JP2010216338A - Cooling structure of cylinder head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling structure of a cylinder head superior in both productivity and cooling performance. <P>SOLUTION: The cooling structure of the cylinder head 3 includes a lower water jacket 7 disposed at a lower part of the cylinder head 3 and to which cooling water is supplied from the outside, an upper water jacket 8 disposed at an upper part of the lower water jacket 7 and to which cooling water is supplied from the lower water jacket 7, and a partitioning wall 21 for partitioning the lower water jacket 7 from the upper water jacket 8. The cooling structure further includes an outer wall hole 26 provided in an outer wall 22 of the cylinder head 3 and communicating the upper water jacket 8 with the outside of the cylinder head 3, a communication hole 25 coaxially provided with the outer wall hole 26 and communicating the upper water jacket 8 with the lower water jacket 7, and a bolt 30 for closing the outer wall hole 26 and the communication hole 25. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cooling structure for a cylinder head, and more particularly to a cooling structure for a cylinder head in which a water jacket for cooling the cylinder head is divided in the vertical direction.

  In an internal combustion engine provided in a vehicle such as an automobile, a cylinder head is provided at an upper portion of a cylinder block, and this cylinder head is exhausted through heat generated by combustion of an air-fuel mixture in a combustion chamber or through an exhaust port. It is exposed to the heat of the gas and needs to be cooled to prevent abnormal combustion. In addition, since the lower the cylinder head is, the lower the temperature is near the combustion chamber, it is important to efficiently cool the lower part of the cylinder head.

  As a conventional cooling structure for this type of cylinder head, a water jacket for circulating cooling water in the cylinder head is used as a lower water jacket by a partition wall in order to cope with an increase in the amount of heat generated as the engine output increases. A structure that is divided into an upper water jacket and an upper water jacket is known. The lower water jacket is disposed at the lower portion of the cylinder head so as to cool a portion near the combustion chamber, and the upper water jacket is disposed so as to cool a portion far from the combustion chamber. Also, a water hole for venting air is provided in the partition wall to prevent air from accumulating.

  In this cylinder head, the cooling water delivered by the water pump is caused to flow in both the lower water jacket and the upper water jacket, so that the portion close to the combustion chamber, that is, the lower part of the cylinder head with a high heat load is lowered by the lower water jacket. Cooling can be performed efficiently, and for example, the cooling efficiency of the cylinder head can be improved without increasing the capacity of the water pump in order to increase the flow rate of the cooling water (see, for example, Patent Document 1).

JP 2000-104624 A

  However, in such a conventional cooling structure of the cylinder head, the cooling water flows out from the lower water jacket to the upper water jacket through the air vent water hole provided in the partition wall, and the cooling performance is lowered. There was a fear.

  In addition, even if the partition wall between the upper water jacket and the lower water jacket is not provided with a water hole for venting air, the sand removal and degassing of the core when the cylinder head is manufactured by casting is performed. However, if the communication hole remains open in the partition wall, cooling water may flow out from the lower water jacket to the upper water jacket through the communication hole, which may reduce the cooling performance. there were. That is, in the cylinder head in which the water jacket is divided by the partition walls, there is a problem that it is difficult to achieve both of them because the productivity and the cooling performance by casting are contradictory.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a cylinder head cooling structure excellent in both productivity and cooling performance.

  In order to achieve the above object, the cooling structure for a cylinder head according to the present invention includes (1) a lower water jacket that is arranged at the lower part of the cylinder head and supplied with cooling water from the outside, and an upper part of the lower water jacket. And a cooling structure for a cylinder head comprising an upper water jacket to which cooling water is supplied from the lower water jacket, and a partition wall that separates the lower water jacket and the upper water jacket, and is provided on an outer wall of the cylinder head. An outer wall hole communicating with the upper water jacket and the outside of the cylinder head; a communication hole provided coaxially with the outer wall hole; communicating with the upper water jacket and the lower water jacket; and the outer wall hole And a closing member that closes the communication hole. It has formed.

  With this configuration, when the cylinder head is manufactured by casting, the core is sanded and degassed by the communication hole and the outer wall hole, so that the cylinder head can be manufactured satisfactorily and the cylinder head can be used. Since the communication hole and the outer wall hole are closed by the closing member, the cooling water does not flow from the lower water jacket to the upper water jacket, and the cooling water does not leak from the upper water jacket to the outside of the cylinder head. Good cooling can be performed. Therefore, it is possible to provide a cylinder head cooling structure that is excellent in both productivity and cooling performance.

  The cylinder head cooling structure according to the present invention is the cylinder head cooling structure according to the above (1), wherein (2) the inner diameter of the outer wall hole is larger than the inner diameter of the communication hole, and the blocking member is And a screwing portion that is screwed into the outer wall hole to close the outer wall hole, and a loose fitting portion that is loosely fitted to the communication hole to close the communication hole.

  With this configuration, relative movement in the axial direction is allowed between the loose fitting portion of the closing member and the communication hole, so that excessive stress is not generated on the partition wall and the outer wall, and the distance between the partition wall and the outer wall changes. Even in this case, it is possible to prevent the partition wall or the outer wall from being distorted, fatigued or cracked due to excessive stress. Further, since the screwing portion is screwed into the outer wall hole, it is reliably prevented that the closing member is dropped or the cooling water flowing through the upper water jacket is leaked from the outer wall hole to the outside of the cylinder head. Further, since the inner diameter of the outer wall hole is larger than the inner diameter of the communication hole, the closing member can be easily inserted into the outer wall hole and the communication hole in the assembly process.

  The cylinder head cooling structure according to the present invention is the cylinder head cooling structure according to the above (2), in which (3) the loose fitting portion is inserted into the communication hole through a gap of 0.1 mm to 3 mm. It has a configuration that fits loosely.

  This configuration minimizes the amount of cooling water that flows from the lower water jacket to the upper water jacket through the gap between the loose-fitting part and the communication hole, thus preventing the cooling performance of the lower water jacket from being impaired. In addition, the loose fitting portion and the communication hole may not be smoothly inserted into the communication hole in the assembly process due to variation in the size of the loose fitting portion and the communication hole or thermal expansion, or the loose fitting portion may be tightly fitted into the communication hole. Thus, it is possible to prevent excessive stress from being generated on the partition wall and the outer wall.

  According to the present invention, when the cylinder head is manufactured by casting, the core is sanded and degassed by the communication hole and the outer wall hole so that the cylinder head can be manufactured satisfactorily, and the cylinder head is used. In this case, since the communication hole and the outer wall hole are closed by the closing member, good cooling can be performed. As a result, a cylinder head cooling structure excellent in both productivity and cooling performance can be provided.

It is a figure which shows the cooling structure of the cylinder head which concerns on one embodiment of this invention, and is a schematic structure of the exhaust system for vehicles provided with the cooling structure of a cylinder head. It is a front sectional view showing a cooling structure of a cylinder head according to an embodiment of the present invention, and is a view taken along the line BB in FIG. It is an AA arrow directional view of the cylinder head shown in FIG. (A) is a figure which shows the state which closed the communicating hole and the outer wall hole with the obstruction | occlusion member in the AA arrow directional view of FIG. 3, (b) is a figure which shows the obstruction | occlusion member.

  Embodiments of a cylinder head cooling structure according to the present invention will be described below with reference to the drawings.

  1-4 is a figure which shows one Embodiment of the cooling structure of the cylinder head based on this invention.

First, the configuration will be described.
In FIG. 1, an engine 1 as an internal combustion engine includes a cylinder block 2 and a cylinder head 3 mounted on the upper portion of the cylinder block 2. Cooling water is supplied to the engine 1 from a water pump 4. It comes to be supplied.

  A water jacket 5 is formed in the cylinder block 2, and the water jacket 5 is provided around a plurality of cylinders 15 (see FIGS. 2 to 4).

  The cylinder head 3 is provided with a water jacket 6, and the water jacket 6 has a two-layer structure composed of a lower water jacket 7 and an upper water jacket 8.

  In the present embodiment, the cooling water supplied from the water pump 4 to the engine 1 flows from the lower side of the engine 1 to the upper side so as to flow through the water jacket 5 of the cylinder block 2, and then the water jacket of the cylinder head 3. 6 is supplied.

  The water pump 4 is connected to a crankshaft (not shown) of the engine 1 and is driven by the rotation of the crankshaft. The water pump 4 may be driven by an electric motor or the like.

  The cooling water supplied from the water pump 4 to the engine 1 flows through the water jacket 5 and the water jacket 6 and then supplied to the radiator 10. The radiator 10 heats the cooling water and air. Allow to replace and cool the cooling water.

  Note that the engine 1, the water pump 3, and the radiator 10 are connected to each other by pipes 9 through which cooling water passes.

  As shown in FIGS. 2 to 4, the cylinder block 2 is provided with a plurality of (four in the present embodiment) cylinders 15 in a row. The cylinder head 3 is disposed on the upper side of the cylinder block 2 and is fastened to the cylinder block 2 by bolts (not shown) inserted through a plurality of bolt holes 12. The cylinder head 3 of the present embodiment is manufactured by casting in which molten metal is poured into a mold.

  A combustion chamber 13 is provided at a position corresponding to each cylinder 15 on the bottom surface 16 of the cylinder head 3. FIG. 3 shows only the end of the combustion chamber 13.

  In the cylinder head 3, intake ports 14 for guiding intake air to the combustion chambers 13 are arranged in the arrangement direction of the cylinders 15 (the vertical direction in FIG. 2 and the direction orthogonal to the paper surface in FIGS. 3 and 4). Is provided. The downstream end of the intake port 14 opens at the wall surface of the combustion chamber 13. Further, the two intake ports 14 connected to one cylinder 15 merge on the upstream side in the intake flow direction (the right side in FIG. 2) to form one flow path for each cylinder 15 and intake air of the cylinder head 3. It opens at the side wall surface 17. An intake valve (not shown) that opens and closes the opening of the intake port 14 in each combustion chamber 13 is attached to the cylinder head 3 so as to be able to reciprocate in a substantially vertical direction.

  The cylinder head 3 is provided with exhaust ports 18 arranged in the direction in which the cylinders 15 are arranged for leading exhaust gas generated in the combustion chamber 13 to the outside of the engine 1. The upstream end of the exhaust port 18 opens at the wall surface of the combustion chamber 13. Further, the exhaust port 18 joins downstream of the combustion chamber 13 in the exhaust flow direction (left side in FIG. 2), and the downstream end is opened at the wall 23 on the exhaust side of the cylinder head 3. An exhaust valve (not shown) that opens and closes the opening of the exhaust port 18 in each combustion chamber 13 is attached to the cylinder head 3 so as to be able to reciprocate in a substantially vertical direction.

  In the cylinder head 3, a plug mounting hole 24 extending in the vertical direction is provided at a location corresponding to the top of the combustion chamber 13, and a spark plug (not shown) is mounted here.

  In the cylinder head 3, due to the heat accompanying combustion of the air-fuel mixture in the combustion chamber 13, the portion closer to the combustion chamber 13, that is, the lower the cylinder head 3, the higher the temperature.

  In the cylinder head 3, the above-described water jacket 6 is provided as a cooling water passage for cooling each part of the cylinder head 3. The water jacket 6 is disposed on the upper portion of the lower water jacket 7 and the lower water jacket 7 for cooling the lower portion of the cylinder head 3 that is close to the combustion chamber 13 and relatively high in temperature, and relatively far from the combustion chamber 13. The lower water jacket 7 and the upper water jacket 8 are separated from each other by a partition wall 21. The lower water jacket 7 extends in the arrangement direction of the cylinders 15 so that cooling water supplied from one end side in the extending direction flows to the other end side. The upper water jacket 8 extends in the direction in which the cylinders 15 are arranged, and the cooling water that is branched and supplied from the lower water jacket 7 on one end side in the extending direction flows to the other end side and flows into the lower water jacket. 7 to join.

  The lower water jacket 7 is set so that the flow rate of the cooling water flowing inside is larger than that of the upper water jacket 8. Such a flow rate relationship between the lower water jacket 7 and the upper water jacket 8 depends on the shape of the part where the lower water jacket 7 and the upper water jacket 8 start to branch, and the inside of the lower water jacket 7 and the upper water jacket 8. Is set by the ratio of pressure loss of cooling water. The lower water jacket 7 is set to have a narrow cross-sectional area so that the flow rate of the cooling water is faster than that of the upper water jacket 8. That is, the cooling capacity of the lower water jacket 7 having a relatively high cooling water flow rate and a large flow rate is set to be higher than that of the upper water jacket 8 having a relatively low cooling water flow rate and a low flow rate. For this reason, the lower part of the cylinder head 3 having a relatively high temperature close to the combustion chamber 13 is mainly cooled by the lower water jacket 7 having a high cooling capacity. Further, the upper water jacket 8 mainly cools the heat transmitted from the exhaust port 18. The lower water jacket 7 and the upper water jacket 8 are integrally formed by disposing a core in the mold when the cylinder head 3 is cast.

  In order to remove sand and remove gas from the core during casting of the cylinder head 3, the partition wall 21 is formed with a communication hole 25 that allows the lower water jacket 7 and the upper water jacket 8 to communicate with each other. The outer wall 22 is formed with an outer wall hole 26 that communicates the outside of the cylinder head 3 with the upper water jacket 8.

  The communication hole 25 and the outer wall hole 26 are provided coaxially with each other. That is, the communication hole 25 and the outer wall hole 26 are arranged so that the axis of the communication hole 25 and the axis of the outer wall hole 26 are aligned. A female thread portion 26 a is formed in the outer wall hole 26 by processing the cylinder head 3 after casting. Further, the inner diameter of the outer wall hole 26 is configured to be larger than the inner diameter of the communication hole 25.

  As shown in FIG. 4A, the communication hole 25 and the outer wall hole 26 are closed by a bolt 30 as a closing member. As shown in FIG. 4B, the bolt 30 has a large-diameter portion 31 on the side close to the head 33 and a small-diameter portion 32 on the end portion side opposite to the head 33. The outer diameter of the portion 31 is configured to be larger than the outer diameter of the small diameter portion 32. The large-diameter portion 31 is formed with a male screw portion 31a, and the large-diameter portion 31 is screwed into the outer wall hole 26 in which the female screw portion 26a is formed. The large-diameter portion 31 of the present embodiment constitutes the screwing portion of the present invention.

  Further, the small diameter portion 32 has an outer diameter smaller than the inner diameter of the communication hole 25 so as to be loosely fitted into the communication hole 25. Specifically, a gap of 0.1 mm or more and 3 mm or less is formed between the small diameter portion 32 and the communication hole 25. That is, between the small-diameter portion 32 of the bolt and the communication hole 25 of the partition wall 21 is a so-called clearance fit or loose fit. The small diameter portion 32 of the present embodiment constitutes the loose fitting portion of the present invention.

  For this reason, various deformations such as expansion and contraction due to temperature change, deformation due to release of residual stress at the time of casting due to temperature rise, deformation due to combustion pressure, and the like occur in the cylinder head 3, and the partition wall 21. Even if the distance between the outer wall 22 and the outer wall 22 changes, only the large diameter portion 31 of the bolt 30 and the outer wall hole 26 of the outer wall 22 are screwed together, and the small diameter portion 32 of the bolt 30 and the communication hole 25 are Since relative movement in the axial direction is allowed, excessive stress is not generated on the partition wall 21 and the outer wall 22. Therefore, even if the interval between the partition wall 21 and the outer wall 22 changes, it is possible to prevent the partition wall 21 or the outer wall 22 from being distorted or fatigued or cracked due to excessive stress.

  Further, since the gap between the small diameter portion 32 and the communication hole 25 is as small as 0.1 mm or more and 3 mm or less, only a small amount of cooling water flows from the lower water jacket 7 to the upper water jacket 8 through this gap. The cooling performance of the lower water jacket 7 is not impaired.

  When the gap between the small diameter portion 32 and the communication hole 25 is larger than 3 mm, the amount of cooling water flowing out from the lower water jacket 7 to the upper water jacket 8 through this gap increases, There is a possibility that the cooling performance of the water jacket 7 may be deteriorated, and when the gap between the small diameter portion 32 and the communication hole 25 is made smaller than 0.1 mm, the size of the small diameter portion 32 and the communication hole 25 may vary due to variations or thermal expansion. In the assembling process, the small diameter portion 32 may not smoothly enter the communication hole 25, or the small diameter portion 32 may be tightly fitted in the communication hole 25, and excessive stress may be generated in the partition wall 21 and the outer wall 22. There is. Therefore, it is preferable that the gap between the small diameter portion 32 and the communication hole 25 is 0.1 mm or more and 3 mm or less.

  The large diameter portion 31 has a tapered portion 31b at the boundary with the small diameter portion 32, and the tip of the small diameter portion 32 has a tapered portion 32a. These inclined surfaces of the tapered portions 31 b and 32 a allow the bolt 30 to be smoothly inserted without being caught by the outer wall hole 26 and the communication hole 25.

Next, the operation of the cylinder head 3 configured as described above will be described.
When the engine 1 is operated and the water pump 4 is operated, cooling water circulates between the engine 1 and the radiator 10. Specifically, the cooling water delivered from the water pump 4 passes through the water jacket 5 of the cylinder block 2 to cool the cylinder block 2, and then passes through the water jacket 6 of the cylinder head 3 to cool the cylinder head 3. Then, heat exchange with the outside air is performed by the radiator 10 and the water pump 4 sends the heat again.

  Of the lower water jacket 7 and the upper water jacket 8 constituting the water jacket 6 of the cylinder head 3, a relatively high speed and high flow rate of cooling water passing through the lower water jacket 7 is generated from the combustion chamber 13 to generate the cylinder head. The cooling water that mainly cools the heat transferred to 3 and passes through the upper water jacket 8 and has a relatively low speed and a small flow rate mainly cools the heat transferred from the exhaust port 18.

  The cooling water flowing through the lower water jacket 7 flows out only slightly to the upper water jacket 8 through the communication hole 25 because the communication hole 25 formed in the partition wall 21 is closed by the small diameter portion 32 of the bolt 30. The lower part of the cylinder head 3 is cooled efficiently.

  If the clearance between the communication hole 25 of the partition wall 21 and the small diameter portion 32 of the bolt 30 is 3 mm or less, the lower water jacket can be used even if cooling water slightly flows out from the lower water jacket 7 to the upper water jacket 8. It has been confirmed by tests that the cooling capacity of No. 7 does not cause a significant difference compared to the case where there is no gap between the communication hole 25 of the partition wall 21 and the small diameter portion 32 of the bolt 30.

  Further, each part of the cylinder head 3 undergoes various deformations such as expansion and contraction due to temperature change, deformation due to release of residual stress during casting due to temperature rise, and deformation due to combustion pressure. Although the interval with the outer wall 22 also changes slightly, the small diameter portion 32 of the bolt 30 is loosely fitted to the communication hole 25 through a gap of 0.1 mm or more and 3 mm or less, and the small diameter portion 32 of the bolt 30 and the communication hole Since 25 is allowed to move in the axial direction, excessive stress is not generated on the partition wall 21 and the outer wall 22. Therefore, even if the distance between the partition wall 21 and the outer wall 22 is changed, excessive stress is not generated on the partition wall 21 and the outer wall 22, and the partition wall 21 and the outer wall 22 may be distorted, metal fatigued, or cracked. Is prevented.

  On the other hand, the coolant flowing through the upper water jacket 8 leaks to the outside of the cylinder head 3 through the outer wall hole 26 because the outer wall hole 26 formed in the outer wall 22 is closed by the large-diameter portion 31 of the bolt 30. The heat around the exhaust port 18 is efficiently cooled. The outer wall hole 26 of the outer wall 22 and the large diameter portion 31 of the bolt 30 are firmly screwed together by the female screw portion 26a of the outer wall hole 26 and the male screw portion 31a of the large diameter portion 31, so that the bolt 30 is dropped. The cooling water flowing through the upper water jacket 8 is reliably prevented from leaking from the outer wall hole 26 to the outside of the cylinder head 3.

  As described above, in the cooling structure of the cylinder head according to the embodiment of the present invention, the outer wall hole 26 provided on the outer wall 22 of the cylinder head 3 and communicating the upper water jacket 8 and the outside of the cylinder head 3; The cylinder head is provided with a communication hole 25 that is provided coaxially with the outer wall hole 26 and communicates the upper water jacket 8 and the lower water jacket 7 and a bolt 30 that closes the outer wall hole 26 and the communication hole 25. 3 is produced by casting, the core sand is removed and vented by the communication hole 25 and the outer wall hole 26, and the cylinder head 3 can be manufactured satisfactorily. When the cylinder head 3 is used, Since the communication hole 25 and the outer wall hole 26 are closed by the bolt 30, cooling water is transferred from the lower water jacket 7 to the upper water jacket 8. Outlet or, without an external cooling water in the cylinder head 3 from the upper water jacket 8 is leaked, it is possible to perform a good cooling. Therefore, it is possible to provide a cooling structure for the cylinder head 3 that is excellent in both productivity and cooling performance.

  In the cylinder head cooling structure according to the embodiment of the present invention, the inner diameter of the outer wall hole 26 is made larger than the inner diameter of the communication hole 25, and the bolt 30 is screwed into the outer wall hole 26 so that the outer wall hole 26 is formed. Since the large-diameter portion 31 that is closed and the small-diameter portion 32 that loosely fits in the communication hole 25 and closes the communication hole 25 are provided, relative movement in the axial direction between the small-diameter portion 32 and the communication hole 25 is achieved. Therefore, excessive stress is not generated on the partition wall 21 and the outer wall 22, and even if the distance between the partition wall 21 and the outer wall 22 changes, distortion or metal fatigue is caused on the partition wall 21 or the outer wall 22 due to excessive stress. It is possible to prevent occurrence or cracking. Further, since the large-diameter portion 31 is screwed into the outer wall hole 26, it is ensured that the bolt 30 falls off or the coolant flowing through the upper water jacket 8 leaks from the outer wall hole 26 to the outside of the cylinder head 3. Is prevented. Further, since the inner diameter of the outer wall hole 26 is larger than the inner diameter of the communication hole 25, the bolt 30 can be easily inserted into the outer wall hole 26 and the communication hole 25 in the assembly process.

  Further, in the cylinder head cooling structure according to the embodiment of the present invention, the small diameter portion 32 has a configuration in which the small diameter portion 32 is loosely fitted into the communication hole 25 through a gap of 0.1 mm or more and 3 mm or less. Since the amount of cooling water flowing out from the lower water jacket 7 to the upper water jacket 8 through the gap between the portion 32 and the communication hole 25 is minimized, the cooling performance of the lower water jacket 7 is impaired. In addition, the small diameter portion 32 and the communication hole 25 may not be smoothly inserted into the communication hole 25 or the small diameter portion 32 may be tightened into the communication hole 25 due to variation in the dimensions of the small diameter portion 32 and the communication hole 25 or thermal expansion. It can be prevented that an excessive stress is generated in the partition wall 21 and the outer wall 22 due to the fitted state.

  The embodiment disclosed this time is illustrative in all points, and is not limited to this embodiment. The scope of the present invention is illustrated not by the above description of the embodiments but by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. For example, an O-ring made of an elastic member is provided on the small diameter portion 32 of the bolt 30 so as to slidably liquid-tightly seal between the small diameter portion 32 and the communication hole 25, thereby allowing the lower water jacket 7 to the upper water jacket 8. In addition, it is possible to completely prevent the cooling water from flowing out and to allow relative movement in the axial direction between the small diameter portion 32 of the bolt 30 and the communication hole 25, so that excessive stress is generated in the partition wall 21 and the outer wall 22. Can be prevented.

  As described above, the cooling structure of the cylinder head according to the present invention has an effect that both the productivity and the cooling performance are excellent, and the cylinder head is obtained by dividing the water jacket for cooling the cylinder head in the vertical direction. Useful for cooling structures.

2 Cylinder block 3 Cylinder head 5, 6 Water jacket 7 Lower water jacket 8 Upper water jacket 13 Combustion chamber 15 Cylinder 16 Bottom surface 21 Bulkhead 22 Outer wall 25 Communication hole 26 Outer wall hole 26a Female thread part 30 Bolt (blocking member)
31 Large diameter part (screwed part)
31a Male thread part 31b, 32a Taper part 32 Small diameter part (free fitting part)

Claims (3)

A lower water jacket disposed at the bottom of the cylinder head and supplied with cooling water from the outside;
An upper water jacket that is disposed on top of the lower water jacket and is supplied with cooling water from the lower water jacket;
In the cooling structure of the cylinder head comprising a partition wall separating the lower water jacket and the upper water jacket,
An outer wall hole provided in an outer wall of the cylinder head and communicating the upper water jacket and the outside of the cylinder head;
A communication hole provided coaxially with the outer wall hole, and communicating the upper water jacket and the lower water jacket;
A cooling structure for a cylinder head, comprising: a closing member that closes the outer wall hole and the communication hole. While making the inner diameter of the outer wall hole larger than the inner diameter of the communication hole,
The closing member includes a screwing portion that is screwed into the outer wall hole to close the outer wall hole, and a loose fitting portion that is loosely fitted to the communication hole to close the communication hole. The cooling structure of the cylinder head according to claim 1.   The cylinder head cooling structure according to claim 2, wherein the loosely fitting portion loosely fits into the communication hole through a gap of 0.1 mm to 3 mm.

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