Abstract:
A reusable plastic fastener has an elongated shank having two flexible curved flanges secured thereto and a head secured to a central portion of the shank. The flanges are secured at a leading edge to the central portion and curve away to terminate in a trailing edge that is unsupported between a distal end and a base of the central portion. A top edge of each of the flanges is secured to the head of the fastener by a tab. The exterior of the flexible flanges extends outwardly away from the central portion beginning at the distal end of the central portion and is angled back in towards the central portion near the base of the central portion so as to form a shoulder between the flexible flanges and the head of the fastener. The central portion of the shank has at least one cored-out section.

Description:
FIELD OF THE INVENTION 
   The present invention relates to plastic fasteners for securing objects to a framework such as the sheet metal frame or body of an automobile. 
   BACKGROUND OF THE INVENTION 
   Plastic fasteners enjoy widespread use in the automotive industries and in other industries in applications where an object must be secured to a relatively thin substrate such as the sheet metal frame or body of an automobile. An ideal plastic fastener can be inserted into a bore formed through a substrate relatively easy but is difficult to withdraw. 
   Unfortunately, one characteristic of plastic fasteners of this type is that because the fasteners themselves are fashioned of relatively flexible materials, fasteners that are easy to insert into a bore formed through a substrate tend to be relatively easy to remove from the substrate. Similarly, where a fastener is difficult to remove from a substrate, it is generally correspondingly difficult to insert that fastener into the bore formed through the substrate. Accordingly, there is a need for a reusable plastic fastener that may be easily inserted into a bore formed through a substrate, yet is difficult to remove from the substrate. In addition, it is desirable to provide a fastener that may be reused so that fasteners need not be replaced each time they are disassembled. This former need is particularly useful considering that in the manufacture of an object such as an automobile, a component being attached to an automobile frame or body may need to be removed temporarily for repair or adjustment. 
   U.S. Pat. No. 6,305,055 to Castro, hereby incorporated by reference, is intended to meet the aforementioned needs by providing a plastic fastener having a shaft with two curved, flexible flanges secured thereto that flex inwardly as the shaft of the fastener is forced into a bore formed through a substrate. The flanges resist withdrawal once the fastener had been fully inserted into the bore. While the fastener described in the &#39;055 patent performs admirably, the ratio of the force required to insert the fastener into a bore to the force required to withdraw the fastener from the bore is not ideal. Accordingly, the present invention provides a fastener having an improved insertion to withdrawal force ratio and which is constructed so as to be easily reused after disassembly. 
   SUMMARY OF THE INVENTION 
   The objects of the present invention are realized in a fastener having a head, a shank with a cored-out section, and a pair of flexible flanges secured to and between the shank and to the head of the fastener. 
   The head of the fastener is secured to the shank of the fastener in a generally perpendicular relation thereto. The shank has a central portion with a distal end and a base end. The head is connected to the base end of the shank. The pair of flexible flanges is secured at their leading edge to the central portion of the shank on opposing sides of the shank and preferably in diagonal opposition to one another. The flanges curve away from the central portion of the shank and the trailing edges of each flange are generally unsupported between the distal end of the shank and the base end of the shank. In a preferred embodiment, a top portion of the trailing edge of each of the flanges is secured to the head of the fastener by a tab that extends between the flange and the head of the fastener. The flanges define a shoulder adjacent to the base end of the shank that opposes the head of the fastener so as to define an aperture therebetween for receiving and retaining a panel therebetween. 
   A cored-out section formed into the central portion of the shank is deformed inwardly as the shank of the fastener is inserted into a bore formed through a panel. This deformation is created by inwardly directed forces applied to the flanges as the fastener is inserted into a bore in a substrate. The deformation of the cored-out section lowers the force required to insert the fastener into the bore formed through the substrate. 
   A preferred embodiment of the head of the fastener includes a laterally extending lip or flange that is biased toward the shank of the fastener, though it is to be understood that the head may be made up of a lip or flange that is perpendicular to or biased away from the shank of the fastener, as the case may be. In addition, the head of the fastener may include structures for securing the fastener to another object or structure such as a doghouse connector in addition to or in lieu of a lip or flange. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front elevation of a preferred embodiment of a fastener of the present invention shown adjacent to a bore formed through a substrate; 
       FIG. 2  is a side elevation of a fastener of  FIG. 1 ; 
       FIG. 3  is a cross-sectional view of a fastener of the present invention taken along cutting lines  3 — 3  in  FIG. 1 ; 
       FIG. 4  is a cross-sectional view of the fastener taken along cutting lines  4 — 4  in  FIG. 3 ; and, 
       FIG. 5  is a bottom view of the fastener of the present invention. 
   

   DETAILED DESCRIPTION 
   Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
     FIGS. 1 and 2  show a front and a side view, respectively, of a fastener  10  constructed and arranged according to the principals of the present invention. Fastener  10  generally comprises a shank  12  that extends downwardly and generally perpendicularly to a head  14 . The head  14  of the fastener  10  is illustrated in  FIG. 2  in phantom lines to indicate that the head  14  may take many configurations and is not limited to the preferred embodiment illustrated most clearly in  FIG. 1 . 
   The shank  12  of the fastener  10  has a central structure  16  that extends the entire length of the shank  12 . At a base end  18 , the central structure  16  is connected to the head  14  of the fastener  10 . A distal end  20  of the central structure  16  terminates in a generally pointed tip that eases the entry of the shank  12  into a bore  8  formed through a substrate  9  as shown most clearly in  FIG. 1 . Attached to the central structure  16  is a pair of curved, flexible flanges  22  and  24 . The flanges  22 ,  24  together comprise a retaining mechanism that acts to retain the shank  12  of the fastener  10  within a bore  8  of a substrate  9 . 
   As can best be seen in  FIG. 3 , each of the flanges  22 ,  24  are secured at a leading edge  26  thereof to the central structure  16 . Each of the flanges  22 ,  24  extends away from the central structure  16  and curves in relation thereto, having a generally elliptical cross-sectional shape. Note that the cross-sectional shape of the flanges  22 ,  24  may take on any useful geometry and can be uniform over the entire height of the flanges  22 ,  24  or may vary over the height of the flanges  22 ,  24 . 
   A bottom edge  30  of the flanges  22 ,  24  is secured to the central structure  16  at the distal end  20  of the shank  12 . The trailing edges  28  of the flanges  22 ,  24  are generally unsupported and extend from the distal end  20  of the shank  16  upwardly toward the base end  18  of the shank. A top edge  32  of the flanges  22 ,  24  is preferably secured to the head  14  of the fastener  10  by a tab  34 , though the tabs  34  may be omitted where the application of the fastener  10  so dictates. The unsupported trailing edge  28  of the flanges  22 ,  24  increases the generally flexibility of the flanges  22 ,  24 , and decreases the magnitude of the force required to insert the fastener  10  into a bore  8  formed through a substrate  9 . Tabs  34  fix the position of the top edge  32  of the flanges  22 ,  24  with respect to the central structure  16  of the shank  12  and increase the rigidity of the flanges  22 ,  24  near the top edge  32  of the flanges  22 ,  24  while permitting the remaining portions of the flanges  22 ,  24  to be relatively flexible. 
   Each of the flanges  22 ,  24  extends generally outwardly from the central structure  16  of the shank  12  from the distal end thereof. Keeping in mind that the cross-sectional shape of the flanges  22 ,  24  may be circular, elliptical, or irregularly shaped, the exterior surface generally established by the flanges  22 ,  24  is roughly frustoconical in shape. The flanges  22 ,  24  together define a ridge  36  that itself defines a shoulder  37  that opposes the head  14  of the fastener  10 . 
   As can best be seen in  FIG. 4 , the flanges  22 ,  24  act to retain the shank  12  of the fastener  10  within a bore  8  formed through a substrate  9 . The flanges  22 ,  24  are constructed and arranged such that when the fastener  10  is fully inserted in the bore  8 , the head  14  and shoulder  37  of flanges  22 ,  24  will abut opposing sides of the substrate  9  so as to secure the fastener  10  within the bore  8 . As can be appreciated, the flexibility of the flanges  22 ,  24  is directly related to the magnitude of force required to insert the fastener  10  into the bore  8 . As the top edges  32  of the flanges  22 ,  24  are secured to the head  14  by means of tab  34 , the rigidity of the flanges  22 ,  24  at ridge  36  is increased. Accordingly, the tab  34  is very useful in increasing the withdrawal force required to remove the fastener  10  from the bore  8  of the substrate  9 . 
   In order to ensure that the required insertion force remains relatively low, the central structure  16  has been provided with a cored-out section  17 . In a preferred embodiment of the fastener  10 , cored-out section  17  passes entirely through the central structure  16  over substantially all of its height though is to be understood that the cored-out section  17  may extend over only a portion of the height of the central structure  16  and/or may be formed only partially into the depth of the central structure  16 . In any case, the cored-out section  17  increases the flexibility of the central srtucture of the shank  12  so as to reduce the magnitude of the insertion force required to seat the fastener  10  within the bore  8 . As the shank  12  is inserted into the bore  8 , the inwardly directed forces applied to the flanges  22 ,  24  are at least partially transmitted to the central structure  16  which is deflected or deferred into this cored-out section  17 . 
   Because the flexibility, and hence the deformability, of the shank  12  is increased primarily in its central portion midway between the distal end  20  and the base  18 , the provision of the cored-out section  17  through the central structure  16  does not significantly reduce the rigidity of the flanges  22 ,  24  where they are secured by tab  34  to the head  14 . Accordingly, the withdrawal force is higher relative to the insertion force required to seat the fastener  10  within the bore  8 . 
   As indicated above, the head  14  of the fastener  10  may take any useful configuration. In one embodiment, the head  14 , may have a structure, such as flange  40  that is wide enough with respect to the dimensions of the bore  8  formed through the substrate  9  so as to prevent the fastener  10  from passing entirely therethrough. As can best be seen in  FIG. 4 , the flange  40  abuts a first side of the substrate  9  whereas the shoulder  37  of flanges  22 ,  24  abuts the second side of the substrate  9  so as to oppose one another and retain the fastener  10  in the bore  8  formed through the substrate  9 . The flange  40  in a preferred embodiment of the present invention is biased downwardly toward the shank  12  of the fastener  10  so as to create a resilient seal against the substrate  9  when the fastener  10  is received within the bore  8  and to prevent unwanted movement in the fastener  10  once it has been installed. Alternatively, the flange  40  may be flat or even biased away from the shank  12 . In any case, the distance between the flange  40  and the ridge  36  defined by the flanges  22 ,  24  is generally related to the thickness of the substrate  9  and is arranged so as to permit the flange  40  and the ridge  36  to engage the opposing sides of the substrate  9  so as to secure the fastener  10  within the bore  8 . 
   While the flange  40  is preferably larger than the bore  8  formed through a substrate  9 , the flange  40  may be reduced in size or omitted altogether where the head  14  is otherwise constructed and arranged such that it cannot pass through the bore  8 . One example of such a head  14  (not shown) involves providing a structure for mechanically or adhesively securing the head  14  to another structure so as to prevent the fastener  10  from passing through the bore  8 . 
   A preferred embodiment of the head  14  illustrated in  FIG. 1  includes a post  42  that extends upwardly away from the flange  40  and which has mounted thereon a pair of subflanges  44 ,  46 . The subflanges  44 ,  46  are spaced apart upon post  42  so as to create an aperture  48  therebetween. The aperture  48  is sized so that the post  42  may be received within a slot formed in a structure such as a “doghouse”, a standard attachment structure for molded items (not shown). Post  42  is retained in the slot in the object preferably by a snap-in type force fit engagement. In order to ensure that the post  42  is not deformed when it is received into a slot formed in an object, reinforcement vanes  50  may be formed between the subflange  44  and the flange  40  so as to increase the rigidity of the post  42 . 
   Removal of the fastener  10  from a bore  8  is effected by applying a withdrawal force to the fastener  10  such that the rigidity of the flanges  22 ,  24  at their shoulders  37  is overcome and the flanges  22 ,  24  are deflected inwardly to a sufficient degree to allow the fastener  10  to be removed from the bore  8 . While the flanges  22 ,  24  are fairly rigid near the shoulder  37 , the overall flexibility of the flanges  22 ,  24  away from the shoulders  37  and the flexibility imparted to the shank  12  by the cored-out section  17  minimize damage to the fastener  10  upon disassembly, thereby allowing for reuse of the undamaged fasteners  10 . 
   While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations and equivalents of the specific exemplary embodiments herein. The invention is therefore to be limited not by the exemplary embodiments herein, but by all embodiments within the scope and spirit of the appended claims.