WO2017068730A1

WO2017068730A1 - Water jacket structure for cylinder head

Info

Publication number: WO2017068730A1
Application number: PCT/JP2015/080041
Authority: WO
Inventors: ヘルフェンヨンファン; リュディガーバイキルヒ; 浅利　大
Original assignee: 本田技研工業株式会社; エフエーファウゲゼルシャフトミットベシュレンクテルハフツング
Priority date: 2015-10-23
Filing date: 2015-10-23
Publication date: 2017-04-27
Also published as: CN108138690B; CN108138690A; JPWO2017068730A1; DE112015007043T5; JP6449477B2

Abstract

According to the present invention, a plurality of connecting portions (13g, 13h) that connect a lower water jacket (15) and upper water jacket (16) formed inside a cylinder head (13) are further downstream than an exhaust collection portion (28) in the flow direction of cooling water, and a volume expansion portion (15b) is provided in the vicinity of the connecting portion (13g) that is closest to the exhaust collection portion (28), and thus the stagnation of cooling water in the vicinity of said connecting portion (13g) is resolved by the volume expansion portion (15b), and the flow rate of the cooling water that flows through a channel upstream of said connecting portion (13g) is prevented from decreasing, thereby making it possible to make the flow rate of the cooling water that flows through each part of the lower water jacket (15) uniform and increase cooling performance. In particular, although the cooling water channel becomes narrow in the vicinity of the exhaust collection portion (28) and cooling performance deteriorates, because the volume expansion portion (15b) is further downstream than the exhaust collection portion (28), the cooling water can pass smoothly through the vicinity of the exhaust collection portion (28) and cooling performance is improved.

Description

Cylinder head water jacket structure

In the present invention, the lower water jacket and the upper water jacket are formed inside the cylinder head with the exhaust collecting portion interposed therebetween, and after the cooling water supplied to the intake side of the lower water jacket flows toward the exhaust side, The present invention relates to a water jacket structure of a cylinder head that is supplied to the upper water jacket through a plurality of communication portions from the exhaust side of the lower water jacket.

A water jacket structure of a cylinder head in which a lower water jacket and an upper water jacket are formed with an exhaust collecting portion sandwiched inside the cylinder head is known from Patent Document 1 below.

Japanese Unexamined Patent Publication No. 2014-84736

By the way, when cooling water that has flowed through a plurality of flow paths formed inside the lower water jacket of the cylinder head merges and then passes through a plurality of communication portions and is supplied to the upper water jacket, a plurality of lower water jackets are provided. If the flow rate of the cooling water in the flow path is uneven, there is a possibility that sufficient cooling performance cannot be obtained at the portion where the flow rate of the cooling water is reduced. In particular, since the flow of the cooling water is stagnant in the vicinity of the communication portion provided at a position where a large number of flow paths merge among the plurality of communication portions that communicate the lower water jacket and the upper water jacket, the flow of the cooling water It is necessary to eliminate the stagnation and make the flow rate of the cooling water flowing through each part of the lower water jacket uniform.

The present invention has been made in view of the above-mentioned circumstances, and in the case where the lower water jacket and the upper water jacket of the cylinder head are communicated with each other through a plurality of communicating portions, the flow rate of the cooling water flowing through each portion of the lower water jacket is made uniform. The purpose is to do.

In order to achieve the above object, according to the present invention, a lower water jacket and an upper water jacket are formed inside a cylinder head with an exhaust collecting portion interposed therebetween, and cooling water supplied to the intake side of the lower water jacket is supplied. A water jacket structure of a cylinder head that is supplied to the upper water jacket through a plurality of communication portions from the exhaust side of the lower water jacket after flowing toward the exhaust side, and includes a plurality of the communication portions. The at least two communicating portions are downstream of the exhaust collecting portion in the flow direction of the cooling water, and the lower water jacket has a volume in the vicinity of the communicating portion closest to the exhaust collecting portion of the at least two communicating portions. A water jacket structure for a cylinder head, characterized in that it is provided with an enlarged portion, is proposed.

According to the present invention, in addition to the first feature, the lower water jacket is connected to the upper water jacket on the upstream side in the flow direction of the cooling water from the volume expansion portion on the exhaust side of the lower water jacket. An air vent hole for discharging air bubbles is provided, and an exhaust side portion of the lower water jacket is rapidly lowered from a portion provided with the air vent hole toward a lower portion of the exhaust collect portion, and the exhaust collect portion A water jacket structure for a cylinder head is proposed, which is characterized in that a flow path of cooling water that rises rapidly from below to the volume expansion portion is formed.

According to the first feature of the present invention, the lower water jacket and the upper water jacket are formed inside the cylinder head with the exhaust collecting portion interposed therebetween, and the cooling water supplied from the intake side to the lower water jacket is directed to the exhaust side. After flowing toward the upper water jacket, the lower water jacket passes through the communicating portion and is supplied to the upper water jacket. Since at least two of the plurality of communication portions are downstream of the exhaust collecting portion in the flow direction of the cooling water, the communication portion closest to the exhaust collecting portion has a large number of passages from a large number of flow paths of the lower water jacket. There is a possibility that the cooling water collects, and the flow of the cooling water in the vicinity of the communicating portion is stagnated, so that the flow rate of the cooling water in the upstream flow path is lowered. However, since the lower water jacket has a volume expansion portion in the vicinity of the communication portion closest to the exhaust collecting portion of the at least two communication portions, the stagnation of the cooling water in the vicinity of the communication portion is eliminated by the volume expansion portion. By preventing a decrease in the flow rate of the cooling water flowing through the flow path on the upstream side of the communication portion, the flow rate of the cooling water flowing through each portion of the lower water jacket can be made uniform to improve the cooling performance. In particular, the cooling water flow path becomes narrow in the vicinity of the exhaust collecting part and the cooling performance is lowered, but the cooling water smoothly flows in the vicinity of the exhaust collecting part because there is a volume expansion part on the downstream side of the exhaust collecting part. It is possible to pass through and the cooling performance is improved.

Further, according to the second feature of the present invention, an air vent hole for discharging air bubbles from the lower water jacket to the upper water jacket is provided upstream of the volume expansion portion on the exhaust side of the lower water jacket in the flow direction of the cooling water. The exhaust portion of the lower water jacket is rapidly lowered from the portion provided with the air vent hole toward the lower portion of the exhaust collecting portion, and rapidly from the lower portion of the exhaust collecting portion toward the volume expanding portion. Since the rising cooling water flow path is formed, air bubbles contained in the cooling water flowing through the lower water jacket are blocked by the descending portion of the cooling water flow path so as to stay in the vicinity of the air vent hole, from the lower water jacket. It can be smoothly discharged to the upper water jacket through the air vent hole. Moreover, even if it becomes difficult for the cooling water to flow because the flow path of the cooling water below the exhaust collecting portion falls and rises, smooth passage of the cooling water in that portion can be promoted by the volume expanding portion.

The cylinder head side lower water jacket 15 of the embodiment corresponds to the lower water jacket of the present invention, and the cylinder head side upper water jacket 16 of the embodiment corresponds to the upper water jacket of the present invention. The first communication portion 13g and the second communication portion 13h correspond to the communication portion of the present invention.

FIG. 1 is a diagram showing the shape of the water jacket (core) of the cylinder block and cylinder head and the flow of cooling water. (First embodiment) FIG. 2 is a view showing the top surface of the cylinder block, the gasket, and the bottom surface of the cylinder head (viewed in the direction of

arrows

2A, 2B, and 2C in FIG. 1). (First embodiment) FIG. 3 is a view of the water jacket of the cylinder head as viewed from the exhaust side (viewed in the direction of arrow 3 in FIG. 1). (First embodiment) FIG. 4 is a top view of the water jacket of the cylinder head (viewed in the direction of arrow 4 in FIG. 3). (First embodiment) FIG. 5 is a top view of the water jacket of the cylinder head (viewed in the direction of arrow 5 in FIG. 3). (First embodiment) FIG. 6 is a view showing the upper surface of the cylinder head side lower water jacket and the lower surface of the cylinder head side upper water jacket. (First embodiment) FIG. 7 is a side view of the cylinder block on the exhaust side (seen in the direction of arrow 7 in FIG. 1). (First embodiment) 8 is a cross-sectional view taken along line 8-8 of FIG. (First embodiment) 9 is a cross-sectional view taken along line 9-9 of FIG. (First embodiment) 10 is a cross-sectional view taken along line 10-10 of FIG. (First embodiment)

13 Cylinder head 13f Air vent hole 13g First communication part (communication part)
13h Second communication part (communication part)
15 Cylinder head side lower water jacket (lower water jacket)
15b Volume expansion part 16 Cylinder head side upper water jacket (upper water jacket)
28 Exhaust collecting part

Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the present specification, the vertical direction is defined as the cylinder axis direction and the cylinder block side as the lower side, and the cylinder axis direction and the cylinder head side as the upper side, regardless of the mounting orientation of the engine.

First embodiment

1 and 2, the water-cooled in-line three-cylinder engine includes a cylinder block 11 and a cylinder head 13 having a bottom surface coupled to a top surface of the cylinder block 11 with a gasket 12 interposed therebetween. The cylinder block 11 includes a cylinder block-side water jacket 14 surrounding the periphery of three cylinder bores arranged in series along the cylinder row line, and the cylinder head 13 is vertically moved with an exhaust manifold (not shown) interposed therebetween. A cylinder head side lower water jacket 15 and a cylinder head side upper water jacket 16 are provided. In the upper left part of FIG. 1, a state in which only the cylinder head side lower water jacket 15 is drawn inside the cylinder head 13 and a state in which only the cylinder head side upper water jacket 16 is drawn inside the cylinder head 13 are separated. Shown in The shape of the water jacket in each drawing is also the shape of a core for forming the water jacket by casting.

A sub-water jacket 17 extending in the cylinder row line direction is formed on the intake side of the cylinder block 11, and a cooling water introduction port through which cooling water is supplied from the cooling water pump 18 to one end side (# 1 cylinder side). 11a is formed. The cylinder block side water jacket 15 is provided with a cooling water inlet 11b on the intake side of the cylinder bore of the # 2 cylinder, and the cooling water inlet 11b and the sub water jacket 17 are connected via a thermo valve 19. The thermo valve 19 automatically opens and closes depending on the temperature of the cooling water. The thermo valve 19 is closed at a low temperature and shuts off the supply of the cooling water to the cylinder block side water jacket 15 to promote engine warm-up. The cooling of the engine is promoted by opening the valve and permitting the supply of the cooling water to the cylinder block side water jacket 15.

The cylinder block side water jacket 14 includes a cooling water outlet 11c that discharges cooling water toward the cylinder head side lower water jacket 15 on the other end side (# 3 cylinder side). Therefore, in the cooling water flow path in which the cooling water supplied to the cooling water inlet 11b of the cylinder block side water jacket 14 flows toward the cooling water outlet 11c, the intake air of the cylinder block side water jacket 14 in FIG. A short flow path that reaches half of the side portion counterclockwise and reaches the cooling water outlet 11c, and the other half of the intake side portion and the exhaust side portion of the cylinder block side water jacket 14 flow clockwise and the cooling water. There is a long channel that reaches the outlet 11c. A partition member 20 for partitioning a part of the cylinder block side water jacket 14 and suppressing the flow of the cooling water is attached to the shorter flow path.

As described above, since only one cooling water outlet 11c for supplying the cooling water from the cylinder block side water jacket 14 to the cylinder head side lower water jacket 15 is provided, the cooling water inlet 11b is connected to the cylinder block side water jacket 14. The supplied cooling water can reach all locations of the cylinder block side water jacket 14 without passing through the cooling water outlet 11c, and the entire cylinder block 11 can be effectively cooled.

Assuming that the partition member 20 is not present, most of the cooling water supplied from the cooling water inlet 11b to the cylinder block water jacket 14 flows through the shorter flow path and reaches the cooling water outlet 11c. There is a possibility that the flow rate of the cooling water flowing through the longer flow path becomes small, and the exhaust side of the cylinder block 11 that becomes high temperature cannot be sufficiently cooled. However, according to the present embodiment, the partition member 20 is attached to the shorter flow path to restrict the flow rate of the cooling water, so the flow rate of the cooling water flowing through the longer flow path is increased and the temperature becomes high. Cooling of the exhaust side of the cylinder block 11 can be promoted.

Two groove-shaped

cooling water passages

11d and 11d extending in a direction crossing between the three cylinder bores are formed on the top surface of the cylinder block 11. The inlet side of the cooling

water passages

11d and 11d communicates with the exhaust side of the cylinder block side water jacket 14, and the outlet side of the cooling

water passages

11d and 11d is a dead end near the intake side of the cylinder block side water jacket 14. .

The gasket 12 is formed with three

first communication holes

12a, 12b, 12c, one second communication hole 12d, and two

third communication holes

12e, 12e. In addition, on the bottom surface of the cylinder head 13, three first

cooling water inlets

13a, 13b, 13c, one second cooling water inlet 13d, and two second cooling water inlets communicating with the cylinder head side lower water jacket 15, respectively. Three cooling

water inlets

13e and 13e are formed.

The sub-water jacket 17 of the cylinder block 11 is connected to the three first

cooling water inlets

13a, 13b, 13c of the cylinder head side lower water jacket 15 through the three

first communication holes

12a, 12b, 12c of the gasket 12. Communicate. At this time, the three

first communication holes

12a, 12b, 12c of the gasket 12 have the smallest opening area of the first communication hole 12a closest to the cooling water inlet 11a of the subwater jacket 17, and the subwater jacket 17 The first communication hole 12c farthest from the cooling water introduction port 11a has the largest opening area, and the first communication hole 12b having a medium distance from the cooling water introduction port 11a of the subwater jacket 17 has a medium opening area. It has.

If it is assumed that the opening areas of the three

first communication holes

12a, 12b, and 12c of the gasket 12 are the same, the cooling water that passes through the first communication hole 12a closest to the cooling water inlet 11a of the subwater jacket 17 is used. And the flow rate of the cooling water passing through the first communication hole 12c farthest from the cooling water introduction port 11a of the subwater jacket 17 decreases, but the three

first communication holes

12a, 12b, and 12c are opened. By changing the area according to the distance of the subwater jacket 17 from the cooling water inlet 11a, the cooling water is evenly distributed to the three first

cooling water inlets

13a, 13b, 13c of the cylinder head side lower water jacket 15. Can be supplied.

The cooling water outlet 11c of the cylinder block side water jacket 14 communicates with the second cooling water inlet 13d of the cylinder head side lower water jacket 15 through the second communication hole 12d of the gasket 12. The intake-side end portions of the two cooling

water passages

11d and 11d formed on the top surface of the cylinder block 11 become dead ends through the

third communication holes

12e and 12e of the gasket 12, respectively. The jacket 15 communicates with the two third

cooling water inlets

13e and 13e. When the thermo valve 19 is open, the flow rate of the cooling water supplied from the sub water jacket 17 directly to the cylinder head side lower water jacket 15 without passing through the cylinder block side water jacket 14 is about the total flow rate. The flow rate of the cooling water supplied from the subwater jacket 17 to the cylinder head side lower water jacket 15 via the cylinder block side water jacket 14 is about 30% of the total flow rate.

Next, the structure of the cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16 will be described with reference to FIGS.

The cylinder head side upper water jacket 16 is about half the size of the cylinder head side lower water jacket 15 and is disposed above the exhaust side of the cylinder head side lower water jacket 15.

The cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16 are provided with six baseboard portions 21 to 26 projecting outward. The skirting portions 21 to 26 hold a sand core for casting the cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16 in the mold when the cylinder head 13 is cast. When the core is discharged after casting, the skirting portions 21 to 26 become openings that constitute a part of the cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16. The ends of the skirting portions 21 to 26 open to the surface of the cylinder head 13, and are blocked by plugs 27 (see FIGS. 7 to 10) in order to prevent leakage of cooling water from that portion.

7 and 8, the cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16 communicate with each other through the air vent hole 13f inside the baseboard portion 22. The air vent hole 13f is processed by inserting a drill in the horizontal direction from the opening of the skirting board 23 which is a space. In this way, by drilling the air vent hole 13f using the baseboard portion 22, an unnecessary drill hole is prevented from being formed in the cylinder head 13, and a process for closing the drill hole is unnecessary. Thus, the processing of the air vent hole 13f is facilitated.

4 and 9, the cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16 communicate with each other through the first communication portion 13g in the skirting board portion 23. As shown in FIGS. 4 and 10, the cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16 communicate with each other through the second communication portion 13h in the skirting board 24.

3 and FIG. 7, both of which are viewed from the exhaust side, as is clear, the recess 15 a on the upper surface on the exhaust side of the cylinder head side lower water jacket 15 and the exhaust of the cylinder head side upper water jacket 16. An exhaust manifold portion 28 of the exhaust manifold extends to the outside from between the concave portion 16a on the lower surface side. A baseboard 22 having an air vent hole 13f formed adjacent to the exhaust collecting portion 28 on the # 3 cylinder side in the cylinder row direction is located adjacent to the exhaust collecting portion 28, and # 1 in the cylinder row direction with respect to the exhaust collecting portion 28. A base board 23 having a first communication part 13g formed on the cylinder side is located adjacent to the cylinder side, and a second communication part 13h is formed on the # 1 cylinder side in the cylinder row direction with respect to the base board part 23. The skirting board part 24 is located adjacently.

Since the baseboard portion 22 (air vent hole 13f) and baseboard portion 23 (first communication portion 13g) located on both sides of the concave portion 15a are positioned higher than the concave portion 15a of the cylinder head side lower water jacket 15. The flow path of the cooling water on the exhaust side of the cylinder head side lower water jacket 15 rises toward the air vent hole 13f, then descends below the recess 15a, and further from the lower part of the recess 15a to the first communication portion 13g. It will bend so that it will rise again toward.

The cylinder head-side lower water jacket 15 and the cylinder head-side upper water jacket 16 adjacent to the skirting board portion 23 have

volume expanding portions

15b and 16b (see FIGS. 3 to 5) that bulge outward in a triangular shape. It is formed. Further, in the portion where the cooling water flow path suddenly descends from the position where the air vent hole 13f of the cylinder head side lower water jacket 15 is provided to the lower part of the recess 15a, the flow passage cross-sectional area is narrowed. The narrowed portion 15c (see FIG. 3) is formed.

Next, the operation of the embodiment of the present invention having the above configuration will be described.

The cooling water supplied from the cooling water pump 18 to the sub water jacket 17 of the cylinder block 11 passes through the thermo valve 19 from the sub water jacket 17 and is supplied to the cooling water inlet 11 b on the intake side of the cylinder block side water jacket 14. The cooling water branched in two directions at the cooling water inlet 11b flows in the clockwise and counterclockwise directions inside the cylinder block side water jacket 14 and merges at the cooling water outlet 11c, and then passes through the second communication hole 12d of the gasket 12. It passes through and is supplied to the # 3 cylinder side of the cylinder head side lower water jacket 15.

The cooling water flowing from the # 1 cylinder side to the # 3 cylinder side inside the sub-water jacket 17 is the

first communication holes

12a, 12b, 12c of the gasket 12 and the first

cooling water inlets

13a, 13b, 13c of the cylinder head 13. Is supplied to the intake side of the cylinder head side lower water jacket 15 and flows from there through the inside of the cylinder head side lower water jacket 15 toward the exhaust side.

The dead ends of the two cooling

water passages

11d and 11d whose inlet ends communicate with the exhaust side of the cylinder block-side water jacket 14 are the

third communication holes

12e and 12e of the gasket 12 and the third cooling water of the cylinder head 13. The third

cooling water inlets

13e and 13e of the cylinder head 13 are communicated with the cylinder head side lower water jacket 15 through the

inlets

13e and 13e, and the third

cooling water inlets

13a and 13e of the cylinder head 13 are viewed from the first

cooling water inlets

13a, 13b and 13c. Therefore, since the cooling water passes over the third

cooling water inlets

13e and 13e at a high flow rate, a large negative pressure is generated.

As a result, due to the negative pressure generated at the third

cooling water inlets

13e and 13e, the high temperature cooling water on the exhaust side of the cylinder block side water jacket 14 passes through the two cooling

water passages

11d and 11d, and the cylinder head side lower water. By sucking up the jacket 15 and eliminating the stagnation of the cooling water on the exhaust side of the cylinder block side water jacket 14, the exhaust side of the cylinder block 11 that is hotter than the intake side of the cylinder block 11 is effectively cooled. can do.

Without passing through the cylinder block-side water jacket 14 from the sub-water jacket 17, the cooling water flowing directly into the three first

cooling water inlets

13a, 13b, 13c of the cylinder head-side lower water jacket 15 It bifurcates so as to detour around and flows from the intake side to the exhaust side. On the other hand, the cooling water supplied from the cooling water outlet 11 c located on the # 3 cylinder side of the cylinder block side water jacket 14 to the second cooling water inlet 13 d of the cylinder head 13 flows to the # 1 cylinder side, and from the sub water jacket 17. While joining the cooling water flowing directly into the cylinder head side lower water jacket 15, the exhaust side of the cylinder head side lower water jacket 15 flows toward the # 1 cylinder side toward the first communication portion 13g and the second communication portion 13h. Then, the coolant flowing from the cylinder head side lower water jacket 15 through the first communication portion 13g and the second communication portion 13h into the cylinder head side upper water jacket 16 moves the cylinder head side upper water jacket 16 to the # 1 cylinder side. From # 3 to the cylinder side and then discharged from a coolant discharge port 13i of the cylinder head 13 toward a radiator (not shown).

Since the air vent hole 13f is provided so as to short-circuit the cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16, air bubbles contained in the cooling water flowing through the cylinder head side lower water jacket 15 are removed from the air vent hole. It is possible to prevent air bubbles from remaining in the cylinder head side lower water jacket 15 by passing through 13f and discharged to the cylinder head side upper water jacket 16.

As is apparent from FIG. 3, the air vent hole 13f is provided at the highest position of the cylinder head side lower water jacket 15, and on the downstream side of the air vent hole 13f in the flow direction of the cooling water, Since the concave portion 15a of the jacket 15 is located, the flow path of the cooling water flowing from the # 3 cylinder side to the # 1 cylinder side on the exhaust side of the cylinder head side lower water jacket 15 rapidly rises toward the air vent hole 13f. Later, it will fall rapidly and then rise again suddenly. As a result, bubbles easily gather below the air vent hole 13f, and the accumulated bubbles are smoothly discharged from the cylinder head side lower water jacket 15 to the cylinder head side upper water jacket 16 through the air vent hole 13f.

Further, on the exhaust side of the lower water jacket 15 on the cylinder head side, a throttle portion 15c (see FIG. 3) in which the cross-sectional area of the flow path is reduced between the portion provided with the air vent hole 13f and the lower portion of the exhaust collecting portion 28. Therefore, by increasing the flow rate of the cooling water in the vicinity of the exhaust collecting portion 28 by the throttle portion, the cooling effect of the exhaust collecting portion 28 that becomes high temperature can be enhanced.

The cooling water that has passed under the recess 15a is supplied from the cylinder head-side lower water jacket 15 to the cylinder head-side upper water jacket 16 through the first communication portion 13g and the second communication portion 13h. The first communication portion 13g on the upstream side in the flow direction collects cooling water from the multiple flow paths of the cylinder head side lower water jacket 15 compared to the second communication portion 13h on the downstream side in the flow direction of the cooling water. The flow of the cooling water is stagnated in the vicinity of the first communication portion 13g, and the flow rate of the cooling water in the flow path on the upstream side of the first communication portion 13g is greater than the flow speed of the cooling water in the flow path on the upstream side of the second communication portion 13h. Can also be slow.

However, according to the present embodiment, since the

volume expansion portions

15b and 16b (see FIGS. 3 to 5) in which the volume of the flow path of the cooling water is increased are provided in the vicinity of the first communication portion 13g on the upstream side, The

volume expansion portions

15b and 16b eliminate the stagnation of the flow of the cooling water in the vicinity of the first communication portion 13g, and a sufficient amount of cooling water can pass through the first communication portion 13g. As a result, a decrease in the flow rate of the cooling water in the flow path upstream of the first communication portion 13g is prevented, and the flow rate of the cooling water flowing in each flow path of the cylinder head side lower water jacket 15 is made uniform, thereby improving the cooling performance. improves.

In addition, since the flow path of the cooling water suddenly descends and then rapidly rises below the recess 15a of the cylinder head side lower water jacket 15, there is a possibility that the smooth flow of cooling water may be obstructed. Since the

volume expansion portions

15b and 16b in which the volume of the flow path expands are formed on the downstream side in the flow direction of the cooling water, the cooling water can smoothly pass under the recess 15a of the cylinder head side lower water jacket 15. Thus, the high temperature exhaust collecting portion 28 can be effectively cooled.

Although the embodiments of the present invention have been described above, various design changes can be made without departing from the scope of the present invention.

For example, although the engine of the embodiment is an in-line three-cylinder engine, the number and arrangement of the engine cylinders are not limited to those of the embodiment.

In addition, although there are two communication parts of the embodiment, the first communication part 13g and the second communication part 13h, the number of communication parts may be three or more.

In the embodiment, the cylinder head side lower water jacket 15 and the cylinder head side upper water jacket 16 are respectively provided with

volume expanding portions

15b and 16b. However, the volume expanding portion 15b is provided at least in the cylinder head side lower water jacket 15. It only has to be done.

Claims

The lower water jacket (15) and the upper water jacket (16) are formed inside the cylinder head (13) with the exhaust collecting portion (28) interposed therebetween, and the cooling water supplied to the intake side of the lower water jacket (15) After flowing toward the exhaust side, the water jacket of the cylinder head is supplied to the upper water jacket (16) from the exhaust side of the lower water jacket (15) through the plurality of communication portions (13g, 13h). Structure,
At least two communication parts (13g, 13h) of the plurality of communication parts (13g, 13h) are located downstream of the exhaust collecting part (28) in the flow direction of the cooling water, and the lower water jacket (15) Is provided with a volume expansion portion (15b) in the vicinity of the communication portion (13g) closest to the exhaust collecting portion (28) of the at least two communication portions (13g, 13h). Jacket structure.
Air bubbles are discharged from the lower water jacket (15) to the upper water jacket (16) upstream of the volume expansion portion (15b) on the exhaust side of the lower water jacket (15) in the flow direction of the cooling water. An air vent hole (13f) is provided, and an exhaust side portion of the lower water jacket (15) is suddenly lowered from the portion provided with the air vent hole (13f) toward the lower portion of the exhaust collecting portion (28). The flow path of the cooling water that descends to the abruptly and rises rapidly from below the exhaust collecting part (28) toward the volume expansion part (15b) is formed. Cylinder head water jacket structure.