Cylinder head for vehicle engine

This application incorporates by references the subject matter of Application No. 2016-080990 filed in Japan on Apr. 14, 2016 on which a priority claim is based under 35 U.S.C. § 119(a).

The present invention relates to a cylinder head containing an exhaust system manifold for an engine.

A cylinder head integrally formed with an exhaust system manifold has been conventionally developed, wherein multiple exhaust ports connected to combustion chambers of an engine merge inside the cylinder head. Such a cylinder head is advantageous in that a shorter distance between an exhaust purification catalyst provided in the exhaust system and the engine improves the performance of the exhaust purification, and that a shorter exhaust system per se reduces the pressure loss of the exhaust and enhances the size reduction of the engine. Such a cylinder head, on the other hand, has a disadvantage in that the temperature may be increased due to exhaust heat, as compared to a cylinder head provided separately with a manifold. To address this issue, techniques have been proposed to improve the cooling performance by permitting engine cooling water (coolant) to flow around an exhaust port and in the vicinity of an outlet of a manifold (refer to Japanese Laid-open Patent Publication No. 2008-309158).

In the meantime, the temperature tends to rise at an outlet of a manifold contained in a cylinder head particularly because exhausts from exhaust ports tend to converge in the vicinity of the outlet of the manifold. Because downstream side exhaust pipes are fastened and secured to outlets of a manifold, there is a need for a structure that can efficiently cool the vicinity of the outlet, for the purpose of suppressing a reduction in the clamping force of fastening members, thereby maintaining a stable clamping force.

Technical Problems

The present disclosure is conceived of in view of the issues set forth above, and an object thereof is to provide a cylinder head for an engine that can suppress a reduction in the clamping force of fastening members, thereby maintaining a stable clamping force. Any other advantages and effects that can be achieved by configurations described in a mode for embodying the invention described later, and that cannot be obtained by conventional techniques, are also other objects of the present disclosure.

Solution To Problems

A cylinder head discloses herein is a cylinder head including a manifold provided inside the cylinder for an exhaust system of an engine; screw holes formed through a fastening face of the cylinder head and an exhaust pipe; and outlet cooling channels that are provided adjacent to an outlet of a confluence of the manifold, and are disposed between the screw holes and the outlet, such that coolant flows through the outlet cooling channels.

The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein:

FIG. 1 is a perspective diagram exemplifying a cylinder head and a cylinder block for an engine according to an embodiment;

FIG. 2 is a vertical cross-sectional schematic diagram of the engine;

FIG. 3 is a horizontal cross-sectional diagram showing the configuration of an exhaust port inside the cylinder head;

FIG. 4 is a perspective diagram showing an exhaust side cooling channel in the cylinder head;

FIG. 5A is a horizontal cross-sectional diagram showing a top of the cooling channel (upper cooling channel) in FIG. 4 , and FIG. 5B is a horizontal cross-sectional diagram showing a bottom of the cooling channel (lower cooling channel) in FIG. 4 ;

FIG. 6A is a diagram of a fastening face of the cylinder head in the frontal view, and FIG. 6B is a schematic diagram for illustrating the configuration of cooling channels in FIG. 6A ; and

FIG. 7A and FIG. 7B are schematic diagrams for illustrating the configuration of cooling channels provided in a cylinder head in accordance with a modification.

A cylinder head for an engine as an embodiment will be described with reference to the drawings. Embodiments that will be described below are merely exemplary, and it is not intended to exclude modifications and applications of techniques that are not discussed explicitly in the following embodiments. The configurations of the present embodiment maybe practiced in a wide variety of modifications without departing from the spirit thereof. In addition, the configurations may be selected where necessary, or may be combined in any combinations.

(1. Overview of Configuration)

A cylinder head 1 of the present embodiment is an exhaust-manifold integrated-type cylinder head having an exhaust system manifold integrated in the cylinder head 1 , and is to be attached to a cylinder block 2 of a water-cooled multi-cylinder engine 10 . In the following descriptions, the “lower” defined as the side on which the cylinder block 2 is secured to the cylinder head 1 , and the opposite side is defined as the “upper”. Multiple cylinders 3 are disposed in a bank in the engine 10 . The example shown in FIG. 1 is a three-cylinder engine 10 , wherein three cylinders 3 are arranged in series, and the cylinder 3 at one (front) of ends of the long side direction of the engine 10 is denoted by # 1 , followed by # 2 and # 3 toward the other end (rear). The direction along which the cylinders 3 are arranged in a bank (long side direction) is denoted by the reference symbol L.

As shown in FIGS. 1 and 2 , a cooling channel 30 (water jacket) is grooved in curved configuration along the cylinder surface 3 B of each cylinder 3 . The top of the cooling channel 30 opens at the top face of the cylinder block 2 , for permitting communications between an exhaust side cooling channel 4 ( 4 B) and an intake side cooling channel 5 formed inside the cylinder head 1 . As a result, the outer periphery of an exhaust port 6 is cooled by engine cooling water (hereinafter referred to as “coolant”). While the cooling channels 4 and 5 on the side of the cylinder head 1 on the exhaust side and on the intake side are denoted by different reference symbols in this example for the sake of convenience, the cooling channels 4 and 5 are provided integrally inside the cylinder head 1 .

As shown in FIG. 2 , a depression defining a ceiling face 3 A of a combustion chamber is formed in the bottom face of the cylinder head 1 . The exhaust ports 6 are branched exhaust flow channels, and are connected to respective combustion chambers. The exhaust ports 6 merge together and the number of branches reduces as the exhaust ports 6 extend farther from the combustion chambers, and form the manifold inside the cylinder head 1 . As shown in FIG. 3 , the upstream end of the exhaust ports 6 has six branches, which are connected to corresponding exhaust valve holes 12 . In the downstream to the exhaust ports 6 , the channels are merged into a single channel inside the cylinder head 1 . Hereinafter, the merged part of the exhaust ports 6 is referred to as an exhaust confluence 6 A.

Considering a line vertical to the cylinder bank direction L of imaginary lines extending horizontally through the center of the cylinder # 2 as the center line C of the engine 10 , the exhaust confluence 6 A is displaced to the rear side of the engine 10 relative to the center line C. Similarly, a single opening at the downstream end of the exhaust confluence 6 A (hereinafter referred to as the “exhaust port 7 ”) is also displaced to the rear side relative to the center line C. As shown in FIGS. 1-3 , a protruding section 14 surrounding the entire exhaust port 6 is provided on a side wall 8 on the exhaust side so as to protrude outwardly from the cylinder head 1 in a semicircular shape.

As shown in FIG. 6A , a flange section 15 is provided which has a planer fastening face 15 A that is vertical to the flow direction of the exhaust gas surrounding the exhaust port 7 . On the flange section 15 , an unillustrated downstream side exhaust pipe (including pipe members for connecting to a catalyst device, a turbo charger and other devices) is to be fastened and secured to. The fastening face 15 A of the flange section 15 is provided so as to surround the exhaust port 7 annularly on the left, right, top and bottom.

The flange section 15 has multiple boss sections 19 for attaching fastening members (e.g., bolts or screws). Each boss section 19 has a screw hole 20 having a thread groove formed on its inner surface, such that the thread groove is to be threaded with a fasting member. The screw hole 20 is formed in the direction vertical to the fastening face 15 A. The boss sections 19 are positioned surrounding the periphery of the exhaust port 7 and spaced apart from each other at a certain distance. In the example shown in FIG. 6A , the boss sections 19 are formed at the four corners of the fastening face 15 A that has an annular shape.

Two boss sections 19 (the screw holes 20 ) above the exhaust port 7 are positioned on the left and the right of the exhaust port 7 (on the left and the right at substantially equal distances from the center point P of the exhaust port 7 in the frontal view of the fastening face 15 A). Similarly, two boss sections 19 (the screw holes 20 ) below the exhaust port 7 are positioned on the left and the right of the exhaust port 7 (on the left and the right at substantially equal distances from the center point P of the exhaust port 7 ). Among the four boss sections 19 , the boss sections 19 located above are formed such that the upper ends of those two boss sections 19 protrude slightly upwardly relative to the top face 14 A of the protruding section 14 . On the other hand, the boss sections 19 located below are formed such that the lower ends of those two boss sections 19 are aligned with the bottom face 14 B of the protruding section 14 (such that they do not protrude downwardly relative to the bottom face 14 B of the protruding section 14 ).

(2. Cooling Channels)

An example of the exhaust side cooling channel 4 (water jacket) inside the cylinder head 1 is shown in FIG. 4 . The coolant is to flow through the cooling channels 4 in order to cool the outer periphery of the above-described exhaust port 6 (the exhaust system manifold provided in the cylinder head 1 ). The cylinder head 1 is provided with two cooling channels 4 A and 4 B that are disposed to sandwich the exhaust port 6 from the top and the bottom, as a part of the cooling channels 4 . The cylinder head 1 is also provided with outlet cooling channels 4 C and 4 D for cooling the outlet 6 B of the exhaust port 6 .

The cylinder head 1 of the present embodiment is provided with a coolant inlet 44 to which coolant is fed from the water pump side, on the front side of the engine 10 (one end of the long side direction), and a coolant outlet 45 on the rear side (the other end of the long side direction). Therefore, the coolant flows in each of the cooling channels 4 A and 4 B from the front side to the rear side. The cooling channel 4 A and the cooling channel 4 B above and below the exhaust port 6 are disposed along the top and bottom faces of the exhaust port 6 , respectively. The cooling channels 4 A and 4 B communicate to each other in the vicinity of the ceiling face 3 A of the cylinder 3 , and are separated from each other in the protruding section 14 . The cooling channels 4 A and 4 B are provided in planer configurations that are substantially parallel to the top face 14 A and the bottom face 14 B of the protruding section 14 , respectively.

FIGS. 5A and 5B are cross-sectional diagrams showing cross sections of the upper and lower cooling channels 4 A and 4 B on the planes substantially parallel to the top face 14 A and the bottom face 14 B of the protruding section 14 , respectively. Note that the alternate long and two short dashed lines in FIGS. 5A and 5 B represent the contours of the ceiling faces 3 A of the cylinders 3 . Each of the cooling channels 4 A and 4 B in the protruding section 14 is shaped such that the coolant meanders through the cooling channel 4 A, 4 B toward the rear side, while the coolant is branched and merged. Further, as shown in FIG. 6A , the upper cooling channel 4 A of the present embodiment is located downward relative to the upper screw holes 20 not to interfere with these screw holes 20 provided in the fastening face 15 A. On the other hand, the lower cooling channel 4 B is provided at the position to interfere with the lower screw holes 20 in the frontal view of the fastening face 15 A.

The outlet cooling channels 4 C and 4 D are provided adjacent to the outlet 6 B of the exhaust port 6 , and are parts of flow channels disposed between the screw holes 20 and the outlet 6 B, such that the outlet 6 B of the exhaust port 6 is cooled when the coolant passes inside the outlet cooling channels 4 C and 4 D. As used therein the “outlet 6 B” refers to a downstream part of the exhaust confluence 6 A, and the immediate upstream part of the exhaust port 7 , as shown in FIG. 3 . The outlet cooling channels 4 C and 4 D of the present embodiment are disposed between the screw holes 20 provided in the lateral side of the outlet 6 B and the outlet 6 B, and extend in the vertical direction.

As shown in FIGS. 6A and 6B , in the cylinder head 1 of the present embodiment, the two outlet cooling channels 4 C and 4 D are disposed so as to sandwich the outlet 6 B of the exhaust port 6 from the front and the rear. The outlet cooling channels 4 C and 4 D permit communications between the upper and lower cooling channels 4 A and 4 B on the side of the exhaust port 7 relative to the screw holes 20 (i.e., between the screw holes 20 and the outlet 6 B), in the frontal view of the fastening face 15 A. The outlet cooling channels 4 C and 4 D of the present embodiment are provided obliquely relative to the upper and lower cooling channels 4 A and 4 B (in a truncated chevron arrangement), such that the horizontal distance between the outlet cooling channels 4 C and 4 D is reduced as they are located closer to the top. In this manner, the outlet cooling channels 4 C and 4 D form flow channels in the isosceles trapezoid shape, in which the upper bottom is shorter than the lower bottom, around the outlet 6 B of the exhaust port 6 , in the frontal view of the fastening face 15 A.

The coolant flows from the inlet 41 provided in the lower cooling channel 4 B, into the outlet cooling channel 4 C located on the side of the coolant inlet 44 relative to the exhaust port 7 (front side). The coolant that has passed through the outlet cooling channel 4 C merges with the flow of the coolant through the upper cooling channel 4 A. On the other hand, the coolant flows from the inlet 42 provided in the upper cooling channel 4 A, into the outlet cooling channel 4 D located on the side of the coolant outlet 45 relative to the exhaust port 7 (rear side). The coolant that has passed through the outlet cooling channel 4 D merges with the flow of the coolant through the lower cooling channel 4 B. The outlet cooling channels 4 C and 4 D of the present embodiment are formed to have the substantially same cross-sectional areas of the flow channels.

As shown in FIG. 5B , a part of the flow (hereinafter referred to as “branched flow”) branched out from the coolant flowing through the lower cooling channel 4 B (hereinafter referred to as “the main stream”) flows into the inlet 41 of the outlet cooling channel 4 C. The inlet 41 is disposed on the rear side relative to the front side screw holes 20 and outside the cylinder head 1 relative to the ends of the screw holes 20 . The lower cooling channel 4 B is shaped to circumvent the front side screw holes 20 , and the inlet 41 is positioned at the end of the circumventing section (hereinafter referred to as “the circumvention section 46 ”).

The lower cooling channel 4 B of the present embodiment is provided with a guide section 17 for guiding the coolant to the outlet cooling channel 4 C. The guide section 17 is disposed on the side of the coolant outlet 45 relative to the inlet 41 (downstream to the flow direction of the coolant), as a protrusion protruding inwardly from the outer wall of the cylinder head 1 defining the lower cooling channel 4 B (i.e., the side wall section of the protruding section 14 ). As shown in FIG. 4 , since no coolant flows at the position where the guide section 17 is provided, a flow channel toward the inlet 41 is formed by the guide section 17 .

As shown in FIG. 5B , the guide section 17 of the present embodiment protrudes obliquely from the outer wall of the cylinder head 1 toward the front side. The surface of the guide section 17 on the side of the inlet 41 is curved such that the guide section 17 and the circumvention section 46 together form a flow channel having a constant cross-sectional area of the flow channel. As a result, a flow of coolant from the front side is smoothly guided to the inlet 41 . Further, the guide section 17 is formed to protrude for reducing the cross-sectional area of the flow channel of the main stream through the lower cooling channel 4 B. In this manner, the guide section 17 of the present embodiment is configured to separate the flow of the coolant flowing through the lower cooling channel 4 B into the main stream and the branched flow and to increase the flow speed of the main stream, as well as enhancing the flow volume of the branched flow.

As shown in FIG. 5A , the inlet 42 of the outlet cooling channel 4 D on the rear side is disposed outside the upper cooling channel 4 A and at the rear side corner. As a result, the outer wall of the cylinder head 1 (the side wall section of the protruding section 14 ) per se function as a guide section, such that a part of the coolant flowing through the upper cooling channel 4 A is guided to the outlet cooling channel 4 D. Note that the outlet cooling channels 4 C and 4 D of the present embodiment are formed by perforating the top face or the bottom face of the protruding section 14 , and sealing a resultant opening in the top face or the bottom face with a plug, for example.

(3. Advantages and Effects)

(1) In accordance with the cylinder head 1 described above, because it is possible to cool the outlet 6 B of the exhaust port 6 (manifold) by the outlet cooling channels 4 C and 4 D, an exhaust gas ejected from the exhaust port 6 is cooled efficiently. Further, because the outlet cooling channels 4 C and 4 D are disposed between the screw holes 20 and the outlet 6 B of the exhaust port 6 (manifold), heat of the exhaust gas ejected from the exhaust port 7 is prevented from being conducted. This helps to suppress a reduction in the clamping force by fastening members (e.g., bolts or screws) engaged with the screw holes 20 , and hence it is possible to maintain a stable clamping force.

(2) In the cylinder head 1 described above, since the coolant flows above and below the exhaust port 6 through the upper cooling channel 4 A and the lower cooling channel 4 B, it is possible to enhance the efficiency of the cooling around the exhaust port 6 inside the cylinder head 1 . Further, because the outlet cooling channels 4 C and 4 D permit communications between the upper and lower cooling channels 4 A and 4 B, it is possible to form the outlet cooling channels 4 C and 4 D with simplified processing, by perforation and subsequent sealing of the resultant openings.

(3) In the cylinder head 1 described above, the lower cooling channel 4 B connected to the inlet 41 of the outlet cooling channel 4 C includes the guide section 17 for guiding the coolant to the outlet cooling channel 4 C. Because the guide section 17 enhances influx of the coolant into the outlet cooling channel 4 C, it is possible to enhance the efficiency of the cooling of the exhaust.

(4) Further, the guide section 17 is disposed downstream to the flow direction of the coolant relative to the inlet 41 of the outlet cooling channel 4 C, and is provided as a protrusion protruding inwardly from the outer wall of the cylinder head 1 defining the lower cooling channel 4 B. As a result, it is possible to guide the coolant efficiently to the inlet 41 of the outlet cooling channel 4 C, and the efficiency of the cooling of the exhaust gas can be further improved.

(5) In the cylinder head 1 described above, because the outlet cooling channels 4 C and 4 D are provided extending in the vertical direction and are disposed so as to sandwich the outlet 6 B of the exhaust port 6 from the front and the rear, the efficiency of the cooling of the exhaust gas can be further improved. Further, heat conduction to the screw holes 20 located at the lateral sides (left and right sides) of the exhaust port 7 can be prevented.

(6) Further, the outlet cooling channels 4 C and 4 D described above are provided obliquely relative to the upper and lower cooling channels 4 A and 4 B (in a truncated chevron arrangement), such that the horizontal distance between the outlet cooling channels 4 C and 4 D is reduced as they are located closer to the top. As a result, the coolant flows from the lower cooling channel 4 B, into the outlet cooling channel 4 C upstream to (here, on the front side of) the flow direction of the coolant. The temperature of the coolant flowing through the upper and lower cooling channels 4 A and 4 B is generally lower on the upstream than that on the downstream. To address this issue, it is possible to make the coolant with relatively low temperatures flow into the outlet cooling channel 4 C. Further, the coolant flows from the upper cooling channel 4 A, into the outlet cooling channel 4 D downstream to (here, on the rear side of) the flow direction of the coolant. The temperature of the coolant flowing through the upper and lower cooling channels 4 A and 4 B is generally lower on the upstream than that on the downstream, and the temperature of the upper cooling channel 4 A is generally lower than that of the lower cooling channel 4 B. To address this issue, it is also possible to make the coolant with relatively low temperatures flow into the outlet cooling channel 4 D. As a result, in the cylinder head 1 described above, the efficiency of the cooling of the exhaust gas can be further improved.

Further, because the outlet cooling channels 4 C and 4 D described above are arranged in a truncated chevron arrangement, it is possible to ensure that a sufficient volume of coolant flows through the outlet cooling channel 4 C when the flow volume of the coolant in the lower cooling channel 4 B is greater than that in the upper cooling channel 4 A. In other words, when the flow volume of the coolant through the upper cooling channel 4 A is different from that through the lower cooling channel 4 B and the lower flow volume is greater, it is possible to make coolant in the substantially equal flow volumes flow through the two outlet cooling channels 4 C and 4 D by arranging the outlet cooling channels 4 C and 4 D in the truncated chevron arrangement, as in the cylinder head 1 of the present embodiment. This can prevent heat from conducting to the screw holes 20 located on the left and the right of the exhaust port 7 .

(7) In the cylinder head 1 described above, the respective two screw holes 20 perforated in the fastening face 15 A of the flange section 15 are provided both above and below an outlet 6 B (an exhaust port 7 ), and respective fastening members are to be engaged with the screw holes 20 . In the cylinder head 1 described above, because the periphery of the outlet 6 B of the exhaust port 6 is cooled by coolant flowing through the outlet cooling channels 4 C and 4 D, the peripheries of the screw holes 20 are also cooled. Thus, it is possible to enhance the clamping force of the fastening members. Because the respective two screw holes 20 are provided both above and below the exhaust port 7 (at the four corners of the fastening face 15 A) in the cylinder head 1 described above, it is possible to tighten the exhaust pipes securely.

(4. Miscellaneous)

While an embodiment of the present invention has been described, the present invention is not limited to the embodiment set forth above, and the present invention may be practiced in a wide varieties of modification without departing from the point thereof.

The configurations of the outlet cooling channels 4 C and 4 D described above are merely exemplary and are non-limiting. For example, as shown in FIG. 7A , two outlet cooling channels 4 C and 4 D may be provided obliquely relative to the upper and lower cooling channels 4 A and 4 B (in an inversed truncated chevron arrangement), such that the horizontal distance between the outlet cooling channels 4 C and 4 D is increased as they are located closer to the top. In this case, the coolant will flow from the upper cooling channel 4 A into the outlet cooling channel 4 C upstream to the flow direction of the coolant, and the coolant will flow from the lower cooling channel 4 B into the other outlet cooling channel 4 D.

Even in such a configuration, the outlet 6 B of the exhaust port 6 can be cooled, and the exhaust gas ejected from the exhaust port 6 can be efficiently cooled. Further, the heat of the exhaust gas ejected from the exhaust port 7 is prevented from being conducted to fastening members engaged with the screw holes 20 . This prevents a reduction in the clamping force of the fastening members engaged with the screw holes 20 , and it is possible to maintain a stable clamping force. Further, as shown in FIG. 7A , when the two outlet cooling channels 4 C and 4 D are arranged in an inversed truncated chevron arrangement, the efficiency of the cooling of the exhaust gas can be further improved because the distance between the outlet cooling channels 4 C and 4 D and the outlet 6 B is reduced as they are located closer to the bottom.

Further, the inversed truncated chevron arrangement of two outlet cooling channels 4 C and 4 D ensures that a sufficient volume of coolant flows through the outlet cooling channel 4 C when the flow volume of coolant through the upper cooling channel 4 A is greater than that through the lower cooling channel 4 B. In other words, when the flow volume of the coolant through the upper cooling channel 4 A is different from that through the lower cooling channel 4 B and the upper flow volume is greater, it is possible to make coolant in the substantially equal flow volumes flow through the two outlet cooling channels 4 C and 4 D by arranging the outlet cooling channels 4 C and 4 D in the inversed truncated chevron arrangement, as shown in FIG. 7A . This can prevent heat from conducting to the screw holes 20 on the left and the right of the exhaust port 7 . In this manner, conduction of the exhaust heat to the screw holes 20 can be suppressed in an efficient manner by selecting either a truncated chevron or inversed truncated chevron arrangement as the arrangement of the outlet cooling channels 4 C and 4 D, depending on the flow volume of the coolant through the upper and lower cooling channels 4 A and 4 B.

In such a configuration, by providing the upper cooling channel 4 A with a guide section that is similar to the above-described guide section 17 , an inflow of the coolant into the outlet cooling channel 4 C can be enhanced. The above-described configuration of the guide section 17 is merely exemplary, and is non-limiting. Further, another guide section for guiding coolant may also be provided to the inlet 42 of the outlet cooling channel 4 D downstream to the flow direction of the coolant. Note that the guide section 17 is not an essential configuration and may be omitted. If the guide section 17 is not provided, the areas of the openings of the inlets 41 and 42 of the outlet cooling channels 4 C and 4 D may be increased to facilitate an inflow of the coolant, for example. Further, the outlet cooling channels 4 C and 4 D may not have constant cross-sectional areas of the flow channels, and the outlet cooling channels 4 C and 4 D may be formed such that the cross-sectional areas of the flow channels maybe gradually reduced as they are located closer to the outlets, for example. Note that the orientation of the two outlet cooling channels 4 C and 4 D may be perpendicular to the orientation of the upper and lower cooling channels 4 A and 4 B.

Further, the positional relationships of the upper and lower cooling channels 4 A and 4 B and the boss sections 19 (the screw holes 20 ) are not limited to the those described above. For example, as shown in FIG. 7B , the upper cooling channel 4 A may be disposed above the upper screw holes 20 , and the lower cooling channel 4 B may be disposed in the position not to interfere with the lower screw holes 20 (below the lower screw hole 20 ), in the frontal view of the fastening face 15 A. In such a case, it is suffice that both of the outlet cooling channels 4 C and 4 D are disposed on the side of the exhaust port 7 relative to the two screw holes 20 that are aligned vertically.

Even in such a configuration, because the outlet cooling channels 4 C and 4 D are disposed between the outlet 6 B of the exhaust port 6 and the screw holes 20 , heat conduction to the fastening members engaged with the screw holes 20 can be suppressed and it is possible to maintain a stable clamping force by suppressing a reduction in the clamping force. Note that the upper cooling channel 4 A may be disposed at a position interfering with the upper screw holes 20 . Further, the lower cooling channel 4 B may be disposed above the lower screw holes 20 .

The outlet cooling channels 4 C and 4 D may not permit communications between the upper and lower cooling channels 4 A and 4 B, or the outlet cooling channels 4 C and 4 D may be formed not to merge with one of the upper and lower cooling channels 4 A and 4 B.

Further, only one of the outlet cooling channels 4 C and 4 D may be provided, or the outlet cooling channels 4 C and 4 D may not extend in the vertical direction. For example, a water channel located on the side of the outlet 6 B relative to the screw holes 20 may be provided as an outlet cooling channel for flowing the coolant around the outlet 6 B. Alternatively, a part of the upper and lower cooling channels 4 A and 4 B may be configured to function as an outlet cooling channel such that the coolant flows between the screw holes 20 and the outlet 6 B.

Note that the shape of the flange section 15 and the arrangements and number of the boss sections 19 (the screw holes 20 ) are not limited to those described above. Further, coolant in the cooling channels 4 A and 4 B may flow from the rear toward the front. Furthermore, the number of cylinders in the engine 10 and the position of the exhaust port 7 of the cylinder head 1 are not limited to the configurations described above.

1 CYLINDER HEAD

4 EXHAUST SIDE COOLING CHANNEL

4 A UPPER COOLING CHANNEL

4 B LOWER COOLING CHANNEL

4 C, 4 D OUTLET COOLING CHANNEL

6 EXHAUST PORT (MANIFOLD)

6 A EXHAUST CONFLUENCE (CONFLUENCE)

6 B OUTLET

10 ENGINE

12 EXHAUST VALVE HOLE

15 A FASTENING FACE

17 GUIDE SECTION

20 SCREW HOLE

41 , 42 INLET

The invention thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.