CA1168639A - Low-profile railway car retarder - Google Patents

Abstract

(Case No. 7032) ABSTRACT OF THE DISCLOSURE
A low-profile railway car retarder having a pair of braking bars disposed parallel and on opposite sides of a track rail and having an upper and lower pivotal lever carrying a respective one of the pairs of braking bars.
A pneumatic motor pivotally connected to the outer extremi-ties of the upper and lower levers, and the height of the pivotal connection of the upper lever is substantially at the same level as the track rail so that a humped railway vehicle is permitted to freely pass through the car retarder.
The pneumatic motor lifts the upper lever and depresses the lower lever to move the pair of braking bars to a closed braking position wherein pressure is supplied to the pneu-matic motor so that the pair of braking bars engage the opposite side of the wheels of a traversing vehicle at a relatively high point to exert a greater amount of retarda-tion of the vehicle.

Description

3~3 hOW-PROFILE RAI~W~ CAR RETARD~R

FIELD OF TH~ INVENTION
This invention relates to railway braking apparatus and, more particularly, to a railroad p~a~matically operated rail-road car retarder employing a pair of braking ~ars disposedparallel to the track rail which ara carried by a pair of respective pivoted levers that are opened and closed ~y a pneumatic pressure piston-cylinder actuator having increased braking effort to provide greater retardation, having a low-profile design to provide more vehicle clearance, and havingan improved brake hoa wear and lever spring stop adjusting features.
BACKGROUMD OF THE I~VE~TIO~
In certain railroad operations, such as, in a classi~i-cation processing yard, the railway cars or vehicles ofincoming trains are sorted or classified in accordance with con~ist and destination in a given one of a plurality o~
class or receiving tracks. In hump types of classification yards, it i~ necessary to control the velocity or speed of the free-rolling vehicles by suitable braking apparatus.
Generally, the braking apparatus takes the form of power .
operated frictional car retarders having braking bars which engage and gxip the sides of the passing wheele of the humped railway vehicles. It will be appreciated that the amount of retardation or braking effort which is exerted on the pas~ing wheels by the car retarder is dependent upon the xolla~ility and the distance that the humped vehicle or cut of vehicles 3~

have to travel -to safely couple with the foregoing vehicle in the appropriate class track. It has been found that the most effective retardation occurs when the frictional braking force is applied to a relatively high point on the sides of the car wheels. The ensuing benefits of higher wheel contact braking results in the ability to construct and utiliæe shorter car retarders in the classification yards. It will be appreciated that the shortening of the overall length of the car retarder not only reduces the initial manufacturing cost~ but also results in the more economical use of the available space of the yard since the required length of the approach track is proportionally reduced. Further, it has been found that the leading edges, corner sill portions, or side ladders on locomotives and/or vehicles hit the upper levers and cause damage to the ~ehicl~s and retarders Further, since some humped cars were unable to clear~freely pass through the existing car retarders~the amount of retarda-tion was not always accurately controlled. Thus, it would be highly advantageous to provide a low-profile car retarder to allow the unimpeded passage of the locomotives and particu-larly, the humped cars. An additional problem in conven-tional braking apparatus resides in the difficulty in making the necessary adjustments for brake shoe wear and lever stop-ping. Thus, it is desirable to provide a simple time-saving method of brake shoe and stop adjustment.

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OBJECTS AND SUMMARY OE THE INVENTION
Accordingly, it is an object of this invention to provide a new and improved railway braking apparatus for effectively retarding railway cars.
: 5 Still another object of this invention is to provide a unique low-profile railway car retarder which allows the free, unimpeded passage of humped vehicles.
Still a further ob~ect of this invention is to provide a novel frictional-type of gripping railway brakin~ apparatus which more effectively retards passing vehicles by having the brake shoes engage the sides of the wheels at a relatively higher level.
Yet another object of this invention is to provide an improved railway car retarder which is readily adjusted for compensating for brake shoe wear.
Yet a further object of this invention is to provide a new ~ow-profile pneumatically operated car retarder having a pair of braking bars disposed parallel and on opposite sides of a track rail which is mounted on cross t.ies, an upper and a lower pivotal lever, each of the upper and lower pivotal levers having a platform portion for carrying a respective one of the pair of braking bars, the lower pivotal lever having a laterally extending arm, the upper lever initially extending upwardly and outwardly, and subsequently extendiny outwardly to form a horizontal arm, a pneumatic piston~
: cylinder actuator, the piston of the pneumatic piston-cylinder actuator pivotally connected to the cuter extremity of the laterally extending arm of the lower pivotal lever, the cylinder of ~he pneumatic piston-cylinder actuator pivo~ally connected to the outer extremity of the horizontal arm of the upper pivotal lever, the height of the pivotal connect-ion of the cylinder with the outer extremity of the horizontalarm of the upper pivotal lever is approximately fifteen inches from ~the top of the cross ties and is substantially at the same level as the top of the track rail so that a low sluny railway vehicle is permitted to freely pass through the car retarder, and the pneumatic piston-cylinder actuator lifting the upper pivotal lever and depressing the lower pivotal lever for moving the pair of braking bars to a closed braking position when pressure is supplied to the pneumatic piston-cylinder a~tuator so that the pair of braking bars engage the opposite sides of the vehicle wheels at approximately .
three and three sixteenth inches from the top of the runni.ng rail to exert a greater amount of retardation on the passing vehicle.
An additional object of this invention is to provide a new and improved railway car retarder which is economical in cost, simple in construction, dependable in service, easy to maintain, durable in use, efficient in operation, and facile to repair.
B_IEF DESCRIPTION OF THE DRAWINGS
The above ohjects and other attendant advantages of the present invention will become more readily apparent from the following detailed description when analyzed and considered in conjunction with the accompanying drawinys, wherein:

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FIG. 1 is a partial top plan view showing a staggered '.~ dual track railway braking apparatus or car retarder in accordance with the present invention.
FIG. 2 is an enlarged vertical sectional view of the car retardex in its opened nonbraking position ~aken sub-stantially along lines II-II of FIG. 1.

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Referring now to the drawings, and in particular to FI~. 1, there is ~hown a seckion or stretch of railway track which may be located in the ~ump or group area of a railroad clasqification yard. The trackway includes a pair of running track rails 1 and 2 which are suitably supported on usual cross-ties 3. In practice, the track rails 1 and 2 are mounted on a plurality of rail supports or chairs 4 which are securely fastened to the tops of cross-ties 3. As sh~wn in FIG~ 2, the rail support 4 is a prefabricated weldment structure having a lower base plate 5 and an upper box-like stand 6. The bearing plate S is situated on t~e tvp of cross-tie 3 and is bolted in place by through bolts 7. The rail 1 is disposed on top of stand 6 and is securely held in place by flange gripping member~ 8 which are bolted to the top of the stand 6.
As shown in FIG. 1, the brak.ing apparatus or car retarder is disposed about each of the rails 1 and 2 so that both wheels of each axle of the railway vehicles may be simul-taneou31y retarded to control the exiting speed of humped vehicles. It will be seen that a pair of braking bars 10 and 10' extend parallel and on opposite sides of running rail 1 while a pair of braking bars 11 and 11' extend parallel and on opposite sides o~ running rail 2. It will be noted that the entering ends of the braking shoes 10, 10' are of~set in relation to the entering ends of the braking shoes 11, 11' to allow the wheels on rail 2 to initially enter the retarder and then to allow the wheels on rail 1 to subQe~uently enter 3~3 the retarder for a smoother transitional ingreiss. In viewing FI&. 1, it will be observed tha~ the braXing bars are adapted to be moved toward and away from the respective running rails in braking and no~braking positibn~ by a plurality of pneu-matic power operating units OU. The operatiny units OU for braking bars 10 and 10' are staggered in relationship to the operating unit OU for hraking bar~ 11 and 11' which ~acilit~
tes the installation and maintenance of the braking apparatus.
In practice, a source o pneumatic or air pressure (not shown) 0 i8 piped to the individual operating units via trunk line or conduit 12 which is connected to bran~h pipes 13. The branch lines or pipes are connected to the respective operating units ~ c~ 5~'- 5 OU via flexible conduits or metal ~u~ 14. Each of the opera~
ting units OU is substantially identical in construction and includes a pneumatic piston-cylinder actuator or fluid motor 15 and a pair of upper and lawer pivotal levers 16 and 17, respectively. The upper levers 16 carry the outer braking bars 10 and 11 while the lower levers 17 carry the inner braking bars 10' and 11'. The briaking bars lOt 10' and 11, 11' con~ist of a series of elongated brake beams 20, 20' and 21, 21' jointed together at their adjoining ends by an overlap connec-tion. Each of the braking bars also includes a series of replaceable braXe shoes 22, 22' and 23, 23' which are carried by the respective brake beams 20t 20' and 21, 21'. As shown in FIG. 1, the adjacent ends of the brake shoes are stagyered with respect to the overlapping ends of the brake beams.
Further, the track rail 1 include~ an inner guide rail 24 "

and an outer guide rail 2~' at the exiting end of the retarder while the track rail 2 includes an inner guide rail 25 and an outer guide rail 25' at the exiting end of the retarder for rerailing purposes.
; 5 Turning now to FIG. 2, there is shown one of the opera-ting units OU of the car retarder which is illustrated in its opened nonbraking position for allowing the wheel W to pass through without any retardation or frictional braking. Each of the operating units OU includes a short-stro~e pneumatic piston-cylinder actuator 15, which may be of the type shown and disclosed in our copending application Ser. ~o. 367,012, filed concurrently herewith, entitled Pneumatic Pressure Actu-ator, and a pair of pivotal levers 16 and 17. The pneumatic motor 15 includes a cylinder assemblage 26 having an upper casting 27, a lower casting 28, and a plastic casing 29 held together by a plurality of tie bolts 30. The fluid pressure motor 15 also includes an internal reciprocating piston and a piston rod 31 which extends through the lower casting 28.
A pipe fitting 18 is threaded in the top of the upper casting 27 for supplying air pressure to the top of the piston by flexible conduit 14. A pipe fitting 19 is threaded in the bottom of the lower casting 28 to vent the underside of the piston to atmosphere-. As shown, the outer extremity of the upper lever 16 is pivotally connected to a trunnion portion of the upper casting 27 by a pivot or fulcrum pin 32 while the outer extremity of the lower lever 17 is pivotally con-nected to the end of the piston rod 31 by pivot or fulcrum .~, ' .
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pln 33. The pivot pins 32 and 33 are loc~ed in position by retaining eye_pins 34 and 35, respectively, which are bolted to the respective levers.
It will be seen that the upper and lower levers are pivoted about a common ulcrum point or pivot pin 37 carried by the associated rail su~ports 4 mounted on tha two adjacent cros~-ties 3. As shown in FIG. 2, the pivot pin 37 passes through sleeva beaxings in levers 16 and 17, and the pin 37 i9 locked in place by retaining eye-pins 38, each of which is bolted to the respective associated rail ~upport 4. A grease fitting 39 is provided to lubricate the mutual center bearing of the upper and lower levers 16 and 17 while grease fittings 40 and 41 are provided to lubricate the respective end bearings of uppar and lower lever~ 16 and 17. It will be seen that the upper lever 16 initially extends upwardly and outwardly from its journaled end with pivot pin 37 and that intermediat~ its free end the lever 17 is bent and extends horizontally, the purpose of which will be described hereinafter. A platform structure 45 is disposed between the bifurcated arms of upper lever 16 intermediate its pivoted ends. The platform 45 is preferably a prefabricated weldment which is fixedly secured to lever 16 by fillet welding the contiguous surfaces. Also, a bored apertured spring retaining block 46 is fillet welded to each of the outside surfaces of the bifurcated lever 16 for holding the two resilient stop - 8 ~

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units SUl and SU2~ Each of the spring units includes a bolt 48 extending downwardly with some clearance through an aper-ture formed in the retaining block 46. A long collar unit 49 is threadedly screwed onto the lower end of the bolt 48.
biasing spring 50 ~urrounds the upper collar portion o~ nut 49 and the lower portion of bolt 48. The spring is entrapped between the flange portion of nut 49 and a circular collar provided on the underside of retaining block 46. It will be seen that the resilient spring 50 is slightly depxessed by the weight of the lever assembly so that the head of the bolt 48 is spaced rom the top surface 51 of block 46.
It will be seen that the upper surface of platfo~m 45 is provided with an upstanding lug 53 which includes centrally a threaded aperture for receiving an adjusting bolt 54. The outer end of bolt 54 is provided with a hexagonal or square head 55 to facilitate turning the bolts by means of a wrench.
A lock nut 56 is provided at the end of the adjusting bolt 54 to allow the bolt to be locked in place after adjuætment.
Further, the adjusting bolt 54 i~ provided with an enlarged head portion 57 which is adapted to engage and cooperate with bifurcated members or hook portions 58 provided on the outer edge of the brake beam 20. The platform 45 includes a flat upper surface 45a which supports the braking bar lOo. As mentioned above~ the braking bar 10 includes the brake beam 20 and the replaceable bxake shoe 22 which is secured to the inside vertical surface by threaded bolts or the like. In viewing FIG. 2, it will be observed that the underside of ~ g _ ~g~

the elonga~ed braXe beam 20 is pxo~id~d with a pair of oppo~ing hook portion~ 20a which are initially aliyned with a pair of no~ches 45b formed in the opposite ~ide~ of tha flat upper surface portion A5a. In practice, the adjusting bolt 54 is suf~icien~ly bac~ed off to allow the enlarged head 57 to be disposed between the two hook portions 58 as well as to allow the hooXR to become aligned with notches 45b. Under this condition; the periphery of the hooks easily clears the edges of notche~ 45b to allow the brake beam 20 to be seated on the upper flat surface o the platorm for allowing the brake beam~ 20 to be interlocked with the supporting platform 45. That is, the adju~ting bolt 54 is turned to slide the braking bar 10 t~ward the track rail 1 so that the tong~ of the hook~ 20a will b~ situated under projecting ears 45d of platform 45~ :
Ik will be appreciated that the lower lever 17 include~
a prefabricated weldment platform tructure 45' whic~ is fixedly ~ecured by fillet welding or the like to the re te end of the lever 17. ~ike platform 45, the pla~form support 45' includes a 1at upper surface 45a' ha~ing an upstanding lug 53' welded to the top of support 45. The lug 53' is centrally bored and threaded to receive a screw-threaded adjusting bolt 54' which is pxovided with a wrench accommo-dating head 55' and a locX nut 56'. T~e adjusting bolt 54' also includes an enlarged head 57' which cooperates with hook portion 58' to move the braking bar 10' t~ward and away from the center o the track rail 1. m e brake beam 20' includes -- 10 ~

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a pair of opposing hoo~ portions 20a' which are initlally aligned with a pair of notches 45b' and subsequently are dis-posed beneath projecting ears 45d' to interlock the braking bar 10' with respect to platform 45i.
It will be seen that a resilient spring retu.rn and stop unit SU3 is also cooperatively associated with the lower lever 17. The spring unit SU3 is disposed within a fabricated hous-ing 60 formed between the bottom side of the upper plate 45a and the upper side o* the top plate of lever 17. A cixcular opening 61 is formed in the top plate of lever 17. The spring unit SU3 includes a spring bolt 63 havins an enlarged circular head 63a, a shank 63b, and a shoulder 63c. An inner s~op spring 64 and an outer return sprlng 65 are disposed about the shank portion of bolt 63~ A flanged sleeve 66 is disposed on bolt 63. m e stop spring 64 is trapped between the circular head ~3a of bolt 63 and the shoulder 63c. The return spring 65 is trapped between the enlarged head 63a o~ bolt 63 and the top surface o~ end plate 67 which is bolted to the underside of the top plate o~ the lever 17. A spring stop nut 68 is threaded onto the bolt 63 while a ~pring lock nut 69 is also threaded onto the end of bolt 63. As shown, an L,shaped angle bracket 70 is disposed between the two adjacent cross-ties 3.
An L-shaped angle iron 71 has its vertical leg welded to.each end of bracket 70 and has its horizontal leg bolted to t~e top of cross-ties 3 by through bolts 7, one of which is shown in FIG. 2. The l~wer end of bolt 63 extends downwardly through a lateral elongated slot 7Oa formed in the angle bracket 70 and is secured to bracket ~0 b~ stop nut 68 and lock nut 69 which is held in place by a cotter pin 72.
In describing the operation of the car retarder, it will be appreciated that the braking bars 10 and 10' are adjusted to have a six inch gap between the ~pposing faces of the brake shoes 22 and 22' when the retarder is in its open nonbraking position and to have a five inch gap ~etween the opposing wheel engaging surfaces of the brake shoe~ 22 and 22' when the retarder is in its clos~d braking position. For adjusting the car retarder in its open position~ a maintainer initially turns the heads of spring bolts 4~ of spring units SUl and SU2 which is readily exposed from the top of the retarder until the distance from the top of cross-ties 3 to the center of pivot pin 32 is fifteen inches. It will be appreciated that in the subject low-profile con~iguration, this distance is approximately ~wenty-five percent less than in previous frictional car retarders, namely, fifteen inches versus nineteen and three-quarter inches. ~IUS, the present low-profile car retarder i5 less likely to impede the free passage of humped railway cars. For example, low hanging side car ladders and corner sills will not engage the outer extremity of the upper lever 16 as was common occurrence in existing car retarders. It has been found that the railway cars sway or move from side-to-side as they negotiate their way from the crest ~f the hump to the ~torage tracks 50 that ~he lower corner side structuxe o the cars previously struck _ 12 -the upstanding ends of the upper levers of the prior art car retarders. Thus r less damage to rolling stock as well as -to ~he retarder proper is realized due to the unique low-profile structural configuration of the present car retarder. Fuxther, it will be appreciated that the opened and clo~ed brake shoe distances are initially adjusted by turning the stop and lock ~ 5~' nuts ~-a~2-6~' and heads 55 and 55' of khe adjusting bolts 54 and 54'~ Subsequent compensation for braXe shoe wear may be accomplished by turning the bolt~ 54 and 54' inwardly to obtain the five inch gap in the closed braking position.
Let us assume that the car retarder is in its opened non-braking position as show~ in FIG. 2 and that it is desîred that the retarder be moved to its closed braking position.
~hus, fluid pressure or air is admitted rom the supply source through lines 12, 13, and 14 to each piston-cylinder actuator or motor 15. When the fluid pressure enters the cylinder 26, ~he piston begins to move dawnwardly causing the extension of the piston rod 31. The initial downward movement of the piston rod 31 causes the lower lever 17 to rotate in a counterclockwise direction about fulcrum pin 37 thereby raising and moving the brake shoe 22' to its closed braking position as shown in phantom in FIG. 2. Further rotational movement of the l~wer lever 17 is restricted by the spring stop unit SU3. That is, when the stop spring 64 becomes fully compressed, it stops any furth~r rotation of lever 17, and thus the cylinder 26 begins to move up~ardly to cause the upper lever 16 to rotate in a clockwi~e direction about _ 13 -fulcrum pin 37. The upward movement of pi~o~al lever 16 causes the brake shoe 22 to rise and m~e the brake shoe 22 to its closed braking p~sition as denoted by the phantom lines Ln FIG. 2 when the piston-cylindex actuator reaches its fully extended position. Thus, the car retarder assumes its closed braking position so that the brake shoes 22 and 22' will engage and grip the xespective sides of ~he wheel W
or wheels of a railway car traversing the xails 1 and 2~ It will be seen that the tops of the brake shoes 22 and 22' engage the sides o~ the wheel W at the height of three and three-sixteenth inches from the top of running rail 1 which is effectively on~-quarter inch more than existing conven-tional car retarders. It has been found that by increasing the height of fxictional engagement by a quarter of an inch lS results in a ten percent increase in the retardation or braking action of the car retarder. ~hus, the overall length of the car retarder may be proportionally reduced to more e~ficiently and effectively utilize the master and group track lengths in a hump~type of classification yard where space is generally at a premium. That is, in many classi-fication yards, the amount of straight track lengths in the master and group areas is ver~ limited so that it is highly advantageous to have a car retarder as short as possible yet capable of applying the required maximum braking force on the passing car wheels. It will also be appreciated that a shorter length car retarder is not only less costly to initially purchase but also less expensi~e to subse~uently _ 14 -maintain and repair du~ to the les~er num~er o~ operating unit~ OU and brake ~hoe lengths.
In viewing FI~. 1, it will be ~een that when a vehicle enters the car retarder at the left a~ indicated by arrow A, the right wheel~ moving on rail 2 initially engage the brake shoe~ 23 and 23' and then the left wheel~ moving on rail 1 engage the brake ~hoe~ 22 and 22' due to the staggered arrange-ment of the braking bar3. Thi8 staggering of the braking apparatus of rail 2 with respect to the braking apparatus of rail 1 reduce~ entrance 8hock and jolting to the entering car and it~ lading.
If it is now desired to move the braking bar~ to their no~braking positions, it is simply necessary to e~haust the fluid or air from the piston-~ylinder actuators or fluid motors 15. In viewing FIG. 2, it will be seen that under this condition, the upper lever 16 moves in a counterclockwise direction by gravity and comes to rest when the nut 49 strike~
tha stop boss 51 provided on the bearing plate 5. Then, the lower lever 17 move~ in a clockwi~e direction about pivot pin 37 under the force of gravity and spring~ 64 and 65 and comes to re~t when the pi~ton i8 retracted to its fully extended position within cylinder 26. The spring stop units SUl and SU2 of the upper lever and spriny ~top unit SU3 of the lower lever are arranged and designed to permit the levers, motors, and as~ociated braking bar to ~wing a limited amount about the fulcrum pin 37~ In e:Efect, the limited amount of swing permits the brake ~hoes to move or travel approximately _ 15 -3~-3 one-hal of an inch on either ~ide of their:positions 80 khat the brake shoe~ may adju~t themselves to the various widths of ~he passing car wheels when the retarder i~ in i~ braking position. Further, ~he brake ~hoes may al~o adjust themselves to allow the passage o~ all cars and locomotives when the retarder i~ in it8 nonbraking po~ition.
Although we have herein sh~wn and described only one form of our invention, it is understood that various change~, modification~, and alterations may be made therein within the spirit and scope of the appended claim~ and without departing from the spirit and scope of our in~ention.

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A low-profile pneumatically operated car retarder comprising, a pair of braking bars disposed parallel and on opposite sides of a track rail, which is mounted on cross ties, an upper and a lower pivotal lever, each of said upper and lower pivotal levers having a platform portion for carrying a respective one of said pair of braking bars, said lower pi-votal lever having a laterally extending arm, said upper lever initially extending upwardly and outwardly and subse-quently extending outwardly to form a horizontal arm, a pneu-matic piston-cylinder actuator, said piston of said pneumatic piston-cylinder actuator pivotally connected to the outer ex-tremity of said laterally extending arm of said lower pivotal lever, said cylinder of said pneumatic piston-cylinder actuator pivotally connected to the outer extremity of said horizontal arm of said upper pivotal lever, the height of the pivotal connection of said cylinder with the outer extremity of said horizontal arm of said upper pivotal lever is approximately fifteen inches from the top of the crossties and is substanti-ally at the same level as the top of the track rail so that a low slung railway vehicle is permitted to freely pass through the car retarder, and said pneumatic piston-cylinder actuator lifting said upper pivotal lever and depressing said lower pi-votal lever for moving said pair of braking bars to a closed braking position when pressure is supplied to said pneumatic piston-cylinder actuator so that said pair of braking bars engage the opposite sides of the vehicle wheels at approxi-mately three and three sixteenth inches from the top of the running rail to exert a greater amount of retardation on the passing vehicles.

2. The low-profile pneumatically operated car retarder as defined in claim 1, wherein said horizontally extending arm of said upper pivotal lever is arranged to extend hori-zontally to provide a greater amount of clearance for passing vehicles.

3. The low-profile pneumatically operated car retarder as defined in claim 2, wherein the longitudinal axis of said pneumatic piston-cylinder actuator is arranged in a near vertical disposition when said upper and lower pivotal levers are in their non-braking positions.

4. The low-profile pneumatically operated car retarder as defined in claim 1, wherein said upper and lower pivotal levers are pivoted about a fulcrum point located beneath the track rail.

5. The low-profile pneumatically operated car retarder as defined in claim 1, wherein said upper pivotal lever in-cludes a spring-loaded stop for limiting the movement of said upper and lower pivotal levers in their open non-braking positions.

6. The low-profile pneumatically operated car retarder as defined in claim 1, wherein said lower pivotal lever includes a spring-loaded stop for limiting the movement of said upper and lower pivotal levers in their closed braking positions.

7. The low-profile pneumatically operated car retarder as defined in claim 1, wherein each of said pairs of braking bars includes a brake beam and a brake shoe and an adjusting bolt cooperating with said brake beam to compensate for wear on said brake shoe.

8. The low-profile pneumatically operated car retarder as defined in claim 1, wherein said pneumatic piston-cylinder actuator includes a short-stroke piston and a cylinder assem-blage having a plastic casing.

9. The low-profile pneumatically operated car retarder as defined in claim 7, wherein said brake beam includes a depending hook retaining member which fits into a slot formed in said platform portion for limiting the amount of lift of said braking bars when said brake shoes engage the sides of the vehicle wheels.

10. The low-profile pneumatically operated car retarder as defined in claim 6, wherein said upper and lower pivotal levers are biased to the open non-braking position by gravity and the resiliency of said spring-loaded stop of said lower pivotal lever.

11. A low-profile pneumatically operated car retarder com-prising, a pair of braking bars disposed parallel and on opposite sides of a track rail, an upper and a lower pivotal lever, each of said upper and lower pivotal levers having a platform portion for carrying a respective one of said pair of braking bars, said lower pivotal lever having a laterally extending arm, said upper lever initially extending upwardly and outwardly and subsequently bent outwardly to form a hori-zontal arm, a pneumatic piston-cylinder actuator, said piston of said pneumatic piston cylinder actuator pivotally con-nected to the outer extremity of said laterally extending arm of said lower pivotal lever, said cylinder of said pneu-matic piston-cylinder actuator includes an upper casting, a lower casting and an intermediate casing which is held toget-her by a plurality of tie bolts, said upper casting of said pneumatic piston-cylinder actuator pivotally connected to the outer extremity of said horizontal arm of said upper pi-votal lever, the height of the pivotal connection of said cy-linder with the outer extremity of said horizontal arm of said upper pivotal lever is substantially at the same level as the top of the track rail so that a low slung railway vehicle is permitted to freely pass through the car retarder, and said pneumatic piston-cylinder actuator lifting said upper pi-votal lever and depressing said lower pivotal lever for moving said pair of braking bars to a closed braking posi-tion when pressure is supplied to said pneumatic piston-cylinder actuator so that said pair of braking bars engage the opposite sides of the vehicle wheels at a relatively high point to exert approximately ten percent greater amount of retardation on the passing vehicles than if said pair of braking bars engaged the opposite sides of the vehicle wheels a quarter of an inch below the high point.