Patent Publication Number: US-2005125963-A1

Title: Elements for fixing components such as to be able to slide

Description:
The invention relates to elements for fastening structural components such that they can slide.  
      As compared to chassis elements made of steel, chassis elements made of plastic require special fastening elements and/or a combination of special fastening elements for the fastening because of their greater expansion lengthwise.  
      The installations of plastic fenders, for example, requires above all rigid fasteners in the area of transition to the doors, whereas sliding fastening elements are necessary in the area of transition to the engine hood and in the front-end region to ensure the required accuracy to size and the opening and closing functions for doors and hoods.  
      For the installation on the vehicle, it is particularly important for fastenings with the ability to slide that the component is mounted precisely in the rated position. During later position changes of the component, for example caused by temperature changes, the spaces provided for movement between component and fastening element must actually exist. An installation outside of the rated position correspondingly restricts the prescribed freedom of movement of the component.  
      A number of design solutions are provided for this according to prior art.  
      For example, reference EP 0 799 758 teaches the embodiment of a fastening element made of plastic with formed-on lamellar springs which move the sliding element into the rated position before the parts are screwed together.  
      A plastic element, permitting a fastening with ability to slide, is described in U.S. Pat. No. 5,098,765. The element is provided on one side with a pin for adjusting the rated position, wherein this pin rests against the component to be fastened during the installation of the component.  
      The pin is designed to be thin enough in the front to break off when force is applied, for example if the component to be fastened expands as a result of heat, thus freeing the structural space for the movement of the component to be fastened.  
      Metal adjusting washers can also be used as alternatives for the plastic elements to ensure a proper screw connection with the plastic elements. These adjusting washers consist of discs, having an opening in the center with formed on flange, wherein the flange depth at the fastening location slightly exceeds the material thickness of the component to be fastened.  
      However, the known solutions do not provide a sufficiently secure fastening of the elements in the rated position, meaning it is possible that even with a slight, unintended force exerted during the installation, the screw connection is no longer in the rated position. However, the defined, rated position must definitely be maintained and installation tolerances in X and Y direction must furthermore be considered. With the plastic solutions according to prior art, this is possible only to a limited degree with.  
      Standard plastic elements furthermore have the disadvantage of requiring a relatively large structural space and are too expensive to produce. Metal adjusting washers, on the other hand, are problematic with respect to fastening the washer in the component while simultaneously allowing it to slide in the fastened state and additionally require a high installation expenditure. 
    
    
      The object of the present invention consequently is to provide fastening elements which: 
          require the smallest possible structural space while maintaining the required installation tolerances;     ensure that the rated position is maintained during the installation;     permit an easy installation of the chassis element;     make it possible for the chassis element to be fastened in such a way that they can slide in the fastening element during heat expansion;     can be produced cheaply and so as to be corrosion-resistant.        

      According to the invention, this object was solved with a fastening element produced with the injection-molding technique and having the features as disclosed in claim  1 .  
      Above all, the advantages of the invention can be found in: 
          the reduction of the production costs as compared to metal adjusting washers and/or traditional plastic elements;     the reduction of the installation expenditure as compared to metal adjusting washers;     a higher accuracy of the rated position definition;     the realization of larger installation tolerances in X and Y direction;     the option of realizing a small structural space as compared to existing plastic solutions;     the option of mounting components with greater wall thicknesses;     the option of a longer sliding distance as compared to metal adjusting washers.        

      For one exemplary embodiment of the fastening element according to the invention, the fastening of a front fender made of plastic on a passenger vehicle is explained as follows:  
      The fastening element, as described in  FIG. 1 , is pushed in the direction Z into the installation recess on the fender until it engages, so that the undercut, resulting from the slightly wedge-shaped engagement elements, holds the fastening element inside the installation recess on the fender.  
      For the present embodiment, the engagement elements simultaneously function as guide elements which for the most part prevent a movement of the fender in Y direction. Depending on the structural requirements, the engagement elements and the guide elements can also be separate elements. The fastening element is then displaced inside the installation recess in X direction until the two spring elements with their wedge-shaped indentations in the center engage in the two corresponding wedge-shaped protrusions formed in the installation recess of the fender, thereby ensuring that the rated position is maintained precisely. The collar screw is then pushed through the opening in the planar portion of the fastening element, is screwed into the metal chassis frame, and is tightened with a torque wrench. The fender is thus securely fastened to the chassis while a displacement in X direction due to heat expansion is still possible.  
      On the material side, the fastening element is made from a material having simultaneously high consistency and toughness.  
      If the varnishing temperatures for the fender are in the range of 140° C. (online varnishing) to 190° C. for cathode diving varnishing (KTL), polyamides, polyester and compound products based on these are in particular considered. Filler materials are normally added, in particular glass fibers, as well as slip additives and in particular PTFE, MoS2, UHMW-PE or chalk.  
      For the so-called off-line varnishing at temperatures of up to approximately 100° C., POM generally is the material of choice, if necessary with the addition of filler materials and/or slip additives.  
      A first embodiment option according to the invention is described in  FIG. 1 , wherein:  
       10  represents a view from above,  9  the three-dimensional view at a slant from the bottom,  8  the view from the bottom, and  10   a  a view from above of a chassis part. Illustration  10  shows the planar region  3 , designed as screw supporting surface for collar screws with 20 mm washer diameter, as well as the opening  4  in the planar part  3  for compensating the installation tolerances in two spatial directions. The ring-shaped region  6 , which is easy to see in  8  and  9  and is integrated on the underside, is provided with two opposite arranged spring elements  1  with respectively one wedge-shaped indentation  1   a  in the center.  
      The protrusion  11 , which is formed onto the component  13  to be fastened in the region of the installation opening  12 , engages into this wedge-shaped indentation during the installation of the fastening element, thus ensuring that the rated position is maintained.  
      Combination guide and engagement elements  2 , slightly wedge-shaped, which form an undercut with respect to the installation direction and thus ensure a reliable hold of the fastening element in the component to be fastened, ensure the guidance inside the installation opening  12  of fender  13  and protect against loss during the installation.  
       FIG. 2  illustrates a second embodiment option according to the invention.  
       21  represents a view from above of the planar region  31  and the opening  32  for receiving the collar screw. In addition, the planar region  31  has two recesses  33  for maintaining the flexibility of the flange, formed onto the inside, which rests perpendicular on the planar region.  
       22  offers a three-dimensional view of the fastening element, seen at a slant from below, while  23  is a view from above of a chassis part. The fastening element is guided inside the installation recess  38  of the component  39  to be fastened by the guide elements  34  and is held in place there by the spring elements  35  which function here as engagement elements in Z direction. At the same time, however, the spring elements  35  are provided with a protrusion  36 , which in turn engages in the indentation  37  of the installation recess  38 , thus ensuring that the rated position during the installation of the chassis element is maintained precisely.  
      The above-disclosed and described embodiments are only intended as examples for illustrating the invention.