FLANGE JOINING STRUCTURE

A flange joining structure comprises flanges of a cylinder head of an internal combustion engine and a turbine housing joined through a gasket. The flange of cylinder head has, in an end face thereof, end parts of a first collecting exhaust pipe and a second collecting exhaust pipe; the flange of turbine housing has, in an end face thereof, end parts of a first pre-merge exhaust pipe and a second pre-merge exhaust pipe corresponding to the end parts of the first collecting exhaust pipe and the second collecting exhaust pipe; and the gasket has, on a face on the cylinder head side, a bead formed into an edge-rounded rectangle having a straight part shorter than the radius of curvature thereof, and surrounding the end parts of the first collecting exhaust pipe and the second collecting exhaust pipe.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2017-101466, filed May 23, 2017, entitled “ FLANGE JOINING STRUCTURE.” The contents of this application are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a flange joining structure. More specifically, the disclosure relates to a flange joining structure in which a flange formed in a cylinder head of an internal combustion engine and a flange formed in an exhaust member are connected through a plate-like gasket.

BACKGROUND

Heretofore, a gasket has been provided between a flange formed in a cylinder head of an internal combustion engine and a flange formed in an exhaust member of an exhaust pipe, a turbine housing, or the like, to prevent leakage of exhaust gas between the cylinder head and exhaust member. For example, Japanese Patent Application Publication No. Hei 10-169456 discloses a technique of joining a flange of a cylinder head and a flange of an exhaust gas turbine through a plate-like gasket. In the technique of Japanese Patent Application Publication No. Hei 10-169456, each of the flange of the cylinder head and the flange of the exhaust gas turbine has two substantially rectangular openings each connected to two exhaust passages. Additionally, in the technique of Japanese Patent Application Publication No. Hei 10-169456, the flanges are joined through a gasket that has a substantially rectangular through hole surrounding the two openings.

SUMMARY

Incidentally, since high-temperature exhaust gas continuously flows through the inside of the flange of the cylinder head and the flange of the turbine housing, end faces of both flanges deform slightly by heat of exhaust gas. Hence, the flange joining structure using the plate-like gasket disclosed in Japanese Patent Application Publication No. Hei 10-169456 may be incapable of maintaining a sufficient sealing property because of the heat of exhaust gas.

Thus, it is preferable to provide a flange joining structure that can maintain a sealing property even when high-temperature exhaust gas continuously flows therethrough.

(1) A flange joining structure joins a flange (e.g., later-mentioned flange21) formed in a cylinder head (e.g., later-mentioned cylinder head2H) of an internal combustion engine (e.g., later-mentioned internal combustion engine2) and a flange (e.g., later-mentioned flange22) formed in an exhaust member (e.g., later-mentioned turbine housing4) through a gasket (e.g., later-mentioned gasket23). The flange joining structure is characterized in that: multiple openings (e.g., later-mentioned upstream openings11a,12a) of multiple exhaust passages (e.g., later-mentioned collecting exhaust pipelines11,12) connected to a combustion chamber of the internal combustion engine are formed in an end face (e.g., later-mentioned21a) of the flange of the cylinder head; multiple openings (e.g., later-mentioned downstream openings13a,14a) corresponding to the multiple openings formed in the end face of the flange of the cylinder head are formed in an end face (e.g., later-mentioned end face22a) of the flange of the exhaust member; and the gasket has a bead (e.g., later-mentioned bead39) that protrudes toward any one of parts which are the cylinder head and the exhaust member, and, in plan view, is formed into a perfect circle or an edge-rounded rectangle having a straight part shorter than the radius of curvature thereof, that surrounds adjacent two or more openings from among multiple openings formed in the flange of the one part.

(2) In this case, it is preferable that a flange of any one of parts which are the cylinder head and the exhaust member include a partition wall part (e.g., later-mentioned partition wall portion30) that separates the adjacent two openings as well as two passages connected to the two openings, and a weakened part (e.g., later-mentioned weakened portion31) be provided in the thinnest part of the partition wall part.

(3) In this case, it is preferable that a cooling water passage (e.g., later-mentioned cooling water passages27to29) through which cooling water flows be formed in the flange of the cylinder head, no passage through which cooling water passes be formed in the flange of the exhaust member, and the weakened part be formed in the partition wall part of the exhaust member.

(4) In this case, it is preferable that the partition wall part is a plate that extends in a flow direction of exhaust gas flowing through the two passages, and the weakened part is a groove that extends in the flow direction of the exhaust gas, and be formed on both sides of the partition wall part.

(5) In this case, it is preferable that the weakened part is a groove that is substantially V-shaped in cross-sectional view substantially perpendicular to the flow direction of the exhaust gas.

(6) In this case, it is preferable that the exhaust member is a turbine housing (e.g., later-mentioned turbine housing4) of a turbocharger that compresses intake air by use of energy of exhaust gas of the internal combustion engine.

(7) In this case, it is preferable that the internal combustion engine includes multiple cylinders (e.g., later-mentioned cylinders CY1to CY4), and the cylinder head has multiple bifurcated pipelines (e.g., later-mentioned bifurcated pipelines7,8,9,10) that extend from combustion chambers of the multiple cylinders, and multiple collecting pipelines (e.g., later-mentioned collecting exhaust pipelines11,12) that collect the exhaust gas flowing through the multiple bifurcated pipelines and guide the exhaust gas to the multiple openings. In the above explanation of the exemplary embodiment, specific elements with their reference numerals are indicated by using brackets. These specific elements are presented as mere examples in order to facilitate understanding, and thus, should not be interpreted as any limitation to the accompanying claims.

(1) In one embodiment, the gasket has a bead that protrudes toward any one of parts which are the cylinder head and the exhaust member, and, in plan view, is formed into a perfect circle or an edge-rounded rectangle having a straight part shorter than the radius of curvature thereof, that surrounds adjacent two or more openings from among multiple openings formed in the end face of the flange of the one part. Here, when high-temperature exhaust gas is continuously discharged through the multiple exhaust passages formed inside the flange of the cylinder head and the flange of the exhaust member, the end faces of the flanges deform such that an opening is formed (hereinafter, such deformation is referred to as “opening deformation”) due to heat of exhaust gas. The amounts of displacement due to such opening deformation is characterized by maximizing at the center, which is between the two adjacent openings, and decreasing concentrically from the center. According to this characteristic of the opening deformation of the end face of the flange, the flange joining structure has the circular or substantially circular (more specifically, an edge-rounded rectangle having a straight part shorter than the radius of curvature thereof) bead that surrounds the two or more adjacent openings, on a face of the plate-like gasket on the side of any of the parts which are the cylinder head and the exhaust member. When both of the flanges are joined through such a gasket, the bead formed in the gasket comes into contact with parts of both of the flanges where the amounts of displacement caused by the opening deformation are almost the same. Hence, even when opening deformation occurs due to the heat of exhaust gas, a substantially uniform contact pressure is applied on the gasket, so that the sealing property between both of the flanges can be maintained.

(2) In another embodiment, a flange of at least one of parts which are the cylinder head and the exhaust member includes a partition wall part that separates the adjacent two openings as well as two passages connected to the two openings. Such a partition wall part may crack due to thermal expansion, when high-temperature exhaust gas continuously flows through the two passages separated by the partition wall part. Moreover, the weakened part is provided in the thinnest part of the above partition wall part. Accordingly, upon occurrence of a thermal expansion large enough to cause a crack as mentioned earlier, the crack may be formed in the most easily breakable weakened part. In other words, since the flange joining structure can prevent occurrence of a crack in an unintended part other than the weakened part, behavior of the gasket can be stabilized, whereby the sealing property of the gasket can be maintained.

(3) In another embodiment, a cooling water passage through which cooling water flows is formed in the flange of the cylinder head, while no passage through which cooling water passes is formed in the flange of the exhaust member. For this reason, the temperature of the flange of the exhaust member tends to become higher than that of the flange of the cylinder head, and a crack is more likely to occur in its partition wall part due to thermal expansion. Moreover, the aforementioned weakened part is formed in the partition wall part of the flange of the exhaust member in which such a crack is more likely to occur. Hence, it is possible to prevent occurrence of a crack in an unintended part other than the weakened part of the partition wall part of the exhaust member, to stabilize behavior of the gasket, and maintain the sealing property of the gasket.

(4) In another embodiment, the partition wall part is a plate that extends in a flow direction of exhaust gas flowing through the two passages, and the weakened part is a groove that extends in the flow direction of the exhaust gas, and is formed on both sides (i.e., faces contacting the two passages) of the partition wall part. Hence, a crack can be formed in the partition wall part in the flow direction of the exhaust gas, behavior of the gasket can be stabilized even more, and therefore the sealing property of the gasket can be maintained more securely.

(5) In another embodiment, a groove substantially V-shaped in cross-sectional view substantially perpendicular to the flow direction of the exhaust gas is formed as the weakened part in the partition wall part. Hence, a crack can be caused more easily in the weakened part, behavior of the gasket can be stabilized even more, and therefore the sealing property of the gasket can be maintained more securely.

(6) In another embodiment, the exhaust member is a turbine housing of a turbocharger, and a flange formed in the turbine housing and the flange formed in the cylinder head are joined through the gasket. Since a turbocharger compresses intake air by use of energy of exhaust gas, it is preferable that the heat of exhaust gas be higher to improve turbine efficiency. The flange joining structure is applied to joining of the flange of the turbine housing through which such high-temperature exhaust gas flows and the flange of the cylinder head, whereby the aforementioned effect of maintaining the sealing property can be enhanced further.

(7) In another embodiment, the cylinder head has multiple bifurcated pipelines that extend from combustion chambers of the multiple cylinders, and multiple collecting pipelines that collect the exhaust gas flowing through the multiple bifurcated pipelines and guide the exhaust gas to the multiple openings of the flange. In other words, since the exhaust manifold is formed in the cylinder head of the flange joining structure, the number of parts can be reduced, and the device as a whole can be downsized. In addition, when the whole device is thus downsized, the temperature of exhaust gas flowing through the flange of the cylinder head tends to become high. Since the flange joining structure is applied to joining of the flange of the cylinder head through which such high-temperature exhaust gas flows and the flange of the exhaust member, the aforementioned effect of maintaining the sealing property can be enhanced even further.

DETAILED DESCRIPTION

FIG. 1is a cross-sectional view of an internal combustion engine2and a turbine housing4that are joined by applying a flange joining structure of the embodiment of the present disclosure. As will be described later with reference toFIG. 2and other drawings, the internal combustion engine2is an inline-four engine configured by arranging multiple, or more specifically, four cylinders in series.FIG. 1is a cross-sectional view including a second cylinder CY2of the internal combustion engine2and the turbine housing4.

The internal combustion engine2is configured by combining a cylinder block2B in which multiple cylinders including the second cylinder CY2are formed, and a cylinder head2H provided with parts such as multiple exhaust passages that allow passage of exhaust gas discharged from combustion chambers in the cylinders, and exhaust valves2V. The turbine housing4is a part of a turbocharger that compresses intake air of the internal combustion engine2by use of energy of exhaust gas of the internal combustion engine2. The turbine housing4has an exhaust passage that introduces the exhaust gas discharged from the combustion chamber of the internal combustion engine2into an unillustrated turbine impeller room. Accordingly, when a flange21formed in the cylinder head2H of the internal combustion engine2and a flange22formed in the turbine housing4are joined through a later-mentioned plate-like gasket23, a single exhaust passage introducing the exhaust gas to the turbine impeller room from the combustion chamber in each cylinder of the internal combustion engine2is formed.

FIG. 2is a side view of the pipe-like exhaust passage formed by the cylinder head2H and the turbine housing4.FIG. 3is a plan view of the exhaust passage. Note that inFIGS. 2 and 3, the cylinder head2H and the turbine housing4are omitted for simplicity of the description, while the exhaust passage and the cylinder block2B formed by the cylinder head2H and the turbine housing4are indicated by solid lines. In addition, of the exhaust passage illustrated inFIGS. 2 and 3, apart on the left side of a broken line la is a passage formed by the cylinder head2H, and a part on the right side of the broken line1ais passage formed by the turbine housing4. Hereinafter, of the exhaust passage, the passage formed by the cylinder head2H is also generically called an exhaust manifold5. Meanwhile, of the exhaust passage, the passage formed by the turbine housing4is also generically called a housing passage41.

As illustrated inFIG. 3, four cylinders CY1, CY2, CY3, CY4arranged in series are formed in the cylinder block2B. The exhaust manifold5has exhaust ports PO11, PO12connected to the first cylinder CY1, exhaust ports PO21, PO22connected to the second cylinder CY2, exhaust ports PO31, PO32connected to the third cylinder CY3, and exhaust ports PO41, PO42connected to the fourth cylinder CY4.

The exhaust manifold5includes a first bifurcated pipeline7connected to the exhaust ports PO11, PO12on the upstream side, a second bifurcated pipeline8connected to the exhaust ports PO21, PO22on the upstream side, a third bifurcated pipeline9connected to the exhaust ports PO31, PO32on the upstream side, a fourth bifurcated pipeline10connected to the exhaust ports PO41, PO42on the upstream side, a first upstream collecting exhaust pipeline11connected to the first bifurcated pipeline7and the fourth bifurcated pipeline10on the upstream side and collecting the exhaust gas flowing through the bifurcated pipelines7,10, and a second upstream collecting exhaust pipeline12connected to the second bifurcated pipeline8and the third bifurcated pipeline9on the upstream side and collecting the exhaust gas flowing through the bifurcated pipelines8,9.

The first bifurcated pipeline7is connected to the first cylinder CY1through the two exhaust ports PO11, PO12on the upstream side, and includes a Y-shaped junction passage that merges the exhaust gas from the exhaust ports PO11, PO12. The first bifurcated pipeline7is connected to the first upstream collecting exhaust pipeline11together with the fourth bifurcated pipeline10on the downstream side, and guides the exhaust gas from the exhaust ports PO11, PO12to the first upstream collecting exhaust pipeline11.

The second bifurcated pipeline8is connected to the second cylinder CY2through the two exhaust ports PO21, PO22on the upstream side, and includes a Y-shaped junction passage that merges the exhaust gas from the exhaust ports PO21, PO22. The second bifurcated pipeline8is connected to the second upstream collecting exhaust pipeline12together with the third bifurcated pipeline9on the downstream side, and guides the exhaust gas from the exhaust ports PO21, PO22to the second upstream collecting exhaust pipeline12.

The third bifurcated pipeline9is connected to the third cylinder CY3through the two exhaust ports PO31, PO32on the upstream side, and includes a Y-shaped junction passage that merges the exhaust gas from the exhaust ports PO31, PO32. The third bifurcated pipeline9is connected to the second upstream collecting exhaust pipeline12together with the second bifurcated pipeline8on the downstream side, and guides the exhaust gas from the exhaust ports PO31, PO32to the second upstream collecting exhaust pipeline12.

The fourth bifurcated pipeline10is connected to the fourth cylinder CY4through the two exhaust ports PO41, PO42on the upstream side, and includes a Y-shaped junction passage that merges the exhaust gas from the exhaust ports PO41, PO42. The fourth bifurcated pipeline10is connected to the first upstream collecting exhaust pipeline11together with the first bifurcated pipeline7on the downstream side, and guides the exhaust gas from the exhaust ports PO41, PO42to the first upstream collecting exhaust pipeline11.

The first upstream collecting exhaust pipeline11is connected to the bifurcated pipelines7,10on the upstream side, merges the exhaust gas flowing through the first bifurcated pipeline7and the exhaust gas flowing through the fourth bifurcated pipeline10, and guides the exhaust gas to the downstream turbine housing4. The first upstream collecting exhaust pipeline11is connected to a later-mentioned first passage13of the turbine housing4on the downstream side. The first upstream collecting exhaust pipeline11guides the exhaust gas from the combustion chambers of a first cylinder group configured of the first cylinder CY1and the fourth cylinder CY4, to the first passage13of the turbine housing4.

The second upstream collecting exhaust pipeline12is connected to the bifurcated pipelines8,9on the upstream side, merges the exhaust gas flowing through the second bifurcated pipeline8and the exhaust gas flowing through the third bifurcated pipeline9, and guides the exhaust gas to the downstream turbine housing4. The second upstream collecting exhaust pipeline12is connected to a later-mentioned second passage14of the turbine housing4on the downstream side. The second upstream collecting exhaust pipeline12guides the exhaust gas from the combustion chambers of a second cylinder group configured of the second cylinder CY2and the third cylinder CY3, to the second passage14of the turbine housing4

As illustrated inFIGS. 2 and 3, the housing passage41includes, from this order from the upstream side toward the downstream side, the first passage13connected to the first upstream collecting exhaust pipeline11of the exhaust manifold5, the second passage14connected to the second upstream collecting exhaust pipeline12of the exhaust manifold5, a Y-shaped junction passage18connected to the first passage13and the second passage14, an annular scroll passage42for accelerating the exhaust gas flowing from the junction passage18, and an impeller room43into which the exhaust gas accelerated by the scroll passage42flows and in which an unillustrated turbine impeller is stored.

The first passage13is connected to the first upstream collecting exhaust pipeline11of the exhaust manifold5. The exhaust gas from the combustion chambers of the first cylinder group flows through the first passage13. The second passage14is connected to the second upstream collecting exhaust pipeline12of the exhaust manifold5. The exhaust gas from the combustion chambers of the second cylinder group flows through the second passage14. The junction passage18is connected to the first passage13and the second passage14, and merges the exhaust gas flowing through the first passage13and the exhaust gas flowing through the second passage14.

Next, a joining structure of the cylinder head2H and the turbine housing4will be described.

As illustrated inFIG. 1, the aforementioned first upstream collecting exhaust pipeline11and second upstream collecting exhaust pipeline12extending substantially parallel to each other are formed as through holes, in the flange21formed in the cylinder head2H. In addition, a first upstream opening11acommunicating into the first upstream collecting exhaust pipeline11, and a second upstream opening12acommunicating into the second upstream collecting exhaust pipeline12are formed in an end face21aof the flange21.

Additionally, the flange21of the cylinder head2H includes a plate-like partition wall portion24that separates the first upstream collecting exhaust pipeline11and the first upstream opening11afrom the second upstream collecting exhaust pipeline12and the second upstream opening12a,and extends in the flow direction of the exhaust gas. Moreover, in the flange21, cooling water passages27,28,29throughwhich cooling water flows are formed around the pipelines11,12through which the high-temperature exhaust gas flows.

The aforementioned first passage13and second passage14extending substantially parallel to each other are formed as through holes, in the flange22formed in the turbine housing4. In addition, a first downstream opening13acommunicating into the first passage13and slightly larger than the aforementioned first upstream opening11a,and a second downstream opening14acommunicating into the second passage14and slightly larger than the aforementioned second upstream opening12aare formed in an end face22aof the flange22. As illustrated inFIG. 1, when the flange21of the cylinder head2H and the flange22of the turbine housing4are joined to each other, the first upstream opening11afaces the first downstream opening13a,and the second upstream opening12afaces the second downstream opening14a.Thus, the first upstream collecting exhaust pipeline11is connected with the first passage13, and the second upstream collecting exhaust pipeline12is connected with the second passage14.

Additionally, the flange22of the turbine housing4includes a plate-like partition wall portion30that separates the first passage13and the first downstream opening13afrom the second passage14and the second downstream opening14a, and extends in the flow direction of the exhaust gas. Note that unlike the flange21of the cylinder head2H, the flange22does not have any passages through which cooling water flows.

FIG. 4is a perspective view of the gasket23. More specifically,FIG. 4is a perspective view of the gasket23assembled onto the flange22of the turbine housing4.

FIG. 5is a cross-sectional view taken along line A-A ofFIG. 1. More specifically,FIG. 5is a view of the partition wall portion30as seen from the junction passage18side.

As illustrated inFIGS. 4 and 5, in the turbine housing4, the partition wall portion30separating the first passage13from the second passage14has, in its center part having the smallest thickness, a weakened portion31which is a groove extending in the flow direction of the exhaust gas flowing through the passages13,14. The weakened portion31is formed in parts of the partition wall portion30except for an end part on the gasket23side, and extends over a face on the first passage13side, a face on the junction passage18side, and a face on the second passage14side.

FIG. 6is a cross-sectional view of the partition wall portion30, taken along a plane substantially perpendicular to the flow direction of the exhaust gas. The weakened portion31formed in the partition wall portion30is a substantially V-shaped groove in cross-sectional view. The weakened portion31has a width W of about 2 mm, and a depth D of about 0.5 mm, for example. Additionally, a bottom part of the weakened portion31is chamfered by an arc having a radius of curvature R of about 1 mm.

As illustrated inFIG. 4, the gasket23is formed into a plate shape, and has a total of four fastening holes32,33,34,35respectively formed in four corners thereof. The cylinder head2H and the turbine housing4are joined by providing the gasket23between the flanges21,22, inserting unillustrated bolts into the fastening holes32to35formed in the gasket23, and fastening the bolts.

Additionally, the gasket23has, in its center, an opening36as a substantially circular through hole that surrounds the first downstream opening13aand the second downstream opening14awhen the gasket23is placed on the end face22aof the flange22of the turbine housing4. Here, “substantially circular” is, more specifically, an edge-rounded rectangle having a straight part shorter than the radius of curvature thereof. Note that an “edge-rounded rectangle” is, more specifically, an oblong shape whose arcs are connected by parallel straight lines. Note that although the embodiment describes a case in which the shape of the opening36is substantially circular in plan view, the present invention is not limited to this, and the opening may be formed into a perfect circle.

Additionally, the gasket23has, on the outer side of the aforementioned opening36, a substantially circular bead39that surrounds the first downstream opening13aand the second downstream opening14ain plan view. Note that although the embodiment describes a case in which the shape of the bead39is substantially circular in plan view, the present invention is not limited to this, and the bead may be formed into a perfect circle. In addition, as illustrated inFIG. 4, the bead39protrudes to the cylinder head2H side. Note that although the embodiment describes a case in which the bead39protrudes to the cylinder head2H side, the present invention is not limited to this, and the bead may protrude to the turbine housing4side.

As illustrated inFIG. 1, the first upstream opening11aand second upstream opening12aformed in the end face21aof the flange21of the cylinder head2H respectively face the first downstream opening13aand second downstream opening14aformed in the end face22aof the flange22of the turbine housing4. Hence, when the end face21aof the flange21of the cylinder head2H and the end face22aof the flange22of the turbine housing4are joined through the gasket23, the bead39formed in the gasket23surrounds the first upstream opening11aand the second upstream opening12ain plan view.

FIG. 7is a cross-sectional view taken along line B-B ofFIG. 4. To be more precise,FIG. 7is a cross-sectional view taken along the thickness direction specifically of the opening36and the bead39of the gasket23. Note that inFIG. 7, the upper part is the cylinder head2H side and the lower part is the turbine housing4side.

As illustrated inFIG. 7, the gasket23is formed by layering multiple plates, more specifically, a first plate231, a second plate232, and a third plate233. Of the three plates231to233, the first plate231is in contact with the cylinder head2H, and the third plate233is in contact with the turbine housing4.

Three plates231to233have substantially the same shape in plan view, but have different sectional shapes. The first plate231has a first plane portion231ain a part corresponding to the opening36in plan view, and a first protruding portion231bprotruding further to the cylinder head2H side than the first plane portion231ain a part corresponding to the bead39in plan view. The third plate233has a third plane portion233ain a part corresponding to the opening36in plan view, and a third protruding portion233bprotruding further to the cylinder head2H side than the third plane portion233ain a part corresponding to the bead39in plan view. Additionally, the second plate232has a second plane portion232ain a part corresponding to the opening36in plan view, and a second recessed portion232bprotruding further to the turbine housing4side than the second plane portion232ain a part corresponding to the bead39in plan view.

The first plate231and the second plate232are at least joined at the first plane portion231aand the second plane portion232a,and spaced apart from each other in the thickness direction at the first protruding portion231band the second recessed portion232b.The second plate232and the third plate233are joined at least in the second recessed portion232band the third protruding portion233b,and spaced apart from each other in the thickness direction at the second plane portion232aand the third plane portion233a.By combining the three plates231to233described above in the gasket23, a thickness Db of the bead39is made larger than a thickness Da of the opening36

The flange joining structure of the embodiment has the following effects.

(1) In the flange joining structure of the embodiment, the plate-like gasket23has a substantially circular bead that protrudes to the cylinder head2H side and surrounds the first upstream opening11aand the second upstream opening12aformed in the end face21aof the flange21of the cylinder head2H in plan view. Here, when high-temperature exhaust gas is continuously discharged through the upstream collecting exhaust pipelines11,12formed inside the flange21of the cylinder head2H, opening deformation occurs in the end face21aof the flange21. The amounts of displacement due to such opening deformation is characterized by maximizing at the center, which is between the two adjacent openings11a,12a, and decreasing concentrically from the center. According to this characteristic of the opening deformation of the end face21aof the flange21, the flange joining structure of the embodiment has the substantially circular bead39of the plate-like gasket23that protrudes to the cylinder head2H side and surrounds the two adjacent openings11a,12a.When both of the flanges21,22are joined through such a gasket23, the bead39formed in the gasket23comes into contact with parts of both of the flanges21,22where the amounts of displacement caused by the opening deformation are almost the same. Hence, even when opening deformation occurs due to the heat of exhaust gas, a substantially uniform contact pressure is applied on the gasket23, so that the sealing property between both of the flanges21,22can be maintained.

(2) In the flange joining structure of the embodiment, the flange22of the turbine housing4has the partition wall portion30that separates the two adjacent openings13a,14a, as well as the two passages13,14respectively connected to the two openings13a,14a.Such a partition wall portion30may crack due to thermal expansion, when high-temperature exhaust gas continuously flows through the two passages13,14separated by the partition wall portion30. In the flange joining structure of the embodiment, the weakened portion31is provided in the thinnest part of the above partition wall portion30. Accordingly, upon occurrence of a thermal expansion large enough to cause a crack as mentioned earlier, the crack may be formed in the most easily breakable weakened portion31. In other words, since the flange joining structure of the embodiment can prevent occurrence of a crack in an unintended part other than the weakened portion31, behavior of the gasket23can be stabilized, whereby the sealing property of the gasket23can be maintained.

(3) In the flange joining structure of the embodiment, the cooling water passages27to29through which cooling water flows are formed in the flange21of the cylinder head2H, and such cooling water passages are not formed in the flange22of the turbine housing4. For this reason, the temperature of the flange22of the turbine housing4tends to become higher than that of the flange21of the cylinder head2H, and a crack is more likely to occur in its partition wall portion due to thermal expansion. Moreover, in the flange joining structure of the embodiment, the aforementioned weakened part is formed in the partition wall part of the flange of the exhaust member in which such a crack is more likely to occur. Hence, it is possible to prevent occurrence of a crack in an unintended part other than the weakened part of the partition wall part of the exhaust member, to stabilize behavior of the gasket23, and maintain the sealing property of the gasket23.

(4) In the flange joining structure of the embodiment, the partition wall portion30is a plate that extends in the flow direction of the exhaust gas flowing through the two passages13,14, while the weakened portion31is a groove that extends in the flow direction of the exhaust gas and formed on both sides of the partition wall portion30. Hence, a crack can be formed in the partition wall portion30in the flow direction of the exhaust gas, behavior of the gasket23can be stabilized even more, and therefore the sealing property of the gasket23can be maintained more securely.

(5) In the flange joining structure of the embodiment, a groove that is substantially V-shaped in cross-sectional view substantially perpendicular to the flow direction of the exhaust gas, is formed as the weakened portion31in the partition wall portion30. Hence, a crack can be caused more easily in the weakened portion31, behavior of the gasket23can be stabilized even more, and therefore the sealing property of the gasket23can be maintained more securely.

(6) In the flange joining structure of the embodiment, the flange22formed in the turbine housing4of a turbocharger and the flange21formed in the cylinder head2H are joined through the gasket23. Since a turbocharger compresses intake air by use of energy of exhaust gas, it is preferable that the heat of exhaust gas be higher to improve turbine efficiency. The flange joining structure of the embodiment is applied to joining of the flange22of the turbine housing4through which such high-temperature exhaust gas flows and the flange21of the cylinder head2H, whereby the aforementioned effect of maintaining the sealing property can be enhanced further.

(7) In the flange joining structure of the embodiment, the cylinder head2H has the four bifurcated pipelines7to10extending from the combustion chambers of the four cylinders CY1to CY4, and the two collecting exhaust pipelines11,12that collect the exhaust gas flowing through the bifurcated pipelines7to10and guide the exhaust gas to the multiple openings11a,12aof the flange21. In other words, since the exhaust manifold5is formed in the cylinder head2H of the flange joining structure of the embodiment, the number of parts can be reduced, and the device as a whole can be downsized. In addition, when the whole device is thus downsized, the temperature of exhaust gas flowing through the flange21of the cylinder head2H tends to become high. Since the flange joining structure of the embodiment is applied to joining of the flange21of the cylinder head2H through which such high-temperature exhaust gas flows and the flange22of the turbine housing4, the aforementioned effect of maintaining the sealing property can be enhanced even further.

Note that the present invention is not limited to the above embodiment, and modifications, improvements, and the like within the scope of achieving the objective of the disclosure are included in the invention.

Although the above embodiment describes a case of forming the weakened portion31in the partition wall portion30formed in the turbine housing4, the present invention is not limited to this. A weakened part may also be formed in a part of the cylinder head2H where high-temperature exhaust gas flows, that is, the partition wall portion24formed in the cylinder head2H. Although a specific form of embodiment has been described above and illustrated in the accompanying drawings in order to be more clearly understood, the above description is made by way of example and not as limiting the scope of the invention defined by the accompanying claims. The scope of the invention is to be determined by the accompanying claims. Various modifications apparent to one of ordinary skill in the art could be made without departing from the scope of the invention. The accompanying claims cover such modifications.