JP2018109360A - Cooling structure for water-cooled engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling structure for a water-cooled engine that can perform sufficient inter-bore cooling without causing an increase in engine length with further structural devising and strike a balance between miniaturization of the engine length and cooling performance.SOLUTION: A cooling structure for a water-cooled engine includes: a plurality of cylinders 2 aligned in a cylinder block 1; and a water jacket W formed in the periphery of the plurality of cylinders 2. The water jacket W includes inter-bore flow passages 9, 10 formed between the adjacent cylinders 2, 2. Upper end parts of the inter-bore flow passages 9, 10 constitute tapered flow passage parts 9a, 10a in which a width in an inter-bore direction becomes narrower as proceeding on a side of a cylinder head.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a cooling structure applied to an industrial diesel engine or the like, and more specifically, 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. Concerning structure.

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

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

  The drilling holes allow cooling water to pass between the bores and improve the cooling performance. However, if the thermal load is higher, such as a high compression engine or a large displacement engine, it is desirable to enhance the cooling between the bores. . Therefore, conventionally, a means for further improving the cooling performance by using a core kelen or the like to clearly separate adjacent cylinders and provide a clear water jacket between the bores has been adopted.

  In the latter prior art, although the cooling performance can be improved, the distance between the bores is required, and as a result, there is a problem that the engine length tends to be large. The former prior art is advantageous in terms of engine length, but is inferior to the latter prior art in terms of cooling. Thus, the conventional cooling structure for a water-cooled engine has advantages and disadvantages in terms of suppressing the increase in engine length and improving the cooling performance.

JP 2007-023824 A JP 2003-193836 A

  The object of the present invention is to provide a cooling structure for a water-cooled engine that can achieve sufficient cooling between the engine length and cooling performance by allowing further cooling between the bores without causing an increase in the length of the engine by further structural improvements. Is to provide

The invention according to claim 1 is a cooling structure of 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 inter-bore passages 9, 10 formed between adjacent cylinders 2, 2.
The upper end portions of the inter-bore passages 9 and 10 are configured as tapered flow passage portions 9a and 10a that become narrower toward the cylinder head side in the direction between the bores.

  According to a second aspect of the present invention, in the cooling structure of the water-cooled engine according to the first aspect, the constriction angle β of the constricted flow path portions 9a and 10a is set to 0.5 to 3 degrees. It is characterized by.

The invention according to claim 3 is a cooling structure of 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 inter-bore passages 9, 10 formed between adjacent cylinders 2, 2.
A rib wall 22 for guiding cooling water flowing through the inter-bore channels 9 and 10 to the cylinder head side is formed in the barrel portion 4 forming the inter-bore channels 9 and 10 in the cylinder block 1. Raised in a state extending in the axial direction,
The rib wall 22 is configured to have a pre-expanded 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 of the water-cooled engine according to claim 3,
The forward expansion angle α of the rib wall 22 is set to 3 to 7 degrees.

The invention according to claim 5 is the cooling structure of the water-cooled engine according to claim 3 or 4,
The rib wall 22 is configured such that the tip of the rib wall 22 does not reach the cylinder head side end of the inter-bore channels 9 and 10.

  According to the present invention, the following effects can be obtained. That is, between the adjacent cylinders, the upper end of the cylinder block should be closed (connected) in terms of strength and rigidity, but it is difficult to bring cooling water close to the upper end of the cylinder block having the most severe thermal conditions. This is disadvantageous. Therefore, if the cylinder head side end of the flow path between the bores is tapered, the flow path between the bores is widened to the vicinity of the upper end while the closed type ensures the strength and rigidity of the upper end of the cylinder block. It becomes possible.

Therefore, while it is a closed type cylinder block that is basically advantageous in terms of strength and rigidity, it is possible to expand the flow path between bores, which has severe thermal conditions, to the cylinder head side, and supply cooling water sufficiently to the flow path between bores. become. As a result, a cooling structure for a water-cooled engine capable of achieving both a reduction in the engine length and a cooling performance is provided by further structural improvements so that sufficient cooling between the bores can be performed without causing an increase in the engine length. be able to.

Plan view of cylinder part showing cylinder block Aa line sectional view of the cylinder block shown in FIG. Bb sectional view of the cylinder block shown in FIG. Cc line sectional view of the cylinder block shown in FIG. The flow of the cooling water in a water jacket is shown, (a) is a case where it is a guide wall of a mutually reverse direction (Embodiment 1), (b) is a case where it is a guide wall of the same direction mutually (Embodiment 2). An enlarged cross-sectional view of the flow path between bores cut back and forth at the center of the left and right

  Hereinafter, an embodiment of a cooling structure for a water-cooled engine according to the present invention will be described as applied to a vertical in-line three-cylinder water-cooled diesel engine with reference to the drawings.

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

1 and 4, the intake side of the cylinder block 1 is on the left, the exhaust side is on the 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 paths that are formed outside the cylinder 2 (barrel portion 4) in the cylinder arrangement direction, and is a pair of main flow paths 7 and an exhaust side main flow path 8 and a pair of main flow paths 7. , 8 are connected to each other between adjacent cylinders 2 (barrel portion 4), and the first and second bore channels 9, 10 are connected to the main channels 7, 8 at the start and end. It has front and rear end flow paths wf, wr.

  As shown in FIGS. 1 and 4, the cylinder ceiling wall 3 to which the cylinder head (not shown) is connected to the upper surface 3A via a gasket (not shown) has a bolt insertion hole 3a, a communication hole 3b, a drill hole. A 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 passed, and are opened at a plurality of locations (14 locations) around each cylinder 2. The communication hole 3b is a relatively large passage for flowing the cooling water from the water jacket W to the water jacket of the cylinder head (cylinder head jacket: not shown), and communicates with any 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 locations at the front and rear ends of the cylinder ceiling wall 3 so as to communicate with the front and rear ends of the front end flow path wf and the rear end flow path wr of the water jacket W, respectively. In addition, between the cylinders 2 and 2 adjacent to each other on the cylinder ceiling wall 3, as an oblique hole extending from the upper left to the lower right in a state of communicating with the first inter-bore channel 9 and the second inter-bore channel 10. , Each one is formed.

  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 provided with an auxiliary device such as a thermostat (not shown) or a sensor (not shown) for measuring the coolant temperature. The mounting hole 25 for mounting may be used.

  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 from the front end flow path wf to the left and right to move backward through the intake side main flow path 7 and the exhaust side main flow path 8. And also flows in the first and second flow paths 9, 10 along the way. Then, the cooling water flows upward while flowing backward through the water jacket W, and flows into the cylinder head jacket (not shown) through the plurality of communication holes 3b and the plurality of drill holes 3c. It flows toward the cooling water outlet (not shown).

  As shown in FIG. 4 and FIG. 5A, guide walls h (11 to 14) capable of guiding cooling water flowing through the main flow paths 7 and 8 to the inter-bore flow paths 9 and 10 in the cylinder block 1. Are formed in four places. Specifically, the first guide wall 11 projecting from the front portion of the second barrel portion 4 between the front and rear to the intake-side main flow channel 7 and the first guide wall 11 projecting from the rear portion of the front first barrel portion 4 to the exhaust-side main flow channel 8. Two guide walls 12, a third guide wall 13 protruding from the rear side portion of the second barrel portion 4 in the middle of the front and rear to the intake side main flow channel 7, and a front side portion of the rear third barrel portion 4 to the exhaust side main flow channel 8. Each of the protruding fourth guide walls 14 constitutes a guide wall h.

  The cooling water flowing from the front to the rear in the intake-side main flow path 7 near the first cylinder 2 by 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. The guide action leading to the first inter-bore channel 9 toward the right is exhibited. Due to the second guide wall 12 having an arc shape along the circumferential direction of the second cylinder 2 in the middle of the front and rear as viewed in the vertical direction, it flows from the left to the right (from the intake side to the exhaust side) in the first bore passage 9. A guide action for joining the cooling water to the exhaust-side main flow path 8 while guiding the cooling water obliquely rearward to the right is exhibited.

  By the fourth guide wall 14 having an arc 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. The guide action leading to the second inter-bore channel 10 is exhibited. The third guide wall 13 having an arc shape along the circumferential direction of the rear third cylinder 2 when viewed in the vertical direction flows from right to left (from the exhaust side to the intake side) in the second bore channel 10. A guide action for merging the cooling water into the intake-side main flow path 7 while guiding it to the left obliquely rearward is exhibited.

  As described above, the first guide wall 11 and the third guide wall 13 corresponding to the inter-bore channels 9 and 10 adjacent in the cylinder arrangement direction are opposite to each other in the direction in which the cooling water is guided to the inter-bore channels 9 and 10. It is formed in a state that becomes a direction. Then, to the second guide wall 12 for restricting the cooling water flowing through the exhaust-side main flow path 8 from entering the first inter-bore flow path 9 and to the second inter-bore flow path 10 of the cooling water flowing through the exhaust-side main flow path 8. The fourth guide wall 14 that promotes the entry of is also formed in a state in which it acts as a guide in opposite directions.

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

  That is, in the first inter-bore channel 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 width between the bores is widened. It is possible to obtain an efficient water cooling effect through a sufficient flow rate without any problem. Similarly, in the second inter-bore channel 10, 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. 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 passages 9 and 10 adjacent in the cylinder arrangement direction are The directions in which the cooling water is guided to the inter-bore channels 9 and 10 are formed in opposite directions. Accordingly, the moving path of the cooling water flowing through the two inter-bore channels 9 and 10 can be lengthened, and the endothermic action by the cooling water can be efficiently exhibited.
Further, since the guide wall h has an arc shape concentrically or substantially concentric with the cylinder bore of the inter-bore passages 9 and 10 to which the cooling water is sent, the inter-bore flow passages 9 and 10 are more smoothly supplied. 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) comparable to the vertical length of the barrel portion 4.
As shown in FIG. 2, between the bores, a damming wall 16 that integrates the lower half portions of the adjacent barrel portions 4 and 4 is formed so as to race up from the jacket bottom 15, and A point connection wall 17 is formed to integrate the upper portions of the matching barrel portions 4 and 4 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 rear is formed into a trapezoidal shape having upper and lower inclined side surfaces 18 and 19. The inclined side surfaces 18 and 19 may be formed as vertical side surfaces, and may be a rectangular damming wall 16 in the front-rear direction view. The cooling water that is about to flow into the inter-bore channels 9 and 10 is guided by the inclined side surfaces 18 and 19 so that the components of the flow that flows obliquely upward in the horizontal direction are promoted in the inter-bore channels 9 and 10. Become. In addition, the upper surfaces of the inter-bore channels 9 and 10 may be formed in a bowl-shaped curved ceiling surface 20, so that the flow between the upper and lower bores 9 and 10 is relatively promoted. It is configured.

  Between the upper and lower sides of the damming wall 16 and the point connection wall 17, an upper trapezoid trapezoidal lower rib wall 21 is formed so as to project from the barrel portion 4 in the front-rear direction. On the upper side of the point connection wall 17, an upper rib wall (an example of a rib wall) 22 is provided so as to project from the barrel portion 4 in the front-rear direction. The lower rib wall 21 and the upper rib wall 22 regulate the path width (front-rear width) of the inter-bore channels 9 and 10, and can achieve the effect of increasing the flow rate of the cooling water and the effect of guiding it upward. The amount of protrusion from the outer peripheral surface of the barrel portion 4 of the upper rib wall 22 is preferably 0.5 to 2 mm. More desirably, the thickness is 0.5 to 1 mm.

  Further, a drill hole 3c penetrating vertically through the cylinder ceiling wall 3 in the upper left and right middle of the inter-bore channels 9, 10 is formed as an inclined hole that extends obliquely from the bottom to the left. This drill hole 3c allows flow from the top of the inter-bore channels 9, 10 to the cylinder head jacket (not shown), increasing the flow velocity in the inter-bore channels 9, 10 and increasing the cooling area. The cooling efficiency is increased.

  Thus, between the adjacent barrel portions 4 and 4 in the water jacket W, there is a damming wall 16 in the lower half, and the upper portion of the cylinder 2 has a cross-sectional area that is about half the depth of the main flow paths 7 and 8. Are formed in the inter-bore channels 9 and 10 in the state of The damming wall 16 and the point connecting wall 17 integrate the barrel portions 4 and 4 so that the cylinder block 1 can contribute to improvement 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 up from the jacket bottom 15. The upper ends of the first and third guide walls 11 and 13 are positioned in the upper and lower middles of the inter-bore channels 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 high. 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 middles of the inter-bore channels 9 and 10, and the vertical width (depth) of the water jacket W is increased. The height is set to be 1/2 to 2/3.

  In addition, regarding the guide wall h, the structure shown by FIG.5 (b) may be sufficient. That is, the third guide wall 13 has an arc shape along the circumferential direction of the second cylinder 2 between the front and rear in the vertical direction, and is formed so as to protrude from the third barrel portion 4 to the intake side main flow path 7. ing. The fourth guide wall 14 has an arc shape along the circumferential direction of the rear third cylinder 2 when viewed in the vertical direction, and is formed so as to protrude 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 exhibits a guide action so as to promote the flow of the cooling water flowing through the intake-side main flow path 7 to the second inter-bore flow path 10. . Then, the fourth guide wall 14 smoothly joins the coolant flowing in the second inter-bore channel 10 from the intake side to the exhaust side (from left to right) into the exhaust side main channel 8 while guiding the coolant diagonally rearward to the right. Guide action is demonstrated.

  That is, as shown in FIG. 5B, the coolant flows from the left to the right (from the intake side to the exhaust side) in any of the flow paths 9 and 10 between the bores by the guide walls h (11 to 14). Guided to flow. Except for the difference in the flow direction in the second inter-bore channel 10, it is the same as the case shown in FIG. Although the flow direction is different from the case shown in FIG. 5A, the same effect can be achieved with respect to the water cooling effect of the inter-bore channels 9 and 10.

  In this case, as shown in FIG. 5 (b), the amount of protrusion 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 that of the third guide wall 13. It is advantageous that the cooling water is balanced so that the inflow amounts of cooling water into the first and second bore passages 9, 10 are equal to each other. In addition, a means for making 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 is also effective.

  In the cooling structure shown in FIG. 5B, the guide walls 11 (h) and 13 (h) corresponding to the inter-bore passages 9 and 10 adjacent in the cylinder arrangement direction pass cooling water between the bores. 9 and 10 are formed in the same direction. Therefore, the flow of the cooling water to the two inter-bore flow paths 9 and 10 both flows from the intake-side main flow path 7 to the exhaust-side main flow path 8, and is more efficient due to the smooth flow in the water jacket W. A cooling effect can be obtained.

  The configuration of the inter-bore channel will be further described. As shown in FIG. 2 and FIG. 6, the upper part for guiding the cooling water flowing through the inter-bore channels 9 and 10 to the outer peripheral wall 4A of the barrel portion 4 forming the inter-bore channels 9 and 10 to the cylinder head side. The rib wall 22 is raised so as to extend in the axial direction (vertical direction) of the cylinder 2. The upper rib wall 22 is configured to have a pre-expanded shape whose width in the bore circumferential direction (left-right width) becomes wider as it approaches the cylinder head. The upper rib wall 22 is set so that the forward expansion angle α of the left and right side surfaces 22a, 22a having an extremely narrow width is 3 degrees ≦ α ≦ 7 degrees (example: 6 degrees).

As described above, since the left and right side surfaces 22a of the upper rib wall 22 are overhanged (reverse gradient), sand removal after casting using a sand mold core is promoted, and sand removal work can be performed quickly. Become. This is a preferable structure that is advantageous for the core between the bores that are likely to have a complicated shape.

  And since the pre-expansion angle α is set to 3 to 7 degrees, there is no effect that the angle is too small and easy to remove sand, or if the angle is too large, the upper rib wall 22 is enlarged to the left and right, and between the bores There is an advantage that productivity can be improved while securing the flow path between the bores 9 and 10 without the flow paths 9 and 10 becoming narrower.

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

  As shown in FIG. 6, the upper end portions of the inter-bore channels 9 and 10 which are narrowing paths are constricted flows whose width in the inter-bore direction (front-rear direction) becomes narrower toward the cylinder head side (upper side). It is comprised by the road part 9a (10a). The pair of outer peripheral walls 4A and 4A constituting the inter-bore channels 9 and 10 are formed in a tapered upper wall 27 that is inclined in a direction in which the respective upper ends approach each other, and the tip of the tapered channel portion 9a is formed. The constriction angle β is set to be 0.5 to 3 degrees (0.5 degrees ≦ β ≦ 3 degrees).

  The upper end of the cylinder block is better not to open the water jacket W from the point of strength and rigidity, and it is desirable that at least the adjacent cylinders are closed, but on the other hand, it is the upper end of the cylinder block with the most severe thermal conditions. This is disadvantageous in that it is difficult to approach the cooling water. Therefore, as in the present invention, if the cylinder head side ends of the inter-bore passages 9 and 10 are tapered to form a passage portion 9a (10a), the closing and securing the strength and rigidity of the upper end portion of the cylinder block 1 are ensured. Although it is a type, it becomes possible to widen the flow paths 9 and 10 between the bores just to the upper end. As a result, a closed type cylinder block 1 that is basically advantageous in terms of strength and rigidity, but has a cooling structure that can sufficiently cool the bore passages 9 and 10 having severe thermal conditions upward. Can be realized.

  As described above, since the cylinder block 1 is produced by casting using a sand mold core, the bore-to-bore passages 9 and 10 which are narrowing paths are inherently difficult to remove sand after casting. It is. In the present invention, the upper end portions of the inter-bore channels 9 and 10 are formed in the tapered channel portions 9a and 10a having a tapered angle β of 1 to 6 degrees, so that sand removal after casting is performed. It is smooth and has the effect of speeding up and ensuring the sand removal work.

  Since the taper angle β is set to 0.5 to 3 degrees, there is no effect that it is easy to remove sand because the angle is too small. There is an advantage that the width of the inter-flow path is not unnecessarily increased, and the productivity can be improved without causing an increase in the width of the inter-bore flow paths 9 and 10.

[Another Example]
In FIG. 6, the tapered upper wall 27 is depicted as having a certain vertical length, but it may be a structure extending further downward or a shorter vertical length.

1 Cylinder block 2 Cylinder 4 Barrel part 9, 10 Flow path between bores 9a, 10a Constricted flow path part 22 Rib wall W Water jacket α Widening 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 a flow path between bores formed between adjacent cylinders,
The cooling structure of the water-cooled engine, wherein the upper end portion of the inter-bore flow path is configured as a tapered flow path portion that becomes narrower as the width in the bore-to-bore direction goes to the cylinder head side.   The cooling structure for a water-cooled engine according to claim 1, wherein a tapered angle of the tapered flow path 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 a flow path between bores formed between adjacent cylinders,
A rib wall for guiding cooling water flowing through the inter-bore channel to the cylinder head side is raised in the barrel portion forming the inter-bore channel in the cylinder block so as to extend in the axial direction of the cylinder. ,
The cooling structure of the water-cooled engine, wherein the rib wall is configured to have a flared shape that becomes wider as the bore circumferential direction approaches the cylinder head.   The cooling structure for a water-cooled engine according to claim 3, wherein an angle of forward expansion of the rib wall is set to 3 to 7 degrees.   The cooling structure for a water-cooled engine according to claim 3 or 4, wherein the rib wall is configured such that a tip thereof does not reach a cylinder head side end of the inter-bore channel.

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