Patent Publication Number: US-2016223085-A1

Title: Metal gasket

Description:
TECHNICAL FIELD 
     The present invention relates to a metal gasket that can be used in high temperature applications, 
     BACKGROUND ART 
     Conventionally, the metal gasket has been used as a sealing structure for fastening surfaces or mating surfaces between a cylinder block and a cylinder head, and between a cylinder head and an exhaust manifold of an engine which are placed under high temperature conditions. 
     As the metal gasket thermally expands under a high temperature condition, if the two parts that interpose the metal gasket therebetween have different thermal expansion coefficients from that of the metal gasket, a stress is created in the metal gasket to such an extent that the resulting deformation may impair the sealing performance of the metal gasket. To overcome this problem, with respect to a metal gasket interposed between a cylinder head and an exhaust manifold, a proposal was made to form a through hole in each of the connecting parts positioned. between the sealing parts corresponding to the respective exhaust ports so that the connecting parts may fracture when the gasket is subjected to a significant tensile stress. See JPS62-167812U, for instance. This metal gasket consists of a single piece so that the mounting work is facilitated, and once installed in the engine, the connecting parts fracture under stress, and the sealing parts are separated from each other so that each sealing part is not interfered by a tensile stress from the adjoining sealing parts, 
     However, the metal gasket disclosed in JPS62-167812U does not allow the stress created in each individual sealing part which has been separated from the adjoining sealing parts to be reduced. Even after each sealing part has been separated, the sealing part is at least partly fixed to the cylinder head and the exhaust manifold by the force applied by the fastening bolts so that some stress is inevitably created in each sealing part because the thermal expansion coefficient of the metal gasket differs from those of the exhaust manifold and the cylinder head. As a result, each sealing part, in particular a bead thereof, could be distorted and/or fractured, and the designed sealing performance may not be maintained. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of such a problem of the prior art, a primary object of the present invention is to provide a metal gasket that can minimize localized concentration of stress. 
     To achieve such an object, the present invention provides a metal gasket ( 1 ) configured to be interposed between fastening surfaces ( 8 A,  16 E) of component parts ( 3 ,  4 ), and comprising a passage hole ( 34 ) corresponding to a passage ( 11 ,  18 ) of the component parts opening out on the fastening surfaces, a bead ( 38 ) surrounding the passage hole in an endless manner, at least three bolt holes ( 35 ) formed outside of the bead to allow fastening bolts ( 40 ) for fastening the component parts to each other to be passed therethrough, a bolt pressure receiving region ( 41 ) being defined around each bolt hole so as to correspond to a head ( 40 A) of the corresponding fastening bolt, a first region ( 42 ) being defined by linearly connecting the bolt pressure receiving regions of two adjoining bolt holes each other and being provided with a width equal to a diameter of the bolt pressure receiving regions, a second region ( 43 ) being defined as a part of the first region ( 42 ) located outside of the head, and a through hole ( 36 ) formed in the second region ( 43 ). 
     Thus, even when the thermal expansion coefficient of the metal gasket may differ from those of the component parts interposing the metal gasket, and stress may be thereby created in the metal gasket, localized stress concentration can be minimized. Stress tends to concentrate in a low stiffness part of the first region located between the bolt pressure receiving regions which are constrained by the fastening bolts, but by providing the through hole in the second region and thereby reducing the stiffness of this part, the stress is spread around the through hole so that localized concentration of stress in the low stiffness part of the first region can be minimized. As a result, the distortion and fracture of the metal gasket can be effectively prevented. 
     In this invention, it may be arranged such that the through hole is positioned in the second region in a radially outwardly offset relationship with respect to the passage hole, 
     According to this arrangement, because the through hole is located remotely from the bead, even though the stiffness of the part surrounding the through hole is reduced, the stiffness of the part adjoining the bead can be maintained so that the chance of causing distortion and fracture in the bead can be minimized, 
     In this invention, it may be arranged such that the through hole is positioned in the second region in an offset relationship thereto toward one of the bolt pressure receiving regions along a lengthwise direction of the first region. 
     According to this arrangement, because the stress caused in the metal gasket owing to the difference of the thermal expansion coefficient of the metal gasket from those of the component parts interposing the metal gasket tends to concentrate in the low stiffness part of the first region, by lowering the stiffness of the part adjoining the fastening bolt which is otherwise higher than the surrounding part, the stress can be effectively distributed over a wide area so that the chance of distorting and fracturing the head of the metal gasket can be minimized. 
     In this invention, it may be arranged such that the metal gasket comprises a plurality of laminated conformal metallic sheets ( 30 ), each metallic sheet being provided with a projection ( 32 ) extending out of the fastening surfaces of the component parts, and the metallic sheets being joined one another at the projections, wherein the through hole is formed in a part of the second region adjoining the projections. 
     Because the through hole is provided in a part of the metal gasket which is given with a large width and a high stiffness owing to the provision of the projection on each metallic sheet, an unevenness in stiffness can be minimized, and concentration of stress in any localized low stiffness part can be avoided. Also, even when stress is produced around the through hole, the distortion of the affected part can be minimized. 
     in this invention, it may be arranged such that the first region is defined between two of the adjoining bolt holes which are spaced apart farthest. 
     Thus, the through hole is located in a part where a localized stress concentration tends to occur owing to the difference in the thermal expansion coefficients of the associated parts so that localized concentration of stress in this part of the metal gasket can be minimized. 
     In this invention, it may be arranged such that the first region is defined between two of the adjoining bolt holes which are located on either side of a part of the metal gasket defining a smallest distance between the passage hole and an adjoining outer edge ( 39 ) of the metal gasket. 
     According to this arrangement, the through hole is located in a part where a localized stress concentration tends to occur owing to the small width and the low stiffness thereof so that the localized concentration of stress in this part of the metal gasket can be minimized. 
     According to a preferred embodiment of the present invention, the metal gasket is provided with an outer profile of a substantially triangular configuration, and the bolt holes comprise three bolt holes positioned in respective corner portions of the triangular configuration. 
     Thus, according to the present invention, localized concentration of stress in the metal gasket can be minimized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of an exhaust system of an internal combustion engine embodying the present invention; 
         FIG. 2  is a plan view of the metal gasket; and 
         FIG. 3  is a sectional view taken along III-III of  FIG. 2 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     An embodiment of the metal gasket of the present invention as applied to the exhaust system of an internal combustion engine is described in the following with reference to the appended drawings. 
     As shown in  FIG. 1 , the metal gasket of the illustrated embodiment is used in an exhaust system  2  of an internal combustion engine. The exhaust system  2  comprises an exhaust manifold  3  connected to a cylinder head of the engine and a turbocharger  4  connected to the downstream end of the exhaust manifold  3 . 
     The exhaust manifold  3  includes a branch pipe portion  6  communicating with the exhaust ports formed in the cylinder head and a merging portion  7  provided at the downstream end of the branch pipe portion  6  in which individual pipes forming the branch pipe portion  6  merge into one passage. The downstream end of the merging portion  7  is formed with a manifold side flange  8  extending radially outward. The end surface of the manifold-side flange  8  defines a manifold-side fastening surface  8 A perpendicular to an axial center line of the merging portion  7 . To the manifold-side fastening surface  8 A open out a merging passage  11  having a circular cross section and three female threaded holes  12  arranged around the merging passage  11  at a regular interval. The manifold-side fastening surface  8 A is provided with a substantially triangular profile, and defines the merging passage  11  in the center and the three female threaded holes  12  at the respective corner portions. 
     The turbocharger  4  is provided with a turbine  14  and a compressor  15 . The turbine  14  includes a turbine housing  16  and a plurality of turbine blades (not shown in the drawings) disposed in a rotatable manner in the turbine housing  16 . The turbine housing  16  includes a main body  16 A given with a disk shape and receiving the turbine blades in a rotatable manner therein, a turbine inlet  16 B extending tangentially from a peripheral part of the main body  16 A and a turbine outlet  16 C extending axially from the central part of the main body  16 A so that a continuous exhaust passage is defined in the turbine housing  16 . 
     A terminal end of the turbine inlet  16 B is formed with a turbine-side flange  16 D extending radially outward. The end surface of the turbine-side flange  16 D defines a turbine-side fastening surface  16 E perpendicular to an axial line of the turbine inlet  16 B. The turbine-side fastening surface  16 E is substantially conformal to the manifold-side fastening surface  8 A, or is provided with a substantially triangular profile. To the turbine-side fastening surface  16 E open out a turbine inlet passage  18  having a circular cross section and three turbine-side bolt holes  19  arranged around the turbine inlet passage  18  at a regular interval. Each turbine-side bolt hole  19  is passed through the turbine-side flange  16 D. The turbine inlet passage  18  is located substantially in the center of the turbine-side fastening surface  16 E given with the triangular shape, and the turbine-side bolt holes  19  are positioned in the respective corners of the turbine-side fastening surface  16 E. The turbine-side fastening surface  16 E opposes the manifold-side fastening surface  8 A via the metal gasket  1 . In the assembled state, the merging passage  11  and the turbine inlet passage  18  communicate with each other, and the female threaded holes  12  are aligned with the corresponding turbine-side bolt holes  19 . 
     The compressor  15  includes a compressor housing  15 A and compressor blades (not shown in the drawings) rotatably disposed in the compressor housing  15 A. A continuous passage is defined in the compressor housing  15 A, and this passage forms a part of the intake passage communicating with the intake ports. The compressor blades are connected to the turbine blades via a connecting shaft (not shown in the drawings) so as to integrally rotate with the turbine blades. 
     As shown in  FIGS. 2 and 3 , the metal gasket  1  comprises at least a single metallic plate  30 . In the illustrated embodiment, the metal gasket  1  is formed by laminating a plurality of metallic plates  30  one over another. The metallic plates  30  are named as a first plate  30 A, a second plate  30 B, a third plate  30 C, a fourth plate  30 D a fifth plate  30 E and a sixth plate  30 F from one side to the other in that order, and are conformal to one another. Each metallic plate  30  includes a substantially triangular base portion  31  substantially conformal to the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E and a pair of projections  32  projecting outwardly from an outer edge  39  of the base portion  31 . The metallic plates  30  are joined to one another at the projections  32 . The projections  32  of one metallic plate may be joined to those of another metallic plate by any per se known method such as crimping and welding. 
     The metal gasket  1  is formed with a single passage hole  34 , three bolt holes  35  and a single through hole  36 , all passed through the thickness of the metallic plates  30 . The passage hole  34  is circular, and is conformal to the merging passage  11  and the turbine inlet passage  18 . 
     The passage hole  34  is surrounded by an annular bead  38  having an endless configuration. The bead  38  is formed by bending at least one of the metallic plates  30  in the thickness-wise direction, and ensures an adequate contact pressure to be produced between the metal gasket  1  and the manifold-side fastening surface  8 A, and between the metal gasket  1  and the turbine-side fastening surface  16 E. In the illustrated embodiment, the bead  38  is formed by bending all of the metallic plates  30 . The first plate  30 A is formed with a first half bead  38 A projecting away from the second plate  30 B in an annular shape surrounding the passage hole  34 . The second plate  30 B is formed with a second half bead  38 B projecting away from the first plate  30 A in an annular shape surrounding the passage hole  34 . The third plate  30 C is formed with a third half bead  38 C projecting away from the fourth plate  30 D in an annular shape surrounding the passage hole  34 . The fourth plate  30 D is formed with a fourth half bead  38 D projecting away from the third plate  30 C in an annular shape surrounding the passage hole  34 . The fifth plate  30 E is formed with a fifth half bead  38 E projecting away from the sixth plate  30 F in an annular shape surrounding the passage hole  34 . The sixth plate  30 F is formed with a sixth half bead  38 F projecting away from the fifth plate  30 E in an annular shape surrounding the passage hole  34 . The first to the sixth half beads  38 A to  38 F are positioned in a mutually corresponding relationship in the thickness-wise direction, and jointly define the bead  38 . The metal gasket  1  is allowed to intimately contact with the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E at this annular bead  38  so that the merging passage  11  and the turbine inlet passage  18  can be connected to each other in a gas-tight relationship. 
     As shown in  FIG. 2 , the three bolt holes  35  are arranged around and radially outwardly of the bead  38  at a circumferentially regular interval. The three bolt holes  35  are positioned so as to correspond to the female threaded holes  12  and the turbine-side bolt holes  19 . The turbine  14  and the exhaust manifold  3  are connected to each other with the metal gasket  1  interposed between them by fastening bolts  40  that are passed through the turbine-side bolt holes  19  and the bolt holes  35 , and threaded into the female threaded holes  12 , respectively. In the metal gasket  1 , an annular bolt pressure receiving region  41  is defined around each holt hole  35  as a region corresponding to the head  40 A of the corresponding fastening bolt  40 . Each bolt pressure receiving region  41  receives the pressure in the thickness-wise direction from the head  40 A of the corresponding fastening bolt  40 . In the illustrated embodiment, the fastening bolts  40  are flange bolts so that the head  40 A of each fastening bolt  40  defines a circular contact surface. Each bolt pressure receiving region  41  is fixedly engaged by the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E such that the bolt pressure receiving region  41  moves integrally with the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E. 
     Each bolt pressure receiving region  41  is placed outwardly of the head  38  so as not to overlap with the bead  38 . The outer edge  39  of the base portion  31  does not overlap with any of the bolt pressure receiving regions  41 . The three bolt pressure receiving regions  41  and the bolt holes  35  are positioned at the respective corners of the base portion  31  having the substantially triangular configuration. 
     Because the base portion  31  is provided with the substantially triangular profile, and centrally provided with the passage hole  34 , the distance between the passage hole  34  and the outer edge  39  is smallest at the central part of each side of the triangular configuration of the outer edge  39 . In other words, the radial width of the metal gasket  1  about the center of the passage hole  34  is smallest at the central part of each side of the triangular configuration of the outer edge  39 . 
     The region extending between the two adjoining bolt pressure receiving regions  41  is defined as a first region  42 . The first region  42  extends linearly between the adjoining bolt pressure receiving regions  41 , and has a same width as the diameter of the bolt pressure receiving regions  41 . The first region  42  is defined as a region that does not overlap with any of the bolt pressure receiving regions  41 , and abuts the corresponding bolt pressure receiving region  41  at each length-wise terminal end thereof. The first region  42  may overlap with any of the passage hole  34 , the bead  38  and the outer edge of the base portion  31 . In  FIG. 2 , as an example of the first region  42 , the first region  42  is defined between the two bolt holes  35  that are located in an upper part in  FIG. 2 . The distance between these two bolt holes  35  is the longest of the distances defined between the adjoining bolt holes  35 . The distance (or the width of the metal gasket  1 ) between the passage hole  34  and the outer edge  39  of the base portion  31  (of the metal gasket  1 ) is the smallest of all when the bolt holes  35  are selected from the two located in an upper part of  FIG. 2 . 
     One of the projections  32  is located between these two bolt pressure receiving regions  41 , and is offset toward one of the bolt pressure receiving regions  41 . In other words, the projection  32  is positioned outwardly of the first region  42  and offset toward one of the terminal ends of the first region  42 . 
     The through hole  36  is formed in a second region  43  which is defined as a part of the first region  42  located radially outwardly of the bead  38 . The through hole  36  is preferably located in a part of the second region  43  which is radially outwardly offset about the center of the passage hole  34 . The through hole  36  is preferably located in a part of the second region  43  which is offset toward one of the bolt pressure receiving regions  41  along the lengthwise direction of the first region  42 . The through hole  36  is preferably located in a part of the second region  43  adjoining the projection  32 . The second region  43  in the illustrated embodiment consists of two parts that are separated by the passage hole  34 , but may also consist of a single integral region. 
     The through hole  36  may be provided with any cross sectional shape such as circular, elliptic, track and polygonal (such as triangular and rectangular) shapes. In the illustrated embodiment, the cross sectional shape of the through hole  36  is circular. 
     The effect of the metal gasket of the illustrated embodiment is discussed in the following. By threading the fastening bolts  40  into the respective female threaded holes  12 , the metal gasket  1  is interposed between the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E at the base portion  31 . The projections  32  are positioned externally of the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E. The metal gasket  1  achieves a line contact with the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E at the bead  38 , and connects the merging passage  11  and the turbine inlet passage  18  with each other via the passage hole  34  in a gas tight manner. 
     When the engine is in operation, exhaust gas of a high temperature is passed through the exhaust manifold  3  and the turbine  14  so that the exhaust manifold  3 , the metal gasket  1  and the turbine  14  are heated. When the linear thermal expansion coefficients of the exhaust manifold  3 , the metal gasket  1  and the turbine  14  differ from one another, because the bolt pressure receiving regions  41  are constrained between the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E, tensile or compressive stress is created in the metal gasket  1 . This stress is particularly pronounced in the region located between the adjoining bolt pressure receiving regions  41  or in the first region  42 . In particular, in the lengthwise central part of each first region  42 , because the width (the distance between the peripheral edge of the passage hole  34  and the outer edge  39 ) of the metal gasket  1  is narrower than other parts, and therefore the stiffness of this part is reduced, the stress tends to concentrate in this area. 
     In the metal gasket  1  of the illustrated embodiment, because the through hole  36  is provided in the second region  43  which is located in a part of the first region  42  located outwardly of the bead  38 , the stiffness of the area surrounding the through hole  36  is reduced so that the stress is favorably spread around the through hole  36 . As a result, localized concentration of stress in a length-wise central part of the first region  42  can be reduced so that distortion, collapsing and/or fracture of this part can be minimized. Also, because the through hole  36  is located outwardly of the bead  38 , the through hole  36  does not adversely affect the sealing performance of the bead  38 . 
     Because the through hole  36  is located in a part of the second region  43  radially outwardly offset about the center of the passage hole  34 , a significant distance is ensured between the through hole  36  and the bead  38  so that the influences of the stress caused by the presence of the through hole  36  on the bead  38  is minimized, and the distortion of the bead  38  is minimized. Thereby, the impairment of the sealing performance can be avoided. 
     Because the through hole  36  is located in a part of the second region  43  which is offset toward one of the bolt pressure receiving regions  41  along the lengthwise direction of the first region  42  away from the central part of the first region  42 , the variation in stiffness within the first region  42  is mitigated so that concentration of stress in a lengthwise central part of the first region  42  can be minimized. The parts of the metal gasket  1  where the bolt pressure receiving regions  41  are located are provided with a relatively large width, and therefore have a relatively high stiffness, whereas the central part of the first region  42  along the lengthwise direction thereof is provided with a relatively small width, and therefore has a relatively low stiffness. Therefore, a stress concentration tends to occur in the central part of the first region  42  along the lengthwise direction thereof, but owing to the provision of the through hole  36 , the variation in stiffness is mitigated, and the stress concentration can be minimized. Also, because the part where the through hole  36  is located has a relatively high stiffness, even when a stress is created around the through hole  36 , the deformation of this part can be minimized. 
     Because the through hole  36  is formed in a part of the second region  43  adjoining the projection  32 , the variation in stiffness in the first region  42  is mitigated, and concentration of stress in the central part of the first region  42  along the lengthwise direction thereof can he avoided. The part of the metal gasket  1  where the projection  32  is located has a relatively large width and a high stiffness, whereas the central part of the first region  42  along the lengthwise direction thereof has a relatively small width and a low stiffness. Therefore, concentration of stress which otherwise could occur in the central part of the first region  42  along the lengthwise direction of the first region  42  can be minimized owing to the reduction in the variation in stiffness in the first region  42 . 
     The through hole  36  is located in the second region  43  defined between the two bolt holes  35  (the two upper bolt holes  35  in  FIG. 2 ) which are spaced apart farthest. When heated, the part of the metal gasket  1  located between the adjoining bolt holes  35  that are more spaced apart than any other pair of adjoining bolt holes  35  demonstrates the greatest expansion or contraction relative to the manifold-side fastening surface  8 A and the turbine-side fastening surface  16 E, and hence is most likely to experience a concentration of stress. By providing the through hole  36  in this part, such a localized stress concentration can be minimized. 
     The through hole  36  is located in the second region  43  defined between the two bolt holes  35  (the two upper bolt holes  35  in  FIG. 2 ) which are located on either side of the part where the distance (the width of the metal gasket  1 ) between the passage hole  34  and the outer edge  39  is the smallest. As the narrow part of the metal gasket  1  is provided with a low stiffness, a stress concentration tends to occur in such a part. Therefore, by providing the through hole  36  in such a part, the localized stress concentration can be minimized. 
     Because the through hole  36  consists of a circular hole, a relatively uniform stress distribution is produced around the through hole  36  so that localized deformation can be avoided. 
     The present invention has been described in terms of a specific embodiment, but the present invention is not limited by such an embodiment. In the foregoing embodiment, in a metal gasket  1  having three bolt holes  35 , a single through hole  36  was provided between a selected pair of bolt holes  35 , but two or more through holes  36  may also be formed. It is also possible to define a second region  43  between any other pair of adjoining bolt holes  35 , and form one or more through holes  36  in the second region  43 . 
     In an alternate embodiment, four or more bolt holes  35  are provided, and one or more through holes  36  are provided in a second region  43  defined between a freely selected pair of adjoining bolt holes  35 . 
     The fastening bolts  40  consisted of flange bolts in the foregoing embodiment, but may also consist of any other per se known bolts such as hex bolts. In such a case, a circular washer may be interposed between the head  40 A and the turbine-side flange  16 D. 
     The foregoing embodiment was directed to a metal gasket  1  interposed in the fastening part between the exhaust manifold  3  and the turbine  14  of the turbocharger  4 , but the metal gasket  1  of the present invention can be applied to other applications for high temperature environments. For instance, the metal gasket of the present invention can be used in the fastening part between a cylinder block and a cylinder head, the fastening part between a cylinder head and an exhaust manifold and the fastening part between an exhaust manifold and a catalytic converter. 
     GLOSSARY OF TERMS 
     
         
           1  metal gasket 
           3  exhaust manifold. 
           4  turbocharger 
           8 A manifold-side fastening surface 
           11  merging passage 
           12  female threaded hole 
           14  turbine 
           16 B turbine inlet 
           16 E turbine-side fastening surface 
           18  turbine inlet passage 
           19  turbine-side bolt hole 
           30 A- 30 F first to sixth plates 
           31  base portion 
           32  projection 
           34  passage hole 
           35  bolt hole 
           36  through hole 
           38  bead 
           38 A- 38 F first to sixth half beads 
           39  outer edge 
           40  fastening bolt 
           40 A head 
           41  bolt pressure receiving region 
           42  first region 
           43  second region