Patent Publication Number: US-11046339-B2

Title: Friction end-of-car cushioning assembly

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of pending U.S. Non-Provisional patent application Ser. No. 15/901,484 filed Feb. 21, 2018 by Shaun Richmond, and entitled “Friction End-of-Car Cushioning Assembly,” which claims benefit of U.S. Provisional Patent Application No. 62/473,165 filed Mar. 17, 2017 by Shaun Richmond, and entitled “Friction End-of-Car Cushioning Assembly” which are incorporated herein by reference as if reproduced in their entirety. 
    
    
     TECHNICAL HELP 
     This disclosure relates generally to railcars and, more particularly, to a railcar coupler system. 
     BACKGROUND 
     Railcars that carry sensitive lading, such as box cars, flat cars, and coil cars, require protection from the high impact forces that can develop when railcars are impacted into one another in classification yards. This protection is provided by two distinct types of “shock absorbing” devices. For railcars where the lading is not subject to damage, such as coal and grain cars, a short travel (e.g. less than 5″) unit called a draft gear is used. These units predominantly use friction as a means of absorbing the energy of impact. When the lading is more likely to be damaged, such as consumer products, a longer travel unit (e.g. 10″, 15″, or 18″) is used. These units are universally hydraulic and are referred to as an end-of-car cushioning (EOC) units. Hydraulic EOCs are excellent at protecting railcars and lading from impact damage. However, hydraulic EOCs tend to leak, are expensive, and their softness produces excessive train action forces in service. It is desirable to provide a solution that overcomes the problems associated with hydraulic EOCs while providing adequate protection for railcars and lading. 
     SUMMARY 
     In one embodiment, the disclosure includes a friction end-of-car cushioning (EOC) assembly with a housing coupled to a railcar. The housing has a chamber formed within a bore of the housing that includes a first contact surface comprising an angled contact surface at a first end of the chamber and a second contact surface at a second end of the chamber. The friction EOC assembly also includes a center shaft disposed at least partially within the bore of the housing. The center shaft has a head portion at a first end of the center shaft, a coupler interface at a second end of the center shaft, and a rod portion spanning between the head portion and the coupler interface. The rod portion of the center shaft is tapered from the second end of the center shaft to the first end of the center shaft. 
     The friction EOC assembly also includes a sliding wedge disposed within the chamber. The sliding wedge has a first contact surface tapered toward the first contact surface of the housing, a second contact surface perpendicular to the bore of the housing, and a third contact surface parallel to the bore of the housing. The sliding wedge is positioned to allow the rod portion of the center shaft to pass through a bore defined by the third contact surface of the sliding wedge. The sliding wedge is also configured such that the first contact surface of the sliding wedge is positioned to apply a force onto the angled contact surface of the housing and the third contact surface of the sliding wedge is positioned to apply a frictional force to the rod portion of the center shaft. 
     The friction EOC assembly also includes a load spring disposed within the chamber. The load spring is positioned to allow the rod portion of the center shaft to pass through a bore of the load spring. The load spring is compressed between the second contact surface of the chamber and the second contact surface of the sliding wedge and is positioned to apply a compressive force onto the second contact surface of sliding wedge toward the angled contact surface of the housing. The load spring is configured to not further compress as the center shaft moves within the bore of the housing. 
     In another embodiment, the disclosure includes a damping method that involves configuring a friction EOC assembly on a railcar in a first configuration. In the first configuration, a head portion of a center shaft is positioned adjacent to a chamber formed within a bore of a housing. The method further involves applying a force onto a coupler interface portion of the center shaft in a direction toward the first end of the chamber to transition the friction end-of-car cushioning assembly to a second configuration. Applying the force onto the center shaft moves the head portion of the center shaft away from the chamber and moves the coupler interface portion of the center shaft toward the chamber. 
     In yet another embodiment, the disclosure includes a damping method that involves configuring a friction EOC assembly on a railcar in a first configuration. In the first configuration, a coupler interface portion of a center shaft is positioned adjacent to a chamber formed within a bore of a housing. The method involves applying a force onto the coupler interface portion of the center shaft in a direction away the first end of the chamber to transition the friction end-of-car cushioning assembly to a second configuration. Applying the force onto the center shaft moves a head portion of the center shaft toward the chamber and moves the coupler interface portion of the center shaft away the chamber. 
     Disclosed herein are various embodiments of a friction EOC assembly for a railcar that provide several technical advantages. After a rapid rise in force, the force generated by the friction EOC assembly is essentially constant since the spring is pre-compressed and the compression on it does not change significantly during the stroke. In one embodiment, the friction EOC assembly is entirely mechanical and does not involve hydraulics, which allows the friction EOC assembly to be less expensive and more reliable than hydraulic EOCs. In one embodiment, the friction EOC assembly can be incorporated into a draft sill and does not require an additional housing, which may reduce weight und cost. The friction EOC assembly force levels can be adjusted by changing spring stiffness, spring pre-compression, and/or wedge angles. The friction EOC assembly design allows the friction EOC assembly to have any length of draft gear travel, and does not restrict travel of draft gear unlike existing systems. 
     Certain embodiments of the present disclosure may include some, all, or none of these advantages. These advantages and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. 
         FIG. 1  is a side view of a railcar system using a friction end-of-car cushioning (EOC) assembly to couple railcars; 
         FIG. 2  is a cutaway view of an embodiment of a friction EOC assembly in a first configuration; 
         FIG. 3  is a cutaway view of an embodiment of the friction EOC assembly in a second configuration; 
         FIG. 4  is a cutaway view of another embodiment of a friction EOC assembly; 
         FIG. 5  is partial cutaway view of an embodiment of a wedge configuration for the friction EOC assembly; 
         FIG. 6  is partial cutaway view of another embodiment of a wedge configuration for the friction EOC assembly; 
         FIG. 7  is partial cutaway view of another embodiment of a wedge configuration for the friction EOC assembly; 
         FIG. 8  is partial cutaway view of another embodiment of a wedge configuration for the friction EOC assembly; 
         FIG. 9  is partial cutaway view of another embodiment of a wedge configuration for the friction EOC assembly; 
         FIG. 10  is an embodiment of a damping method using a friction EOC assembly; 
         FIG. 11  is a partial cutaway view of a portion of another embodiment of a friction EOC assembly in a first configuration; 
         FIG. 12  is a partial cutaway view of a portion of another embodiment of a friction EOC assembly in a second configuration; 
         FIG. 13  is a partial cutaway view of another embodiment of a friction EOC assembly; 
         FIG. 14  is a cross section view of an embodiment of sliding wedge segments within the housing of a friction EOC assembly; 
         FIG. 15  is a cross section view of another embodiment of sliding wedge segments within the homing of a friction EOC assembly; 
         FIG. 16  is a cross section view of another embodiment of sliding wedge segments within the housing of a friction EOC assembly; 
         FIG. 17  is a cross section view of another embodiment of sliding wedge segments within the housing of a friction EOC assembly; 
         FIG. 18  is a cross section view of another embodiment of sliding wedge segments within the housing of a friction EOC assembly; and 
         FIG. 19  is a partial cutaway view of a portion of another embodiment of a friction EOC assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Conventional friction draft gears use friction wedges backed by a spring that compresses as the draft gear is compressed. These types of friction draft gears cannot be extended to have significantly longer travel. As the spring is compressed, the spring applies a force on the wedges and the friction resisting compression of the draft gear increases. The force generated by these systems is a roughly linear increase of force with compression. However, the design of conventional draft gear limits its travel to about 4″ to 5″ due to the maximum practical compression of the spring. Conventional hydraulic end-of-car cushionings (EOCs) exhibit a rapid rise in force to an approximately constant level. This application of force allows hydraulic EOCs to absorb more energy than conventional friction draft gears. Hydraulic EOCs are more effective than even multiple friction draft gears in tandem. 
     Disclosed herein are various embodiments of a friction EOC assembly for a railcar. After a rapid rise in force, the force generated by the friction EOC assembly is essentially constant since the spring is pre-compressed and the compression on it does not change significantly during the stroke. In one embodiment, the friction EOC assembly is entirely mechanical and does not involve hydraulics, which allows the friction EOC assembly to be less expensive and more reliable than hydraulic EOCs. In one embodiment, the friction EOC assembly can be incorporated into a draft sill and does not require an additional housing, which may reduce weight and cost. The friction EOC assembly force levels can be adjusted by changing spring stiffness, spring pre-compression, and/or wedge angles. The friction EOC assembly design allows the friction EOC assembly to have any length of draft gear travel, and does not restrict travel of draft gear unlike existing systems. 
     In some embodiments, the friction EOC assembly can be used as a direct replacement for existing hydraulic EOCs. The friction EOC assembly may be configured to integrate with existing end fittings for hydraulic EOCs. For example, the friction EOC assembly may be configured with the same interface on the ends of the center shaft to allow the friction EOC assembly to be retrofitted to existing systems. 
       FIG. 1  is a side view of a railcar system  100  using a friction EOC assembly  200  to couple railcars  102 A and  102 B. Examples of railcars  102 A and  102 B include, but are not limited to, box cars, flat cars, autorack cars, tank cars, hopper cars, coil cars, or any other suitable type of railcar. The friction EOC assembly  200  is generally configured to protect railcars  102 A and  102 B and their payloads by dampening the high impact forces that can develop when the railcars  102 A and  102 B are impacted into one another. For example, the friction EOC assembly  200  may provide shock absorption when the railcars  102 A and  102 B are coupled to each other. 
       FIG. 2  is a cutaway view of an embodiment of a friction EOC assembly  200  in a first configuration. The friction EOC assembly  200  comprises a housing  202 , a load spring  204 , a sliding wedge  206 , a backing wedge  208 , a center shaft  210 , a coupler  212 , and a draft spring  214 . The friction EOC assembly  200  may be configured as shown or in any other suitable configuration. 
     The housing  202  comprises an axial bore  203  that allows the center shaft  210  to move within the bore  203  of the housing  202 . The housing  202  may be constructed using metals or any other suitable material. The housing  202  structure may be a square, circular, hexagonal, or any other suitable shape along the length of the housing  202 . In other words, the housing  202  comprise a circular cross section, a rectangular cross section, a hexagonal cross section, or any other suitable shape cross section. In one embodiment, the housing  202  is supported by a draft stop welded to the draft sill, which allows the housing  202  to remain in a fixed position as the center shaft  210  slides through the housing  202 . 
     The center shaft  210  comprises a head portion  209 , a rod portion  211 , and a coupler interface portion  213 . The head portion  209  is located at a first end of the center shaft  210 . The coupler interface portion  213  is located at a second end of the center shaft  210 . The rod portion  211  spans between the head portion  209  and the coupler interface portion  213  of the center shaft  210 . The rod portion  211  comprise a circular cross section, a rectangular cross section, or any other suitable shape cross section. In one embodiment, the head portion  209  and/or the coupler interface portion  213  have a circumferential diameter larger than the diameter of the rod portion  211  of the center shaft  210 . The coupler interface portion  213  of the center shaft  210  is coupled to a coupler  212  which may be used to connect a railcar with the friction EOC assembly  200  to another railcar. The coupler  212  may be any suitable type of coupler for connecting railcars. 
     The center shaft  210  is disposed at least partially within the bore  203  of the housing  202 . The center shaft  210  is positioned such that at least a portion (e.g. the rod portion  211 ) of the center shaft  210  passes through the chamber  205  of the housing  202 . In  FIG. 2 , the center shaft  210  is shown in an extended position, such that the center shaft  210  is extending in a direction out of the housing  202  and toward the coupler  212 . The center shaft  210  is configured to move (e.g. slide) within the bore  203  of the housing  202 . 
     The center shaft  210  may have any suitable length  220  and/or stroke length  222 . For example, the center shaft  210  may have a length  220  of about 30 inches (in) and a stroke length  222  of about 10 in. In other examples, the center shaft  210  may be any other suitable length  220  and/or stroke length  222 . The center shaft  210  structure may be a square, circular, hexagonal, or any other suitable shape along the length of the center shaft  210 . 
     The housing  202  comprises a chamber  205  configured to house the loud spring  204 , the sliding wedge  206 , and the backing wedge  208 . The chamber  205  is formed within the bore  203  of the housing  201 . The chamber  205  is configured to allow a rod portion  211  of the center shaft  210  to pass through an opening or bore formed by the chamber  205 . 
     The backing wedge  208  is disposed within the chamber  205  such that at least a portion of the backing wedge  208  is in contact with a first contact surface  215  at a first end of the chamber  205 . The backing wedge  208  comprises on angled contact surface  219 . The angled contact surface  219  is a surface that tapers away from the first end of the chamber  205 . The angled contact surface  219  may have suitable angle or rate of tapering. The backing wedge  208  is positioned to allow the rod portion  211  of the center shaft  210  to pass through a bore or opening defined by the angled contact surface  219  of the backing wedge  208 . 
     The sliding wedge  206  is disposed within the chamber  205 . The sliding wedge  206  comprises a first contact surface  224  tapered toward the first contact surface  215  of the chamber  205 . The first contact surface  224  of the sliding wedge  206  is positioned to apply a force (e.g. a compressive force and/or a frictional force) onto the angled contact surface  219  of the backing wedge  208 . The sliding wedge  206  comprises a second contact surface  226  configured substantially perpendicular to the bore  203  of the housing  202 . The sliding wedge  206  comprises a third contact surface  228  configured substantially parallel to the bore  203  of the housing  202 . The sliding wedge  206  is positioned to allow the rod portion  211  of the center shaft  210  to pass through a bore or opening defined by the third contact surface  228  of the sliding wedge  206 . In addition, the third contact surface  228  is at least partially in contact with the rod portion  211  of the center shaft  210  and is positioned to apply a frictional force onto the rod portion  211  of the center shaft  210 . 
     The load spring  204  is disposed within the chamber  205 . Examples of the load spring  204  include, but are not limited to, coil springs, elastomer springs, and rubber dampeners. The load spring  204  is portioned to allow the rod portion  211  of the center shaft  210  to pass within a bore or opening defined by the loud spring  204 . The load spring  204  is configured to be pre-compressed within the chamber  205 . The load spring  204  is compressed between a second contact surface  216  at a second end of the chamber  205  and the second contact surface  226  of the sliding wedge  206 . In such a configuration, the load spring  204  is configured to apply a compressive force to the second contact surface  226  of the sliding wedge  206  toward the angled contact surface  219  of the backing wedge  208 . 
     Unlike conventional friction draft gears which use a spring that is initially unloaded, the load spring  204  is configured to be preloaded (i.e. pre-compressed) which constantly applies a force to the sliding wedge  206 . Although the load spring  204  is shown as an elastomeric spring, the load spring  204  may be any other suitable type of spring or mechanism. The force applied to the end of the sliding wedge  206  causes the sliding wedge  206  to apply a force to both the angled contact surface  219  of the backing wedge  208  and the rod portion  211  of the center shaft  210 . The force applied to the center shaft  210  by the sliding wedge  206  results in friction between the center shaft  210  and the sliding wedge  206 . In one embodiment, the load spring  204  is configured to not further compress as the center shaft  210  moves within the bore  203  of the housing  202 . In other words, the compression of the load spring  204  remains substantially constant when the center shaft  210  moves within the bore  203  of the housing  202 . 
     In one embodiment, the friction EOC assembly  200  comprises a draft spring  214  disposed within the housing  102 . Examples of the draft spring  214  include, but are not limited to, coil springs, elastomer springs, and rubber dampeners. The draft spring  214  is positioned between the head portion  209  of the center shaft  210  and a third contact surface  217  at the first end of the chamber  205 . The draft spring  214  is configured such that the rod portion  211  of the center shaft  210  passes through the draft spring  214 . The draft spring  214  is configured to provide cushioning to the center shalt  210  by applying a force to the head portion  209  of the center shaft  210  when the center shaft  210  extends out of the housing  202 . Without the draft spring  214 , the head portion  209  of the center shaft  210  would make contact with the third contact surface  217  of the chamber  205  which would cause the center shaft  210  to stop abruptly at full travel. Although the draft spring  214  is shown as an elastomeric spring, the draft spring  214  may be any other suitable type of spring or mechanism. In some embodiments, the draft spring  214  is optional. 
       FIG. 3  is a cutaway view of an embodiment of the friction EOC assembly  200  in a second configuration. In  FIG. 3 , the center shaft  210  is shown in a retracted position, such that the center rod  200  is retracted into the housing  202 . During an impact event, the center shaft  210  is pushed into the housing  202 . The load spring  204  constantly applies a force to the second contact surface  226  of the sliding wedge  206 , which pushes the sliding wedge  206  down the slope of the angled contact surface  219  of the backing wedge  208  between the center shaft  210  and the backing wedge  208 . This produces a magnified normal force between the sliding wedge  206  and the center shaft  210 . This force resists the motion of the center shaft  210  and absorbs the energy of impact. The motion of the center shaft  210  also enhances the wedge action and further increases the force. 
       FIG. 4  is a cutaway view of another embodiment of a friction EOC assembly  200 . In one embodiment, the friction EOC assembly  200  comprises a return spring  402  disposed within the housing  202 . Examples of the return spring  402  include, but are not limited to, coil springs, elastomer springs, and rubber dampeners. The return spring  402  is positioned between the coupler interface  213  and a fourth contact surface  218  at the second end of the chamber  205 . The return spring  402  is configured to allow the rod portion  211  of the center shaft  210  to pass through the return spring  402 . The return spring  402  is configured such that when a force is no longer pushing the center shaft  210  into the housing  202 , the return spring  402  pushes the center shaft  210  back into the extended position, for example, as shown in  FIG. 1 . Although the return spring  402  is shown as a coil spring, the return spring  402  may be any other suitable type of spring or mechanism. In some embodiments, the return spring  402  is optional. 
       FIG. 5  is partial cutaway view of an embodiment of a wedge configuration for the friction EOC assembly  200 . In one embodiment, the friction EOC assembly  200  comprises a spring or an elastomer liner  502  between the first contact surface  224  of the sliding wedge  106  and the angled contact surface  219  of the backing wedge  108 . In this configuration, the friction EOC assembly  200  is configured such that the sliding wedge  206  and the backing wedge  208  do not slide past each other. The elastomer liner  502  is configured to deflect in shear, which allows motion for the sliding wedge  206 . Such a configuration may be more consistent than only relying on friction. In one embodiment, the elastomer liner  502  could also represent a low friction lining material between the sliding wedge  206  and the backing wedge  208 . In this configuration, the low friction between the sliding wedge  206  and the backing wedge  208  may produce more consistent and lower friction which may enhance the operation of the sliding wedge  206 . 
       FIG. 6  is partial cutaway view of another embodiment of a wedge configuration for the friction EOC assembly  200 . In one embodiment, the friction EOC assembly  200  comprises an insert  602  between the third contact surface  228  of the sliding wedge  206  and lite rod portion  211  of the center shaft  210 . The insert  602  may be a sliding material such as a brake lining material which could provide improved friction characteristics. In some embodiments, the insert  602  may be produced by inserting slugs of lubrication material onto slots in the faces (e.g. the third contact surface  228 ) of the sliding wedge  206  and the rod portion  211  of the center shaft  210 . In this example, the lubrication material is spread over the surface as the center shaft  210  slides to form the insert  602 . 
       FIG. 7  is partial cutaway view of another embodiment of a wedge configuration for the friction EOC assembly  200 . In one embodiment, the first contact surface  224  of the sliding wedge  206  has a rounded surface. For example, the sliding wedge  206  may be configured such that first contact surface  224  of the sliding wedge  206  has a curved or rounded surface. The first contact surface  224  of the sliding wedge  206  may have any suitable amount of curvature or roundedness. The curvature of the sliding wedge  206  may allow the sliding wedge  206  to properly align with the center shaft  210  even if the backing wedge  208  is not at exactly the correct angle or is not flat. Properly aligning the center shaft  210  may help the friction EOC assembly  200  generate more force for absorbing energy. 
       FIG. 8  is partial cutaway view of another embodiment of a wedge configuration for the friction EOC assembly  200 . In one embodiment, the backing wedge  208  is formed by the chamber  205 . In other words, an interior portion of the chamber is configured to serve as the previously described backing wedge  208 . 
       FIG. 9  is partial cutaway view of another embodiment of a wedge configuration for the friction EOC assembly  200 . In one embodiment, the backing wedge  208  is configured into a cone shape. The sliding wedge  106  is configured to be curved and to fit within the cone shape structure of the backing wedge  208 . 
     In one embodiment, the sliding wedge  206  comprises a plurality of sliding wedge segments  902  and a plurality of elastomer lining segments  904 . Each of the plurality of elastomer lining segments  904  may be disposed between a pair of sliding wedge segments  902  from the plurality of sliding wedge segments  902 . In this example, the sliding wedges  902  are evenly spaced by inserting a soft elastomer  904  between the sliding wedges  902 . The sliding wedge  206  may comprise any suitable number of sliding wedge segments  902  and/or elastomer lining segments  904 . In addition, the elastomer lining segments  904  may have any suitable thickness. 
       FIG. 10  is an embodiment of a damping method  1000  using a friction EOC assembly  200 . An operator may employ method  1000  with the friction EOC assembly  200  to provide shock absorption when connecting two railcars together. 
     At step  1002 , an operator configures the friction EOC assembly  200  on a railcar in a first configuration. In the first configuration, the friction EOC assembly  200  may be configured with the center shaft  210  positioned similar to the configuration shown in  FIG. 2 . 
     At step  1004 , a first force is applied onto the coupler interface portion  213  of the center shaft  210  in a first direction toward the first end of the chamber  205  to transition the friction EOC assembly  200  to a second configuration. For example, as the railcars begin to engage each other, the coupler  212  attached to the coupler interface portion  213  of the center shaft  210  may experience a force that moves the coupler interface portion  213  of the center shaft  210  toward the chamber  205  and moves the head portion  209  of the center shaft  210  away the chamber  205 . In the second configuration, the friction EOC assembly  200  may be configured with the center shaft  210  positioned similar to the configuration shown in  FIG. 3 . 
     At step  1006 , a second force is applied onto the coupler interface portion  213  of the center shaft  210  in a second direction away from the first end of the chamber  205  to transition the friction EOC assembly  200  back to the first configuration. For example, as the railcars begin to separate from each other, the coupler  212  attached to the coupler interface portion  213  of the center shaft  210  may experience a force that moves the coupler interface portion  213  of the center shaft  210  away the chamber  205  and moves the head portion  209  of the center shaft  210  toward the chamber  205 . In one embodiment, the second force is applied to the coupler interface portion  213  of the center shaft  210  by a return spring (e.g. return spring  402 ). In another embodiment, the second force is applied to the coupler interface portion  213  of the center shaft  210  by the coupler  212  pulling away from the friction EOC assembly  200 . In other embodiments, the second force is applied to the coupler interface portion  213  of the center shaft  210  by any other suitable method as would be appreciated by one of ordinary skill in the art upon viewing this disclosure. 
       FIG. 11  is a partial cutaway view of a portion of another embodiment of a friction EOC assembly  200  in a first configuration. In  FIG. 11 , the diameter  1114  of the rod portion  211  of the center shaft  210  is tapered in a direction from the coupler interface portion  213  at the second end of the center shaft  210  to the head portion  209  at the first end of the center shaft  210 . The tapering of the rod portion  211  of the center shaft  210  causes the diameter  1114  of the center shaft  210  to vary along the length of the rod portion  211  of the eerier shaft  210 . In some embodiments, the rod portion  211  of the center shaft  210  may be configured such that different portions of the center shaft  210  have different tapering rates. For example, the rod portion  211  of the center shaft  210  may comprise a first tapered portion  1106  and a second tapered portion  1108 . In this example, the first tapered portion  1106  may taper at a greater rate than the second tapered portion  1108 . In other words, the diameter  1114  of the first tapered portion  1106  may reduce more rapidly than the diameter  1114  of the second tapered portion  1108 . The tapering of the center shaft  210  effectively causes the diameter  1114  of the center shaft  210  to increase as the center shaft  210  moves in the first direction  1110 . This causes the closing force of the friction EOC assembly  200  to increase which allows for a less abrupt slowing of a railcar under low velocity impacts and a higher force under high velocity impacts. The center shaft  210  may have a cross section that is a rectangular, circular, hexagonal, or any other suitable shape along the length of the center shaft  210 . 
     In  FIG. 11 , the previously described backing wedge  208  may be integrated within the chamber  205  of the housing  202 . For example, the chamber  205  may comprise an angled contact surface  1102  that operates similar to the backing wedge  208  described in  FIG. 2 . In the first configuration, the sliding wedge  206  is configured to move along the angled contact surface  1102  as the center shaft  210  traverses the bore  203  of the housing  202 . As the center shaft  210  traverses the bore  203  of the housing  202  in a first direction  1110 , the diameter  1114  of the rod portion  211  of the center shaft  210  that passes through the sliding wedge  206  increases. The increasing diameter  1114  of the center shaft  210  causes the sliding wedge  206  move or expand outwardly toward the sidewalls of the housing  202 . An example of the sliding wedge  206  moving outwardly toward the sidewalls of the housing  202  is shown in  FIG. 12 . As the center shaft  210  traverses the bore  203  of the housing  202  in a second direction  1112 , the diameter  1114  of the rod portion  211  of the center shaft  210  that passes through the sliding wedge  206  decreases. The decreasing diameter  1114  of the center shaft  210  causes the sliding wedge  206  move or contract inwardly toward the bore  203  of the housing  202 . 
     In one embodiment, the friction EOC assembly  200  may comprise a spring seat or backing plate  1104  disposed between the sliding wedge  206  and the load spring  204 . In this configuration, the load spring  204  is configured to apply a force onto the sliding wedge  206  via the spring seal  1104 . 
       FIG. 12  is a partial cutaway view of a portion of another embodiment of a friction EOC assembly  200  in a second configuration. In the second configuration, the sliding wedge  206  has moved or expanded outwardly toward the sidewalls of the housing  202 . In this configuration, the normal force between the sliding wedge  206  and the center shaft  210  is magnified. This force resists the motion of the center shaft  210  and absorbs the energy of an impact. The motion of the center shaft  210  also enhances the wedge action between the sliding wedge  206  and the angled contact surface  1102  of the housing  202  which further increases the resistive force. 
       FIG. 13  is a partial cutaway view of another embodiment of a friction EOC assembly  200 . In  FIG. 13 , the angled contact surface  1102  of the housing  202  is curved toward the sliding wedge  206 . In addition, the first contact surface  215  of the sliding wedge  206  is curved away from the angled contact surface  1102  of the housing  202  to substantially match the curvature of the angled contact surface  1102  of the housing  202 . The angled contact surface  1102  of the housing  202  and the first contact surface  215  of the sliding wedge  206  may each have any suitable amount of curvature or roundness. The curvature of the angled contact surface  1102  of the housing  202  and the first contact surface  215  of the sliding wedge  206  may prevent or mitigate the ends of the sliding wedge  206  from rotating against the angled contact surface  1102  of the housing  202 . 
     In one embodiment, the third contact surface  228  of the sliding wedge  206  may be curved toward the center shaft  210 . The curvature of the third contact surface  228  of the sliding wedge  206  may allow the amount of friction and force between the sliding wedge  206  and the center shaft  210  to vary as the center shaft  210  traverses the bore  203  of the housing  202 . 
     In some embodiments, one of the angled contact surface  1102  or the first contact surface  215  of the sliding wedge  206  may be curved while the other contact surface remains flat. For example, the angled contact surface  1102  may be flat while the first contact surface  215  of the sliding wedge  206  is curved. In this example, the first contact surface  215  of the sliding wedge  206  may be curved in a direction toward the angled contact surface  1102 . In this configuration, the point of contact between the angled contact surface  1102  and the first contact surface  215  of the sliding wedge  206  moves outward as the sliding wedge  206  rotates when the center shaft  210  traverses the bore  203  of the housing  202 . 
       FIGS. 14-18  are cross-sectional views of examples of different configurations for sliding wedge segments  206  within the housing  202  of friction EOC assembly  200 . As an example, the cross-sectional views may be from location  1116  shown in  FIG. 11 . In  FIGS. 14-18 , the housing  202  has a rectangular cross section that comprises four edges  1402  (e.g. sidewalls) and four corners  1404 . In this example, the center shaft  210  also has a rectangular cross section that comprises four edges  1406  and four corners  1408 . The sliding wedge segments  206  may be configured to be in different shapes and/or positions within the housing  202 .  FIGS. 14-18  illustrate examples with four sliding wedge segments  206 . In other examples, the friction EOC assembly  200  may comprise any other suitable number of sliding wedge segments  206 . 
       FIG. 14  is a cross section view of an embodiment of sliding wedge segments  206  within the housing of a friction EOC assembly  200 . In  FIG. 14 , each sliding wedge segment  206  has a rectangular cross section and is configured to apply a force to an edge  1402  of the housing  202  and an edge  1406  of the center shaft  210 . 
       FIG. 15  is a cross section view of another embodiment of sliding wedge segments  206  within the housing of a friction EOC assembly  200 . In  FIG. 15 , each sliding wedge segment  206  has a trapezoidal cross section and is configured to apply a force to an edge  1402  of the housing  202  and an edge  1406  of the center shaft  210 . In this configuration, the sliding wedge segments  206  have a larger contact surface with the edge  1402  of the housing  202  compared to the sliding wedge segment  206  configuration described in  FIG. 14 . The larger contact surface provides increased stiffening of the housing  202  against frictional forces. 
       FIG. 16  is a cross section view of another embodiment of sliding wedge segments  206  within the housing of a friction EOC assembly  200 . In  FIG. 16 , each sliding wedge segment  206  has a rectangular cross section and is configured to apply a force to two edges  1402  and a corner  1404  of the housing  202  and two edges  1406  and a corner  1408  of the center shaft  210 . In this configuration, the corners  1404  of the housing  202  and the corners  1408  of the center shaft  210  may act as guides for the sliding wedge segments  206 . 
       FIG. 17  is a cross section view of another embodiment of sliding wedge segments  206  within the housing of a friction EOC assembly  200 . In  FIG. 17 , each sliding wedge segment  206  has a rectangular cross section and is configured to apply a force to two edges  1402  and a corner  1404  of the housing  202  and an edge  1406  of the center shaft  210 . In this configuration, the center shaft  210  is rotated 45 degrees from the example shown in  FIG. 16 . 
       FIG. 18  is a cross section view of another embodiment of sliding wedge segments within the housing of a friction EOC assembly  200 . In  FIG. 18 , each sliding wedge segment  206  has a rectangular cross section and is configured to apply a force to two edges  1402  and a corner  1404  of the housing  202  and on edge  1406  of the center shaft  210 . In this configuration, the friction EOC assembly  200  further comprises a low modulus material  1802  disposed between the sliding wedge segments  206  and the housing  202 . In one embodiment, the low modulus material  1802  has an elastic modulus that is less than steel. Examples of the low modulus material  1802  include, but are not limited to, a polymer material, a hard rubber, rubber, urethane, and any other suitable type of material. The low modulus material  1802  may be formed to be any suitable shape or thickness. An expansion force is applied to the housing  202  as the sliding wedge segments  206  move along the angled contact surface  1102  of the housing  202 . The low modulus material  1802  provides increased stiffening to the sidewalk housing  202  to mitigate any expansion of the housing  202  due to the expansion force. 
       FIG. 19  is a partial cutaway view of a portion of another embodiment of a friction EOC assembly  200 . In  FIG. 19 , the friction EOC assembly  200  is configured similar to the friction EOC assembly  200  described in  FIG. 18 . For example, the friction EOC assembly  200  comprises a low modulus material  1802  disposed between the sliding wedge segments  206  and the housing  202  similar to the low modulus material  1802  described in  FIG. 18 . In  FIG. 19 , the friction EOC assembly  200  comprise a semi-static block  1902  that is interlocked with a fixed shear backer  1904 . In this configuration, the semi-static block  1902  is configured to provide the angled contact surface  1102  for the housing  202 . The fixed shear backer  1904  is configured to prevent lateral movement of the semi-static block  1902  as the center shaft  210  traverses the housing  202 . 
     One of ordinary skill in the art would appreciate that the various configurations of the friction EOC assembly  200  described in  FIGS. 1-19  may be combined and/or used interchangeably with each other. For example, the friction EOC assembly  200  may comprise any suitable combination and configuration of components as described in  FIGS. 1-19 . In addition, one of ordinary skill in the art would appreciate that the configurations of the friction EOC assembly  200  described in  FIGS. 1-19  may be used with the dampening method  1000  described in  FIG. 10 . 
     While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. 
     In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be mode without departing from the spirit and scope disclosed herein. 
     To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112(f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.