Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application represents the national stage entry of PCT International Application No. PCT/US2010/042843 filed Jul. 23, 2010 which claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/227,992 filed Jul. 23, 2009, both of which are hereby incorporated herein by reference for all purposes. 
    
    
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     FIELD OF THE INVENTION 
     This invention relates to compression limiters, and particularly compression limiters for automotive assemblies. 
     BACKGROUND OF THE INVENTION 
     Fasteners are often used to connect a plastic component to another component in various types of assemblies, especially automotive assemblies. However, the fastener must usually be loaded to an extent that would cause the plastic component to quickly deform, fracture or creep over time, thereby reducing the load carried by the fastener. As such, a metal compression limiter (sometimes simply referred to as a bushing or insert) is commonly used in assemblies in which a compressive load is applied to a plastic component. The compression limiter strengthens the plastic component and resists the load applied by the fastener. Therefore, the integrity of the plastic is not compromised and the compression limiter reduces creep of the plastic component. 
     Typically, a compression limiter has a tubular shape with an outer surface that engages the plastic component. The inner surface of the compression limiter defines a passageway that accommodates the fastener. Most simple compression limiters do not include additional features; as such, the compression limiter may fall out of the plastic component during manufacturing if the compression limiter is inserted by overmolding or press-fitting. To address this problem, some compression limiters include retaining features to provide a more secure connection to the plastic component. For example, some compression limiters include a flanged end that engages a surface of the plastic component outside the hole. Other designs include perforations into which the plastic component flows during an overmolding process. 
     However, the retention features of the aforementioned designs typically require additional processing steps that significantly increase the overall manufacturing time, and therefore cost, of the compression limiter. For example, some compression limiters are perforated by a punch and then moved to another tooling assembly to be rolled into a cylindrical shape. Considering the limitations of previous designs, a need exists for an improved compression limiter that is easily manufactured. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention provides a compression limiter that comprises an upper surface and a lower surface. A distance between the lower surface and the upper surface defines a longitudinal direction. The compression limiter further comprises an inner surface that defines a passageway configured to accommodate a fastener and an outer surface configured to engage a structure in which the compression limiter is placed. A distance between the outer surface and the inner surface defines a radial direction perpendicular to the longitudinal direction. The compression limiter further comprises a first retainer that projects outwardly from the outer surface. The first retainer includes a first retention surface that has at least a planar portion perpendicular to the radial direction. The first retainer further includes an undercut surface disposed radially inwardly from the first retention surface so as to create a corner extending in a direction with at least a component perpendicular to the longitudinal direction. 
     In another aspect, the present invention provides a method for forming the compression limiter from powder metal. The method includes the step of pressing the powder metal in a longitudinal direction with a movable punch and thereby shaping an outer surface of the compression limiter against an inner die surface of a die cavity. An inner surface of the compression limiter is shaped against a core rod disposed in the die cavity while simultaneously shaping the outer surface. A distance between the outer surface and the inner surface of the compression limiter defines a radial direction perpendicular to the longitudinal direction. A retainer projecting from the outer surface of the compression limiter is shaped against a side punch disposed in the die cavity while simultaneously shaping the outer surface. The retainer includes a first retention surface that has at least a planar portion perpendicular to the radial direction. The retainer further includes an undercut surface disposed radially inwardly from the first retention surface. The method further includes the step of removing the compression limiter from the die cavity by lowering the die cavity relative to the side punch. In some embodiments, a plurality of compression limiters are formed simultaneously in a single die cavity. 
     The foregoing and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a perspective view of a compression limiter of the present invention; 
         FIG. 2  is a top view of the compression limiter of  FIG. 1 ; 
         FIG. 3  is a side view of the compression limiter of  FIG. 1  showing a retainer; 
         FIG. 4  is a front view of the compression limiter of  FIG. 1 ; 
         FIG. 5  is a sectional view along line  5 - 5  of  FIG. 4 ; 
         FIG. 6  is a detail view of the area enclosed by line  6 - 6  of  FIG. 5 ; 
         FIG. 7  is a perspective view of a second embodiment of the compression limiter of the present invention; 
         FIG. 8  is a top view of the compression limiter of  FIG. 7 ; 
         FIG. 9  is a side view of the compression limiter of  FIG. 7  showing a retainer; 
         FIG. 10  is a front view of the compression limiter of  FIG. 7 ; 
         FIG. 11  is a sectional view along line  11 - 11  of  FIG. 8 ; 
         FIG. 12  is a perspective view of a third embodiment of the compression limiter of the present invention; 
         FIG. 13  is a top view of the compression limiter of  FIG. 12 ; 
         FIG. 14  is a side view of the compression limiter of  FIG. 12  showing a retainer; 
         FIG. 15  is a front view of the compression limiter of  FIG. 12 ; 
         FIG. 16  is an exploded perspective view of a tooling assembly for manufacturing the compression limiter; 
         FIG. 17  is a perspective view of a first manufacturing step for the compression limiter; 
         FIG. 18  is a sectional view along line  18 - 18  of  FIG. 17 ; 
         FIG. 19  is a perspective view of a second manufacturing step for the compression limiter; 
         FIG. 20  is a sectional view along line  20 - 20  of  FIG. 19 ; 
         FIG. 21  is a perspective view of a third manufacturing step for the compression limiter; and 
         FIG. 22  is a sectional view along line  22 - 22  of  FIG. 21 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The particulars shown herein are by way of example and only for purposes of illustrative discussion of the embodiments of the invention. The particulars shown herein are presented to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for the fundamental understanding of the invention. The description taken with the drawings should make apparent to those skilled in the art how the several forms of the present invention may be embodied in practice. 
     Referring now to  FIGS. 1-6 , a compression limiter  10  of the present invention includes a body  12  that defines a passageway  14  to accommodate a fastener (not shown). The passageway  14  extends from an upper surface  16  to a lower surface  18  in a longitudinal direction  20  defined by a distance between the upper and lower surfaces  16 ,  18 . An inner surface  22  and an outer surface  24  opposite the inner surface  22  provide the compression limiter  10  with a generally open-cylindrical shape. One or more retainers  26  project outwardly from the outer surface  24  to secure the compression limiter  10  to the fastened component (i.e., a component in which the compression limiter  10  is press fitted, over-molded, or the like to prevent deformation due to the load applied by the fastener). These structures are described in further detail in the following paragraphs, beginning with the upper surface  16  and concluding with the retainers  26 . 
     Still referring to  FIGS. 1-6 , the upper and lower surfaces  16 ,  18  are preferably planar surfaces that are identical to one another. Such identical surfaces, as well as other structures described in further detail below, provide the compression limiter  10  with a symmetric shape over a plane perpendicular to the longitudinal direction  20  and bisecting the compression limiter  10 . That is, the compression limiter  10  may be symmetric over a horizontal plane. The upper and lower surfaces  16 ,  18  may further include inner shoulder surfaces  28  and outer shoulder surfaces  30  (both of which are mostly easily seen in  FIG. 6 ) proximate the inner and outer surfaces  22  and  24 , respectively. The inner shoulder surfaces  28  help position the fastener within the passageway  14 . The outer shoulder surfaces  30  provide additional features to assist in securing the compression limiter  10  within the fastened component. 
     The inner and outer surfaces  22 ,  24  are preferably arcuate surfaces or include arcuate portions to provide the overall generally open-cylindrical shape of the compression limiter  10 . However, it is also contemplated that the shapes of the inner and outer surfaces  22 ,  24  may vary to provide a different compression limiter shape. As yet another alternative, the inner and outer surfaces  22 ,  24  may have an additional opening (not shown) extending from the upper surface  16  to the lower surface  18  to provide a horseshoe-shaped compression limiter  10 . In a preferred embodiment, a distance between the inner and outer surfaces  22 ,  24 , or simply the thickness of the body  12 , defines a radial direction perpendicular to the longitudinal direction  20 . Referring specifically to  FIGS. 1 and 2 , the outer surface  24  includes arcuate surfaces  32  adjacent planar surfaces  34  from which the retainers  26  project. The width of the arcuate and planar surfaces  32 ,  34  may be varied to change the distance between the retainers  26  as viewed in  FIGS. 2 and 4 . 
     Referring again to  FIGS. 1-4 , the compression limiter  10  preferably includes two retainers  26  that are diametrically opposed to one another. As such, the compression limiter  10  may have a symmetric shape over planes in the longitudinal direction  20  that bisect the compression limiter  10  (e.g., the vertical planes  42  and  44  of  FIG. 2 ). Each retainer  26  includes an undercut surface  36  disposed between an upper retention surface  38  and a lower retention surface  40 . The upper and lower retention surfaces  38 ,  40  are preferably planar surfaces that are perpendicular to the radial direction. As such, the upper and lower retention surfaces  38 ,  40  help secure the compression limiter  10  within the fastened component and prevent the compression limiter  10  from rotating relative to the fastened component. The undercut surface  36  is disposed radially inwardly relative to the retention surfaces  38 ,  40  and may have a arcuate shape. Alternatively, the undercut surface  36  may have a different shape that forms corners between the undercut surface  36  and the retention surfaces  38 ,  40  that are greater than 90 degrees (e.g., a curved shape, a diagonal surface, or the like). Such a corner is easier to manufacture than a sharp corner and reduces wear on the manufacturing tools described below. 
     In any case, a portion of the fastened component extends between the retention surfaces  38 ,  40  and engages the undercut surface  36 . This helps secure the compression limiter  10  within the fastened component and prevents the compression limiter  10  from moving longitudinally relative to the fastened component. Each of the surfaces  36 ,  38  and  40  of the retainer  26  may have a uniform shape as viewed along the surfaces  36 ,  38  and  40  and in a direction perpendicular to the longitudinal direction  20 . Alternatively, the undercut surface  36  may extend in a direction with only a component perpendicular to the longitudinal direction  20  (e.g., the undercut surface  36  may extend diagonally). 
     Each retainer  26  also includes retention edges  39  between which the retention surfaces  38 ,  40  are disposed. The retention edges  39  are preferably perpendicular to the retention surfaces  38 ,  40  and extend in the longitudinal direction  20 . However, in some embodiments the retention edges  39  may extend in a direction with only a component parallel to the longitudinal direction  20  (e.g., the retention edges  39  may extend diagonally). Furthermore, the corner between each retention edge  39  and adjacent retention surfaces  40  is preferably disposed radially inwardly relative to a projection  41  of the arcuate surfaces  32  having the same radius and center as the arcuate surfaces  32 . Such a feature permits the compression limiter  10  to be presented by typical automated feeding systems. In any case, the retention edges  39  help prevent the compression limiter  10  from rotating relative to the fastened component. 
     The aforementioned surfaces may vary from the shapes described above without departing from the scope of the invention. For example, in a second embodiment shown in  FIGS. 7-11 , the compression limiter  110  includes a body  112  that defines a passageway  114  as described above. The body  112  also includes an upper surface  116 , a lower surface  118 , an inner surface  122 , and an outer surface  124  from which one or more retainers  126  project. As shown most clearly in  FIGS. 10 and 11 , outer shoulder surfaces  130  are spaced apart from axial surfaces  146  of the retainers  126 . In addition, each retainer  126  includes an undercut surface  136  disposed between an upper retention surface  138  and a lower retention surface  140 . Referring specifically again to  FIGS. 10 and 11 , each undercut surface  136  includes a planar surface  148  disposed between an upper arcuate surface  150  and a lower arcuate surface  152 . 
     In a third embodiment shown in  FIGS. 12-15 , the compression limiter  210  includes a body  212  that defines a passageway  214  as described above. The body  212  also includes an upper surface  216 , a lower surface  218 , an inner surface  222 , and an arcuate outer surface  224  from which one or more retainers  226  project. That is, unlike the previously-described embodiments, the outer surface  224  does not include planar surfaces from which the retainers  226  project. 
     Each of the embodiments described above may include additional undercut surfaces. For example, the compression limiters  10 ,  110 , and  210  may include undercut surfaces extending along lower surfaces  18 ,  118 , and  218 , respectively. 
     Referring now to  FIGS. 16-22 , the compression limiter  210  is preferably manufactured as follows. The compression limiters  10 ,  110  are also preferably manufactured as follows, but only the compression limiter  210  and its features are referenced for simplicity. Referring to  FIGS. 16-18 , powder metal  360  (made from a carbon steel, stainless steel, aluminum alloy, bronze alloy, or the like) is filled into a die cavity  364  of a die  366 . Several different components are disposed within the die cavity  364  and interact with the powder metal  360 . For example, the powder metal  360  is positioned about core rods  368  and  370 . The powder metal  360  is also supported by lower punches  372  and  374  ( FIGS. 16 and 18 ). Some of the powder metal  360  is disposed between a right side punch  376  and a central punch  378 . The rest of the powder metal  360  is disposed between the central punch  378  and a left side punch  380 . Referring now to  FIGS. 16 ,  19 , and  20 , the powder metal  360  is next pressed by the lower punches  372  and  374  and upper punches  382  and  384 . This action causes an inner surface  386  of the die cavity  364  ( FIG. 16 ) to shape the outer surfaces of the compression limiters  210 . The core rods  368 ,  370  simultaneously shape the inner surfaces  222  of the compression limiters  210 . Further still, the side punches  376 ,  380  and the central punch  378  simultaneously shape the retainers  226  of the compression limiters  210 . Specifically, the right side punch  376  shapes a first retainer  226  on a first compression limiter  210 , the central punch  378  shapes a second retainer  226  on the first compression limiter  210 , the central punch  378  shapes a first retainer  226  on a second compression limiter  210 , and the left side punch  380  shapes a second retainer  226  on the second compression limiter  210 . As shown most clearly in  FIG. 16 , each of the side punches  376 ,  380  includes a protrusion  388  to shape an undercut surface  236  on one of the retainers  226 , and the central punch  378  includes two protrusions  388  to shape an undercut surfaces  236  on each of the retainers  226 . Referring now to  FIGS. 16 ,  21 , and  22 , the compression limiters  210  are removed from the die cavity  364  by lowering the die  366  in the compression direction relative to the side punches  376 ,  380  and the central punch  378 . The compression limiters  210  may be collected by sliding them laterally relative to the longitudinal direction  20  (i.e., in the direction permitted by the protrusions  388 ). Finally, a coating may be applied to the compression limiters  210 , such as a zinc and clear chromate coating as provided by ASTM B633 type 3 class 1 or the like. 
     Those skilled in the art will appreciate changes to the apparatus described above that permit three or more compression limiters  210  to be manufactured during each cycle. Furthermore, those skilled in the art may appreciate that the compression limiter  210  may be formed by a simplified process wherein a single compression limiter  210  is manufactured during each cycle. However, it is preferred to manufacture two or more compression limiters  210  during each cycle so that the net transverse load applied to the die  366  is reduced. That is, a single upper punch may apply a transverse load (e.g., towards one of the side punches  376 ,  380 ) in addition to the load in the compression direction. The transverse load must be resisted by the die  366  and can cause wear on the punches and the die  366 . However, the transverse loads applied by two or more upper punches  382 ,  384  operating simultaneously may cancel each other and thereby reduce the net transverse load applied to the die  366 . 
     From the above disclosure, it should be apparent that the present invention provides a compression limiter with retention features that resist both translational and rotational motion. In addition, the compression limiter is easily shaped in a single tooling assembly. 
     A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiment described, but should be defined by the claims that follow.

Technology Category: f