US2176616A - Apparatus for decreasing rail contact resistance - Google Patents

Description

' Oct. 17, 1939. H. A. THOMPSON 2,176,616

APPARATUS FOR DECREASING RAIL CONTACT RESISTMCE Filed Aug. 16, 1932 3 Sheets-Sheet 1 mm HowaniA 172011908012 Q1 HIS AITORNEY Oct. 17, 1939. H. A. THOMPSON 2,176,616

APPARATUS FOR DECREASING RAIL CONTACT RESISTANCE Filed Aug. 16, 1932 5 Sheets-Sheet 2 g l I T 7 T 6' 5 X 9 .4 5 [5 51 F L 7? Lia u r- K p 11 44 1 3 T 14 y W (,7 I vi r 2%. 6 32 INVENTOR. H0wa dAJ/2omps012 BY QM HIS A TT ORNE Y.

Oct. 17, H. A. THOMPSON APPARATUS FOR DECREASING RAIL CONTACT RESISTANCE Filed Aug. 16, 1952 3 Sheets-Sheet 3 Generator A V QRW 6 55 HIS ATTORNEY.

[ 1:970. 57 B I INVENTOR.

Patented Oct. 17, 1939 UNiTED STA'l Ziitfilt APPARATUS FOR D'ECREASING RAIL CONTACT RESISTANCE Application August 16, 1932, Serial No. 629,030

32 Claims.

My invention relates to apparatus for decreasing rail contact resistance, and more specifically to apparatus for improving track circuit shunting by light weight rail vehicles.

I will describe several forms of apparatus for decreasing rail contact resistance embodying my invention, and will then point out the novel features thereof in claims.

The present application is a continuation in part of my copending application, filed May 31, 1932, Serial No. 614,325, for Apparatus for decreasing rail contact resistance, in so far as the subject matter common to the two cases is concerned.

In the accompanying drawings, Fig. 1 shows in elevation a rail vehicle equipped with apparatus embodying my invention. Fig. 2 is a diagrammatic view showing in detail one form of the apparatus for decreasing rail contact resistance embodying my invention. Fig. 3 is a diagrammatic view showing a modification of a portion of the apparatus illustrated in Fig. 2. Fig. 4 is a diagrammatic view showing a modified form of the apparatus embodying my invention which is applicable to either direct or alternating current track circuits. Fig. 5 shows a modification of the apparatus of Fig. 4, being particularly applicable to alternating current track circuits. Fig. 6 is a diagrammatic view showing a further modified form of the apparatus embodying my invention. Fig. 7 is a diagrammatic view showing, in elevation, a rail vehicle equipped with another form of the apparatus embodying my invention. Fig. 8 is a diagrammatic view showing the trackway apparatus associated with the apparatus of Fig. '7. Figs. 9 and 10 are diagrammatic views showing modified forms of the apparatus of Fig. 7.

Similar reference characters refer to similar partsin each of the several views.

It is well known that a bright rail surface having low contact resistance initially, if exposed to atmospheric conditions for a period of time will usually have a film of appreciable resistance formed thereon. Where heavy rolling stock of the usual type is used, the weight effective upon the wheels of a rail vehicle is ordinarily suiiicient to crush or destroy this high resistance film thereby making it possible to shunt the track circuit through .the medium of the wheels and axles of the vehicle. If, however, a light Weight rail vehicle such, for example, as the gas electric car used upon some railroads, is employed, some difficulty is frequently experienced in obtaining satisfactory shunting because of the inability of the wheels of such a car to penetrate through the insulating film upon the rail surface. Furthermore, if the wheels of a car are equipped with pneumatic tires, special means must be provided for shunting the track circuit. My invention is of particular utility in the provision of shunting protection by a car having wheels which do not make electrical contact with the rail surface and can be applied as well to a steel-wheeled car of insufficient weight for satisfactory shunting, or to a heavy car of the ordinary type operating over track circuits the rails of which have abnormally high contact resistance.

Referring to Fig. 1 of the drawings, the reference character A designates a rail vehicle in which the sets of wheels i and 2 have rubber tires, therefore making no electrical contact with the rails. One way in which I accomplish the purpose of my invention is by adding the pairs of wheels 3 and 4 in a manner which will be more clearly understood in connection with the description of the diagram of Fig. 2.

In Fig. 2 of the drawings, I have shown a stretch of railway track divided into block sections by means ofinsulated joints 1, one such section EF being illustrated. Connected across the rails at one end of the section E-F is a battery 8 which supplies energy to a track relay R connected across the rails at the other end of the section, in the usual manner. Connected in series with the battery 8 is the usual current limiting resistor R as well as the reactor X, the purpose of which will be explained hereinafter. Insulated from the body of the car A are two pairs of auxiliary wheels 5 and t which make electrical contact with the rails 5 and 6, the wheels of each of these pairs being insulated from one another by insulating blocks 9.

The reference character G designates an alternating current generator arranged to be carried upon car A, the output of this generator being connected across one winding it) of a transformer T The secondary winding H of transformer T is connected by suitable contacts to each half of the axle l4, whereby a potential from generator G may be impressed across the rails 5 and 5. One winding !2 ofa transformer T is connected to the two halves of axle l5 and the other winding is of this transformer is connected across an alternating current detecting relay D, carried upon the car. Front contact it of relay D is included in the circuit for an indicator L which is energized from a suitable source having terminals B and C. Transformer T is designed to have a high leakage reactance so that a comparatively high voltage will be applied to wheels value of rail contact resistance will become estab-.-

lished between wheels 3 and the rails, so that relay R will become released through the medium of the shunt formed by wheels 3 and winding II. If the voltage delivered by winding H of trans former T is suificiently high, the contact resistance at wheels 4 will be broken down simultaneously with the breakdown of the resistance at wheels 3, thus providing an additional shunt for the release of relay B through the medium of wheels 6 and winding l2 of transformer T That is, a current path of low resistance as indicated by the arrows in the diagram will be established which will include winding H of transformer T wheels 3, rails 5 and 6, wheels 4, and winding l2 of transformer T windings H and i2 of transformers T and T respectively are constructed of heavy wire for the purpose of providing low shunting resistance from rail 5 to rail 6. Reactor X and resistor R in series with battery 8 are useful in preventing an appreciable portion of the current supplied by winding H from being by-passed around wheels and winding l2, through the path formed by battery 8 and its track connections.

As long as the system is functioning properly, relay D will remain energized, thereby energizing indicator L to provide a visual indication that the rail film has been broken down at both shunt paths. Relay D may also be used to perform any other desired function such as applying the brakes on the car in case the apparatus ceases to function, or applying any other auxiliary shunt to the track circuit.

Where direct current track circuits are used, the generator G should be of the'alternating current type in order that false energization of relay R may not result. If alternating current track circuits are used, the frequency of the current supplied by generator G should be sufficiently different from the track circuit frequency to prevent false operation of the track relay.

The wheels 3 and 4 may rest on the rails due to their own weight or, if desired, the weight may be increased in any suitable manner, or they may be held against the rails by auxiliary springs or by air pressure. Although I have shown the current from winding H conducted to rails 5 and 5 by means of the wheels 3, it will be understood that my invention is not limited to this particular arrangement, as any method for conducting the current into rails 5 and 6 such, for example, as by means of contact shoes or brushes can be used to produce a similar result.

It will also be understood that it is not essential to the operativeness of my invention to employ the second pair of auxiliary wheels 4 and transformer T since a, closed circuit for shunting relay R is provided by wheels 3 and winding ll, once the rail film is broken down, the current from winding ll flowing over a return path which may include one or more of the following: the ballast resistance, track battery, or winding of the track relay. Also, in certain cases such, for example, as where alternating current track circuits are used, direct current from a suitable car carried generator can be applied to the two halves of axle M for breaking down the rail film, and if the second pair of wheels 4 is used, the winding of relay D can be connected directly to the two halves of axle l5, omitting transformer T If the wheels 4 are joined by a solid axle [5 to eliminate the resistance of winding l2 from the shunt path, omitting the insulation 9, relay D may be energized from a stationary Winding of the axle transformer type surrounding axle i5 and threaded by the flux set up by the axle current, or, if an axle transformer is not used, relay D may be connected in series with winding i i of transformer T although in the latter case, relay D will not check the integrity of insulation 9 in axle I l. Furthermore, if it is desired to eliminate the contact resistance of the brushes which conduct current from the secondary winding H of transformer T into the axle l4, transformer T can be rigidly fastened to axle M for rotation therewith, slip rings being used to admit current from generator G into the primary winding It By applying a sufiiciently high value of potential to the rail surface, the apparatus can also be used for breaking down an insulating film of appreciable thickness, such as an ice layer for example.

Referring to Fig. 3, the apparatus shown,

T Transformer T has preferably a one to one ratio in windings I? and. I8, and these windings are wound of heavy wire in order to keep the shunt path resistance as low as possible. The connections of winding it are so chosen with respect to the winding N, that the current flowing in winding l8 as a result of the potential impressed across wheels 3 will oppose the current flowing in winding ll, thereby creating in well known manner an equalizing action between the current which flows in winding ll and the current which flows in Winding E8.

The chief purpose of transformer T is to confine the current flowing from winding H of transformer T to the rail path between wheels 3 and 4 and to axle l5 and winding E2 of transformer T rather than to permit an appreciable portion of this current to stray into the ballast resistance, the circuit of battery 8, or the circuit of relay R. By increasing the current flowing between wheels 4 and the rails improved rail film windings of transformer T.

Referring to Fig. 4, the apparatus shown therein is similar to that illustrated in Fig. 2, with the exception that the second auxiliary pair of wheels -2 is not used, being replaced by a resonant shunt connected across the rails 5 and 6, to provide a low impedance return path for the current supplied by winding ll. This resonant shunt is of the usual type and comprises a transformer T the secondary winding of which is closed through a reactor X and condenser C in series, the parts being so proportioned as to provide a low impedance path through the primary winding at the frequency of generator G. The purpose of resistor R is to limit the current drain on battery 8 when section EF is unoccupied. As shown, the resonant shunt is part of the wayside equipment; it can,'however, be carried by the rail vehicle, connection to the rails being made by movable contacts. In the latter case, resistor B may be omitted.

Assuming that the car occupies section EF, a portion of the current delivered by winding ll will flow through the ballast resistance, battery 8, and relay R, the remainder flowing through the resonant shunt. However, all of this current will flow between wheels 3 and the rails, breaking down the rail contact resistance to provide effective shunting of relay R. The detecting relay D is energized from a winding 29 of the axle transformer type and provides an indication that the rail contact resistance has been broken down.

Referring to Fig. 5, the apparatus shown therein is particularly applicable to alternating current track circuits, and is similar to the apparatus of Fig. 4, except for the use of a third winding 38 on transformer T Winding 30 is connected for co-nsonance with winding H, through a reactor X and condenser C the constants of which are so chosen that resonance is produced in winding It at the frequency of the track circuit current supplied by track transformer T It will now be apparent that when the car enters section E F a maximum value of the auxiliary film break-down current will flow through transformer T which is resonated to the frequency of generator G, and a minimum impedance of winding l i for shunting the track relay will result because transformer T is resonated to the track circuit frequency.

In order to economize the power output of generator G and to'aid shunting, I have shown in Fig. 6 a rail cleaning device K carried by the car whichmakes it possibleto obtain effective shunting by wheels 3 andwinding ii at relatively low values of voltage and current delivered by the generator. For this purpose, any suitable rail cleaning device such as a pair ofwire wheels 3| and 32 mounted on a shaft 33 and arranged to be driven by the car or by auxiliary power in a direction opposite to the direction of car travel, can be used. For obvious reasons, the rail cleaning device should be located ahead of the resistance break-down and track shunting apparatus, in the direction of car travel, as indicated by the arrow.

Referring now to Fig. '7, the gas electric car A of this figure is equipped with steelwheel groups l9 and 20, of the ordinary type, the wheels of each group being in electrical contact with other wheels of the group through the axles and truck frame, but at least one group being insulated from the body of car A by an insulating block 2-5. The motive power for car A is furnished by a gas engine driven generator N carried on the car, the output of generator N being supplied to a driving motor Msuitably geared towheels l9 and governed by a controller which is not shown for simplicity.

Fig. 7 I have utilized the propulsion current for breaking down the rail contact resistance, without the necessity for using an auxiliary generator such as generator G of Fig. 2 for this purpose. Once the contact resistance is broken down, the wheels and axles of both groups 19 and 20 will provide the necessary shunt for releasing the track relay.

In order to take care of the condition when the car is coasting or standing still, motor M being idle, I have provided a resistor H which is constantly connected across generator N in such manner as to draw current over the same rail circuit traversed by the propulsion current, the circuit for resistor H extending from one terminal of generator N, wires 2i and 28, resistor H, wire 2'5, wheels !9, the rails between Wheels l9 and iii, wheels 29, and wire 23, to the other terminal of generator N. For giving an indication that current is flowing over the rail path at all times and that the rail resistance is broken down, I have provided an indicator L, connected across a portion of the resistor II.

The advantages of the arrangement of Fig. 7 can also be obtained on a car having wheels insulated from the rails, such as car A of Fig. 1, by providing a pair of contact shoes heavily bonded together, one for each rail, one such pair being located at one end of the car, and another similar pair being located at the other end of the car, to establish a path for the propulsion current from generator N to the rails, which path in Fig. 4 is provided by Wheels I9 and 20. The connections to these shoes would be made by means of wires 2? and 23, as in Fig. 7. To insure that the propulsion current will pass through both rails at all times, the contact shoes of the pair which replaces wheels l9 can be insulated from each other to force the propulsion current,

well as the current through resistor H, to follow a series path including one of said insulated contact shoes, one rail, the other contact shoe pair which is bonded together, and the other rail to the remaining insulated contact shoe. In this manner, there will be greater certainty that the contact resistance at both rails is broken down, particularly when the car is at a standstill, or is coasting, with no propulsion current flowing.

In the track circuit diagram of Fig. 8, I have shown the customary track transformers T and T and the track relays R and R having shown, in addition, impedance bonds W and W connected across the rails of adjoining track circuits and having their midpoints bonded together by a connector 28. The bonds W and W are necessary for the purpose of permitting propulsion energy to iiow through the rail path when wheel groups la and iii straddle the insulated rail joints l. Since these bonds carry propulsion current at such times only when car A is spanning the rail joints, they can be designed to have relatively small current carrying capacity for this intermittent type of service. Should car A stand over the joints'for an appreciable time interval, motor M being deenergized, the only load on the bonds will be the current taken by resistor H plus any current required by the lighting, ventiiating, or other auxiliary equipment on the car.

It will be obvious that car A can be equipped with a trolley or pantograph for operation in electrified territory, the terminals of generator N being disconnected under this condition, and wire 2! being connected to the propulsion wire.

Also, car A may be arranged for alternating instead of direct current propulsion, in which case direct current track circuits can be used, or if alternating current track circuits are preferred, the track transformers T and T of Fig. 5 can supply current of a frequency differing from the propulsion frequency and frequency selective track relays can be used.

Referring to Fig. 9, the resistance break-down apparatus shown therein insures that the contact resistance at each rail is broken down sufficiently for satisfactory shunting. To accomplish this result, the rail contacts 35 and 36 are heavily bonded together to form a low resistance shunt path from rail to rail, and are connected by a wire 38 with the secondary winding of each of two independent transformers T and T designed to have a relatively high leakage reactance. The remaining terminal of each secondary winding of the above transformers is connected respectively to the rail contacts 34 and 31, through an indicator L and L both primary windings of transformers 'I and T being supplied with alternating current from a generator G, the frequency of which is materially different from the track circuit frequency, unless direct current track circuits are used in which case the frequency of generator G may be determined from other considerations.

As long as a low resistance contact is being made at each rail and the circuits are intact, both indicators L and L will remain energized; but should high contact resistance or other circuit defect develop, one or both of the above indicators will become deenergized to warn the car operator of a possible dangerous condition. As in Fig. 8, the bonds W and W provide a path for the current from transformers T and T when the rail contacts 31 and 36, and 34 and 35 span the rail joints '1. If direct current track circuits are used, the bonds W and W can be replaced by suitable resistors connected in the same manner as the bonds.

Should it be desired merely to check the contact resistance of the rail contacts of Fig. 9 without employing voltage apparatus for breaking down the rail resistance, the apparatus of Fig. 10 can be used. The detecting relays D and D are connected in series with low voltage sources B and B respectively, and with the pairs of rail contacts 3435 and 331, in such manner that a detecting current will flow through the rail portion included between the rail contacts of a pair, causing relays D and D tobecome energized to close an energizing circuit for an indicator L which includes a front contact of each relay. If the contact resistance at each rail contact is sufficiently lcw for satisfactory shunting by the bonded contacts 35-36, indicator L will remain energized, but will become deenergized when the contact resistance increases above this value.

It will be understood that the rail contacts 34, 36 and 31 of Fig. 10 are designed in such manner that reliable mechanical contact with the rail surface is maintained at all times, and that these contacts can be of any suitable type as for example, of the friction shoe contact, rolling wheel contact, or rotating friction type of contact. If necessary to prevent loss of contact at rail joints due to Vibration when the car travels at an appreciable speed, each of the rail contacts can be replaced by a spaced pair of indcpendently'movable contacts.

Where it is desiredto obtain fouling protection, the rail contact apparatus may be dupli-' cated at each end of the car being placed as near to the end of the car as practicable, for greatest protection, in order that the track circuit will be shunted when any portion of the car stands thereon. With the shunting equipment duplicated in this manner, the bonds W and W of Fig. 9 can be eliminated, as one or the other group of rail contacts will always lie wholly Within one track circuit.

It will be understood that the apparatus embodying my invention is not necessarily limited to the provision of decreased contact resistance in track shunting circuits, as this apparatus can be used equally well for breaking down the resistance film between a pair of contact members which may be included in any one of a large number of circuits having insufficient voltage or current to cause a break-down of the contact surface resistance film.

Although I have herein shown and described only a few forms of apparatus for decreasing rail contact resistance 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 divided into a track circuit section having a source of current and a track relay associated therewith, a rail vehicle, a second source of current carried upon said vehicle, and means including a low resistance track shunt for causing a current to flow from said second source into the rails of said stretch for breaking down the resistance of the rail surface and for effectively shunting the rails of said track circuit section so as to cause a release of said track relay.

2. In combination with a rail vehicle and a stretch of railway track, a source of current; a first pair of rail contacts, one for each rail, carried by said vehicle and connected with said source for applying a potential to said rails for breaking down the resistance of the rail surface; and a second pair of rail contacts, one for each rail, carried by said vehicle and joined together by a connector of negligible resistance for providing a low resistance shunt path between said rails and for completing a return path for the rail current caused to flow by said potential.

3. In combination with a rail vehicle and a stretch of railway track, a first pair of wheels in electrical contact with said track and carried by said vehicle, said wheels being electrically insulated from each other, a second pair of wheels electrically connected with each other and in electrical contact with said track also carried by said vehicle, a source of current, and means for applying a potential from said source across said first pair of wheels whereby current will flow over a path which includes said first pair of wheels, a portion of said track, and said second pair of wheels.

4. In combination with a rail vehicle and a stretch of railway track of metallic rails with a ballast resistance therebetween divided into block sections, a source of track circuit current and a track relay for each section, a pair of rail contacts carried by said vehicle one for each rail of said track, an auxiliary source of current of such character as to be incapable of operating said track relay, and means for applying a sumcient potential from said auxiliary source across said rail contacts whereby current will flow over a path which includes the rails of said track and the ballast resistance therebetween thereby breaking down the resistance between the rail contact and the rail surface to improve shunting of said track relay by said rail contacts.

5. In combination with a rail vehicle and a stretch of railway track divided into block sections, a source of track circuit current and a track relay for each section, a pair of rail contacts carried by said vehicle one for each rail of said track and in engagement therewith, an auxiliary source of varying current of such character as to be incapable of operating said track relay, and a transformer having a high leakage reactance one winding of which is connected across said auxiliary source and another low resistance track shunting winding of which is connected across said rail contacts whereby sufiicient current will flow from said other winding over a path which includes said rail contacts, the rails of said track, and the ballast resistance so as to break down the resistance of the rail surface at said contacts and so to improve shunting of said track relay by said rail contacts and said other winding.

6. In combination with a rail vehicle and a stretch of railway track, said Vehicle having a first traction wheel pair the axle of which is insulated from the car body, a source of propulsion current for said vehicle having one terminal connected to one terminal of a driving motor aboard said vehicle the other terminal of said motor being connected to a second traction wheel pair joined by an axle, and means for connecting the other terminal of said source to said first wheel pair whereby the propulsion current will flow over a path which includes the portion of each rail between said first and said second wheel pairs, thereby breaking down the resistance of the rail surface to improve shunting of the track by said wheel pairs.

7. In combination with a stretch of railway track and a rail vehicle the wheels of which do not make electrical contact with the rails of said track, a .first pair of rail contacts one for each rail and connected together electrically, a second pair of rail contacts one for each rail and also connected together electrically, a source of propulsion current for said vehicle having one terminal connected to one terminal of a driving motor aboard the vehicle the other terminal of said motor being connected to said first pair of rail contacts, and means for connecting the other terminal of said source to said second pair of rail contacts whereby the propulsion current will flow over a path which includes the portion of each rail between said first and said second contact pairs, thereby breaking down the resistance of the rail surface to improve shunting of the track by said contact pairs.

8. In combination with a rail vehicle and a stretch of railway track, said vehicle having a first traction wheel pair the axle of which is insulated from the car body, a source of current having one terminal connected to said first wheel pair, an impedance having one terminal connected to the other terminal of said source, an indicator connected across a portion of said impedance for indicating the flow of current through said impedance, and means for connecting the other terminal of said impedance to a second traction wheel pair joined by an axle whereby current from said source will flow through said impedance over a circuit which includes the portion of each rail between said first and said second wheel pairs, thereby breaking down the resistance of the rail surface to improve shunting of the track by said wheel pairs.

9. In combination, a stretch of railway track divided into track circuit sections, a track transformer and a track relay for each section, a rail vehicle having a first traction wheel pair the axle of which is insulated from the car body, a source of current having one terminal connected to said first wheel pair, an impedance having one terminal connected to the other terminal of said source, means for connecting the other terminal of said impedance to a second traction wheel pair joined by an axle whereby current from said source will flow through said impedance over a circuit which includes the portion of each rail between said first and said second wheel pairs thereby breaking down the resistance of the rail surface to improve shunting of said track relay by said wheel pairs, and two impedance bonds, one connected across the rails at the exit end of one track circuit and the other connected across the rails at the entrance end of the adjoining track circuit, the midpoints of said bonds being connected together electrically to permit the flow of current from said source through said rail portions when said first and said second wheel pairs occupy adjoining track circuits.

10. In combination with a rail vehicle and a stretch of railway track, a first pair of rail contacts one for each rail carried by said vehicle and joined by a conductor of low impedance, a second pair of rail contacts one for each rail also carried by said vehicle, two transformers each having high leakage reactance, one terminal of the secondary winding of each of said transformers being connected with said conductor, the remaining terminal of one secondary winding being connected with one contact of said second pair and the remaining terminal of the other secondary winding being connected with the other contact of said second pair; a source of varying current, and means for supplying current from said source to the primary winding of each of said transformers whereby current will fiow over two paths each of which includes one contact of each of said pairs and the rail portion therebetween, thereby breaking down the resistance of the rail surface to improve shunting of said track by said first pair of contacts.

11. In combination with a rail vehicle and a stretch of railway track, a first pair of rail contacts one for each rail carried by said vehicle and joined by a conductor of low impedance, a second pair of rail contacts one for each rail also carried by said vehicle; two sources of current on said vehicle, one terminal of each source being connected with said conductor, the remaining terminal of one source being connected with one contact of said second pair and the remaining terminal of the other source being connected with the other contact of said second pair whereby current will flow over two paths each of which includes one contact of each of said pairs and the rail portion therebetween, and two indicators each governed by the current flowing in the respective rail path for providing an indication when the rail contact resistance in the respective path exceeds a predetermined value.

12. In combination with a section of railway track and a rail vehicle, two track shunts for said track, each including a pair of running wheels of the Vehicle and an axle, at least one of said axles being electrically insulated from the vehicle body, a source of current, and means for passing current from said source over two paths one of which includes one half of each of said two track shunts and the rail portion therebetween, and the other of which includes the remaining half of each of said two track shunts and the rail portion therebetween, said current aiding to break down the rail film in both of said paths to improve shunting of the track by said two track shunts.

13. In combination with a rail vehicle and a stretch of railway track, a source of current on the vehicle, a low impedance shunting connection from one to the other rail of said track and carried by said vehicle, and means for conducting current from said source over two paths, one of which includes one rail of said track and the associated rail terminal of said connection and the other of which includes the other rail of said track and the other rail terminal of said connection, thereby breaking down the resistance of the rail surface at the rail terminals of said connection to improve shunting of said track.

14. In combination with a rail vehicle and a stretch of railway track, an impedance connected between the rails of said track, a source of current, a pair of rail contacts one for each rail and carried by the vehicle, and means for applying a sufficient potential from said source across said rail contacts whereby a current will fiow over a path which includes a portion of each rail and said impedance thereby breaking down the resistance between the rail contacts and the rail surface to improve shunting of said track by said rail contacts.

15. In a shunting system for railway track circuits, said system comprising track engaging brushes, a plurality of energizing circuits, said energizing circuits connecting pairs of brushes at opposite sides of the vehicle and in staggered relation longitudinally of the vehicle, and bridging circuits, each including a portion of one of said energizing circuits and a part of said track.

16. In combination with a vehicle out of electrical contact with its running rails, current conducting means contacting with each of the rails, circuits conducting continuous current from the current conducting means contacting with one rail to the current conducting means contacting with the opposite rail, means causing alternating current to fiow in series through pairs of the conducting means which contact with the same rail and means detecting the flow of said alternating current.

17. In combination with a railway car, a track circuit including two spaced trackway conductors, a first pair of insulated brushes on the car in contact with one of the trackway conductors, a second pair of insulated brushes on the car in contact with the other of the trackway conductors, a shunt circuit connecting the first and second pairs of brushes, a source of alternating current on the car, a first circuit for said alternating current including the brushes of the first pair in series, a second circuit for said alternating current including the brushes of the second pair in series, and means for determining the effectiveness of said shunt circuit to interconnect the two trackway conductors in accordance with the fiow of current in the first and second circuits.

18. In a railway signalling system, spaced insulated conductors, a signal control track circuit including the conductors, a Vehicle moving along the conductors, two right-hand spaced shunt shoes on the Vehicle in contact with one of the conductors, an alternating current source of energy on the vehicle, a first circuit energized by said source of energy and including the two right hand shunt shoes in series and a section of the associated conductor spanned thereby, two left hand shunt shoes on the vehicle in contact; with the other of the conductors, a second circuit energized by said source of energy and including the two left hand shunt shoes in series and a section of said other conductor spanned thereby, and an electrical connection between like potential points of said first circuit and said second circuit.

19. In occupancy detecting means for vehicles, in combination with a pair of spaced conductors, a pair of spaced brushes in contact with one conductor, a like pair of spaced brushes in contact with the other conductor, a low resistance conductor connecting one brush of a pair to one brush of the other pair, and two independent circuits, each including a said pair of brushes in series and means for energizing these ircuits independently of each other.

20. In occupancy detecting means for vehicles, in combination with a pair of spaced conductors, a pair of spaced brushes in contact with one conductor, a like pair of spaced brushes in contact with the other conductor, a low resistance conductor connecting one brush of a pair to one brush of the other pair, and two independent circuits, each including a said pair of brushes in series and means for energizing these circuitsv independently of each other with alternating current.

21. In combination with a railway car, a track circuit including two spaced trackway conductors, a first pair of insulated brushes on the car in contact with one of the trackway conductors, a second pair of insulated brushes on the car in contact with the other of the trackway conductors, a shunt circuit connecting the first and second pairs of brushes, a source of alternating current on the car, a first circuit for said alternating current including the brushes of the first pair in series, and a second circuit for said alternating current, including the brushes of the second pair in series.

22. In occupancy detecting means for vehicles, in combination with a pair of spaced conductors, a pair of spaced contactors in contact with one conductor, a pair of spaced contactors in contact with the other conductor, a low resistance conductor connecting one contactor of a pair to one contactor of the other pair, two circuits, each including the respective pair of said contactors in series, and means for energizing said circuits.

23. A device for facilitating closing of track signal circuits by a car comprising means within the car for passing current through a portion of each rail to penetrate the same, and a connection between said portions of the respective rails.

24. A device for facilitating closing of track signal circuits by a car comprising means within the car for passing current through a portion of each rail to penetrate the same, and a connection between points of substantially equal potential in said portions of the respective rails.

25. In combination with a stretch of railway track and a rail vehicle thereon, a circuit including a rail of said track and a source of current on the vehicle for breaking down the resistance film on the rail surface, and means on the vehicle for increasing the voltage applied to said circuit in the event of failure of the flow of current therein from said source.

26. In combination with a stretch of railway track and a vehicle thereon, a circuit including a source of current on the Vehicle and a short section of each track rail in series for breaking down the resistance films on the rail surfaces, and means on the vehicle for increasing the voltage applied to said circuit in the event of failure of the flow of current therein from said source.

27. In combination with a rail vehicle and a stretch of railway track, a vehicle-carried track shunt comprising a pair of rail contacts engaging the respective rails of the track and joined by a conductor of low impedance, means on the vehicle for passing sufficient current through the rail contacts of said track shunt into the rails to break down the rail film resistance and establish an effective short circuit between the two rails, and means governed in accordance with the magnitude of the current flowing through said rail contacts for providing an indication when the rail film resistance at the contacts of said track shunt is broken down.

28. In combination with a rail vehicle operable along metallic rails, two pairs of shunt shoes on the vehicle one pair in contact with each of the two rails, a first circuit including the pair of shunt shoes contacting with one rail, a second circuit including the pair of shunt shoes contacting with the other rail, a source of alternating current on the vehicle, and means for inducing current from said source in each of said first and second circuits.

29. In combination, a section of railway track, a low resistance conducting path from one to the other rail established by a rail vehicle occupying said section, a first circuit for applying a relatively high voltage and low current to said conducting path for breaking down the rail film resistance in the track shunting path established by said rail vehicle, and a second circuit for applying a relatively low voltage and high current to said conducting path for maintaining the low resistance of said track shunting path during oocupancy of said section by the rail vehicle once said rail film resistance is broken down.

30. In combination with a section of railway track and a vehicle arranged for travel thereon, a low resistance conducting path from one to the other rail established by said vehicle, a vehiclecarried circuit for applying a relatively high voltage and low current to said conducting path for breaking down the rail film resistance in the track shunting path established between the rails of said section by said vehicle, and a wayside circuit forapplying a relatively low voltage and high current to said conducting path for maintaining the low resistance of said track shunting path during occupancy of said section by the vehicle once said rail film resistance is broken down.

31. In combination, a section of railway track, a low resistance conducting path extending from one to the other rail of said section to provide a track shunt for the section, means. for applying a sufficient rail film breakdown voltage to said conducting path to break down the resistance between the rail terminals of said path and the respective rails, and other means for causing a suificient current to flow through said conducting path and the rails once said rail film resistance has been broken down for maintaining the low resistance of the track shunt provided by said path.

32. In combination with a rail vehicle and a stretch of railway track having a source of current and a track relay associated therewith, a second source of current and a track shunt both carried on the vehicle, means for applying a sufilcient potential from said second source to the rails of said stretch for breaking down the resistance of the rail surface at the rail contacts of said track shunt so as to release said track relay, and an indicator governed by the current flowing from said second source when said resistance is broken down.

HOWARD A. THOMPSON.

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