Patent Application
20070034108
The present invention relates to rail car trucks having a pair of laterally spaced side frames carrying pairs of spaced apart wheel sets wherein each side frame has an opening between the wheel sets for receiving one of the ends of a transversely extending bolster. The ends of the bolster are supported by groups of springs mounted within the side frame openings. More particularly, the invention relates to improvements to wedging devices mounted within the side frame openings for dampening relative motion between the bolster and the side frames, thereby maintaining truck squareness and reducing hunting.
In rail car truck assemblies of the type to which this invention relates, it is known to provide friction wedges housed within pairs of bolster pockets located on opposite sides of the bolster adjacent its ends. The friction wedges are preferably provided in pairs which are biased upwardly by springs urging them against a sloped surface within a pocket of the rail car bolster and a wear surface which defines a side frame column at an end of the side frame opening.
In a rail car truck of the type that this invention is particularly applicable to, the bolster pockets have a sloped back surface and use a wear insert bearing on the sloped surface. This wear insert is a separate part which interfaces with correspondingly sloped surfaces of a pair of split wedges. It is known to provide the sloped pocket surfaces with a laterally extending taper or bevel so that the biasing force exerted on a wedge causes it to bear against a side wall surface of the bolster pocket. The wedge action within the pocket thus produces biasing forces jointly against the sloped surface of the pocket, the side edge of the side frame opening and against the pocket side walls generating damping forces which keep the truck square, thereby counteracting truck hunting and reducing wheel wear.
U.S. Pat. No. 4,244,298, issued Jan. 13, 1981, and U.S. Pat. No. 5,943,961, issued Aug. 31, 1999, constitute prior art over which the present invention is an improvement. In these patents, wedges are shown which are split into two side-by-side pieces in spaced relationship to one another. According to both of these patents, the two wedges are biased into full-faced engagement with correspondingly sloped sections of the pocket. In both patents, a side of each wedge section is also biased into face-to-face engagement with a side surface of the bolster pocket side wall.
In U.S. Pat. No. 4,244,298, the sloping surfaces of the pocket are integrally formed with the bolster. In practice, this is accomplished either by welding forged inserts into the pocket having the required shape, by casting the pocket with the corresponding shape or by building up the pocket by welding. In the '961 patent, the problems and expense of the required welding operation are eliminated by providing a removable insert having the required shape which is supported within the pocket without any need for welding it in place.
In service, the forces holding the side of a wedge against the side of the pocket, while increasing the capability of the wedges to square the truck, result in wear of the corresponding pocket side wall. Eventually, during the course of normal use of the truck, this wear may be as great as ⅛″ to 3/16″ or even more, requiring a rebuild of the bolster pockets.
Rebuilding a worn pocket is a difficult and time consuming operation at best. One method employed is to build up the pocket with molten material by welding, then grinding to the original pocket dimensions the material added by welding. An alternative method is to weld a small wear pad onto the side wall surfaces of the pocket. However, building up the pocket by either of these methods is a difficult proposition because the interiors of the pockets are relatively inaccessible, being only 5-¾″ to about 7-½″ wide for a typical freight car bolster.
In accordance with the invention, the problem described above is solved by providing a non-metallic insert on the side of the wedge which interfaces with a side wall of the bolster pocket. The non-metallic insert is preferably a polymeric material which eliminates wear on the bolster pocket as there is no metal-to-metal contact, only the contact of the polymer insert against the side wall of the pocket. The non-metallic inserts of the invention are each detachably secured to one side wall of each of a pair of wedges and can be readily easily replaced as necessary when the trucks are periodically inspected. By the use of such inserts, it is reasonably expected that the bolster pocket will last for the life of the rail car.
The use of such inserts achieves the objective of substantially reducing maintenance costs and prolonging the life of truck components, while promoting squareness of the truck and achieving thereby a reduction of wheel wear.
The foregoing and other objects and advantages of the invention will be apparent from the following detailed description of a preferred embodiment, taken in conjunction with the accompanying drawings. dr
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In order to secure the pads within the recesses in the wedges, each pad 34 is preferably provided with a countersunk hole 38 generally centrally located in alignment with a threaded bore 40 in the side wall of the wedge. A flat headed threaded fastener 42 fits within hole 38 and is threaded into threaded bore 40 to attach the pad to the side wall of the wedge. The head of the fastener should be flush with the wedge surface or slightly recessed when the fastener is tightened. Preferably, the fasteners are made of the same material as the pad. If a metal fastener is employed, the hole 38 should be countersunk sufficiently to avoid contact of the fastener head with the pocket side wall under normal conditions of wear. The pad also has a hole 46 aligned with openings 48 in the split wedges 10 and 12 and the recess 36 in the web of the insert for temporary insertion of a locking pin used during installation as explained in the '961 patent.
In the preferred embodiment of the invention, the pads are formed of nylon, although other wear resistant polymers such as Delrin, urethane or UHMW may be employed. By UHMW is meant ultra high molecular weight polyethylene preferably having a molecular weight of between about 3 and about 6 million. The pads preferably have a hardness in the range of about 700 to about 900 and most preferably a hardness of about 800.
Pads made from such materials may be provided by casting or molding.
In use, the wedges 10 and 12 are biased upwardly by biasing means such as the coil springs 44 against the sloped surfaces 18 and 20 within pocket 22a, the wear surface 30 and the pocket side walls, thereby providing support for the bolster and the car body and providing damping forces which promote truck squareness and reduce hunting. With the use of the wear resistant, non-metallic pads, wear of the pocket side walls is substantially eliminated. The pads 34 are extremely durable and exhibit little wear in use but are, nevertheless, readily replaceable if observable wear is encountered. The pads are relatively inexpensive, can be changed quickly and easily without the need for welding and, with periodic inspection and replacement when necessary, are expected to extend the life of the bolster pocket indefinitely.
