Abstract:
A railroad car draft gear is provided which includes a housing. The housing is a unitary structure, having an open end and a closed end. Compressible spring elements are located inside the housing, with an end of the spring element located against the interior side of the closed end. A friction assembly is also located within the housing, near the open end. The friction assembly provides energy absorption during compression cycles. The spring element restores the friction assembly to its fully extended positon after a compression event.

Description:
RELATED APPLICATIONS 
       [0001]    The application claims the benefit of U.S. provisional application 62/056,862, filed Sep. 26, 2014, the entirety of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a railroad car draft gear and more particularly, to a railroad car draft gear having an improved, strengthened housing and an improved friction mechanism. 
         [0003]    A railroad car draft gear typically comprises a housing in which a friction mechanism and spring are located. The friction mechanism and spring provide damping during a buff or compression event, when a railcar in a train is exposed to a deceleration or braking event. The spring restores the friction mechanism back to its fully extended position upon release of the braking event and typically upon a draft or acceleration event. The draft gear provides damping in draft as well once the neutral position is reestablished. 
         [0004]    The draft gear housing must withstand axial compressive forces and radial stresses in the area of the friction mechanism. 
       SUMMARY OF THE INVENTION 
       [0005]    The draft gear of the present invention provides an improved draft gear housing with improved fatigue resistance and strength due to the minimization of stress concentrations in the housing. The minimization of stress concentrations in the housing is accomplished by redesigning the housing to include more robust cross sections, along with more generous radii and blends of joining surfaces. 
         [0006]    The spring element in the housing can be a steel coil spring. Further, the spring element can also be a combination of elastomeric pads and steel plates. The elastomeric pad embodiment is preferred due to its lighter weight and the ability of the elastomeric pads to absorb energy during a compression event. various elastomeric materials such as Hytrel, Arnitel, rubber or copolyester materials can be utilized. However, the preferred elastomer material for the spring of the present invention is Arnitel, available from the DSM company. This copolyester material is preferred due to its ability to be cold worked, good mechanical bonding to the steel plates, resulting spring and damping properties, toughness, resistance to compression set and stress relaxation, and broad application temperature range. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    In the drawings, 
           [0008]      FIG. 1  is a perspective view of a draft gear assembly in accordance with an embodiment of the present invention; 
           [0009]      FIG. 2  is a perspective view of a draft gear housing in accordance with an embodiment of the present invention; 
           [0010]      FIG. 3  is a perspective view of an elastomeric spring assembly inside a draft gear housing in accordance with an embodiment of the present invention; 
           [0011]      FIG. 4  is a perspective view of an elastomeric spring element in accordance with an embodiment of the present invention, and 
           [0012]      FIG. 5  is an end view of a draft gear housing and an elastomeric spring assembly in accordance with an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    Referring now to  FIGS. 1 and 2 , a draft gear is shown generally at  10 . Draft gear  10  is seen to comprise a draft gear housing  12 . Draft gear housing  12  is an elongated, generally rectangular structure, with a central structure somewhat cylindrical in shape with external walls and internal wall surfaces forming an internal cavity. Front end  14  of draft gear housing  12  is preferably cast into a six sided structure forming an opening  30  leading into the internal cavity  15 , but it should be understood that a four or eight sided structure could also be considered embodiments of the present invention. The walls of draft gear housing  12  at front end  14  are about 1 inch (2.54 cm) in thickness to provide improved strength and reductions in stress concentrations. Draft gear housing  12  is usually formed in a casting operation, with finish machining, and is usually comprised of steel. 
         [0014]    Draft gear housing  12  also comprises rear end  32 . Draft gear housing rear end  32  is usually comprised of a closed steel plate structure that is part of the unitary casting of draft gear housing  12 . Rear end  32  has a thickness of about 1.3 inch (3.3 cm). 
         [0015]    Draft gear housing  12  also comprises edge supports  34  and  36 , each of which is seen to be an integral, generally triangular structural member that has a top portion that extends from a point about half way between front end  14  and rear end  32  on the body of draft gear housing  12  and a bottom portion that extends to a line of intersection with an edge of draft gear housing rear end  32 . In certain embodiments, the line of intersection of the bottom portion of each edge support extends for the entire length of an edge of the rear end. Draft gear housing edge supports are seen to be generally triangular in shape, with a thickness of about 0.63 inch (1.6 cm). 
         [0016]    Draft gear housing  12  also comprises center rib  38  which is comprised of a raised rib extending from a point about half way between front end  14  and rear end  32  on the body of draft gear housing  12  to a point about one fourth the length of draft gear housing  12  from rear end  32 . 
         [0017]    At such point, center rib  38 , in a preferred embodiment, is split into two laterally spaced center rib base supports  40  and  42  to help reduce stresses in the housing. Each of center rib base supports  40  and  42  extend from an intersection with center rib  38  to an intersection with draft gear housing rear end  32 . Note that center rib base supports  40  and  42  have footings that extend to edge  44  of rear end  32 . In an alternative embodiment, center rib  32  could itself extend to an intersection with rear end  32 . A similar center rib and base supports are present on the side of draft gear housing  12  not visible in  FIGS. 1 and 2 . 
         [0018]    The lower 1/10 th    45  of the housing body  12  gradually increases in diameter starting from a position approximately 1/10 th  up from the base (rear end  32 ) and ending at the base such that internal clearance is created to allow a steel plate  22  to be incorporated onto to last plastic spring element  18  for the purposes of superior spring stack alignment and guidance when compared to some prior art. Protrusions  47  on the steel plate  22  align with depressions (blind holes)  48  in the housing  12  base to provide said positional guidance. Shown in this embodiment is a pair of protrusion/hole features. It should be understood that multiple such pairings could be employed to increase manufacturing flexibility. Additionally, such protrusion/hole pairings are employed at the opposite end (top end) of the spring stack for similar reasons such that the Top Follower 
         [0019]    Plate  8  is oriented to, and provides guidance for the spring stack. Furthermore the protrusion/hole pairings are “clocked” such that a manufacturing reference is created for ease of the spring stack placement where the steel plate  22  “notch” (1 of 3) indicated by a “V” marking  49  aligns with the corresponding housing protrusion in the “3 o&#39;clock” position  51  on the housing  12 . 
         [0020]    Referring now to  FIG. 3 , a view of draft gear  10  is shown with draft gear housing  12  opened in order to view friction wedge  20  and other internal components. Friction wedge  20  is seen to comprise a generally cylindrical structure having an end  46  that protrudes from opening  30  in front end of draft gear housing  12 . Under a buff condition, wherein a train would be decelerating or a railroad car would otherwise be subjected to a compressive force through its coupler system, friction wedge  20  would be forced partially inward into the cavity of draft gear housing opening  30 . 
         [0021]    Draft gear  10  is further seen to comprise friction wedge shoes  22  on the outer surface of friction wedge  20 . Friction wedge shoes  22  are usually present in a set of three, when draft gear  100  housing  12  has a six sided configuration at front end  14 . Friction wedge shoes  22  are seen to have an angled outer surface that corresponds to the interior surface of the draft gear housing near opening  30 . Friction wedge shoes  22  are usually made of steel. Further, solid friction wedge bearings  27 , usually made of brass, are present as raised linear surfaces on the outer surface of friction wedge shoes  22 . Friction wedge shoes  22  with friction wedge bearings  27   105  provide a friction damping effect when draft gear friction wedge  20  is pushed inwardly into the draft gear housing  12  in a buff condition for the railroad car. 
         [0022]    Draft gear  10  is further seen to comprise a series of stacked compression springs in the form of elastomer pads  18 . Such a stack of compression springs extends into draft gear housing  12  to rest against the inner surface of rear end  32 . Each elastomer pad  18  is pre-compressed  110  between two circular plates  22 . The usual material for circular plates  22  is sheet steel. The preferred material for elastomer pads  18  is a suitable copolymer, with Arnitel being the preferred material. The preferred number of compression springs in a typical railroad car draft gear in accordance with the present invention is about eight for normal freight car installations, but it should be understood that the number of compression springs can vary based on application.