Patent Publication Number: US-6701850-B2

Title: Friction wedge liner with backing plate

Description:
FIELD OF THE INVENTION 
     The present invention relates, in general, to a wedge shaped friction casting that serves as a shock absorber in the suspension of railroad cars and, more particularly, the present invention relates to a composition liner bonded to a backing plate for such wedge shaped friction casting. 
     BACKGROUND OF THE INVENTION 
     The suspension of railroad trucks include a wedge shaped friction casting which serves as a shock absorber. The wedge is supported by a spring and works between the bolster and the side frame. The sloped face of the wedge maintains contact with a mating face of the bolster while the vertical face of the wedge slides against a metal wear liner on the side frame. The spring pushes on the bottom face of the wedge thereby providing the load to force the wedge between the bolster and the side frame. The friction between the wedge and the side frame wear plate provides damping for the truck suspension. 
     Certain truck designs use a wedge with a composition friction liner bonded to the vertical face of the wedge. This composition liner provides the desired friction characteristics, particularly static friction similar to dynamic friction. The difficulty encountered with this design has been in obtaining a satisfactory bond of the composition liner to the cast metal wedge. Various methods of gluing a molded sheet of composition material and of bonding the material to the casting have been used. Under the severe operating and environmental conditions of railroad service, the composition liner sometimes separates from the cast metal wedge. 
     SUMMARY OF THE INVENTION 
     The present invention, therefore, provides a friction wedge assembly for use in a suspension system of railroad car trucks. The friction wedge assembly comprises a cast metal wedge having a bottom face, a vertical face that is substantially perpendicular to the bottom face and a sloped face for contacting a mating surface on a bolster of such railroad car truck. 
     There is a metal backing plate that has a first side removably engageable with the vertical face of the cast metal wedge and a means for securing the metal backing plate to the cast metal wedge. There is further a composition liner disposed on a second side of the metal backing plate for engaging such metal wear liner on such side frame of such railroad car truck. 
     OBJECTS OF THE INVENTION 
     It is, therefore, one of the primary objects of the present invention to provide a composition liner with a backing plate for a friction wedge assembly to eliminate the need for bonding the composition material to the cast metal wedge. 
     Another object of the present invention is to provide a composition liner with a backing plate for a friction wedge assembly that can be replaced easily thereby renewing the wear surface without having to install a new wedge casting. 
     Still another object of the present invention is to provide a composition liner with a backing plate for a friction wedge assembly that will reduce the need for handling the heavy wedge casting. 
     Yet another object of the present invention is to provide a composition liner with a backing plate for a friction wedge assembly that will be easily made interchangeable with existing wedge castings. 
     Another object of the present invention is to provide a composition liner with a backing plate for a friction wedge assembly in which the bonding of the composition friction surface is improved. 
     It is yet another object of the present invention to provide a composition liner with a backing plate for a friction wedge assembly that can be installed without the need for special tools. 
     Still another object of the present invention is to provide a composition liner with a backing plate for a friction wedge assembly wherein the composition liner can be assembled to the wedge casting at any location. 
     Another object of the present invention is to provide a composition liner with a backing plate for a friction wedge assembly in which the friction wedge casting is cost effective. 
     Yet another object of the present invention is to provide a composition liner with a backing plate for a friction wedge assembly which will reduce maintenance. 
     These and various other objects and advantages of this invention will become apparent after a full reading of the following detailed description, particularly, when read in conjunction with the attached drawings as described below and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a friction wedge assembly with a composition wedge liner with a metal backing plate according to an embodiment of the invention. 
     FIG. 2 is an exploded view of the friction wedge assembly with composition wedge liner with a metal backing plate according to an embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE PRESENTLY PREFERRED AND ALTERNATE EMBODIMENTS OF THE INVENTION 
     Prior to proceeding with the more detailed description of the present invention it should be noted that, for the sake of clarity, identical components which have identical functions have been designated by identical reference numerals throughout the several views illustrated in the drawings. 
     Illustrated in FIGS. 1 and 2 is a friction wedge assembly, generally designated  10 , for use in a suspension system of railroad car trucks. Such friction wedge assembly  10  includes is a cast metal wedge  1  that has a bottom face  2 , a vertical face  4  that is substantially perpendicular to the bottom face  2  and a sloped face  6 . The sloped face  6  contacts a mating surface on a bolster of such railroad car truck (not shown). Although it is presently preferred that such wedge  1  be a metal casting it is within the scope of the invention that such wedge  1  be of other material. 
     The present invention provides a metal backing plate  8  that has a first side that is removably engageable with the vertical face  4  of the cast metal wedge  1 . There is also a means, generally designated  20 , for securing the metal backing plate  8  to the cast metal wedge  1 . A composition liner  12  is disposed on a second side of such metal backing plate  8  for engaging such metal wear liner (not shown) on such side frame of such railroad car truck. 
     In a presently preferred embodiment of the invention such means  20  for securing the metal backing plate  8  to the cast metal wedge  1  includes a locking tab  14 . Such locking tab  14  on the metal backing plate  8  is designed to protrude through a mating aperture  16  in the cast metal wedge  1 . The locking tab  14  is secured to the cast metal wedge  1  by one of a cotter pin (not shown) which can be inserted in the opening in the locking tab  14  and by simply manually bending the locking tab  14 . In a presently preferred embodiment of the invention such locking tab  14  is simply bent manually to hold the backing plate  8  and composition liner  12  in place on the cast metal wedge  1 . 
     Thus, the use of the locking tab  14  permits for easy insertion but resists removal. This attachment feature, locking tab  14 , need only hold the composition liner  12  and backing plate  8  in place on the cast metal wedge  1  until it is installed in the railroad car truck. Thereafter, the composition liner  12  is constrained between the cast metal wedge  1  and the metal wear liner on the railroad car truck frame. The composition liner  12 , according to the present invention, can be replaced easily and thereby have a renewed wearing surface without the necessity of installing a completely new wedge casting or having the wedge casting sent out to have a new liner molded directly to it as is presently done. In an embodiment of the invention such locking tab  14  is formed integrally with the backing plate as a punching. 
     The backing plate  8 , according to an embodiment of the invention, further includes a shallow lip  16  that is disposed substantially around the exterior of the backing plate  8  and is substantially perpendicular to the second side of the backing plate  8 . Such shallow lip  16  partially encloses the composition liner  12  and keeps it in place even in the event of a loss of bond between the composition liner  12  and such metal backing plate  8 . Additional features could be incorporated into the second side of the backing plate  8  that could create a mechanical interlock between the metal backing plate  8  and the composition liner  12 . However, in a presently preferred embodiment of the invention such composition liner  12  is bonded to the second side of the metal backing plate  8 . 
     The metal backing plate  8  also incorporates locating features on the first side which is the side that is engageable with the cast wedge assembly  1 . The locating features include at least one locating pin  18  which mates with an aperture(s) on the vertical side  4  of the cast metal wedge  1  and permit the proper positioning of the metal backing plate  8  to the cast metal wedge  1 . It is presently preferred that there are a plurality of locating pins  18  on the backing plate  8 . It is further preferred that such plurality of locating pins  18  are four on such first side of such metal backing plate  8 . It is also preferred that there be a plurality of matching apertures on the vertical side of the cast metal wedge  1 . It is further preferred that this plurality be four mating apertures for the locating pins  18  on the vertical side  4  of the cast metal wedge  1 . 
     These locating pins  18  serve both to accurately locate the composition liner  12  and backing plate  8  on the cast metal wedge  1  and to take the shear load between the cast metal wedge  1  and the backing plate  8  with the composition liner  12 , keeping the assembly in place while in service. The shear strength of this arrangement is much higher than that found in prior art. To accept the new backing plate  8  and composition liner  12  the cast metal wedge  1  need only have suitable mating holes drilled into its vertical face. New castings can be produced with the holes cast in place, needing only a finish drilling to provide suitable tolerances for the locating pins  18 . In this manner, existing cast metal wedges  1  can be modified at very low cost and new castings produced with only minor additional work. The present invention has the same overall dimensions as prior art liners; therefore, the operation of such complete friction wedge assembly  10  is identical to one utilizing prior art. 
     The present invention provides a composition liner  12  that is bonded to a metal backing plate  8  that mechanically connects to a modified cast metal wedge  1 . This allows the use of a metal for the metal backing plate  8  which provides a superior bond to the composition material of the composition liner  12 , compared to the bond with the cast metal that is used in the wedge. Also there are features included in the backing plate  8  which further improve the bond and hold the composition liner  12  in place even if the bond should fail. Such backing plate  8  and composition liner  12  can be replaced easily, when required, without the need of any special equipment or tools which should reduce maintenance costs. 
     While both the presently preferred and a number of alternative embodiments of the present invention have been described in detail above it should be understood that various other adaptations and modifications of the present invention can be envisioned by those persons who are skilled in the relevant art of railway braking systems without departing from either the spirit of the invention or the scope of the appended claims.