Abstract:
A one-piece screw grommet provides improvements in the key areas of screw grommet performance, including lower push-in effort, higher screw retention capabilities, and improved strip torque capabilities. The grommet of the invention that achieves these improvements includes generally a grommet body and a grommet head. The body includes four retention legs, with two retention legs positioned on a body wall and two retention legs positioned on an opposite body wall. The grommet further includes four support ribs that extend between a screw boss and the body walls.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This Non-Provisional application claims benefit to U.S. Provisional Application Ser. No. 60/620,445 filed Oct. 20, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to grommets, and more particularly to improved strength screw grommets.  
       BACKGROUND OF THE INVENTION  
       [0003]     Grommets are known and are used in a wide range of applications. Grommets can be metal, plastic or rubber ring-type devices that are inserted into a pre-formed or pre-drilled hole made through another material or substrate. The grommets may be used to reinforce the hole, to shield a rope or cord from any sharp edges of the hole, or to mount an item or other structure to the hole through the use of a screw or fastener that is inserted into the grommet. If used in the latter application, that is, as a device for mounting an item or other structure to a pre-formed hole, the grommet is first inserted into the pre-formed hole and is held in position by flexible prongs or retention legs formed from the grommet. Once anchored to the hole, the screw can then be threaded into a hole formed in the grommet for mounting an item, structure or additional substrates to the hole. In some applications, the insertion of the screw into the hole in the grommet causes the prongs or retention legs to expand, thereby further securing the grommet to the hole.  
         [0004]     Grommets are typically rated based on performance data that includes push-in effort, screw retention, and strip-out torque. While this data is somewhat dependent on the specific size of the screw and the application, it is desirable to improve the grommets&#39; strength capabilities, including the grommets&#39; push-in, screw retention and strip-out torque capabilities. The present invention is directed at providing such improvements over existing grommet designs.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention is directed to a one-piece screw grommet that provides improvements in the key areas of screw grommet performance. That is, the grommet of the invention provides lower push-in effort, higher screw retention capabilities, and improved strip torque over the known grommet designs. The exemplary grommet of the invention includes generally a grommet body and a grommet head. The grommet body includes four retention legs, with two retention legs positioned on one body wall and two retention legs positioned on an opposite body wall. The grommet further includes a screw boss defining a hole in which may be mounted a screw or fastener. The screw boss is secured to the body walls of the grommet body through the use of four support ribs that are spaced around the screw boss and extend between the screw boss and the body walls.  
         [0006]     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is an isometric view of a prior art screw grommet.  
         [0008]      FIG. 2  is an isometric view of an exemplary grommet of the present invention.  
         [0009]      FIG. 3  is an isometric bottom view of the grommet of  FIG. 2 .  
         [0010]      FIG. 4  is a top view of the grommet of  FIG. 2 .  
         [0011]      FIG. 5  is a side view of the grommet of  FIG. 2 .  
         [0012]      FIG. 6  is another side view of the grommet of  FIG. 2 . 
     
    
       [0013]     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof.  
       DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0014]     Referring to  FIG. 1 , there is illustrated a prior art screw grommet  10  defining a head  12  and a body  14 . A screw boss  16  which defines a hole  18  extends through the head  12  and body  14  to mount a screw or other fastener. The head  12  and body  14  are generally square-shaped. The body  14  further defines opposing retention legs  20  that permit the grommet to be snap-fit into a pre-formed mating hole and held in position after it has been mounted. Opposing support ribs  22  are used to secure the screw boss  16  relative to walls  24  of the body  14 .  
         [0015]     Referring to  FIGS. 2-6 , there is depicted an exemplary grommet  40  of the present invention. In the exemplary embodiment, the grommet  40  may be made as a one-piece device and made of a plastic material, such as nylon 6/6. The grommet  40  may define a grommet head  42  and a grommet body  44 . In the illustrated embodiment, the head and body are generally square-shaped, though other shapes and configurations of the head and body are possible with the invention. The head  42  serves to hold the grommet  40  to the pre-formed or pre-drilled hole, not shown, to prevent the grommet from being pushed through the hole.  
         [0016]     The body  44  includes retention legs  46 , support ribs  48 , and a screw boss  50 . The retention legs  46  may be four retention legs positioned on the body  44 . In the illustrated embodiment, two retention legs  46  are positioned on body wall  52 , while two retention legs  46  are positioned on opposing body wall  54 . As can be seen in the Figures, each retention leg  46  is positioned near a corner of the body—a corner formed by the body walls. The advantages of this placement are described below. Each retention leg  46  is configured as a living hinge in that the leg  46  is connected at one end to the body wall and is flexible at the legs opposite end. The flexible opposite end permits the leg  46  to flex inward toward the body wall as the grommet is mounted to the pre-formed hole, not shown, and will flex or snap back to its original position once the leg  46  passes through the pre-formed hole. Once in this position, the leg  46  will contact the back side of the surface wall or substrate surrounding the pre-formed hole, preventing the grommet from being pulled out of the hole. With the grommet  40  of the invention, the retention legs  46  in combination with the head  42  provide a secure attachment of the grommet  40  to the pre-formed hole in the wall or substrate.  
         [0017]     As shown in  FIG. 3 , four support ribs  48  extend between the screw boss  50  and walls  52 ,  54 ,  56 , and  58  of the body  44 . The support ribs  48  are spaced equidistant around the screw boss  50  and provide improved structural integrity for the screw boss  50  relative to the body  44 . The support ribs  48  extend substantially the length of the screw boss  50 . The walls  52 ,  54 ,  56 , and  58  of the body  44  may define tapered surfaces  60 ,  62 ,  64 , and  66  that assist in the insertion of the grommet  40  into the pre-formed hole.  
         [0018]     The screw boss  50  defines a hole  68  extending through the head  42  and body  44  of the grommet  40 . The hole  68  is sized and shaped to receive a mounting screw or fastener, such as a self-tapping screw or the like, not shown. With many applications, the mounting screw may be driven through additional substrates and into the hole  68  to attach the additional substrates to the wall on which the grommet is mounted to clamp them together tightly.  
         [0019]     The grommet  40  of the invention overcomes the problems encountered with the grommet  10  design when subject to high strip torques. Specifically, a known problem with the prior art grommet  10  is that as high strip torques are reached, the screw boss  16  can begin to twist under the load. In an effort to overcome this problem, the wall thicknesses of the ribs  22  were increased. However, increasing the wall thickness of the two ribs  22  can cause additional problems because such an effort can result in non-uniform wall thicknesses, which encourage non-uniform shrink and additional molded-in stresses. The grommet  40  overcomes these problems by providing four support ribs  48  spaced equidistant around the screw boss  50 , as depicted in  FIG. 3 , the four support ribs providing added strength to the screw boss  50 . With the use of the four support ribs  48 , the uniformity of the wall thicknesses is maintained and higher values of strip torque are achieved.  
         [0020]     Moreover, by using four independent retention legs  46 , rather than the known two retention legs  20 , screw retention within the grommet  40  is enhanced and the installation of the grommet  40  is improved. More specifically, with respect to the enhanced screw retention, the four retention legs  46  are configured and positioned near the corners of the body  44 , as illustrated in the Figures. With this configuration, the retention legs  46  distribute the screw loading to areas of the mating hole that are better supported, that is, closer to the corners of the mating square-shaped pre-formed hole. In contrast, the prior art retention legs  20  place the loading in the weakest part of the square-shaped hole, namely, at the center of the square-shaped hole, that is, at or near the midpoint between the corners of the hole. Additionally, with the use of the four retention legs  46 , the installation into the mating hole will be improved because the illustrated configuration results in a grommet that is easier to install than the two-legged design of the prior art grommet  10 .  
         [0021]     Also, in many of the grommet applications, the grommet is installed in a punched hole in sheet metal. The punching process can result in burrs on the back side of the panel and these burrs often occur in localized areas. Under these circumstances, if the prior art grommet  10  is used, a burr anywhere along one of the retention legs can prevent engagement of that side of the grommet and thus preventing the secure mounting of the grommet to the panel. With the grommet  40  having the four retention legs  46 , a local burr could prevent one retention leg from engaging the back side of the panel but the other retention leg on the same side of the grommet can still properly engage the panel due to its independence from the other leg that is being hampered by the burr. Consequently, the grommet  40  can be properly secured to the panel despite the occurrence of a localized burr.  
         [0022]     Variations and modifications of the foregoing are within the scope of the present invention. It should be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.  
         [0023]     Various features of the invention are set forth in the following claims.