INTERNAL COMBUSTION ENGINE EXHAUST COOLING SYSTEM

Abstract

An internal combustion engine exhaust cooling system includes an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head, and an exhaust branch pipe, and cools exhaust gas that flows through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage. The coolant passage includes a first passage and a second passage being provided according to an offset of an amount of heat received from exhaust gas in a circumferential direction of an inner surface of the exhaust passage, and two middle passages that connect the first passage with the second passage at both ends of the two middle passages, and a coolant delivery direction is a direction from the second passage side of a first middle passage, of the two middle passages, toward the first passage side.

Description

INCORPORATION BY REFERENCE

This application claims priority to Japanese Patent Application No. 2010-066974 filed on Mar. 23, 2010, which is incorporated herein by reference in its entirety including the specification, drawings and abstract.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an internal combustion engine exhaust cooling system in which an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head and an exhaust branch pipe, and that cools exhaust gas flowing through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage.

2. Description of the Related Art Japanese Patent Application Publication No. 11-49096 (JP-A-11-49096) and Japanese Utility Model Application Publication No. 64-15718 (JP-U-64-15718), for example, describe technologies for cooling exhaust gas in order to suppress heat damage to the internal combustion engine exhaust system. In JP-A-11-49096, a connecting member is provided between a cylinder head and an exhaust branch pipe, and a coolant passage is provided in this connecting member. This coolant passage is formed as a concave portion. Coolant introduced from both ends on the lower side of the coolant passage flows directly into the coolant passage on the exhaust branch pipe side.

In JP-U-64-15718, a first exhaust gas cooling adapter is arranged between a cylinder head and an exhaust branch pipe, and a second exhaust gas cooling adapter is arranged between the exhaust branch pipe and a turbocharger. A coolant passage of the first exhaust gas cooling adapter passes from an inlet provided on a lower side of one end of an arrangement of exhaust passages corresponding to exhaust ports, through the lower side of the arrangement, turns back at the opposite end, and passes through the upper side of the arrangement, and discharges coolant out from an outlet directly above the inlet. As a result, the exhaust gas that has just come out of the exhaust ports is cooled by the exhaust gas cooling adapter. With the second exhaust gas cooling adapter, a coolant inlet and a coolant outlet are formed on opposite corners of a cooling passage formed around a single exhaust passage. This second exhaust gas cooling adapter runs coolant around the exhaust passage, thus cooling the exhaust gas that has already been cooled by the first exhaust gas cooling adapter.

Exhaust gas discharged from a combustion chamber of an internal combustion engine via an exhaust port does not flow uniformly through the exhaust passage. That is, the flow of exhaust gas may become uneven or the exhaust gas may bump along due to the shape of the exhaust port, the positional relationship between the exhaust port and an exhaust gas cooling adapter that is connected to the exhaust port, or the shape of the exhaust gas cooling adapter. As a result, a large difference in temperature may occur at the inner surface of the exhaust gas cooling adapter, which may cause the exhaust cooling performance to decrease.

With the connecting member in JP-A-11-49096, the concave portion that serves as the coolant passage is provided to supply coolant to the exhaust branch pipe side. Therefore, the shape of the concave portion itself does not sufficiently surround the exhaust passage. Moreover, coolant flows directly out to the exhaust branch pipe side without sufficiently flowing into the concave portion, so the function of cooling the exhaust gas that has been discharged from the exhaust port on the cylinder head side is extremely low. Therefore, this technology does not enable the exhaust passage of the exhaust gas cooling adapter to be efficiently cooled.

With the first exhaust gas cooling adapter in JP-U-64-15718, exhaust gas discharged from the exhaust port of the internal combustion engine is cooled by running coolant uniformly along the entire periphery of the exhaust passage. With such uniform cooling, in order to sufficiently cool the exhaust gas even at a high temperature portion that occurs due to the temperature difference described above, it is necessary to run an overall large amount of coolant inside the water jacket of the first exhaust gas cooling adapter. Such an approach, however, increases the size of the exhaust gas cooling adapter and increases the load on the water-jet pump. As a result, the internal combustion engine may become heavier and less fuel efficient.

With the second exhaust gas cooling adapter in JP-U-64-15718, cooling is simply performed a second time in order to protect the turbocharger. Cooling is not aimed at the high temperature exhaust gas from the exhaust port. Moreover, the temperature difference described above is not taken into account, and the flow of coolant is not one that actually addresses the temperature difference.

SUMMARY OF THE INVENTION

The invention thus provides an internal combustion engine exhaust cooling system capable of efficiently cooling an exhaust passage of an exhaust gas cooling adapter without increasing either the size of the exhaust gas cooling adapter or the load on a water-jet pump.

A first aspect of the invention relates to an internal combustion engine exhaust cooling system that includes an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head, and an exhaust branch pipe, and cools exhaust gas that flows through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage. The exhaust gas cooling adapter includes a coolant inlet that introduces coolant into the coolant passage, and a coolant outlet that discharges coolant outside from the coolant passage. The coolant passage includes a first passage that is on a high heat receiving side and a second passage that is on a low heat receiving side, the first passage and the second passage being provided according to an offset of an amount of heat received from exhaust gas in a circumferential direction of an inner surface of the exhaust passage, and two middle passages that connect the first passage with the second passage at both ends of the two middle passages. A coolant delivery direction of the coolant inlet is a direction from the second passage side of a first middle passage, of the two middle passages, toward the first passage side. Also, the coolant outlet discharges coolant from a location where a second middle passage, of the two middle passages, is connected with the first passage, or from near the location.

With this internal combustion engine exhaust cooling system, in the exhaust gas cooling adapter, coolant that is delivered from the coolant inlet to the coolant passage immediately heads from the second passage side of the first middle passage, of the two middle passages, toward the first passage side.

As a result, the pressure of the coolant delivered from the coolant inlet is sufficiently transmitted to the first passage, while little coolant pressure is transmitted to the second passage. Thus, coolant flows faster in the first passage than it does in the second passage. As a result, the flow rate of coolant that flows through the coolant passage is greater in the first passage and smaller in the second passage, so the temperature at the exhaust passage portion on the first passage side that tends to increase can be inhibited from increasing. The exhaust passage portion on the second passage side essentially tends not to increase in temperature, so the temperature is able to be inhibited from increasing even if the coolant flow rate is reduced.

Therefore, the exhaust passage of the exhaust gas cooling adapter can be efficiently cooled without increasing the total coolant flow rate, so the exhaust gas cooling adapter will not become larger and the load on the water-jet pump will not increase.

A second aspect of the invention relates to an internal combustion engine exhaust cooling system that includes an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head, and an exhaust branch pipe, and cools exhaust gas that flows through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage. The exhaust gas cooling adapter includes a coolant inlet that introduces coolant into the coolant passage, and a coolant outlet that discharges coolant outside from the coolant passage. The coolant passage includes an outside passage of a curve and an inside passage of a curve that are provided according to a curve in an exhaust flow produced by a curved shape of the exhaust port, and two middle passages that connect the outside passage with the inside passage at both ends of the two middle passages. A coolant delivery direction of the coolant inlet is a direction from the inside passage side of a first middle passage, of the two middle passages, toward the outside passage side. Also, the coolant outlet discharges coolant from a location where a second middle passage, of the two middle passages, is connected with the outside passage, or from near the location.

In this aspect, in the exhaust gas cooling adapter, coolant that is delivered from the coolant inlet to the coolant passage immediately heads from the inside passage side of the first middle passage, of the two middle passages, toward the outside passage side.

As a result, the pressure of the coolant delivered from the coolant inlet is sufficiently transmitted to the first passage, while little coolant pressure is transmitted to the inside passage. Thus, coolant flows faster in the outside passage than it does in the inside passage, so the flow rate of coolant that flows through the coolant passage is greater in the outside passage and smaller in the inside passage.

The exhaust port is curved, so a curve is produced in the exhaust flow until the exhaust gas reaches the exhaust gas cooling adapter. Therefore, in the exhaust gas cooling adapter, the inner surface of the exhaust passage that corresponds to the outside of the curve of the exhaust flow tends to increase in temperature due to the fast exhaust flow and the exhaust gas striking it.

In this internal combustion engine exhaust cooling system, as described above, the coolant flow rate is greater in the outside passage, that is a coolant passage that corresponds to an exhaust passage inner surface that tends to increase in temperature, than it is in the inside passage, so an increase in temperature at the exhaust passage portion that tends to increase in temperature can be suppressed. The exhaust passage portion that corresponds to the inside passage essentially tends not to increase in temperature, so the temperature is able to be inhibited from increasing even if the coolant flow rate is reduced.

Therefore, the exhaust passage of the exhaust gas cooling adapter can be efficiently cooled without increasing the total coolant flow rate, so the exhaust gas cooling adapter will not become larger and the load on the water-jet pump will not increase.

A third aspect of the invention relates to an internal combustion engine exhaust cooling system that includes an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head, and an exhaust branch pipe, and cools exhaust gas that flows through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage. The exhaust gas cooling adapter includes a coolant inlet that introduces coolant into the coolant passage, and a coolant outlet that discharges coolant outside from the coolant passage. The coolant passage includes an outside passage of a curve and an inside passage of a curve that are provided according to a curve in an exhaust flow produced by a bent shape of a connecting portion between the exhaust port and the exhaust passage, and two middle passages that connect the outside passage with the inside passage at both ends of the two middle passages. A coolant delivery direction of the coolant inlet is a direction from the inside passage side of a first middle passage, of the two middle passages, toward the outside passage side. Also, the coolant outlet discharges coolant from a location where a second middle passage, of the two middle passages, is connected with the outside passage, or from near the location.

In this aspect, in the exhaust gas cooling adapter, coolant that is delivered from the coolant inlet to the coolant passage immediately heads from the inside passage side of the first middle passage, of the two middle passages, toward the outside passage side.

As a result, the pressure of the coolant delivered from the coolant inlet is sufficiently transmitted to the outside passage, while little coolant pressure is transmitted to the inside passage. Thus, coolant flows faster in the outside passage than it does in the inside passage, so the flow rate of coolant that flows through the coolant passage is greater in the outside passage and smaller in the inside passage.

The connecting portion of the exhaust port on the cylinder head side and the exhaust passage of the exhaust gas cooling adapter is bent, so a curve is produced in the exhaust flow until the exhaust gas reaches the exhaust gas cooling adapter. Therefore, in the exhaust gas cooling adapter, the inner surface of the exhaust passage that corresponds to the outside of the curve of the exhaust flow tends to increase in temperature due to the fast exhaust flow and the exhaust gas striking it.

In the foregoing aspect, as described above, the coolant flow rate is greater in the outside passage, that is a coolant passage that corresponds to an exhaust passage inner surface that tends to increase in temperature, than it is in the inside passage, so an increase in temperature at the exhaust passage portion that tends to increase in temperature can be suppressed. The exhaust passage portion that corresponds to the inside passage essentially tends not to increase in temperature, so the temperature is able to be inhibited from increasing even if the coolant flow rate is reduced.

Therefore, the exhaust passage of the exhaust gas cooling adapter can be efficiently cooled without increasing the total coolant flow rate, so the exhaust gas cooling adapter will not become larger and the load on the water-jet pump will not increase.

In the aspect described above, the coolant outlet may discharge coolant in the same direction as a flow direction of coolant in the first passage.

Also, the coolant outlet is a passage that discharges coolant in the same direction as the flow direction of coolant in the first passage. Therefore, the flow direction of coolant that has flowed through the first passage at a fast rate does not change when the coolant flows out to the coolant outlet. As a result, the flow resistance does not increase when coolant is discharged from the coolant passage, so the fast coolant flow of the first passage is not impeded. Therefore, the coolant flows more smoothly, which further increases the effects of suppressing the exhaust gas cooling adapter from becoming larger and suppressing the load on the water-jet pump from increasing.

In the structure described above, the coolant outlet may discharge coolant in the same direction as a flow direction of coolant in the outside passage.

Also, the coolant outlet is a passage that discharges coolant in the same direction as the flow direction of coolant in the outside passage. Therefore, the flow direction of coolant that has flowed through the outside passage at a fast rate does not change when the coolant flows out to the coolant outlet. As a result, the flow resistance does not increase when coolant is discharged from the coolant passage, so the fast coolant flow of the outside passage is not impeded. Therefore, the coolant flows more smoothly, which further increases the effects of suppressing the exhaust gas cooling adapter from becoming larger and suppressing the load on the water-jet pump from increasing.

In the aspect described above, a plurality of the exhaust ports may be provided, and each of the plurality of exhaust ports may be arranged and open in a cylinder head. A plurality of the exhaust passages may be formed in an arrangement inside the exhaust gas cooling adapter, the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports. Further, the exhaust ports may be formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages may be connected bent in a direction orthogonal to the arrangement direction.

In this way, each of the exhaust ports in the cylinder head and the exhaust passages of the exhaust gas cooling adapter are arranged (i.e., aligned), and, as described above, the exhaust ports are formed curved in a direction orthogonal to the arrangement direction, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction. With this kind of structure, the first passage or the outside passage, and the second passage or the inside passage, are formed along the arrangement direction, as described above.

Therefore, the coolant flow rate is increased on the side that tends to increase in temperature, and the coolant flow rate is suppressed on the side that tends not to increase in temperature, as described above. As a result, the exhaust passage of the exhaust gas cooling adapter can be efficiently cooled without increasing the total coolant flow rate, so the exhaust gas cooling adapter will not become larger and the load on the water-jet pump will not increase.

In the aspect described above, a plurality of the exhaust ports may be provided, and each of the plurality of exhaust ports may be arranged and open in a cylinder head. A plurality of the exhaust passages may be formed in an arrangement inside the exhaust gas cooling adapter, the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports. Further, the exhaust ports may be formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages may be connected bent in a direction orthogonal to the arrangement direction. Also, the coolant inlet may deliver coolant from the second passage toward the first passage via a middle passage on one end side in the arrangement direction, and the coolant outlet may discharge coolant from a location where a middle passage on the other end side in the arrangement direction is connected to the first passage, or from near the location.

In this way, each of the exhaust ports in the cylinder head and the exhaust passages of the exhaust gas cooling adapter are arranged (i.e., aligned), and, as described above, the exhaust ports are formed curved in a direction orthogonal to the arrangement direction, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction. With this kind of structure, the first passage and the second passage are formed along the arrangement direction, as described above.

Arranging the coolant inlet and the coolant outlet in this way with respect to the first passage and the second passage makes it possible to increase the coolant flow rate on the first passage side that tends to increase in temperature, and suppress the coolant flow rate on the second passage side that tends not to increase in temperature, as described above. As a result, the exhaust passage of the exhaust gas cooling adapter can be efficiently cooled without increasing the total coolant flow rate, so the exhaust gas cooling adapter will not become larger and the load on the water-jet pump will not increase.

In the structure described above, a plurality of the exhaust ports may be provided, and each of the plurality of exhaust ports may be arranged and open in a cylinder head. A plurality of the exhaust passages may be formed in an arrangement inside the exhaust gas cooling adapter, the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports. Further, the exhaust ports may be formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages may be connected bent in a direction orthogonal to the arrangement direction. Also, the coolant inlet may deliver coolant from the inside passage toward the outside passage via a middle passage on one end side in the arrangement direction, and the coolant outlet may discharge coolant from a location where a middle passage on the other end side in the arrangement direction is connected to the outside passage, or from near the location.

In this way, each of the exhaust ports in the cylinder head and the exhaust passages of the exhaust gas cooling adapter are arranged (i.e., aligned), and, as described above, the exhaust ports are formed curved in a direction orthogonal to the arrangement direction, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction. With this kind of structure, the outside passage and the inside passage are formed along the arrangement direction, as described above.

Arranging the coolant inlet and the coolant outlet in this way with respect to the outside passage and the inside passage makes it possible to increase the coolant flow rate on the outside passage side that tends to increase in temperature, and suppress the coolant flow rate on the inside passage side that tends not to increase in temperature, as described above. As a result, the exhaust passage of the exhaust gas cooling adapter can be efficiently cooled without increasing the total coolant flow rate, so the exhaust gas cooling adapter will not become larger and the load on the water-jet pump will not increase.

In the structure described above, the arrangement direction of the exhaust ports in the cylinder head may be a horizontal direction, and the direction orthogonal to the arrangement direction may be vertically downward.

When the arrangement direction of the exhaust ports in the cylinder head and the exhaust passages of the exhaust gas cooling adapter are set and the direction of the curve of the exhaust flow is set in this way, the coolant flow rate in the coolant passage provided on the vertically upper side and extending in the arrangement direction inside the exhaust gas cooling adapter (i.e., the first passage or the outside passage) is increased. Also, the coolant flow rate in the coolant passage provided on the vertically lower side and extending in the arrangement direction (i.e., the second passage or the inside passage) is suppressed. Therefore, the exhaust passage of the exhaust gas cooling adapter can be efficiently cooled without increasing the total coolant flow rate, so the exhaust gas cooling adapter will not become larger and the load on the water-jet pump will not increase.

In the aspect described above, a flow direction guide that guides a flow of coolant delivered from the coolant inlet to a first middle passage, of the two middle passages, may be provided in the coolant passage, in a location near the coolant inlet.

In this way, the flow direction guide that guides the flow of coolant to an appropriate middle passage may be provided in the coolant passage. Doing so makes it easy to appropriately split the flow of the coolant between the first passage and the second passage or between the outside passage and the inside passage, such that the flow rate becomes larger in the first passage or the outside passage.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a longitudinal sectional view of an internal combustion engine exhaust cooling system according to a first example embodiment of the invention;

FIGS. 2A and 2B are perspective views of an exhaust gas cooling adapter used in the internal combustion engine exhaust cooling system;

FIGS. 3A, 3B, and 3C are views of the structure of the exhaust gas cooling adapter used in the internal combustion engine exhaust cooling system;

FIGS. 4A, 4B, and 4C are views of the structure of the exhaust gas cooling adapter used in the internal combustion engine exhaust cooling system;

FIGS. 5A and 5B are views of the spatial configuration of the water jacket inside the exhaust gas cooling adapter used in the internal combustion engine exhaust cooling system;

FIGS. 6A, 6B, and 6C are sectional views of an exhaust gas cooling adapter used in an internal combustion engine exhaust cooling system according to a second example embodiment of the invention; and

FIGS. 7A and 7B are sectional views of exhaust gas cooling adapters used in internal combustion engine exhaust cooling systems according to other example embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

First Example Embodiment

FIG. 1 is a longitudinal sectional view of the structure of an exhaust cooling system 4 in an exhaust system of an internal combustion engine 2 according to an example embodiment of the invention. This internal combustion engine 2 is a V-type 6 cylinder gasoline engine mounted in a vehicle, and has two banks, one arranged on the left and one arranged on the right, with a bank angle of 60°. FIG. 1 shows the exhaust cooling system 4 of the right bank 6.

Intake air and fuel are introduced as an air-fuel mixture into a combustion chamber 6b of a cylinder 6a in the right bank 6 via an intake port 8 and an intake valve 10 from an intake system during an intake stroke. The air-fuel mixture is compressed by a piston 6c during a compression stroke, and ignited and combusted by a spark plug 6d during a combustion stroke. Then gas inside the combustion chamber 6b is discharged as exhaust gas to the exhaust system by opening an exhaust valve 12 during an exhaust stroke. Exhaust gas is also discharged to the exhaust system during the exhaust stroke from the other two cylinders of the right bank 6 and the three cylinders of the left bank as well.

Here, the exhaust system for the right bank 6 side includes an exhaust port 16 (i.e., a total of three exhaust ports for all of the cylinders of the right bank 6) formed in a cylinder head 14, an exhaust gas cooling adapter 18 that is connected to the cylinder head 14 at the opening of the exhaust port 16, and an exhaust branch pipe 20 that is connected to the exhaust gas cooling adapter 18. Other than these, an exhaust gas control catalyst and the like are provided downstream in the exhaust system of the right bank 6. The exhaust system of the left bank similarly includes a total of three exhaust ports formed in the cylinder head, an exhaust gas cooling adapter, and an exhaust branch pipe. In this example embodiment, the exhaust gas cooling adapter of the left bank has the same structure as the exhaust gas cooling adapter 18 of the right bank 6. However, the positional relationship of the axis with the exhaust port side, the angle at which it is mounted to the cylinder head, or the length or curved shape or the like may be different.

FIGS. 2 to 4 are views of the structure of the exhaust gas cooling adapter 18 of the exhaust system of the right bank 6. FIG. 2A is a perspective view from an exhaust inlet 22 side, and FIG. 2B is a perspective view from an exhaust outlet 24 side. FIG. 3A is a plan view, FIG. 3B is a front view, and FIG. 3C is a bottom view. FIG. 4A is a left side view, FIG. 4B is a right side view, and FIG. 4C is a rear view. Incidentally, in FIGS. 2A and 2B, the spatial configuration of a water jacket 34 on the inside is indicated by the broken line.

The exhaust gas cooling adapter 18 is arranged between the exhaust port 16 that opens in the cylinder head 14 of the right bank 6 and the exhaust branch pipe 20, as shown in FIG. 1. The exhaust gas cooling adapter 18 cools exhaust gas discharged from the exhaust port 16 and discharges the cooled exhaust gas to the exhaust branch pipe 20 side, thereby inhibiting heat damage to the exhaust system of the right bank 6.

This kind of exhaust gas cooling adapter 18 is molded out of metal material such as aluminum alloy or iron alloy, for example, and has a cylinder head side connecting surface 28 with an open exhaust inlet 22 formed on the exhaust upstream side. Three of these exhaust inlets 22 are provided arranged in a straight line, corresponding to the position and number of the exhaust ports 16 of the cylinder head 14 of the right bank 6.

On the exhaust downstream side, an exhaust branch pipe side connecting surface 30 with an open exhaust outlet 24 is formed. Three of these exhaust outlets 24 are provided arranged in a straight line, corresponding to the exhaust inlets 22. Each exhaust inlet 22 is connected to a corresponding exhaust outlet 24 by a corresponding exhaust passage 32 formed inside the exhaust gas cooling adapter 18.

Bolt fastening portions 28a for fastening the exhaust gas cooling adapter 18 itself to an adapter connecting surface 14a on the cylinder head 14 side with bolts are formed on the exhaust gas cooling adapter 18 at peripheral portions of the cylinder head side connecting surface 28. The exhaust gas cooling adapter 18 is fixed to the cylinder head 14 by inserting bolts into bolt insertion holes 28b formed in the bolt fastening portions 28a and screwing them into threaded holes in the adapter connecting surface 14a on the cylinder head 14 side. As a result, the exhaust port 16 on the cylinder head 14 side can be connected with the exhaust passage 32 on the exhaust gas cooling adapter 18 side.

Moreover, bolt fastening portions 30a for fastening the exhaust branch pipe 20 with bolts are formed on the exhaust gas cooling adapter 18 at peripheral portions of the exhaust branch pipe side connecting surface 30. Threaded holes 30b are formed in these bolt fastening portions 30a. The exhaust branch pipe 20 is connected by screwing in bolts through insertion holes formed in flanges 20a on the exhaust branch pipe 20 side. As a result, the exhaust passage 32 on the exhaust gas cooling adapter 18 side can be connected with the exhaust passage 20b on the exhaust branch pipe 20 side.

In this way, a water jacket 34 is formed around the exhaust passage 32, inside the wall of the exhaust gas cooling adapter 18 that is mounted to the internal combustion engine 2. FIGS. 5A and 5B are views of the spatial configuration of the water jacket 34 inside the exhaust gas cooling adapter 18. FIGS. 5A and 5A is a perspective view from the exhaust inlet 22 side, and FIGS. 5A and 5B is a perspective view from the exhaust outlet 24 side.

As shown in FIGS. 2 to 4, a coolant introducing portion 36 is provided on the vertically lower side of the water jacket 34 on the exhaust gas cooling adapter 18, and a coolant discharging portion 38 is provided on the vertically upper side of the water jacket 34 in the exhaust gas cooling adapter 18.

Coolant is introduced into the water jacket 34 from a coolant inlet 36a formed in the coolant introducing portion 36, and after flowing through the water jacket 34, is discharged to an external coolant circulation path via a coolant outlet 38a formed in the coolant discharging portion 38, as shown by the arrows in FIGS. 5A and 5B.

As a result, the amount of heat transmitted from high temperature exhaust gas via inner peripheral surfaces 32a and 32b (FIG. 1) of the exhaust passage 32 is absorbed by the coolant flowing through coolant passages 34a, 34b, 34c, 34d, and 34e of the water jacket 34, thereby cooling the exhaust gas. The cooled exhaust gas is then discharged to the exhaust branch pipe 20 side.

Here, as shown by the alternate long and short dash lines in FIG. 1, the axis X1 of the exhaust port 16 is at an angle θ to the axis X2 of the exhaust passage 32. Instead of the axes X1 and X2 crossing each other, they may also be non-crossing and non-parallel by an angle θ.

In this example embodiment, the axis X2 of the exhaust passage 32 is bent vertically downward at an angle θ with respect to the axis X1 of the exhaust port 16. Therefore, the inner peripheral surface 32a on the vertically upper side of the exhaust passage 32 forms an area that slopes toward the exhaust port 16. The inner peripheral surface 32b on the vertically lower side is not an area that slopes toward the exhaust port 16, but instead slopes in the opposite direction, i.e., away from the exhaust port 16.

In this way, the inner peripheral surface 32a on the vertically upper side of the exhaust passage 32 has a shape that slopes toward the exhaust port 16. Therefore, exhaust gas that has been introduced from the exhaust port 16 into the exhaust passage 32 of the exhaust gas cooling adapter 18 strikes the inner peripheral surface 32a on the vertically upper side comparatively harder than it strikes the inner peripheral surface 32b on the vertically lower side.

Moreover, the exhaust port 16 extends in a curved shape from the combustion chamber 6b to the exhaust gas cooling adapter 18, and the vertically upper side is on the outside of the curve. Therefore, high temperature exhaust flows faster at the inner peripheral surface 32a on the vertically upper side than it does at the inner peripheral surface 32b on the vertically lower side, so high temperature exhaust gas strikes the inner peripheral surface 32a on the vertically upper side hard. Thus, the inner peripheral surface 32a on the vertically upper side receives a particularly large amount of heat. That is, the inner peripheral surface 32a on the vertically upper side is a high heat receiving side and the inner peripheral surface 32b on the vertically lower side is a low heat receiving side.

In this kind of flow state, high temperature exhaust gas transfers heat to the inner peripheral surfaces 32a and 32b, such that the exhaust gas itself is cooled, after which it flows out to the exhaust passage 20b on the exhaust branch pipe 20 side. Here, in the water jacket 34, the position where coolant is introduced at the coolant inlet 36a is a position, near the coolant passage 34b, of the coolant passage 34d that communicates the coolant passage 34b on the vertically lower side with the coolant passage 34a on the vertically upper side on one end side of the exhaust passages 32 in the direction in which the exhaust passages 32 are arranged (also simply referred to as the “arrangement direction”). The coolant inlet 36a delivers coolant toward the coolant passage 34a on the vertically upper side from a position on the coolant passage 34b side that is on the vertically lower side.

That is, the direction in which coolant is delivered from the coolant inlet 36a is the direction from the coolant passage 34b side of the coolant passage 34d, that is one of the middle passages, toward the coolant passage 34a side. The coolant passage 34b is on the vertically lower side and is a passage on the inside of the curve of the exhaust flow that follows the curve of the exhaust port 16 (the coolant passage 34b may also be referred to as an “inside passage” in this specification). The coolant passage 34a, on the other hand, is on the vertically upper side and is a passage on the outside of the curve of the exhaust flow (the coolant passage 34a may also be referred to as an “outside passage” in this specification).

Also, the direction in which coolant is delivered from the coolant inlet 36a is the direction from the coolant passage 34b side of the coolant passage 34d, that is one of the middle passages, toward the coolant passage 34a side. The coolant passage 34b is on the vertically lower side and is a passage on the inside of the curve of the exhaust flow that follows the bend at the connection of the exhaust port 16 and the exhaust passage 32 (the coolant passage 34b may also be referred to as an “inside passage” in this specification). The coolant passage 34a, on the other hand, is on the vertically upper side and is a passage on the outside of the curve of the exhaust flow (the coolant passage 34a may also be referred to as an “outside passage” in this specification).

Therefore, coolant flows faster through the coolant passage 34a that is the outside passage than it does through the coolant passage 34b that is the inside passage. The following effects are able to be obtained with the first example embodiment described above.

As described above, the exhaust port 16 is curved in a direction orthogonal to the arrangement direction thereof. Moreover, the connecting portion of the exhaust port 16 and the exhaust passage 32 of the exhaust gas cooling adapter 18 that is connected to the exhaust port 16 is bent in a direction orthogonal to the arrangement direction. The curve and the bend are both vertically downward. In accordance with this, the exhaust flow is in a direction that is orthogonal to the arrangement direction, and curves vertically downward.

As a result of this curve in the exhaust flow, the coolant passage 34a that is formed in the arrangement direction in the exhaust gas cooling adapter 18 and arranged on the vertically upper side functions as a first passage and an outside passage that corresponds to the inner peripheral surface 32a on the high heat receiving side of the exhaust passage 32. The coolant passage 34b that is formed in the arrangement direction and arranged on the vertically lower side functions as a second passage and an inside passage that corresponds to the inner peripheral surface 32b on the low heat receiving side of the exhaust passage 32. Also, the two coolant passages 34d and 34e that connect these coolant passages 34a and 34b together at the both ends function as middle passages.

In this exhaust gas cooling adapter 18, the flow direction of coolant delivered from the coolant inlet 36a into the water jacket 34 is toward the coolant passage 34a side. Therefore, as shown by the arrows in FIGS. 5A and 5B, the main stream of the coolant flows through the coolant passage 34d that is the first middle passage of the two middle passages (i.e., coolant passages 34d and 34e) from the coolant passage 34b side toward the coolant passage 34a side. Accordingly, the amount (i.e., the flow rate) of coolant that flows toward the coolant passage 34b is small. Incidentally, in this example embodiment, the coolant passage 34d is located closer to the coolant inlet 36 than the coolant passage 34e is.

As a result, the pressure of the coolant delivered from the coolant inlet 36a is sufficiently transmitted to the coolant passage 34a, while little coolant pressure is transmitted to the coolant passage 34b. Thus, coolant flows faster in the coolant passage 34a than it does in the coolant passage 34b. As a result, the flow rate of coolant that flows through the water jacket 34 is greater in the coolant passage 34a and smaller in the coolant passage 34b, so the temperature at the inner peripheral surface 32a on the vertically upper side of the exhaust passage 32 that tends to increase can be inhibited from increasing. Therefore, resistance to boiling at the coolant passage 34a as a result of heat transfer from the inner peripheral surface 32a can also be improved.

The inner peripheral surface 32b on the vertically lower side essentially tends not to increase in temperature, so the temperature is able to be inhibited from increasing even if the coolant flow rate in the corresponding coolant passage 34b is reduced. In this way, the exhaust passage 32 of the exhaust gas cooling adapter 18 can be efficiently cooled without increasing the total flow rate of coolant that flows through the water jacket 34, so the exhaust gas cooling adapter 18 will not become larger and the load on the water-jet pump will not increase.

Also, the coolant outlet 38a is a passage that discharges coolant in the same direction as the direction in which coolant flows (i.e., the flow direction of coolant) in the coolant passage 34a. Therefore, as shown by the arrows in FIGS. 5A and 5B, the flow direction of coolant that has flowed through the coolant passage 34a at a fast rate does not change when the coolant flows out to the coolant outlet 38a. As a result, the flow resistance does not increase when the coolant flows out of the coolant passage 34a, so the fast coolant flow of the coolant passage 34a is not impeded.

Therefore, the coolant flows more smoothly, which further increases the effects of suppressing the exhaust gas cooling adapter 18 from becoming larger and suppressing the load on the water-jet pump from increasing.

Second Example Embodiment

FIG. 6 is a sectional view of exhaust gas cooling adapters 118, 218, and 318 used in an exhaust cooling system according to a second example embodiment of the invention. Incidentally, the other structure of the exhaust cooling system is the same as it is in the first example embodiment described above.

With the exhaust gas cooling adapter 118 shown in FIG. 6A, a coolant inlet 136a of a coolant introducing portion 136 that introduces coolant into a water jacket 134 opens into a coolant passage 134b (that functions as a second passage and an inside passage) that is arranged on the vertically lower side and extends in the direction in which exhaust passages 132 are arranged (i.e., in the arrangement direction of the exhaust passages 132), and delivers coolant into this coolant passage 134b.

A flow direction guide 136b is formed on a side of an edge portion of a portion of the coolant inlet 136a that opens to the coolant passage 134b side, that is opposite a coolant passage 134d (that functions as a middle passage) side. A tip end of this flow direction guide 136b points toward the coolant passage 134d side. Therefore, the pressure of the coolant that has been introduced from the coolant inlet 136a into the coolant passage 134b is directed toward the coolant passage 134d side by the flow direction guide 136b.

As a result, as shown by the arrows in the drawing, the main stream of the coolant flows toward the coolant passage 134d side, and the flow rate of this coolant is large. The flow rate of the coolant that flows through the coolant passage 134b toward the side with a coolant passage 134e that is a middle passage on the opposite side is small.

The flow of the coolant (i.e., the coolant pressure) in the coolant passage 134d turns directly into the flow in a coolant passage 134a (that functions as a first passage and an outside passage) that is arranged on the vertically upper side and extends in the direction in which the exhaust passages 132 are arranged (i.e., the arrangement direction of the exhaust passages 132), and then flows to a coolant discharging portion 138.

The direction of a coolant outlet 138a of the coolant discharging portion 138 is the same as the direction of the coolant passage 134a, so the coolant also flows inside the coolant outlet 138a without losing any pressure, and is discharged outside as it is from the coolant outlet 138a.

With the exhaust gas cooling adapter 218 shown in FIG. 6B, a coolant inlet 236a of a coolant introducing portion 236 that introduces coolant into a water jacket 234 opens into a coolant passage 234b (that functions as a second passage and an inside passage) that is arranged on the vertically lower side and extends in the direction in which exhaust passages 232 are arranged (i.e., in the arrangement direction of the exhaust passages 232), and delivers the coolant into this coolant passage 234b, similar to FIG. 6A.

However, in the example shown in FIG. 6B, a flow direction guide 236b is formed on a wall portion side of an opposing exhaust passage 232, instead of on an edge portion of the coolant inlet 236a. A tip end of this flow direction guide 236b is formed pointed toward an edge portion of the coolant inlet 236a, that is on the side opposite a coolant passage 234d (that functions as a middle passage) side.

Accordingly, the pressure of the coolant that has been introduced from the coolant inlet 236a into the coolant passage 234b is directed toward the coolant passage 234d side by the sloped surface of the flow direction guide 236b. As a result, as shown by the arrows in the drawing, the main stream of the coolant flows toward the coolant passage 234d side, and the flow rate of this coolant is large. The flow rate of the coolant that flows through the coolant passage 234b toward the side with a coolant passage 234e that is a middle passage on the opposite side is small.

The flow of the coolant (i.e., the coolant pressure) in this coolant passage 234d turns directly into the flow in a coolant passage 234a (that functions as a first passage and an outside passage) that is arranged on the vertically upper side and extends in the direction in which the exhaust passages 232 are arranged (i.e., the arrangement direction of the exhaust passages 232), and then flows to a coolant discharging portion 238.

The direction of a coolant outlet 238a of the coolant discharging portion 238 is the same as the direction of the coolant passage 234a, so the coolant flows without losing any pressure, and is discharged outside as it is from the coolant outlet 238a.

With the exhaust gas cooling adapter 318 shown in FIG. 6C, a coolant inlet 336a of a coolant introducing portion 336 that introduces coolant into a water jacket 334 opens into a coolant passage 334b (that functions as a second passage and an inside passage) that is arranged on the vertically lower side and extends in the direction in which exhaust passages 332 are arranged (i.e., in the arrangement direction of the exhaust passages 332), and delivers the coolant into this coolant passage 334b. This is the same as in FIG. 6A.

However, compared with FIG. 6A, the coolant inlet 336a of the coolant introducing portion 336 is farther away from a coolant passage 334d (that functions as a middle passage) and is provided in a position facing a coolant passage 334c that connects a coolant passage 334a (that functions as a first passage and an outside passage) with the coolant passage 334b at a center portion. Therefore, a flow direction guide 336b that is formed on an opening edge portion of a coolant inlet 336a on the side opposite the coolant passage 334d (that functions as a middle passage) is formed longer and extending toward the coolant passage 334d side, such that sufficient coolant pressure reliably reaches the coolant passage 334d.

As a result, as shown by the arrows in the drawing, the main stream of the coolant flows toward the coolant passage 334d side, and the flow rate of this coolant is large. The flow rate of the coolant that flows through the coolant passage 334b toward the side with a coolant passage 334e that is a middle passage on the opposite side is small.

The flow of the coolant (i.e., the coolant pressure) in the coolant passage 334d turns directly into the flow in a coolant passage 334a that is arranged on the vertically upper side and extends in the direction in which the exhaust passages 332 are arranged (i.e., in the arrangement direction of the exhaust passages 332), and then flows to a coolant discharging portion 338.

The direction of a coolant outlet 338a of the coolant discharging portion 338 is the same as the direction of the coolant passage 334a, so the coolant flows without losing any pressure, and is discharged outside as it is from the coolant outlet 338a.

The following effects are able to be obtained with the second example embodiment described above. The main flow of coolant is able to be directed toward the coolant passage 134a, 234a, or 334a via the coolant passage 134d, 234d, or 334d by the flow direction guide 136b, 236b, or 336b also when the coolant introducing portion 136, 236, or 336 is mounted on the coolant passage 134b, 234b, or 334b side in this way.

As a result, effects similar to those described in the first example embodiment are able to be obtained.

Other Example Embodiments

With an exhaust gas cooling adapter 418 shown in FIG. 7A, when a coolant inlet 436a of a coolant introducing portion 436 is connected to a coolant passage 434b that functions as a second passage and an inside passage, the coolant inlet 436a may be formed at an angle such that the main stream of coolant is directed toward a coolant passage 434d that is a middle passage, instead of using a flow direction guide.

As a result, as shown by the arrows in the drawing, the flow of the coolant (i.e., the coolant pressure) in the coolant passage 434d turns directly into the flow in a coolant passage 434a that functions as a first passage and an outside passage, and then flows to a coolant discharging portion 438. The coolant then flows without losing any pressure, and is discharged outside as it is from a coolant outlet 438a. This structure also enables effects similar to those obtained in the first example embodiment to be obtained.

In the foregoing example embodiments, the direction of the coolant outlet of the coolant discharging portion follows the flow direction of coolant in the coolant passage that functions as the first passage and the outside passage. Alternatively, however, the direction of a coolant outlet 538a of a coolant discharging portion 538 may be a direction that is different from the flow direction of coolant in a coolant passage 534a that functions as a first passage and an outside passage, as shown in FIG. 7B. In the example shown in FIG. 7B, the direction of the coolant outlet 538a is a direction that is orthogonal to the flow direction of coolant in the coolant passage 534a. With this structure as well, the pressure of coolant delivered from a coolant inlet 536a of a coolant introducing portion 536 is transmitted to the coolant passage 534a via a coolant passage 534d that serves as a middle passage, so a sufficiently large coolant flow rate is able to be ensured in the coolant passage 534a. As a result, effects similar to those obtained in the first example embodiment are able to be obtained.

Even if the exhaust port and the exhaust passage of the exhaust cooling adaptor are not bent, and there is only the curve of the exhaust port, the inner peripheral surface of the exhaust passage of the exhaust gas cooling adapter that is on the outside of the curve will become the high temperature receiving side, and the coolant passage that corresponds to this inner peripheral surface will become the first passage. Therefore, the effects described above can be obtained by having coolant flow in the manner described in the example embodiments described above.

Incidentally, even if only the connecting portion of the exhaust port and the exhaust passage of the exhaust gas cooling adapter is bent, the inner peripheral surface of the exhaust passage of the exhaust gas cooling adapter that is on the outside of the bend will become the high temperature receiving side, and the coolant passage that corresponds to this inner peripheral surface will become the first passage. Therefore, the effects described above can be obtained by having coolant flow in the manner described in the example embodiments described above.

FIG. 1 is a view of an example in which the invention is applied to a V-type 6 cylinder internal combustion engine. However, the invention may also be applied to an engine having in-line configuration, as well as to an engine with a number of cylinders other than six, such as four cylinders or eight cylinders or the like.

Claims

1. An internal combustion engine exhaust cooling system comprising:

an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head, and an exhaust branch pipe, and cools exhaust gas that flows through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage,

wherein the exhaust gas cooling adapter includes a coolant inlet that introduces coolant into the coolant passage, and a coolant outlet that discharges coolant outside from the coolant passage;

the coolant passage includes a first passage that is on a high heat receiving side and a second passage that is on a low heat receiving side, the first passage and the second passage being provided according to an offset of an amount of heat received from exhaust gas in a circumferential direction of an inner surface of the exhaust passage, and two middle passages that connect the first passage with the second passage at both ends of the two middle passages;

a coolant delivery direction of the coolant inlet is a direction from the second passage side of a first middle passage, of the two middle passages, toward the first passage side; and

the coolant outlet discharges coolant from a location where a second middle passage, of the two middle passages, is connected with the first passage, or from near the location.

2. The internal combustion engine exhaust cooling system according to claim 1, wherein the first middle passage is located closer to the coolant inlet than the second middle passage is.

3. The internal combustion engine exhaust cooling system according to claim 1, wherein the coolant outlet discharges coolant in the same direction as a flow direction of coolant in the first passage.

4. The internal combustion engine exhaust cooling system according to claim 1, wherein a plurality of the exhaust ports are provided; the exhaust ports are formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction.

each of the plurality of exhaust ports is arranged and open in a cylinder head;

a plurality of the exhaust passages are formed in an arrangement inside the exhaust gas cooling adapter,

the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports; and

5. The internal combustion engine exhaust cooling system according to claim 4, wherein the arrangement direction of the exhaust ports in the cylinder head is a horizontal direction, and the direction orthogonal to the arrangement direction is vertically downward.

6. The internal combustion engine exhaust cooling system according to claim 1, wherein a plurality of the exhaust ports are provided;

each of the plurality of exhaust ports is arranged and open in a cylinder head; a plurality of the exhaust passages are formed in an arrangement inside the exhaust gas cooling adapter,

the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports;

the exhaust ports are formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction;

the coolant inlet delivers coolant from the second passage toward the first passage via a middle passage on one end side in the arrangement direction; and

the coolant outlet discharges coolant from a location where a middle passage on the other end side in the arrangement direction is connected to the first passage, or from near the location.

7. The internal combustion engine exhaust cooling system according to claim 1, wherein a flow direction guide that guides a flow of coolant delivered from the coolant inlet to a first middle passage, of the two middle passages, is provided in the coolant passage, in a location near the coolant inlet.

8. An internal combustion engine exhaust cooling system comprising:

an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head, and an exhaust branch pipe, and cools exhaust gas that flows through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage,

wherein the exhaust gas cooling adapter includes a coolant inlet that introduces coolant into the coolant passage, and a coolant outlet that discharges coolant outside from the coolant passage;

the coolant passage includes an outside passage of a curve and an inside passage of a curve that are provided according to a curve in an exhaust flow produced by a curved shape of the exhaust port, and two middle passages that connect the outside passage with the inside passage at both ends of the two middle passages;

a coolant delivery direction of the coolant inlet is a direction from the inside passage side of a first middle passage, of the two middle passages, toward the outside passage side; and

the coolant outlet discharges coolant from a location where a second middle passage, of the two middle passages, is connected with the outside passage, or from near the location.

9. The internal combustion engine exhaust cooling system according to claim 8, wherein the first middle passage is located closer to the coolant inlet than the second middle passage.

10. The internal combustion engine exhaust cooling system according to claim 8, wherein the exhaust passage is bent with respect to the exhaust port.

11. The internal combustion engine exhaust cooling system according to claim 8, wherein the coolant outlet discharges coolant in the same direction as a flow direction of coolant in the outside passage.

12. The internal combustion engine exhaust cooling system according to claim 8, wherein a plurality of the exhaust ports are provided;

each of the plurality of exhaust ports is arranged and open in a cylinder head;

a plurality of the exhaust passages are formed in an arrangement inside the exhaust gas cooling adapter,

the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports; and

the exhaust ports are formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction.

13. The internal combustion engine exhaust cooling system according to claim 12, wherein the arrangement direction of the exhaust ports in the cylinder head is a horizontal direction, and the direction orthogonal to the arrangement direction is vertically downward.

14. The internal combustion engine exhaust cooling system according to claim 8, wherein a plurality of the exhaust ports are provided;

each of the plurality of exhaust ports is arranged and open in a cylinder head;

a plurality of the exhaust passages are formed in an arrangement inside the exhaust gas cooling adapter,

the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports;

the exhaust ports are formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction;

the coolant inlet delivers coolant from the inside passage toward the outside passage via a middle passage on one end side in the arrangement direction; and

the coolant outlet discharges coolant from a location where a middle passage on the other end side in the arrangement direction is connected to the outside passage, or from near the location.

15. The internal combustion engine exhaust cooling system according to claim 8, wherein a flow direction guide that guides a flow of coolant delivered from the coolant inlet to a first middle passage, of the two middle passages, is provided in the coolant passage, in a location near the coolant inlet.

16. An internal combustion engine exhaust cooling system comprising: the coolant outlet discharges coolant from a location where a second middle passage, of the two middle passages, is connected with the outside passage, or from near the location.

an exhaust gas cooling adapter that is arranged between an exhaust port that opens in a cylinder head, and an exhaust branch pipe, and cools exhaust gas that flows through an exhaust passage by running coolant through a coolant passage formed inside of a wall that surrounds the exhaust passage,

wherein the exhaust gas cooling adapter includes a coolant inlet that introduces coolant into the coolant passage, and a coolant outlet that discharges coolant outside from the coolant passage;

the coolant passage includes an outside passage of a curve and an inside passage of a curve that are provided according to a curve in an exhaust flow produced by a bent shape of a connecting portion between the exhaust port and the exhaust passage, and two middle passages that connect the outside passage with the inside passage at both ends of the two middle passages;

a coolant delivery direction of the coolant inlet is a direction from the inside passage side of a first middle passage, of the two middle passages, toward the outside passage side; and

17. The internal combustion engine exhaust cooling system according to claim 16, wherein the first middle passage is located closer to the coolant inlet than the second middle passage.

18. The internal combustion engine exhaust cooling system according to claim 16, wherein a plurality of the exhaust ports are provided; the exhaust ports are formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction.

each of the plurality of exhaust ports is arranged and open in a cylinder head;

a plurality of the exhaust passages are formed in an arrangement inside the exhaust gas cooling adapter,

the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports; and

19. The internal combustion engine exhaust cooling system according to claim 18, wherein the arrangement direction of the exhaust ports in the cylinder head is a horizontal direction, and the direction orthogonal to the arrangement direction is vertically downward.

20. The internal combustion engine exhaust cooling system according to claim 16, wherein a plurality of the exhaust ports are provided; the coolant outlet discharges coolant from a location where a middle passage on the other end side in the arrangement direction is connected to the outside passage, or from near the location.

each of the plurality of exhaust ports is arranged and open in a cylinder head;

a plurality of the exhaust passages are formed in an arrangement inside the exhaust gas cooling adapter, the arrangement of the plurality of exhaust passages corresponding to an arrangement of the plurality of exhaust ports;

the exhaust ports are formed curved in a direction orthogonal to an arrangement direction of the exhaust passages, or the exhaust ports and the exhaust passages are connected bent in a direction orthogonal to the arrangement direction;

the coolant inlet delivers coolant from the inside passage toward the outside passage via a middle passage on one end side in the arrangement direction; and

21. The internal combustion engine exhaust cooling system according to claim 16, wherein a flow direction guide that guides a flow of coolant delivered from the coolant inlet to a first middle passage, of the two middle passages, is provided in the coolant passage, in a location near the coolant inlet.