JP3358916B2 - Engine cooling system - Google Patents

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 having a relief valve for controlling the amount of cooling water supplied to a water jacket.

[0002]

2. Description of the Related Art A supply side and a discharge side of a cooling water passage are communicated via a relief valve, and when the supply pressure of the cooling water increases, the relief valve is opened to partly cool the cooling water. One that is discharged without being supplied to the present inventors has been proposed by the present applicant (see Japanese Patent Application No. 6-236638).

[0003] In the above-mentioned prior art, a cooling water distribution chamber to which cooling water is supplied from a cooling water supply passage is provided on a side surface of a cylinder block. The cylinder block and the cooling water distribution chamber are provided through a plurality of through holes. Cooling water is supplied to the water jacket of the cylinder head. The relief valve is provided in a bypass passage connecting an intermediate portion of the cooling water distribution chamber and the cooling water discharge passage.

[0004]

By the way, the above-mentioned conventional one is one of a plurality of through holes provided in the cooling water distribution chamber.
One or some are located upstream near the cooling water supply passage, and the other one or some are located downstream far away from the cooling water supply passage, so that when the relief valve opens, The amount of cooling water supplied to the cylinder block and the water jacket of the cylinder head from the through hole on the upstream side of the connection with the bypass passage hardly decreases, while the amount of cooling water from the through hole on the downstream side of the connection with the bypass passage decreases. The amount of cooling water supplied to the jacket is greatly reduced, and the cooling effect of the cylinder block and the cylinder head may be partially uneven.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in an engine having a relief valve for bypassing cooling water, even when the relief valve is opened, the cooling water is uniformly supplied to the water jacket. With the goal.

[0006]

To achieve the above object, the present invention provides a first water jacket provided on a cylinder block, a second water jacket provided on a cylinder head, a first water jacket and a second water jacket. A cooling water distribution chamber that distributes cooling water to the water jacket through a plurality of through holes, a cooling water supply passage that supplies cooling water to the cooling water distribution chamber, and a first water jacket and a second water jacket. The cooling water discharge passage where the cooling water joins, a bypass passage that connects the cooling water supply passage and the cooling water discharge passage, and a relief valve that opens and closes the bypass passage are provided.

[0007]

According to the above construction, when the pressure of the cooling water in the cooling water supply passage exceeds a predetermined value, the relief valve provided in the bypass passage is opened, and the cooling water is discharged from the cooling water supply passage through the water jacket. Part of the cooling water flowing back to the passage is discharged directly to the cooling water discharge passage via the bypass passage. Since the bypass passage is connected to the cooling water supply passage upstream of the cooling water distribution chamber, even if the relief valve is opened, the cooling water is distributed to the first water jacket and the second water jacket from the plurality of through holes of the cooling water distribution chamber. The amount of cooling water to be supplied does not become uneven.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 9 show an embodiment of the present invention. FIG. 1 is an overall side view of an outboard motor, FIG. 2 is a left side view of an engine, and FIG. 3 is an enlarged view of a main part of FIG. 2, FIG. 4 is an enlarged sectional view taken along line 4-4 of FIG. 2, FIG. 5 is an enlarged sectional view taken along line 5-5 of FIG. 2, FIG. 6 is an enlarged sectional view taken along line 6-6 of FIG. 7 is an enlarged sectional view taken along line 7-7, FIG. 8 is an enlarged sectional view taken along line 8-8 in FIG. 2, and FIG. 9 is a schematic view showing a cooling water flow path.

As shown in FIG. 1, an outboard motor O includes a mounting case 2 coupled to an upper portion of an extension case 1.
The in-line 4-cylinder 4-cycle engine E is supported on the upper surface of the mount case 2. An undercase 3 having an open upper surface is coupled to the mount case 2, and an engine cover 4 is detachably mounted on an upper portion of the undercase 3. An under cover 5 is mounted between the lower edge of the under case 3 and the upper edge of the extension case 1 so as to cover the outside of the mount case 2.

The engine E includes a cylinder block 6, a crankcase 7, a cylinder head 8, a head cover 9, a lower belt cover 10, and an upper belt cover 11. The cylinder block 6 and the crankcase 7 are mounted on the upper surface of the mount case 2. Supported.

A piston 13 is slidably fitted to each of the four cylinders 12 formed in the cylinder block 6, and each of the pistons 13 is connected to the connecting rod 1.
4 are connected to a crankshaft 15 arranged in the vertical direction.

The flywheel 1 is provided at the lower end of the crankshaft 15.
The drive shaft 17 connected with the extension case 6 extends downward inside the extension case 1, and the lower end thereof is connected to the gear case 18.
Is connected to a propeller shaft 21 having a propeller 20 at the rear end via a shift gear mechanism 19 provided inside the. A lower end of a shift rod 22 is connected to a front portion of the shift gear mechanism 19 to switch the rotation direction of the propeller shaft 21.

Two cooling water inlets 29 opening into the water
A cooling water pump 31 provided on the drive shaft 17 is interposed at an intermediate portion of a cooling water supply pipe 30 extending upward from a and 29b and connected to the lower surface of the mount case 2. Incidentally, one of the two cooling water inlets 29a and 29b can be omitted.

A swivel shaft 25 is fixed between an upper mount 23 provided on the mount case 2 and a lower mount 24 provided on the extension case 1, and a swivel case 26 rotatably supporting the swivel shaft 25.
Is supported by a stern bracket 27 attached to the stern S via a tilt shaft 28 so as to be vertically swingable.

Next, a cooling system of the engine E will be described with reference to FIGS.

[0017] to form an exhaust passage 46 to be described later to the convex portion 6 ₁ provided so as to away from the cylinder 12 ... to the left side surface of the cylinder block 6 of the engine E, further cooling water passage cover 34 to the protrusion ₆₁ By fixing with a plurality of bolts 35, a cooling water distribution chamber 32 and a cooling water discharge passage 33 to be described later are formed. Reference numeral 6 ₂ in FIG. 5, the cylinder block adjacent to the first water jacket 52 downstream of the cooling water distribution chamber 32 to be described later and an exhaust passage 46 6
The wall.

A thermo valve cover 36 is fixed to the upper end of the cooling water passage cover 34 with two bolts 37, 37, and a relief valve housing 38 and a relief valve The cover 42 is fixed with three bolts 39.
6 and a large number of radiation fins 4 between the relief valve cover 42.
A regulator rectifier 40 having O ₁ ... Is fixed with two bolts 41.

As is apparent from FIG. 2, the three bolts 39 for fixing the relief valve cover 42 are located above the upper end of the under case 3, and the two bolts 39 for fixing the thermo valve cover 36. Since the bolts 37 are located further upward, maintenance without the relief valve cover 42 and the thermo-valve cover 36 can be easily performed.

FIG. 3 shows the condition of removing the cooling water passage cover 34 from the cylinder block 6, the inside of the convex portion 6 ₁ constituting the parting plane, the cooling water distribution chamber extending in the vertical direction 32 And the cooling water discharge passage 33 is formed in parallel. An exhaust passage 46 connected to the downstream side of the four exhaust ports 45 formed in the cylinder head 8 is provided.
It is formed in the convex portion 6 ₁ of the cylinder block 6 so as to be parallel to the cooling water distribution chamber 32 and the cooling water discharge passage 33.

As is apparent from FIG. 4, the mounting case 2 connected to the lower surface of the cylinder block 6 includes the cooling water distribution chamber 32, the cooling water discharge passage 33, and the exhaust passage 46.
, A cooling water supply passage 47, a cooling water discharge passage 48, and an exhaust passage 49 penetrate vertically. Therefore, the cooling water pumped by the cooling water pump 31 is supplied to the cooling water supply passage 47 of the mount case 2 to which the upper end of the cooling water supply pipe 30 is connected.
Is supplied to the lower end of the cooling water distribution chamber 32 of the cylinder block 6. On the other hand, the cooling water from the cooling water discharge passage 33 of the cylinder block 6 passes through the cooling water discharge passage 48 of the mount case 2 and further punches the gasket 50 (see FIG. 2) sandwiched between the mount case 2 and the extension case 1. Extension case 1 through the hole
Is discharged into the internal space of

As is clear from FIGS. 3 and 5, the cooling water distribution chamber 32 of the cylinder block 6 has two through holes 53 vertically arranged in a first water jacket 52 formed on the outer periphery of the cylinders 12. _1, 53 communicates via a _2, thus cooling water fed from the cooling water distribution chamber 32 to the first water jacket 52. Hole 53 ₁ of the lower close to the cooling water supply passage 47 of the mount case 2, through hole 53 ₂ of the upper is far from the cooling water supply passage 47 of the mount case 2. The cooling water distribution chamber 32 and the first water jacket 52 are arranged so as to surround the three surfaces of the exhaust passage 46, and effective cooling near the exhaust passage 46 where the temperature becomes high can be achieved.

As is apparent from FIG.
A first water jacket 52 formed on the outer periphery of the cylinder block 6 extends to the upper end of the cylinder block 6, and a thermo valve 54 covered by the cooling water passage cover 34 and the thermo valve cover 36 is provided therein. The thermo valve 54 includes a valve spring 55
And a valve body 57 urged in a direction to be seated on the valve seat 56. The second water jacket 58 formed on the cylinder head 8 joins a junction 51 (see FIG. 9) provided on the first water jacket 52 upstream of the thermo valve 54.

As is apparent from FIGS. 3 and 6, the second water jacket 58 formed on the cylinder head 8 is
The cooling water distribution chamber 32 formed in the cylinder block 6 communicates through a plurality of (five on the packing surface) through holes 59 which are vertically arranged side by side and open on the packing surface. The cooling water is supplied from the cooling water distribution chamber 32 to the second water jacket 58. The cooling water distribution chamber 32 and the second water jacket 58 are arranged so as to surround three surfaces of the exhaust passage 46, and effective cooling near the exhaust passage 46 where the temperature becomes high can be achieved.

As is clear from FIGS. 6 and 7, the rear chamber 60 formed inside the cooling water passage cover 34 and the front chamber 61 formed inside the relief valve housing 38 are formed by the partition wall 3.
8 _{1 is} defined. A relief valve 62 for bypassing the cooling water from the front chamber 61 to rear chamber 60 includes a valve seat 63 provided in the partition wall 38 _1, a valve body 64 that can be seated on the valve seat 63,
A valve spring 65 for urging the valve body 64 toward the valve seat 63. The partition wall 38 _1, a front chamber 61 and the small diameter of the drainage holes mutual communicating to the lowest and most tilt axis 28 side to a position near the rear chamber 60 38 ₂ is bored.

As shown in FIGS. 2 and 3, the mount case 2 is provided with a joint 66 communicating with the cooling water supply passage 47, and the joint 66 and the front chamber 61 of the relief valve 62 are connected to a hose 67. Connected by A water test tube 68 is connected to the joint 66, and the water test tube 68 is connected to a water test outlet 69 (see FIG. 4) provided on the right side surface of the undercase 3. The hose 67, the front chamber 61 and the rear chamber 60 form a bypass passage connecting the cooling water supply passage 47 and the cooling water discharge passage 33.

As shown in FIGS. 2 and 7, a drain passage 70 extending downward from the rear chamber 60 of the relief valve 62 is formed in the cooling water passage cover 34, and the lower end of the drain passage 70 has a through hole. It communicates with the cooling water discharge passage 33 through the hole 71.

Next, the operation of the embodiment of the present invention having the above configuration will be described mainly with reference to FIG.

At a low temperature immediately after the start of the engine E, the thermo valve 54 closes, and the cooling water is discharged from the first water jacket 52 of the cylinder block 6 and the second water jacket 58 of the cylinder head 8 (see FIG. 6). Passage 3
3 and prevents the engine E from warming up. At this time, when the cooling water pressure in the cooling water supply passage 47 becomes high due to the closing of the thermo valve 54, the relief valve 62
Is opened, the cooling water in the cooling water supply passage 47 is supplied to the joint 66,
The hose 67, the front chamber 61, and the clearance between the valve seat 63 of the relief valve 62 and the valve body 64 reach the rear chamber 60, from which a part of the cooling water is directly discharged to the cooling water discharge passage 33, and the cooling water is discharged. Is discharged to the cooling water discharge passage 33 through the drain passage 70 and the through hole 71.

When the warm-up is completed, the temperature of the cooling water rises and the thermo valve 54 automatically opens. As a result, when the pressure of the cooling water in the cooling water supply passage 47 decreases, the relief valve 62 closes. Thereby, the cooling water pumped by the cooling water pump 31 is supplied from the cooling water supply passage 47 to the cylinder block 6.
Flows into the cooling water distribution chamber 32 of the cylinder block 6 through _two through holes 53 ₁ and 53 ₂ arranged vertically therefrom.
Into the first water jacket 52 of
The fluid flows into the second water jacket 58 of the cylinder head 8 through a plurality of vertically arranged through holes 59. The cooling water that has cooled the second water jacket 58 merges with the cooling water that has cooled the first water jacket 52 through the through hole 51, and from there, the thermo valve 54, the cooling water discharge passage 33 of the cylinder block 6, and the mounting case 2. Is discharged into the extension case 1 through the cooling water discharge passage 48.

When the cooling water pump 31 is operating and pumping the cooling water, a part of the cooling water in the cooling water supply passage 47 passes through the joint 66 and the water detecting tube 68 and the water discharging outlet 69. , The operating state of the cooling water pump 31 can be confirmed based on the state of discharging the cooling water.

When the cooling water pressure in the cooling water supply passage 47 becomes high during the high-speed operation of the engine E, both the thermo valve 54 and the relief valve 62 are opened. When the thermo valve 54 is in a half-open state during the warm-up operation of the engine E, the pressure of the cooling water in the cooling water supply passage 47 becomes high and the relief valve 62 is also opened. When the thermo valve 54 and the relief valve 62 are both opened in this way, as shown by a chain line in FIG. 9, if the intermediate portion of the cooling water distribution chamber 32 and the relief valve 62 are connected by the bypass passage 67 '. Assuming (see the chain line in FIG. 9), while the entire amount of the cooling water flows through the lower half of the cooling water distribution chamber 32 located on the side of the cooling water supply passage 47, the connection branch with the bypass passage 67 '. In the upper half part of the cooling water distribution chamber 32 located downstream of the part, the flow of the cooling water decreases because the cooling water bypassing the relief valve 62 does not flow. for that reason,
The amount of cooling water flowing through the lower half of the cooling water distribution chamber 32 is large,
The amount of cooling water flowing in the upper half is reduced, and the cooling water distribution chamber 3
The flow rate of the cooling water in 2 becomes partially unbalanced.

As a result, two through holes 53 ₁ , 53 ₂ connected to the first water jacket 52 of the cylinder block 6.
Of the cooling water passing through the second water jacket 58 of the cylinder head 8 (5 on the packing surface).
Becomes both unbalanced and the amount of cooling water which passes through the holes 59 ... of the number), uniform cooling of the cylinder block 6 and the cylinder head 8 is difficult, see the wall 6 ₂ (FIG. 5 in particular in contact with the exhaust passage 46 ) Is difficult to cool.

According to the present embodiment, however, the hose 67 connected to the relief valve 62 is branched from the cooling water supply passage 47 on the upstream side of the cooling water distribution chamber 32, so that the cooling is performed even when the relief valve 62 is opened. The amount of cooling water flowing in the lower half of the cooling water distribution chamber 32 and the amount of cooling water flowing in the upper half thereof do not become uneven only by reducing the amount of cooling water flowing through the water distribution chamber 32 as a whole. The cylinder block 6 and the cylinder head 8 can be cooled uniformly.

When the thermo valve 54 is closed, the first
Water jacket 52 and second water jacket 5
Since the cooling water held in the cooling water 8 is not discharged from the relief valve 62, the temperature of the cooling water in the first water jacket 52 and the second water jacket 58 is quickly raised to complete the warm-up in a short time. Can be done.

As shown in FIG. 6, of the cooling water discharge passage 33 and the water drain passage 70 connected to the rear chamber 60 of the relief valve 62, the water drain passage 70 is the lowest position of the rear chamber 60 and the tilt shaft. The opening of the drain passage 70 has a shape such that the rear chamber 60 is maintained at the lowest position of the rear chamber 60 even when the outboard motor O is slightly tilted up. Is set. Therefore, as shown in FIG. 7, the water remaining in the rear chamber 60 of the relief valve 62 is discharged through the drain passage 70, the through hole 71, the cooling water discharge passage 33, and the cooling water discharge passage 48.

The water remaining in the front chamber 61 of the relief valve 62 is discharged through the hose 67, the joint 66, the cooling water supply passage 47, the cooling water supply pipe 30, and the cooling water pump 31. When the machine O is tilted up, some water may remain in the lower part of the front chamber 61. Thus even if the residual water at the bottom of the front chamber 61 when tilted up the outboard motor O, the aqueous flows from the drain hole 38 ₂ formed in the partition wall 38 ₁ in the rear chamber 60, drainage therefrom It is discharged through a passage 70.

Next, a second embodiment of the present invention will be described with reference to FIGS.

In the first embodiment described above, the relief valve 62 is provided on the cylinder block 6, but in the second embodiment, the relief valve 62 having the same structure is provided on the mount case 2. That is, the exhaust passage 46 is provided in the mount case 2.
Cooling water supply passage 47 and cooling water discharge passage 4
8 extends vertically, and the relief valve 62 directly bypasses the cooling water from the cooling water supply passage 47 to the cooling water discharge passage 48. Compared with the first embodiment, the cooling water discharge passage 48 of the second embodiment is closer to the tilt shaft 28 side. A relief valve housing 38 and a relief valve cover 42 are fixed to the left side surface of the mount case 2 with three bolts 39... A front chamber 61 provided in the relief valve housing 38 and a rear chamber provided in the mount case 2. 60 communicates via the relief valve 62.

The front chamber 61 communicates with the cooling water supply passage 47 through a through hole 72 forming a part of a bypass passage, and the rear chamber 60 communicates with a through hole 73 forming a part of a bypass passage.
Through the cooling water discharge passage 48. As described above, since the cooling water discharge passage 48 is located at a position near the tilt shaft 28, the through hole 72 connecting the front chamber 61 and the cooling water supply passage 47 is located closer to the anti-tilt shaft 28 than the cooling water discharge passage 48. (Right side of FIG. 11). Further, the front chamber 61 and rear chamber 60 communicates through a small diameter drain hole 38 _2, the drain hole 70 opening into the interior of the extension case 1 to the rear chamber 60 through the mount case 2 downward Is provided. The drain holes 38 ₂ , 70 are formed in the front chamber 61 and the rear chamber 60 on the side closest to the tilt shaft 28 (the left side in FIG. 11) in consideration of draining when the outboard motor O is tilted up. I have. Most or all of the through holes 72 and 73 and the drain holes 38 ₂ and 70 can be formed by molding, so that the number of manufacturing steps can be reduced.

6 and 11, the cooling water discharge passage 48 of the second embodiment passes through a position closer to the relief valve 62 than the cooling water discharge passage 33 of the first embodiment. Therefore, the volume of the rear chamber 60 can be reduced. According to the second embodiment, the hose 6 of the first embodiment is used.
7 becomes unnecessary, and instead, it is only necessary to form the through-hole 72 for communicating the cooling water supply passage 47 and the front chamber 61, so that the number of parts can be reduced and the structure can be simplified.

Next, a third embodiment of the present invention will be described with reference to FIG.

In the third embodiment, the relief valve 62 is provided on the mount case 2 as in the second embodiment, but the relief valve is located on the rear surface of the mount case 2 instead of the left side surface. The front chamber 61 has a through-hole 72 which forms a part of a bypass passage in the cooling water supply passage 47 of the mount case 2 as in the second embodiment, and the hose 67 of the first embodiment is omitted. The rear chamber 60 does not communicate with the cooling water discharge passage 48, but penetrates vertically through the mount case 2 and communicates with a through hole 73 which forms a part of a bypass passage. Further, a rear chamber 60 is formed closer to the tilt shaft 28 than the front chamber 61 (the left side in FIG. 12).
Since the through hole 73 is formed on the 8 side, drainage of the cooling water in a state where the outboard motor O is tilted up is performed more reliably.

Next, a fourth embodiment of the present invention will be described with reference to FIG.

As is apparent from a comparison between FIG. 3 of the first embodiment and FIG. 13 of the fourth embodiment, in the fourth embodiment, the cooling water discharge passage 33 is located in front of the cooling water distribution chamber 32 (tilt shaft 2).
8 side). That is, in the first embodiment and the fourth embodiment, and the positional relationship of the front and rear of the cylinder block cooling water discharge passage 33 formed on the protrusion ₆₁ of the 6 and the cooling water distribution chamber 32 is reversed, they The cooling water discharge passage 33 and the cooling water distribution chamber 32 form a cooling water passage cover 34 (not shown).
Covered by Due to the positional relationship between the cooling water discharge passage 33 and the cooling water distribution chamber 32, the relief valve 62 can be provided in a layout similar to that of the second embodiment shown in FIG.

[0046] That is, to form a rear chamber 60 communicating with the convex portion ₆₁ of the cylinder block 6 to the cooling water discharge passage 33 directly to the cooling water passage cover 34 to be coupled to the protrusion ₆₁ prechamber 6
Form one. The front chamber 61 is covered with a relief valve cover 42 fixed to the cooling water passage cover 34 with bolts 39. Then, the cooling water supply passage 47 of the mount case 2
And the front chamber 61 are connected by a hose 67.

Thus, according to the fourth embodiment, the relief valve housing 38 of the first embodiment becomes unnecessary and the number of parts is reduced.

Although the embodiments of the present invention have been described in detail, various design changes can be made in the present invention without departing from the gist thereof.

For example, in the first embodiment, the rear chamber 60 of the relief valve 62 is communicated with the cooling water discharge passage 33 of the cylinder block 6, but this may be communicated with the cooling water discharge passage 48 of the mount case 2. good.

[0050]

As described above, according to the present invention, the bypass passage provided with the relief valve which opens when the supply pressure of the cooling water exceeds a predetermined value connects the cooling water supply passage and the cooling water discharge passage. Therefore, even if the relief valve is opened, the flow pattern of the cooling water flowing through the cooling water distribution chamber located downstream of the cooling water supply passage does not partially change. Thus, the amount of cooling water supplied from the cooling water distribution chamber to the first water jacket and the second water jacket via the plurality of through holes does not become uneven.

[Brief description of the drawings]

FIG. 1 is an overall side view of an outboard motor.

FIG. 2 is a left side view of the engine.

FIG. 3 is an enlarged view of a main part of FIG. 2;

FIG. 4 is an enlarged view taken along line 4-4 in FIG. 2;

FIG. 5 is an enlarged sectional view taken along line 5-5 of FIG. 2;

FIG. 6 is an enlarged sectional view taken along line 6-6 of FIG. 2;

FIG. 7 is an enlarged sectional view taken along line 7-7 of FIG. 2;

FIG. 8 is an enlarged sectional view taken along line 8-8 in FIG. 2;

FIG. 9 is a schematic diagram showing a cooling water flow path.

FIG. 10 corresponds to FIG. 3 according to the second embodiment.

11 is a sectional view taken along line 11-11 of FIG. 10;

FIG. 12 is a view according to a third embodiment and corresponding to FIG. 11;

FIG. 13 shows a view corresponding to FIG. 3 according to a fourth embodiment.

[Explanation of symbols]

6 Cylinder block 8 Cylinder head 32 Cooling water distribution chamber 33 Cooling water discharge passage 47 Cooling water supply passage 48 Cooling water discharge passage 52 First water jacket 53 ₁ through hole 53 ₂ through hole 58 Second water jacket 59 through hole 60 Rear chamber (Bypass passage) 61 Front chamber (Bypass passage) 62 Relief valve 67 Hose (Bypass passage) 72 Through hole (Bypass passage) 73 Through hole (Bypass passage)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-107563 (JP, A) JP-A-5-321662 (JP, A) JP-A-7-158443 (JP, A) JP-A-1- 182521 (JP, A) Japanese Utility Model Showa 60-23212 (JP, U) Japanese Utility Model Application Hei 6-60731 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01P 7/14 B63H 20 / 28 F01P 3/02 F01P 3/20

Claims (1)

(57) [Claims] 1. A first water jacket (52) provided on a cylinder block (6), a second water jacket (58) provided on a cylinder head (8), a first water jacket (52) and a second water. A plurality of through holes (53 ₁ , 5
3 _2, 59) via a distributing cooling water cooling water distribution chamber (32), the cooling water distribution chamber (32) cooling water supply passage for supplying cooling water to (47), a first water jacket (52 ) And the cooling water discharge passages (33, 48) where the cooling water passing through the second water jacket (58) merges, the cooling water supply passage (47) and the cooling water discharge passages (33, 4).
8) connecting the bypass passages (60, 61, 67, 7)
2, 73) and a relief valve (62) for opening and closing the bypass passages (60, 61, 67, 72, 73).