Abstract:
A fastening element includes a holding part with a support plate and expanding cheeks, and a locking part guidingly received in the holding part. The expanding cheeks include cantilevered walls formed adjacent the support plate, which are offset radially outwardly with respect to a guide wall of the support plate which guides the locking part. The locking part can be pushed through the support plate substantially without force until it reaches inwardly protruding ramp projections formed on the expanding cheeks, which provide a better lever ratio for spreading the expanding cheeks.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a U.S. National Phase Patent Application based on International Application Serial No. PCT/EP2008/005921 filed Jul. 18, 2008, the disclosure of which is hereby explicitly incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to a fastening element for connecting a support part to an add-on part. 
     2. Description of the Related Art 
     One fastening element is known from DE 34 24 075 C2. This fastening element for connecting a support part to an add-on part is provided with a holding part, which is to be inserted into a clamping opening in the support part and which comprises a support plate and, formed on the support plate, a number of expanding checks that are offset radially inwardly from the support plate. Each expanding cheek comprises a ramp projection that protrudes radially inwardly at a distance from the support plate. The fastening element of the species in question is further equipped with an elongated locking part that can be pushed, by a shaft portion, between the expanding cheeks into the holding part through a guide opening formed in the support plate with a guide wall so as to fit flush with the locking part. The locking part moves the expanding cheeks radially outward by running up onto the ramp projection, with the result that an add-on part disposed between the support part and the support plate is connected to the support plate by the clamping action. 
     Known from JP 61 167708 A is a fastening element for connecting a support part to an add-on part and comprising a holding part that is to be inserted in a clamping opening in the support part. The holding part has a support plate and, formed on the support plate, a number of expanding cheeks that are offset radially inwardly from the support plate. The expanding cheeks are provided with outer walls which in a relaxed arrangement rest on a cylinder surface, and each of which is provided at a distance from the support plate with a respective radially inwardly protruding ramp projection. This fastening element is also equipped with an elongated locking part, whose diameter in a region disposed forward of the ramp projections in the insertion direction is smaller than the interior spacing between the expanding cheeks, and which can therefore be inserted into the holding part with a certain play. When the locking part runs up onto the ramp projection, the expanding cheeks splay outward. 
     Known from DE 198 16 533 A1 is an inner liner panel comprising expanding cheeks that are to be inserted in a clamping opening of a thin metal inner door panel and whose outer walls rest on a cylindrical surface. Also present is an elongated locking part with a paddle-shaped end portion that has two different widthwise dimensions. Formed in an end portion of the expanding cheeks are ramp projections and a cavity whose diameter is approximately equal to the largest width of the paddle-shaped end portion of the locking part, with the result that when the expanding cheeks are relaxed, the locking part can be pushed in with relatively little insertion force and, in order to splay out the expanding cheeks, can be rotated into a final position in such a way that the larger width of the paddle-shaped end portion acts on the ramp projections. 
     SUMMARY OF THE INVENTION 
     The present invention provides a fastening element which, despite a relatively low insertion force, is distinguished by high clamping action and a high pull-out force even with relatively large tolerances in the dimensions of a clamping opening in a support part, even in the lower tolerance range. 
     By virtue of the fact that a cantilevered wall that is offset radially outwardly from the guide wall is formed on each expanding cheek between the guide opening and the ramp projection, the shaft portion, after passing through the guide opening, passes in between the expanding cheeks substantially without force even if the latter are flexed inward from their idle position owing to relative underdimensioning of the throughpass opening in the support part. As a result, even if the expanding cheeks are flexed—an occurrence that is not provided for per se—and, all the more so, should the holding part be disposed in a throughpass opening of a support part with substantially no interaction between these components, a foot end located in front in the insertion direction of the fastening part does not exert an effect on the expanding checks until it is a certain distance from the support plate, with the result that, owing to the then-favorable lever ratio, high clamping forces are induced with relatively low insertion forces. 
     In one form thereof, the present invention provides a tfastening element for connecting a support part to an add-on part, including a holding part that has a support plate and, formed onto the support plate, a number of expanding cheeks that are offset radially inwardly from the support plate, the expanding cheeks each being provided, at a distance from the support plate, with a respective radially inwardly protruding ramp projection and a respective outer wall that widens radially outwardly; and including an elongated locking part that can be pushed by a shaft portion between the expanding checks into the holding part through a guide opening configured in the support plate with a guide wall in a manner that provides a flush fit with the shaft portion, the locking part moving the expanding cheeks radially outwardly by running up onto the ramp projections, characterized in that configured on each expanding cheek, adjacent to the support plate, between the guide opening and the respective ramp projection, is a cantilevered wall that is offset radially outwardly from the guide wall of the guide opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a first exemplary embodiment of a fastening element according to the invention, having a holding part and a locking part; 
         FIG. 2  is a sectional view of the exemplary embodiment according to  FIG. 1  with the locking part in a pre-assembly position; 
         FIG. 3  is a sectional view of the exemplary embodiment according to  FIG. 1  with the locking part in a final assembly position; 
         FIG. 4  is a perspective view of another exemplary embodiment of a fastening element according to the invention, comprising a holding part and a locking part that is provided with a latching means; 
         FIG. 5  is a sectional view of the exemplary embodiment according to  FIG. 4  in a final assembly position of the locking part, in combination with a first embodiment of sealing elements; and 
         FIG. 6  is a sectional view of the exemplary embodiment according to  FIG. 4  in a final assembly position of the locking part, in combination with a second embodiment of sealing elements. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplifications set out herein illustrate embodiments of the invention, in several forms, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise forms disclosed. 
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a first exemplary embodiment of fastening element  1  according to the invention, made of a hard elastic synthetic material and comprising a holding part  2  and an elongated locking part  3  that is displaceably seated in the holding part  2 . The holding part  2  is provided with a flat, disk-like support plate  4 , formed on one side of which are a number of expanding cheeks  5  disposed circumferentially about the locking part  3 . The locking part  3  has a shaft portion  6 , which is cylindrical except for a planar flattening  7  serving to secure it against rotation. The flattening  7  extends, with the formation of a stop step  10 , from a head portion  8  configured with a circumferential annular groove  9  serving as a grasping aid to a foot portion  11 , which is disposed oppositely from the head portion  8  and which in the arrangement according to  FIG. 1  is inserted in a guide opening  12  formed in the support plate  4 . The guide opening  12  is configured with a guide wall  13  that flushly surrounds the shaft portion  6 , with the result that the locking part  3 , guided substantially without play by the guide opening  12 , can be pushed into the holding part  2  until support plate  4  butts against stop step  10  in the holding part  2 . 
       FIG. 2  is a sectional view of the exemplary embodiment according to  FIG. 1  with the locking part  3  in an extended, pre-assembly position, in which the foot portion  11  is disposed in the guide opening  12 . It is apparent from  FIG. 2  that the expanding cheeks  5  are configured, at a distance from the support plate  4 , with radially inwardly protruding ramp projections  14 , each of which has, in the longitudinal direction of the fastening element  1 , a ramp wall  15  that ascends shallowly radially inward from its end proximate the support plate  4  to the end remote from the support plate  4 . It can also be seen from the representation according to  FIG. 2  that configured on each expanding cheek  5 , between the support plate  4  and the ramp projections  14 , are a cantilevered wall  16 , which is offset radially outwardly from the guide wall  13 , and a circumferentially extending female wall  17 , which is oriented substantially perpendicular to the guide wall  13  and extends from said guide wall  13  to the cantilevered walls  16 . 
     In the representation according to  FIG. 2 , the fastening element  1  is inserted in a clamping opening  19  formed in a support part  18  and through a throughpass opening  21  provided in an add-on part  20 , whereupon, in this arrangement, the support plate  4  bears against the add-on part  20 , and the expanding cheeks  5 , by virtue of having an outer wall  22  that widens radially outwardly beginning at a distance from the support plate  4  that is roughly equal to the thickness of the add-on part  20 , is fixed against the support part  18  with a pre-assembly holding force that corresponds to the spring force with which the expanding cheeks  5  resist deflection. 
     It can further be seen from  FIG. 2  that the support plate  4  has on the side facing toward the expanding cheeks  5  a radially outward, circumambient sealing lip  23 , by virtue of the single-component construction of this exemplary embodiment as a hard-elastic sealing means, which protrudes in the axial direction slightly beyond a bottom wall  24  facing toward the expanding cheeks  5  and is bounded radially inwardly by a circumferential marginal groove  25  that is sunk in a circular-segment-like shape, to impart a certain deformability to the sealing lip  23 . 
       FIG. 3  shows the exemplary embodiment explained with reference to  FIGS. 1 and 2  with the locking part  3  in a final assembly position in which it is pushed into the holding part  2 . It is apparent from  FIG. 3  that space exists in the radial direction between the head portion  8  of the locking part  3  and each cantilevered wall  16 , with the result that only after a certain insertion movement of, for example, approximately one-third the length of the expanding cheeks  5  has been executed in the axial direction substantially without force, even when the expanding cheeks  5  are biased radially inward, for example due to a clamping opening  19  that is dimensioned in the lower tolerance range, does it transpire that the foot portion  11  comes into contact with the ramp walls  15  of the ramp projection  14  and the expanding cheeks  5  flare, thus clamping the holding part  2  in the clamping opening  19  of the support part  18 . By virtue of the clamping action that occurs after the expanding cheeks  5  flare out in the radial direction, the fastening element  1  is stably anchored in the support part  18  with a high pull-out force, the sealing lip  23  resting with a slight bias flush against the add-on part  20  and thereby sealing the clamping opening  19  and the throughpass opening  21 . 
     In addition, because the foot portion  11  acts on the ramp projection  14  at a relatively large distance from the support plate  4 , a favorable lever ratio for spreading the expanding cheeks  5  is obtained, and is even preserved when the expanding checks  5  are flexed radially inwardly and are over-biased due to a too-small diameter of the clamping opening  19  compared to the nominal diameter. 
     To release the fastening element from engagement with the support part  18 , the locking part  3  can be grasped, for example with two fingers or by means of a gripping tool, preferably in the region of the annular groove  9 , and moved back out of the final assembly position shown in  FIG. 3  into the pre-assembly position shown in  FIG. 2 , so that the fastening element  1  can again be removed from the support part  18 . 
       FIG. 4  is a perspective view of another exemplary embodiment of a fastening element  100  according to the invention, it being noted that like elements in  FIGS. 1 to 3  and in  FIG. 4  are provided with the same reference numerals and will not be described more closely below. It can be seen from  FIG. 3  that in the second exemplary embodiment, formed as a latching means on the shaft portion  106  of the locking part  103  is an elastic latching tongue  26 , which projects radially beyond shaft portion  106  and extends in the direction of head portion  108 , and which is able to dip toward the shaft portion  106  into a clearance  27 . 
     In the second exemplary embodiment according to  FIG. 4 , configured in the head portion  108  of the locking part  103  is a circumambient elastic head seal  28  made of soft elastic media, also projecting radially outwardly beyond the shaft portion  106 . Finally, in the second exemplary embodiment the head portion  108  comprises, on the side facing away from the shaft portion  106 , a head plate  29 , which also projects radially outwardly beyond the shaft portion  106 . 
       FIG. 5  shows the second exemplary embodiment according to  FIG. 4  after the locking part  103  has been shifted from the pre-assembly position shown in  FIG. 4  into a final assembly position, in which, by suitable adaptation of the distance between the free end of the latching tongue  26  and the side of the head plate  29  facing toward the latching tongue  26 , the latching tongue  26  rearwardly engages the female wall  117  and thereby locks the locking part  103  in the holding part  102  with a high pull-out force, until a the fastening element  100 . In the final assembly position, the head seal  28  is compressed by contact with the guide wall  113  of the guide opening  112 . 
     It can also be seen from  FIG. 5  that in a first embodiment of the sealing means, formed onto a circumambient edge web  30  configured radially outwardly of the head plate  29  is an elastic collar lip  31  made of a soft component, which approximately matches the radial extent of the side of the support plate  4  facing toward the expanding cheeks  105 . The collar lip  31  thus has a relatively large contact area with the add-on part  20 , resulting in good sealing action. 
       FIG. 6  shows the second exemplary embodiment according to  FIG. 4  and  FIG. 5  with another embodiment of sealing means. In the embodiment according to  FIG. 6 , the sealing means comprise, in the radially outer edge region of the support plate  4 , a bridging lip  32  made of a soft component, which is joined flush to a smooth outer edge wall of the support plate  4 , and which brings about satisfactory sealing action with less material expenditure than in the case of the embodiment of  FIG. 5 . 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.