JP2018131921A - Water cooled SOHC engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water cooled SOHC engine that can improve cooling performance.SOLUTION: A water cooled SOHC engine comprises a water jacket 30 provided in a cylinder head 6. The water jacket 30 includes an annular outer peripheral flow passage 34 arranged around a plurality of intake outlets 14o and a plurality of exhaust inlets 16i, a central flow passage 39 arranged inside the outer peripheral flow passage 34 and overlapping with an ignition plug 24, an upstream connection flow passage 38 extending from the outer peripheral flow passage 34 to the central flow passage 39, and a downstream connection flow passage 40 having a larger cross-sectional area than the cross-sectional area of the upstream connection flow passage 38 and extending from the central flow passage 39 to the outer peripheral flow passage 34.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a water-cooled SOHC (Single OverHead Camshaft) engine.

  Patent Document 1 discloses a water-cooled-SOHC-V-2 cylinder engine. Two intake valves and two exhaust valves are provided in each cylinder. The intake valve and the exhaust valve corresponding to the same cylinder are opened and closed as the same camshaft rotates. As shown in FIG. 3 of Patent Document 1, the spark plug is inclined obliquely with respect to the center line of the cylinder. Each part of the engine is cooled by a coolant flowing through a water jacket provided in the cylinder head and the cylinder body.

Japanese Patent No. 4514637

  In a water-cooled engine, each part of the engine is cooled by coolant flowing through a water jacket provided in the engine. In the SOHC engine, the spark plug may be disposed at an inclination. Therefore, the restrictions of the water jacket regarding a shape and a size may be severe. In particular, as the number of intake valves and exhaust valves corresponding to the same cylinder increases, the water jacket restrictions on shape and size become more severe. Therefore, it is difficult to ensure high cooling performance with a water-cooled SOHC engine.

  Accordingly, one of the objects of the present invention is to provide a water-cooled SOHC engine that can enhance the cooling performance.

  An embodiment of the present invention includes a cylinder body including a cylinder having a center line extending in the vertical direction, a piston that reciprocates in the vertical direction in the cylinder, and an upper end portion of the cylinder body. A cylinder head that forms a combustion chamber with the cylinder and the piston; a spark plug that is attached to the cylinder head and that burns the air-fuel mixture in the combustion chamber; an intake air that is supplied to the combustion chamber; A water-cooled SOHC engine comprising a valve device that controls exhaust gas discharged from a combustion chamber.

  The cylinder head includes an intake port that includes a plurality of intake outlets that open on the inner surface of the combustion chamber, an exhaust port that includes a plurality of exhaust inlets that opens on the inner surface of the combustion chamber, and a plug that opens on the inner surface of the combustion chamber A plug hole including an outlet and a water jacket for a head for guiding the coolant are included. The spark plug is inserted into the plug hole and is inclined obliquely with respect to the center line of the cylinder. The valve device includes: a camshaft that rotates about a rotation axis that extends in a left-right direction; a plurality of intake valves that respectively open and close the plurality of intake outlets according to the rotation of the camshaft; and the rotation of the camshaft. A plurality of exhaust valves that respectively open and close the plurality of exhaust inlets.

  The water jacket for the head is opened on the outer surface of the cylinder head, and a water supply port for receiving coolant, and a drain port for opening the coolant that has flowed into the water supply port, opened on the outer surface of the cylinder head, An annular outer peripheral channel that is disposed around the plurality of intake outlets and the plurality of exhaust inlets when viewed in the vertical direction and guides the coolant flowing into the water supply port toward the drainage port. And disposed inward of the outer peripheral flow path when viewed in the vertical direction, and overlaps the spark plug when viewed in the vertical direction, and extends from the outer peripheral flow path to the central flow path. An upstream connection channel that guides the coolant from the outer peripheral channel to the central channel, and extends from the central channel to the outer peripheral channel, away from the upstream connection channel, and Guided to the central channel by the connecting channel The coolant containing a downstream connecting channel for guiding the peripheral channels from the central channel. The cross-sectional area of the upstream connection channel is smaller than the cross-sectional area of the downstream connection channel.

  According to this configuration, the coolant for cooling the engine enters the head water jacket from the water supply port of the head water jacket, and flows through the outer peripheral flow path of the head water jacket toward the drain port of the head water jacket. The coolant flows from the outer peripheral flow path to the central flow path of the head water jacket via the upstream connection flow path of the head water jacket, and from the central flow path to the peripheral flow path via the downstream connection flow path of the head water jacket. Flowing into. During this time, each part of the cylinder head, in particular, the exhaust port and the plug hole and the parts in the vicinity thereof are cooled.

  The central flow path of the head water jacket is disposed inside the outer peripheral flow path when viewed in the vertical direction parallel to the axial direction of the cylinder. The spark plug and the central channel overlap each other when viewed in the vertical direction. Therefore, the central flow path is disposed near the tip of the spark plug that emits a spark. Therefore, the tip of the spark plug is mainly cooled by the coolant flowing through the central flow path.

  The cross-sectional area of the upstream connection channel is smaller than the cross-sectional area of the downstream connection channel. Since the cross-sectional area of the upstream connection channel is small, the flow of the coolant in the upstream connection channel is fast. Since the coolant having a high flow rate flows from the upstream connection channel to the central channel, the coolant flows in the central channel at high speed. When the coolant flow is fast, heat is released efficiently. Accordingly, the temperature around the plug, that is, the portion around the plug hole on the inner surface of the combustion chamber can be effectively reduced. In addition, the temperature of the portion between the exhaust sheets, that is, the portion between the exhaust inlets on the inner surface of the combustion chamber can be effectively reduced.

  Furthermore, both the upstream connection flow path and the downstream connection flow path are not thin, but only the upstream connection flow path is thin. When casting the material of the cylinder head (cylinder head before being subjected to machining such as cutting), a sand core having the same shape as the water jacket for the head is used. If both the upstream connection flow path and the downstream connection flow path are thin, the strength of the sand core is reduced. Therefore, by narrowing only the upstream connection flow path, the cooling performance of the engine can be enhanced while suppressing a decrease in the strength of the sand core.

In the present embodiment, at least one of the following features may be added to the water-cooled SOHC engine.
The width of the upstream connection channel when viewed in the vertical direction is smaller than the width of the downstream connection channel when viewed in the vertical direction. According to this configuration, since the width of the upstream connection channel is smaller than the width of the downstream connection channel, the cross-sectional area of the upstream connection channel can be easily made smaller than the cross-sectional area of the downstream connection channel. Thereby, the flow rate of the coolant in the central flow path can be increased, and the cooling performance of the engine can be improved.

The length of the upstream connection channel in the vertical direction is smaller than the length of the downstream connection channel in the vertical direction. According to this configuration, since the upstream connection flow path is shorter in the vertical direction than the downstream connection flow path, the cross-sectional area of the upstream connection flow path can be easily made smaller than the cross-sectional area of the downstream connection flow path. Thereby, the flow rate of the coolant in the central flow path can be increased, and the cooling performance of the engine can be improved.
The outer peripheral surface of the outer peripheral flow path is an arcuate arc portion coaxial with the inner peripheral surface of the cylinder when viewed in the vertical direction, and from the arc portion toward the center line of the cylinder when viewed in the vertical direction. And an inward convex portion that overlaps the spark plug when viewed in the vertical direction.

The center line of the head water jacket means a line connecting the center of gravity of the cross section of the head water jacket perpendicular to the direction in which the coolant flows. Inward means the direction toward the center line of the cylinder. Outward means the direction away from the center line of the cylinder.
According to this structure, the inward convex part which protrudes toward the centerline of the water jacket for heads is provided in the outer peripheral surface of an outer periphery flow path. The inward convex portion of the outer peripheral flow path protrudes from the arc portion coaxial with the inner peripheral surface of the cylinder toward the center line of the cylinder. In other words, the cross-sectional area of the outer peripheral flow path is reduced as compared with the case where no inward convex portion is provided. Accordingly, a fast flow of the coolant is formed on the inward convex portion of the outer peripheral flow path. The inward convex portion of the outer peripheral channel overlaps with the spark plug when viewed in the vertical direction, and is disposed near the spark plug. Therefore, the spark plug and the vicinity thereof can be efficiently cooled.

The cylinder head further includes a gas vent hole extending upward from the central flow path, and the water-cooled SOHC engine further includes a plug that closes the gas vent hole, and the center of the cylinder from the center line of the gas vent hole The distance to the line is smaller than the diameter of the vent hole.
The center line of the gas vent hole may be a straight line parallel to the center line of the cylinder, or may be a straight line inclined obliquely with respect to the center line of the cylinder. In the latter case, “the distance from the center line of the vent hole to the center line of the cylinder” is the center line of the cylinder from the center line of the vent hole in the range from the upper end of the vent hole to the lower end of the vent hole. Means the shortest distance to.

According to this configuration, the gas vent hole for discharging the sand core forming the water jacket for the head when the cylinder head material is cast is provided in the cylinder head and is closed by the plug. The gas vent hole is disposed near the center line of the cylinder, and the distance from the center line of the gas vent hole to the center line of the cylinder is smaller than the diameter of the gas vent hole.
The vent hole extends upward from the central flow path for cooling the spark plug and the vicinity thereof. The front end surface of the central channel is usually disposed near the spark plug. If the vent hole is far from the center line of the cylinder, the width of the central flow path increases and the flow rate of the coolant in the central flow path decreases. On the other hand, if the vent hole is brought close to the center line of the cylinder, the central flow path can be narrowed, and the flow rate of the coolant in the central flow path can be increased. Thereby, a spark plug and its vicinity part can be cooled efficiently.

The upstream connection flow channel, the central flow channel, and the downstream connection flow channel have a chevron that extends toward the central flow channel when viewed in the vertical direction between the upstream connection flow channel and the downstream connection flow channel. The length of the central flow path in the left-right direction is smaller than the length of the central flow path in the front-rear direction orthogonal to both the vertical direction and the left-right direction.
According to this configuration, the mountain-shaped convex portion that extends toward the central flow path when viewed in the vertical direction is disposed between the upstream connection flow path and the downstream connection flow path. The tip of the chevron convex portion is formed by an upstream connection channel, a central channel, and a downstream connection channel. The tip of the chevron protrudes into the central channel, and the central channel is narrowed in the left-right direction. The length of the central channel in the left-right direction is smaller than the length of the central channel in the front-rear direction. Thus, since the central channel is thin in the left-right direction, the flow rate of the coolant in the central channel can be increased.

The length of the central channel in the left-right direction is larger than the width of the upstream connection channel when viewed in the up-down direction.
According to this configuration, the length of the central flow path in the left-right direction is not only smaller than the length of the central flow path in the front-rear direction, but is larger than the width of the upstream connection flow path when viewed in the vertical direction. . If the central flow path is too thin, the strength of the sand core forming the head water jacket will be reduced. Therefore, the cooling performance of the engine can be enhanced while suppressing a decrease in the strength of the sand core.

The central flow path includes a lower convex portion that protrudes downward from the upper surface of the central flow path, and the lower convex portion includes a pair of side surfaces respectively disposed in the exhaust region and the intake region, and a pair of side surfaces. And a top surface disposed between the lower ends.
According to this structure, the downward convex part which protrudes toward the centerline of the water jacket for heads is provided in the central flow path. The central channel protrudes downward from the upper surface of the central channel. Therefore, the cross-sectional area of the central flow path is reduced as compared with the case where no downward convex portion is provided. Thereby, the flow rate of the coolant in the central flow path can be increased, and the cooling performance can be improved.

  Further, the pair of side surfaces of the downward convex portion are disposed in the exhaust region and the intake region, respectively. In this case, when the pair of side surfaces are not provided, that is, compared with the case where the central flow path is simply thinned in the vertical direction, the contact area between the portion near the exhaust port and the intake port and the head water jacket is reduced. The reduction can be reduced.

It is a mimetic diagram showing the vertical section of the engine concerning a 1st embodiment of the present invention. It is sectional drawing which shows the vertical cross section of a cylinder head and a cylinder body. It is the figure which looked at the cylinder head from the bottom upwards. It is the figure which looked at the water jacket for heads from top to bottom. It is the figure which looked at the water jacket for heads from top to bottom. It is the figure which looked at the water jacket for heads from diagonally lower. FIG. 7 is an enlarged view showing a part of the head water jacket viewed in the direction of arrow VII shown in FIG. 5. It is the figure which looked at the upstream connection flow path, the center flow path, and the downstream connection flow path of the water jacket for heads from top to bottom. It is sectional drawing which shows the vertical cross section which follows the IX-IX line shown in FIG. It is sectional drawing which shows the vertical cross section which follows the XX line shown in FIG. It is the top view which looked at the water jacket for heads concerning 2nd Embodiment of this invention from the top to the downward direction. It is the figure which looked at the central flow path of the water jacket for heads from diagonally upward. It is sectional drawing which shows the vertical cross section along a 2nd virtual plane. It is sectional drawing which shows the vertical cross section along the XIV-XIV line | wire shown in FIG. It is sectional drawing which shows the vertical cross section which follows the XV-XV line | wire shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The definition of the direction in the following description is as follows.
The vertical direction Dud is a direction parallel to the center line C <b> 1 of the cylinder 9. The upward direction is parallel to the center line C <b> 1 of the cylinder 9 and is directed from the piston 2 toward the combustion chamber 15. The downward direction is parallel to the center line C <b> 1 of the cylinder 9 and is directed from the combustion chamber 15 toward the piston 2.

The left-right direction Dlr is a virtual plane including the center line C1 of the cylinder 9, and when viewed in the up-down direction Dud, the intake region where all of the plurality of intake outlets 14o are arranged and all of the plurality of exhaust inlets 16i are arranged. This is a direction parallel to the first virtual plane P1 (see FIG. 4) partitioning the space into the exhaust region and orthogonal to the vertical direction Dud.
The front-rear direction Dfr is a virtual plane including the center line C1 of the cylinder 9, and is parallel to the second virtual plane P2 (see FIG. 4) orthogonal to the first virtual plane P1 and orthogonal to the vertical direction Dud. It is. The front-rear direction Dfr is a direction orthogonal to both the up-down direction Dud and the left-right direction Dlr.

FIG. 1 is a schematic diagram showing a vertical section of an engine 1 according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a vertical cross section of the cylinder head 6 and the cylinder body 8. FIG. 3 is a view of the cylinder head 6 as viewed from the bottom upward.
As shown in FIG. 1, the engine 1 is a water-cooled-SOHC-single cylinder engine. The engine 1 may be a multi-cylinder engine. The engine 1 may be mounted on a land or snow vehicle such as a saddle type vehicle, or may be mounted on a ship propulsion device such as an inboard motor, an outboard motor, or an inboard / outboard motor, or in an aircraft such as a helicopter. It may be mounted. Of course, the engine 1 may be mounted on a machine other than these.

  The engine 1 includes a piston 2 that reciprocates in the cylinder 9 as the air-fuel mixture burns, a crankshaft 4 that converts the reciprocating motion of the piston 2 into rotation, and the operation of the piston 2 is transmitted to the crankshaft 4. Connecting rod 3 to be connected. The engine 1 further includes a cylinder body 8 that forms a cylinder 9, a cylinder head 6 that forms a combustion chamber 15 in which an air-fuel mixture burns, a crankcase 10 that houses the crankshaft 4 together with the cylinder body 8, and the cylinder head 6. And a head cover 5 attached to the head.

  The cylinder head 6 is disposed above the cylinder body 8. The head cover 5 is disposed above the cylinder head 6. The crankcase 10 is disposed below the cylinder body 8. The crankcase 10 may be integrated with the cylinder body 8 or may be a member different from the cylinder body 8 fixed to the cylinder body 8 with bolts. The cylinder head 6 is fixed to the cylinder body 8 with bolts. A gap between the cylinder body 8 and the cylinder head 6 is closed with a gasket 7.

  The cylinder head 6 includes an intake port 14 for supplying gas to the combustion chamber 15 and an exhaust port 16 for discharging gas such as exhaust gas from the combustion chamber 15. As shown in FIGS. 1 and 3, the intake port 14 includes one intake inlet 14 i that opens at the outer surface 6 a of the cylinder head 6 and two intake outlets 14 o that open at the inner surface of the combustion chamber 15. The exhaust port 16 includes two exhaust inlets 16 i that open at the inner surface of the combustion chamber 15, and one exhaust outlet 16 o that opens at the outer surface 6 a of the cylinder head 6. The valve device of the engine 1 includes two intake valves 18 that open and close two intake outlets 14o, and two exhaust valves 19 that open and close two exhaust inlets 16i, respectively.

  As shown in FIG. 2, the engine 1 includes a spark plug 24 that ignites the air-fuel mixture in the combustion chamber 15. The spark plug 24 is inserted into a plug hole 25 provided in the cylinder head 6. The plug hole 25 includes one plug inlet 25 i that opens at the outer surface 6 a of the cylinder head 6 and one plug outlet 25 o that opens at the inner surface of the combustion chamber 15. The spark plug 24 is inclined with respect to the center line C1 of the cylinder 9. The center electrode 24 c and the side electrode 24 b are provided at the tip 24 a of the spark plug 24.

  As shown in FIG. 1, the engine 1 is discharged from the combustion chamber 15 via an intake pipe 11 that forms an intake passage that guides gas supplied to the combustion chamber 15 via an intake port 14 and an exhaust port 16. And an exhaust pipe 17 forming an exhaust passage for guiding the gas. The engine 1 further includes a throttle valve 12 that changes the flow rate of the gas supplied to the combustion chamber 15, and a fuel supply device 13 that supplies fuel to the combustion chamber 15. The fuel supply device 13 may be either a carburetor or a fuel injector. Further, the fuel supply device 13 may supply fuel to the combustion chamber 15 through the intake passage, or may supply fuel directly to the combustion chamber 15.

  The valve device of the engine 1 includes a valve operating device 20 that operates an intake valve 18 and an exhaust valve 19. The valve gear 20 includes a camshaft 21 that rotates around a rotation axis A2 parallel to the rotation axis A1 of the crankshaft 4, a drive gear that rotates at the same speed in the same direction as the crankshaft 4, and the same direction as the camshaft 21. And a driven gear that rotates at the same speed and an endless chain that transmits the rotation of the drive gear to the driven gear. The rotation axis A1 of the crankshaft 4 and the rotation axis A2 of the camshaft 21 extend in the left-right direction Dlr.

  The valve gear 20 further includes an intake spring 23i that generates a force that moves the intake valve 18 toward the closed position, an exhaust spring 23e that generates a force that moves the exhaust valve 19 toward the closed position, It includes an intake rocker arm 22i that pushes the intake valve 18 toward the open position, and an exhaust rocker arm 22e that pushes the exhaust valve 19 toward the open position. The valve gear 20 may include a variable valve mechanism that changes the opening / closing timing and lift amount of the intake valve 18 and the exhaust valve 19.

  The camshaft 21, the intake rocker arm 22 i, the exhaust rocker arm 22 e, the intake spring 23 i, and the exhaust spring 23 e are disposed between the cylinder head 6 and the head cover 5. The camshaft 21 extends in a direction parallel to the rotation axis A1 of the crankshaft 4. The camshaft 21 is disposed between the intake valve 18 and the exhaust valve 19. The camshaft 21 is disposed below the intake rocker arm 22i and the exhaust rocker arm 22e.

  The power generated by the combustion of the air-fuel mixture is transmitted from the crankshaft 4 to the camshaft 21 via the drive gear, chain, and driven gear. The camshaft 21 includes an intake cam 21i that moves the intake valve 18 toward the open position by transmitting the force transmitted to the camshaft 21 to the intake rocker arm 22i. The camshaft 21 further includes an exhaust cam 21e that moves the exhaust valve 19 toward the open position by transmitting the force transmitted to the camshaft 21 to the exhaust rocker arm 22e.

  When the camshaft 21 rotates, the intake cam 21i contacts the intake rocker arm 22i, and the intake rocker arm 22i swings around the swing axis A3. As a result, the intake valve 18 is pushed toward the open position by the intake rocker arm 22i, and the intake port 14 is opened. Thereafter, the intake cam 21i is separated from the intake rocker arm 22i, and the intake valve 18 returns to the closed position by the force of the intake spring 23i. Thereby, the intake port 14 is closed.

  Similarly, when the camshaft 21 rotates, the exhaust cam 21e contacts the exhaust rocker arm 22e, and the exhaust rocker arm 22e swings around the swing axis A4. As a result, the exhaust valve 19 is pushed toward the open position by the exhaust rocker arm 22e, and the exhaust port 16 is opened. Thereafter, the exhaust cam 21e is separated from the exhaust rocker arm 22e, and the exhaust valve 19 returns to the closed position by the force of the exhaust spring 23e. As a result, the exhaust port 16 is closed.

Next, a cooling system for the engine 1 will be described.
As shown in FIG. 1, the engine 1 includes water jackets 29 and 30 that guide the coolant that cools each part of the engine 1, and a water pump 28 that sends the coolant to the water jackets 29 and 30. The water jackets 29 and 30 include a body water jacket 29 provided on the cylinder body 8 and a head water jacket 30 provided on the cylinder head 6.

  The water pump 28 is driven by power generated by the combustion of the air-fuel mixture. The water pump 28 includes an impeller that is rotationally driven by the power generated by the combustion of the air-fuel mixture, and a pump case that houses the impeller. The impeller is, for example, coaxial with the camshaft 21. The impeller rotates at the same speed in the same direction as the camshaft 21. The water pump 28 may be another type of pump such as a gear pump.

  The body water jacket 29 is disposed around the inner peripheral surface 9 a of the cylinder 9. The body water jacket 29 has a cylindrical shape continuous over the entire circumference. The head water jacket 30 is disposed above the body water jacket 29. The head water jacket 30 includes a plurality of relay ports 44 that open on the lower surface of the cylinder head 6 (see FIG. 3). The plurality of relay ports 44 are connected to the body water jacket 29 via a plurality of through holes 7 a penetrating the gasket 7.

  The coolant sent by the water pump 28 enters the head water jacket 30 through the water supply port 31 (see FIG. 4) of the head water jacket 30 and flows through the head water jacket 30. Thereafter, the coolant is discharged from the head water jacket 30 through the drain port 42 (see FIG. 4) of the head water jacket 30. A part of the coolant supplied to the head water jacket 30 is supplied to the body water jacket 29 via the plurality of relay ports 44 and returns to the head water jacket 30 via the plurality of relay ports 44. .

  When the engine 1 is mounted on a motorcycle that is an example of a saddle-ride type vehicle, the coolant discharged from the cylinder head 6 is supplied to a thermostat. When the warm-up operation of the engine 1 is completed, the coolant supplied to the thermostat is sent to the radiator and cooled by the radiator. Thereafter, the cooled coolant is supplied to the water pump 28 again. On the other hand, when the engine 1 is mounted on a marine vessel propulsion device such as an outboard motor, water outside the marine vessel propulsion device is taken into the marine vessel propulsion device by the suction force of the water pump 28, and the water jacket for the head is used. 30. Thereafter, the coolant is discharged out of the ship propulsion device.

Below, the water jacket 30 for heads is demonstrated in detail.
4 and 5 are views of the head water jacket 30 as viewed from above. FIG. 6 is a view of the head water jacket 30 as viewed obliquely from below. FIG. 7 is an enlarged view showing a part of the head water jacket 30 viewed in the direction of the arrow VII shown in FIG. In FIG. 4, the intake port 14, the exhaust port 16, and the spark plug 24 are indicated by thick two-dot chain lines. In FIG. 5, the direction in which the coolant flows is indicated by a thick arrow.

  The head water jacket 30 includes a space through which the cooling liquid passes and an inner surface that forms the space. The space of the head water jacket 30 is a space inside the cylinder head 6. The inner surface of the head water jacket 30 is the inner surface of the cylinder head 6 and is not visible from the outside of the engine 1. Therefore, in FIGS. 4 to 7, a part of the cylinder head 6 is omitted, and the appearance of the head water jacket 30 is shown. The same applies to FIG.

  The first virtual plane P1 in the following description has a space between an intake region where all of the plurality of intake outlets 14o are arranged and an exhaust region where all of the plurality of exhaust inlets 16i are arranged when viewed in the vertical direction Dud. It is a virtual plane including the center line C1 of the cylinder 9 that partitions. The second virtual plane P2 is a virtual plane including the center line C1 of the cylinder 9 that is orthogonal to the first virtual plane P1. The second virtual plane P2 divides the space into an upstream region and a downstream region.

  The first virtual plane P1 and the second virtual plane P2 partition the space into four areas. Hereinafter, a region belonging to both the upstream region and the exhaust region is referred to as an “upstream exhaust region Rue”, and a region belonging to both the downstream region and the exhaust region is referred to as a “downstream exhaust region Rde”. Further, a region belonging to both the upstream region and the intake region is referred to as “upstream intake region Rui”, and a region belonging to both the downstream region and the intake region is referred to as “downstream intake region Rdi”.

  As shown in FIG. 4, the head water jacket 30 includes a water supply port 31 into which the coolant enters, a drain port 42 through which the coolant is discharged, and a flow path 32 that extends from the water supply port 31 to the drain port 42. As shown in FIG. 6, the head water jacket 30 further includes a plurality of relay ports 44 through which the coolant flowing between the body water jacket 29 (see FIG. 1) and the head water jacket 30 passes, And a plurality of relay flow paths 43 extending from the path 32 to the plurality of relay ports 44.

  As shown in FIG. 4, the flow path 32 includes an annular outer peripheral flow path 34 disposed around the two intake outlets 14 o and the two exhaust inlets 16 i, and a center disposed inside the outer peripheral flow path 34. It includes a flow path 39, an upstream connection flow path 38 extending from the outer peripheral flow path 34 to the central flow path 39, and a downstream connection flow path 40 extending from the central flow path 39 to the outer peripheral flow path 34. The flow path 32 further includes an upstream flow path 33 extending from the water supply port 31 to the outer peripheral flow path 34 and a downstream flow path 41 extending from the outer peripheral flow path 34 to the drain outlet 42.

  As shown in FIG. 4, the water supply port 31 and the drain port 42 are arranged around the outer peripheral flow path 34. The water supply port 31 and the drain port 42 are opened at the outer surface 6 a of the cylinder head 6. The upstream flow path 33 extends from the water supply port 31 toward the center line C1 of the cylinder 9. The downstream flow path 41 extends from the drain port 42 toward the center line C1 of the cylinder 9. The water supply port 31 and the upstream flow path 33 are disposed in the upstream exhaust region Rue. The drain port 42 and the downstream flow path 41 are disposed in the downstream intake region Rdi.

  As shown in FIG. 4, the downstream flow path 41 forms a through hole 41 a that surrounds the bolt B <b> 1 that fixes the cylinder head 6 to the cylinder body 8. In other words, the bolt B1 penetrates the downstream flow path 41 in the vertical direction Dud. Therefore, the cross-sectional area of the downstream flow path 41 is reduced as compared with the case where the bolt B1 does not penetrate the downstream flow path 41. When the bolt B1 does not penetrate the downstream flow path 41, such a through hole 41a is unnecessary. The bolt hole 45 into which the bolt B1 is inserted opens at the lower surface of the cylinder head 6 (see FIG. 3).

  As shown in FIG. 4, the central flow path 39 is surrounded by the inner peripheral surface 9 a of the cylinder 9. The central flow path 39 overlaps the center line C1 of the cylinder 9. Similarly, the tip 24 a of the spark plug 24 overlaps the center line C <b> 1 of the cylinder 9. The central flow path 39 is disposed above the tip portion 24 a of the spark plug 24 and overlaps the tip portion 24 a of the spark plug 24. The tip 24 a of the spark plug 24 is disposed between the intake port 14 and the exhaust port 16.

  As shown in FIG. 4, the central flow path 39 is disposed above the two intake outlets 14o and the two exhaust inlets 16i, and overlaps the two intake outlets 14o and the two exhaust inlets 16i. At least a part of the upstream connection channel 38 is disposed in the upstream exhaust region Rue, and at least a part of the downstream connection channel 40 is disposed in the upstream intake region Rui. As shown in FIG. 4, the upstream connection flow path 38 is disposed above the exhaust inlet 16i disposed in the upstream exhaust region Rue and overlaps the exhaust inlet 16i. As shown in FIG. 4, the downstream connection flow path 40 is disposed above the intake outlet 14o disposed in the upstream intake region Rui and overlaps the intake outlet 14o.

  As shown in FIG. 4, the outer peripheral flow path 34 is disposed above the body water jacket 29 and overlaps the body water jacket 29. The plurality of relay flow paths 43 extend from the outer peripheral flow path 34 toward the body water jacket 29. At least a part of the outer peripheral flow path 34 is disposed around the inner peripheral surface 9 a of the cylinder 9. The entire outer peripheral flow path 34 may be arranged around the inner peripheral surface 9 a of the cylinder 9, or only a part of the outer peripheral flow path 34 may be arranged around the inner peripheral surface 9 a of the cylinder 9. .

  The outer peripheral flow path 34 includes an exhaust side flow path 35 disposed in the exhaust area, an intake side flow path 37 disposed in the intake area, and an intermediate flow path that connects the exhaust side flow path 35 and the intake side flow path 37 to each other. 36. The intermediate flow path 36 is disposed in the downstream region. As shown in FIG. 4, the intermediate flow path 36 is disposed below the spark plug 24 and overlaps the spark plug 24. As shown in FIG. 4, the exhaust side flow path 35 is disposed below the exhaust port 16 and overlaps the exhaust port 16. As shown in FIG. 4, the intake-side flow path 37 is disposed below the intake port 14 and overlaps the intake port 14.

  As shown in FIG. 5, the outer peripheral surface 35 a of the exhaust side flow path 35 includes an arc portion 51 that is coaxial with the center line C <b> 1 of the cylinder 9. The outer peripheral surface 36 a of the intermediate flow path 36 includes an inward convex part 52 that protrudes from the arc part 51 of the exhaust side flow path 35 toward the center line C <b> 1 of the cylinder 9. The inward convex portion 52 protrudes toward the center line of the head water jacket 30. As shown in FIG. 4, the inward convex portion 52 is disposed below the spark plug 24 and overlaps the spark plug 24. Since the inward convex portion 52 is provided, the cross-sectional area of the intermediate flow path 36 is reduced as compared with the case where the outer peripheral surface 36a of the intermediate flow path 36 has an arc shape coaxial with the center line C1 of the cylinder 9. ing.

  As shown in FIG. 6, the exhaust side flow path 35 includes an upper convex portion 53 protruding upward from the lower surface of the exhaust side flow path 35. The upper protrusion 53 protrudes upward from the lower surface of the exhaust side flow path 35 and protrudes from the outer peripheral surface 35a of the exhaust side flow path 35 toward the center line C1 of the cylinder 9. The upper convex portion 53 is disposed below the upper surface of the exhaust side flow path 35. As shown in FIG. 5, when the head water jacket 30 is viewed from above, the upper convex portion 53 is hidden on the upper surface of the exhaust side flow path 35.

  As shown in FIG. 7, the upper convex portion 53 is disposed between the plurality of relay flow paths 43 in the circumferential direction of the cylinder 9 (left-right direction in FIG. 7). The upper convex portion 53 guides the coolant in the exhaust side passage 35 upward toward the center line C <b> 1 of the cylinder 9. The flow of the coolant flowing downstream toward the relay flow path 43 is rectified in a direction away from the plurality of relay flow paths 43. Thereby, the resistance added to the coolant can be reduced, and the decrease in the flow rate of the coolant can be reduced.

FIG. 8 is a view of the upstream connection channel 38, the central channel 39, and the downstream connection channel 40 of the head water jacket 30 as viewed from above. FIG. 9 is a cross-sectional view showing a vertical cross section along the line IX-IX shown in FIG. FIG. 10 is a cross-sectional view showing a vertical cross section along the line XX shown in FIG.
As shown in FIG. 8, the upstream connection channel 38 and the downstream connection channel 40 are separated from each other in the front-rear direction Dfr. The upstream connection channel 38, the central channel 39, and the downstream connection channel 40 are formed by forming a mountain-shaped convex portion 54 extending toward the central channel 39 between the upstream connection channel 38 and the downstream connection channel 40. Yes. The width W1 of the tip 54a of the mountain-shaped protrusion 54 in the front-rear direction Dfr is smaller than the width Wu of the upstream connection flow path 38 in the front-rear direction Dfr. The length Llr of the central channel 39 in the left-right direction Dlr is smaller than the length Lfr of the central channel 39 in the front-rear direction Dfr and larger than the width Wu of the upstream connection channel 38 in the front-rear direction Dfr.

  FIG. 9 shows a vertical cross section of the cylinder head 6 and the head water jacket 30. The material of the cylinder head 6, that is, the cylinder head 6 before being subjected to machining such as cutting is manufactured by casting, for example. In this case, a sand core having the same shape as the head water jacket 30 is placed inside the mold, and then the molten metal is poured into the mold. When the metal hardens and the material of the cylinder head 6 is formed, the collapsed sand core, that is, the sand particles are removed from the material of the cylinder head 6. As a result, a cavity having the same shape as the head water jacket 30 is formed in the material of the cylinder head 6.

  As shown in FIG. 9, the cylinder head 6 includes a gas vent hole 55 for discharging sand particles in the head water jacket 30. The gas vent hole 55 extends upward from the central flow path 39. The gas vent hole 55 is opened at the outer surface 6 a of the cylinder head 6 and the inner surface of the head water jacket 30. The gas vent hole 55 is closed by a cylindrical plug 56 attached to the cylinder head 6. The plug 56 is fixed to the cylinder head 6 by a male screw provided on the outer peripheral surface of the plug 56 and a female screw provided on the inner peripheral surface of the gas vent hole 55.

  FIG. 9 shows an example in which the circular bottom surface 56 a of the plug 56 is arranged on the same plane as the lower end of the gas vent hole 55. The bottom surface 56 a of the plug 56 may be arranged at a height different from the lower end of the gas vent hole 55. When the bottom surface 56 a of the plug 56 protrudes downward from the lower end of the gas vent hole 55, the cross-sectional area of the head water jacket 30 decreases below the plug 56. Thereby, the flow rate of the cooling liquid can be increased, or a part of the cooling liquid flowing toward the plug 56 can be bypassed around the plug 56.

  As shown in FIG. 8, the gas vent hole 55 overlaps the spark plug 24. The center line C2 of the gas vent hole 55 is parallel to the center line C1 of the cylinder 9. The shortest distance D2 from the center line C1 of the cylinder 9 to the center line C2 of the gas vent hole 55 is shorter than the diameter Φ2 of the gas vent hole 55. FIG. 8 shows an example in which the center line C <b> 1 of the cylinder 9 does not overlap the gas vent hole 55 and is arranged around the gas vent hole 55. The center line C <b> 1 of the cylinder 9 may overlap with the gas vent hole 55. That is, the distance D2 from the center line C1 of the cylinder 9 to the center line C2 of the gas vent hole 55 may be smaller than the radius of the gas vent hole 55.

  FIG. 10 shows a vertical cross section of the upstream connection flow path 38 and the downstream connection flow path 40 along a cutting plane parallel to the second virtual plane P2. The width Wu of the upstream connection channel 38 in the front-rear direction Dfr increases continuously or stepwise from the lower end of the upstream connection channel 38 to the upper end of the upstream connection channel 38. Similarly, the width Wd of the downstream connection channel 40 in the front-rear direction Dfr increases continuously or stepwise from the lower end of the downstream connection channel 40 to the upper end of the downstream connection channel 40.

  The maximum value of the width Wu of the upstream connection flow path 38 in the front-rear direction Dfr is smaller than the maximum value of the width Wd of the downstream connection flow path 40 in the front-rear direction Dfr. The maximum value of the length Lu (height) of the upstream connection channel 38 in the vertical direction Dud is smaller than the length Ld of the downstream connection channel 40 in the vertical direction Dud. The cross-sectional area of the upstream connection channel 38 is smaller than the cross-sectional area of the downstream connection channel 40. The coolant flows from the upstream connection flow path 38 to the central flow path 39 and from the central flow path 39 to the downstream connection flow path 40. Since the cross-sectional area of the upstream connection channel 38 is small, a fast coolant flow is formed in the upstream connection channel 38. Therefore, the coolant having a high flow rate flows from the upstream connection channel 38 to the central channel 39.

  As described above, in the first embodiment, the coolant flowing through the head water jacket 30 cools each part of the cylinder head 6, in particular, the exhaust port 16 and the plug hole 25 and parts in the vicinity thereof. The central flow path 39 of the head water jacket 30 overlaps the spark plug 24 when viewed in the vertical direction Dud. Therefore, the central flow path 39 is disposed near the distal end portion 24 a of the spark plug 24. Therefore, the tip end portion 24 a of the spark plug 24 is mainly cooled by the coolant flowing through the central flow path 39.

  The cross-sectional area of the upstream connection channel 38 is smaller than the cross-sectional area of the downstream connection channel 40. Since the cross-sectional area of the upstream connection channel 38 is small, the flow of the coolant in the upstream connection channel 38 is fast. Since the coolant having a high flow rate flows from the upstream connection channel 38 to the central channel 39, the coolant flows in the central channel 39 quickly. When the coolant flow is fast, heat is released efficiently. Therefore, the temperature around the plug, that is, the portion around the plug hole 25 on the inner surface of the combustion chamber 15 can be effectively reduced. In addition, the temperature of the portion between the exhaust sheets, that is, the portion between the exhaust inlets 16 i on the inner surface of the combustion chamber 15 can be effectively reduced.

  Furthermore, both the upstream connection flow path 38 and the downstream connection flow path 40 are not thin, but only the upstream connection flow path 38 is thin. When casting the material of the cylinder head 6, a sand core having the same shape as the head water jacket 30 is used. If both the upstream connection flow path 38 and the downstream connection flow path 40 are thin, the strength of the sand core is reduced. Therefore, by narrowing only the upstream connection flow path 38, the cooling performance of the engine 1 can be enhanced while suppressing a decrease in the strength of the sand core.

  In the first embodiment, an inward convex portion 52 that protrudes toward the center line of the head water jacket 30 is provided on the outer peripheral surface of the outer peripheral flow path 34. The inward convex portion 52 of the outer peripheral flow path 34 protrudes from the arc portion 51 coaxial with the inner peripheral surface 9a of the cylinder 9 toward the center line C1 of the cylinder 9. In other words, the cross-sectional area of the outer peripheral flow path 34 is reduced as compared with the case where the inward convex portion 52 is not provided. Therefore, a fast flow of the coolant is formed on the inward convex portion 52 of the outer peripheral flow path 34. The inward convex portion 52 of the outer peripheral flow path 34 overlaps with the spark plug 24 when viewed in the vertical direction Dud, and is disposed near the spark plug 24. Therefore, the spark plug 24 and its vicinity can be efficiently cooled.

  In the first embodiment, the cylinder head 6 is provided with a gas vent hole 55 for discharging the sand core for forming the head water jacket 30 when the material of the cylinder head 6 is cast. It is peeling off. The gas vent hole 55 is disposed near the center line C1 of the cylinder 9, and the distance D2 from the center line C2 of the gas vent hole 55 to the center line C1 of the cylinder 9 is larger than the diameter Φ2 of the gas vent hole 55. small.

  The gas vent hole 55 extends upward from the central flow path 39 that cools the spark plug 24 and the vicinity thereof. The front end surface 39a (see FIG. 4) of the central flow path 39 is usually disposed near the spark plug 24. When the gas vent hole 55 is far from the center line C1 of the cylinder 9, the width of the central flow path 39 increases, and the flow rate of the coolant in the central flow path 39 decreases. On the other hand, if the gas vent hole 55 is brought close to the center line C1 of the cylinder 9, the central flow path 39 can be narrowed, and the flow rate of the coolant in the central flow path 39 can be increased. Thereby, the spark plug 24 and the vicinity thereof can be efficiently cooled.

  In the first embodiment, a mountain-shaped convex portion 54 extending toward the central flow path 39 when viewed in the vertical direction Dud is disposed between the upstream connection flow path 38 and the downstream connection flow path 40. The tip 54 a of the chevron convex portion 54 is formed by the upstream connection channel 38, the central channel 39, and the downstream connection channel 40. The tip 54a of the chevron convex portion 54 enters the central flow path 39, and the central flow path 39 is narrowed in the left-right direction Dlr. The length Llr of the central flow path 39 in the left-right direction Dlr is smaller than the length Lfr of the central flow path 39 in the front-rear direction Dfr. Thus, since the central flow path 39 is thin in the left-right direction Dlr, the flow rate of the coolant in the central flow path 39 can be increased.

  In the first embodiment, the length Llr of the central flow path 39 in the left-right direction Dlr is not only smaller than the length Lfr of the central flow path 39 in the front-rear direction Dfr, but is also upstream when viewed in the vertical direction Dud. It is larger than the width Wu of the connection channel 38. If the central flow path 39 is too thin, the strength of the sand core forming the head water jacket 30 is reduced. Therefore, the cooling performance of the engine 1 can be enhanced while suppressing a decrease in the strength of the sand core.

Second Embodiment In FIGS. 11 to 15 below, the same components as those shown in FIGS. 1 to 10 are denoted by the same reference numerals as those in FIG. 1 and the description thereof is omitted.
FIG. 11 is a plan view of the head water jacket 30 according to the second embodiment of the present invention as seen from above. FIG. 12 is a view of the central flow path 39 of the head water jacket 30 as viewed obliquely from above. FIG. 13 is a cross-sectional view showing a vertical cross section along the second virtual plane P2.

  As shown in FIG. 12, the central flow path 39 includes a lower protrusion 61 that protrudes downward from the upper surface of the central flow path 39. As shown in FIG. 13, the downward convex portion 61 has a U-shaped vertical section that opens upward. The downward convex portion 61 includes a pair of side surfaces 61b disposed in the exhaust region and the intake region, respectively, and a top surface 61a disposed between the lower ends of the pair of side surfaces 61b. As shown in FIG. 12, the central flow path 39 includes a front end surface 39 a located toward the spark plug 24. The tip surface 39a extends downward from the tip edge of the top surface 61a (the edge located at the spark plug 24).

  As shown in FIG. 11, the upstream connection flow path 38 and the downstream connection flow path 40 extend from the outer peripheral flow path 34 toward the center line C <b> 1 of the cylinder 9. The center line Cu of the upstream connection flow path 38 passes through the center line C1 of the cylinder 9. Similarly, the center line Cd of the downstream connection flow path 40 passes through the center line C1 of the cylinder 9. The center line Cu of the upstream connection flow path 38 and the center line Cd of the downstream connection flow path 40 are inclined in directions opposite to each other with respect to the first virtual plane P1. The absolute value of the inclination angle θu of the center line Cu of the upstream connection flow path 38 with respect to the first virtual plane P1 is larger than the absolute value of the inclination angle θd of the center line Cd of the downstream connection flow path 40 with respect to the first virtual plane P1.

  14 is a cross-sectional view showing a vertical cross section taken along the line XIV-XIV shown in FIG. 15 is a cross-sectional view showing a vertical cross section taken along line XV-XV shown in FIG. The distance from the center line C1 of the cylinder 9 to the cross section shown in FIG. 14 is equal to the distance from the center line C1 of the cylinder 9 to the cross section shown in FIG. Further, the scale of the cross section shown in FIG. 14 is equal to the scale of the cross section shown in FIG. Therefore, the cross-sectional area of the upstream connection channel 38 is smaller than the cross-sectional area of the downstream connection channel 40. Thereby, the flow rate of the coolant in the upstream connection channel 38 can be increased, and the coolant having a high flow rate can be sent from the upstream connection channel 38 to the central channel 39.

  In 2nd Embodiment, in addition to the effect which concerns on 1st Embodiment, there can exist the following effect. Specifically, in the second embodiment, a lower convex portion 61 that protrudes toward the center line of the head water jacket 30 is provided in the central flow path 39. The central flow path 39 protrudes downward from the upper surface of the central flow path 39. Therefore, compared with the case where the downward convex part 61 is not provided, the cross-sectional area of the center flow path 39 reduces. Thereby, the flow rate of the coolant in the central flow path 39 can be increased, and the cooling performance can be improved.

  Further, the pair of side surfaces 61b of the downward convex portion 61 are disposed in the exhaust region and the intake region, respectively. In this case, in the case where the pair of side surfaces 61b are not provided, that is, as compared with the case where the central flow path 39 is simply thinned in the vertical direction Dud, the portion near the exhaust port 16 and the intake port 14 and the head water jacket. The reduction in contact area with 30 can be reduced.

Other Embodiments The present invention is not limited to the contents of the above-described embodiments, and various modifications can be made.
For example, the number of intake valves 18 and exhaust valves 19 corresponding to the same cylinder 9 may be four or more. For example, three intake valves 18 and two exhaust valves 19 may be provided in the same cylinder 9.

One of the intake rocker arm 22i and the exhaust rocker arm 22e may be omitted. In this case, the intake valve 18 or the exhaust valve 19 may be pushed by the intake cam 21i or the exhaust cam 21e.
The water supply port 31 and the upstream flow path 33 may be omitted. Alternatively, the drain port 42 and the downstream flow path 41 may be omitted. In these cases, the plurality of relay ports 44 may function as the water supply port 31 or the drain port 42. For example, the coolant sent by the water pump 28 may be supplied to the head water jacket 30 via a plurality of relay ports 44 as the water supply ports 31.

If the cross-sectional area of the upstream connection flow path 38 is smaller than the cross-sectional area of the downstream connection flow path 40, the width Wu of the upstream connection flow path 38 may be equal to the width Wd of the downstream connection flow path 40, or the downstream connection flow It may be larger than the width Wd of the path 40.
Similarly, if the cross-sectional area of the upstream connection flow path 38 is smaller than the cross-sectional area of the downstream connection flow path 40, the length Lu of the upstream connection flow path 38 in the vertical direction Dud is equal to the downstream connection flow path in the vertical direction Dud. It may be equal to the length Ld of 40, or may be larger than the length Ld of the downstream connection flow path 40 in the vertical direction Dud.

The width Wu of the upstream connection channel 38 may be constant from the upper end of the upstream connection channel 38 to the lower end of the upstream connection channel 38. The same applies to the downstream connection flow path 40.
The inward convex portion 52 may not be provided in the intermediate flow path 36 of the outer peripheral flow path 34, and the outer peripheral surface 36 a of the intermediate flow path 36 may have an arc shape coaxial with the center line C <b> 1 of the cylinder 9.
The distance D2 from the center line C2 of the gas vent hole 55 to the center line C1 of the cylinder 9 may be equal to the diameter Φ2 of the gas vent hole 55 or may be larger than the diameter Φ2 of the gas vent hole 55.

The length Llr of the central channel 39 in the left-right direction Dlr may be equal to the length Lfr of the central channel 39 in the front-rear direction Dfr, or is longer than the length Lfr of the central channel 39 in the front-rear direction Dfr. It can be large.
The width W1 of the tip 54a of the mountain-shaped convex portion 54 in the front-rear direction Dfr may be equal to the width Wd of the downstream connection channel 40 or may be larger than the width Wd of the downstream connection channel 40.

Two or more of all the aforementioned configurations may be combined.
In addition, various design changes can be made within the scope of matters described in the claims.

1: Engine 2: Piston 6: Cylinder head 6a: Cylinder head outer surface 8: Cylinder body 9: Cylinder 9a: Cylinder inner peripheral surface 14: Intake port 14i: Intake inlet 14o: Intake outlet 15: Combustion chamber 16: Exhaust port 16i: Exhaust inlet 16o: Exhaust outlet 18: Intake valve 19: Exhaust valve 21: Cam shaft 21i: Intake cam 21e: Exhaust cam 22i: Intake rocker arm 22e: Exhaust rocker arm 23i: Intake spring 23e: Exhaust Spring 24: Spark plug 24a: Spark plug tip 24c: Center electrode 24b: Side electrode 25: Plug hole 25i: Plug inlet 25o: Plug outlet 28: Water pump 29: Body water jacket 30: Head water jacket 31: Water supply port 32: Channel 33: Upstream channel 34: Outer channel 35: Exhaust side channel 35a: Outer channel outer surface 36: Intermediate channel 36a: Intermediate channel outer surface 37: Intake channel 38: Upstream connection flow path 39: Central flow path 39a: Front end surface 40 of the central flow path: Downstream connection flow path 41: Downstream flow path 42: Drainage port 43: Relay flow path 44: Relay port 51: Arc portion 52: Inside Direction convex part 53: Upward convex part 54: Angle convex part 54a: Tip part 55 of the convex part: Gas vent hole 56: Plug 61: Down convex part 61a: Top face 61b: Side face C1: Center line C2 of cylinder: Center line D2 of the vent hole: Distance from the center line of the cylinder to the center line of the vent hole Lfr: Length of the central channel in the front-rear direction Llr: Length of the central channel in the left-right direction Ld: Vertical direction Length Lu of the downstream connection flow path to the upstream connection flow path in the vertical direction Length P1: first virtual plane P2: second virtual plane Wd: width of the downstream connecting channel Wu: width of the upstream connecting channel .phi.2: diameter of vent holes

Claims (8)

A cylinder body including a cylinder having a center line extending in the vertical direction;
A piston that reciprocates up and down in the cylinder;
A cylinder head disposed at an upper end portion of the cylinder body and forming a combustion chamber in which an air-fuel mixture burns together with the cylinder and the piston;
A spark plug attached to the cylinder head and combusting the air-fuel mixture in the combustion chamber;
A valve device for controlling intake air supplied to the combustion chamber and exhaust gas exhausted from the combustion chamber;
The cylinder head includes an intake port that includes a plurality of intake outlets that open on the inner surface of the combustion chamber, an exhaust port that includes a plurality of exhaust inlets that opens on the inner surface of the combustion chamber, and a plug that opens on the inner surface of the combustion chamber Including a plug hole including an outlet and a water jacket for a head for guiding a coolant;
The spark plug is inserted into the plug hole and inclined obliquely with respect to the center line of the cylinder,
The valve device is
A camshaft rotating around a rotation axis extending in the left-right direction;
A plurality of intake valves that respectively open and close the plurality of intake outlets according to rotation of the camshaft;
A plurality of exhaust valves that respectively open and close the plurality of exhaust inlets according to rotation of the camshaft,
The water jacket for the head is
An opening on the outer surface of the cylinder head, and a water supply port into which a coolant enters,
A drain port that opens at the outer surface of the cylinder head and that discharges the coolant that has flowed into the water supply port;
An annular outer peripheral flow path that is disposed around the plurality of intake outlets and the plurality of exhaust inlets when viewed in the vertical direction and guides the coolant flowing into the water supply port toward the drainage port; ,
A central flow path that is disposed inward of the outer peripheral flow path when viewed in the vertical direction and overlaps the spark plug when viewed in the vertical direction;
An upstream connection channel extending from the outer peripheral channel to the central channel and guiding the coolant from the outer peripheral channel to the central channel;
The coolant extending from the central flow path to the outer peripheral flow path, away from the upstream connection flow path, and guided to the central flow path by the upstream connection flow path from the central flow path to the outer peripheral flow path. A downstream connection flow path that guides to
The water-cooled SOHC engine, wherein a cross-sectional area of the upstream connection channel is smaller than a cross-sectional area of the downstream connection channel.   The water-cooled SOHC engine according to claim 1, wherein a width of the upstream connection channel when viewed in the vertical direction is smaller than a width of the downstream connection channel when viewed in the vertical direction.   The water-cooled SOHC engine according to claim 1 or 2, wherein a length of the upstream connection channel in the vertical direction is smaller than a length of the downstream connection channel in the vertical direction.   The outer peripheral surface of the outer peripheral flow path is an arcuate arc portion coaxial with the inner peripheral surface of the cylinder when viewed in the vertical direction, and from the arc portion toward the center line of the cylinder when viewed in the vertical direction. The water-cooled SOHC engine according to any one of claims 1 to 3, further comprising an inward projecting portion that overlaps the spark plug when viewed in a vertical direction. The cylinder head further includes a vent hole extending upward from the central flow path,
The water-cooled SOHC engine further includes a plug that closes the vent hole,
The water-cooled SOHC engine according to any one of claims 1 to 4, wherein a distance from a center line of the gas vent hole to a center line of the cylinder is smaller than a diameter of the gas vent hole. The upstream connection flow channel, the central flow channel, and the downstream connection flow channel have a chevron that extends toward the central flow channel when viewed in the vertical direction between the upstream connection flow channel and the downstream connection flow channel. Formed into
The length of the central flow path in the left-right direction is smaller than the length of the central flow path in the front-rear direction orthogonal to both the up-down direction and the left-right direction, according to any one of claims 1 to 5. Water-cooled SOHC engine.   The water-cooled SOHC engine according to claim 6, wherein a length of the central flow path in the left-right direction is larger than a width of the upstream connection flow path when viewed in the vertical direction. The central flow path includes a lower convex portion that protrudes downward from the upper surface of the central flow path,
The lower projection includes a pair of side surfaces respectively disposed in the exhaust region and the intake region, and a top surface disposed between lower ends of the pair of side surfaces. The water-cooled SOHC engine described in 1.

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