JPH10103053A - Engine cooling system - Google Patents

Abstract

(57) [Summary] PROBLEM TO BE SOLVED: To positively cool a knocking zone by prior cooling of intake air to improve knock resistance, and to improve cooling performance around a spark plug hole. SOLUTION: A water jacket of a cylinder head 1 is divided into a water jacket 8 on a lower side of intake air and a water jacket 9 on a spark plug hole side, and intake ports 5 and 5 are provided.
A communication path 10 having one end opened at the base of the spark plug hole 4 is provided therebetween. The water jacket of the cylinder block 2 is formed by partitioning the water jacket 11 on the intake side and the water jacket 12 on the exhaust side, and a communication path 13 is provided above the cylinder bores 3. The water pump 20 is disposed between the outlet of the water jacket 11 on the intake side of the cylinder block 2 and the inlet of the water jacket 12 on the exhaust side, the thermostat valve 21 is disposed, and the bottom bypass passage 22 and the radiator bypass passage 23 are provided. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling system for an engine, in which an intake side is pre-cooled so as to mainly cool an intake side combustion chamber wall which is a knocking zone of a gasoline engine.

[0002]

2. Description of the Related Art In a gasoline engine, the combustion chamber wall on the exhaust side has a high temperature and the flame propagation speed is high, so that knocking hardly occurs. Since knocking is likely to occur due to a low propagation speed, it has been conventionally considered to cool the knocking zone on the intake side so that knocking does not occur. In order to cool the knocking zone on the intake side, the water jacket of the cylinder head is partitioned into the intake side and the exhaust side including around the spark plug hole, and the cooling water flows from the intake side first. Such is known. JP-A-6
Japanese Patent No. 81643 discloses a cooling device for an engine that performs such intake pre-cooling, in which a water pipe is provided between cylinder bores in order to enhance a cooling effect of a wall surface between cylinder bores.
It describes that one end of the water pipe is disposed in an exhaust water jacket and the other end is disposed in an intake water jacket.

[0003]

The prior intake cooling is a promising means for actively cooling the combustion chamber wall on the intake side to improve knock resistance.
In many cases, the water jacket of the cylinder head is divided into the intake side and the exhaust side including the area around the spark plug hole, and only the cooling water flows in the direction of the cylinder rows. Too much problem with thermal reliability.

In the apparatus described in Japanese Patent Application Laid-Open No. Hei 6-81643, since the cooling water of the exhaust water jacket flows through the water pipe to the intake water jacket, the flow rate of the cooling water near the wall surface in the intake water jacket is reduced. Although it has an effect of improving the cooling performance by partially increasing the cooling performance, it does not generate a water flow that enhances the cooling performance around the plug hole in the exhaust water jacket.

[0005] Therefore, it is an object to improve knock resistance by pre-cooling the intake air and to improve cooling performance around the ignition plug hole. An object of the present invention is to solve such a problem.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a cooling device for an engine, in which the port walls of a plurality of intake ports for each cylinder of a cylinder head are connected in the direction of cylinder rows by connecting portions. A cooling water circulation passage is provided so as to circulate the cooling water from the intake port lower water jacket first, and to provide a cooling water circulation passage. A water pump is provided in the cooling water circulation passage so as to be located between the jacket and the spark plug hole side water jacket, and between the intake port of each cylinder, a plug hole root portion of the spark plug hole side water jacket and the intake port lower water. By providing a communication path that communicates with the jacket, the solution is That. At this time, the water pump is preferably provided, for example, between the outlet side of the water jacket below the intake port and the inlet side of the spark plug hole side water jacket. Further, it is preferable that the communication passage is provided at a position near the valve seat on the intake side.

[0007] According to the engine cooling device configured as described above, the knocking zone is actively cooled by the intake pre-cooling, the knock resistance is enhanced, and the pressure difference due to the interposition of the water pump causes the water to enter the communication passage. In particular, the communication passage is provided between the intake ports of the cylinder head and communicates with the root portion of the plug hole, so that a water flow is generated around the ignition plug hole in the ignition plug hole side water jacket, The area around the spark plug hole is effectively cooled.

In order to improve knock resistance, it is important to improve the cooling performance of the knocking zone also on the cylinder block side. Therefore, the outlet of the water jacket on the exhaust side of the cylinder block is connected to the inlet of the water jacket on the ignition plug side of the cylinder head so that the cylinder block also performs pre-intake cooling, and the water jacket on the intake side and the water jacket on the exhaust side. It is preferable to provide a communication passage in the upper portion between the cylinder bores of the cylinder block so as to communicate with the cylinder block.

In this case, a partition wall is provided for separating the intake-side water jacket and the exhaust-side water jacket of the cylinder block, and the outlet side of the intake-side water jacket communicates with the inlet side of the exhaust-side water jacket to circulate the cooling water. It is preferable to provide a water pump in the cooling water circulation passage.

In this case, a radiator bypass passage for bypassing the radiator is provided between the outlet side of the exhaust-side water jacket of the cylinder block and the inlet side of the intake-side water jacket, and the radiator bypass passage is provided when the engine has a predetermined low load. It is preferable to provide bypass opening / closing means so as to open the bypass passage, so that the cylinder is warmed by high-temperature cooling water at a low load when the need for cooling is low, the oil viscosity is reduced, and the sliding resistance of the piston is reduced. As a result, fuel efficiency can be improved. Further, for example, means for restricting the water flow to the radiator may be arranged between the radiator and the inlet of the water jacket downstream of the intake port of the cylinder head to restrict the water flow to the radiator side.

A bottom bypass passage for bypassing the radiator is provided between the outlet side of the exhaust-side water jacket of the cylinder head and the outlet side of the intake-side water jacket of the cylinder block, and flows to the radiator bypass passage side when cold. It is preferable to provide a means for cutting off the water flow, so that during cold start, while preventing backflow from the radiator bypass passage to the intake side,
By bypassing the radiator, the cooling water can be circulated only on the exhaust side to promote warm-up.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a system diagram of an engine cooling system, FIG. 2 is an exploded perspective view (a) and a schematic explanatory view (b) showing a flow of cooling water under a high load, and FIG. FIG. 4 is an exploded perspective view (a) and a schematic explanatory view (b) showing the flow of water, and FIG. 4 is an exploded perspective view (a) and a schematic explanatory view (b) showing the flow of cooling water in a cold state. 5 is a longitudinal sectional view of the cylinder head taken along a plane orthogonal to the cylinder row direction and viewed from the front side, FIG. 6 is a sectional view taken along line AA of FIG. 5, and FIG. Figure seen from
FIG. 8 is a plan view of the cylinder block, and FIG. 9 is BB of FIG.
FIG. 10 is a cross-sectional view taken along line CC of FIG. 7, and FIG. 11 is a cross-sectional view taken along line DD of FIG.

In FIG. 1, 1 is a cylinder head of an engine, and 2 is a cylinder block. The cylinder head 1 is mounted on the upper end of the cylinder block 2 and connected by bolts.

The cylinder head 1 is provided with a spark plug hole 4 in the center of the cylinder bore 3 of each cylinder in a plan view, and is arranged in the cylinder row direction (up and down in FIG. 1) for each cylinder with the spark plug hole 4 interposed therebetween. Direction), two intake ports 5 are provided on one side and two exhaust ports 6 are provided on the other side. Although only one cylinder is shown in FIG. 1, this engine is an in-line four-cylinder engine, and the other cylinders have the same configuration.

A space is formed inside the cylinder head 1 along the combustion chamber wall so as to surround the ignition plug hole 4, the intake port 5, and the exhaust port 6. A partition wall 7 set at the position of the wall separates an intake-side water jacket 8 and an exhaust-side water jacket 9 that extend and communicate with each other in the cylinder row direction. Also, the two intake ports 5 for each cylinder,
A communication passage 10 communicating between the root of the spark plug hole 4 of the exhaust-side water jacket 9 and the intake-side water jacket 8 is provided between them.

The cylinder block 2 has an intake-side water jacket 11 and an exhaust-side water jacket 12 which extend in communication with each other in the cylinder row direction and are formed around a cylinder bore 3 of each cylinder.
The upper ends of the water jackets 11, 12 to which the cylinder head 1 is connected are open. A communication passage 13 is provided above the cylinder block 2 between the cylinder bores 3.

The water jackets 8, 9, 1 on the cylinder head 1 side and the cylinder block 2 side are provided.
A cooling water passage 15 is provided as a cooling water circulation passage for flowing the cooling water through the cylinder head 1, between the outlet of the radiator 14 and the inlet of the water jacket 8 on the intake side of the cylinder head 1. Water passage 1 connecting between the outlet of the water jacket 8 on the side and the inlet of the water jacket 11 on the intake side of the cylinder block 2
6, a cooling water passage 1 connecting the outlet of the water jacket 11 on the intake side of the cylinder block 2 and the inlet of the water jacket 12 on the exhaust side of the cylinder block 2.
7, a cooling water passage 18 is provided to connect between the outlet of the exhaust-side water jacket 12 of the cylinder block 2 and the inlet of the exhaust-side water jacket 9 of the cylinder head 1, and the exhaust-side water jacket 9 of the cylinder head 1 is provided. A cooling water passage 19 is provided to connect between an outlet of the radiator 14 and an inlet of the radiator 14.

A water pump 20 is provided in a cooling water passage 17 connecting the outlet of the water jacket 11 on the intake side of the cylinder block 2 and the inlet of the water jacket 12 on the exhaust side of the cylinder block 2. A thermostat valve for switching the flow path is provided on the inlet side of the water pump 20 of the cooling water passage 17 connecting the outlet of the water jacket 11 on the intake side of the cylinder block 2 and the inlet of the water jacket 12 on the exhaust side of the cylinder block 2. The cooling water passage 19 connecting the outlet of the exhaust-side water jacket 9 of the cylinder head 1 and the inlet of the radiator 14 and the thermostat valve 2
A bottom bypass passage 22 is provided between the first bypass inlet and the one inlet. The thermostat valve 21 opens the bottom bypass passage 22 until the water temperature reaches a predetermined temperature (80 ° C. to 90 ° C.) to form a bypass path that does not pass through the radiator 14. When the temperature reaches 90 ° C.), the bottom bypass passage 22 is closed to form a circulation path flowing through the radiator 14.

The cooling water passage 1 connects the outlet of the water jacket 12 on the exhaust side of the cylinder block 2 and the inlet of the water jacket 9 on the exhaust side of the cylinder head 1.
8 and the water jacket 8 on the intake side of the cylinder head 1
And a cooling water passage 16 that connects between the outlet of the cylinder block 2 and the inlet of the water jacket 11 on the intake side of the cylinder block 2.
A radiator bypass passage 23 is provided, and a bypass control valve 24 that opens and closes the passage 23 is provided in the radiator bypass passage 23. A flow control valve 25 for controlling the flow rate of the cooling water flowing through the cooling water passage 15 is provided in the middle of the cooling water passage 15 connecting the outlet of the radiator 14 and the inlet of the water jacket 8 on the intake side of the cylinder head 1. Have been. These bypass control valves 24
The flow control valve 25 operates in conjunction with the accelerator. When the accelerator opening increases, the flow control valve 25 opens and the bypass control valve 24 closes, and when the accelerator opening decreases, the flow control valve 2
5 is configured such that the bypass control valve 24 is opened by closing or the opening degree is reduced.

The basic flow of the cooling water under a high load (full load) is as shown in FIGS. 2 (a) and 2 (b). At a high load, the flow control valve 25 opens and the bypass control valve closes. The thermostat valve 21 is open to the radiator circulation side. At this time, the cooling water cooled by the radiator 14 enters the intake-side water jacket 8 of the cylinder head 1 from the rear end, flows forward in the intake-side water jacket 8 in the direction of the cylinder rows, and passes through a plurality of points on the way. (Three places in the example in the figure), and each cooling water passage 16
And enters the intake-side water jacket 11 on the cylinder block 2 side. The thermostat valve 2 passes through a cooling water passage 17 formed at the front end of the cylinder block 2.
After that, the water pump 20 is entered. Then, it is pressurized by the water pump 20 and enters the exhaust-side water jacket 12 of the cylinder block 2 from the front end side, flows backward in the exhaust-side water jacket 12 in the direction of the cylinder, and exits from a plurality of points on the way. Then, the coolant enters the exhaust-side water jacket 9 of the cylinder head 1 through each cooling water passage 18. Then, it flows forward in the exhaust-side water jacket 9 of the cylinder head 1, exits from the outlet on the front end side, passes through the cooling water passage 19, and flows to the radiator 14. At high load,
In this way, a circulation path of the cooling water passing through the radiator 14 is formed, and the precedent cooling of the intake air from the cylinder head 1 side is performed.

The basic flow of the cooling water at the time of low load (partial load) and warm-up is as shown in FIGS. 3 (a) and 3 (b). When the load is low, the flow control valve 25 is closed or the opening degree is reduced, and the bypass control valve is opened. In a warm-up state where the water temperature is equal to or higher than a predetermined temperature (80 ° C. to 90 ° C.), the thermostat valve 21 is open to the radiator circulation side. At this time, the cooling water pressurized by the water pump 20 flows to the radiator bypass passage 23, bypasses the radiator 14, and repeatedly flows through the intake-side water jacket 11 and the exhaust-side water jacket 12 of the cylinder block 2. In addition, the flow control valve 2
When the cooling water passage 5 is not fully closed, a part of the cooling water flows from the exhaust water jacket 12 through the cooling water passage 18 into the exhaust water jacket 9 of the cylinder head 1 and exits from the front end outlet. It flows through 19 to the radiator 14. Then, from the radiator 14 to the cylinder head 1
, Flows forward in the cylinder row direction in the intake-side water jacket 8, flows out from a plurality of locations on the way, and passes through the cooling water passages 16, and passes through the cooling water passages 16, and the intake-side water jacket on the cylinder block 2 side. Flows to 11. In any case, when the load is low, the flow of the cooling water flowing through the radiator bypass passage 23 and circulating only on the cylinder block 2 side is the main flow.

The flow of the cooling water in a cold state (before warming up) is as shown in FIGS. 4 (a) and 4 (b). At the time of cold, both the bypass control valve 24 and the flow control valve 25 are forcibly closed. Further, the thermostat valve 21 opens to the bottom bypass passage 22 side. At this time, the cooling water pressurized by the water pump 20 flows from the exhaust-side water jacket 12 of the cylinder block 2 to the exhaust-side water jacket 9 of the cylinder head 1 through the cooling water passage 18, and the cooling water to the radiator 14 side. Flowing from the middle of the passage 19 to the bottom bypass passage 23, the thermostat valve 21
And returns to the water pump 20. In the cold state, the cooling water bypasses the radiator 14 and circulates only on the exhaust side, thereby promoting warm-up.

Next, the specific structures of the cylinder head 1 and the cylinder block 2 constituting the engine body will be described.

The cylinder head 1 is as shown in FIG. 5 and FIG. 6, in which four spark plug holes 4 are arranged in the cylinder row direction (vertical direction in FIG. 5), and are located on one side with the spark plug holes 4 interposed therebetween. As for the arranged intake ports 5, all eight ports for four cylinders are arranged in the cylinder row direction, and for the exhaust ports 6 arranged on the other side, all eight ports for four cylinders are also arranged in the cylinder row direction. Eight valve guide holes 31 are provided on the intake side corresponding to the openings of each intake port 5, and eight valve guide holes 31 are provided on the exhaust side.
The valve guide holes 32 are provided, and are arranged in the cylinder row direction.

The cylinder head 1 is provided with five pairs of through bolts, which are paired on the intake side and the exhaust side, at portions corresponding to between the cylinder bores and at both ends in the cylinder row direction for bolt connection to the cylinder block 2. Holes 33 are provided, and the through bolt holes 33 are arranged in the cylinder row direction on the intake side and the exhaust side.

A combustion chamber recess 34 is formed on the lower surface of the cylinder head 1 at a position corresponding to the cylinder bore 3 of each cylinder. The ignition plug hole 4, the intake port 5, and the exhaust port 6 open to these combustion chamber recesses 34 for each cylinder. Also, the walls (combustion chamber walls) 35 of these combustion chamber concave portions 34
A closed space is formed between the lower deck 36 and the lower deck 36. The port wall 5a of each intake port 5 is
7, a partition wall (partition wall 7a in FIG. 1) extending in the cylinder row direction is formed by the port wall 5a, the bolt boss portion 33a, and the connecting portion 37. The partition wall 7a is connected to the bolt boss portion 33a of the through bolt hole 33. The space is divided into an intake water jacket (a lower water jacket on the intake port) 8 below the intake port 5 and an exhaust water jacket (a water jacket on the ignition plug hole side) 9 which is enlarged around the spark plug hole 4. I have.

An exhaust water jacket 9 and an intake water jacket 8 are provided between the two intake ports 5 and 5 of each cylinder.
Is formed in the vicinity of the valve seat mounting portion 35a by drilling from the lower surface side of the cylinder head 1.

The cylinder head 1 is provided with a plurality of outlet holes 38 on the lower surface of the water jacket 8 on the intake side for draining cooling water toward the cylinder block 2, and on the lower surface of the water jacket 9 on the exhaust side. Inlet holes 39 and 40 for introducing cooling water from the cylinder block 2 side are provided at a plurality of locations. Although not shown in the figure, an inlet of the intake-side water jacket 8 and an outlet of the exhaust-side water jacket 9 are formed at the rear end of the cylinder head 1.

The cylinder block 2 is as shown in FIGS. 7 to 11, and a liner portion 41 constituting the cylinder bore 3 of each cylinder is connected to a siamese type by a connecting portion 42. Then, along the siamese type liner portion 41, the intake side water jacket 1 is arranged in the cylinder row direction.
1 and the exhaust-side water jacket 12 extend. At both ends in the cylinder row direction of the cylinder block 2, connecting portions 43 and 44 are provided for connecting the liner portion 41 to the block end walls 2a and 2b at a center position aligned with the connecting portion 42. As described above, the liner portion 41 is connected in a siamese shape by the connecting portion 42, and both ends are connected by the connecting portions 43, 43.
By being connected to the block end walls 2a, 2b by 44, these liner portions 41 and connecting portions 42, 43, 44
A partition wall (partition wall 7b in FIG. 1) is constituted by the water jacket 11 on the intake side and the water jacket 12 on the exhaust side.
And are completely separated. However, the communication path 13 is formed in the upper part of the connection part 42 for connecting the liner part 41 by a drill from above the exhaust side.

The cylinder block 2 has an open deck structure, and upper ends of the intake water jacket 11 and the exhaust water jacket 12 are completely open.
Further, fastening screw holes 45 are formed in the block side walls 2 c and 2 d on the intake side and the exhaust side at positions corresponding to the through bolt holes 33 of the cylinder head 1.

The water jacket 11 on the intake side of the cylinder block 2 is formed to a depth substantially up to the center of the bore height in the cylinder axis direction. A space 46 extending between the block side walls 2c in the cylinder row direction is formed.

On the other hand, the exhaust-side water jacket 12 of the cylinder block 2 is shallower in the cylinder axis direction than the intake-side water jacket 11, and
The volume is made smaller than that of 1. In addition, below the jacket bottom wall 12a of the exhaust side water jacket 12,
The space between the exhaust-side block side wall 2d is a space, and the space is formed by a cooling water circulation jacket 47 at the front end side in the cylinder row direction.
The remaining part is a blow-by chamber 48. At the front end of the cylinder block 2 in the cylinder row direction, the intake water jacket 11 and the jacket 47 are provided.
The cooling water passage 17 which communicates with the cooling water passage 17 is provided.

The jacket 4 formed on the lower front end side of the exhaust-side water jacket 12 of the cylinder block 2
The thermostat valve 21 is attached to 7 so that one inlet communicates with the hole 49 of the block side wall 2d. A water pump 20 is attached to the cylinder block 2 in front of the thermostat valve 21. The outlet of the thermostat valve 21 and the inlet of the water pump 20 are connected by a communication pipe 17a, and the outlet of the water pump 20 and the inlet 12a of the exhaust-side water jacket 12 of the cylinder block 2 are connected by a communication pipe 17b.
Is communicated by These communication pipes 17a, 17b
Is formed integrally with the main casing 20a of the water pump 20 together with the bottom bypass pipe 22a connected to the other inlet of the thermostat valve 21. The water pump 20 includes a main body casing 20a and a lid 20b.
The impeller 20c is configured to rotate inside a pump chamber formed by the impeller.

In the drawing, 51 is a blow-by passage, 52 is a main gallery of lubricating oil, 53
Is an oil passage to the cylinder head 1 side, 54 is an oil passage to the crank journal, and 55 is a crankshaft.
Reference numeral 56 denotes an inlet of the space 46 below the intake-side water jacket 11. Also, holes 57, 58 and 59 are
This is a hole in the block side wall 2d similar to the above. These holes 4
Reference numerals 9, 58, and 59 denote baseboard holes for the core during block production. The thermostat valve 21 is attached using one of them.

[0036]

According to the present invention, the knocking zone can be actively cooled by the intake pre-cooling to improve the knock resistance, and the ignition can be performed by the water flow flowing through the communication passage provided between the intake ports of the cylinder head. By generating a water flow wrapping around the plug hole, cooling performance around the ignition plug hole can be improved.

At the same time, the cooling performance of the knocking zone on the cylinder block side can be enhanced.

[Brief description of the drawings]

FIG. 1 is a system diagram of an engine cooling system according to an example of an embodiment;

FIGS. 2A and 2B are an exploded perspective view and a schematic explanatory view showing a flow of cooling water under a high load in the example of FIG.

FIGS. 3A and 3B are an exploded perspective view and a schematic explanatory view showing a flow of cooling water at a low load in the example of FIG.

FIG. 4 is an exploded perspective view (a) and a schematic explanatory view (b) showing a flow of cooling water in a cold state in the example of FIG. 1;

FIG. 5 is a longitudinal sectional view of the cylinder head of the example of FIG. 1 taken along a plane orthogonal to the cylinder row direction and viewed from the front side.

6 is a sectional view taken along line AA of FIG.

FIG. 7 is a view of the cylinder block in the example of FIG. 1 as viewed from the right side as viewed from the front.

FIG. 8 is a plan view of the cylinder block of FIG. 7;

FIG. 9 is a sectional view taken along line BB of FIG. 7;

FIG. 10 is a sectional view taken along line CC of FIG. 7;

FIG. 11 is a sectional view taken along line DD of FIG. 8;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Cylinder block 3 Cylinder bore 4 Spark plug hole 5 Intake port 6 Exhaust port 7 Partition wall 8 Intake port lower side water jacket (intake side) 9 Ignition plug hole side water jacket (exhaust side) 10 Communication passage 11 Intake side water Jacket 12 Exhaust-side water jacket 13 Communication path 14 Radiator 15, 16, 17, 18, 19 Cooling water circulation path 20 Water pump 21 Thermostat valve 22 Bottom bypass path 23 Radiator bypass path 24 Bypass control valve (bypass opening / closing means, bypass water flow cutoff means) 25) Flow control valve (radiator water flow restriction means, bypass water flow cutoff means)

Claims (9)

[Claims] An ignition plug hole is provided at a center portion of a cylinder bore of each cylinder in a plan view. A plurality of intake ports of each cylinder are provided on one side of each ignition plug hole, and an exhaust port of each cylinder is provided on the other side. A space is formed around the ignition plug hole, the intake port, and the exhaust port, and a connecting portion is provided for connecting the port wall of the intake port of each of the cylinders in the cylinder row direction. A cylinder head formed with a partition wall for partitioning the space into an intake port lower water jacket extending in the cylinder row direction and an ignition plug hole side water jacket extending in the cylinder row direction. An engine provided with a cooling water circulation passage so as to circulate cooling water first from a water jacket below an intake port. A water pump is provided in the cooling water circulation passage so as to be located between the lower water jacket and the spark plug hole side water jacket, and a plug hole of the spark plug hole side water jacket is provided between the intake ports of each cylinder. A cooling device for an engine, wherein a communication passage is provided for connecting a root portion and the water jacket below the intake port. 2. The cooling system for an engine according to claim 1, wherein the water pump is provided between an outlet side of the water jacket below the intake port and an inlet side of the water jacket on the side of the spark plug hole. 3. The cooling device for an engine according to claim 1, wherein the communication path is provided at a position adjacent to a valve seat on the intake side. 4. The cylinder head is mounted and connected to a cylinder block having an intake water jacket extending around the cylinder bore in the cylinder row direction and an exhaust water jacket extending in the cylinder row direction.
The inlet of the water jacket on the intake side of the cylinder block is connected to the outlet of the water jacket below the intake port of the cylinder head, and the outlet of the water jacket on the exhaust side is connected to the inlet of the water jacket on the ignition plug side of the cylinder head. 4. A communication path is provided in an upper portion between cylinder bores of the cylinder block so as to be connected and communicate between the intake-side water jacket and the exhaust-side water jacket.
A cooling device for the engine as described. 5. A partition wall for partitioning the intake-side water jacket and the exhaust-side water jacket of the cylinder block, and connects an outlet side of the intake-side water jacket and an inlet side of the exhaust-side water jacket. The engine cooling device according to claim 4, wherein the water pump is disposed in a cooling water circulation passage that circulates cooling water. 6. A radiator is disposed in the cooling water circulation passage, and a radiator bypass that bypasses the radiator between an outlet side of the exhaust-side water jacket of the cylinder block and an inlet side of the intake-side water jacket. 6. The engine cooling device according to claim 4, wherein a passage is provided, and bypass opening / closing means for opening the radiator bypass passage at a predetermined low load of the engine is provided. 7. The engine cooling device according to claim 6, further comprising radiator water flow restricting means for restricting a water flow flowing to the radiator when the engine is under a low load. 8. The engine cooling device according to claim 7, wherein said radiator water flow restricting means is disposed between said radiator and an inlet of a water jacket downstream of an intake port of said cylinder head. 9. A bottom bypass passage which bypasses the radiator is provided between an outlet side of the exhaust side water jacket of the cylinder head and an outlet side of the intake side water jacket of the cylinder block, and a cooling water temperature is reduced. 9. The cooling device for an engine according to claim 6, further comprising: a bypass water flow blocking unit configured to block a water flow flowing to the radiator bypass passage when the temperature is lower than a predetermined temperature.