Abstract:
Provided is a metal gasket, which is capable of limiting localized decreases in contact pressure of the seal bead and of securing superior sealing over long periods. In order to achieve said purpose, the invention is a metal gasket, in which an opening that is open in the shape of the opening of the space to be sealed and a seal bead that extends along the perimeter of the opening are formed in a metal plate. The seal bead is one in which two or more portions from among half bead portions, fold-up bead portions and full bead portions are continuous with each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/JP2013/061144 filed on Apr. 15, 2013, and published in Japanese as WO 201 3/1 61 596 Al on Oct. 31, 2013. This application claims priority to Japanese Application No. 2012-102392 filed on Apr. 27, 2012. The entire 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 metal gasket which is used as a seal means of a joint portion between an exhaust manifold and an exhaust pipe of an internal combustion engine and a joint portion between a cylinder block and a cylinder head, and a manufacturing method of the metal gasket. 
         [0004]    2. Description of the Conventional Art 
         [0005]    A metal gasket which is used as a seal means of a joint portion between an exhaust manifold and an exhaust pipe of an internal combustion engine or between an intake manifold and an intake pipe is pinched between joint surfaces which faces to each other, and is structured such as to seal exhaust gas and air-fuel mixture of air and fuel by a seal bead which is bending formed so as to surround an opening portion which is open to the joint surface. 
         [0006]    Here, in the case of the exhaust manifold and the intake manifold, an opening shape in the joint portion in relation to the exhaust pipe or the intake pipe is non-circular shapes (for example, a rectangular ring shape), and a metal gasket having a seal bead formed into a similar shape to the opening shape is used in this portion (refer, for example, to Japanese Unexamined Patent Publication No. 08-014394). However, the metal gasket tends to deform in a portion in which the seal bead extends linearly rather than a portion extending like a curve, when the metal gasket is exposed to a fastening load. Accordingly, there is a problem that leakage tends to be generated in the linear portion of the seal bead due to lack of surface pressure. In order to solve the problem mentioned above, it has been known to secure the necessary surface pressure by enlarging a width and a height of the seal bead in the portion in which the surface pressure short tends to be generated, thereby enhancing a rigidity (refer, for example, to Japanese Unexamined Patent Publication No. 08-159284). 
       SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
       [0007]    However, according to the prior art, since a cross sectional shape itself of the seal bead is approximately the same, a range of the surface pressure which can be adjusted by changing the width or the height of the seal bead is small. 
         [0008]    The present invention is made by taking the points mentioned above into consideration, and a technical object of the present invention is to provide a metal gasket which can secure an excellent sealing performance over a long period of time by suppressing partial reduction of the surface pressure of the seal bead. 
       Means for Solving the Problem 
       [0009]    As a means for effectively solving the technical problem mentioned above, according to the invention of a first aspect, there is provided a metal gasket comprising:
       a metal plate;   an opening portion which is provided like an opening shape of a space to be sealed;   a seal bead which extends along a periphery of the opening portion; and   the opening portion and the seal bead being formed in the metal plate,   wherein the seal bead is structured such that two or more portions among a portion constructed by a half bead, a portion constructed by a flip-up bead and a portion constructed by a full bead are connected to each other.       
 
         [0015]    The term “half bead” here is a protruding shaped bead which forms an end edge of a ridge portion in an opening edge portion of the metal plate and is constructed by a one-side inclined surface, the flip-up bead is a protruding shaped bead which runs to the other inclined surface portion from one bottom portion via one inclined surface portion and the ridge portion, and the full bead is a protruding shaped bead which is formed like a chevron shape in its cross sectional shape, and runs to the other bottom portion from one bottom portion via one inclined surface portion, the ridge portion and the other inclined surface portion. 
         [0016]    In the metal gasket having the structure described in the first aspect, spring constant of the seal bead when a fastening load is applied is higher in the portion constructed by the flip-up bead than in the portion constructed by the half bead, and is higher in the portion constructed by the full bead than in the portion constructed by the flip-up bead. As a result, in the case that the seal bead extends along a non-circular opening portion, surface pressure can be suppressed, for example, by constructing a portion in which the surface pressure rises on the basis of great curvature (small radius of curvature) of the seal bead, by the half bead, and reduction of the surface pressure can be suppressed by constructing a portion in which the surface pressure comes down on the basis of small curvature (great radius of curvature) of the seal bead, by the flip-up bead or the full bead. Therefore, it is possible to appropriately adjust the surface pressure. 
         [0017]    According to the invention of a second aspect, there is provided a manufacturing method of a metal gasket comprising:
       a step of forming a bead in a metal plate by a concave mold and a convex mold which are arranged in both sides in a thickness direction of the metal plate; and   a step of forming an opening portion in the metal plate, the opening portion in which an opening edge goes through two or more of a ridge portion, an inclined portion and a bottom portion of the bead.       
 
         [0020]    According to the invention of a third aspect, there is provided a manufacturing method of a metal gasket comprising:
       a step of forming a bead in a metal plate by a concave mold and a convex mold which are arranged in both sides in a thickness direction of the metal plate; and   a step of forming an opening portion in the metal plate, the opening portion in which an opening edge goes through two or more of a ridge portion, an inclined portion and a bottom portion of the bead, the two or more including the ridge portion,   wherein the method previously forms a portion in which the opening edge goes through the ridge portion among the opening portion, before forming the bead.       
 
         [0024]    According to the manufacturing method described in the second or third aspect, the bead formed in the metal plate by the concave mold and the convex mold comes to the half bead in the portion in which the opening edge of the opening portion passes through the ridge portion of the bead, comes to the flip-up bead in the portion in which the opening edge of the opening portion passes through the inclined surface portion of the bead, and comes to the full bead in the portion in which the opening edge of the opening portion passes through the bottom portion of the bead. 
       Effect of the Invention 
       [0025]    On the basis of the metal gasket according to the invention of the first aspect, the spring constant of the seal bead greatly changes among the portion constructed by the half bead, the portion constructed by the flip-up bead and the portion constructed by the full bead. Therefore, an excellent sealing performance can be secured over a long period of time by suppressing dispersion of the surface pressure of the seal bead due to difference in curvature in the case that the seal bead extends non-circularly. 
         [0026]    On the basis of the manufacturing method of the metal gasket according to the invention of the second or third aspect, it is possible to easily manufacture the metal gasket according to the invention of the first aspect. 
     
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         [0027]      FIG. 1  is a plan view showing a preferable embodiment of a metal gasket according to the present invention; 
           [0028]      FIGS. 2A and 2B  are cross sectional views of a substantial part of the embodiment shown in  FIG. 1 , in which  FIG. 2A  is a cross sectional view along a line A-A in  FIG. 1 , and  FIG. 2B  is a cross sectional view along a line B-B in  FIG. 1 ; 
           [0029]      FIG. 3  is a plan view showing a state in which a preliminary hole coming to a part of a port hole portion is previously formed in a metal plate, in a preferable embodiment of a manufacturing method of a metal gasket according to the present invention; 
           [0030]      FIG. 4  is a top elevational view showing a convex mold which is used in the preferable embodiment of the manufacturing method of the metal gasket according to the present invention; 
           [0031]      FIGS. 5A and 5B  are cross sectional views of a substantial part of the convex mold shown in  FIG. 4 , in which  FIG. 5A  is a cross sectional view along a line A-A in  FIG. 4 , and  FIG. 5B  is a cross sectional view along a line B-B in  FIG. 4 ; 
           [0032]      FIG. 6  is a bottom elevational view showing a concave mold which is used in the preferable embodiment of the manufacturing method of the metal gasket according to the present invention; 
           [0033]      FIGS. 7A and 7B  are cross sectional views of a substantial part of the concave mold shown in  FIG. 6 , in which  FIG. 7A  is a cross sectional view along a line A-A in  FIG. 6 , and  FIG. 7B  is a cross sectional view along a line B-B in  FIG. 6 ; 
           [0034]      FIG. 8  is a plan view showing a step of forming a bead in the metal plate by the convex mold and the concave mold, in the preferable embodiment of the manufacturing method of the metal gasket according to the present invention; 
           [0035]      FIGS. 9A and 9B  are cross sectional views of a substantial part of the forming step by the convex mold and the concave mold shown in  FIG. 8 , in which  FIG. 9A  is a cross sectional view along a line A-A in  FIG. 8 , and  FIG. 9B  is a cross sectional view along a line B-B in  FIG. 8 ; and 
           [0036]      FIG. 10  is a plan view showing a step of forming a port hole portion in the metal plate according to a secondary processing, in the preferable embodiment of the manufacturing method of the metal gasket according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0037]    A description will be given of preferable embodiments of a metal gasket and a manufacturing method of the metal gasket according to the present invention with reference to the accompanying drawings. First of all,  FIG. 1  shows the preferable embodiment of the metal gasket according to the present invention, and the metal gasket MG is structured, for example, such as to be interposed between an exhaust manifold of an automotive internal combustion engine and a joint surface of an exhaust pipe. 
         [0038]    The metal plate MG is structured such that a port hole portion  2  and a plurality of bolt insertion holes  3  are provided in a metal plate  1 , and a seal bead  4  extending along a periphery of the port hole portion  2  is formed. The metal plate  1  is constructed by a thin plate which is selected from a stainless steel, a cold-rolled steel, a galvanized sheet iron and an aluminum alloy plate and has an elasticity. The bolt insertion holes  3  are arranged at a plurality of positions between the port hole portion  2  and an outer peripheral edge of the metal plate  1  and are provided for inserting bolts connecting an exhaust manifold and an exhaust pipe which are not shown. 
         [0039]    The port hole portion  2  corresponds to the opening portion described in the first to third aspects, and is formed into a projection geometry of an exhaust gas passage which is constructed by the exhaust manifold and the exhaust pipe, in other words, an approximately oval shape obtained by projecting an opening shape of the exhaust gas passage which is open to joint surfaces of the exhaust manifold and the exhaust pipe. In more detail, an opening edge of the port hole portion  2  is constructed by a pair of semicircular arc shaped opening edges  2   a , and a linear opening edge  2   b  and a gentle curve shaped opening edge  2   c  which extend between the semicircular arc shaped opening edges  2   a.  The gentle curve shaped opening edge  2   c  is structured such as to have much smaller curvature (greater radius of curvature) in comparison with the semicircular arc shaped opening edge  2   a.    
         [0040]    The seal bead  4  extending along the periphery of the port hole portion  2  is constructed by a half bead  41  in a portion which is along the semicircular arc shaped opening edge  2   a,  and is constructed by a flip-up bead  42  in a portion which is along the linear opening edge  2   b  and the gentle curve shaped opening edge  2   c.    
         [0041]    Among them, the half bead  41  is formed into a protruding shape which runs to a tabular ridge portion  4   c  from an outer peripheral bottom portion  4   a  via a diagonally uprising outer periphery inclined surface portion  4   b,  as shown in  FIG. 2A  showing a cross section along a line A-A in  FIG. 1 , and an end edge in an inner peripheral side of the ridge portion  4   c  comes to the semicircular arc shaped opening edge  2   a  in the port hole portion  2 . Further, the flip-up bead  42  is formed into a protruding shape which runs to an inner periphery inclined surface portion  4   d  in an opposite side to the outer periphery inclined surface portion  4   b  via the outer periphery inclined surface portion  4   b  uprising diagonally from the outer periphery bottom portion  4   a,  and the ridge portion  4   c  which is bent like a convex shape to an upper side in an upper end of the outer periphery inclined surface portion  4   b,  as shown in  FIG. 2B  showing a cross section along a line B-B in  FIG. 1 , and an inner peripheral end edge of the inner periphery inclined surface portion  4   d  comes to the linear opening edge  2   b  or the gentle curve shaped opening edge  2   c  in the port hole portion  2  of the metal plate  1 . 
         [0042]    In a transition portion from the semicircular arc shaped opening edge  2   a  in the opening edge of the port hole portion  2  to the linear opening edge  2   b  or the gentle curve shaped opening edge  2   c  (a transition portion from the linear opening edge  2   b  or the gentle curve shaped opening edge  2   c  to the semicircular arc shaped opening edge  2   a )  2   d,  the seal bead  4  continuously transits from the half bead  41  to the flip-up bead  42  (from the flip-up bead  42  to the half bead  41 ). 
         [0043]    The metal gasket MG constructed as mentioned above is interposed, for example, between the exhaust manifold of the automotive internal combustion engine and the joint surface of the exhaust pipe singly or in a state in which a plurality of metal gaskets are laminated, the seal bead  4  is compression deformed by fastening the metal gasket MG, and the surface pressure required for sealing is obtained by a repulsive load, thereby preventing the exhaust gas from leaking from the portion between the joint surfaces. 
         [0044]    In this kind of metal gasket, in the case that the shape of the seal bead  4  is non-circular such as the illustrated example, there is a tendency that the spring constant becomes higher in the portion having the great curvature (having the small radius of curvature) and the surface pressure becomes excessively high, and there is a tendency that the spring constant becomes lower inversely in the portion having the small curvature (having the great radius of curvature and being similar to a straight line) and lack of surface pressure tends to be generated. However, according to the metal gasket MG of the illustrated embodiment, since the portion along the semicircular arc shaped opening edge  2   a  having the great curvature is constructed by the half bead  41  among the seal bead  4 , the surface pressure can be prevented from becoming excessively great. Further, since the portion along the linear opening edge  2   b  or the gentle curve shaped opening edge  2   c  having the small curvature is constructed by the flip-up bead  42 , the surface pressure can be prevented from becoming excessively small. 
         [0045]      FIGS. 3 to 10  show a method for manufacturing the metal gasket MG mentioned above according to a process sequence. In other words, in the manufacturing of the metal gasket MG, the process first of all forms the bolt insertion hole  3 , a pair of preliminary holes  21  having a portion in which the opening edge comes to the semicircular arc shaped opening edge  2   a  in the port hole portion  2  in  FIG. 1 , and a pair of positioning holes  22 , in the metal plate  1 , as shown in  FIG. 3 . These elements can be formed by punching at the same time of punching an outer edge of the metal plate  1 . 
         [0046]    A convex mold  5  shown in  FIG. 4  is structured such that a bead forming convex portion  50  and a plurality of positioning convex portions  5   a  are formed on its upper surface, the positioning convex portions  5   a  being provided for positioning and setting the metal plate  1  on the upper surface by being fitted to the positioning holes  22  of the metal plate  1 . The bead forming convex portion  50  corresponds to the ridge portion  4   c  of the seal bead  4  shown in  FIG. 1 , and is constructed by a portion (hereinafter, refer to as a half bead forming convex portion)  51  which forms the half bead  41  and a portion (hereinafter, refer to as a flip-up bead forming convex portion)  52  which forms the flip-up bead  42 , and the half bead forming convex portion  51  is formed to be wider than the flip-up bead forming convex portion  52  as shown in  FIGS. 5A and 5B . 
         [0047]    Further, in the bead forming convex portion  50  in the convex mold  5 , the half bead forming convex portion  51  is formed into a crescent shape, an outer edge  51   a  thereof extends in correspondence to an outer edge of the ridge portion  41  c of the half bead  41 , that is, the outer edge  51  a is formed so as to be positioned in an outer peripheral side of the preliminary hole  21  in the case that the metal plate  1  shown in  FIG. 3  is set to the convex mold  5 , and an inner edge  51   b  is on the contrary formed so as to pass through an inner side of the preliminary hole  21 . 
         [0048]    On the other hand, a convex mold  6  shown in  FIG. 6  is structured such that a bead forming concave portion  60  is formed in its lower surface. Reference symbol  6   a  denotes a positioning concave portion or hole which can be fitted to the positioning convex portion  5   a  of the convex mold  5 . The bead forming concave portion  60  is constructed by a portion (hereinafter, refer to as a half bead forming concave portion)  61  which formed the half bead  41  of the seal bead  4  shown in  FIG. 1 , and a portion (hereinafter, refer to as a flip-up bead forming concave portion)  62  which forms the flip-up bead  42 , and the half bead forming concave portion  61  is formed to be wider than the flip-up bead forming concave portion  62 , as shown in  FIGS. 7A and 7B . Further, the half bead forming concave portion  61  is formed to be wider than the half bead forming convex portion  51  of the convex mold  5 , and the flip-up bead forming concave portion  62  is formed to be wider than the flip-up bead forming convex portion  52  of the concave mold  5 . 
         [0049]    In more detail, an outer edge  61   a  of the hold bead forming concave portion  61  and an outer edge  62   a  of the flip-up bead forming concave portion  62  in the concave mold  6  are structured such as to extend in correspondence to the bottom portion  4   a  of the seal bead  4  shown in  FIGS. 1 and 2 , and are positioned closer to an outer peripheral side than the outer edge  51   a  of the half bead forming convex portion  51  and the outer edge  52   a  of the flip-up bead forming convex portion  52  in the convex mold  5 , in the case of being combined with the convex mold  5 . Further, an inner edge  61   b  of the half bead forming concave portion  61  and an inner edge  62   b  of the flip-up bead forming concave portion  62  in the concave mold  6  are positioned closer to an inner peripheral side than the inner edge  51   b  of the half bead forming convex portion  51  and the inner edge  52   b  of the flip-up bead forming convex portion  52  in the convex mold  5 , in the case of being combined with the convex mold  5 . 
         [0050]    Next, in the case that the metal plate  1  shown in  FIG. 3  is positioned and set between the convex mold  5  and the concave mold  6  so as to be press molded as shown in  FIGS. 8 and 9 , the metal plate  1  is bent only in the outer edge  51   a  of the half bead forming convex portion  51  and the outer edge  61   a  of the half bead forming concave portion  61  as shown in  FIG. 9A , between the half bead forming convex portion  51  and the half bead forming concave portion  61  on the basis of existence of the preliminary hole  21 . As a result, the half bead  41  is formed along the semicircular arc shaped opening edge  2   a  of the preliminary hole  21 . On the other hand, since the preliminary hole  21  does not exist in the metal plate  1  between the flip-up bead forming convex portion  52  and the flip-up bead forming concave portion  62 , the metal plate  1  is bent at three positions including the ridge portion of the flip-up bead forming concave portion  52 , and the outer edge  62   a  and the inner edge  62   b  of the flip-up bead forming concave portion  62  as shown in  FIG. 9B . As a result, a full bead  42 ′ having a chevron cross sectional shape is formed. 
         [0051]    Next, the metal plate  1  in which the seal bead constructed by the half bead  41  and the full bead  42 ′ is formed is cut as shown by a single-dot chain line in  FIG. 10 . In other words, an area (an area shown by hatching in  FIG. 10 )  1  a surrounded by a pair of preliminary holes  21  and the full beads  42 ′ and  42 ′ is punched. 
         [0052]    In this step, the port hole portion  2  is formed and the flip-up bead  42  is formed along the linear opening edge  2   b  and the gentle curve shaped opening edge  2   c  of the port hole portion  2 , as shown in  FIG. 1 , by cutting the inner periphery inclined surface portion  4   d  in the full bead  42 ′ shown in  FIG. 9B  at a position closer to a inner periphery bottom portion  4   e,  and the manufacturing of the metal gasket MG is finished. 
         [0053]    Accordingly, it is possible to easily manufacture the metal gasket MG having the seal bead  4  in which the half beads  41  and the flip-up beads  42  are continuously provided, the half beads  41  being along the semicircular arc shaped opening edges  2   a  of the port hole portion  2 , and the flip-up beads  42  being along the linear opening edge  2   b  and the gentle curve shaped opening edge  2   c.    
         [0054]    In the case that the inner periphery inclined surface portion  4   d  shown in  FIG. 9B  is cut by the inner periphery bottom portion  4   e  in the step of forming the port hole portion  2 , it is possible to construct the portion of the flip-up bead  42  along the linear opening edge  2   b  and the gentle curve shaped opening edge  2   c  by the full bead. In addition, various changes can be employed, for example, the portion along the semicircular arc shaped opening edge  2   a  is constructed by the flip-up bead, in a relationship between shapes of the convex mold  5 , and the bead forming convex portion and the bead forming concave portion of the concave mold  6 , and a cutting position for forming the port hole portion  2 .