Abstract:
A friction/elastomeric pad draft gear to cushion and absorb impacting forces on a railroad car coupler system. The friction/elastomeric pad draft gear includes a housing with a closed end and an open opposite end with a major axis extending therebetween. The open opposite end is provided with inwardly tapered extended internal friction surfaces. A wedge is mounted for axial movement in the open end of said housing and friction devices are positioned within the housing between the wedge and the extended internal friction surfaces. A spring seat is positioned adjacent the friction devices and on top of the elastomeric pad stack. The friction devices engagement with the wedge: forms a first selected angle of about 35 degrees ±3 degrees; forms a second selected angle of about 2.25 degrees, ± about 0.25 degrees, with the extended tapered internal friction surface; and forms a third selected angle of about 90 degrees, ±4 degrees, with the spring seat, all in respect to the major axis.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to draft gears and, in particular, to an improved friction/elastomeric pad draft gear having an extended travel for the absorption and dissipation of input forces. 
     2. Prior Art 
     Coupler systems for modern railroad cars typically have included a draft gear assembly to cushion and absorb forces placed on the system during car operation. Devices to cushion and absorb such forces may comprise an elastomeric spring package coupled with a frictional restraint device. 
     Examples of such devices are exemplified by U.S. Pat. Nos. 4,556,149 and 4,591,059 both of which are assigned to the assignee of the present invention and incorporated by reference herein. 
     While such draft gear devices have high shock absorbing capacities they tend to transmit a high magnitude of force to the car structure during a work cycle. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disabilities of the prior art by providing a friction/elastomeric pad draft gear which absorbs energy over a longer distance of travel than prior art devices thereby enabling the transmission of lower levels of force to the rail car structure when cushioning a given energy input. In accordance with friction/elastomeric pad draft gears, the present invention includes a housing with a closed end and an open opposite end which is provided with an extended tapered internal friction surface. A wedge is mounted for axial movement in the open end of the housing and is situated for direct application of draft or buff forces. Friction devices or stepped friction shoes are positioned within the housing, between the wedge and the extended tapered internal friction surface to absorb some of the shock created by the application of a force to the wedge. A spring seat is positioned between the friction devices and the elastomeric pad stack. The stepped friction shoes cooperate with the spring seat to increase the available space for the elastomeric pad stack. A guide spike is secured to the closed end of the housing and passes through the elastomeric pad stack, spring seat and wedge to lessen the potential of buckling of the pad column. 
     The friction devices of this invention include a series of annularly spaced friction shoes each having a first, flat beveled inner surface in engagement with a flat beveled inner surface of the wedge. The beveled inner surfaces are formed at a first selected angle with respect to the major axis of the housing. Each of the friction shoes also has a second flat, beveled outer face in engagement with the extended tapered internal friction surface, located in the open end of the housing, forming a second selected angle with the major axis of the housing. Each of the friction shoes also has a third flat, inner face in engagement with a flat, outer face formed in the spring seat, the third flat inner face of the shoe and the outer face of the spring seat being formed at a third selected angle with respect to the major axis of the housing. The guide spike is held stationary at all times as a result of the head of the spike being kept tight against the rear wall of the housing by virtue of the preload to which the elastomeric pad is subjected. A pilot hole through the center of the spring seat and through the center of the wedge enables inward displacement of the wedge and spring seat while maintaining the spike&#39;s central alignment. 
     In the preferred embodiment of the invention, the first selected angle of the adjoining surfaces of the friction shoe and the wedge is approximately 35 degrees plus or minus about 3 degrees. The second selected angle of the adjoining surfaces of the friction shoe and the extended tapered internal friction surface is approximately 2.25 degrees plus or minus about 0.25 degrees. The third selected angle of the adjoining surfaces of the friction shoe and the spring seat surface is approximately 90 degrees plus or minus about 4 degrees. The elastomeric pad stack comprises a plurality of concentric springs which are made in accordance with U.S. Pat. Nos. 4,198,037 and 4,566,678 which are incorporated by reference herein. 
     Thus, an object of this invention is the provision of a draft gear wherein the available travel to installed length ratio is about 0.21. The ratio of the available travel to the installed length of modern draft gears has heretofore ranged from about 0.11 to about 0.16 with the vast majority having a ratio of about 0.14. 
     Still a further object of the invention is to provide a draft gear which employs friction/elastomeric devices, fits in a standard pocket, and has 120 mm of travel. This extent of travel having been possible heretofore only with expensive hydraulic draft gears. 
     An additional, object of this invention is to provide a draft gear for application in a standard pocket which has 120 mm of travel, weighs less and can absorb more energy than a conventional draft gear. 
     Another object of this invention is to provide a stepped friction shoe in combination with a spring seat whereby allowing a longer elastomeric spring column to be located within the draft gear housing. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will become apparent in the following description of the preferred embodiment taken in conjunction with the drawings, in which: 
     FIG. 1 is a longitudinal cross-sectional illustration of one form of a draft gear embodying principals of the present invention; 
     FIG. 2 is a front elevational view of the draft gear illustrated in FIG. 1; 
     FIG. 3 is a plan view of an inner or inside surface of a friction shoe forming part of the draft gear illustrated in FIG. 1; 
     FIG. 4 is a cross sectional view of the friction shoe taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a back end elevational view of the friction shoe of FIG. 3; 
     FIG. 6 is a front end elevational view of the friction shoe of FIG. 3; 
     FIG. 7 is a side elevational view of the fricton shoe of FIG. 3; 
     FIG. 8 is an outer elevational view of a spring seat forming part of the draft gear illustrated in FIG. 1; 
     FIG. 9 is a cross sectional view of the spring seat taken along line  9 — 9  of FIG. 8; 
     FIG. 10 is a front elevational view of a guide forming part of the draft gear illustrated in FIG. 1; 
     FIG. 11 is a diagrammatic comparison between the force vs. draft gear stroke of a conventional draft gear and a draft gear embodying principals of the present invention, for the same energy input; 
     FIG. 12 is an inside elevational illustration of a wedge forming part of the draft gear illustrated in FIG. 1; and 
     FIG. 13 is a outside elevational illustration of the wedge shown in FIG.  12 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As illustrated in the drawings, a friction/elastomeric pad draft gear  9 , according to the present invention, includes an axially bored or hollow housing or casing  10  with a first end being open and an opposed second end being closed by a fixed, enlarged end wall or plate  12 . The housing  10  is provided, adjacent its open end  50 , with a thick walled friction shell section  14  having three longitudinally extended and tapered internal or inner friction surfaces  28 ,  30  and  32  (FIG.  2 ); with each tapered surface converging toward the closed end of the housing  10  and with the extended and tapered internal friction surface, generally identified by reference numeral  28  in FIG. 1, being representative of any one of the three inner friction surfaces  28 ,  30  and  32  on housing  10 . Spaced longitudinally or axially inwardly inward of the shell section  14 , the housing  10  is provided with an internal bore  18  which opens to the first end of housing  10  and terminates at the end wall  12 . As shown in FIG. 1, that portion of the housing  10  longitudinally or axially spaced inwardly from the shell section  14  is characterized by a thinner wall section and by a generally cylindrical inner configuration. The shell section  14  and the bore  18  are integrally interconnected by a transition wall section  20  which serves to blend the configuration of the shell section  14  and the bore  18  into each other. 
     As is conventional, a series of three friction shoes  22 ,  24  and  26  are circumferentially spaced as shown in FIG. 2 in the shell section  14  in sliding friction-producing engagement with associated extended tapered internal friction surfaces  28 ,  30  and  32  of the shell section  14 . The three friction shoes  22 ,  24  and  26  when assembled as shown, define an outwardly opening pocket for receiving the inner end  35  of a wedge  34 . 
     In addition to the resistance developed in the shell section  14  during inward movement of the friction shoes  22 ,  24  and  26  and the wedge  34 , an elastomeric spring  36  comprised of a resilient material is provided in the internal bore  18  of housing  10 . Such resilient material, because it was precompressed during assembly, maintains the wedge and friction shoes in operative engagement with each other and within the housing, both during the operation of the draft gear, as well as during periods of non-operation. The resilient material also resists inward movement of the friction shoes  22 ,  24  and  26  to cushion some of the draft forces applied to the draft gear. 
     To retain the wedge  34  and the friction shoes  22 ,  24  and  26  in the open end  50  of the housing  10 , a series of circumferentially spaced flanges  38 ,  40  and  42  (FIG. 2) are provided toward an inner end  35  of the wedge  34 . In the illustrated embodiment, each flange  38 ,  40  and  42  radially projects outwardly from the wedge  34  with an opening being provided between adjacent flanges  38 ,  40  and  42 . In the illustrated embodiment, housing  10  is provided with a corresponding number of circumferentially spaced inwardly projecting lugs  44 ,  46  and  48  at its open end  50 . In the illustrated embodiment, each lug  44 ,  46  and  48  radially projects inwardly toward the major axis of the housing  10  with an opening being provided between adjacent lugs so as to permit the wedge flanges  38 ,  40  and  42  to move axially therepast. During assembly of the draft gear the wedge flanges  38 ,  40  and  42  are moved past and, ultimately, arranged behind or axially inwardly of the housing lugs  44 ,  46  and  48  so the wedge  34  and the friction shoes  22 ,  24  and  26  are positively retained in assembled relationship in the housing  10 . As will be appreciated by those skilled in the art, and after the wedge  34  is assembled in the draft gear  10 , the wedge flanges  38 ,  40  and  42  are inhibited from rotating into alignment with the openings between adjacent housing lugs  44 ,  46  and  48  due in part to the forces generated by the preload to which the elastomeric pad stack  36  is subject. 
     The elastomeric spring  36  is formed from a resilient material and, in a preferred form, is comprised of a series or longitudinal stack of concentric elastomeric springs, generally identified by reference numeral  52  in FIG.  1 . Preferably, each elastomeric spring or pad in the stack  52  has a centrally disposed pilot hole or throughbore, generally identified by reference numeral  53  in FIG.  1 . As shown, the axially innermost elastomeric pad or spring in the elastomeric spring stack  52  is seated against the inner face of the end wall  12 . The individual pads are stacked such that the pilot hole  53  in each pad comprising the elastomeric spring stack  52  is substantially aligned with the pilot hole  53  in the adjacent elastomeric pad in the spring stack whereby a single center pilot hole extends through the entire pad stack  52 . Further, each individual pad is preferably provided with metal plates  37  and  39  preferably secured to opposed parallel surfaces, as shown in FIG.  1 . As will be more filly explained, the metal plate  39  of the axially innermost elastomeric pad or spring in the elastomeric spring stack  52  aids in securing an axially innermost end of an elongated guide  62  which longitudinally extends away from the end wall or plate  12  of housing  10 . In the illustrated embodiment, the metal plate  37  of the elastomeric spring or pad closest to the open end  50  of the housing  10  abuts with a heel portion  73  of each friction shoe  22 ,  24  and  26 . In a preferred embodiment, the elastomeric pad stack  52  is manufactured in accordance with U.S. Pat. Nos. 4,198,037 and 4,566,678, although other suitable resilient material could be used without detracting or departing from the spirit and scope of the present invention. 
     A generally flat symmetrically contoured spring seat  54  is disposed between the outer end  56  of the elastomeric pad stack  36  and the inner end  70  of the friction shoes  22 ,  24  and  26 , and is adapted for longitudinal movement in the housing  10  to compress the pad stack  36 , when force is applied to the wedge  34 . The center hole  60  in the spring seat  54 , accommodates and stabilizes the guide spike  62  and allows for the spring seat&#39;s movement during a work cycle. As shown in FIG. 8 the spring seat  54  includes first, second and third flat, outer faces  64 ,  66  and  68 . First outer face  64 , for example, which cooperates with the third flat, inner face  70 , of friction shoe  22 , as shown in FIG.1, to form a third selected angle of about 90 degrees plus or minus 4 degrees with respect to the major axis  88  of the draft gear  9 . Although not shown, each of the flat outer faces  66  and  68  cooperate with the flat inner faces of friction shoes  24  and  26  (not shown). As seen in FIG.1 the spring seat  54  fits into a recess  71  created in the bottom portion  73  of the friction shoe  22 . Although not shown, each friction shoe  24  and  26  also have such a recess or step in the bottom or heel portion. This arrangement provides more space in the internal transition section  20  and bore section  18  for additional elastomeric pad material and thus allows a more elastic spring column having greater energy absorption. 
     Each of the friction shoes  22 ,  24  and  26  are the same in size, shape and function and, thus, discussion will be limited to friction shoe  22  with the understanding that such description equally applies to friction shoes  24  and  26 . In other words, friction shoes  24  and  26  include flat faces corresponding to face  70 , recess or steps  71 , and heel portions  73 , and etc. as described above regarding shoe  22 . Suffice it to say, each friction shoe  22 ,  24  and  26  includes a first preferably flat, beveled or tapered inner angling surface  82 , a second preferably flat, beveled or tapered outer angling surface  84 , and a third preferably flat, inner face  70 . 
     The wedge  34  has a series of circumferentially and equally spaced, preferably flat outer surfaces  76 ,  78  and  80  all of which are the same in size, shape and function and, thus, discussion will be limited to the preferably flat angling outer surface  76  on wedge  34  as seen in FIG. 1 with the understanding such description equally applies in full to flat outer surfaces  78  and  80  on the wedge  34 . After the draft gear  9  is assembled, the flat outer surface  76  slidably engages with the first preferably flat, beveled inner surface  82  of the friction shoe  22  forming a first select angle of about 35 degrees plus or minus 3 degrees with the major axis  88  of the draft gear  9 . 
     As previously discussed, the thick-walled friction shell section  14  of housing  10  has three equally spaced and longitudinally extending tapered internal or inner friction surfaces  28 ,  30  and  32  all being the same in size, shape and function and, thus, discussion will be limited to the tapered internal or inner friction surface  28  on housing  10  with the understanding that such description equally applies to the other two tapered internal or inner friction surfaces  30  and  32  on housing  10 . The extended tapered internal or inner friction surface  28  on housing  10  slidably engages with the second flat, beveled or angled surface  84  on friction shoe  22  whereby forming a second selected angle of about 2.25 degrees plus of or minus 0.25 degrees with the major axis  88  of the draft gear  9 . In order to provide the draft gear  9  with an unconventional axial or longitudinally extended travel, the extended tapered internal or inner friction surface  28  on housing  10  longitudinally extends is about 5.5 inches or 140 mm in length. As schematically represented in FIG. 1, the longitudinally extended inner angled surface  28  extends from the open end  50  of housing  10  to an area, generally represented in FIG. 1 by reference numeral  51 , which is spaced a significant longitudinal or axial distance inwardly from the open end  50  of housing  10 . 
     The guide spike  62  is held stationary at all times by virtue of the head portion  86  thereof being compressed tight against the end wall  12  by the fact that the elastomeric pad stack  36  has a preload. During a work cycle the pilot hole  53  of the elastomeric pad stack  36 , the center hole  60  of the spring seat  54  and center bore  72  of the wedge  34  move relative to the spike  62 , enabling inward displacement of the wedge  34  and spring seat  54 . The guide spike  62  is sized to be approximately 0.25 inches shorter than the inside length of the housing to allow the follower block (not shown) to butt against the end  50  of the draft gear at full travel, without damaging the spike  62 . 
     The draft gear  9  described and illustrated herein also has a working stroke of about 116 mm to about 120 mm. The working stroke is the amount of travel of the gear  9  and is the distance the outer face  33  of wedge  34  moves with respect to the open end  50  during a work cycle. 
     A further characteristic of the draft gear  9  is the available travel to installed length ratio. This term is the working stroke divided by the distance from the outer face  33  of wedge  34  to the outer surface  39  of the end plate  12 . As an approximation, dividing about 118 mm by the distance from the outer face  33  to the outer surface  39  which is approximately 568.4 mm results in an available travel to installed length ratio of about 0.21. 
     Still a further characteristic of the draft gear of this invention is its ability to cushion an impact and transmit a low level of force in doing so. It can be seen from FIG. 11 that when a mass having kinetic energy strikes a conventional elastomer/friction draft gear, a certain force/travel relationship  101  results. When that same mass, having the same kinetic energy, strikes the draft gear described herein, the resulting force/travel relationship  103  is characterized by a generally lower level of force, that is, spread over a greater range of travel. As would be expected, the work done by either draft gear in cushioning the impact of the moving mass is the same and is confirmed by the same total area beneath the upper graph line and the horizontal axis for either force/travel relationship. By taking advantage of a greater working stroke, the draft gear of this invention can transmit less force to the car structure while dissipating the same energy. 
     While embodiments of this invention have been shown and described, it should be understood that this invention is not limited hereto except by the scope of the claims. Various modifications and changes may be made without departing from the scope and spirit of the invention as the same will be understood by those skilled in the art.