Abstract:
In order to prevent gaps from occurring in corner sections in a section where three surfaces are joined together, comprising the combination of a housing, grommet and cover, or the like, thereby improve sealing, a seal structure, which is provided with a housing in which a notch-shaped grommet-mounting section is disposed, a grommet, a cover and a metal substrate gasket, is provided, wherein the grommet is provided with a seal projection, and the seal projection forms a protruding section due to a portion of the seal projection protruding toward the metal substrate gasket when the seal projection makes intimate contact with the inner surface of the grommet-mounting section. The metal substrate gasket is provided with two seal lines and a groove-shaped recess between the seal lines. When nipped, the protruding section of the seal projection is tightly compressed inside the groove-shaped recess in the metal substrate gasket.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/JP2012/056337, filed on Mar. 13, 2012, and published in Japanese as WO 2013/051301 A1 on Apr. 11, 2013. This application claims priority to Japanese Application Nos. 2011-221943, 2011-221944 and 2011-221945, all of which were filed on Oct. 6, 2011. The disclosures of the above applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a seal structure according to a sealing technique. The seal structure according to the present invention is used for sealing a section where three surfaces are joined together, for example, in an electric equipment device and an engine. 
         [0004]    2. Description of the Conventional Art 
         [0005]    In the electric equipment device such as an electronically controlled unit, a power control unit or a DC-DC converter for an electric vehicle or a hybrid vehicle, a grommet is installed to a casing for sealing an insertion port of a harness or a piping which is connected to an external portion (refer to Japanese Unexamined Patent Publication Nos. 2002-369346, 2004-72877 and 2009-153264). 
         [0006]    In other words,  FIG. 20A  is an explanatory view showing a typical conventional example. A notch-like grommet installation portion  53  is provided in a wall portion  52  of a casing  51 , and a cover  55  is put on the casing  51  and a grommet  54  in a state in which the grommet  54  is installed to the grommet installation portion  53 , whereby an insertion port of the harness or the piping is sealed. A through hole  56  for inserting the harness or the piping is provided in the grommet  54 . 
         [0007]    In this case, the grommet  54  achieves a sealing action by being pinched and compressed between the casing  51  and the cover  55 , however, a gap c tends to be generated in a corner portion in a position where respective surfaces of the casing  51 , the grommet  54  and the cover  55  intersect (a section where three surfaces are joined together) as shown in  FIG. 20B  due to a problem on a shape of the grommet  54 . Accordingly, there is a case that a seal leakage generates a problem. 
         [0008]    Further, the problem of the seal leakage due to the intersection among three members also exists in a connecting position between a cylinder portion of the engine and various covers (refer to Japanese Utility Model Publication Nos. 61-23713 and 61-23714, and Japanese Unexamined Patent Publication No. 2-241956). 
         [0009]    Further, there has been proposed a structure which intends to reduce the gap c by arranging a seal projection in a thick surface (a side surface or an upper surface) of the grommet  54 , as a prior art, however, there is a case that the gap c can not be done away only by arranging the seal projection as mentioned above, and it is an insufficient countermeasure. 
       SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
       [0010]    The present invention is made by taking the above points into consideration, and an object of the present invention is to provide a seal structure which can inhibit a gap from being generated at a corner portion in a section where three surfaces are joined together, the section being constructed by a combination of a casing, a grommet and a cover, whereby it is possible to improve a sealing performance. 
       Means for Solving the Problem 
       [0011]    In order to achieve the object, a seal structure according to a first aspect of the present invention is a seal structure comprising a casing which is provided in its wall portion with a notch-like grommet installation portion, a grommet which is installed to the grommet installation portion, a cover which is put on the wall portion and the grommet, and a metal base plate gasket which is installed between the wall portion and the grommet, and the cover, wherein the grommet is provided with a seal projection at least on a surface which faces to an inner surface of the grommet installation portion, the seal projection seals between the wall portion and the grommet by coming into close contact with the inner surface of the grommet installation portion, and is provided with a protruding portion generated by a protrusion of a part of the seal projection toward the metal base plate gasket in the case that the seal projection comes into close contact with the inner surface of the grommet installation portion, the metal base plate gasket is provided with two seal lines which are parallel to each other on a surface facing to the wall portion, and is provided with two seal lines which are continuously provided from the seal lines on a surface facing to the grommet, and is further provided with a groove-like concave portion between the two seal lines, and the protruding portion in the seal projection is closely compressed within the groove-like concave portion in the metal base plate gasket. 
         [0012]    Further, a seal structure according to a second aspect of the present invention is the seal structure described in the first aspect mentioned above, wherein the grommet installation portion is provided with a chamfer portion in an edge portion in its inner surface, and the seal projection is formed such a shape that a cross sectional shape of a position facing to the chamfer portion is enlarged little by little in correspondence to the shape of the chamfer portion. 
         [0013]    Further, a seal structure according to a third aspect of the present invention is a seal structure comprising a casing which is provided in its wall portion with a notch-like grommet installation portion, a grommet which is installed to the grommet installation portion, a cover which is put on the wall portion and the grommet, and a metal base plate gasket which is installed between the wall portion and the grommet, and the cover, wherein the grommet is provided with a seal projection at least on a surface which faces to an inner surface of the grommet installation portion, the seal projection seals between the wall portion and the grommet by coming into close contact with the inner surface of the grommet installation portion, and is provided with a protruding portion generated by a protrusion of a part of the seal projection toward the metal base plate gasket in the case that the seal projection comes into close contact with the inner surface of the grommet installation portion, the metal base plate gasket is provided with one seal line and a branch portion in which the seal line is branched into two lines, and is provided with two seal lines which are continuously provided from the branch portion on a surface facing to the grommet, and is further provided with a concave portion which is surrounded by the branch portion and the two seal lines, and the protruding portion in the seal projection is closely compressed in an inner side of the branch portion within the concave portion in the metal base plate gasket. 
         [0014]    Further, a seal structure according to a fourth aspect of the present invention is the seal structure described in the third aspect mentioned above, wherein the grommet installation portion is provided with a chamfer portion in an edge portion in its inner surface, and the seal projection is formed such a shape that a cross sectional shape of a position facing to the chamfer portion is enlarged little by little in correspondence to the shape of the chamfer portion. 
         [0015]    Further, a seal structure according to a fifth aspect of the present invention is a seal structure comprising a casing which is provided in its wall portion with a notch-like grommet installation portion, a grommet which is installed to the grommet installation portion, a cover which is put on the wall portion and the grommet, and a rubber single body gasket which is installed between the wall portion and the grommet, and the cover, wherein the grommet is provided with a seal projection at least on a surface which faces to an inner surface of the grommet installation portion, the seal projection seals between the wall portion and the grommet by coming into close contact with the inner surface of the grommet installation portion, and is provided with a protruding portion generated by a protrusion of a part of the seal projection toward the rubber single body gasket in the case that the seal projection comes into close contact with the inner surface of the grommet installation portion, and the rubber single body gasket is provided with one seal line and a branch portion in which the seal line is branched into two lines, and is provided with two seal lines which are continuously provided from the branch portion on a surface facing to the grommet, and is further provided with a space portion or a concave portion which is surrounded by the branch portion and the two seal lines, and the protruding portion in the seal projection is closely compressed in an inner side of the branch portion within the space portion or the concave portion in the rubber single body gasket. 
         [0016]    Further, a seal structure according to a sixth aspect of the present invention is the seal structure described in the fifth aspect mentioned above, wherein the rubber single body gasket is installed to a gasket installation groove which is provided in the cover. 
         [0017]    In the seal structure according to the first aspect of the present invention having the structure mentioned above, the metal base plate gasket is added to the combination of the casing, the grommet and the cover, and the metal base plate gasket is installed between the wall portion of the casing and the grommet, and the cover. The casing is provided in its wall portion with the notch-like grommet installation portion. The grommet is provided with the seal projection on the surface facing to the inner surface of the grommet installation portion. The seal projection seals between the wall portion and the grommet by coming into close contact with the inner surface of the grommet installation portion, and forms the protruding portion by the protrusion of a part of the seal projection toward the metal base plate gasket in the case that the seal projection comes into close contact with the inner surface of the grommet installation portion. On the other hand, the metal base plate gasket is provided with two seal lines which are parallel to each other on the surface facing to the wall portion in the longitudinal direction, and is further provided with the groove-like concave portion between the two seal lines. Further, in the case that the cover is put on the casing and the seal structure is fastened by the pinching means such as a bolt fastening, the metal base plate gasket and the grommet are crushed, and the protruding portion in the seal projection is closely compressed within the groove-like concave portion in the metal base plate gasket. 
         [0018]    In the case that the metal base plate gasket is not installed, the protruding portion is compressed between the wall portion of the casing and the grommet, and the cover. In this case, since the protruding portion is not surrounded its periphery by the other members, the protruding portion is deformed so as to crush flatly (deformed in a state in which an escaping direction is not restricted). On the contrary, in the present invention, the protruding portion is deformed in a state in which the protruding portion is pinched by two seal lines in the metal base plate gasket and is surrounded by the inner surface of the groove-like concave portion (deformed in a state in which the escaping direction is restricted). Therefore, since the protruding portion is deformed space, the protruding portion comes into close contact with the inner surface of the groove-like concave portion by being compressed. Accordingly, it is possible to effectively inhibit a gap from being formed. 
         [0019]    The casing and the grommet are sealed therebetween by the seal projection. The grommet and the metal base plate gasket, the casing and the metal base plate gasket, and the metal base plate gasket and the cover are respectively sealed therebetween by the close contact of them on the basis of the pinching. 
         [0020]    The metal base plate gasket employs, for example, a structure in which one full bead having a circular arc shaped cross section is provided in a flat base plate portion, and the metal base plate gasket is installed so as to direct a bulge obtained by the full bead toward the cover. Accordingly, in this case, two seal lines are formed by both end portions of the bead circular arc, and the groove-like concave portion is formed by a depression in the inner side of the bead circular arc. 
         [0021]    The seal projection provided in the grommet forms the protruding portion since the seal projection is compression deformed in the case that the seal projection comes into close contact with the inner surface of the grommet installation portion, thereby protruding toward the metal base plate gasket. Therefore, a sufficient cubic volume (volume) to protrude in the case of being compression deformed is necessary for the seal projection. In this regard, in the case that a cross sectional shape of the seal projection is uniform over a whole length, a distance between the grommet and the wall portion is enlarged in the case that the chamber portion is provided in the edge portion of the inner surface in the grommet installation portion. Therefore, the cubic volume of the seal projection is insufficient, that is, a compression amount is insufficient, so that there is fear that a sealing performance of the portion is hard to be secured or the protruding portion is hard to be formed. In order to devise a countermeasure, it is preferable to form a cross sectional shape (a cross sectional area) of the position facing to the chamfer portion in the seal projection as a shape which is enlarged little by little in correspondence to the shape of the chamfer portion, whereby the facing position is sufficiently compressed by the chamfer portion. According to this structure, even in the case that the chamfer portion is provided in the grommet installation portion, it is possible to securely seal between the casing and the grommet, and it is possible to securely form the protruding portion by the seal projection. 
         [0022]    In the seal structure according to the third aspect of the present invention having the structure mentioned above, the metal base plate gasket is added to the combination of the casing, the grommet and the cover, and the metal base plate gasket is installed between the wall portion of the casing and the grommet, and the cover. The casing is provided in its wall portion with the notch-like grommet installation portion. The grommet is provided with the seal projection on the surface facing to the inner surface of the grommet installation portion. The seal projection seals between the wall portion and the grommet by coming into close contact with the inner surface of the grommet installation portion, and forms the protruding portion by the protrusion of a part of the seal projection toward the metal base plate gasket in the case that the seal projection comes into close contact with the inner surface of the grommet installation portion. On the other hand, the metal base plate gasket is provided with one seal line and the branch portion in which the one seal line is branched into two lines on the surface facing to the wall portion in the longitudinal direction, and is provided with two seal lines which are continuously provided from the branch portion on the surface facing to the grommet, and is further provided with the concave portion which is surrounded by the branch portion and two seal lines. Further, in the case that the cover is put on the casing and the seal structure is fastened by the pinching means such as a bolt fastening, the metal base plate gasket and the grommet are crushed, and the protruding portion in the seal projection is closely compressed within the groove-like concave portion in the metal base plate gasket. 
         [0023]    In the case that the metal base plate gasket is not installed, the protruding portion is compressed between the wall portion of the casing and the grommet, and the cover. In this case, since the protruding portion is not surrounded its periphery by the other members, the protruding portion is deformed so as to crush flatly (deformed in a state in which an escaping direction is not restricted). On the contrary, in the present invention, the protruding portion is deformed in a state in which the protruding portion is pinched by the branch portion and two seal lines in the metal base plate gasket and is surrounded by the inner surface of the concave portion (deformed in a state in which the escaping direction is restricted). Therefore, since the protruding portion is deformed space, the protruding portion comes into close contact with the inner surface of the concave portion by being compressed. Accordingly, it is possible to effectively inhibit a gap from being formed. 
         [0024]    Further, since the present invention is particularly structured such that the branch portion of the seal line is provided in the metal base plate gasket, and the branch portion compresses the protruding portion of the seal projection in its inner side, the bifurcated branch portion presses the protruding portion toward the center in a grommet width direction on the basis of the an application of a pinching force. Therefore, since a reaction force to the pressing (a reaction force directed to an end portion in the grommet width direction) is generated in the protruding portion, it is possible to further effectively inhibit the gap from being formed. 
         [0025]    The casing and the grommet are sealed therebetween by the seal projection. The grommet and the metal base plate gasket, the casing and the metal base plate gasket, and the metal base plate gasket and the cover are respectively sealed therebetween by the close contact of them on the basis of the pinching. 
         [0026]    The metal base plate gasket employs, for example, a structure in which full beads having a circular arc shaped cross section is provided in a flat base plate portion, more particularly employs a structure in which one full bead and the branch portion in which one full bead is branched into two beads are provided on the surface facing to the wall portion at the installing time in the gasket longitudinal direction, and two full beads which are continuously provided from the branch portion are provided on the surface facing to the grommet, and the metal base plate gasket is installed so as to direct a bulge obtained by each of the full beads and the branch portion toward the wall portion of the casing and the grommet. Accordingly, in this case, the seal lines are formed by the full beads and the top portion of the branch portion, and the concave portion is formed so as to be surrounded by the branch portion and two full beads. 
         [0027]    The seal projection provided in the grommet forms the protruding portion since the seal projection is compression deformed in the case that the seal projection comes into close contact with the inner surface of the grommet installation portion, thereby protruding toward the metal base plate gasket. Therefore, a sufficient cubic volume (volume) to protrude in the case of being compression deformed is necessary for the seal projection. In this regard, in the case that a cross sectional shape of the seal projection is uniform over a whole length, a distance between the grommet and the wall portion is enlarged in the case that the chamber portion is provided in the edge portion of the inner surface in the grommet installation portion. Therefore, the cubic volume of the seal projection is insufficient, that is, a compression amount is insufficient, so that there is fear that a sealing performance of the portion is hard to be secured or the protruding portion is hard to be formed. In order to devise a countermeasure, it is preferable to form a cross sectional shape (a cross sectional area) of the position facing to the chamfer portion in the seal projection as a shape which is enlarged little by little in correspondence to the shape of the chamfer portion, whereby the facing position is sufficiently compressed by the chamfer portion. According to this structure, even in the case that the chamfer portion is provided in the grommet installation portion, it is possible to securely seal between the casing and the grommet, and it is possible to securely form the protruding portion by the seal projection. 
         [0028]    In the seal structure according to the fifth aspect of the present invention having the structure mentioned above, the rubber single body gasket is added to the combination of the casing, the grommet and the cover, and the rubber single body gasket is installed between the wall portion of the casing and the grommet, and the cover. The rubber single body gasket is made only by a rubber-like elastic material as its name, and is not provided with a metal base plate. Therefore, the rubber single body gasket may be installed to the gasket installation groove provided in the cover for a stable installation. The casing is provided in its wall portion with the notch-like grommet installation portion. The grommet is provided with the seal projection on the surface facing to the inner surface of the grommet installation portion. The seal projection seals between the wall portion and the grommet by coming into close contact with the inner surface of the grommet installation portion, and forms the protruding portion by the protrusion of a part of the seal projection toward the rubber single body gasket in the case that the seal projection comes into close contact with the inner surface of the grommet installation portion. Further, in the case that the cover is put on the casing and the seal structure is fastened by the pinching means such as a bolt fastening, the protruding portion and the rubber single body gasket are both compressed, and the protruding portion strongly comes into close contact with the rubber single body gasket. 
         [0029]    The casing and the grommet are sealed therebetween by the seal projection. The grommet and the rubber single body gasket, the casing and the rubber single body gasket, and the rubber single body gasket and the cover are respectively sealed therebetween by the close contact of them on the basis of the pinching. 
         [0030]    The rubber single body gasket may be constructed by a tabular gasket in which concavity and convexity are not particularly formed on its flat surface, however, may be structured, for example, such that one seal line and a branch portion in which one seal line is branched into two lines are provided on the surface facing to the wall portion in the gasket longitudinal direction, two seal lines which are continuously provided from the branch portion are provided on the surface facing to the grommet, and a space or a concave portion surrounded by the branch portion and two seal lines is provided. Further, in the case that the rubber single body gasket is formed as mentioned above, the protruding portion is deformed in a state in which the protruding portion is pinched by the branch portion and two seal lines (deformed in a state in which the escaping direction is restricted), that is, deformed within the restricted space. Therefore, the protruding portion comes into close contact with the rubber single body gasket by being compressed. Accordingly, it is possible to effectively inhibit the gap from being formed. 
       Effect of the Invention 
       [0031]    The present invention achieves the following effects. 
         [0032]    In other words, in the seal structure according to the first aspect of the present invention, as mentioned above, the seal projection provided in the grommet forms the protruding portion, and the protruding portion is closely compressed within the narrow groove-like concave portion in the metal base plate gasket, whereby it is possible to inhibit the gap from being formed. Therefore, according to the desired object of the present invention, it is possible to inhibit the gap from being generated in the corner portion in the section where three surfaces are joined together, and it is accordingly possible to improve a sealing performance. Further, since the cross sectional shape of the position facing to the chamfer portion in the seal projection is formed such the shape as to be enlarged little by little in correspondence to the shape of the chamfer portion in the case that the chamfer portion is provided in the edge portion in the inner surface in the grommet installation portion, it is possible to securely seal between the casing and the grommet, and it is possible to securely form the protruding portion by the seal projection. 
         [0033]    In the seal structure according to the third aspect of the present invention, as mentioned above, the seal projection provided in the grommet forms the protruding portion, and the protruding portion is closely compressed within the narrow concave portion in the metal base plate gasket, whereby it is possible to inhibit the gap from being formed. Further, since the present invention is particularly structured such that the branch portion of the seal line is provided in the metal base plate gasket, and the branch portion compresses the protruding portion of the seal projection in its inner side, the bifurcated branch portion presses the protruding portion toward the center in the grommet width direction on the basis of the application of the pinching force. Accordingly, since the reaction force to the pressing is generated in the protruding portion, it is possible to further effectively inhibit the gap from being formed. Therefore, according to the desired object of the present invention, it is possible to inhibit the gap from being generated in the corner portion in the section where three surfaces are joined together, and it is accordingly possible to improve a sealing performance. Further, since the cross sectional shape of the position facing to the chamfer portion in the seal projection is formed such the shape as to be enlarged little by little in correspondence to the shape of the chamfer portion in the case that the chamfer portion is provided in the edge portion in the inner surface in the grommet installation portion, it is possible to securely seal between the casing and the grommet, and it is possible to securely form the protruding portion by the seal projection. 
         [0034]    In the seal structure according to the fifth aspect of the present invention, as mentioned above, the seal projection provided in the grommet forms the protruding portion, and the protruding portion comes into close contact with the rubber single body gasket, whereby it is possible to inhibit the gap from being formed. Therefore, according to the desired object of the present invention, it is possible to inhibit the gap from being generated in the corner portion in the section where three surfaces are joined together, and it is accordingly possible to improve a sealing performance. Further, it is possible to secure a stability of the gasket installation, by installing the rubber single body gasket to the gasket installation groove. 
     
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         [0035]      FIG. 1  is a perspective view showing a state before assembling a seal structure according to a first embodiment of the present invention; 
           [0036]      FIG. 2A  is a plan view of a grommet which is provided in the seal structure; 
           [0037]      FIG. 2B  is a front elevational view of the grommet; 
           [0038]      FIG. 2C  is a perspective view of the grommet; 
           [0039]      FIG. 2D  is a perspective view showing the other example of the grommet; 
           [0040]      FIG. 3A  is a plan view of a metal base plate gasket which is provided in the seal structure; 
           [0041]      FIG. 3B  is an enlarged cross sectional view of a substantial part of the metal base plate gasket and corresponds to an enlarged cross sectional view along a line E-E in  FIG. 3A ; 
           [0042]      FIG. 3C  is a cross sectional view of a substantial part and shows the other example of the metal base plate gasket; 
           [0043]      FIG. 4A  is an explanatory view (a front elevational view) showing a state in which a predetermined crush is applied to the grommet in the seal structure; 
           [0044]      FIG. 4B  is an explanatory view (a front elevational view) showing a state after being fastened in the seal structure; 
           [0045]      FIG. 5  is an explanatory view (a plan view) showing a layout of seal lines in the seal structure; 
           [0046]      FIG. 6A  is an explanatory view in the case that a chamfer portion is provided in a grommet installation portion; 
           [0047]      FIGS. 6B and 6C  are explanatory views of seal structures according to the other embodiments of the present invention; 
           [0048]      FIG. 7  is a perspective view showing a state before assembling a seal structure according to a second embodiment of the present invention; 
           [0049]      FIG. 8A  is a plan view of a grommet which is provided in the seal structure; 
           [0050]      FIG. 8B  is a front elevational view of the grommet; 
           [0051]      FIG. 8C  is a perspective view of the grommet; 
           [0052]      FIG. 8D  is a perspective view showing the other example of the grommet; 
           [0053]      FIG. 9A  is a plan view of a metal base plate gasket which is provided in the seal structure; 
           [0054]      FIG. 9B  is an enlarged cross sectional view of a substantial part of the metal base plate gasket and corresponds to an enlarged cross sectional view along a line F-F in  FIG. 9A ; 
           [0055]      FIG. 9C  is an enlarged cross sectional view of a substantial part of the metal base plate gasket and corresponds to an enlarged cross sectional view along a line G-G in  FIG. 9A ; 
           [0056]      FIG. 9D  is a cross sectional view of a substantial part and shows the other example of the metal base plate gasket; 
           [0057]      FIG. 10A  is an explanatory view (a front elevational view) showing a state in which a predetermined crush is applied to the grommet in the seal structure; 
           [0058]      FIG. 10B  is an explanatory view (a front elevational view) showing a state after being fastened in the seal structure; 
           [0059]      FIG. 11A  is an explanatory view (a plan view) showing a layout of seal lines in the seal structure; 
           [0060]      FIG. 11B  is an explanatory view (a plan view) showing the other example of the layout of the seal lines; 
           [0061]      FIG. 12A  is an explanatory view in the case that a chamfer portion is provided in a grommet installation portion; 
           [0062]      FIGS. 12B and 12C  are explanatory views of seal structures according to the other embodiments of the present invention; 
           [0063]      FIG. 13  is a perspective view showing a state before assembling a seal structure according to a third embodiment of the present invention; 
           [0064]      FIG. 14A  is a plan view of a grommet which is provided in the seal structure; 
           [0065]      FIG. 14B  is a front elevational view of the grommet; 
           [0066]      FIG. 14C  is a perspective view of the grommet; 
           [0067]      FIG. 14D  is a perspective view showing the other example of the grommet; 
           [0068]      FIG. 15A  is a plan view of a rubber single body gasket which is provided in the seal structure; 
           [0069]      FIG. 15B  is an enlarged cross sectional view of a substantial part of the rubber single body gasket in an installed state and corresponds to an enlarged cross sectional view along a line I-I in  FIG. 15A ; 
           [0070]      FIG. 15C  is an enlarged cross sectional view of the substantial part of the rubber single body gasket in the installed state and corresponds to an enlarged cross sectional view along a line J-J in  FIG. 15A ; 
           [0071]      FIG. 15D  is a cross sectional view of a substantial part and shows the other example of the grommet installation groove; 
           [0072]      FIG. 16  is a cross sectional view of a substantial part and shows the other example of the rubber single body gasket; 
           [0073]      FIG. 17A  is a bottom elevational view showing the other example of the rubber single body gasket; 
           [0074]      FIG. 17B  is an enlarged cross sectional view of a substantial part of the rubber single body gasket and corresponds to an enlarged cross sectional view along a line K-K in  FIG. 17A ; 
           [0075]      FIG. 17C  is an enlarged cross sectional view of the substantial part of the rubber single body gasket and corresponds to an enlarged cross sectional view along a line L-L in  FIG. 17A ; 
           [0076]      FIG. 18A  is an explanatory view (a front elevational view) showing a state in which a predetermined crush is applied to the grommet in the seal structure; 
           [0077]      FIG. 18B  is an explanatory view (a front elevational view) showing a state after being fastened in the seal structure; 
           [0078]      FIG. 19A  is an explanatory view (a plan view) showing a layout of seal lines in the seal structure; 
           [0079]      FIG. 19B  is an explanatory view (a plan view) showing the other example of the layout of seal lines in the seal structure; 
           [0080]      FIG. 20A  is a front elevational view showing a state before assembling a seal structure according to the prior art; and 
           [0081]      FIG. 20B  is a front elevational view showing a state after assembling. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0082]    The following embodiments are included in the present invention. 
       Relevant to First Aspect 
       [0083]    (1) The present invention provides a seal structure in which a cover member is attached to a casing to which a U-shaped grommet is installed from an opening surface side of the casing, via a metal base plate gasket having a bead, wherein a seal projection is provided at least in a grommet side surface which is bonded to the casing, a part of the seal projection is protruded to three surface portions where the casing, the grommet and the cover member are overlapped, the protruding portion is housed in a bead concave portion, and the protruding portion is compression sealed by the gasket at the assembling time. 
         [0084]    (2) The seal projection of the protruding grommet is housed in an inner side (a concave portion) of the bead of the gasket, and the protruding portion of the seal projection is compressed by a crushing at the installing time of the gasket bead, thereby carrying out a stable seal of three surface portions. 
         [0085]    (3) The surface facing to the cover member of the grommet may be provided with a seal projection which is housed in the bead concave portion of the gasket and serves as a seal at the assembling time. 
         [0086]    (4) In the metal base plate gasket, the effect of the present invention can be aimed by forming the concave portion housing the protruding portion by two rubber projections which are formed in the gasket surface, however, in order to strongly compress and seal the protruding portion, a bead constructed by a metal plate is preferable. 
         [0087]    (5) A volumetric capacity (height and thickness) in the vicinity of the three-surface portion of the seal projection provided in the grommet is enlarged. As a result, a sealing performance can be secured even by arranging a chamfer in the casing. 
         [0088]    (6) According to the present invention, since the seal projection is structured such as to protrude, a sealing performance between the casing and the grommet is excellent in the vicinity of the three-surface portion where a problem is generated in the prior art. Further, in the case that the protrusion is generated, a seal leakage due to the protrusion generates a problem in the prior example, however, since the protrusion is housed in the concave portion of the gasket bead so as to be compressed and form the sealing structure in the present invention, the problem of the seal leakage is done away. 
       Relevant to Third Aspect 
       [0089]    (7) The present invention provides a seal structure in which a cover member is attached to a casing to which a U-shaped grommet is installed from an opening surface side of the casing, via a metal base plate gasket having a bead, wherein a seal projection is provided at least in a grommet side surface which is bonded to the casing, a part of the seal projection is protruded to three surface portions where the casing, the grommet and the cover member are overlapped, the protruding portion is housed between bead concave portions which are bifurcated from a near side of the three-surface portion, and the protruding portion is compression sealed by the gasket at the assembling time. 
         [0090]    (8) The bead concave portion can be formed as long as it is bifurcated at the three-surface portion and comes into contact with the bead, such as a shape that the bead portion of the gasket is bifurcated from the near side of the three-surface portion and the bead portions flow together at an end of the three-surface portion, and a shape that the beads flow together after passing the three-surface portion. 
         [0091]    (9) In the metal base plate gasket, the effect of the present invention can be aimed by forming the concave portion housing the protruding portion by two rubber projections which are formed in the gasket surface, however, in order to strongly compress and seal the protruding portion, a bead constructed by a metal plate is preferable. 
         [0092]    (10) A volumetric capacity (height and thickness) in the vicinity of the three-surface portion of the seal projection provided in the grommet is enlarged. As a result, a sealing performance can be secured even by arranging a chamfer in the casing. 
         [0093]    (11) According to the present invention, the following operations and effects can be achieved. 
         [0094]    (11-1) Since the seal projection is structured such as to protrude, a sealing performance between the casing and the grommet is excellent in the vicinity of the three-surface portion where a problem is generated in the prior art. 
         [0095]    (11-2) A seal leakage due to the protrusion generates a problem in the prior documents, however, the protrusion can be compressed between the bifurcated bead convex portions of the gasket, and it is possible to seal without forming any gap. 
         [0096]    (11-3) Further, the force generally escapes laterally only by applying the pressure from the above since the grommet is made of the rubber, however, the force can be applied from right and left sides of the grommet by providing two beads. Therefore, the force does not escape laterally, and the force can be efficiently applied vertically. 
         [0097]    (11-4) Since the projection is structured such as to come into contact with the confluence portion of the beads in the gasket side, the pressing force can be applied to the projection toward the center of the grommet. 
       Relevant to Fifth Aspect 
       [0098]    (12) The present invention provides a seal structure in which a cover member is attached to a casing to which a U-shaped grommet is installed from an opening surface side of the casing, via a rubber single body gasket, wherein a seal projection is provided at least in a grommet side surface which is bonded to the casing, a part of the seal projection is protruded to three surface portions where the casing, the grommet and the cover member are overlapped, the protruding portion is housed between seal lines which are bifurcated from a near side of the three-surface portion, and the protruding portion is compression sealed by the gasket at the assembling time. 
         [0099]    (13) The seal line can be formed as long as it is bifurcated at the three-surface portion and comes into contact with the bead, such as a shape that the seal line of the gasket is bifurcated from the near side of the three-surface portion and the seal lines flow together at an end of the three-surface portion, and a shape that the seal lines flow together after passing the three-surface portion. 
         [0100]    (14) According to the present invention, the following operations and effects can be achieved. 
         [0101]    (14-1) Since the seal projection is structured such as to protrude, a sealing performance between the casing and the grommet is excellent in the vicinity of the three-surface portion where a problem is generated in the prior art. 
         [0102]    (14-2) A seal leakage due to the protrusion generates a problem in the prior documents, however, the protrusion can be compressed between the bifurcated seal lines of the gasket, and it is possible to seal without forming any gap. 
         [0103]    (14-3) Further, the force generally escapes laterally only by applying the pressure from the above since the grommet is made of the rubber, however, the force can be applied from right and left sides of the grommet by providing two seal lines. Therefore, the force does not escape laterally, and the force can be efficiently applied vertically. 
         [0104]    (14-4) Since the projection is structured such as to come into contact with the confluence portion of the seal lines in the gasket side, the pressing force can be applied to the projection toward the center of the grommet. 
       EMBODIMENTS 
       [0105]    Next, a description will be given of embodiments according to the present invention with reference to the accompanying drawings. 
       First Embodiment 
       [0106]      FIG. 1  shows a state before assembling a seal structure according to a first embodiment of the present invention, and a casing  11 , a grommet  21 , a cover  31  and a metal base plate gasket  41  are drawn.  FIGS. 2A ,  2 B and  2 C are views of a single part of the grommet  21 ,  FIGS. 3A and 3B  are views of a single part of the metal base plate gasket  41 ,  FIGS. 4A and 4B  and  FIG. 5  are explanatory views of the seal structure. The seal structure according to the embodiment is structured such as to seal a section where three surfaces are joined together in an electric equipment device and an engine, and may be also called as a three-surface seal in the light of its function. 
         [0107]    The casing  11  is formed by a rigid member such as a predetermined metal or a hard resin, and is provided with a vertically planate wall portion  12  as a rising portion in a side wall of the casing, and a notch-like grommet installation portion  13  is provided in the wall portion  12  so as to pass through in a wall portion thickness direction. The grommet installation portion  13  is open to an upper surface  12   a  of the wall portion  12 . The grommet installation portion  13  is an insertion port of a harness or a piping in the electronic equipment device and the engine, and is sealed its opening by installing the grommet  21  thereto. Accordingly, in the present invention, the insertion port is called as a grommet installation portion. A front elevational shape of the grommet installation portion  13  is formed as a U-shaped form, that is, formed such a shape that is provided with a pair of right and left linear portions  13   a  which are parallel to each other and a curved portion  13   b  which is formed as a circular arc shape in a bottom portion, however, may be formed as the other shapes. For example, a pair of right and left linear portions  13   a  may be formed as an inverted trapezoidal shape that a width (a distance) is enlarged little by little toward the above. Further, it is possible to employ a shape which is provided only with the curved portion without any linear portion as shown in  FIG. 20 , as long as a protruding portion  25  by a seal projection  24  mentioned later can be formed. 
         [0108]    The grommet  21  is formed by a predetermined rubber-like elastic body, and is formed as a block shape which approximately has the same shape and the same magnitude as a volumetric capacity shape of the grommet installation portion  13  for sealing the grommet installation portion  13  serving as the insertion port by being closely installed thereto. In the illustrated embodiment, since the grommet installation portion  13  is formed as a U-shaped form in its front surface as mentioned above, the grommet  21  is formed as a block shape which is provided with six surfaces constituted by a planate front surface  21   a , a back surface  21   b , a pair of right and left side surfaces  21   c , an upper surface  21   d  and a curved bottom surface  21   e  in correspondence to the grommet installation portion  13 . A through hole  22  for inserting the harness or the piping is provided in the center of a front surface of the grommet  21  so as to pass through in a grommet thickness direction. A sleeve  23  made of a rigid material for fitting the piping is installed to an inner peripheral surface of the through hole  22 , however, the sleeve  23  may be omitted. 
         [0109]    Further, one continuous seal projection  24  is provided in a surface facing to the inner surface  13   c  of the grommet installation portion  13  in the grommet  21 , that is, a pair of right and left side surfaces and the curved bottom surface  21   e  so as to be positioned at the center in the grommet thickness direction, and the seal projection  24  is provided over a whole length in an arranging direction of three surfaces  21   c  and  21   e . Therefore, one end portion  24   a  of the seal projection  24  is arranged in an upper side portion of one side surface  21   c , and the other end portion  24   a  is arranged in an upper side portion of the other side surface  21   c . As a result, the formation of the protruding portion  25  mentioned later is facilitated. 
         [0110]    The seal projection  24  is compression deformed in the case that the seal projection is pressed to the inner surface  13   c  of the grommet installation portion  13 , comes into close contact with the inner surface  13   c  of the grommet installation portion  13  on the basis of a reaction force generated at that time, and seals between the wall portion  12  and the grommet  21 . Further, the seal projection  24  is compression deformed in the case that the seal projection is pressed to the inner surface  13   c  of the grommet installation portion  13 , and the end portion  24   a  protrudes upward from the upper surfaces  12   a  and  21   d  of the wall portion  12  and the grommet  21  as shown in  FIG. 4A  at that time, thereby forming the protruding portion  25 . In order to securely form the protruding portion  25 , it is preferable to carry out an installing work from a direction which is opposite to a protruding direction of the protruding portion  25  in the case that the grommet  21  is installed to the grommet installation portion  13 , and this direction is the same direction as a direction in which the cover  31  is put on the casing  11  (in other words, the grommet  21  is installed to the grommet installation portion  13  from the above in place of back and front sides in  FIG. 1 ). 
         [0111]    The metal base plate gasket  41  is structured such as to be interposed between the wall portion  12  of the casing  11  and the grommet  21 , and the cover  31 , and is provided with a planate base plate portion  42 , a width of the base plate portion  42  is made approximately equal to a width of the upper surface  12   a  of the wall portion  12 , and one full bead  43  having a circular arc cross sectional shape is integrally provided so as to be positioned at the center in a width direction of the base plate portion  42 . Since the metal base plate gasket  41  is structured such as to seal between the wall portion  12  of the casing  11  and the cover  31  over a whole periphery, the metal base plate gasket is formed as an endless shape while being provided with the same plane shape as a plane shape of the wall portion  12  as shown in  FIG. 3A , and the full bead  43  is also formed as an endless shape in the same manner. Further, the metal base plate gasket  41  is formed as a laminated type gasket in which a rubber layer  45  is attached to both surfaces in the thickness direction of the metal plate  44  as shown in  FIG. 3B  so as to enhance a sealing performance between the wall portion  12  and the cover  31 , however, may be formed as a single layer type gasket which is constructed only by the metal plate  44  by omitting the rubber layer  45 . 
         [0112]    The metal base plate gasket  41  is installed so as to direct a bulge (a circular arc bulge) constructed by the full bead  43  to the cover  31  (upward in  FIG. 1 ), and is pinched in this state. Therefore, one seal line  51  (not shown) constructed by a top portion of the bead circular arc is formed in an upper surface of the metal base plate gasket  41  in relation to the cover  31  above the gasket, at the pinching time. Further, two seal lines S 2  which are parallel to each other and are constructed by both ends of the bead circular arc are formed in a lower surface of the metal base plate gasket  41  in relation to the wall portion  12  below the gasket, and two seal lines S 3  which are parallel to each other and are constructed by both ends of the bead circular arc are formed in relation to the grommet  21  below the gasket in the same manner, as shown in  FIG. 5 . The seal lines S 2  and the seal lines S 3  are continuously provided with each other. Further, a series of groove-like concave portion  46  is formed by a depression in the inner side of the bead circular arc, on the lower surface of the gasket  41 , and the groove-like concave portion  46  is sandwiched in its both sides in a width direction by two seal lines S 2  and S 3 . 
         [0113]    In the case that the seal structure having the constructing elements is assembled, and the grommet  21  and the metal base plate gasket  41  are pinched in a vertical direction between the casing  11  and the cover  31 , the seal projection  24  provided in a thickness surface of the grommet  21  (a pair of right and left side surfaces  21   c  and the bottom surface  21   e ) comes into close contact with the inner surface  13   c  of the grommet installation portion  13 . As a result, the wall portion  12  of the casing  11  and the grommet  21  are sealed therebetween. The grommet  21  and the metal base plate gasket  41 , the wall portion  12  of the casing  11  and the metal base plate gasket  41 , and the metal base plate gasket  41  and the cover  31  are respectively sealed therebetween on the basis of the close contact by the pinching. 
         [0114]    Further, since a position where respective surfaces of the wall portion  12  of the casing  11 , the grommet  21  and the metal base plate gasket  41  intersect is formed as a section where three surfaces are joined together, there is fear that a gap is generated in the corner portion, however, in the seal structure having the structure mentioned above, the protruding portion  25  is formed in the end portion of the seal projection  24 , and the protruding portion  25  is closely compressed within the groove-like concave portion  46  in the metal base plate gasket  41  at the pinching time, as shown in  FIGS. 4A and 4B . As a result, since the protruding portion  25  securely comes into contact with the metal base plate gasket  41 , a gap is not generated. 
         [0115]    Accordingly, since the gap is not generated in the corner portion of the section where three surfaces are joined together, and a sealing performance can be secured over a whole periphery of the thickness surface of the grommet  21 , it is possible to provide the three-surface seal structure which can achieve an excellent sealing performance. 
         [0116]    With regard to the seal projection  24 , the seal projection  24  is continuously provided in a pair of right and left side surfaces  21   c  and the bottom surface  21   e  in the thickness surface of the grommet  21  in the embodiment mentioned above, however, the seal projection  24  may be continuously provided in the upper surface  21   d  in addition to a pair of right and left side surfaces  21   c  and the bottom surface  21   e . In this case, since a position where the seal projection provided in the side surfaces  21   c  and the seal projection provided in the upper surface  21   d  intersect protrudes further upward from the seal projection provided in the upper surface  21   d  at the pinching time, this position is utilized as the protruding portion  25 . 
         [0117]    As an example of this, in  FIG. 2D , the seal projection  24  is continuously provided in the upper surface  21   d  in addition to a pair of right and left side surfaces  21   c  and the bottom surface  21   e , and the seal projection  24  is provided as an endless shaped structure over a whole periphery of the thickness surface of the grommet  21  (a pair of right and left side surfaces  21   c , the bottom surface  21   e  and the upper surface  21   d ). 
         [0118]    Further, in the embodiment mentioned above, with regard to the metal base plate gasket  41 , the full bead  43  having the circular arc shaped cross section is provided by applying a press molding to the planate base plate portion  42 , however, two seal beads  47  made of a rubber-like elastic material may be alternatively adhered in parallel to one surface in a thickness direction of the planate base plate portion  42  as shown in  FIG. 3C . In this case, since two seal lines are formed by two seal beads  47  and the groove-like concave portion  46  is formed by a depression between two seal beads  47 , the metal base plate gasket  41  is installed so that two seal beads  47  are directed to the wall portion  12  of the casing  11  and the grommet  21 . In the example in  FIG. 3C , since the metal base plate gasket  41  is formed as the laminated type gasket in which the rubber layer  45  is attached to both surfaces in the thickness direction of the metal plate  44 , two seal beads  47  are integrally provided in one rubber layer  45 , however, in the case that the rubber layer  45  is omitted, the seal beads  47  are directly adhered to the metal plate  44 . 
         [0119]    Further, although an illustration will be omitted, the metal base plate gasket may be structured such that two full beads each having a circular arc shaped cross section are provided in a planate base plate portion. In this case, since two seal lines are formed by top portions of the bead circular arcs and the groove-like concave portion is formed by the depression between two full beads, the metal base plate gasket is installed so that a bulge formed by the full beads is directed to the wall portion  12  of the casing  11  and the grommet  21 . 
         [0120]    Further, with regard to the notch-like grommet installation portion  13  provided in the casing  11 , there can be thought that a chamfer portion  14  is provided in an edge portion of the inner surface  13   c  in the grommet installation portion  13  (a portion where the upper surface  12   a  of the wall portion  12  intersects the inner surface  13   c  of the grommet installation portion  13 ) as shown in  FIG. 6A  so as to facilitate a grommet installing work. In this case, the seal projection  24  is not sufficiently compressed in the position at which the seal projection  24  faces to the chamfer portion  14 , in the case that a cross sectional shape of the seal projection  24  is uniform over a whole length of the seal projection  24 . As a result, there is fear that a sealing performance of the portion is hard to be secured, and the protruding portion  25  is hard to be formed. Therefore, in order to devise a countermeasure thereof, it is preferable to set a cross sectional shape (a cross sectional area) of the position facing to the chamfer portion  14  in the seal projection  24  to a shape which is enlarged little by little in correspondence to the shape of the chamfer portion  14 , and make this position be sufficiently compressed by the chamfer portion  14 . The position facing to the chamfer portion  14  in the seal projection  24  is formed so that its cross sectional shape becomes larger in correspondence to an enlargement of the distance between the grommet  21  and the casing  11 . 
         [0121]    As an example thereof, in  FIG. 6B , the seal projection  24  is provided in the side surface  21   c  of the grommet  21 , and an overhanging portion  26  overhanging toward the chamfer portion  14  (toward a lateral direction) is provided at a position facing to the chamfer portion  14  in the seal projection  24 . As a result, the cross sectional shape of this position is formed as a shape which is enlarged little by little in correspondence to the shape of the chamfer portion  14 . 
         [0122]    Further, in an example in  FIG. 6C , the seal projection  24  is provided in the side surfaces  21   c  and the upper surface  21   d  of the grommet  21 , and an overhanging portion  26  overhanging toward the chamfer portion  14  (toward a diagonally upward side) is provided at a position facing to the chamfer portion  14  in the seal projection  24 . As a result, the cross sectional shape of this position is formed as a shape which is enlarged little by little in correspondence to the shape of the chamfer portion  14 . 
         [0123]    Therefore, according to these structures, even in the case that the chamfer portion  14  is provided in the edge portion of the inner surface  13   c  in the grommet installation portion  13 , it is possible to securely seal between the wall portion  12  of the casing  11  and the grommet  21 , and it is possible to securely form the protruding portion  25  by the seal projection  24 . 
       Second Embodiment 
       [0124]      FIG. 7  shows a state before assembling a seal structure according to a second embodiment of the present invention, and a casing  11 , a grommet  21 , a cover  31  and a metal base plate gasket  141  are drawn.  FIGS. 8A ,  8 B and  8 C are views of a single part of the grommet  21 ,  FIGS. 9A ,  9 B and  9 C are views of a single part of the metal base plate gasket  141 ,  FIGS. 10A and 10B  and  FIG. 11A  are explanatory views of the seal structure. The seal structure according to the embodiment is structured such as to seal a section where three surfaces are joined together in an electric equipment device and an engine, and may be also called as a three-surface seal in the light of its function. 
         [0125]    The casing  11  is formed by a rigid member such as a predetermined metal or a hard resin, and is provided with a vertically planate wall portion  12  as a rising portion in a side wall of the casing, and a notch-like grommet installation portion  13  is provided in the wall portion  12  so as to pass through in a wall portion thickness direction. The grommet installation portion  13  is open to an upper surface  12   a  of the wall portion  12 . The grommet installation portion  13  is an insertion port of a harness or a piping in the electronic equipment device and the engine, and is sealed its opening by installing the grommet  21  thereto. Accordingly, in the present invention, the insertion port is called as a grommet installation portion. A front elevational shape of the grommet installation portion  13  is formed as a U-shaped form, that is, formed such a shape that is provided with a pair of right and left linear portions  13   a  which are parallel to each other and a curved portion  13   b  which is formed as a circular arc shape in a bottom portion, however, may be formed as the other shapes. For example, a pair of right and left linear portions  13   a  may be formed as an inverted trapezoidal shape that a width (a distance) is enlarged little by little toward the above. Further, it is possible to employ a shape which is provided only with the curved portion without any linear portion as shown in  FIG. 20 , as long as a protruding portion  25  by a seal projection  24  mentioned later can be formed. 
         [0126]    The grommet  21  is formed by a predetermined rubber-like elastic body, and is formed as a block shape which approximately has the same shape and the same magnitude as a volumetric capacity shape of the grommet installation portion  13  for sealing the grommet installation portion  13  serving as the insertion port by being closely installed thereto. In the illustrated embodiment, since the grommet installation portion  13  is formed as a U-shaped form in its front surface as mentioned above, the grommet  21  is formed as a block shape which is provided with six surfaces constituted by a planate front surface  21   a , a back surface  21   b , a pair of right and left side surfaces  21   c , an upper surface  21   d  and a curved bottom surface  21   e  in correspondence to the grommet installation portion  13 . A through hole  22  for inserting the harness or the piping is provided in the center of a front surface of the grommet  21  so as to pass through in a grommet thickness direction. A sleeve  23  made of a rigid material for fitting the piping is installed to an inner peripheral surface of the through hole  22 , however, the sleeve  23  may be omitted. 
         [0127]    Further, one continuous seal projection  24  is provided in a surface facing to the inner surface  13   c  of the grommet installation portion  13  in the grommet  21 , that is, a pair of right and left side surfaces and the curved bottom surface  21   e  so as to be positioned at the center in the grommet thickness direction, and the seal projection  24  is provided over a whole length in an arranging direction of three surfaces  21   c  and  21   e . Therefore, one end portion  24   a  of the seal projection  24  is arranged in an upper side portion of one side surface  21   c , and the other end portion  24   a  is arranged in an upper side portion of the other side surface  21   c . As a result, the formation of the protruding portion  25  mentioned later is facilitated. 
         [0128]    The seal projection  24  is compression deformed in the case that the seal projection is pressed to the inner surface  13   c  of the grommet installation portion  13 , comes into close contact with the inner surface  13   c  of the grommet installation portion  13  on the basis of a reaction force generated at that time, and seals between the wall portion  12  and the grommet  21 . Further, the seal projection  24  is compression deformed in the case that the seal projection is pressed to the inner surface  13   c  of the grommet installation portion  13 , and the end portion  24   a  protrudes upward from the upper surfaces  12   a  and  21   d  of the wall portion  12  and the grommet  21  as shown in  FIG. 10A  at that time, thereby forming the protruding portion  25 . In order to securely form the protruding portion  25 , it is preferable to carry out an installing work from a direction which is opposite to a protruding direction of the protruding portion  25  in the case that the grommet  21  is installed to the grommet installation portion  13 , and this direction is the same direction as a direction in which the cover  31  is put on the casing  11  (in other words, the grommet  21  is installed to the grommet installation portion  13  from the above in place of back and front sides in  FIG. 7 ). 
         [0129]    The metal base plate gasket  141  is structured such as to be interposed between the wall portion  12  of the casing  11  and the grommet  21 , and the cover  31 , and is provided with a planate base plate portion  142 , a width of the base plate portion  142  is made approximately equal to a width of the upper surface  12   a  of the wall portion  12 , one full bead  143  having a circular arc shaped cross section and branch portions  144  obtained by branching one full bead  143  into two sections and having a Y-shaped plane are integrally provided in a surface facing to the wall portion  12  at the installing time in a gasket longitudinal direction in the base plate portion  142 , and two full beads  145  continuously arranged from the branch portions  144  are integrally provided in a surface facing to the grommet  21 . Further, since the branch portions  144  provided in the surface facing to the wall portion  12  are respectively provided in both sides while sandwiching the surface facing to the grommet  21  therebetween, and are provided so as to be opposed to each other, two full beads  145  are provided so as to connect a pair of branch portions  144 . Since the metal base plate gasket  141  is structured such as to seal between the wall portion  12  of the casing  11  and the cover  31  over a whole periphery, the metal base plate gasket is formed as an endless shape while being provided with the same plane shape as a plane shape of the wall portion  12  as shown in  FIG. 9A , and the bead portion constructed by one full bead  143 , the branch portions  144  and two full beads  145  is also formed as an endless shape in the same manner. Further, the metal base plate gasket  141  is formed as a laminated type gasket in which a rubber layer  147  is attached to both surfaces in the thickness direction of a metal plate  146  as shown in  FIGS. 9B and 9C  so as to enhance a sealing performance between the wall portion  12  and the cover  31 , however, may be formed as a single layer type gasket which is constructed only by the metal plate  146  by omitting the rubber layer  147 . 
         [0130]    The metal base plate gasket  141  is installed in a state in which the bulge (the circular arc shaped bulge) constructed by the full beads  143  and  145  and the branch portion  144  is directed to the wall portion  12  of the casing  11  and the grommet  21  (a downward direction in  FIG. 7 ), and is pinched in the state. Accordingly, as shown in  FIG. 11A , one seal line  51  constructed by a top portion of one full bead  143  and a branch portion line S 2  constructed by a top portion of the branch portion  144  and having a Y-shaped plane are formed in a surface facing to the wall portion  12  in a lower surface of the metal base plate gasket  141 , and two seal lines S 3  constructed by respective top portions of two full beads  145  are formed in a surface facing to the grommet  21 , at the pinching time. Further, they are continuously provided as illustrated. Further, a concave portion  148  is formed in a lower surface of the gasket  141  so as to be surrounded by the branch portion  144  and two full beads  145 , and the concave portion  148  is structured such that its periphery is surrounded by the branch portion line S 2  and two seal lines S 3 , as shown in  FIG. 11A . Therefore, the concave portion  148  is finite in a gasket longitudinal direction, its end portion in the longitudinal direction is arranged so as to face to the wall portion  12  in place of the grommet  21 , and the protruding portion  25  constructed by the seal projection  24  is accordingly arranged just inside the branch portion  144  within the concave portion  148 . Further, a plane shape of the end portion in the longitudinal direction of the concave portion  148  is formed as a V-shaped plane narrowing forward in connection with the Y-shaped plane of the plane shape in the branch portion  144 . 
         [0131]    In the case that the seal structure having the constructing elements is assembled, and the grommet  21  and the metal base plate gasket  141  are pinched in a vertical direction between the casing  11  and the cover  31 , the seal projection  24  provided in a thickness surface of the grommet  21  (a pair of right and left side surfaces  21   c  and the bottom surface  21   e ) comes into close contact with the inner surface  13   c  of the grommet installation portion  13 . As a result, the wall portion  12  of the casing  11  and the grommet  21  are sealed therebetween. The grommet  21  and the metal base plate gasket  141 , the wall portion  12  of the casing  11  and the metal base plate gasket  141 , and the metal base plate gasket  141  and the cover  31  are respectively sealed therebetween on the basis of the close contact by the pinching. 
         [0132]    Further, since a position where respective surfaces of the wall portion  12  of the casing  11 , the grommet  21  and the metal base plate gasket  141  intersect is formed as a section where three surfaces are joined together, there is fear that a gap is generated in the corner portion, however, in the seal structure having the structure mentioned above, the protruding portion  25  is formed in the end portion of the seal projection  24 , and the protruding portion  25  is closely compressed within the concave portion  148  in the metal base plate gasket  141  at the pinching time, as shown in  FIGS. 10A and 10B . As a result, since the protruding portion  25  securely comes into contact with the metal base plate gasket  141 , a gap is not generated. 
         [0133]    Further, in the embodiment according to the present invention, since the branch portion  144  having the Y-shaped plane is provided in the metal base plate gasket  141 , and the branch portion  144  is structured such as to compress the protruding portion  25  of the seal projection  24  in its inner side, the bifurcated branch portion  144  presses the protruding portion  25  toward the center in a grommet width direction on the basis of the application of the pinching force (since the protruding portion  25  is pressed to the end portion in the longitudinal direction of the concave portion  148  having the V-shaped plane, the protruding portion  25  is pressed toward the center in the grommet width direction (a lateral direction in  FIG. 11A ) by the branch portion  144  as shown by an arrow H in  FIG. 11A ). Therefore, since a reaction force to the pressing force (a reaction force toward the end portion in the grommet width direction) is generated in the protruding portion  25 , it is possible to further effectively inhibit the gap from being formed. 
         [0134]    Accordingly, since the gap is not generated in the corner portion of the section where three surfaces are joined together, and a sealing performance can be secured over a whole periphery of the thickness surface of the grommet  21 , it is possible to provide the three-surface seal structure which can achieve an excellent sealing performance. 
         [0135]    With regard to the seal projection  24 , the seal projection  24  is continuously provided in a pair of right and left side surfaces  21   c  and the bottom surface  21   e  in the thickness surface of the grommet  21  in the embodiment mentioned above, however, the seal projection  24  may be continuously provided in the upper surface  21   d  in addition to a pair of right and left side surfaces  21   c  and the bottom surface  21   e . In this case, since a position where the seal projection provided in the side surfaces  21   c  and the seal projection provided in the upper surface  21   d  intersect protrudes further upward from the seal projection provided in the upper surface  21   d  at the pinching time, this position is utilized as the protruding portion  25 . 
         [0136]    As an example of this, in  FIG. 8D , the seal projection  24  is continuously provided in the upper surface  21   d  in addition to a pair of right and left side surfaces  21   c  and the bottom surface  21   e , and the seal projection  24  is provided as an endless shaped structure over a whole periphery of the thickness surface of the grommet  21  (a pair of right and left side surfaces  21   c , the bottom surface  21   e  and the upper surface  21   d ). 
         [0137]    Further, in the embodiment mentioned above, with regard to the metal base plate gasket  141 , the bead portion constructed by one full bead  143 , the branch portion  144  and two full beads  145  is provided by applying a press molding to the planate base plate portion  142 , however, seal beads  149  made of a rubber-like elastic material may be alternatively provided on one surface in a thickness direction of the planate base plate portion  142  according to the same plane layout, as shown in  FIG. 9D . In the example in  FIG. 9D , since the metal base plate gasket  141  is formed as the laminated type gasket in which the rubber layer  147  is attached to both surfaces in the thickness direction of the metal plate  146 , the seal beads  149  are integrally provided in one rubber layer  147 , however, in the case that the rubber layer  147  is omitted, the seal beads  149  are directly adhered to the metal plate  146 . 
         [0138]    Further, in the embodiment mentioned above, with regard to the metal base plate gasket  141 , two full beads  145  which are continuously provided from the branch portion  144  are arranged in the surface facing to the grommet  21 , and two seal lines S 3  are formed by these two full beads  145 , however, these two full beads  145  and two seal lines S 3  may be converted into one within the surface facing to the grommet  21  as shown in  FIG. 11B . In this case, the concave portion  148  housing the protruding portion  25  is set at two positions in the gasket longitudinal direction. 
         [0139]    Further, with regard to the notch-like grommet installation portion  13  provided in the casing  11 , there can be thought that a chamfer portion  14  is provided in an edge portion of the inner surface  13   c  in the grommet installation portion  13  (a portion where the upper surface  12   a  of the wall portion  12  intersects the inner surface  13   c  of the grommet installation portion  13 ) as shown in  FIG. 12A  so as to facilitate a grommet installing work. In this case, the seal projection  24  is not sufficiently compressed in the position at which the seal projection  24  faces to the chamfer portion  14 , in the case that a cross sectional shape of the seal projection  24  is uniform over a whole length of the seal projection  24 . As a result, there is fear that a sealing performance of the portion is hard to be secured, and the protruding portion  25  is hard to be formed. Therefore, in order to devise a countermeasure thereof, it is preferable to set a cross sectional shape (a cross sectional area) of the position facing to the chamfer portion  14  in the seal projection  24  to a shape which is enlarged little by little in correspondence to the shape of the chamfer portion  14 , and make this position be sufficiently compressed by the chamfer portion  14 . The position facing to the chamfer portion  14  in the seal projection  24  is formed so that its cross sectional shape becomes larger in correspondence to an enlargement of the distance between the grommet  21  and the casing  11 . 
         [0140]    As an example thereof, in  FIG. 12B , the seal projection  24  is provided in the side surface  21   c  of the grommet  21 , and an overhanging portion  26  overhanging toward the chamfer portion  14  (toward a lateral direction) is provided at a position facing to the chamfer portion  14  in the seal projection  24 . As a result, the cross sectional shape of this position is formed as a shape which is enlarged little by little in correspondence to the shape of the chamfer portion  14 . 
         [0141]    Further, in an example in  FIG. 12C , the seal projection  24  is provided in the side surfaces  21   c  and the upper surface  21   d  of the grommet  21 , and an overhanging portion  26  overhanging toward the chamfer portion  14  (toward a diagonally upward side) is provided at a position facing to the chamfer portion  14  in the seal projection  24 . As a result, the cross sectional shape of this position is formed as a shape which is enlarged little by little in correspondence to the shape of the chamfer portion  14 . 
         [0142]    Therefore, according to these structures, even in the case that the chamfer portion  14  is provided in the edge portion of the inner surface  13   c  in the grommet installation portion  13 , it is possible to securely seal between the wall portion  12  of the casing  11  and the grommet  21 , and it is possible to securely form the protruding portion  25  by the seal projection  24 . 
       Third Embodiment 
       [0143]      FIG. 13  shows a state before assembling a seal structure according to a third embodiment of the present invention, and a casing  11 , a grommet  21 , a cover  31  and a rubber single body gasket  241  are drawn.  FIGS. 14A ,  14 B and  14 C are views of a single part of the grommet  21 ,  FIGS. 15A ,  15 B and  15 C are view of a single part of the rubber single body gasket  241 ,  FIGS. 18A and 18B  and  FIG. 19A  are explanatory views of the seal structure. The seal structure according to the embodiment is structured such as to seal a section where three surfaces are joined together in an electric equipment device and an engine, and may be also called as a three-surface seal in the light of its function. 
         [0144]    The casing  11  is formed by a rigid member such as a predetermined metal or a hard resin, and is provided with a vertically planate wall portion  12  as a rising portion in a side wall of the casing, and a notch-like grommet installation portion  13  is provided in the wall portion  12  so as to pass through in a wall portion thickness direction. The grommet installation portion  13  is open to an upper surface  12   a  of the wall portion  12 . The grommet installation portion  13  is an insertion port of a harness or a piping in the electronic equipment device and the engine, and is sealed its opening by installing the grommet  21  thereto. Accordingly, in the present invention, the insertion port is called as a grommet installation portion. A front elevational shape of the grommet installation portion  13  is formed as a U-shaped form, that is, formed such a shape that is provided with a pair of right and left linear portions  13   a  which are parallel to each other and a curved portion  13   b  which is formed as a circular arc shape in a bottom portion, however, may be formed as the other shapes. For example, a pair of right and left linear portions  13   a  may be formed as an inverted trapezoidal shape that a width (a distance) is enlarged little by little toward the above. Further, it is possible to employ a shape which is provided only with the curved portion without any linear portion as shown in  FIG. 20 , as long as a protruding portion  25  by a seal projection  24  mentioned later can be formed. 
         [0145]    The grommet  21  is formed by a predetermined rubber-like elastic body, and is formed as a block shape which approximately has the same shape and the same magnitude as a volumetric capacity shape of the grommet installation portion  13  for sealing the grommet installation portion  13  serving as the insertion port by being closely installed thereto. In the illustrated embodiment, since the grommet installation portion  13  is formed as a U-shaped form in its front surface as mentioned above, the grommet  21  is formed as a block shape which is provided with six surfaces constituted by a planate front surface  21   a , a back surface  21   b , a pair of right and left side surfaces  21   c , an upper surface  21   d  and a curved bottom surface  21   e  in correspondence to the grommet installation portion  13 . A through hole  22  for inserting the harness or the piping is provided in the center of a front surface of the grommet  21  so as to pass through in a grommet thickness direction. A sleeve  23  made of a rigid material for fitting the piping is installed to an inner peripheral surface of the through hole  22 , however, the sleeve  23  may be omitted. 
         [0146]    Further, one continuous seal projection  24  is provided in a surface facing to the inner surface  13   c  of the grommet installation portion  13  in the grommet  21 , that is, a pair of right and left side surfaces and the curved bottom surface  21   e  so as to be positioned at the center in the grommet thickness direction, and the seal projection  24  is provided over a whole length in an arranging direction of three surfaces  21   c  and  21   e . Therefore, one end portion  24   a  of the seal projection  24  is arranged in an upper side portion of one side surface  21   c , and the other end portion  24   a  is arranged in an upper side portion of the other side surface  21   c . As a result, the formation of the protruding portion  25  mentioned later is facilitated. 
         [0147]    The seal projection  24  is compression deformed in the case that the seal projection is pressed to the inner surface  13   c  of the grommet installation portion  13 , comes into close contact with the inner surface  13   c  of the grommet installation portion  13  on the basis of a reaction force generated at that time, and seals between the wall portion  12  and the grommet  21 . Further, the seal projection  24  is compression deformed in the case that the seal projection is pressed to the inner surface  13   c  of the grommet installation portion  13 , and the end portion  24   a  protrudes upward from the upper surfaces  12   a  and  21   d  of the wall portion  12  and the grommet  21  as shown in  FIG. 18A  at that time, thereby forming the protruding portion  25 . In order to securely form the protruding portion  25 , it is preferable to carry out an installing work from a direction which is opposite to a protruding direction of the protruding portion  25  in the case that the grommet  21  is installed to the grommet installation portion  13 , and this direction is the same direction as a direction in which the cover  31  is put on the casing  11  (in other words, the grommet  21  is installed to the grommet installation portion  13  from the above in place of back and front sides in  FIG. 13 ). 
         [0148]    The rubber single body gasket  241  is structured such as to be interposed between the wall portion  12  of the casing  11  and the grommet  21 , and the cover  31 , and is previously installed to a gasket installation groove  32  which is provided in the cover  31 . 
         [0149]    Further, the rubber single body gasket  241  is formed as an O-ring shape having a circular cross section as shown in  FIGS. 15A and 15B , a gasket single portion  242  and branch portions  243  obtained by branching the gasket single portion  242  into two sections and having a Y-shaped plane are integrally provided in a portion facing to the wall portion  12  at the installing time in a gasket longitudinal direction, and gasket double portions  244  continuously arranged from the branch portions  243  are integrally provided in a portion facing to the grommet  21 . Further, since the branch portions  243  provided in the surface facing to the wall portion  12  are respectively provided in both sides while sandwiching the portion facing to the grommet  21  therebetween, and are provided so as to be opposed to each other, the gasket double portions  244  are provided so as to connect a pair of branch portions  243 . Accordingly, a portion surrounded by a pair of branch portions  243  and the gasket double portions  244  is formed as a space portion  245  which passes through in a gasket height direction. Since the rubber single body gasket  241  is structured such as to seal between the wall portion  12  of the casing  11  and the cover  31  over a whole periphery, the rubber single body gasket is formed as an endless shape while being provided with the same plane shape as a plane shape of the wall portion  12  as shown in  FIG. 15A . As a result, the gasket installation groove  32  to which the rubber single body gasket  241  is installed is also formed as an endless shape in the same manner, however, in a portion to which the gasket double portions  244  are installed, two grooves are provided as shown in  FIG. 15C  or a groove width is enlarged as shown in  FIG. 15D . 
         [0150]    The rubber single body gasket  241  is installed to the gasket installation groove  32  as shown in  FIGS. 15B ,  15 C and  15 D, and is pinched in the state. Accordingly, as shown in  FIG. 19A , one seal line  51  constructed by the gasket single portion  242  and branch portion lines S 2  constructed by the branch portions  243  and having a Y-shaped plane are formed in a surface facing to the wall portion  12  in a lower surface of the rubber single body gasket  241 , and two seal lines S 3  constructed by the gasket double portions  244  are formed in a surface facing to the grommet  21 , at the pinching time. Further, they are continuously provided as illustrated. Further, the space portion  245  is surrounded by the branch portion lines S 2  and two seal lines S 3 . Therefore, the space portion  245  is finite in the gasket longitudinal direction, and the end portions in the longitudinal direction are arranged so as to face to the wall portion  12  in place of the grommet  21 , and the protruding portion  25  constructed by the seal projection  24  is accordingly arranged just inside the branch portion  243  within the space portion  245 . Further, a plane shape of the end portions in the longitudinal direction of the space portion  245  is formed as a V-shaped plane narrowing forward in connection with the Y-shaped plane of the plane shape in the branch portion  243 . 
         [0151]    In the case that the seal structure having the constructing elements is assembled, and the grommet  21  and the rubber single body gasket  241  are pinched in a vertical direction between the casing  11  and the cover  31 , the seal projection  24  provided in a thickness surface of the grommet  21  (a pair of right and left side surfaces  21   c  and the bottom surface  21   e ) comes into close contact with the inner surface  13   c  of the grommet installation portion  13 . As a result, the wall portion  12  of the casing  11  and the grommet  21  are sealed therebetween. The grommet  21  and the rubber single body gasket  241 , the wall portion  12  of the casing  11  and the rubber single body gasket  241 , and the rubber single body gasket  241  and the cover  31  are respectively sealed therebetween on the basis of the close contact by the pinching. 
         [0152]    Further, since a position where respective surfaces of the wall portion  12  of the casing  11 , the grommet  21  and the rubber single body gasket  241  intersect is formed as a section where three surfaces are joined together, there is fear that a gap is generated in the corner portion, however, in the seal structure having the structure mentioned above, the protruding portion  25  is formed in the end portion of the seal projection  24 , and the protruding portion  25  is closely compressed within the space portion  245  in the rubber single body gasket  241  at the pinching time, as shown in  FIGS. 18A and 18B . As a result, since the protruding portion  25  securely comes into contact with the rubber single body gasket  241 , a gap is not generated. 
         [0153]    Further, in the embodiment according to the present invention, since the branch portion  243  having the Y-shaped plane is provided in the rubber single body gasket  241 , and the branch portion  243  is structured such as to compress the protruding portion  25  of the seal projection  24  in its inner side, the bifurcated branch portion  243  presses the protruding portion  25  toward the center in a grommet width direction on the basis of the application of the pinching force (since the protruding portion  25  is pressed to the end portion in the longitudinal direction of the space portion  245  having the V-shaped plane, the protruding portion  25  is pressed toward the center in the grommet width direction (a lateral direction in  FIG. 19A ) by the branch portion  144  as shown by an arrow M in  FIG. 19A ). Therefore, since a reaction force to the pressing force (a reaction force toward the end portion in the grommet width direction) is generated in the protruding portion  25 , it is possible to further effectively inhibit the gap from being formed. 
         [0154]    Accordingly, since the gap is not generated in the corner portion of the section where three surfaces are joined together, and a sealing performance can be secured over a whole periphery of the thickness surface of the grommet  21 , it is possible to provide the three-surface seal structure which can achieve an excellent sealing performance. 
         [0155]    With regard to the seal projection  24 , the seal projection  24  is continuously provided in a pair of right and left side surfaces  21   c  and the bottom surface  21   e  in the thickness surface of the grommet  21  in the embodiment mentioned above, however, the seal projection  24  may be continuously provided in the upper surface  21   d  in addition to a pair of right and left side surfaces  21   c  and the bottom surface  21   e . In this case, since a position where the seal projection provided in the side surfaces  21   c  and the seal projection provided in the upper surface  21   d  intersect protrudes further upward from the seal projection provided in the upper surface  21   d  at the pinching time, this position is utilized as the protruding portion  25 . 
         [0156]    As an example of this, in  FIG. 14D , the seal projection  24  is continuously provided in the upper surface  21   d  in addition to a pair of right and left side surfaces  21   c  and the bottom surface  21   e , and the seal projection  24  is provided as an endless shaped structure over a whole periphery of the thickness surface of the grommet  21  (a pair of right and left side surfaces  21   c , the bottom surface  21   e  and the upper surface  21   d ). 
         [0157]    Further, in the embodiment mentioned above, the rubber single body gasket  241  is constructed by the O-ring shape having the circular cross section, however, a shape (a cross sectional shape and/or a plane shape) of the rubber single body gasket  241  is not particularly limited, but may employ, for example, the following shapes. 
         [0158]    In a gasket  241  shown in  FIG. 16 , an attaching portion  246  having a rectangular cross sectional shape is provided, and the attaching portion  246  is bifurcated in a part in the gasket longitudinal direction. As a result, the gasket single portion  242 , a pair of branch portions  243 , the gasket double portions  244  and the space portion  245  are formed. Further, a seal lip  247  for enhancing a seal surface pressure is provided in a lower surface of the attaching portion  246 . 
         [0159]    In a gasket  241  shown in  FIGS. 17A ,  17 B and  17 C, an attaching portion having a rectangular cross sectional shape is provided, a seal lip  247  is provided in a lower surface of the attaching portion  246 , and the seal lip  247  is bifurcated in a part in the gasket longitudinal direction. As a result, the one seal line  51 , the branch portion lines S 2  and two seal lines S 3  are formed, and a closed-end concave portion  248  is formed in place of the space portion  245  (the attaching portion  246  is formed one over its whole length (whole periphery), and only the seal lip  247  is bifurcated in a part in the gasket longitudinal direction). 
         [0160]    Further, in the embodiment mentioned above, with regard to the rubber single body gasket  241 , the gasket double portions  244  continuously provided from the branch portions  243  are arranged in the surface facing to the grommet  21 , and two seal lines S 3  are formed by the gasket double portions  244 , however, the gasket double portions  244  and two seal lines S 3  may be converged into one within the surface facing to the grommet  21  as shown in  FIG. 19B . In this case, the space portion  245  (or the concave portion  248 ) housing the protruding portion  25  is set at two positions in the gasket longitudinal direction.