gasket

Abstract

A gasket includes an annular portion having a gas passage hole, a first fastening portion having a first bolt hole, a second fastening portion having a second bolt hole, a first arm portion configured to couple the annular portion and the first fastening portion, and a second arm portion configured to couple the annular portion and the second fastening portion. A planar shape of a gasket main body made up of the annular portion, the first fastening portion, the second fastening portion, the first arm portion, and the second arm portion is asymmetric with respect to a reference line perpendicular to a center line of the gas passage hole.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority from Japanese Patent Application No. 2025-010528 filed on January 24, 2025, the entire contents of which are hereby incorporated by reference.BACKGROUND

[0002] This disclosure relates to a gasket. Vehicles such as automobiles include an engine having intake pipes and exhaust pipes. Also, gaskets for ensuring airtightness are attached at connections of the intake pipes and the exhaust pipes (refer to Japanese Unexamined Utility Model Application Publication No. H01-15719 (Patent Document 1), Japanese Unexamined Patent Application Publication No. 2004-360801 (Patent Document 2), Japanese Unexamined Utility Model Application Publication No. H02-61166 (Patent Document 3), and Japanese Unexamined Patent Application Publication No. H11-264471 (Patent Document 4)).SUMMARY

[0003] According to this disclosure, a gasket includes an annular portion having a gas passage hole, a first fastening portion having a first bolt hole, a second fastening portion having a second bolt hole, a first arm portion configured to couple the annular portion and the first fastening portion, and a second arm portion configured to couple the annular portion and the second fastening portion. A planar shape of a gasket main body made up of the annular portion, the first fastening portion, the second fastening portion, the first arm portion, and the second arm portion is asymmetric with respect to a reference line perpendicular to a center line of the gas passage hole.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 is a diagram illustrating an example of a vehicle including an engine.

[0005] FIG. 2 is a diagram illustrating an example of the engine.

[0006] FIG. 3 is an exploded perspective view illustrating an example of a mounting structure of a gasket.

[0007] FIG. 4A is a plan view illustrating the gasket according to an embodiment of this disclosure.

[0008] FIG. 4B is a cross-sectional view illustrating the gasket taken along the line 4B-4B in FIG. 4A.

[0009] FIG. 5 is a perspective view illustrating a part of a first reference plane and a second reference plane using hatching.

[0010] FIG. 6A is a diagram illustrating a deformation state of the gasket under a high-temperature environment.

[0011] FIG. 6B is a diagram illustrating a deformation state of a gasket according to a comparative example under a high-temperature environment.

[0012] FIG. 7 is a plan view illustrating a gasket according to a modification.

[0013] FIG. 8 is a plan view illustrating a gasket according to a modification.

[0014] FIG. 9 is a plan view illustrating a gasket according to a modification.DETAILED DESCRIPTION

[0015] Incidentally, since the gasket attached to the intake pipe and the exhaust pipe is used under various temperature environments, it is preferable to take the expansion and contraction of the gasket into consideration. In other words, since the expansion and contraction are factors that may reduce the durability of the gasket, it is desirable to protect the gasket from the expansion and contraction by determining the shape of the gasket in consideration of the expansion and contraction.

[0016] Hereinafter, an embodiment of this disclosure will be described in detail with reference to drawings. In the following descriptions, the same or substantially same components and elements are denoted by the same reference signs and repetitive descriptions are omitted.Engine

[0017] FIG. 1 is a diagram illustrating an example of a vehicle 11 including an engine 10. FIG. 2 is a diagram illustrating an example of the engine 10. As illustrated in FIG. 1, the vehicle 11 includes a power unit 13 made up of the engine 10 and a transmission 12. As illustrated in FIG. 2, the engine 10 includes a cylinder block 14 and a cylinder head 15 attached to the cylinder block 14.

[0018] The engine 10 includes an intake system 20 coupled to an intake port 16 of the cylinder head 15 and an exhaust system 30 coupled to an exhaust port 17 of the cylinder head 15. The intake system 20 is provided with an air cleaner box 21, a throttle valve 22, an intake manifold 23, and intake pipes 24 and 25 coupled to these parts. Also, the exhaust system 30 is provided with an exhaust manifold 31, a catalyst converter 32, a muffler 33, and exhaust pipes 34 and 35 coupled to these parts.

[0019] The engine 10 includes an EGR system 40 configured to supply a part of exhaust gas from the exhaust system 30 to the intake system 20. The EGR system 40 includes an EGR cooler 41, an EGR valve 42, and EGR pipes 43, 44, and 45 coupled to these parts. The exhaust manifold 31 and the EGR cooler 41 are coupled via the EGR pipe 43, and the EGR cooler 41 and the EGR valve 42 are coupled via the EGR pipe 44. Also, the EGR valve 42 and the intake manifold 23 are coupled via the EGR pipe 45. Note that EGR stands for “Exhaust Gas Recirculation”.Structure of Gasket

[0020] Subsequently, a gasket 50 attached between the exhaust manifold 31 and the EGR pipe 43, that is, the gasket 50 according to an embodiment of this disclosure will be described. FIG. 3 is an exploded perspective view illustrating an example of a mounting structure of the gasket 50. FIG. 4A is a plan view illustrating the gasket 50 according to the embodiment of this disclosure, and FIG. 4B is a cross-sectional view illustrating the gasket 50 taken along the line 4B-4B in FIG. 4A. Note that broken lines illustrated in FIG. 4A are lines indicating boundaries of a first arm portion 63 and a second arm portion 64.

[0021] As illustrated in the enlarged part of FIG. 2 and FIG. 3, the gasket 50 is disposed between a flange 31a of the exhaust manifold 31 and a flange 43a of the EGR pipe 43. Also, the flanges 31a and 43a of the exhaust manifold 31 and the EGR pipe 43 are fastened to each other by fastening bolts 46 and fastening nuts 47. The gasket 50 is in close contact with both of the flanges 31a and 43a, and the gasket 50 ensures airtightness of gas passages 31b and 43b provided in the exhaust manifold 31 and the EGR pipe 43.

[0022] In order to ensure the spring characteristics of the gasket 50 under a high-temperature environment, the gasket 50 is formed of a material having a large thermal expansion coefficient. For example, an austenitic stainless steel is used as a material of the gasket 50. In addition, since the exhaust manifold 31 holds a metal catalyst therein, the exhaust manifold 31 is formed of a material having a small thermal expansion coefficient. For example, a ferritic stainless steel is used as materials of the exhaust manifold 31 and the EGR pipe 43. That is, the material forming the gasket 50 has a larger thermal expansion coefficient than the materials forming the exhaust manifold 31 and the EGR pipe 43.

[0023] As illustrated in FIG. 4A and FIG. 4B, the gasket 50 includes a gasket main body 55 made up of multiple metal sheets 51, 52, 53, and 54 stacked on one another. The gasket main body 55 includes an annular portion 57 having a gas passage hole 56, a first fastening portion 59 having a first bolt hole 58, and a second fastening portion 61 having a second bolt hole 60. As illustrated in the enlarged part of FIG. 4B, the annular portion 57 of the gasket main body 55 has a bead 62 with a so-called half-bead structure. Also, as illustrated in FIG. 4A, the gasket main body 55 includes the first arm portion 63 coupling the annular portion 57 and the first fastening portion 59 and the second arm portion 64 coupling the annular portion 57 and the second fastening portion 61. The first arm portion 63 extends in a tangential direction of the annular portion 57, and the second arm portion 64 extends in another tangential direction of the annular portion 57.

[0024] FIG. 5 is a perspective view illustrating a part of a first reference plane S1 and a second reference plane S2 using hatching. As illustrated in FIG. 4A and FIG. 5, a plane extending radially from a center line Cx of the gas passage hole 56 and passing through a center line C1 of the first bolt hole 58 is defined as the first reference plane S1, and a plane extending radially from the center line Cx of the gas passage hole 56 and passing through a center line C2 of the second bolt hole 60 is defined as the second reference plane S2. Here, the annular portion 57 includes a first arc portion 65 partitioned between the first reference plane S1 and the second reference plane S2 and a second arc portion 66 continuous with the first arc portion 65 and partitioned between the second reference plane S2 and the first reference plane S1.

[0025] As described above, the annular portion 57 and the first fastening portion 59 are coupled to each other via the first arm portion 63, and the annular portion 57 and the second fastening portion 61 are coupled to each other via the second arm portion 64. Here, the first arm portion 63 is coupled to the first arc portion 65 of the annular portion 57, and the second arm portion 64 is coupled to the second arc portion 66 of the annular portion 57. In other words, the first arm portion 63 does not intersect with the first reference plane S1, and the second arm portion 64 does not intersect with the second reference plane S2.

[0026] As illustrated in FIG. 4A, the gasket 50 including the arm portions 63 and 64 is not line-symmetric (asymmetric) with respect to a reference line Lx perpendicular to the center line Cx of the gas passage hole 56. In other words, the planar shape of the gasket main body 55 made up of the annular portion 57, the first fastening portion 59, the second fastening portion 61, the first arm portion 63, and the second arm portion 64 is not line-symmetric (asymmetric) with respect to the reference line Lx perpendicular to the center line Cx of the gas passage hole 56. The planar shape of the gasket main body 55 is also not line-symmetric (asymmetric) with respect to other reference lines perpendicular to the center line Cx of the gas passage hole 56.Deformation State of Gasket

[0027] FIG. 6A is a diagram illustrating a deformation state of the gasket 50 under a high-temperature environment, and FIG. 6B is a diagram illustrating a deformation state of a gasket 100 according to a comparative example under a high-temperature environment. As described above, the material forming the gasket 50 has a larger thermal expansion coefficient than the materials forming the exhaust manifold 31 and the EGR pipe 43. Therefore, under the high-temperature environment in which exhaust gas flows through the exhaust manifold 31, the gasket 50 expands more largely than the flanges 31a and 43a. That is, as illustrated in FIG. 6A, a distance P between the center line C1 and the center line C2 of the gasket 50 is restricted by the flanges 31a and 43a with a smaller expansion amount.

[0028] As described above, since the gasket 50 expands in the state where the fastening portions 59 and 61 are constrained, the first arm portion 63 stretches toward the annular portion 57 as indicated by an arrow Aa1 in FIG. 6A, and the second arm portion 64 stretches toward the annular portion 57 as indicated by an arrow Aa2 in FIG. 6A. In other words, the first arm portion 63 pushes the first arc portion 65 of the annular portion 57 in the tangential direction, and the second arm portion 64 pushes the second arc portion 66 of the annular portion 57 in the tangential direction. Consequently, as indicated by arrows Ab1 and Ab2, both the arm portions 63 and 64 push the annular portion 57 in the same circumferential direction, causing the annular portion 57 to be displaced in a direction rotating around the center line Cx. That is, since the planar shape of the gasket main body 55 is not line-symmetric (asymmetric) with respect to the reference line Lx perpendicular to the center line Cx of the gas passage hole 56, the annular portion 57 is displaced in the direction rotating around the center line Cx when the gasket 50 thermally expands. This can reduce the compressive stress generated during thermal expansion, and protect the gasket 50 from thermal expansion.

[0029] Also, since the annular portion 57 and the first fastening portion 59 are coupled via the first arm portion 63 and the annular portion 57 and the second fastening portion 61 are coupled via the second arm portion 64, an outer edge 57a of the annular portion 57 can be largely exposed. This makes it possible to enhance the heat dissipation properties of the annular portion 57 that comes in contact with exhaust gas, so that the durability of the gasket 50 can be enhanced by reducing the temperature thereof. Further, since the annular portion 57 and the first fastening portion 59 are coupled via the first arm portion 63 and the annular portion 57 and the second fastening portion 61 are coupled via the second arm portion 64, if the gasket 50 is excessively expanded, either the first arm portion 63 or the second arm portion 64 can be fractured. In other words, even when the gasket 50 is excessively expanded, either the first arm portion 63 or the second arm portion 64 can be fractured before the annular portion 57, so that the shape of the annular portion 57 can be maintained and the leakage of exhaust gas can be prevented.

[0030] In the description above, the gasket 50 is protected from thermal expansion. In addition, it is also possible to protect the gasket 50 from thermal contraction. When the gasket 50 contracts due to temperature decrease, that is, when the arm portions 63 and 64 shrink, the annular portion 57 is displaced in a direction rotating around the center line Cx as indicated by arrows α in FIG. 6A. This can reduce the tensile stress generated during thermal contraction, and also protect the gasket 50 from thermal contraction.Comparative Example

[0031] As illustrated in FIG. 6B, the gasket 100 according to the comparative example includes an annular portion 102 having a gas passage hole 101, a first fastening portion 104 having a first bolt hole 103, and a second fastening portion 106 having a second bolt hole 105. In addition, the gasket 100 includes a first plate portion 107 coupling the annular portion 102 and the first fastening portion 104 and a second plate portion 108 coupling the annular portion 102 and the second fastening portion 106. The planar shape of this gasket 100 is line-symmetric with respect to a reference line Lx100 perpendicular to a center line Cx100 of the gas passage hole 101.

[0032] When the planar shape of the gasket 100 is line-symmetric with respect to the reference line Lx100 as described above, it is difficult to reduce the compressive stress generated during thermal expansion. That is, since the gasket 100 expands in the state where the fastening portions 104 and 106 are constrained, the first plate portion 107 and the second plate portion 108 compress the annular portion 102 from opposite directions as indicated by arrows Ba1 and Ba2 in FIG. 6B. In other words, since the force acting on the gasket 100 is applied to an edge 109 as indicated by arrows Bb1 and Bb2, the edge 109 may be fractured depending on the expansion amount of the gasket 100. On the other hand, in the gasket 50 according to this disclosure, the compressive stress generated during thermal expansion can be reduced, so that the gasket 50 can be protected from thermal expansion.First Modification

[0033] In the example illustrated in FIG. 4A, the two fastening portions 59 and 61 are provided in the gasket 50, but the number of fastening portions provided in the gasket 50 is not limited to this, and it can be changed to three or more. FIG. 7 is a plan view illustrating a gasket 70 according to a modification. Note that broken lines illustrated in FIG. 7 are lines indicating boundaries of a first arm portion 76, a second arm portion 77, and a third arm portion 78.

[0034] As illustrated in FIG. 7, the gasket 70 includes a gasket main body 71 made up of multiple metal sheets stacked on one another. The gasket main body 71 includes an annular portion 72 having a gas passage hole 72a, a first fastening portion 73 having a first bolt hole 73a, a second fastening portion 74 having a second bolt hole 74a, and a third fastening portion 75 having a third bolt hole 75a. Also, the gasket main body 71 includes a first arm portion 76 coupling the annular portion 72 and the first fastening portion 73, a second arm portion 77 coupling the annular portion 72 and the second fastening portion 74, and a third arm portion 78 coupling the annular portion 72 and the third fastening portion 75. The first arm portion 76 extends in a tangential direction of the annular portion 72, the second arm portion 77 extends in another tangential direction of the annular portion 72, and the third arm portion 78 extends in another tangential direction of the annular portion 72.

[0035] As illustrated in FIG. 7, a plane extending radially from a center line Cx10 of the gas passage hole 72a and passing through a center line C11 of the first bolt hole 73a is defined as a first reference plane S11, and a plane extending radially from the center line Cx10 of the gas passage hole 72a and passing through a center line C12 of the second bolt hole 74a is defined as a second reference plane S12. In addition, a plane extending radially from the center line Cx10 of the gas passage hole 72a and passing through a center line C13 of the third bolt hole 75a is defined as a third reference plane S13. Here, the annular portion 72 includes a first arc portion 72b partitioned between the first reference plane S11 and the second reference plane S12 and a second arc portion 72c continuous with the first arc portion 72b and partitioned between the second reference plane S12 and the third reference plane S13. Also, the annular portion 72 includes a third arc portion 72d continuous with the second arc portion 72c and partitioned between the third reference plane S13 and the first reference plane S11.

[0036] As described above, the annular portion 72 and the first fastening portion 73 are coupled to each other via the first arm portion 76, the annular portion 72 and the second fastening portion 74 are coupled to each other via the second arm portion 77, and the annular portion 72 and the third fastening portion 75 are coupled to each other via the third arm portion 78. Here, the first arm portion 76 is coupled to the first arc portion 72b of the annular portion 72, the second arm portion 77 is coupled to the second arc portion 72c of the annular portion 72, and the third arm portion 78 is coupled to the third arc portion 72d of the annular portion 72. In other words, the first arm portion 76 does not intersect with the first reference plane S11, the second arm portion 77 does not intersect with the second reference plane S12, and the third arm portion 78 does not intersect with the third reference plane S13.

[0037] The gasket 70 including the arm portions 76, 77, and 78 with the structure described above is not line-symmetric (asymmetric) with respect to a reference line Lx10 perpendicular to the center line Cx10 of the gas passage hole 72a. In other words, the planar shape of the gasket main body 71 made up of the annular portion 72, the first fastening portion 73, the second fastening portion 74, the third fastening potion 75, the first arm portion 76, the second arm portion 77, and the third arm portion 78 is not line-symmetric (asymmetric) with respect to the reference line Lx10 perpendicular to the center line Cx10 of the gas passage hole 72a. The planar shape of the gasket main body 71 is also not line-symmetric (asymmetric) with respect to other reference lines perpendicular to the center line Cx10 of the gas passage hole 72a.

[0038] As described above, since the planar shape of the gasket main body 71 is not line-symmetric (asymmetric) with respect to the reference line Lx10, the annular portion 72 is displaced in a direction rotating around the center line Cx10 as indicated by arrows α2 when the gasket 70 thermally expands. That is, since the compressive stress generated during thermal expansion can be reduced, it is possible to protect the gasket 70 from thermal expansion. On the other hand, the annular portion 72 is displaced in a direction rotating around the center line Cx10 as indicated by arrows β2 when the gasket 70 thermally contracts. That is, since the compressive stress generated during thermal contraction can be reduced, it is possible to protect the gasket 70 from thermal contraction.Second Modification

[0039] In the example illustrated in FIG. 4A, the planar shape of the gasket main body 55 is rotationally symmetric, that is, twofold symmetric about the center of the gas passage hole 56 as a symmetric point, but the planar shape is not limited to this. In other words, in the example illustrated in FIG. 4A, an angle formed between the first reference plane S1 and the second reference plane S2 is “180°”, but the angle is not limited to this. Here, FIG. 8 is a plan view illustrating a gasket 80 according to a modification. Note that broken lines illustrated in FIG. 8 are lines indicating boundaries of a first arm portion 85 and a second arm portion 86.

[0040] As illustrated in FIG. 8, the gasket 80 includes a gasket main body 81 made up of multiple metal sheets stacked on one another. The gasket main body 81 includes an annular portion 82 having a gas passage hole 82a, a first fastening portion 83 having a first bolt hole 83a, and a second fastening portion 84 having a second bolt hole 84a. Also, the gasket main body 81 includes the first arm portion 85 coupling the annular portion 82 and the first fastening portion 83 and the second arm portion 86 coupling the annular portion 82 and the second fastening portion 84. The first arm portion 85 extends in a tangential direction of the annular portion 82, and the second arm portion 86 extends in another tangential direction of the annular portion 82.

[0041] As illustrated in FIG. 8, a plane extending radially from a center line Cx20 of the gas passage hole 82a and passing through a center line C21 of the first bolt hole 83a is defined as a first reference plane S21, and a plane extending radially from the center line Cx20 of the gas passage hole 82a and passing through a center line C22 of the second bolt hole 84a is defined as a second reference plane S22. Here, the annular portion 82 includes a first arc portion 82b partitioned between the first reference plane S21 and the second reference plane S22 and a second arc portion 82c continuous with the first arc portion 82b and partitioned between the second reference plane S22 and the first reference plane S21.

[0042] As described above, the annular portion 82 and the first fastening portion 83 are coupled to each other via the first arm portion 85, and the annular portion 82 and the second fastening portion 84 are coupled to each other via the second arm portion 86. Here, the first arm portion 85 is coupled to the first arc portion 82b of the annular portion 82, and the second arm portion 86 is coupled to the second arc portion 82c of the annular portion 82. In other words, the first arm portion 85 does not intersect with the first reference plane S21, and the second arm portion 86 does not intersect with the second reference plane S22.

[0043] The gasket 80 including the arm portions 85 and 86 with the structure described above is not line-symmetric (asymmetric) with respect to a reference line Lx20 perpendicular to the center line Cx20 of the gas passage hole 82a. In other words, the planar shape of the gasket main body 81 made up of the annular portion 82, the first fastening portion 83, the second fastening portion 84, the first arm portion 85, and the second arm portion 86 is not line-symmetric (asymmetric) with respect to the reference line Lx20 perpendicular to the center line Cx20 of the gas passage hole 82a. As described above, since the planar shape of the gasket main body 81 is not line-symmetric (asymmetric) with respect to the reference line Lx20, the compressive stress and the tensile stress can be reduced as in the gasket 50 illustrated in FIG. 4A, so that it is possible to protect the gasket 80 from thermal expansion and thermal contraction. The planar shape of the gasket main body 81 is also not line-symmetric (asymmetric) with respect to other reference lines perpendicular to the center line Cx20 of the gas passage hole 82a.Third Modification

[0044] In the example illustrated in FIG. 7, the planar shape of the gasket main body 71 is rotationally symmetric, that is, threefold symmetric about the center of the gas passage hole 72a as a symmetric point, but the planar shape is not limited to this. In other words, in the example illustrated in FIG. 7, an angle formed between the first reference plane S11 and the second reference plane S12 is “120°” and an angle formed between the first reference plane S11 and the third reference plane S13 is “120°”, but the angles are not limited to these. Here, FIG. 9 is a plan view illustrating a gasket 90 according to a modification. Note that broken lines illustrated in FIG. 9 are lines indicating boundaries of a first arm portion 96, a second arm portion 97, and a third arm portion 98.

[0045] As illustrated in FIG. 9, the gasket 90 includes a gasket main body 91 made up of multiple metal sheets stacked on one another. The gasket main body 91 includes an annular portion 92 having a gas passage hole 92a, a first fastening portion 93 having a first bolt hole 93a, a second fastening portion 94 having a second bolt hole 94a, and a third fastening portion 95 having a third bolt hole 95a. Also, the gasket main body 91 includes the first arm portion 96 coupling the annular portion 92 and the first fastening portion 93, the second arm portion 97 coupling the annular portion 92 and the second fastening portion 94, and the third arm portion 98 coupling the annular portion 92 and the third fastening portion 95. The first arm portion 96 extends in a tangential direction of the annular portion 92, the second arm portion 97 extends in another tangential direction of the annular portion 92, and the third arm portion 98 extends in another tangential direction of the annular portion 92.

[0046] As illustrated in FIG. 9, a plane extending radially from a center line Cx30 of the gas passage hole 92a and passing through a center line C31 of the first bolt hole 93a is defined as a first reference plane S31, and a plane extending radially from the center line Cx30 of the gas passage hole 92a and passing through a center line C32 of the second bolt hole 94a is defined as a second reference plane S32. In addition, a plane extending radially from the center line Cx30 of the gas passage hole 92a and passing through a center line C33 of the third bolt hole 95a is defined as a third reference plane S33. Here, the annular portion 92 includes a first arc portion 92b partitioned between the first reference plane S31 and the second reference plane S32 and a second arc portion 92c continuous with the first arc portion 92b and partitioned between the second reference plane S32 and the third reference plane S33. Also, the annular portion 92 includes a third arc portion 92d continuous with the second arc portion 92c and partitioned between the third reference plane S33 and the first reference plane S31.

[0047] As described above, the annular portion 92 and the first fastening portion 93 are coupled to each other via the first arm portion 96, the annular portion 92 and the second fastening portion 94 are coupled to each other via the second arm portion 97, and the annular portion 92 and the third fastening portion 95 are coupled to each other via the third arm portion 98. Here, the first arm portion 96 is coupled to the first arc portion 92b of the annular portion 92, the second arm portion 97 is coupled to the second arc portion 92c of the annular portion 92, and the third arm portion 98 is coupled to the third arc portion 92d of the annular portion 92. In other words, the first arm portion 96 does not intersect with the first reference plane S31, the second arm portion 97 does not intersect with the second reference plane S32, and the third arm portion 98 does not intersect with the third reference plane S33.

[0048] The gasket 90 including the arm portions 96, 97, and 98 with the structure described above is not line-symmetric (asymmetric) with respect to a reference line Lx30 perpendicular to the center line Cx30 of the gas passage hole 92a. In other words, the planar shape of the gasket main body 91 made up of the annular portion 92, the first fastening portion 93, the second fastening portion 94, the third fastening portion 95, the first arm portion 96, the second arm portion 97, and the third arm portion 98 is not line-symmetric (asymmetric) with respect to the reference line Lx30 perpendicular to the center line Cx30 of the gas passage hole 92a. As described above, since the planar shape of the gasket main body 91 is not line-symmetric (asymmetric) with respect to the reference line Lx30, the compressive stress and the tensile stress can be reduced as in the gasket 70 illustrated in FIG. 7, so that it is possible to protect the gasket 90 from thermal expansion and thermal contraction. The planar shape of the gasket main body 91 is also not line-symmetric (asymmetric) with respect to other reference lines perpendicular to the center line Cx30 of the gas passage hole 92a.Other Modifications

[0049] This disclosure is not limited to the embodiment above, and can be modified in various ways within the range not departing from the gist thereof. In the description above, the gaskets 50, 70, 80, and 90 are attached at connections between the exhaust system 30 and the EGR system 40, but are not limited to these. For example, the gaskets 50, 70, 80, and 90 may be attached to the exhaust system 30, or the gaskets 50, 70, 80, and 90 may be attached to the EGR system 40. Also, the gaskets 50, 70, 80, and 90 may be attached to the intake system 20, or the gaskets 50, 70, 80, and 90 may be attached to a device other than the engine. In the illustrated examples, the arm portions 63, 64, 76 to 78, 85, 86, and 96 to 98 extending linearly are provided in the gasket main bodies 55, 71, 81, and 91, but are not limited to these. For example, the arm portions extending in a curved shape may be provided in the gasket main bodies 55, 71, 81, and 91.

[0050] In the example illustrated in FIG. 4B, the gasket main body 55 is formed of the four metal sheets 51, 52, 53, and 54, but is not limited to this, and the gasket main body 55 may be formed of one metal sheet or two or more metal sheets. Also, in the example illustrated in FIG. 4B, the bead 62 with a half-bead structure is formed in the annular portion 57, but is not limited to this, and a bead with a full-bead structure may be formed in the annular portion 57 or the bead 62 may be eliminated from the annular portion 57. Further, in the description above, the gasket main body 55 is formed of a metal material such as an austenitic stainless steel, but is not limited to this, and any material can be used as long as it thermally expands. For example, the gasket main bodies 55, 71, 81, and 91 may be formed of a resin material or the gasket main bodies 55, 71, 81, and 91 may be formed of a rubber material.

[0051] In the illustrated examples, the gas passage holes 56, 72a, 82a, and 92a are formed to have a circular shape, but are not limited to these, and the gas passage holes 56, 72a, 82a, and 92a may be formed to have, for example, an oblong or elliptical shape. Also, when the gas passage holes 56, 72a, 82a, and 92a are formed to have an oblong or elliptical shape, the center lines of the gas passage holes 56, 72a, 82a, and 92a are located at the center of the major axis or the minor axis. In addition, in the illustrated examples, the bolt holes 58, 60, 73a to 75a, 83a, 84a, and 93a to 95a are formed to have a circular shape, but are not limited to these, and the bolt holes 58, 60, 73a to 75a, 83a, 84a, and 93a to 95a may be formed to have, for example, an oblong or elliptical shape. Also, when the bolt holes 58, 60, 73a to 75a, 83a, 84a, and 93a to 95a are formed to have an oblong or elliptical shape, the center lines of the bolt holes 58, 60, 73a to 75a, 83a, 84a, and 93a to 95a are located at the center of the major axis or the minor axis.

[0052] According to this disclosure, the planar shape of the gasket main body is not line-symmetric (asymmetric) with respect to the reference line perpendicular to the center line of the gas passage hole. This allows the gasket to be protected from expansion and contraction.

Claims

1. A gasket comprising:an annular portion having a gas passage hole;a first fastening portion having a first bolt hole;a second fastening portion having a second bolt hole;a first arm portion configured to couple the annular portion and the first fastening portion; anda second arm portion configured to couple the annular portion and the second fastening portion,wherein a planar shape of a gasket main body made up of the annular portion, the first fastening portion, the second fastening portion, the first arm portion, and the second arm portion is asymmetric with respect to a reference line perpendicular to a center line of the gas passage hole.

2. The gasket according to claim 1,wherein the first arm portion extends in a tangential direction of the annular portion, andwherein the second arm portion extends in another tangential direction of the annular portion.

3. The gasket according to claim 1,wherein when a plane extending radially from the center line of the gas passage hole and passing through a center line of the first bolt hole is defined as a first reference plane, and a plane extending radially from the center line of the gas passage hole and passing through a center line of the second bolt hole is defined as a second reference plane,the first arm portion does not intersect with the first reference plane, andthe second arm portion does not intersect with the second reference plane.

4. The gasket according to claim 1,wherein when a plane extending radially from the center line of the gas passage hole and passing through a center line of the first bolt hole is defined as a first reference plane, and a plane extending radially from the center line of the gas passage hole and passing through a center line of the second bolt hole is defined as a second reference plane,the annular portion includes a first arc portion partitioned between the first reference plane and the second reference plane and a second arc portion continuous with the first arc portion and partitioned between the second reference plane and the first reference plane,the first arm portion is coupled to the first arc portion, andthe second arm portion is coupled to the second arc portion.

5. The gasket according to claim 1, further comprising:a third fastening portion having a third bolt hole; anda third arm portion configured to couple the annular portion and the third fastening portion,wherein when a plane extending radially from the center line of the gas passage hole and passing through a center line of the first bolt hole is defined as a first reference plane, a plane extending radially from the center line of the gas passage hole and passing through a center line of the second bolt hole is defined as a second reference plane, and a plane extending radially from the center line of the gas passage hole and passing through a center line of the third bolt hole is defined as a third reference plane,the annular portion includes a first arc portion partitioned between the first reference plane and the second reference plane, a second arc portion continuous with the first arc portion and partitioned between the second reference plane and the third reference plane, and a third arc portion continuous with the second arc portion and partitioned between the third reference plane and the first reference plane,the first arm portion is coupled to the first arc portion,the second arm portion is coupled to the second arc portion, andthe third arm portion is coupled to the third arc portion.

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