JP6712946B2 - Water cooling engine cooling structure - Google Patents

Description

The present invention relates to a cooling structure applied to an industrial diesel engine or the like, and more specifically, to cooling a water-cooled engine including a plurality of cylinders arranged in a cylinder block and a water jacket formed around the plurality of cylinders. It is about structure.

As a cooling structure in a water-cooled engine, a water jacket is generally provided around a cylinder or a cylinder head, which is a heat generating point, and cooling water is circulated. In the case of a multi-cylinder engine having two or more cylinders such as an in-line 4-cylinder engine, cooling between adjacent cylinders, that is, cooling between bores is often necessary.

When there are two or more cylinders, it is preferable to arrange adjacent cylinders as close to each other as possible in order to make the engine length compact. However, the thermal load is most severe between the cylinders, which are also sources of heat, that is, between the bores. Therefore, conventionally, as disclosed in Patent Document 1, a means has been adopted in which a water hole is formed by punching a hole between the bores of the cylinder by post-processing.

By installing drill holes, cooling water is passed between the bores and the cooling performance is improved, but if the thermal load is higher, such as in high compression engines and large displacement engines, strengthening of inter-bore cooling is desired. .. Therefore, in the past, a means for further improving the cooling property has also been adopted, such as by using a core core, by clearly separating adjacent cylinders and providing a clear water jacket between the bores.

In the latter conventional technique, the cooling performance is improved, but the inter-bore distance is required for that amount, and as a result, the engine length tends to increase in size. The former conventional technique is advantageous in terms of engine length, but is inferior to the latter conventional technique in terms of cooling performance. As described above, the conventional cooling structure for a water-cooled engine has advantages and disadvantages in terms of suppressing an increase in engine length and improving cooling performance.

JP-A-2007-023824 JP, 2003-193836, A

An object of the present invention is to provide a cooling structure for a water-cooled engine, which is capable of achieving sufficient cooling between bores without increasing the length of the engine by further improving the structure and achieving both the miniaturization of the engine length and the cooling performance. Is in the point of providing.

The invention according to claim 1 is a cooling structure for a water-cooled engine,
A plurality of cylinders 2 arranged in the cylinder block 1; and a water jacket W formed around the plurality of cylinders 2,
The water jacket W has interbore channels 9 and 10 formed between the outer peripheral walls 4A and 4A of the adjacent cylinders 2 and 2,
Since the upper end portions of the pair of outer peripheral walls 4A, 4A are formed in the tapered upper wall 27 that is inclined in the direction toward each other, the upper end portions of the interbore channels 9 and 10 have a width in the interbore direction. The tapered flow passage portions 9a and 10a are narrowed toward the cylinder head side ,
The portions of the pair of outer peripheral walls 4A, 4A other than the tapered upper wall 27 are parallel to the axis of the cylinder 2 .

According to a second aspect of the present invention, in the cooling structure for a water-cooled engine according to the first aspect, the tapered angle β of the tapered channel portions 9a and 10a is set to 0.5 to 3 degrees. Is characterized by.

The invention according to claim 3 is a cooling structure for a water-cooled engine,
A plurality of cylinders 2 arranged in the cylinder block 1; and a water jacket W formed around the plurality of cylinders 2,
The water jacket W has interbore channels 9 and 10 formed between adjacent cylinders 2 and 2,
In the barrel portion 4 forming the interbore channels 9 and 10 in the cylinder block 1, a rib wall 22 extending from the barrel portion 4 in a state of extending in the axial direction of the cylinder 2 has an axial center of the cylinder 2. Is formed so as to extend in the direction,
The rib wall 22 is characterized in that it has a divergent shape whose width in the bore circumferential direction becomes wider as it approaches the cylinder head.

The invention according to claim 4 is the cooling structure for a water-cooled engine according to claim 3,
The divergence angle α of the rib wall 22 is set to 3 to 7 degrees.

The invention according to claim 5 is the cooling structure for a water-cooled engine according to claim 3 or 4,
The rib wall 22 is characterized in that its tip does not reach the cylinder head side end of the interbore channels 9, 10.

According to the present invention, the following effects can be obtained. That is, the upper end of the cylinder block is preferably closed (connected) between adjacent cylinders from the viewpoint of strength and rigidity, but it is difficult to bring the cooling water close to the upper end of the cylinder block where the thermal conditions are severe. It is disadvantageous in terms. Therefore, if the end of the flow path between bores on the cylinder head side is tapered, it will be a closed type that secures the strength and rigidity of the upper end of the cylinder block, but the flow path between bores will be expanded close to the upper end. It will be possible.

Therefore, even though it is a closed type cylinder block that is basically advantageous in strength and rigidity, it is possible to expand the inter-bore flow passage with severe thermal conditions to the cylinder head side and sufficiently send the cooling water to the inter-bore flow passage. become. As a result, by further devising the structure, it is possible to perform sufficient inter-bore cooling without increasing the engine length, and to provide a cooling structure for a water-cooled engine that achieves both a reduction in engine length and cooling performance. be able to.

Top view of the cylinder section showing the cylinder block A line aa sectional view of the cylinder block shown in FIG. Bb line sectional view of the cylinder block shown in FIG. 2 is a sectional view taken along the line cc of the cylinder block shown in FIG. The flow of cooling water in a water jacket is shown, (a) is a case where guide walls in mutually opposite directions (Embodiment 1), (b) is a case where guide walls in mutually opposite directions (Embodiment 2) Enlarged cross-sectional view of the flow path between bores cut back and forth at the left-right center

An embodiment of a cooling structure for a water-cooled engine according to the present invention will be described below as being applied to a vertical in-line 3-cylinder water-cooled diesel engine with reference to the drawings.

As shown in FIGS. 1 and 4, in this engine, a plurality of (three) cylinders 2 are arranged in series in a cylinder block 1, and a water jacket (cylinder jacket) W formed around the plurality of cylinders 2 is provided. It is equipped with a water-cooled engine. The water jacket W includes barrel portions (cylinder walls) 4, 4, 4 which are formed upright in a substantially tubular shape to form each cylinder 2 in the cylinder block 1, a cylinder outer frame portion 5 in the cylinder block 1, and a cylinder ceiling. It is an internal space for cooling water circulation formed between the wall 3 and the wall 3. A portion of the front side of the cylinder block 1 that extends to the left side is a fuel injection case portion 26.

1 and 4, the intake side of the cylinder block 1 is left, the exhaust side is right, the side with the cooling water inlet 6 to the water jacket W is the front, and the opposite side is the rear.
The water jacket W is a pair of main flow passages that are formed outside the cylinder 2 (barrel portion 4) in a state of extending in the cylinder arrangement direction, that is, an intake-side main flow passage 7 and an exhaust-side main flow passage 8, and a pair of main flow passages 7. , 8 connect the first and second inter-bore channels 9 and 10 formed between adjacent cylinders 2 (barrel portion 4) in a state of connecting them, and the main flow channels 7 and 8 start and end ends It is configured to have front and rear end channels wf and wr.

As shown in FIGS. 1 and 4, in the cylinder ceiling wall 3 to which the cylinder head (not shown) is connected to its upper surface 3A via a gasket (not shown), a bolt insertion hole 3a, a communication hole 3b, a drill hole, and a hole are formed. The hole 3c is formed. The bolt insertion holes 3 a are holes through which bolts for connecting the cylinder block 1 and the cylinder head (not shown) are inserted, and are formed at a plurality of positions (14 positions) around each cylinder 2. The communication hole 3b is a relatively large passage for allowing the cooling water to flow from the water jacket W to the water jacket (cylinder head jacket: not shown) of the cylinder head, and is in a state of communicating with either of the main flow paths 7 and 8. It is formed in plural (12 places).

The drill holes 3c are formed at a total of four positions at the front and rear ends of the cylinder ceiling wall 3 so as to communicate with the front end channel wf and the rear end channel wr of the water jacket W, respectively. In addition, between the adjacent cylinders 2 and 2 of the cylinder ceiling wall 3, in a state of communicating with the first inter-bore channel 9 and the second inter-bore channel 10, respectively, an oblique hole extending from the upper left to the lower right is formed. , Each of which is formed at one place.

3 and 4, the hole provided at the front end of the cylinder block 1 so as to face the front end flow path wf is an auxiliary device such as a thermostat (not shown) or a sensor (not shown) for measuring the cooling water temperature. It may be a mounting hole 25 for mounting.

Now, the cooling water sent from the cooling water inlet 6 to the water jacket W by the water pump (not shown) is first separated into the left and right from the front end flow passage wf, and goes back through the intake side main flow passage 7 and the exhaust side main flow passage 8. To the first and second inter-bore channels 9, 10 on the way. Then, the cooling water flows backward as well as upward in the water jacket W, flows into the cylinder head jacket (not shown) through the plurality of communication holes 3b and the plurality of perforation holes 3c, and flows into the cylinder head jacket (not shown). It flows toward the cooling water outlet (not shown).

As shown in FIG. 4 and FIG. 5( a ), in the cylinder block 1, guide walls h (11 to 14) capable of guiding the cooling water flowing through the main flow paths 7 and 8 to the interbore flow paths 9 and 10. Are formed at four locations. Specifically, the first guide wall 11 protruding from the front side portion of the front and rear intermediate second barrel portion 4 into the intake side main flow passage 7 and the first guide wall 11 protruding from the rear side portion of the front side first barrel portion 4 into the exhaust side main flow passage 8 2 guide walls 12, a third guide wall 13 protruding from the rear part of the front and rear intermediate second barrel part 4 into the intake side main flow path 7, and a front part of the rear side third barrel part 4 to the exhaust side main flow path 8. The protruding fourth guide wall 14 constitutes a guide wall h.

The first guide wall 11 having an arc shape along the circumferential direction of the first cylinder 2 on the front side when viewed in the vertical direction allows the cooling water flowing from the front to the rear in the intake-side main flow path 7 near the first cylinder 2. , A guiding action for guiding the first inter-bore channel 9 to the right is exhibited. Flowing from left to right (from the intake side to the exhaust side) in the first inter-bore flow passage 9 by the second guide wall 12 having an arc shape along the circumferential direction of the second cylinder 2 in the front-rear direction in the vertical direction. A guiding action is exhibited in which the cooling water is guided obliquely rearward to the right and merges with the exhaust-side main flow path 8.

By the fourth guide wall 14 having an arcuate shape along the circumferential direction of the second cylinder 2 when viewed in the vertical direction, the cooling water flowing from the front to the rear in the exhaust side main flow path 8 near the second cylinder 2 is left. A guiding action of guiding the second inter-bore flow path 10 toward is exerted. Flowing from right to left (from exhaust side to intake side) in the second inter-bore flow passage 10 by the third guide wall 13 having an arcuate shape along the circumferential direction of the rear third cylinder 2 when viewed in the vertical direction. A guiding action is exhibited in which the cooling water is guided to the left rear obliquely and merges with the intake side main flow path 7.

As described above, the first guide wall 11 and the third guide wall 13 corresponding to the inter-bore channels 9 and 10 adjacent to each other in the cylinder arranging direction have opposite directions in which the cooling water is guided to the inter-bore channels 9 and 10. It is formed in a direction. Then, to the second guide wall 12 for restricting the inflow of the cooling water flowing through the exhaust side main flow path 8 into the first inter-bore flow path 9, and the second inter-bore flow path 10 for the cooling water flowing through the exhaust side main flow path 8. The fourth guide walls 14 that promote the entry of the guides are also formed so as to guide each other in opposite directions.

As a result, in the water jacket W, as shown in FIG. 5A, the cooling water flows from the front to the rear in the pair of main flow paths 7 and 8 by the guide action of the first to fourth guide walls 11 to 14. And a flow flowing from left to right through the first inter-bore channel 9 and a flow flowing from right to left through the second inter-bore channel 10. Due to this smooth flow of the cooling water, a sufficient flow rate (also the flow rate of the cooling water per unit time) is secured in the first and second inter-bore flow paths 9 and 10, and between the bores that are difficult to cool, A structure that can efficiently cool the cylinders 2 and 2 can be realized without widening the arrangement interval.

In other words, in the first inter-bore flow path 9, the cooling water intake (water intake) promoting action by the first guide wall 11 and the drainage promoting action by the second guide wall 12 are exhibited, so that the inter-bore width is widened. It is possible to obtain an efficient water cooling effect through a sufficient flow rate. Similarly, in the second inter-bore flow path 10, since the cooling water intake (water intake) promoting action by the third guide wall 13 and the drainage promoting action by the fourth guide wall 14 are exhibited, the inter-bore width is reduced. It is possible to obtain an efficient water cooling effect through a sufficient flow rate without spreading.

In the cooling structure including the guide wall h having the configuration shown in FIG. 5A, the guide walls 11(h) and 13(h) corresponding to the inter-bore channels 9 and 10 adjacent in the cylinder arrangement direction are The directions in which the cooling water is guided to the interbore channels 9 and 10 are formed in opposite directions. Therefore, the movement path of the cooling water flowing through the two inter-bore flow paths 9 and 10 can be lengthened, and the heat absorbing action of the cooling water can be efficiently exhibited.
Further, since the guide wall h has an arcuate shape that is concentric or substantially concentric with the cylinder bores of the interbore channels 9 and 10 to which the cooling water is sent, the intercooling channels 9 and 10 can flow the cooling water more smoothly. Can be sent to.

As shown in FIGS. 2 and 3, the water jacket W includes a jacket bottom 15 and has a depth (vertical width) substantially equal to the vertical length of the barrel portion 4.
As shown in FIG. 2, between the bores, a dam wall 16 that integrates the lower halves of the adjacent barrel portions 4 and 4 is formed so as to rise up from the jacket bottom 15, and A point connecting wall 17 is formed that integrates the upper portions of the barrel portions 4 and 4 that fit together with a small cross-sectional area.

As shown in FIG. 2, the damming wall 16 having a shape that is long in the left and right and short in the front and back is provided with left and right inclined side surfaces 18 and 19 and has a trapezoidal shape with an upper constriction. Alternatively, the sloped side surfaces 18 and 19 may be formed as vertical side surfaces and may be a rectangular dam wall 16 as viewed in the front-back direction. The cooling water that tries to flow into the interbore channels 9 and 10 is guided by the inclined side surfaces 18 and 19, so that in the interbore channels 9 and 10, the component of the flow flowing diagonally upward is promoted. Become. The upper surfaces of the interbore channels 9 and 10 may be formed as a bowl-shaped curved ceiling surface 20, so that in the interbore channels 9 and 10, the flow in the upper part is relatively promoted. It is configured.

Between the upper and lower sides of the damming wall 16 and the point connecting wall 17, there is provided an upper narrow trapezoidal lower rib wall 21 formed so as to project forward and backward from the barrel portion 4. On the upper side of the point connection wall 17, an upper rib wall (an example of a rib wall) 22 that is formed so as to extend forward and backward from the barrel portion 4 is provided. The lower rib wall 21 and the upper rib wall 22 regulate the path width (front-rear width) of the interbore channels 9, 10 and thus have the effect of accelerating the flow rate of the cooling water and the effect of leading it upward. The amount of protrusion of the upper rib wall 22 from the outer peripheral surface of the barrel portion 4 is preferably 0.5 to 2 mm. More preferably, it is 0.5 to 1 mm.

Further, a drill hole 3c vertically penetrating the cylinder ceiling wall 3 is formed as an inclined hole extending obliquely upward from the bottom to the left in the middle of the upper and left sides of the inter-bore channels 9, 10. The drill holes 3c allow the flow from the tops of the interbore channels 9 and 10 to the cylinder head jacket (not shown) to increase the flow velocity in the interbore channels 9 and 10 and increase the cooling area. It is configured to enhance cooling efficiency.

Thus, between the adjacent barrel portions 4 and 4 of the water jacket W, there is the dam wall 16 in the lower half, and the upper portion of the cylinder 2 has a cross-sectional area which is about half the depth of the main flow passages 7 and 8. Are formed in the inter-bore channels 9 and 10 in the state of being located at. Barrel portions 4 and 4 are integrated with each other by the damming wall 16 and the point connecting wall 17, so that the cylinder block 1 can be improved in strength and rigidity.

As shown in FIGS. 2 and 3, the lower ends of the guide walls 11 to 14 are integrally formed so as to stand upright from the jacket bottom 15. The upper ends of the first and third guide walls 11 and 13 are located in the upper and lower middle portions of the interbore passages 9 and 10, and are 2/3 to 3/4 of the vertical width (depth) of the water jacket W. The height is set to be the height. The upper ends of the second and fourth guide walls 12 and 14 are slightly lower than the first and third guide walls 11 and 13 in the upper and lower middle portions of the interbore passages 9 and 10, and the upper and lower widths (depth) of the water jacket W are increased. The height is set to be 1/2 to 2/3 of the height.

Note that the guide wall h may have the configuration shown in FIG. That is, the third guide wall 13 is formed in an arc shape along the circumferential direction of the second cylinder 2 in the front-rear direction in the up-down direction, and protrudes from the third barrel portion 4 to the intake-side main flow path 7. ing. The fourth guide wall 14 is formed in an arc shape along the circumferential direction of the rear side third cylinder 2 when viewed in the vertical direction, and is formed to project from the second barrel portion 4 to the exhaust side main flow path 8. ing. The first and second guide walls 11 and 12 are basically the same as those in the first embodiment.

According to the guide walls 11 to 14 having this configuration, the third guide wall 13 exerts a guide action so as to promote the flow of the cooling water flowing through the intake-side main flow passage 7 to the second inter-bore flow passage 10. .. Then, by the fourth guide wall 14, the cooling water flowing from the intake side to the exhaust side (from left to right) through the second inter-bore flow passage 10 is smoothly joined to the exhaust side main flow passage 8 while being guided obliquely to the right rear. Guide action is demonstrated.

That is, as shown in FIG. 5B, the guide wall h (11 to 14) allows the cooling water to flow from left to right (from the intake side to the exhaust side) in any of the inter-bore channels 9, 10. Guided to flow. It is the same as the case shown in FIG. 5A except that the flow direction in the second inter-bore channel 10 is different. Although the flow direction is different from that in the case shown in FIG. 5A, the same effect can be achieved with respect to the water cooling effect of the interbore channels 9 and 10.

In this case, as shown in FIG. 5B, the protrusion amount of the first guide wall 11 closer to the cooling water inlet 6 than the third guide wall 13 to the intake-side main flow path 7 is set to be that of the third guide wall 13. It is convenient to make it smaller than the above and to balance the inflow amounts of the cooling water into the first and second inter-bore channels 9 and 10 so as to be equal to each other. It is also effective to make the height of the third guide wall 13 from the jacket bottom 15 (see FIG. 2) higher than that of the first guide wall 11.

In the cooling structure shown in FIG. 5B, the guide walls 11(h) and 13(h) corresponding to the inter-bore channels 9 and 10 adjacent to each other in the cylinder arranging direction pass the cooling water to the inter-bore channel. 9 and 10 are formed in a state in which the leading directions are the same. Therefore, the cooling water flows to the two inter-bore channels 9 and 10 from the intake side main channel 7 to the exhaust side main channel 8, and the smooth flow in the water jacket W improves the efficiency. The cooling effect can be obtained.

The configuration of the interbore channel will be further described. As shown in FIGS. 2 and 6, the outer wall 4A of the barrel portion 4 forming the inter-bore channels 9, 10 has an upper surface for guiding the cooling water flowing through the inter-bore channels 9, 10 to the cylinder head side. The rib wall 22 is formed so as to extend in the axial direction (vertical direction) of the cylinder 2. The upper rib wall 22 is formed in a divergent shape in which the width (horizontal width) in the circumferential direction of the bore increases as it approaches the cylinder head. The upper rib wall 22 is set such that the divergence angle α of the extremely narrow left and right side surfaces 22a, 22a is 3°≦α≦7° (eg, 6°).

As described above, since the left and right side surfaces 22a of the upper rib wall 22 are overhung (inversely inclined), sand removal after casting using a sand core is promoted, and sand removal work can be performed quickly. Become. This is a preferable structure that provides an advantageous setting for the core between the bores that tends to have a complicated shape.

Further, since the divergence angle α is set to 3 to 7 degrees, the angle is too small and the effect of easy sand removal does not occur, or if the angle is too large, the upper rib wall 22 becomes large left and right and the space between the bores becomes large. There is an advantage that the flow paths 9 and 10 do not become narrower by themselves and the productivity of the flow paths 9 and 10 can be improved while securing the flow paths between the bores.

As shown in FIGS. 2 and 6, the rib wall 22 is curved so that its tip (upper end) does not reach the cylinder head side end of the interbore channels 9, 10, that is, the rib wall 22 is curved with the upper end. A space exists between the ceiling surface 20 and the ceiling surface 20. In this way, the upper end portions of the inter-bore flow passages 9 and 10 are formed into the upper wide passages 9b and 10b having a wider flow passage width than the portions below it, and are cooled to the cylinder ceiling wall 3 portion where the thermal condition is severe. It can be cooled effectively by passing a lot of water.

As shown in FIG. 6, at the upper end portions of the interbore channels 9 and 10 which are the constriction paths, the width of the interbore direction (front-rear direction) becomes narrower toward the cylinder head side (upper side). It is configured in the road portion 9a (10a). The pair of outer peripheral walls 4A, 4A forming the inter-bore flow paths 9, 10 are formed on the tapered upper wall 27 that is inclined in the direction in which the respective upper ends approach each other, and the tip of the tapered flow path section 9a is formed. The constriction angle β is set to a state of 0.5 to 3 degrees (0.5 degrees≦β≦3 degrees).

From the viewpoint of strength and rigidity, it is better not to open the water jacket W at the upper end of the cylinder block, and it is desirable that at least the adjacent cylinders be closed, but on the other hand, at the upper end of the cylinder block where the thermal conditions are the most severe. It is disadvantageous in that it is difficult to bring the cooling water close to it. Therefore, if the end portions of the inter-bore flow passages 9 and 10 on the cylinder head side are tapered passage portions 9a (10a) as in the present invention, the strength and rigidity of the upper end portion of the cylinder block 1 are secured. Even though it is a type, it becomes possible to widen the inter-bore channels 9 and 10 to the very end. As a result, a cooling structure that basically allows the closed-type cylinder block 1 to be advantageous in strength and rigidity, and expands the interbore passages 9 and 10 having severe thermal conditions to the upper side for sufficient cooling. Can be realized.

As described above, since the cylinder block 1 is formed by casting using a sand mold core, the interbore channels 9 and 10 that are narrowed paths are places where sand removal after casting is originally difficult. Is. In the present invention, since the upper end portions of the interbore channels 9 and 10 are formed in the tapered channel portions 9a and 10a where the tapered angle β is 1 to 6 degrees, sand removal after casting is performed. It has the effect of facilitating smoothing and speeding up and ensuring sand removal work.

Since the taper angle β is set to 0.5 to 3 degrees, the angle is too small to easily remove sand, or if the angle is too large, the wall thickness of the barrel portion 4 is ensured. There is an advantage that the width of the inter-flow passage is not unnecessarily increased, and the productivity can be improved without increasing the width of the inter-bore flow passages 9 and 10.

[Another embodiment]
In FIG. 6, the tapered upper wall 27 is drawn to have a certain vertical length, but it may have a structure in which it extends further downward or have a shorter vertical length.

1 Cylinder block 2 Cylinder 4 Barrel part
4A outer peripheral wall 9,10 flow path between bores 9a, 10a tapered flow path part 22 rib wall
27 Tapered upper wall W Water jacket α Converging angle β Converging angle

Claims (5)

A plurality of cylinders arranged in a cylinder block, and a water jacket formed around the plurality of cylinders,
The water jacket has an interbore channel formed between the outer peripheral walls of adjacent cylinders,
By forming the upper end portion of each of the pair of outer peripheral walls into a tapered upper wall that is inclined in a direction toward each other,
The upper end portion of the inter-bore channel is configured as a tapered channel section whose width in the inter-bore direction becomes narrower toward the cylinder head side ,
A cooling structure for a water-cooled engine in which a portion of the pair of outer peripheral walls other than the tapered upper wall is parallel to the axis of the cylinder .
The cooling structure for a water-cooled engine according to claim 1, wherein the tapered angle of the tapered channel portion is set to 0.5 to 3 degrees. A plurality of cylinders arranged in a cylinder block, and a water jacket formed around the plurality of cylinders,
The water jacket has an interbore channel formed between adjacent cylinders,
In the barrel portion forming the interbore flow path in the cylinder block, a rib wall extending from the barrel portion in a state of extending in the axial direction of the cylinder is formed so as to extend in a state of extending in the axial direction of the cylinder,
The cooling structure for a water-cooled engine, wherein the rib wall has a divergent shape whose width in the bore circumferential direction becomes wider as it approaches the cylinder head.
The cooling structure for a water-cooled engine according to claim 3, wherein a divergence angle of the rib wall is set to 3 to 7 degrees. The cooling structure for a water-cooled engine according to claim 3, wherein the rib wall is configured such that the tip thereof does not reach the end of the inter-bore flow path on the cylinder head side.

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