Patent Publication Number: US-10308263-B1

Title: Cushioning apparatus for a railway car

Description:
BACKGROUND OF THE INVENTION 
     The invention is directed to a cushioning apparatus for a railway car, and more particularly to a selective travel apparatus that absorbs draft and buff loads applied to a coupler of a railway car. 
     As is generally known, railway cars are connected to an adjacent car by a coupler. The coupler is joined to a yoke, for example an “E-type” or “F-type” yoke, by a draft key or pin, and the assembly is mounted in a railway car center sill. 
     To prevent damage to the railway cars and the laded goods during operation, and especially during assembly of the railway car train in the yard, various devices have been installed to absorb loads on the coupler so that impact forces are not transmitted to the railway car. 
     In a conventional frictional draft gear, one or more elastic elements, such as a coil spring or a set of elastomeric pads, is enclosed in a housing mounted in the yoke behind the coupler. A piston-like element frictionally received in the housing absorbs buff loads transmitted via a coupler follower which moves inside the yoke in response to buff impact force applied on the coupler, and the draft gear is compressed in the yoke in response to draft loads. The basic draft gear apparatus has been used for decades. However, in many cases unacceptably large forces are transmitted to the railway car. 
     A hydraulic cushioning unit comprises a piston received in a cylinder filled with fluid. Such devices may dissipate more force than a conventional draft gear, but they are known to be prone to leakage. 
     U.S. Pat. No. 2,766,894 describes a selective travel draft gear with separate cushioning elements for buff and draft loads on the coupler. In this design, both of the cushioning elements are located forward of the back wall of the yoke. 
     U.S. Pat. No. 2,825,472 describes a selective travel draft gear which comprises separate cushioning elements for buff and draft loads on the coupler, but both stacks of cushioning elements are attached to the yoke. 
     U.S. Pat. No. 6,446,820 discloses a selective travel draft gear of more recent vintage where the separate draft and buff cushioning elements are coupled and adapted to fit into the draft gear pocket. These apparatuses have not been very well received, and may be prone to buckling, wherein a stack of elastomeric elements is pushed out of alignment and fails to operate according to specifications. 
     All of the above-referenced U.S. Patents are incorporated by reference. 
     SUMMARY OF THE INVENTION 
     In view of the prior art, one object of the invention is to provide an alternative cushioning device that provides cushioning over a range of impact speeds. 
     Another object of the invention is to provide a cushioning apparatus for a railway car that provides cushioning for both draft and buff loads applied to the coupler, limiting force transmitted to the railway car over a range of impact speeds, such as may be encountered during train build, where impact speeds may be in the neighborhood of 4-14 mph or higher, and during start-up and stopping. Embodiments according to the invention may exhibit low displacement per unit of force applied over a range of relevant force levels. 
     Yet another object of the invention is to provide improved alignment and positioning of elastomeric pads in a cushioning device, to prevent over-compression, permanent deformation, and buckling during use. 
     Yet another object of the invention is to provide a cushioning apparatus that absorbs both draft and buff loads in a compact format, more easily installed in a standard pocket such as for an AAR standard EOC-9 or EOC-10 configuration. 
     These and other objects of the invention are met in one aspect with an end-of-car cushioning device for a railway car, comprising: a yoke having aligned apertures at a front end adapted to receive a pin or key for attaching the yoke to a railway car coupler, and having a vertical wall at a second end of the yoke opposite the front end; a coupler-receiving member adapted to receive buff force from the coupler and adapted to move inside the yoke; a first stack of elastomeric units positioned between the coupler-receiving member and the vertical wall of the yoke, said first stack being compressed by draft and buff loads on the coupler; a front buff plate positioned adjacent to and rearward of the yoke and connected to a rear buff plate by a center rod; a second stack of elastomeric units positioned between the front buff plate and the rear buff plate, said second stack being compressed in response to buff loads on the coupler; wherein, the yoke, the front buff plate and the rear buff plate are positioned within a center sill of the railway car; and wherein, the yoke is not mechanically attached to the front buff plate or the rear buff plate. 
     In another aspect, the invention resides in the arrangement of the plurality of elastomeric units, each comprising a plate and an elastomeric pad positioned in the middle of the plate. A first set of the plates is arranged in a rear or “buff” stack and the plates are each sized to fill the sill area to ensure alignment of the elastomeric pads. A second set of plates is arranged in a front or “draft” stack, sized to fit inside a yoke. The edges of the plates extending around the elastomeric pads are configured so that the plates can nest with each other, and at full compression the edges of the plates contact one another to prevent overcompression of the individual elastomeric pads. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
         FIG. 1  is top view of a cushioning device assembly according to the invention assembled in a railway car sill; 
         FIG. 2  is an isometric view of a front portion of a cushioning device according to the invention; 
         FIG. 3  is an isometric view of a rear portion of a cushioning device according to the invention; 
         FIG. 4  is an isometric view of an improved selective travel cushioning device according to the invention attached to an “F” Type coupler; 
         FIG. 5  is a cross sectional view of the improved selective travel cushioning device assembly of  FIG. 1 , taken along view lines  5 - 5  of  FIG. 1 ; and 
         FIG. 6  depicts the response of a cushioning unit to static buff and draft loads. 
     
    
    
     The drawings are not to scale, and features not necessary for an understanding of the invention are not shown. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Directions and orientations herein refer to the normal orientation of a railway car in use. Thus, unless the context clearly requires otherwise, the “front” of a coupler is in a direction away from the body of the car and “rear” is in a direction toward the center of the car. Likewise, the “longitudinal” axis or direction is parallel to the rails and in the direction of movement of the railway car on the track in either direction. The “transverse” or “lateral” axis or direction is in a horizontal plane perpendicular to the longitudinal axis and the rail. The term “inboard” means toward the center of the car, and may mean inboard in a longitudinal direction, a lateral direction, or both. Similarly, “outboard” means away from the center of the car. “Vertical” is the up-and-down direction, and “horizontal” is a plane parallel to the rails including the transverse and longitudinal axes. 
     “Elastomer” and “elastomeric” refer to polymeric materials having elastic properties so that they exert a restoring force when compressed. Examples of such materials include, without limitation, thermoplastic elastomer (TPE), natural and synthetic rubbers such as: neoprene, isoprene, butadiene, styrene-butadiene rubber (SBR), polyurethanes, and derivatives. 
     As used herein, the term “about” associated with a numerical value is understood to encompass a margin of +/−10% of the value. An object is said to “substantially fill” a space (such as a railway car sill) when just enough space is provided to allow the object to move in the space without interference. This may mean a clearance of up to about inch laterally and up to about % inch vertically. 
     In embodiments, a cushioning device according to the invention is adapted to fit into an Association of American Railroads (“AAR”) standard pocket. The dimensions of a standard pocket and permitted tolerances may be set by the AAR from time to time, and reference herein to AAR standards refers to standards in the AAR Manual of Standards and Recommended Practices in effect at the filing date of this application, including performance standards, such as M-921-B, for hydraulic cushioning units. A person having ordinary skill in the art has a general knowledge of AAR standards and the published AAR standards cited herein are incorporated by reference as background. 
       FIG. 1  depicts a cushioning assembly  10  according to one embodiment of the invention, including a sill  13 , coupler  14 , and front and rear units  20 ,  30  of the cushioning device installed in the cushion unit pocket.  FIG. 1  depicts center sill  13  with bell shaped opening  15  adapted to accommodate long shank coupler  14  for a greater range of coupler mobility, although the invention is not limited to a long shank coupler configuration. 
     In embodiments, cushioning device assembly  10  may be characterized by a pocket length of about 38¾ inches described in AAR standard S-183 for an “EOC-9” pocket, or a pocket length of about 48¾ inches described in AAR standard S-184 for an “EOC-10” pocket. In other embodiments, the cushioning device may be adapted to fit other pocket dimensions. 
     In  FIG. 1 , and as used herein, the “cushioning unit pocket”, or simply the “pocket”, is defined by front lugs  11  and rear draft lugs  12  mounted on the interior of center sill  13 . According to embodiments of the invention, the cushioning elements are adapted to be inside the center sill without significantly reconfiguring the sill geometry. 
     In  FIG. 1 , the cushioning apparatus comprises a first stack  17  of elastomeric units positioned forward of vertical wall  21  of the yoke, and a second stack  16  of elastomeric units positioned behind the first stack  17 , between a front buff plate and the rear buff plate (as shown in  FIG. 3 ). The cushioning unit comprises a front portion  20  and a rear portion  30 , which are not fixed to one another. 
       FIG. 2  is a view of a front “draft” portion  20  of a cushioning apparatus according to an embodiment of the invention. Yoke  206  includes rear vertical wall  21  and a front portion including two aligned apertures  23  adapted to receive a pin  42  (not shown in  FIG. 2 ). A coupler-receiving member  22 , conventionally termed a “coupler follower” is adapted to receive buff force from the coupler and adapted to move inside the yoke. In the embodiment shown, coupler follower  22  includes a recess  24  adapted to receive the shank end of the railway car coupler  14 , such that follower  22  moves under buff force from the coupler. The configuration shown in  FIG. 2  is “F-type”, in that a pin is used to attach coupler  14  (shown in  FIG. 4 ) to yoke  206 , and walls  26  are on the top and bottom of the yoke. An “E-type” configuration, using a draft key to attach the coupler to the yoke using draft key, may also be used without departing from the scope of the invention, and indeed without changing the dimensions of elastomeric units  25 , or of the stacks  16 ,  17 . 
     For ease of understanding the invention, a single elastomeric unit  25  is shown in  FIG. 2  in the space between vertical wall  21  and coupler follower  22 , each elastomeric unit comprising a metal plate  225 , and at least one elastomeric pad  27 . In actual usage, several elastomeric units  25  form stack  17  contained in this space (as shown in  FIG. 4  and  FIG. 5 ), which (in one non-limiting example) may be about 9-10 inches from the vertical wall to the follower, in a compressed state, comprising for example, 10-15 plates and a corresponding number of elastomeric pads, although other pad sizes and configurations may be employed to tune performance to a particular type of car or lading. In the embodiment shown, the elastomeric unit  25  includes metal plate  225  and a single elastomeric pad  27 . In other embodiments, multiple elastomeric pads may be positioned on a plate.  FIG. 4  depicts an installed position where coupler pin  42  engages the front side of aperture  23 . When a draft load is applied on coupler  14  through pin  42 , the first stack  17  of elastomeric elements is compressed between vertical wall  21  and coupler follower  22  which abuts stops  11 . The first or “draft” stack  17  is compressed when the coupler is subjected to buff loads and also when the coupler is subjected to draft loads. To install the elastomeric units  25  in the front portion of the cushioning unit, the coupler follower  22  may be held in place with a predetermined pressure on the elastomeric pads  27 , using a set of destructible shear pins fixing the coupler follower to the yoke. In the rear stack, two c-shaped spacers (not shown) may be provided on rear unit  30  between rear plate  32  and nut  54  to provide a pre-load on the rear stack for installation. 
     Referring again to  FIG. 2 , each elastomeric unit  25  comprises elastomeric pad  27  mounted in a recessed area  29  of the metal plate  225 . The rigid plates may be adapted to prevent over-compression of the elastomeric pads  27 . For example, the plates may be made of cast or fabricated metal such as steel, and a stop surface may be provided on the periphery of the plate around the recess. Additionally, protrusions  28  permit a nesting arrangement of elastomeric units  25  in stack  17 , as shown in  FIG. 4  and  FIG. 5 , which also contributes to alignment of the elastomeric units  25 . Metal-to-metal contact on the stop surfaces occurs when an elastomeric pad  27  between two adjacent plates  225  is compressed a predetermined amount, such as 20-80%, and in embodiments 20-60%, of the uncompressed thickness of the pads. In embodiments, the pads in the front or draft stack compress about 0.5 inches (from their uncompressed thickness prior to installation) before metal to metal contact prevents further compression. The plates  225  forming front stack  17  extend to the walls and/or the straps of the yoke  206 . By way of example and not limitation, an uncompressed thickness of each pad  27  forming front stack  17  may be about 1.37 inches. Installed, under a static load of 32 klb, the thickness of the draft pads is 0.92. Fully compressed, at the point when metal-on-metal contact of the plates prevents further compression of the pads, the elastomeric pads  37  in the draft stack may have a thickness of 0.68 inches. These dimensions are provided for guidance and should not be deemed to limit the invention. In practice many configurations are possible without departing from the scope of the invention. 
     The elastomeric pads  27  may be provided with a through hole in the center, which aligns with a protrusion, which may be cast, stamped or fabricated on the plate, for example, and provided to keep the pads in alignment. The diameter of the through hole may be referred to as the “inner diameter”. The lateral edge of each elastomeric pad  27  may be curved in a toroidal manner, and the outside diameter of the pad is measured at the middle of the thickness dimension of the pad. 
       FIG. 3  represents the rear “buff” portion  30  of the cushioning apparatus, positioned adjacent to and rearward of the yoke and comprising front plate  31  connected to rear plate  32  by a rod  34  which passes through a plurality of elastomeric units  35 . Although a single center rod  34  is shown, a plurality of rods may also be used. Each elastomeric unit  35  comprises a plate  226  and at least one elastomeric pad  37 , similar in construction to the elastomeric unit  25 . However, the plate  226  and the elastomeric pad  37  both have a hole to receive rod  34 . As in the description of  FIG. 2 , only a single elastomeric unit  35  is shown in  FIG. 3 , whereas 10-20 plates  226  and a corresponding number of elastomeric pads could be employed, depending on the design. The elastomeric unit(s)  35  substantially fill the sill area to help align elastomeric units  35  and pads  37 . Pads  37  may be shaped like pads  27 . In the embodiment shown, each elastomeric pad  37  may be circular when viewed in plan, having an outer diameter. An “inner diameter” defines a through hole in the middle adapted to receive the center rod. 
     Pads  37  in the buff stack  16  may have the same general shape as pads  27  in the draft stack  17  but they are scaled larger. The maximum design force of the larger pads  37  is higher due to larger surface area, but the surface pressure on each pad is the same. For example, and not by way of limitation, the uncompressed thickness of a pad  37  may be about 1.70 inches and the outer diameter may be about 8.82. Compressed for installation with a force of about 32 klb, the installed thickness of the pads is about 1.24 inches. Under full compression, with metal-to-metal contact of plates  226  preventing further compression of pads  37 , the pad thickness may be about 0.91 inches and the outside diameter may reach 10.63 inches. Thus, in embodiments, the pads and plates are designed to allow compression of 20-80 percent, and in embodiments 40-60 percent, where the amount that the pad is compressed at full compression is expressed as a percentage of the uncompressed thickness of the pad, prior to installation. Bolt head  33  is flush mounted in front plate  31  so that the rear unit  30  may be mounted directly against front unit  20 . In embodiments, rear unit  30  is not attached to the front unit  20 , which facilitates installation. As shown in  FIG. 5 , rod  34  is secured by nut  54 . 
     The same elastomeric material may be used for the elastomeric pads in the draft stack as in the buff stack, such as a thermoplastic elastomer. 
     The elastomeric units of the draft pack are adapted to slide between straps  26  of yoke  20 . In an E-type arrangement, the yoke is attached to the coupler using a draft key, but the performance considerations for the pads and plates are similar. 
     In embodiments, draft stack  17  is provided in a pre-shortened installation configuration, which allows draft portion  20  and the buff portion  30  to slide into the pocket and allows the coupler to be installed without interference. A plurality of shear pins, for example four shear pins pass through the yoke into the coupler follower  22 . The pins break on first impact, and in this fully-installed or post-installation position, the coupler is pre-stressed, applying buff force against the first and second stacks. 
       FIG. 6  depicts performance modeling of a cushioning unit according to the invention using response to static buff and draft loads. The dynamic response of the material would be dependent on impact speed and could approach twice the static load values. Nevertheless, the response to static loads provides information to guide product design to achieve performance objectives. In this example, 11 pads are used in the buff stack, each having an uncompressed thickness of 1.7 inches and an uncompressed diameter of 8.82 inches. The draft stack comprises 14 pads, each having an uncompressed thickness of 1.37 inches and uncompressed diameter of 6.63 inches. A static compression test is performed to obtain the response to static load and subsequent recovery or “release”. Separation of compression and release curves represents hysteresis. The relatively large hysteresis depicted in the response curves is at least partly an advantage of using the plates to limit compression of the elastomeric pads within a predetermined range, resulting in a greater absorption and dissipation of impact energy. At the same time, very little permanent deformation is expected during the lifetime of the cushioning unit, on the order of less than 10%, preferably less than 5%. The stiffening observed under buff loads greater than about 400 klb occurs after the draft stack is fully compressed, and the rear “buff” stack assumes the remainder of the force absorption. Hysteresis may be expressed as the ratio of energy absorbed by cushioning unit (W A ) to the energy input during impact (W E ) (modeled as a static load). Hysteresis for the cushioning unit may be extrapolated from the deflection of the buff and draft pads versus applied static force during compression and release from different starting points (i.e., pre-loaded, uncompressed and fully compressed). In embodiments a cushioning unit according to the invention will have a W A /W E  ratio derived in this manner of 0.3 to 0.65. The large distance between the compression and release curves in  FIG. 6  indicates relatively high hysteresis for a cushioning unit according to the invention. 
     The description of the foregoing preferred embodiments is not to be considered as limiting the invention, which is defined according to the appended claims. The person of ordinary skill in the art, relying on the foregoing disclosure, may practice variants of the embodiments described without departing from the scope of the invention claimed. A feature or dependent claim limitation described in connection with one embodiment or independent claim may be adapted for use with another embodiment or independent claim, without departing from the scope of the invention.