to circulate through the leakage circuit by virtue of the relative differences in reluctances of the two circuits of the core, whereby the magnitude of the electromotive force induced at this time in winding I2 of the relay is very small and approaches a zero value. It follows that a relatively high electromotive force is induced in winding I2 when winding I 'Iis deenergized, and that a relatively low electromotive force is induced in winding I2 when winding I! is energized, or in other words, that a relatively high electromotiveforce is or is not induced in output winding l2 of relay DR according as the control winding of the relay is not or is energized.

From the foregoing, it is readily apparent that relay DR functions as a back contact type saturation relay, in that maximum energy is induced in and supplied from the secondary or output winding of the relay only when the control winding of the relay is deenergized, thereby corresponding in operation to a back contact of a tractive armature type relay, which contact is controlled to a circuit closing position only when the control winding of the armature type relay is deenergized. It will be understood, of course, that relay DR may be constructed as a front contact type saturation relay by mounting the secondary winding I2 on legs 4 and 5 of the leakage circuit, in which event, of course, maximum output will be obtained from the relay when control winding IT is energized. Also, separate secondary windings may be provided on each of the two magnetic circuits of the core, thereby providing a saturation type relay having front contact and back contact secondary windings.

A saturation relay constructed in accordance with my invention may be advantageously utilized as a code following relay in connection with coded track circuits of the type employed in railway signaling systems. In the drawing is shown one such application, in which a back contact type saturation relay embodying my invention is positioned at a cut section location in a track section for cascading trackway energy from one portion of the section to the next adjoining portion of the section.

The typical coded track circuit shown in the drawing comprises the track rails l8 and I8a of a stretch of railway track electrically separated into a track section E-F by means of the usual insulated rail joints I9, and which section E-F is divided by insulated joints I9 located at a cut section location Ea in the section, into an advance subsection E-Ea and a rear subsection EaF.

The particular track circuit illustrated is adapted for use with a railway signaling system for a railway employing electrical propulsion, in which system the track rails I8 and |8a form a portion of the return circuit of the propulsion current. Section E-F, therefore, is shown provided with impedance bonds 20, one for each set of insulation joints I9, and which bonds in the usual form permit the transfer of propulsion current around insulation joints I9 but which prevent a similar transfer of trackway signaling current. ,It is to be understood, of course, that a relay embodying my invention is equally well suited for use in connection with coded track circuits applied to a steam road, in which latter application the impedance bonds 20 would, of course, be omitted. In connection with a steam road, also, the resonant transformer units RU later to be referred to may be replaced by the usual form of relay transformer.

The rails of section E-F are supplied with coded trackway signaling energy in .the usual manner through the medium of the track transformer T'I, which transformer has its secondary winding connected across the track rails of the section at its exit end E, and has its primary winding connected to a source of current (preferably a source of alternating current having its terminals designated in the drawing by the ref-' erence characters BX and CK) over a contact governed by a coding device CT, whichdevice is ber offtimesper minute. It will be understood, of course, that the apparatus supplying track- Way energy to'sectionEa-F may, if so desired, be

governed by traffic conditions in advance of the The: coded track circuit: further comprises a code. responsive relay IR, which receives energy from-thetrackrails: of. the sectioniat its entrance end. through the medium of: a. resonant transformer. unitzRUl ,which unitisefiective to transfer. the. trackway signaling energy from the rails,

of the: section to the associated. code following. relay, but whiohwunit preventsithe transfer of. the electric: propulsion current. to the relay. The code responsive track'relay TR, may be, as shown,

a, code following: relay of the:tractive.armature type, or may beif desired: a code following relay of. the saturation type,.such as for example, as is.

shown in my; oopending application for Letters Patent, SerialNo. 280,997, filed on June for" Railway signaling apparatus.

I'he track circuit for section E-F, as shown,

further is provided at the cut-section location Ea of the sectionwith a saturation type relayDR The magnitude and polarity of current supplied. by transformer unit RU and rectifier R to relay.

DR. are such that the unidirectional impulses supplied to. winding ll cause the two parallel paths 1 and 8 of the main circuit of the relay DR to become magnetically saturated, and alsocause adecrease in the reluctance of the parallel paths 4 and 5 of the leakage circuit of the relay. Re lay DR, therefore, functions in the manner previously described to cause a relatively high electromotive force to be induced in secondary winding E2 of the relay when winding ll of the relay is deenergized (as for example during the off period of the coded trackway energy of subsection EEa), and causes the electrornotive force induced in winding i2 to drop tosubstantially a zero value when. winding ll is energized (during the on period of the code).

It is readily apparent from the foregoing that the trackway energy supplied to subsection EEa is reproduced in kind by relay DR and is supplied to subsection Ea-F, whereby the trackway energy of the advance subsection is cascaded around the insulated joints l9 located at Ea into the rear subsection, so that section EF is provided with coded trackway energy throughout its entire length in the same manner as if the rails of the section were continuous conductors from one end. of the section to the other.

It should be noted that relay DR, being of the back contact type saturation relay, also is effective to; supply steady or non-coded clearing.

out energy to rear. subsection Eta-1 when a train. occupies only subsection E-Ea,.this steady energy being supplied rear subsection EaF by virtue of the fact that. a. train occupying subsection EEa shunts control Winding ll of relay DR, thereby causing the electromotiveforce induced in output winding ll of relay DR and supplied to subsection EaF to be at its maximum.

value. This steady clearing out energy may be utilized to control apparatus. of the wellknown. form (usually located adjacent the entrance end. of the. sectionbut not shown in the drawing) which is desired to be responsive only. to trafiic conditions in subsection Ell-F.

An advantage of a saturation relay constructed in accordance with my present invention is that the residual or minimum output. of such relay is substantially zero; The ratio of the maximum output of the relay to its substantially zero mini mum output accordingly is relatively large, with the result that a saturation relay embodying my inventionhas an. amplification factor which substantially corresponds to the amplification factor possessed bytractivearmature type relays.

Another advantage is that a relayembodying my present invention is particularly well adapted for use as a code following relay in connection with a control circuit which is supplied with coded energy having on periods wherein energy is supplied tothe circuit and off periods wherein energy is not supplied. When so employed, a relay embodying my invention reproduces the coded energy and, supplies from its output winding coded energy having. on. periods. during which maximum output is supplied from the relay and oif periods. during which substantially no energy is supplied. The coded energy produced.

by such relay accordingly corresponds to the form ofcoded energy supplied by the control circuit to the relay control winding, with the result that the saturation relay functions substantially in. the samemanner as a tractive armature type code following relay. Thus, for example, when a saturation relay embodying my invention is employed as a code following relay in cut-sec-.

tion facilities, the coded trackway energy sup-.

plied by such relay to the rails of the rear subsection has substantially the same'characteristics as is possessed by the coded trackway energy supplied to the advance subsection. Improved operation of the code following and decoding apparatus of the section accordingly is effected, since.

there is no residual output supplied to the rails ofthe rear subsection during the oil? periodof the code, andas a result the code. responsive apparatus is fully deenergized and is not improperlypartially energized. during the off period.

of the trackway energy.

Although I have herein shown and described only one formof railway signaling apparatus embodying. my invention, it. is understood that various changes and modifications may be made therein within the scopeof the appended claims withoutdeparting from the spirit and scope of my invention.

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

1. In "combination, a relay of the saturation type comprising a magnetizable core having two magnetic circuits arranged in shunt to each other, said relay having. a primary winding disposed on said core for setting up a primary flux in both of said two magnetic circuits when supplied with periodically varying current, said relay having biasing means disposed on a. particular one of said two magnetic circuits and responsive to the primary flux to set up a unidirectional biasing flux of a particular polarity in said particular one magnetic circuit whereby the re- 55: luctance of that magnetic circuit normally is relatively high with respect to the reluctance of the other of said two magnetic circuits, said relay having a saturation winding comprising two portions one disposed on said particular one magnetic circuit and effective when supplied with unidirectional current of a preselected polarity to set up a saturation flux in opposition to said biasing flux whereby the reluctance of said particular one magnetic circuit is decreased, the

other portion of said saturation winding being disposed on said other magnetic circuit and being effective when supplied with current to set up a saturation flux whereby the reluctance of said other magnetic circuit is increased to a value relatively high with respect to the reluctance of said particular one magnetic circuit, said relay also having a secondary winding disposed on one of said two magnetic circuits whereby the magnitude of the electromotive forces induced therein by the primary flux of the relay is controlled by the flux due to current in said saturation winding in step with the supply of coded current to said saturation winding, means for constantly supplying periodically varying current to said primary winding of said relay, and

means for supplying coded unidirectional current of said preselected polarity to said saturation winding of said relay.

2. The combination with a magnetizable core having two magnetic circuits arranged in shunt to 4 posed on a particular one of the two magnetic circuits of the core and responsive to the-primary flux to supply a biasing flux to said particular one magnetic circuit whereby the reluctance of that magnetic circuit normally is caused to be 45 relatively high with respect to the reluctance of the other of the two magnetic circuits of the core, a control circuit supplied with current from a source of periodically interrupted or coded current, a saturation winding receiving unidirec- 507 tional current of a preselected polarity from said control circuit and comprising two portions one disposed on said particular one magnetic .circuit and effective when supplied with said unidirectional current to supply a saturating flux to said 55 particular one magnetic circuit in opposition to said biasing flux whereby the reluctance of that magnetic circuit is decreased, the other portion of said saturation winding being disposed on said other magnetic circuit and being effective when 60 supplied with said unidirectional current to supply a saturating flux to said other magnetic circuit whereby the reluctance of that magnetic circuit is caused to be increased to a value relatively high with respect to the reluctance of said par- 65 ticular one magnetic circuit, and a secondary winding disposed on one of the two magnetic circuits of the core whereby the magnitude of the electromotive forces induced therein by the primary flux of the core is controlled in step with 70 the supply of unidirectional current to said sat'uration winding from said control circuit.

3. The combination in a relay of the saturation type having a primary winding normally supplied with periodically varying current for 75' setting up a primary flux in both of two magnetic circuits and a secondary winding disposed on one of the two magnetic circuits, of means disposed on a particular one of the two magnetic circuits and responsive to the primary flux for setting up a biasing flux in said particular one magnetic circuit whereby the reluctance of that magnetic circuit normally is caused to be relatively high with respect to the reluctance of the other of the two magnetic circuits, a saturation winding having two portions one disposed on each of the two magnetic circuits in such manner that when said saturation winding is supplied with unidirectional current of a preselected polarity a saturating flux is set up in each of the two magnetic circuits whereby the reluctance of said particular one magnetic circuit is reduced and the reluctance of said other magnetic circuit is increased, and means for at times supplying said saturation winding with unidirectional current of said preselected polarity.

4. The combination in a relay of the saturation type having a primary winding normally supplied with periodically Varying current for setting up a primary flux in both of two magnetic circuits and a secondary winding disposed on a particular one of the two magnetic circuits, of means disposed on the other of the two magnetic circuits and responsive to the primary flux for setting up a biasing flux in said other magnetic circuit whereby the reluctance of that magnetic circuit normally is caused to be relatively high with respect to the reluctance of said one magnetic circuit and an electromotive force of relatively large magnitude is caused to be induced in the secondary winding by the primary flux, a saturation winding having two portions one disposed on each of the two magnetic circuits in such manner that when said winding is supplied with unidirectional .current of a preselected polarity a saturating flux is set up in each of the two magnetic circuits whereby the reluctance of said other magnetic circuit is reduced and the reluctance of said one magnetic circuit is increased to cause an electromotive force of relatively small magnitude to be induced by the primary flux in the secondary winding, and means for at times supplying said saturation winding with unidirectional current of said preselected polarity.

5. In a relay of the saturation type having a primary winding normally supplied with period'- ically varying current for setting up a primary flux in both of two magnetic circuits and a secondary winding disposed on one of the two magnetic circuits, abiasing winding disposed on a particular one of the two magnetic circuits and short-circuited through an asymmetrical unit normally to increase the reluctance of said particular one magnetic circuit by supplying a biasing flux thereto in response to the primary flux, a saturation winding having two portions one disposed on said particular one magnetic circuit and the other disposed on the other of the two magnetic circuits, said one portion of the saturation winding being effective when supplied with unidirectional current of a predetermined magnitude and polarity to decrease the reluctance of said particular one magnetic circuit by supplying a saturating flux thereto in opposition to the biasing flux created by said biasing winding and said other portion of the saturation winding being efiective when supplied with said unidirectional current to increase the reluctance of said other magnetic circuit by supplying a saturating flux thereto, and means for supplying said satuall also

: ration winding-with unidirectional current .of

said predetermined magnitude and polarity.

6. ,A relay of the saturationtype comprising an input winding normally supplied with periodiically varying :currenutwo magnetic circuits for said relay both having 'a portion in common ,:linked by said input winding, a secondary winding disposed on one of said two circuits, a coil short-oircuited by an asymmetrical unit disposed on the other of said two "circuits for increasing normally the reluctance of that :circuit, a saturation Winding having one'portion disposed on said one circuit and another portion disposed on said other circuit, said one portion being efiective when supplied with unidirectional current of a predetermined :magnitude and polarity to increase the reluctanceof said one circuit and said other portion of said saturation winding being 7. A relay of the saturation type comprising, i

in combination, a magnetizable core having two magnetic circuits eachhaving two parallel paths, a primary winding linking both of said two magnetic circuits and normally being supplied with periodically varying current, two biasing coils one disposed on each of the two parallel paths of aparticular one of said two magnetic circuits,

said two biasing coils each being short-circuited by an asymmetrical unit and said two coils cooperating to circulate a flux through a local magnetic circuit formed by the two parallel paths of said particular one magnetic circuit to normally increase the reluctance of said particular one magnetic circuiua secondary winding comprising two coils one disposed on each of the two parallel paths of one of said two magnetic circuits and said two cells being connected in series in 'such manner that any voltages induced therein in response to flux flowing in the same directions through each path are additive, a saturation winding comprising four coils one disposed on each of the parallel paths of said twomagnetic circuits and said coils being connected in series in such manner that when said saturation winding is supplied with unidirectional current of a predetermined value one pair of coils disposed on said particular one of said magnetic circuits opposition to the flux circulated therein by said short-circuited biasing coils to thereby reduce the reluctance of said particular one magnetic circuit and the other pair of coils disposed on the other magnetic circuit of the core cooperate to circulate a flux through the two parallel paths of that circuit to substantially magnetically saturate said other magnetic circuit, and means for supplying unidirectional current of said predetermined value to-said saturation winding.

8. A relay of the saturation type comprising, in combination, a magnetizable core having two magnetic circuits each having two parallel paths, a primary winding linking both of said two magnetic circuits, said primary winding normally being supplied with periodically varying current for setting up a primary flux in caid core, a secondary winding comprising two coils one disposed on eachof the two parallel paths of one of said magnetic circuits, said coils of the secondary winding beingconnectedin series in such manner that-,anyivoltages induced therein in response tosaid primaryflux areadditive, two other coils one disposed on each of the twoparallel paths of, the other of said two magnetic circuits, each ,of said other coils being short-circuited by an asymmetrical unitand said two other coils cooperating to circulate a flux through a local magneticcircuit formed by the two parallel paths of said other circuit to increase the reluctance.

of saidother magnetic circuit wherebythe primary flux is normally circulated through said one magnetic circuit to cause a relatively high electromotive force to be induced in said secondary windingin response to said primary flux, a saturaticn winding comprising four coils one disposed on each of the parallel pathsof said two magnetic :circuits, said four coils of the saturation winding being connected in series in -such-mannerthat when said saturation winding is sup-lplied with unidirectional current of a-predetermined value onepair of coils disposed on the two parallel paths of said one magnetic circuit cooperate to circulate a saturating fluxthrough a local magneticcircuit formed by such two parallel paths to magneticallysaturate said one magnetic circuitand the other pair of coils disposed -'on the two parallel paths of said other magnetic circuit cooperate to circulate a flux through the local magnetic circuit formed by the two parallel legs of said other magnetic circuit in opposition to the flux circulated therein by said two other coils, whereby the reluctance of said other magnetic circuit is decreased, and

means for supplying said saturation winding with: ,7

unidirectional current of said predetermined-1 value.

9. A relay of the saturation type comprising, in combination, a magnetizable core having two magnetic circuits each havingtwo parallel paths f a primary winding linking both of said magnetic:

circuits, said primary Winding-normallybeing supplied with periodically varying current for setting up a primary lux in said core, a secondary winding comprising two coils one disposed on each lot;

circuits, said coils of the secondary windingbeing connected in series in such manner that any voltages induced therein by said primary flux are additive, two biasing coils one disposed on each of the two parallel paths of the other of said magnetic circuits, each of said biasing coils being short-circuited by an asymmetrical unit and being normally effective to supply a flux to said other magnetic circuit which increases the reluctance of that magnetic circuit whereby the primary flux supplied by said primary winding is circulated through said one magnetic circuit to induce a relatively high electromotive force in said secondary winding, a saturation winding comprising four coils one disposed on each of the parallel paths of said two magnetic circuits, said four coils of the saturation winding being connected in series in such manner that the electromotive forces normally induced in the pair of coils disposed on each of said magnetic circuits in response to said A5 the two parallel paths 0i one of said magnetic:

10. In a signaling system for railroads, the combination with a section of railway track electrically separated by insulated rail joints into adjoining advance and rear subsections and having means for supplying coded trackway shunt for the main magnetic circuit coupling the primary and secondary windings, each of the duplicate parallel core portions being provided with a coil short-circuited by an asymmetrical unit and effective when said primary winding is supplied with periodically varying current to increase the reluctance of said parallel core portions whereby the primary flux created by said primary winding is circulated through said main magnetic circuit to induce in said secondary winding a relatively high electromotive force, said relay also being provided with a saturation winding having one portion disposed on the main magnetic circuit and another portion disposed on said parallel core portions, said one portion of the saturation winding being effective when supplied with unidirectional current of a predetermined value to magnetically saturate said main magnetic circuit, said other portion of the saturation winding being effective when supplied with said unidirectional current to decrease the reluctance of said parallel core portions by supplying flux thereto in opposition to the flux created by said short-circuited coils, whereby when said saturation winding is energized by said unidirectional current the primary fiux is shunted from said main magnetic circuit and a relatively low electromotive force is induced in said secondary winding, means for constantly supplying periodically varying current to said primary winding, means for supplying said saturation winding with unidirectional current of said predetermined value from said advance subsection, and means for connecting said secondary Winding to said rear subsection whereby that subsection is supplied with trackway energy in response to the trackway energy supplied from said advance subsection to said saturation winding.

11. In combination, a magnetizable core having two magnetic circuits, a primary winding disposed on said core and connected with a source of alternating current for setting up a primary flux in each of said two circuits, means disposed on one of said circuits and responsive to said primary flux traversing such circuit for normally increasing the reluctance of that circuit to forceujo the major portion of said primary flux through the other magnetic circuit, an output winding disposed on said other magnetic circuit, a control winding having two portions one disposed on each of said two magnetic circuits, and means for sup-L215 plying to said control winding unidirectional energy of a preselected magnitude and polarity for increasing the reluctance of said other magnetic circuit and for decreasing the reluctance of said one magnetic circuit whereby to shunt thee-20 major portion of said primary flux away from said other magnetic circuit.

12. In combination, a magnetizable core having a primary and a secondary winding disposed on a main magnetic circuit and also having a portionqi25 of said core arranged to shunt flux due to current in said primary winding away from said secondary winding, means for constantly supplying said primary winding with alternating current, a coil short-circuited through an asymmetrical unit dis- '30 posed on the shunt portion of said core for normally increasing the reluctance of that portion to force the flux due to current in said primary winding through the main magnetic circuit, a control winding having two portions one disposed 35 on the main magnetic circuit and the other disposed on the shunt portion of said core, and means for supplying to said control winding unidirectional current of a preselected magnitude and polarity for increasing the reluctance of saidn main magnetic circuit and for decreasing the reluctance of said shunt portion of the core whereby to shunt the major portion of the flux due to current in said primary winding away from said main magnetic circuit. {9

BERNARD E. OHAGAN.

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