Patent Publication Number: US-2005120634-A1

Title: Method of manufacturing a sealing gasket, in particular a window run for a motor vehicle, and to a gasket manufactured in this way

Description:
The invention relates to a method of manufacturing a sealing gasket, in particular a window run for a motor vehicle, and to a gasket manufactured in this way.  
     BACKGROUND OF THE INVENTION  
      In general, three major families of window runs or gaskets can be distinguished, e.g. for providing sealing between a window and the window frame of a motor vehicle door, namely: channel-section runs; single-rabbet runs; and hidden frame runs. Hidden frame runs present a mounting clip of U-shaped right section which fits over the window frame of the door and which comprises a metal strength member for strengthening the clip, two asymmetrical legs fitted with sealing lips, and one or two additional lips providing two sealing functions.  
      Such a window run or gasket is made of rubber, being manufactured by extrusion, and after being extruded and cooling down, it presents flexibility enabling it to be deformed so as to fit the shape of the window frame of the door onto which it is engaged. Although such window gaskets provide satisfactory performance, they nevertheless present drawbacks of weight and cost.  
      In order to reduce the weight and the cost of such gaskets, it is advantageous to make them out of thermoplastic materials (thermoplastic elastomer (TPE), thermoplastic olefins (TPO), polypropylene, for example). Nevertheless, under such circumstances, it becomes very difficult, if not impossible, to mount the gasket on a motor vehicle door insofar as the rigidity of thermoplastic materials, and in particular polypropylene for example, does not enable the gasket to match the shape of the door without deforming said gasket in harmful manner, e.g. forming wrinkles or folds.  
     OBJECTS AND SUMMARY OF THE INVENTION  
      An object of the invention is to mitigate the above-mentioned drawbacks and to propose a novel method of manufacturing such gaskets which enables gaskets to be obtained after extrusion and cooling that are automatically and naturally curved.  
      To this end, the invention provides a method of manufacturing a sealing gasket, in particular a hidden frame type window run for a motor vehicle, the method consisting in placing in the gasket that is made from thermoplastic materials, at least one anti-shrinkage element that is placed in a position that is determined so as to obtain automatically and naturally a gasket that is curved after it has been extruded and has cooled down, and the method further consisting in acting on the shrinkage ability of the materials constituting the gasket in order to obtain varying amounts of curvature.  
      Advantageously, the anti-shrinkage element is positioned in the gasket in such a manner as to obtain curvature automatically in at least two different planes.  
      By making the sealing gasket out of thermoplastic materials, it is possible to reduce the cost and the weight thereof, but with the drawback that once cooled after being extruded it presents a shape that is substantially rectilinear and more rigid than a gasket made of rubber. However, the anti-shrinkage element placed in the gasket can enable the lack of gasket flexibility to be compensated because, depending on its position, it makes it possible to obtain automatic and natural curving of the gasket which can be optimized as a function of the shrinkage ability of the materials constituting the gasket.  
      In general, a sealing gasket forming a hidden frame type window run, for example, presents a mounting clip of U-shaped right section with first and second limbs that are parallel to each other, a main leg and a secondary leg which extend perpendicularly to the second limb of the clip, and sealing lips towards the ends of said legs.  
      In the method of the invention, the anti-shrinkage element is placed in the clip of the gasket, and the thermoplastic materials used for manufacturing the gasket preferably have a decreasing shrinkage gradient going from the clip towards the sealing lips, and, for example, polypropylene is used to make the clip, a TPO for making the main leg, and a TPE for making the sealing lips.  
      The anti-shrinkage element may be constituted by a reinforcing member or at least one metal wire or glass fiber, for example.  
      The invention also provides a sealing gasket, in particular of the hidden frame run type, in which the anti-shrinkage element is positioned in the first limb of the clip to provide a top segment for the run, and in which the anti-shrinkage element is positioned in the web of the clip to constitute a vertical segment of the run. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other advantages, characteristics, and details of the invention appear from the additional description below made with reference to the accompanying drawings, given purely as examples, and in which:  
       FIG. 1  is a section view of a sealing gasket forming the top segment of a hidden frame type run of the above-mentioned prior art type;  
       FIGS. 2   a,    2   b,  and  2   c  are diagrammatic side views for showing respectively a front door and a back door of a “Sedan” type vehicle, and a front door of a “people carrier” type vehicle;  
       FIG. 3  is a section view of an embodiment of the invention showing a top segment for a hidden frame type run;  
       FIG. 4  is a top view of a vehicle having doors whose window frames curve in two different planes;  
       FIG. 5  is a section view of another embodiment of the invention showing the top segment of a hidden frame type run;  
       FIG. 6  is a section view of an embodiment of the invention showing a vertical segment of a run;  
       FIG. 7  is a section view of another embodiment of a vertical segment of a hidden frame type run;  
       FIGS. 8 and 9  are views of two other embodiments of the invention showing a top segment and a vertical segment of a hidden frame type run; and  
       FIG. 10  is a section view of another embodiment of the invention showing a single rabbet type run. 
    
    
     MORE DETAILED DESCRIPTION  
      The window gasket  1  shown in  FIG. 1  shows the prior art mentioned in the introduction. The gasket  1  forms a top segment of a window run, and comprises a mounting clip  3  of U-shaped right section in which there is embedded metal reinforcement  4  also of U-shaped right section, two asymmetrical legs  5  and  6  constituting respectively a main leg and a secondary leg which project at substantially  900  from one of the limbs  3   a  of the mounting clip  3  and which terminate in sealing lips  9  suitable for coming into sliding contact with both faces of a window V. The other limb  3   b  of the mounting clip  3  supports sealing lips  9   a  suitable for coming into contact with the body of the vehicle.  
       FIGS. 2   a,    2   b,  and  2   c  are diagrams showing various different doors P for motor vehicles, showing the general shapes of the window gaskets that form window runs.  FIG. 2   a  shows a front door P of a “Sedan” type car, with the top segment  1   a  of the run  1  presenting considerable curvature, whereas its curvature is small in  FIG. 2   b  which shows a back door P for a “Sedan” type car, or else there may be two lightly curved portions as shown in  FIG. 2   c  which shows a front door P of a “people carrier” type car. The vertical side segment  1   b  for each of the runs  1  are secured to the top segment  1   a  by conventional junction molding, and similarly the two portions of the top segment  1   a  shown in  FIG. 2   c  are joined to each other by junction molding.  
      In the examples shown in  FIGS. 2   a,    2   b,  and  2   c,  the curves of the top segments of the runs lie in a plane XOZ, and to obtain the curves automatically and naturally, the invention proposes using a gasket of the kind shown in  FIG. 3  which is manufactured from various different thermoplastic materials having different shrinkage properties.  
      More precisely, the gasket  10  presents a structure similar to that of the gasket shown in  FIG. 1 , but made out of thermoplastic materials, together with the presence of an anti-shrinkage element  12  in the form, for example, of reinforcement or at least a metal wire or a glass fiber, which element, depending on its position in the gasket  10 , serves to obtain a gasket  10  that curves naturally and automatically in at least one plane in order to compensate for the lack of flexibility of the gasket  10  made out of thermoplastic materials, and make it easier to mount on the window frame of the vehicle door.  
      By way of example, with a gasket  10  of the kind shown in  FIG. 3 , constituting a top segment for a hidden frame type run, the anti-shrinkage element  12  is placed in the limb  3   b  of the clip remote from the two legs  5  and  7 , and is generally situated in or on either side of a vertical plane containing the center of gravity G of the gasket when considering the right section thereof. This position of the anti-shrinkage element  12  enables a gasket that is curved in the XOZ plane to be obtained automatically after extrusion and cooling.  
      In order to control the curvature of the curved gasket, action is taken on the shrinkage ability of the thermoplastic materials used for making the gasket, it being understood that it is necessary to have a shrinkage gradient that increases going away from the neutral fiber of the gasket which is formed by the anti-shrinkage element  12 . For this purpose, and by way of example, the clip  3  of the gasket  10  is made of polypropylene which is a material that shrinks little, the main leg  5  of the gasket  10  is made of a TPO that shrinks somewhat more, and the main sealing lip  9  at the end of the main leg  5  is made of a TPE that shrinks even more. The secondary leg  7  of the gasket is considerably shorter than the main leg  5  and can be made out of the same material as the clip  3 . In a variant, the clip can be made of a material such as polypropylene, and the main leg  5  and the sealing lip  9  can be made of TPE, for example.  
      Such a gasket  10  can be used to make the top segment  1   a  of the run  1  shown in  FIG. 2   a  which presents a relatively large amount of curvature.  
      However, to make the top segment  1   a  of the run  1  shown in  FIG. 2   b  or the two portions of the top segment  1   a  of the run shown in  FIG. 2   c  all of which are of small curvature, the position of the anti-shrinkage element  12  is not changed, but the main leg  5  of the gasket is made of a thermoplastic material having smaller shrinkage ability than a TPO. For example, it is possible to use the same material as that constituting the clip  3 , i.e. polypropylene.  
      With reference to  FIG. 4 , the window frames of the door of the motor vehicle V may be curved not only in the XOZ plane, but also in the XOY plane. In order to make it easier to mount the gasket  10  and also obtain curvature in the XOY plane, it suffices to offset the anti-shrinkage element  12  to the right in the limb  3   b  of the clip, as shown in  FIG. 5 .  
      With reference to a vertical segment  10   a  of the run  10 , this segment may present curvature solely in the YOZ plane. Under such circumstances, as shown in  FIG. 6 , the anti-shrinkage element  12  is positioned in part in the web  3   c  of the clip  3  and in part in the secondary leg  7  of the vertical segment  10   a.  This anti-shrinkage element  12  may be constituted by a relatively wide piece of reinforcement presenting a large second moment of area in the XOZ plane so as to prevent material shrinking in said plane, while encouraging material to shrink in the YOZ plane so as to obtain curvature in said plane.  
      However, if the shape of the door requires curvature both in the YOZ plane and in the XOZ plane, then the anti-shrinkage element  12  is narrower so as to lie solely in the web  3   c  of the clip, as shown in  FIG. 7 . It may be constituted by at least one metal wire or glass fiber, for example, so as to present a small second moment of area, thereby encouraging shrinkage of the materials.  
      For a vertical segment  10   a  of a run of the kind shown in  FIGS. 6 and 7 , the thermoplastic materials used can be, for example: polypropylene for the clip  3  and the legs  5  and  7 , and a TPE for the lip  9  situated towards the end of the main leg  5 . In a variant, the clip can be made of a material such as polypropylene while the main leg  5  and the sealing lip  9  are made of TPE, for example. Naturally, the thermoplastic materials used may be different from those mentioned above, but there is preferably a shrinkage gradient in the materials that decreases going from the clip  3  towards the sealing lip  9  situated towards the end of the main leg  5 , so that the materials situated furthest from the anti-shrinkage element  12  shrink the most.  
      In general, it is advantageous for the anti-shrinkage element to be covered in an adhesion promoter to ensure that it bonds well with the material coating it.  
      In a preferred embodiment, shown in  FIG. 8 , which is a variant of the embodiment shown in  FIG. 5 , the clip  3  is replaced by a central barbed member  20  which is anchored in a housing  21  in the rabbet  22  and is itself of generally U-shaped right section.  
      In the embodiment shown in  FIG. 9 , which is a variant of the embodiment shown in  FIG. 7 , the following differences should be observed: 
          the sealing lip  9  situated at the end of the main leg  5  of the gasket is folded over the rabbet  22  beside the window V so as to form a tubular element, and the two sealing lips  9   a  which extend from the limb  3   b  of the gasket are united so as to likewise form a tubular element;     the rabbet  22  of the door presents a crimped portion  24  on top and the clip  3  which is mounted thereon presents a free end that is retained by an internal projection  26  projecting from the inside face of the limb  3   b  of the clip  3 ;     the gasket is also held in the rabbet  22  by a barbed member  28  that is anchored in a housing  30  in the rabbet  22 ; and     a tubular type lip  32  is provided between the leg  5  and the lip  3   a  of the clip  3  that is to come into contact with the top portion of the window V.        

      Finally, the embodiment shown in  FIG. 10  shows a sealing gasket of the invention, but for a gasket for a single-rabbet window run.