US1875839A - Railway traffic controlling apparatus - Google Patents

Description

p 1932- v. s. ALEXANDER ET AL. 1,375,839

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Sept. 29, 1930 570w H's/ 1m g F f 2; I v. I mil-CH5 :51 11 1 B ZQ EM To Sol/me 401 35 L ofiilaid ZG Pnasscwe 41 56 2? 0 0 ill T 57 5270/ a i INV NTOR .S

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J W ATTORNEY Patented Sept? 9 i932 VINCENT S. ALEXANDER, OE SWISSVALE, AND DONALD G. ACKERLY, F WILKINSBURG PENNSYLVANIA, ASSIGNORS TO THE UNION SWITCH & SIGNAL COMPANY, OF SWISS- VALE, PENNSYLVANIA, A CORPORATION OF PENNSYLVANLA LWA'Y a? FFIC CONTROLLING APPARATUS Our invention relates to railway traific controlling apparatus, and is particularly suitable for, although in no way limited to, use for automatically controlling the retarding force exerted by a car retarder in accordance with the speed of a car entering the retarder.

We will describe one form of apparatus embodying our invention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a diagrammatic view illustrating one form of apparatus embodying our invention applied to the control of a railway car retarder. Fig. 2 is a diagrammatic view illustrating'the contact structure for the relay H forming a part of the apparatus illustrated in Fig. 1.

Fig 3 is a view showing a modified form of a portion of the apparatus illustrated in Fig.

1. and also embodying our invention. 1.; Similar reference characters refer to similar parts in all three views.

Referring first to Fig. 1, the reference characters 1 and 1 designate the track rails of a main track A, and the reference characters 2 and 2 designate the track rails of an auxiliary track 0 which is connected with the main trackA by means of a switch D;

Associated with the main track A, for retarding the speed of a car approaching the switch'D from the left, is a car retarder comprising two braking bars 3 and 4 extending parallel with, and located on opposite sides of, the rail 1. The car retarder also comprises two other braking bars 3 and 4 which extend parallel with, and are located on opposite sides of, the rail 1*.

The braking bars 3, 4, 3 and 4 are operated by a fluid pressure motor M comprising a cylinder 5 containing a reciprocable piston 6 which is attached to a piston rod 7. The braking bars 3, 4 3 and 4 are operatively connected with the piston rod 7 of motor M through suitable linkage including a lever 8 pivoted at point 9. When piston 6 occupies its extreme right-hand position, in which it is illustrated in the drawing, the braking bars 3, 4, 3* and 4 occupy their non-braking or ineffective positions in which they are out of engagement with the wheels of a car traversing rails 1 and 1. When the piston 6 is moved to its left-hand position, however, as when fluid pressure is admitted to the'right hand end of cylinder 5, the braking bars 3, 4:,

3 and 1 are moved toward the associated rail to their effective or braking positions in which they engage the wheels of a car traversing the rails 1 and 1 to retard the speed of the car.

The motor M is controlled by two magnet valves E and F, each comprising a valve stem 10 biased to an upper position by means W of a spring 11, and each provided with a winding 12 and an armature 13. hen winding 12 of valve E is deenergized, valve stem.

10 occupies its upper position, in which the left-hand end of cylinder 5 is connected with w atmosphere through a pipe 14 and a port 15.

-When winding 12 of this valve is energized,

however, as illustrated in the drawing, valve stem 10 is moved downwardly to disconnect pipe 14 from port15, andto connect this pipe 7@ with a suitable source of fluid pressure, not shown in the drawing, through a pipe 16. When winding 12 of valve E is energized, therefore, the fluid pressure supplied to the left-hand end of cylinder 5 moves piston 6 7 toward the right, thereby moving the braking bars to their non-braking positions.

When winding 12 of valve F is deenergized, valve stem 1.0 of this valve occupies an upper position, in which the right-hand end of cyl- 30 inder 5 is connected with atmosphere through pipe 17 and a port 18. When winding 12 of valve F is energized, however, valve stem 10 moves downwardly, disconnecting pipe 17 from port 18, and connecting this pipe with $5 the source of fluid pressure through pipe 19.

It will be apparent, therefore, that when valve F is energized, piston 6 is urged toward the left to move the braking bars' into their effective positions by a force which is proportional to the pressure of the fluid supplied to the right-hand end of cylinder 5 under these conditions. I

The reference character 1 designates a circuit controller comprising a Bourdon tube 20 connected with pipe 17 and subjected to the pressure in the right-hand end of cylinder 5. The Bourdon tube 20 controls a contact 21 which is closed at all times except when the pressure exceeds a predetermlned amount, such for example, as 30 pounds per square inch, which pressure is preferably just sufficient to move the braking bars to their effective or braking positions. Circuit controllers 1 and P are similar to the circuit controller P except that the contacts 21 of these circuit controllers are arranged to open successively as the pressure in the right-hand end of cylinder 5 increases. For example, the parts may be so adjusted that for all pressures below 30 pounds per square inch, contact 21 of each of these circuit controllers is closed, but when the pressure exceeds pounds per square inch, contact 21 of circuit controller P opens, and when the pressure exceeds 50 pounds per square inch, contact 21 of circuit controller P opens.

The Valve F is controlled by the circuit controllers P, P and P and by two relays G and-H. Relay G may be similar to any of the well known forms of relays commonly employed for railway signaling purposes. Relay H, however, has slow pick-up characteristics, and, in the form illustrated diagrammatically in Fig. 2, comprises a rocker 27, having pivots 27 mounted in bearings forming no part of our invention and not shown in the drawing. The rocker 27 is also provided with a horizontal arm 28 which is pivotally connected with the upper end of a link 29. The lower end of the link 29 is connected with a motor 30 by means of suitablemechanism, indicated in the drawing by the dash line 31, this mechanism being so constructed that when the relay becomes energized, the rocker 27 will be slowly rotated from the position shown through a comparatively small angle in a counter-clockwise direction, but that when the relay becomes deenergized, the rocker will be immediately returned to the position shown. One form of mechanism which will operate in the manner described is shown and described in an application for Letters Patent of the United States, Serial No. 419,303, filed by Allan T. Johnston, on

Dec. 8, 1929, for electrical relays. When the mechanism-in the said .application is employed, the lower end of the link 29 will be pivotally mounted on the spacing stud 20 of the movable arm G shown in the said application. The rocker 27 is provided with a plurality of contacts adjusted to be operated in a definite order when the relay becomes energized. As here shown, these contacts are ten in number and are designated by the reference characters 32-41, inclusive. When 7 and the contacts 37, 38, 39, 40 and 41 are all closed. When the rocker has been rotated from its normal position through a small angle, for example, contact37 opens. At 1 from its normal position, contact 33 closes; at 2 contact 36 closes; at 3, contact 35 closes, and contact 41 opens; at 4 contact34 closes and contacts 38 and 40 open; at 5 contact 39 opens; and at 5%? or full stroke, contact 32 closes. Of course, it is to be understood that the particular distance from the normal position at which we have described the contacts as opening and closing have been chosen merely for convenience 1n illustrating our invention and may be Varied as conditions require, the only essential requirement being that the contacts are operated in the order specified.

The relay H in addition to controlling the magnet valve F also controls the magnet valve E in a manner which will appear hereinafter.

Relay G is controlled by a light sensitive device J and relay H is controlled by the relay G and by a light sensitive device J The device J is located on one side of the track A, opposite the car retarder R, and located a on the other side of the track also opposite the retarder, isan electric lamp L These two parts are so related that the device J 1 normally receives light from the lamp- L but that this light is intercepted by the body of acar as it moves through the retarder. The device J 2 and an electric lamp L are located in such positions that this latter device normally receives light from the associated lamp, but that this light is intercepted by a 'car approaching the retarder. The devices J and J 2 are similar, and each comprises an enclosing tube which is open at the end-toward the track, in order to prevent the light sensitive element of the device from being influenced by light other than that which is received from the associated lamp. The device J also comprises a contact 42 which is normally closed, 'but which becomes opened when the supply of light to the device J is cut off. Similarly, the device J is provided with a normally open contact 43 which becomes closed when the supply of light to the device J 2 is cut ofi. The devices J and J 2 are constantly supplied with operating current from the terminals B and X of a suitable source not shown in the drawing. The lamps L and L are also supplied with current from the ter- 9 trol circuits.

amaze but becomes energized as soon as a car approaching the retarder intercepts the supply of light to the device J Relay H is also provided with a circuit which includes a back contact 22 of relay G, so that relay H will also be energized whenever relay G is deenergized. The circuit for relay G includes contact 42 of device J and relay G will therefore be energized except when a car intercepts the supply of light to the device J Magnet valve F is provided with four con- The first circuit passes from terminal B through contacts 38 and 33 of relay H, front contact 23 of relay G, contact 21 of circuit controller 1 and winding 12 of magnet valve F to terminal X. The second circuit for magnet valve F passes from terminal B through contacts 39 and 34 of relay H, front contact 24-24 of relay G, contact 21 of circuit controller P and winding 12 of magnet valve F to terminal X. This latter circuit is provided with a branch around front-contact 24-24 of relay G including back contact 24-24 of relay G, as will be apparent from an inspection of the drawing. The third circuit for magnet valve F passes from terminal B through contacts 40 and 35 of relay H, back contact of relay G, contact 21 of circuit controller P and winding 12 of magnet valve F to terminal X. The fourth circuit for magnet valve F passes from terminal B through contacts 41 and 36 of relay H, back contact 26 of relay G, and winding 12 of magnet valve F to terminal X.

As shown in the drawing, the devices J and J are both receiving light from the associated lamps L, so that contact 42 of device J is closed, and contact 43 of device J is open. Relay G is therefore energized, but relay H is deenergized. Since relay H is deenergized, a circuit is completed for valve E which passes from terminal B through contact 37 of relay H and the Winding 12 of valve E to terminal X. Valve E is therefore energized, so that fluid pressure is admitted to the left-hand end of cylinder 5 to hold the braking bars in their open or inefi'ective positions. The contact 21 of each of the pressure responsive devices P 9, P and P is closed, but each of the circuits for valve F is open at a contact of relay H so that valve F is deenergized. The right-hand end of cylinder 5is therefore vented to atmosphere.

We will now assume that a car moving at the fastest speed at which cars are permitted to enter the retarder approaches the retarder from the left. As soon as the front end of the car passes the device J", the supply of light to this device is cut off, and device J 2 therefore closes its normally open contact 43. This completes the circuit for relay H including contact 43, and relay H therefore becomes energized and commences to operate rocker 27. Contact 37 first'opens and interrupts the circuit previously traced for valve E,

sothat valve E becomes deenergized and vents the left-hand end of cylinder 5 to atmosphere. Contact 33 of relay H next becomes closed, thereby completing the circuit for valve F including contact 21 of circuit controller 1?. Valve F therefore becomes energized and admits fluid pressure to the righthand end of cylinder 5 until the pressure in this end of the cylinder exceeds pounds per square inch, at which time contact 21 of circuit controller P opens and deenergizes valve F until the pressure again decreases below 30 pounds per square inch. This pressure, as previously pointed out, is just suficient to move the braking bars to their closed or effective positions, and the parts are so arranged and so proportioned that the braking bars will reach their efiective positions before the wheel-s of the front truck of the car has entered the retarder. When the car has entered the retarder far enough so that the supply of light to the device J is cut off, this device opens its contact 42 and deenergizes relay G. The parts are so designed and disposed that for a car traveling at the maximum speed for which the apparatus is intended to operate, contact 42 opens after contact 36' of relay H closes, but before contact 41 opens. As a result, when back contact 26 of relay G becomes closed, the circuit for valve F including this contact is completed, and valve F again becomes energized, the circuit over which this valve previously became energized having been opened at front contact 23 of relay G when relay G became deenergized. Full line pressure is therefore admitted to the right-handend of cylinder 5, so that the brak ing bars now exert their maximum braking forces. When contact 22 of relay G became closed, it completed the other circuit'previously traced for relay H, so that relay H will now remain energized even though contact 43. of device J becomes opened due to the rear end of the car having passed beyond this device. When contact of relay H becomes closed, contact 41 opens. The circuit forvalve F including contact 41 is then interrupted and the right-hand end of cylinder 5 is exhausted, and when the pressure in the righthand end of this cylinder is brought below pounds per square inch, contact 21 of device P closes and a circuit is closed for valve F over this contact and contact 35 of relay H. Pressure of 50 pounds per square inch is therefore maintained in the right-hand end of cylinder 5 and the braking bars then exert a corresponding braking force. Further operation of relay H causes contacts 38 and to open and contact 34 to close. It will be obvious from the drawing that valve F will then be energized over the circuit previously traced for this valve including contact 34 of relay H and contact 21 of circuit controller P, so

that the braking bars will now exert a braking force corresponding to a pressure of 40 pounds per square inch in the right-hand end of cylinder 5. Just before relay H completes its operation, contact 39 opens and deenergizes valve F, and when relay H has fully completed its operation, contact 32 closes and completes a circuit for valve E which is obvious from the drawing. Valve E therefore becomes energized and admits fluid to the lefthand end of cylinder to restore the braking bars to their open or ineffective positions. When the car has passed beyond device J this device closes its contact 42, thereby energizin g relay G and, hence, deenergizing relay H. Thecontacts of relay H then return to the positions in which they are illustrated in the drawing, and the apparatus is restored to its normal condition. It will be plain from the foregoing that when the car passes lamp L and device J the braking bars are moved to their effective positions by fluid at a low pressure, and that higher pressure is applied to the retarder after the car passes lamp L and device J this higher pressure being graduated depending upon the extent of operation of relay H prior to the'dcenergization of relay G, and hence depending upon the speed of the car.

Thus if the speed of the car is slightly less than the maximum speed discussed above, contact 41 of relay H will open, and contact 35 of this relay will close before relay G becomes deenergized. Under these conditions, the highest braking force exerted by the braking bars would be that corresponding to a pressure of pounds per square inch in the right-hand end of cylinder 5. The operation of the apparatus in all other respects under these conidtions is similar to that previously described.

Furthermore, if the car had approached the retarder at a still slower speed, it would not have intercepted the light from lamp L until contacts 40 and 38 of relay H had opened and contact 34 had closed. It follows, that under these latter conditions, the highest braking force exerted by the braking bars would be that corresponding to a pressure of 40 pounds per square inch in the left-hand end of cylinder 5. v

It will be seen from the foregoing that with apparatus embodying our invention, the fast er a car approaches the retarder, the reater is the braking force applied to it t will.

alsobe apparent from an inspection of the drawing and from the foregoing description that, should the car he stopped for any reason at all before it reaches the end of the retarder, it will be released automatically as soon as relay H is fully picked up.

The maximum distance between the light sensitive devices J and J 2 should not be greater than the minimum car length. In actual practice, the distance in rear of the retarder at which the car intercepts the beam from the lamp L and the position in the retarder at which the car intercepts the beam from the lamp L may be determined by experiment, in order to obtain the desired operation of the apparatus.

As previously pointed out, the circuit for the lamps L and L includes'a manually operable switch S. The function of this switch is to deenergize the lamps L and L so that a shifting engine or a train may be permitted to pass through the retarder without operating the retarder.

In order to insure that the light beams will be intercepted by any car passing through the retarder, the lamps for illuminating the light sensitive devices may, if desired, be placed at a difierent height from the ground than the associated light sensitive device. With this arrangement, the light beams will cross the track in a plane inclined at an angle to the plane of the floor of the car, and will, therefore, be intercepted by a car of any type.

Under some conditions, it may be desirable to control both light sensitive devices by only one light source instead of by two light sources as shown in Fig. 1. This may be accomplished by means of the apparatus illustrated in Fig. 2. As here shown, the electric lamp L is arranged to supply two beams of light, one to each of the devices J and J and the device J 2 is moved far enough in rear of the retarder so that the beam of light from the lamp L to the device J will be intercepted by a car approaching the retarder at the same distance in rear of the retarder as the beam from the lamp L to the device J 2 in Fig. 1 is intercepted by a car approaching the retarder. It will be noted that the enclosing tube of the device J in Fig. 2 is directed'at an angle toward the trackin order to receive the beam of light from. the lamp L in the described manner. The operation of the apparatus with the devices J and J 2 both supplied with light from the lamp L as shown in Fig. 2, is identical with the operation when each device is sup plied with. a separate lamp, and will be readily understood without further explanation.

It should be pointed out that while we have illustrated apparatus embodying our invention as applied to the control of a car retarder, it is not limited to this use, but may be utilized to control any desired type of traflic governing device when it is desired to operate such devices in accordance with the speed at which a car'is moving along a stretch of track.

Although we have herein shown and described only one form of railway traflic con- Ill trolling apparatus embodying our invention,

reraeae mined order upon energization of the relay, means for energizing said first relay when a predetermined point on a car passes a predetermined point along the trackway, a second relay, means for operating said second relay when a predetermined point on the car passes a second point along the trackway located inv advance of said first point, traffic governing means, and means selectively controlled by the contacts of said two relays for controlling said trafiic governing means in accordance with the speed of said car.

2. In combination, a stretch of railway track, a first relay provided with a plurality of normally open and normally closed contacts arranged to be operated in a predetermined order upo'n energization of the relay, means for energizing said first relay when a predetermined polnt on a car passes a predetermined point along the trackway, a second relay, means for operating said second relay when a predetermined point on the car passes a second point along the trackway located in advance of said first point, a plurality of circuits each including a normally open and a normally closed contact of said first relay as well as a contact of said second relay, and trafiic governing means controlled by said circuits.

3. In combination, a strength of railway track, a first relay provided with a plurality of normally open and normally closed contacts arranged to be operated in a predetermined order upon energization of the relay, means for energizing said first relay while a car is passing a predetermined point along the trackway, a second relay, means for operating said second relay while a car is passing a second point along the trackway located in advance of said first point, means controlled by said second relay for energizing said first relay, and traific overning means selectively controlled by t e contacts of said two relays.

4. In combination, a stretch of railway track, a first relay provided with a plurality of normally open and normally closed contacts arranged to be operated in a predetermined order upon energization of the relay, means for energizing said first relay while a car is passing a predetermined point along the trackway, a normally energized relay, means for deenergizing said normally energized relay while a car is passing a second point along the trackway located in advance of said first point, means controlled by said normally energized relay for energizing said first relay, and traffic governing means selectively controlled by the contacts of said two relays.

5. In combination, a stretch of railway track, a slow pick-up relay provided with a plurality of normally open and normally closed contacts arranged to be operated in a predetermined order upon energization of the relay, means for energizing said first relay while a car is passing a predetermined point along the trackway, a second relay,

means for operating said second relay while a car is passing a second point along the trackway located in advance of said first point a distance which is less than the length of said car, means controlled by said second relay for energizing said first relay, a plurality of circuits each including a normally open and a normally closed contact of said first relay as Well as a contact of said second relay, and traflic governing means selectively controlled by said circuits.

6. In combination a stretch of railway track, a slow pick-up relay comprising first and second normally open contacts which become closed successively as the relay picks up and first and second normally closed contacts which become opened successively after said first and second contacts become closed, a normally open circuit for said relay, means for closing said circuit while a car is passing a first predetermined point along the trackway, a second relay, a normally closed circuit for said second relay, means for opening said normally closed circuit while said car is passing a second point along the trackway located in advance of said first point a distance which is less than the minimum length of said car, a second circuit for said first relay controlled by a back contact of said second relay, a fourth circuit including said first normally open contact of said first relay and said second normally closed contact of said first relay as well as a back contact of said second'relay, a fifth circuit including said second normally open contact of said first relay and said first normally closed contact of said second relay as well as a back contact of said first relay, and traffic governing means controlled by said fourth and fifth circuits.

7. In combination, a stretch of railway track, a slow pick-up relay comprising first, second, third, and fourth normally open contacts which become closed successively as the relay picks up, a first normally closed contact which becomes opened at the same time as said third contact becomes closed, second and third normally closed contacts which become opened at the same time as said fourth contact becomes closed, and a fourth normally closed contact which becomes opened after said fourth normally open contact becomes closed; means for energizing said slow (pickup relay while a car is passing a pre etermined point along the trackway, a normally energized rel'ay, means for deenergizing said normally energized relay while the car is passing a second point along the trackway said fourth normally closed contact of said slow pick-up relay and said fourth normally open contact of said slow pick-up relay, a third circuit including said third normally closed contact of said slow pick-up relay and said third normally open contact of said slow pick-up relay as well as a back contact of said normally energized relay, a fourth circuit includingsaid first normally closed contact of said slow pick-up relay and said second normally open contact of said slow pick-up relay as well as a back contact of said normally energized relay, and traflic governing means selectively controlled by said four circuits.

8. In combination, a stretch of railway track, a first relay provided with a plurality of normally open and normally closed contacts arranged to be operated in a predetermined order upon energization of the relay, means for energizing said first relay while a car is passing a predetermined point along the trackway, a normally energized relay, means for deenergizing said second relay while a car is pasing a second point along the trackway located in advance of said first point, means controlled by said normally energized relay for energizing said first relay, and a car retarder automatically controlled by the contacts of said two relays.

9. In combination, a stretch of railway track, a first relay provided with a plurality of normally open and normally closed contacts arranged to be operated in a predetermined order upon energization of the relay, means for energizing said first relay while a car is passing a predetermined point along the trackway, a second relay, means for operating said second relay while a car is passing a second point along the trackway located in advance of said first point, means controlled by said second relay for energizing said first relay, a car retarder associated with said stretch, and operating mechanism for said car retarder controlled by the contacts of said two relays.

10. In combination, a stretch of railway track, a slow pick-up relay comprising first, second, third, and fourth normally open contacts which become closed successively as the relay picks up, a first normally closed contact which becomes opened at the same time as said third contact becomes closed, second and third normally closed contacts which become opened at the same time as said fourth contact becomes closed, and a fourth} normally closed contact which becomes opened after said fourth normally open contact becomes closed; means for energizing said relay while a car is passing a predetermined point along the trackway, a normally energized relay,

means for deenergizing said normally ener- I gized relay while the car is passing a second relay' and said first normally open contact of said slow pick-up relay as well as a front contact of said normally energized relay, a second circuit including said fourth normally closed contact of said slow pick-up relay and said fourth normally open contact of said slow pick-up relay, a third circuit including said third normally closed contact of said slow pick-up relay and said third normally open contact of said slow pick-up relay as well as a back contact of said normally energized relay, a fourth" circuit including said first normally closed contact of said slow pick-up relay and said second normally open contact of said slow pick-up relay as well as a back contact of said normally energized relay, a car retarder, and operating mechanism for said car retarder selectively controlled by said circuits, said mechanism being so constructed that said car retarder exerts a difi'erent braking force for each one of said circuits that is closed.

11. In combination, a stretch of railway track, a car retarder associated with said stretch,;a first and second source of light disposed along the track adjacent said retarder, a first and second light sensitive device normally receiving light from said first and second sources respectively but arranged to be successively obscured by a car traversing said stretch, a slow pick-up relay controlled by said first light sensitive device and provided with normal and reverse contacts which are operated in a predetermined order upon energization of the relay, a second relay controlled by said second light sensitive device, means controlled by said second relay for at times controlling said first relay, a plurality of circuits each including a normal and a reverse contact of said first relay as well as a second contact of said second relay, and operating mechanism for said car retarder controlled by said circuits, said mechanism being so designed that said ear retarder will exert a different braking force for each different circuit which is closed.

12. In combination, a stretch of railway track, a car retarder associated with said stretch, a first source of light disposed along ranged to be obscured by a car approaching said retarder, a second source of light disposed along said stretch, a second li ht sensitive device normally receiving light rom saidsecond source but arranged to be obscured by a car in said retarder, a slow pick-up relay controlled by said first light sensitive device, said relay having a plurality of normally closed and normally open contacts which are arranged to be operated in a predetermined order as the relay picks up, a second relay controlled by said second light sensitive device, means controlled by said second rela for at times controlling said first relay, a p urality of circuit selectively controlled by said two relays and each including a normally closed and a normally open contact of said first relay and a contact of said second relay, and operating mechanism for said retarder controlled by said circuits, said mechanism being so designed that said car retarder will exert a different braking force for each difierent circuit which is closed.

13. In combination a stretch of railway track, a car retarder associated with said stretch, a source of light disposed along said stretch adjacent said retarder, a first light sensitive device located along said stretch in rear of the entrance end of said retarder and normally receiving light from said source but arranged to be obscured by a car approaching said retarder, a second light sensitive device located along said stretch opposite said retarder and normally receiving light, from said source but arranged to be obscured by a car in said retarder, a slow pick-up relay controlled by said first light sensitive device, said relay having a plurality of normally closed and normally open contacts which are arranged to be operated in a predetermined order as the relay picks up, a second relay controlled by said second light sensitive device, means controlled by said second relay for at times controlling said first relay a plurality of circuits selectively controlled by said two relays and each including a normally closed and a normally open contact of said first relay and a contact of sa d second relay, and operating mechanism for said retarder controlled by said circuits, said mechanism being so designed that said car retarder will exert a different braking force for each different circuit which is closed.

14. In. combination, a stretch of railway track, a car retarder associated with said stretch, a fluid pressure motor comprising a cylinder provided with a reciprocable piston which is operatively connect-ed with said retarder, a first magnet valve for controlling the admission of fluid to one end of said cylinder, a.second magnet valve for controlling the admission of fluid to the other end of said cylinder, a first, second, and third normally closed contact arranged to be successively opened as the pressure in said one a second source of light disposed along said stretch, a second light sensitive device normally receiving light from said second source but arranged to be obscured by a car in said retarder, a slow pick-up relay controlled by said first light sensitive device said relay comprising first, second, third, fourth and fifth normally open contacts which become closed successively as the relay picks up, a first normally closed con-.

tact which becomes opened before said first normally open contact becomes'closed, a second normally closed contact Which becomes opened at the same time as said third normally open contact becomes closed, third and fourth normally closed contacts which become opened at the same time as said fourth contact becomes closed, and a fifth normally closed contact which becomes opened after said fourth normally open contact becomes closed and before said fifth normally open contact becomes closed, a second'relay controlled by said second light sensitive device, a circuit for said slow pick-up relay including a back contact of said second relay, a first circuit for said second magnet valve including said first normally closed contact of said first relay, a second circuit for said second magnet valve including said fifth normally open contact of said first relay; a first circuit for said first magnet Valve including said third normally closed contact of said first relay, said first normallyopen contact of saidfirst relay,v a front contact of said second relay, and said first normally closed pressure controlled contact; a second circuit for said first magnet valve including said fifth normally closed contact of said first relay, said fourth normally open contact of said first relay, and, said second normally closed pressure controlled contact; a th rd circuit for said first magnet valve includlng said fourth normally closed contact of said first relay, said third normally open contact of said first relay, a back contact of said second relay, and said third normally closed pressure controlled contact; and a fourth circuit for said first magnet valve including said second normally closed contact of said first relay, said second normally open contact of said first relay, and a back contact of said second relay.

15. In combination, a car retarder capable of assuming a plurality of operating conditions but normall assuming an ineffective condition, two light sensitive units, two

sources of light, one for each unit and each so located that it normally illuminates the associated unit but that rays of light passing from said sources to said units are interrupted successively by a car passing through said retarder, means controlled by one said unit for imposing one operating condition upon the retarder, and means controlled by both said units for subsequently imposing a selected one of said operating conditions upon said retarder depending upon the speed of a car passing through the retarder.

In testimony whereof we aflix our signatures. VINCENT S. ALEXANDER.

DONALD G. ACKERLY.

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