Abstract:
The present invention can provide an inexpensive synthetic resin grommet which is designed to exhibit sealing facility when it is fitted to a body of a car or a home electric appliance and when a part is attached thereto through the grommet, and which can prevent accurately and securely entrance of water into the body without requiring intricate procedures including fitting of sealing annulus.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a synthetic resin grommet used, for example, when parts for an automobile or parts for a home electric appliance (hereinafter simply referred to as parts) are attached to a body of the car or of the appliance (hereinafter simply referred to as body), respectively.  
           [0002]    A synthetic resin grommet as shown in FIG. 4 is widely used for attaching parts to the body  26  using bolts. The grommet has a cylindrical body  21 , a flange portion  22  arranged at a predetermined position of the cylindrical body  21  and stopping claws  24  whose tips face the flange portion. However, the conventional grommet has no sealing mechanism between a bearing face  25   a  of a tapping screw  25  to be inserted to the cavity of the grommet to fasten it and a head portion  23  of the grommet to be come into contact with the bearing face  25   a  when the tapping screw is fully fastened, nor between the lower surface of the flange portion  22  and the tips of the stopping claws  24 , so that it is in danger of entrance of water into the grommet and/or body through these portions. Therefore, entrance of water has been prevented by applying a grommet whose cylindrical body has a closed bottom  28  to the body  26  and by fitting a sealing annulus  27  such as of sponge rubber between the upper surface of the body  26  and the lower surface of the flange portion  22  when the grommet is applied to the body. However, the above contrivances still involve problems that to fit the sealing annulus  27  imposes an extra operation on an operator, and to form a grommet having a main body with a closed bottom impairs moldability of the grommet, preventing providing of grommets inexpensively.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention is directed to solving the problems inherent in the prior art by contriving the configuration of the grommet and providing an inexpensive synthetic resin grommet which can prevent accurately and securely entrance of water into the grommet and/or body with no extra imposition on an operator.  
           [0004]    More specifically, the synthetic resin grommet according to the present invention has a flange portion formed at a predetermined position of a cylindrical body and stopping claws arranged on the outer circumference of the cylindrical body such that their tips face the flange portion, characterized in that the grommet has an annular rib arranged at a top of a head portion of the cylindrical body. Further, the rim portion of the flange portion is preferably formed to have a thin vane-like shape, because sealing between the body and the flange portion can be achieved more accurately and securely. Here, the cylindrical body is preferably designed to have an open bottom, because this improves moldability of the grommet.  
           [0005]    Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings illustrated by way of examples the principles of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The invention together with the objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
         [0007]    [0007]FIG. 1 is a partially cutaway front view showing the grommet according to one embodiment of the present invention attached to a body;  
         [0008]    [0008]FIG. 2 is an enlarged explanatory view showing a major part (the head portion of the cylindrical body) in the embodiment shown in FIG. 1;  
         [0009]    [0009]FIG. 3 is an enlarged explanatory view showing another major part (the rim portion of the flange portion) in the embodiment shown in FIG. 1; and  
         [0010]    [0010]FIG. 4 is a partially cutaway front view showing a typical example of the conventional grommet attached to a body.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]    Next, one embodiment of the present invention will be described specifically referring to the attached drawings.  
         [0012]    In the drawings, the reference number  1  represents a single-piece grommet formed by using a synthetic resin (such as polyamide, polyacetal, polypropylene, polyethylene, urethane series elastomer and polyester series elastomer, preferably polyamide, because of its appropriate strength and appropriate tensile elongation). The grommet  1  has, at a predetermined position on its cylindrical body  2 , a flange portion  3 . The cylindrical body  2  has on the outer circumference thereof stopping claws  5  whose tips face the flange portion  3 .  
         [0013]    The flange portion  3  has an inverted dish-like shape as a whole and has a vane-like rim portion  3   a  which is as thin as can be deformed elastically when tightened with a bolt or tapping screw  11  (hereinafter description is made by means of tapping screw according to the prior art) such that the edge of the rim portion  3   a  is brought into intimate contact with the upper surface of the body  12 . This ensures sealing between the body and the flange portion without interposing afterward a sealing annulus such as of sponge rubber between the flange portion and the body, so that there occurs no entrance of water into the body. Further, the cylindrical body  2  has at the tip of the head portion  4  an annular rib  4   a . Here, this annular rib  4   a  is preferably designed to have a configuration such that it can easily be compressed when fastened with a tapping screw  11 , that is to say, the annular rib  4  can be deformed elastically to be brought into intimate contact with the lower surface of the collar-like portion  11   a  of the tapping screw  11 . The annular rib  4   a  is preferably designed to have a large diameter at the top compared with the bottom thereof. While it is essential that this annular rib  4   a  is present at least at the top of the head portion  4 , the outer the position of the rib  4   a , the better. Particularly preferably, the outer circumference of the top of the head portion  4  is formed to have a tapered cross section, and the annular rib  4   a  is formed at a position on and adjacent to the top of the tapered face  4   b , because this tapered face  4   b  facilitates outward elastic deformation of the annular rib  4   a.    
         [0014]    Concerning to the position of the annular rib  4   a  in terms of sealing effect, the annular rib  4   a  can be arranged on the lower surface of the collar-like portion  11   a  of the tapping screw  11  at a position opposing the top of the head portion. In this case, the head portion is allowed to have a flat top. Meanwhile, if the grommet and the tapping screw are formed using materials having different hardness, and an annular rib having an acute cross section is formed on the harder member of the two, this constitution can also exhibit a satisfactory sealing effect.  
         [0015]    Here, while the object of preventing water from entering the body can be attained so long as an annular rib  4   a , for example the annular rib having an inverted V-shaped cross section, is arranged at the top of the head portion  4  and, as necessary, the rim portion  3   a  of the flange portion  3  is formed to have a thin vane-like shape no matter whether the cylindrical body  2  has a closed bottom or an open bottom. However, the cylindrical body  2  having an open bottom is preferred, since it leads to saving of material costs, facilitates fabrication of molds and improves moldability, realizing mass production of high-quality products inexpensively.  
         [0016]    The grommet  1  having the constitution described above is attached to a body  12  by inserting the cylindrical body  2  to a grommet insertion hole  13  defined in the body  12  such that the bearing face of the flange portion  3  is abutted against the upper surface of the body  12  under the stopping effect to be exerted by the stopping claws  5  arranged on the cylindrical body  2  at predetermined positions such that their tips face the flange portion (here passing of the cylindrical body  2  through the grommet insertion hole  13  is achieved with the aid of elastic deformation of the grommet insertion hole  13 ). Then, a part  14  is fitted in the head portion  4  through a fitting hole defined in the part  14 . If a tapping screw  11  is screwed from the head portion  4  into the cavity of the cylindrical body  2 , the part  14  can be attached accurately and securely to the body  12  through the collar portion  11   a  of the tapping screw  11  and the grommet (more accurately, through a step formed on the upper surface of the flange portion  3  of the grommet  1 ). The insertion of the tapping screw  11  into the grommet  1  and fastening of the grommet therewith cause the annular rib  4   a  to undergo elastic deformation and achieve sealing between the bearing face of the tapping screw  11  (more accurately, the lower surface of the collar portion  11   a ; the same shall apply hereinafter) and the head portion  4  to be abutted against the bearing face, thus preventing accurately and securely rainwater and the like from entering the cavity of the grommet  1  through the gap present between the bearing face of the tapping screw  11  and the part  14 . Simultaneously, the vane-like rim portion  3   a  formed on the flange portion  3  of the grommet  1  also undergoes elastic deformation to be brought into intimate contact with the body  12  (more accurately with the upper surface of the body  12 ) and exhibit excellent sealing effect, so that this also ensures accurate and secured sealing between the body  12  and the flange portion  3 . For example, even if rainwater or the like enters from the gap present between the bearing face of the tapping screw  11  and the part  14  and through the fitting hole  15  of the part  14  into the clearance present between the part  14  and the body  12 , the grommet  1  can prevent accurately and securely the rainwater or the like from entering the inner space of the body  12  any further.  
         [0017]    As is clear from the above description, according to the grommet of the present invention, sealing can be achieved accurately and securely between the bearing face of the tapping screw  11  screwed into the cavity of the grommet  1  to fasten it and the head portion  4  of the grommet  1  to be abutted against it by merely forming an annular rib  4   a  at the top of the head portion  4 . If the flange portion  3  is allowed to have a thin vane-like rim portion  3   a , sealing between the body  12  and the flange portion  3  can also be achieved accurately and securely. According to this constitution, favorable effects can be expected further (including omission of the sealing annulus and the operation of fitting it). In addition, if the cylindrical body  2  is allowed to have an open bottom, it leads to saving of material costs by just that much, facilitates fabrication of molds and improves moldability of the grommet  1 , realizing mass production of high-quality products more inexpensively.  
         [0018]    It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.