Abstract:
A cylinder head gasket for an internal combustion engine with a cylinder bore and a fluid hole includes a first metal plate having a curved portion around the cylinder bore and a folded portion extending from the curved portion, and a second metal plate laminated on the first metal plate and having a first full bead projecting toward the first metal plate. The first full bead is disposed on the folded portion. At least one secondary plate is inserted inside the folded portion.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
       [0001]    The present invention relates to a cylinder head gasket placed between two members, such as a cylinder head and a cylinder block of an engine to seal therebetween. More specifically, even when the members on both sides are rubbed against each other and misaligned due to an external factor, such as a heat deformation of the members, the surface pressure on the end portion of a bore can be controlled not to rise, and indentation generated at the members can be reduced. 
         [0002]    The cylinder head gasket is tightened by head bolts and seals fluid, such as combustion gas, oil, and coolant water in a state of being placed between the cylinder head and the cylinder block (cylinder body) of an automobile engine. 
         [0003]    Also, as the weight and size of an engine have been reduced recently, the engine tends to have lower rigidity. Accordingly, when a large seal surface pressure is provided on the nearest part of the cylinder bore in order to assure a seal quality during the sealing of the cylinder head gasket, the cylinder bore is deformed because the engine member has lower rigidity. When the cylinder bore is deformed, a seal method, such as a bead or a folded portion, does not function well, and an adequate seal quality can not be obtained. 
         [0004]    In order to provide an excellent seal quality by reducing the number of laminated plates, usage of the material, and the thickness of a whole gasket, and also by increasing the tightening pressure of the rim of a cylinder to the highest, metal gaskets, such as those shown in Japanese Patent Publications No. 8-121597 and No. 10-213227, form a wide folded portion (grommet portion) by directly folding back a secondary plate at the rim of the cylinder, and provide a full bead in two sheets of main plates which clamp the secondary plate. The full bead has a projection on the secondary plate side, and comes together with the folded portion. 
         [0005]    However, in this kind of cylinder head gasket, the rim of the cylinder has the highest tightening pressure (seal pressure), so that the deformation of the cylinder bore can be accelerated. Also, the folded portion is directly folded back, and the folded diameter of the folded portion is small, thereby easily creating a crack. 
         [0006]    In view of the problems described above, an object of the present invention is to provide a cylinder head gasket which can provide an excellent seal quality around the cylinder bore, and also can reduce the indentation around the cylinder bore which is generated at the engine member. 
         [0007]    Further objects and advantages of the invention will be apparent from the following description of the invention. 
       SUMMARY OF THE INVENTION 
       [0008]    In order to attain the objects described above, according to the present invention, a cylinder head gasket comprises a first metal plate with a folded portion around a cylinder bore; and a second metal plate which is laminated on the first metal plate and forms a full bead projecting to a first metal plate side. The projected portion of the full bead is disposed on the inner perimeter side of the end portion of the folded portion, and at least one or more sheets of secondary plate is inserted and disposed inside the folded portion. 
         [0009]    According to the structure, by inserting and disposing the secondary plate inside the folded portion, the thickness of the folded portion can be made thicker, so that the curvature of the folded portion increases, hereby preventing the development of a crack. 
         [0010]    In the cylinder head gasket, the second metal plate is laminated on the folded portion side of the first metal plate. In this structure, although the laminated position of the second metal plate comes to the side with the folded portion from the side without the folded portion, the above-mentioned same effect can be obtained. 
         [0011]    In the cylinder head gasket, the thickness around the cylinder bore of the second metal plate is made smaller than half of the thickness of the folded portion. With this structure, even when a large tightening force is generated around the cylinder bore, the end portion of the second metal plate is entered into the rounded portion of the folded portion around the periphery of the cylinder bore, so that an excessive seal pressure is not added in the periphery of the cylinder bore, hereby controlling the deformation of the cylinder bore. 
         [0012]    In the cylinder head gasket, a first secondary plate which is flat on the inner perimeter side of the end portion of the folded portion; and a ring-shape second secondary plate with a bead on the inner perimeter side of the end portion of the folded portion, are inserted and disposed inside the folded portion. Accordingly, the thickness of the folded portion can be adjusted by the first and second secondary plates. In addition, the compressibility of the folded portion can be increased by the bead of the second secondary plate, hereby preventing creep relaxation of the folded portion. 
         [0013]    Also, if the projected portion of the second metal plate and the projected portion (contact portion with the first metal plate) of the bead of the second secondary plate are located in the same position in a plan view, a larger seal pressure can be formed. Also, if the above-mentioned two projected portions are misaligned in the plan view, the area of a relatively large seal pressure can be broadened while the maximum seal pressure is reduced. 
         [0014]    Further, a third metal plate may be laminated on the first metal plate at a side opposite to the second metal plate. The third metal plate includes a full bead projecting toward the first metal plate. The full bead is disposed on the folded portion. 
         [0015]    According to the cylinder head gasket, an excellent seal quality around the cylinder bore can be obtained, and by controlling the seal pressure around the periphery of each cylinder bore to be small, the deformation of the cylinder bore of the engine can be controlled. 
         [0016]    Especially, even when the upper surface side and the lower surface side of the cylinder head gasket are rubbed against each other and misaligned due to an external factor, such as a heat deformation of a cylinder head or a cylinder block, the rise of the surface pressure on the tip of the bore can be controlled, thereby reducing indentation generated in the cylinder head or the cylinder block. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a fragmentary sectional view of a cylinder head gasket according to a first embodiment of the present invention; 
           [0018]      FIG. 2  is an enlarged fragmentary sectional view of the proximity of a folded portion in  FIG. 1 ; 
           [0019]      FIG. 3  is a fragmentary sectional view of the cylinder head gasket according to a second embodiment of the present invention; 
           [0020]      FIG. 4  is an enlarged fragmentary sectional view of the proximity of the folded portion in  FIG. 3 ; 
           [0021]      FIG. 5  is a fragmentary sectional view of the cylinder head gasket according to a third embodiment of the present invention; and 
           [0022]      FIG. 6  is an enlarged fragmentary sectional view of the proximity of the folded portion in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0023]    Hereunder, a cylinder head gasket according to embodiments of the present invention will be described in detail with reference to the attached drawings. Incidentally,  FIGS. 1-6  are schematic explanatory views, in which the thicknesses of plates, and sizes of the cylinder bores, the folded portions, and beads are different from actual ones, so that the cylinder head gaskets are enlarged for the sake of explanation. 
         [0024]    The cylinder head gasket according to the invention is a metal gasket placed between engine members, such as a cylinder head and a cylinder block (cylinder body) of an engine to seal fluid, such as high-temperature and pressure combustion gas in the cylinder bore, and coolant water or oil in passages for the coolant water or cooling oil. 
         [0025]    The cylinder head gasket is formed of single or multiple sheets of metal plates (metal substrates) made of soft steel, annealed stainless (annealed material), or stainless material (spring steel). Also, the cylinder head gasket is produced in a shape corresponding to the shape of the engine member, such as the cylinder block, and is provided with cylinder bores (combustion chamber holes), fluid holes for circulating the coolant water or engine oil, or bolt holes for tightening head bolts. 
         [0026]    Firstly, the first embodiment of the invention will be explained. As shown in  FIGS. 1 and 2 , the cylinder head gasket  1  of the first embodiment is comprised of two sheets of metal plates  10 ,  20 , and three sheets of secondary plates  30 ,  40 ,  50 . The first metal plate  10  is made of annealed stainless, and the second metal plate  20  is made of stainless spring steel. Also, the first secondary plate  30  is made of soft steel or annealed stainless, and the second secondary plate  40  with a full bead  41  is made of stainless material. The third secondary plate  50  with the half bead  51  is made of annealed stainless. 
         [0027]    The first metal plate  10  includes a folded portion or flange  11  which is made by folding back the first metal plate  10  around the cylinder bore  2 . The second metal plate  20  is laminated on the first metal plate  10  on the side where the first metal plate  10  does not include the folded portion  11 ; however, the second metal plate  20  is provided with a full bead  21  which has a projection on the first metal plate  10  side (inside), and a projected portion  21   a  of the full bead  21  is disposed on the inner perimeter side of the end portion  11   a  of the folded portion  11 . 
         [0028]    Also, the first secondary plate  30  and the second secondary plate  40  are inserted and disposed inside the folded portion  11 . The first secondary plate  30  is formed flat on the inner perimeter side of the end portion  11   a  of the folded portion  11 . The second secondary plate  40  is formed in a ring-shaped plate with the full bead  41  on the inner perimeter side of the end portion  11   a  of the folded portion  11 . In a plan view, an end portion  40   a  on the inner perimeter side of the second secondary plate  40  is located in the same position with an end portion  30   a  on the inner perimeter side of the first secondary plate  30 . An end portion  40   b  on the outer perimeter side of the second secondary plate  40  is located in the same position as the end portion  11   a  of the folded portion  11 . The thickness tg of the folded portion  11  can be made thicker by inserting and disposing the secondary plates  30 ,  40 , so that the curvature of the rounded portion  11   b  of the folded portion  11  increases, thereby preventing the development of a crack. 
         [0029]    In addition, the compressibility of the folded portion  11  can be increased by the full bead  41  of the second secondary plate  40 , thereby preventing creep relaxation of the folded portion  11 . Usually, a full bead is used for the bead  41  of the second secondary plate  40 ; however, a half bead may be used, and any bead can be used as long as the bead can prevent creep relaxation of the folded portion  11 . Also, a number of beads may be combined. 
         [0030]    As shown in  FIG. 2 , the plate thickness t 2  around the cylinder bore  2  of the second metal plate  20  is made smaller than the half th of the thickness tg of the folded portion  11 , i.e. t 2 &lt;th (=tg/2). Also, the thickness tg of the folded portion  11  becomes thicker by inserting and disposing the secondary plates  30 ,  40  into the folded portion  11 , so that the plate thickness t 2  around the cylinder bore  2  of the second metal plate  20  can be easily made smaller than the half th of the thickness tg of the folded portion  11 , respectively. 
         [0031]    In addition, around the periphery of the water hole  3 , the second metal plate  20  includes half beads  22 ,  23 . The direction of the projection of the half bead  23  is the same as that of the projected portion  41   a  of the full bead  41  of the second secondary plate  40 . Also, the third secondary plate  50  forms the half bead  51  which projects to the opposite direction relative to the half bead  23 . These two half beads  23 ,  51  are disposed in the same position in the plan view. More specifically, each sloping portion of the half beads  23 ,  51  is disposed in such a way as to overlap each other in the plan view. Also, an end portion  50   a  of the third secondary plate  50  which is located on the side of the perimeter of the cylinder bore  2  is positioned on the outer perimeter side compared to the end portion  11   a  of the folded portion  11 . 
         [0032]    Therefore, the rounded portion  11   b  of the folded portion  11  of the first metal plate  10 , and the end portion  20   a  of the second metal plate  20 , are aligned around the cylinder bore  2 . The end portions  10   b ,  20   b  of the first and second metal plates  10 ,  20 , and the end portions  30   b ,  50   b  of the first and third secondary plates  30 ,  50 , are aligned around the periphery of the water hole  3 . 
         [0033]    According to the cylinder head gasket  1  with the above-mentioned structure, even when a large tightening force is generated around the cylinder bore  2  due to the relationship of thicknesses, the end portion  20   a  of the second metal plate  20  is entered into the rounded portion  11   b  side of the folded portion  11  around the periphery of the cylinder bore  2 . Accordingly, a large surface pressure is not generated around the periphery of the cylinder bore  2 , and the maximum surface pressure is generated on the outer perimeter side. As a result, an excessive seal pressure is not added in the periphery of the cylinder bore of the engine, thereby controlling the deformation of the cylinder bore. More specifically, by minimizing the maximum value of the surface pressure of the periphery of each cylinder bore  2 , the deformation of each cylinder bore can be prevented. Incidentally, the width of the folded portion  11  or shapes or sizes of the beads  21 ,  41  can be obtained by a distribution of the surface pressure which is obtained by an experiment or calculation. 
         [0034]    Also, when a large tightening force is not added, an appropriate seal pressure is added even in the periphery of the cylinder bore by the folded portion  11  and the full bead  21 , and moreover, seal pressure is added by a seal line which is formed by the full bead  2  on the outer perimeter side, thereby exerting an excellent seal quality. 
         [0035]    With the first and second secondary plates  30 ,  40 , the thickness tg of the folded portion  11  can be adjusted, and additionally, the compressibility of the folded portion  11  can be increased by the full bead  41  of the second secondary plate  40 , thereby preventing creep relaxation of the folded portion  11 . Usually, a full bead is used for the bead  41  of the second secondary plate  40 ; however, a half bead may be used, and any bead may be used as long as the bead can prevent creep relaxation of the folded portion  11 . Also, a number of beads may be combined. 
         [0036]    Also, if the projected portion  21   a  of the full bead  21  of the second metal plate  20 , and the projected portion (contact portion with the first metal plate)  41   a  of the full bead  41  of the second secondary plate  40  are located in the same position in a plan view, a larger seal pressure can be generated. Also, if the above-mentioned two projected portions  21   a ,  41   a  are misaligned in the plan view, the area of a relatively large seal pressure can be broadened while the maximum seal pressure is reduced. 
         [0037]    With this structure, even when the upper surface side and the lower surface side of the cylinder head gasket  1  are rubbed against each other and misaligned due to an external factor such as a heat deformation of a cylinder head or a cylinder block, the rise of the surface pressure on the end portion of the bore can be controlled, thereby reducing the indentation generated at the cylinder head or the cylinder block. 
         [0038]    In the above, the full beads  21 ,  41  are explained with the circular bead in the cross-sectional shape. However, the shape of the bead is not specially limited in this invention, and the cross-sectional shape may be a circular arc, sine (cosine), trapezoid, triangle (mountain shape), and the like. 
         [0039]    Next, the second embodiment of the invention will be explained. As shown in  FIGS. 3 and 4 , a cylinder head gasket  1 A of the second embodiment is comprised of two sheets of metal plates  10 ,  20 A and three sheets of secondary plates  30 ,  40 ,  50 . The first metal plate  10  is made of annealed stainless, and the second metal plate  20 A is made of stainless spring steel. Also, the first secondary plate  30  is made of soft steel or annealed stainless, and the second secondary plate  40  including the full bead  41  is made of stainless material. In addition, the third secondary plate  50  including the half bead  51  is made of annealed stainless. 
         [0040]    The first metal plate  10  includes the folded portion  11  which is made by folding back the first metal plate  10  around the cylinder bore  2 . The second metal plate  20 A is laminated in the folded portion  11  on the folded portion  11  side of the first metal plate  10 . However, a full bead  21 A which is projected to the first metal plate  10  side (inside) is provided in the second metal plate  20 A, and a projected portion  21 Aa of the full bead  21 A is located on the inner perimeter side of the end portion  11   a  of the folded portion  11 . 
         [0041]    Also, the first secondary plate  30  and the second secondary plate  40  are inserted and disposed inside the folded portion  11 . The first secondary plate  30  is formed flat on the inner perimeter side of the end portion  11   a  of the folded portion  11 . The second secondary plate  40  is formed in a ring-shaped plate with the full bead  41  on the inner perimeter side of the end portion  11   a  of the folded portion  11 . In a plan view, the end portion  40   a  on the inner perimeter side of the second secondary plate  40  is located in the same position with the end portion  30   a  on the inner perimeter side of the first secondary plate  30 . The end portion  40   b  on the outer perimeter side of the second secondary plate  40  is located in the same position with the end portion  11   a  of the folded portion  11 . The thickness tg of the folded portion  11  can be made thicker by inserting and disposing the secondary plates  30 ,  40 , so that the curvature of the rounded portion  11   b  of the folded portion  11  increases, thereby preventing the development of a crack. In addition, the compressibility of the folded portion  11  can be increased by the full bead  41  of the second secondary plate  40 , thereby preventing creep relaxation of the folded portion  11 . Usually, a full bead is used for the bead  41  of the second secondary plate  40 . However, a half bead may be used, and any bead can be used as long as the bead can prevent creep relaxation of the folded portion  11 . Also, some of beads may be combined. 
         [0042]    In addition, as shown in  FIG. 4 , the plate thickness t 2  around the cylinder bore  2  of the second metal plate  20 A is made smaller than the half th of the thickness tg of the folded portion  11 , i.e. t 2 &lt;th (=tg/2). Incidentally, the thickness tg of the folded portion  11  becomes thicker by inserting and disposing the secondary plates  30 ,  40  into the inside of the folded portion  11 , so that the plate thickness t 2  around the cylinder bore  2  of the second metal plate  20 A can easily be made smaller than the half th of the thickness tg of the folded portion  11 , respectively. 
         [0043]    In addition, the second metal plate  20 A includes a half bead  22 A around the water hole  3 . The direction of the projection of the half bead  22 A is the same as that of the projected portion  41   a  of the full bead  41  of the second secondary plate  40 . Also, the third secondary plate  50  forms the half bead  51  which has the opposite direction of the half bead  22 A. These two half beads  22 A,  51  are disposed in the same position in a plan view. More specifically, each sloping portion of each half bead  22 A,  51  is disposed in such a way as to overlap each other in the plan view. Also, the end portion  50   a  of the third secondary plate  50  which is located on the periphery side of the cylinder bore  2  is positioned on the outer perimeter side compared to the end portion  11   a  of the folded portion  11 . 
         [0044]    Therefore, the rounded portion  11   b  of the folded portion  11  of the first metal plate  10 , and the end portion  20 Aa of the second metal plate  20 A are aligned around the cylinder bore  2 . End portions  10   b ,  20 Ab of the first and second metal plates  10 ,  20 A, and end portions  30   b ,  50   b  of the first and third secondary plates  30 ,  50 , are aligned around the periphery of the water hole  3 . 
         [0045]    According to the cylinder head gasket  1 A with the above-mentioned structure, even when a large tightening force is generated around the cylinder bore  2  due to the relationship of the thicknesses, the end portion  20 Aa of the second metal plate  20 A is entered into the rounded portion  11   b  side of the folded portion  11  around the periphery of the cylinder bore  2 . Accordingly, a large surface pressure is not generated around the periphery of the cylinder bore  2 , and the maximum surface pressure is generated on the outer perimeter side. As a result, an excessive seal pressure is not added in the periphery of the cylinder bore of the engine, thereby controlling the deformation of the cylinder bore. More specifically, by minimizing the maximum value of the surface pressure on the periphery of each cylinder bore  2 , the deformation of each cylinder bore can be prevented. Incidentally, the width of the folded portion  11  or shapes or sizes of the beads  21 A,  41  can be obtained by a distribution of the surface pressure which is obtained by an experiment or calculation. 
         [0046]    Also, when a large tightening force is not added, an appropriate seal pressure is added even in the periphery of the cylinder bore by the folded portion  11  and the full bead  21 A, and moreover, a seal pressure is added by a seal line which is formed by the full bead  21 A on the outer perimeter side, thereby exerting an excellent seal quality. 
         [0047]    With the first and second secondary plates  30 ,  40 , the thickness tg of the folded portion  11  can be adjusted, and moreover, the compressibility of the folded portion  11  can be increased by the full bead  41  of the second secondary plate  40 , thereby preventing creep relaxation of the folded portion  11 . Usually, a full bead is used for the bead  41  of the second secondary plate  40 . However, a half bead may be used, and any bead may be used as long as the bead can prevent creep relaxation of the folded portion  11 . Also, some number of beads may be combined. 
         [0048]    Also, if the projected portion  21 Aa of the full bead  21 A of the second metal plate  20 A, and the projected portion (contact portion with the first metal plate)  41   a  of the full bead  41  of the second secondary plate  40  are located in the same position in a plan view, a larger seal pressure can be generated. Also, if the above-mentioned two projected portions  21 Aa,  41   a  are misaligned in the plan view, the area of a relatively large seal pressure can be broadened while the maximum seal pressure is reduced. 
         [0049]    With this structure, even when the upper surface side and the lower surface side of the cylinder head gasket  1  are rubbed against each other and misaligned due to an external factor, such as the heat deformation of the cylinder head or the cylinder block, the rise of the surface pressure on the end portion of the bore can be controlled, thereby reducing the indentation generated at the cylinder head or the cylinder block. 
         [0050]    In the above, the full beads  21 A,  41  are explained with the circular bead of the cross-sectional shape. However, the shape of the bead is not specially limited in this invention, and the cross-sectional shape may be a circular arc, sine (cosine), trapezoid, triangle (mountain shape), and the like. 
         [0051]    Next, the third embodiment of the invention will be explained. As shown in  FIGS. 5 and 6 , a cylinder head gasket  1 B of the third embodiment is comprised of three sheets of metal plates  10 ,  20 ,  20 A and three sheets of secondary plates  30 ,  40 ,  50 . The first metal plate  10  is made of annealed stainless, and the second metal plates  20 ,  20 A are made of stainless spring steel. Also, the first secondary plate  30  is made of soft steel or annealed stainless, and the second secondary plate  40  including the full bead  41  is made of stainless material. In addition, the third secondary plate  50  including the half bead  51  is made of annealed stainless. 
         [0052]    The first metal plate  10  includes the folded portion  11  which is made by folding back the first metal plate  10  around the cylinder bore  2 . The second and third metal plates  20 ,  20 A are disposed to sandwich the first metal plate  10 . Full beads  21 ,  21 Aa which project to the first metal plate  10  side (inside) are provided in the second and third metal plates  20 ,  20 A. Projected portion  21   a ,  21 Aa of the full bead  21 ,  21 A are located on the inner perimeter side of the end portion  11   a  of the folded portion  11 . 
         [0053]    Also, the first secondary plate  30  and the second secondary plate  40  are inserted and disposed inside the folded portion  11 . The first secondary plate  30  is formed flat on the inner perimeter side of the end portion  11   a  of the folded portion  11 . The second secondary plate  40  is formed in a ring-shaped plate with the full bead  41  on the inner perimeter side of the end portion  11   a  of the folded portion  11 . In a plan view, the end portion  40   a  on the inner perimeter side of the second secondary plate  40  is located in the same position with the end portion  30   a  on the inner perimeter side of the first secondary plate  30 . The end portion  40   b  on the outer perimeter side of the second secondary plate  40  is located in the same position with the end portion  11   a  of the folded portion  11 . The thickness tg of the folded portion  11  can be made thicker by inserting and disposing the secondary plates  30 ,  40 , so that the curvature of the rounded portion  11   b  of the folded portion  11  increases, thereby preventing the development of a crack. In addition, the compressibility of the folded portion  11  can be increased by the full bead  41  of the second secondary plate  40 , thereby preventing creep relaxation of the folded portion  11 . Usually, a full bead is used for the bead  41  of the second secondary plate  40 . However, a half bead may be used, and any bead can be used as long as the bead can prevent creep relaxation of the folded portion  11 . Also, some of beads may be combined. 
         [0054]    In addition, as shown in  FIG. 6 , each of the plate thicknesses t 2 , t 3  around the cylinder bore  2  of the second and third metal plates  20 A is made smaller than the half th of the thickness tg of the folded portion  11 , i.e. t 2 &lt;th and t 3 &lt;th (=tg/2). Incidentally, the thickness tg of the folded portion  11  becomes thicker by inserting and disposing the secondary plates  30 ,  40  into the inside of the folded portion  11 , so that each of the plate thicknesses t 2 , t 3  around the cylinder bore  2  of the second and third metal plates  20 ,  20 A can easily be made smaller than the half th of the thickness tg of the folded portion  11 , respectively. 
         [0055]    In addition, the second metal plate  20  includes half beads  22 ,  23  around the water hole  3 , and the third metal plate  20 A includes a half bead  22 A around the water hole  3 . The directions of the projections of the half bead  23 ,  22 A are the same as the direction of the projected portion  41   a  of the full bead  41  of the second secondary plate  40 . Also, the third secondary plate  50  forms the half bead  51  which has the opposite directions of the half beads  23 ,  22 A. These three half beads  22 A,  23 ,  51  are disposed in the same position in a plan view. More specifically, each sloping portion of each half bead  22 A,  23 ,  51  is disposed in such a way as to overlap each other in the plan view. Also, the end portion of the third secondary plate  50  which is located on the periphery side of the cylinder bore  2  is positioned on the outer perimeter side compared to the end portion  11   a  of the folded portion  11 . 
         [0056]    Therefore, the rounded portion  11   b  of the folded portion  11  of the first metal plate  10 , and the end portions  20   a ,  20 Aa of the second and third metal plate  20 ,  20 A are aligned around the cylinder bore  2 . End portions  10   b ,  20   b ,  20 Ab of the first, second and third metal plates  10 ,  20 ,  20 A, and end portions  30   b ,  50   b  of the first and third secondary plates  30 ,  50 , are aligned around the periphery of the water hole  3 . 
         [0057]    According to the cylinder head gasket  1 B with the above-mentioned structure, even when a large tightening force is generated around the cylinder bore  2  due to the relationship of the thicknesses, the end portions  20   a ,  20 Aa of the second and third metal plates  20 ,  20 A are entered into the rounded portion  11   b  side of the folded portion  11  around the periphery of the cylinder bore  2 . Accordingly, a large surface pressure is not generated around the periphery of the cylinder bore  2 , and the maximum surface pressure is generated on the outer perimeter side. As a result, an excessive seal pressure is not added in the periphery of the cylinder bore of the engine, thereby controlling the deformation of the cylinder bore. More specifically, by minimizing the maximum value of the surface pressure on the periphery of each cylinder bore  2 , the deformation of each cylinder bore can be prevented. Incidentally, the width of the folded portion  11  or shapes or sizes of the beads  21 ,  21 A,  41  can be obtained by a distribution of the surface pressure which is obtained by an experiment or calculation. 
         [0058]    Also, when a large tightening force is not added, an appropriate seal pressure is added even in the periphery of the cylinder bore by the folded portion  11  and the full beads  21 ,  21 A, and moreover, a seal pressure is added by a seal line which is formed by the full bead  21 ,  21 A on the outer perimeter side, thereby exerting an excellent seal quality. 
         [0059]    With the first and second secondary plates  30 ,  40 , the thickness tg of the folded portion  11  can be adjusted, and moreover, the compressibility of the folded portion  11  can be increased by the full bead  41  of the second secondary plate  40 , thereby preventing creep relaxation of the folded portion  11 . Usually, a full bead is used for the bead  41  of the second secondary plate  40 . However, a half bead may be used, and any bead may be used as long as the bead can prevent creep relaxation of the folded portion  11 . Also, some number of beads may be combined. 
         [0060]    Also, if the projected portions  21   a ,  21 Aa of the full beads  21 ,  21 A of the second and third metal plates  20 ,  20 A, and the projected portion (contact portion with the first metal plate)  41   a  of the full bead  41  of the second secondary plate  40  are located in the same position in a plan view, a larger seal pressure can be generated. Also, if the above-mentioned two or three projected portions  21   a ,  21 Aa,  41   a  are misaligned in the plan view, the area of a relatively large seal pressure can be broadened while the maximum seal pressure is reduced. 
         [0061]    With this structure, even when the upper surface side and the lower surface side of the cylinder head gasket  1  are rubbed against each other and misaligned due to an external factor, such as the heat deformation of the cylinder head or the cylinder block, the rise of the surface pressure on the end portion of the bore can be controlled, thereby reducing the indentation generated at the cylinder head or the cylinder block. 
         [0062]    In the above, the full beads  21 ,  21 A,  41  are explained with the circular bead of the cross-sectional shape. However, the shape of the bead is not specially limited in this invention, and the cross-sectional shape may be a circular arc, sine (cosine), trapezoid, triangle (mountain shape), and the like. 
         [0063]    The disclosures of Japanese Patent Applications No. 2006-136162 filed on May 16, 2006 and No. 2006-296644 filed on Oct. 31, 2006 are incorporated in the application. 
         [0064]    While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.