Internal combustion engine

Abstract

To effectively cool an ignition plug and an exhaust valve.SOLUTION: An internal combustion engine 10 comprises a cylinder, a spark plug, an intake passage 12, an exhaust passage 13, a water injection valve, an intake valve 14, and an exhaust valve 15. The intake valve 14 has a stem part 21 and an umbrella part 22 connected to the tip of the stem part 21. The umbrella part 22 has a guide portion 23 located on an upper surface 22A. The guide portion 23 has a specific tangent line ST that intersects with one or more selected from a portion of the spark plug located within the cylinder when the intake valve 14 is in a fully opened state, and a portion of the exhaust valve 15 located within the cylinder in a closed state. When drawing tangent lines in contact with the guide portion 23 on a virtual cross section that is parallel to the central axis C1 of the umbrella part 22 and includes the guide portion 23, and defining, among angles formed by the central axis C1 and the tangent lines, an angle on the side where the contact point of the tangent lines exists and on the intake passage 12 side as a specific angle SA, the specific tangent line ST is the tangent line on which the specific angle SA becomes minimum among the tangent lines.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an internal combustion engine. [Background technology]

[0002] The internal combustion engine described in Patent Document 1 includes a cylinder, an intake passage, and a water injection valve. The cylinder is a space where a mixture of intake air and fuel is burned. The intake passage is connected to the cylinder. The water injection valve is located within the intake passage. The water injection valve injects water into the cylinder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-95899 Summary of the Invention [Problem to be solved by the invention]

[0004] An internal combustion engine such as that described in Patent Document 1 has an exhaust passage for discharging exhaust gas. The internal combustion engine also has an exhaust valve and a spark plug. The exhaust valve opens and closes the end of the exhaust passage on the cylinder side. The spark plug ignites the air-fuel mixture by spark discharge.

[0005] In the internal combustion engine described in Patent Document 1, water is injected into the cylinders by a water injection valve. However, in the internal combustion engine described in Patent Document 1, the water injected by the water injection valve does not easily adhere to the spark plugs and exhaust valves. As a result, the spark plugs and exhaust plugs cannot be cooled efficiently. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides an engine including a cylinder, an ignition plug whose tip is located within the cylinder, an intake passage connected to the cylinder, an exhaust passage connected to the cylinder, a water injection valve located within the intake passage and injecting water toward the intake passage, an intake valve capable of opening and closing the end of the intake passage on the cylinder side, and an exhaust valve capable of opening and closing the end of the exhaust passage on the cylinder side, the water injection valve injects water at least when the intake valve is fully open; The intake valve has a rod-shaped stem and an umbrella portion connected to the tip of the stem and opening and closing the intake passage on the cylinder side. When the outer surface of the umbrella portion facing the intake passage is defined as the upper surface, the umbrella portion has a guide portion located on the upper surface. The guide portion has a specific tangent that intersects with one or more selected from the portion of the ignition plug that is located inside the cylinder when the intake valve is fully open and the portion of the exhaust valve that is located inside the cylinder when the intake valve is closed. When a tangent line is drawn that is tangent to the guide portion on an imaginary cross section that is parallel to the central axis of the umbrella portion and includes the guide portion, the angle formed by the central axis and the tangent line is defined as the angle on the side where the tangent line contacts and on the intake passage side. The specific tangent line is the tangent line that makes the specific angle the smallest among the tangent lines.

[0007] According to the above configuration, water injected from the water injection valve is guided from the intake passage into the cylinder and collides with the umbrella portion. The water that collides with the umbrella portion moves along the guide portion. The water moving along the guide portion then separates from the umbrella portion at a position where the specific angle is smallest and splashes along the specific tangent. In other words, according to the above configuration, the injected water is more likely to collide with the exhaust valve or spark plug that intersects the specific tangent. By guiding the water toward the exhaust valve and the spark plug in this way, these components can be efficiently cooled. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an internal combustion engine. [Figure 2] FIG. 2 is a partial cross-sectional view showing a cylinder of an internal combustion engine and its surrounding area. [Figure 3]FIG. 3 is an enlarged partial cross-sectional view of FIG. [Figure 4] FIG. 4 is a partial cross-sectional view showing a cylinder and its surrounding area of ​​an internal combustion engine according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of an internal combustion engine will be described below with reference to the drawings. <About internal combustion engines> As shown in FIG. 1, the internal combustion engine 10 includes four cylinders 11, an intake passage 12, and an exhaust passage 13.

[0010] The cylinder 11 is a space for burning a mixture of fuel and intake air. The cylinder 11 is approximately cylindrical. Note that FIG. 1 shows only one of the four cylinders 11. Each cylinder 11 has four openings. When viewed from above the axis of the cylinder 11, the four openings are arranged in two rows and two columns.

[0011] The intake passage 12 is a passage through which intake air flows. The intake passage 12 branches into eight passages near its downstream end. Two of the eight branched intake passages 12 are connected to each cylinder 11. That is, each branched intake passage 12 is connected to two of the four openings in each cylinder 11.

[0012] The exhaust passage 13 is a passage through which exhaust gas flows. The exhaust passage 13 branches into eight passages near its upstream end. Two of the eight branched exhaust passages 13 are connected to each cylinder 11. That is, the branched exhaust passages 13 are connected to two of the four openings in each cylinder 11 that are not connected to the intake passage 12.

[0013] The internal combustion engine 10 has eight intake valves 14 and eight exhaust valves 15. Note that only two of the eight intake valves 14 and only two of the eight exhaust valves 15 are shown in FIG.

[0014] Two intake valves 14 are provided for each cylinder 11. Each intake valve 14 is located at a connection point between each intake passage 12 and each cylinder 11. Each intake valve 14 can open and close each opening of each cylinder 11 on the intake passage 12 side.

[0015] As shown in Figures 2 and 3, the intake valve 14 has a stem 21 and an umbrella portion 22. The stem 21 is rod-shaped. The umbrella portion 22 is connected to the tip of the stem 21. When viewed in a direction along the central axis C1 of the stem 21, the umbrella portion 22 is circular. The central axis of the umbrella portion 22 coincides with the central axis C1 of the stem 21. The specific shape of the umbrella portion 22 will be described later.

[0016] The shaft 21 is connected to a valve mechanism (not shown). Power from the valve mechanism allows the intake valve 14 to move in a direction along the central axis C1 of the shaft 21. In response to this movement, the head 22 of the intake valve 14 opens and closes the intake passage 12 on the cylinder 11 side.

[0017] Within the movable range of the intake valve 14, when the intake valve 14 is positioned furthest away from the cylinder 11, the umbrella portion 22 closes the opening of the cylinder 11 on the intake passage 12 side. This state in which the umbrella portion 22 closes the opening of the cylinder 11 on the intake passage 12 side is referred to as the closed state of the intake valve 14.

[0018] Furthermore, when the intake valve 14 is positioned closest to the cylinder 11 within its movable range, the umbrella portion 22 opens the opening of the cylinder 11 on the intake passage 12 side to its maximum. This state in which the umbrella portion 22 opens the opening of the cylinder 11 on the intake passage 12 side to its maximum is referred to as the fully open state of the intake valve 14.

[0019] Two exhaust valves 15 are provided for each cylinder 11. Each exhaust valve 15 is located at a connection point between each exhaust passage 13 and each cylinder 11. Each exhaust valve 15 can open and close each opening on the exhaust passage 13 side of each cylinder 11.

[0020] The exhaust valve 15 has a stem portion 31 and an umbrella portion 32. The stem portion 31 is rod-shaped. The umbrella portion 32 is connected to the tip of the stem portion 31. When viewed in a direction along the central axis C2 of the stem portion 31, the umbrella portion 32 is circular.

[0021] The shaft 31 is connected to a valve train (not shown). Power from the valve train allows the exhaust valve 15 to move in a direction along the central axis C2 of the shaft 31. In response to this movement, the head 32 of the exhaust valve 15 opens and closes the exhaust passage 13 on the cylinder 11 side.

[0022] When the exhaust valve 15 is positioned at the farthest side from the cylinder 11 within the movable range of the exhaust valve 15, the umbrella portion 32 closes the opening of the cylinder 11 on the exhaust passage 13 side. The state in which the umbrella portion 32 closes the opening of the cylinder 11 on the exhaust passage 13 side in this manner is referred to as the closed state of the exhaust valve 15.

[0023] Furthermore, when the exhaust valve 15 is positioned closest to the cylinder 11 within its movable range, the umbrella portion 32 opens the opening of the cylinder 11 on the exhaust passage 13 side to its maximum. The state in which the umbrella portion 32 opens the opening of the cylinder 11 on the exhaust passage 13 side to its maximum in this manner is referred to as the fully open state of the exhaust valve 15.

[0024] As shown in FIG. 1, the internal combustion engine 10 has four spark plugs 16. That is, one spark plug 16 is provided for each cylinder 11. Note that FIG. 1 illustrates only one of the four spark plugs 16. Also, FIG. 1 illustrates only the vicinity of the tip of each spark plug 16. The spark plug 16 is located inside the four openings of each cylinder 11. Most of the spark plug 16 is buried inside the internal combustion engine 10. The tip of the spark plug 16 is located inside the cylinder 11. The spark plug 16 ignites the air-fuel mixture in the cylinder 11.

[0025] As shown in FIG. 2, the internal combustion engine 10 has four water injectors 17. That is, one water injector 17 is provided for each cylinder 11. Note that FIG. 2 shows only one of the four water injectors 17. Also, in FIG. 2, the water injector 17 is schematically shown near the downstream end of the intake passage 12. Each water injector 17 is connected to a water tank (not shown). The water injectors 17 receive a supply of water from the water tank.

[0026] Each water injector 17 is located in the intake passage 12. Each water injector 17 injects water toward the intake passage 12. The water injected from the water injector 17 flows into the cylinder 11 together with the intake air. In addition, the water injected from the water injector 17 flows into each of the two intake passages 12 connected to the same cylinder 11.

[0027] <Intake valve head shape> The intake valves 14 will be described below. Note that the following description will be given for one cylinder 11. Furthermore, of the two intake valves 14 corresponding to one cylinder 11, one intake valve 14 will be described for that cylinder 11.

[0028] 2, of the outer surfaces of the umbrella portion 22 of the intake valve 14, the surface facing the intake passage 12 is referred to as an upper surface 22A. The umbrella portion 22 has a guide portion 23 located on the upper surface 22A. 2, the cross section is taken along a virtual cross section including the internal combustion engine 10, the central axis C1 of the shaft portion 21 of the intake valve 14, and the central axis C2 of the shaft portion 31 of the exhaust valve 15. On this virtual cross section, the guide portion 23 is a portion where the upper surface 22A is convex toward the cylinder 11. Also, on the virtual cross section, the bottom surface of the guide portion 23 is arc-shaped and convex toward the cylinder 11.

[0029] As shown in Fig. 1, when viewed in a direction along the central axis C1 of the shaft portion 21, the guide portion 23 has an annular shape centered on the central axis C1. As shown in Fig. 2, when the dimension of the guide portion 23 in a direction perpendicular to the central axis C1 is defined as a width dimension L2, the width dimension L2 of the guide portion 23 is constant over 360 degrees around the central axis C1. Therefore, the maximum dimension of the guide portion 23 in the direction perpendicular to the central axis C1 is equal to the width dimension L2.

[0030] As shown in FIG. 3, in this embodiment, guide portion 23 is continuous with the outer surface of shaft portion 21. In this embodiment, the outer surface of shaft portion 21 is a straight line on the virtual cross section. Therefore, on the virtual cross section, the point where the straight line of shaft portion 21 intersects with the arc of guide portion 23 is the boundary between shaft portion 21 and guide portion 23. Also, as described above, guide portion 23 is annular. Therefore, on the virtual cross section, guide portions 23 are located on both sides of shaft portion 21 in the direction perpendicular to central axis C1.

[0031] As shown in FIG. 2, the dimension of the umbrella portion 22 in a direction perpendicular to the central axis C1 is defined as the outer diameter L1. The width dimension L2 of the guide portion 23 is equal to or greater than one-fourth of the outer diameter L1 of the umbrella portion 22. Specifically, the width dimension L2 of the guide portion 23 is approximately one-fourth of the outer diameter L1 of the umbrella portion 22. As described above, the guide portions 23 are located on both sides of the shaft portion 21 on the virtual cross section. Therefore, when the two guide portions 23 are combined on the virtual cross section, the two guide portions 23 occupy approximately one-half of the outer diameter L1 of the umbrella portion 22 on the virtual cross section.

[0032] As shown in FIG. 3, the induction portion 23 has a specific tangent line ST. The specific tangent line ST will be described. Suppose a tangent line is drawn on an imaginary cross section that is tangent to the induction portion 23. Of the angles formed by the central axis C1 and the tangent line drawn to the induction portion 23, the angle on the side where the tangent lines contact and on the intake passage 12 side is defined as a specific angle SA. In other words, the specific angle SA is the angle on the upper right side of the angles formed by the central axis C1 and the tangent line drawn to the induction portion 23 in FIG. 3. Of the tangent lines drawn as described above, the specific tangent line ST is the tangent line that has the smallest specific angle SA.

[0033] In this embodiment, the point of contact of the specific tangent ST with the guide portion 23 is the outer end of the guide portion 23 on the imaginary cross section. When the intake valve 14 is fully open, the specific tangent ST intersects with a portion of the exhaust valve 15 that is located inside the cylinder 11 when the exhaust valve 14 is closed. Specifically, the specific tangent ST intersects with a surface of the head portion 32 of the exhaust valve 15 that faces the cylinder 11. The specific tangent ST intersects with the head portion 32 of the exhaust valve 15 on the intake valve 14 side when viewed from the stem portion 31.

[0034] Furthermore, the specific tangent line ST intersects with the portion of the head portion 32 of the exhaust valve 15 that is located inside the cylinder 11 not only when the intake valve 14 is in the fully open state but also when the intake valve 14 is in a certain range of opening degrees including the fully open state. Specifically, when the closed state is defined as 0% opening and the fully open state is defined as 100% opening, the specific tangent line ST intersects with the portion of the exhaust valve 15 that is located inside the cylinder 11 when the intake valve 14 is in the opening degree range of approximately 75% to 100%.

[0035] <Operation of this embodiment> Depending on the operating state of the internal combustion engine 10, the water injector 17 injects water into the intake passage 12. The injected water passes through the gap between the intake valve 14 and the intake passage 12 and flows into the cylinder 11. The water that flows into the cylinder 11 reaches the upper surface 22A of the umbrella portion 22 of the intake valve 14. The water that reaches the upper surface 22A of the umbrella portion 22 flows along the upper surface 22A. That is, the water that reaches the upper surface 22A of the umbrella portion 22 of the intake valve 14 flows along the surface of the induction portion 23. The water splashes from the surface of the induction portion 23 at a contact point where a specific tangent line ST can be drawn on the induction portion 23. The splashed water flows along the specific tangent line ST. That is, the induction portion 23 acts like a jump platform for the water moving along the upper surface 22A.

[0036] <Effects of this embodiment> (1) In the above embodiment, as described above, the water injected from the water injection valve 17 flows along the surface of the guide portion 23. Then, the water is scattered along the specific tangent line ST, and as a result, is guided to the exhaust valve 15. That is, in the above embodiment, the injected water is likely to collide with the exhaust valve 15. By guiding the water toward the exhaust valve 15, the exhaust valve 15 can be cooled efficiently.

[0037] (2) If the curvature of the guide portion 23 is large, the force of water flowing along the upper surface 22A is likely to attenuate in the guide portion 23. In other words, the larger the area of ​​the guide portion 23 in the umbrella portion 22, the smaller the curvature of the curve can be, and therefore the force of water flowing along the upper surface 22A is less likely to attenuate in the guide portion 23. In the above embodiment, the width dimension L2 of the guide portion 23 in the direction perpendicular to the central axis C1 is at least one-fourth the outer diameter L1 of the umbrella portion 22. Therefore, according to the above embodiment, the width dimension L2 of the guide portion 23 extends over a considerable area of ​​the upper surface 22A of the umbrella portion 22. Therefore, the force of water is less likely to attenuate, and water splashing from the umbrella portion 22 is likely to reach the exhaust valve 15.

[0038] (3) In the above embodiment, in the virtual cross section, the bottom surface of guide portion 23 is continuous with the outer surface of shaft portion 21. In other words, there is no step or the like at the boundary between the outer surface of shaft portion 21 and upper surface 22A of umbrella portion 22. This configuration prevents the flow of water from being obstructed at the boundary between the outer surface of shaft portion 21 and upper surface 22A of umbrella portion 22.

[0039] (4) Suppose that the guide portion 23 is not annular, but is provided only in a partial angular range centered on the central axis C1. In this case, when assembling the intake valve 14, it is necessary to align the position of the guide portion 23 toward the exhaust valve 15. It is also necessary to prevent the assembled intake valve 14 from rotating around the central axis C1. On the other hand, in the above embodiment, the guide portion 23 has an annular shape centered on the central axis C1 when viewed in a direction along the central axis C1. Therefore, when assembling the intake valve 14, the above-described alignment is not necessary. In other words, assembling the intake valve 14 is simplified.

[0040] (5) In the above embodiment, the specific tangent line ST intersects with the portion of the exhaust valve 15 located inside the cylinder 11 not only when the intake valve 14 is fully open, but also when the intake valve 14 is open within a certain range including the fully open state. Therefore, even when the intake valve 14 is in the process of moving from the closed state to the fully open state, the guide section 23 guides water toward the portion of the exhaust valve 15 located inside the cylinder 11.

[0041] <Example of change> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0042] In the above embodiment, the specific tangent line ST may intersect with the spark plug 16. Specifically, for example, as shown in FIG. 4 , a tangent line is drawn to the guide portion 23 on an imaginary cross section including the central axis C1 of the head portion 22 of the intake valve 14 and the central axis of the spark plug 16. On this imaginary cross section, the angle between the central axis C1 and the tangent line is defined as a specific angle SA, which is the angle on the side where the tangent line contacts the center axis C1 and the intake passage 12. The tangent line with the smallest specific angle SA is defined as a specific tangent line ST. In this case, when the intake valve 14 is fully open, the specific tangent line ST intersects with a portion of the spark plug 16 located within the cylinder 11. According to this modification, water can be splashed toward the spark plug 16, as described in (1) above. Therefore, the spark plug 16 can be efficiently cooled. Even in this modification, it is preferable that the specific tangent line ST intersect with a portion of the spark plug 16 located within the cylinder 11 when the intake valve 14 is within a certain range of opening angles, including the fully open state.

[0043] In the above embodiment, the configuration of the internal combustion engine 10 is not limited to the example of the above embodiment. For example, the number of cylinders 11 may be different from that of the above embodiment. Furthermore, the number of water injection valves 17 is also not limited to that of the above embodiment.

[0044] In the above embodiment, the specific tangent line ST in the imaginary cross section including the central axis C1 of the shaft portion 21 of the intake valve 14 and the central axis C2 of the shaft portion 31 of the exhaust valve 15 has been described, but the imaginary cross section is not limited to this cross section. The specific tangent line ST may be drawn in an imaginary cross section that is parallel to the central axis C1 of the shaft portion 21 and includes the guide portion 23. It is also sufficient that there is at least one imaginary cross section in which the specific tangent line ST intersects with the portion of the exhaust valve 15 that is located inside the cylinder 11.

[0045] In the above embodiment, the width L2 of the guide portion 23 may be less than one-fourth the outer diameter L1 of the umbrella portion 22. The width L2 can be changed as appropriate depending on the outer diameter L1 of the umbrella portion 22, the curvature of the arc of the guide portion 23, the flow rate of the water injected from the water injection valve 17, etc.

[0046] In the above embodiment, the bottom surface of the guide portion 23 does not have to be continuous with the outer surface of the shaft portion 21. In other words, a slope, a step, or the like may be located between the shaft portion 21 and the guide portion 23.

[0047] In the above embodiment, the guide portion 23 does not have to be annular about the central axis C1. The guide portion 23 may be located on the umbrella portion 22 on the side closer to the exhaust valve 15 with respect to the central axis C1.

[0048] The bottom surface of the guide portion 23 does not necessarily have to be arc-shaped on the virtual cross section. That is, the bottom surface of the guide portion 23 may have a linear portion on the virtual cross section. In the above embodiment, the specific tangent line ST may intersect with the portion of the exhaust valve 15 that is located inside the cylinder 11 when the exhaust valve 15 is closed only when the intake valve 14 is fully open.

[0049] The technical concepts that can be derived from the above-described embodiments and modifications are described below. [1] A cylinder, an ignition plug whose tip is located inside the cylinder, an intake passage connected to the cylinder, an exhaust passage connected to the cylinder, a water injection valve located inside the intake passage and injecting water toward the intake passage, an intake valve capable of opening and closing the cylinder side end of the intake passage, and an exhaust valve capable of opening and closing the cylinder side end of the exhaust passage, wherein the intake valve has a rod-shaped shaft portion and an umbrella portion connected to the tip of the shaft portion and opening and closing the intake passage on the cylinder side, and when the surface of the outer surface of the umbrella portion facing the intake passage side is defined as the upper surface, the umbrella portion has an induction portion located on an upper surface, the induction portion having a specific tangent that intersects with one or more selected from a portion of the ignition plug that is located within the cylinder when the intake valve is fully open and a portion of the exhaust valve that is located within the cylinder when the intake valve is closed; and when a tangent that is parallel to the central axis of the umbrella portion and that is tangent to the induction portion is drawn on an imaginary cross section that includes the induction portion, the angle formed by the central axis and the tangent on the side where the tangent points and is on the intake passage side is defined as a specific angle, the specific tangent is the tangent that makes the specific angle the smallest among the tangents.

[0050] [2] The internal combustion engine according to [1], wherein the maximum dimension of the guide portion in a direction perpendicular to the central axis is equal to or greater than one-fourth of the outer diameter of the umbrella portion. [3] An internal combustion engine according to [1] or [2], wherein, on the virtual cross section, the outer surface of the shaft portion is straight, and the bottom surface of the guide portion is arc-shaped convexly toward the cylinder side and is continuous with the outer surface of the shaft portion.

[0051] [4] The internal combustion engine according to any one of [1] to [3], wherein the guide portion has an annular shape centered on the central axis when viewed in a direction along the central axis. [5] An internal combustion engine described in any one of [1] to [4], wherein when the intake valve is in a certain range of opening degrees including the fully open state, the specific tangent line intersects one or more selected from a portion of the spark plug located within the cylinder and a portion of the exhaust valve located within the cylinder in a closed state. [Explanation of symbols]

[0052] Center axis…C1 Specific angle…SA Specific tangent…ST Internal combustion engines…10 Cylinders: 11 Intake passages…12 Exhaust passages…13 Intake valves…14 Exhaust valves…15 Spark plugs…16 Water injection valves…17 Shaft...21 Umbrella part…22 Top surface…22A Guidance part…23

Claims

1. The cylinder and A spark plug whose tip is located within the cylinder; an intake passage connected to the cylinder; an exhaust passage connected to the cylinder; a water injection valve located in the intake passage and configured to inject water toward the intake passage; an intake valve that is capable of opening and closing an end of the intake passage on the cylinder side; an exhaust valve that can open and close an end of the exhaust passage on the cylinder side; Equipped with The water injection valve injects water at least when the intake valve is fully open, The intake valve has a rod-shaped shaft portion and a head portion connected to a tip of the shaft portion and configured to open and close the intake passage on the cylinder side, When the outer surface of the umbrella portion is a surface facing the intake passage, The umbrella portion has a guide portion located on the upper surface, the induction portion includes a specific tangent line that intersects with at least one selected from a portion of the ignition plug that is located within the cylinder when the intake valve is in a fully open state and a portion of the exhaust valve that is located within the cylinder when the intake valve is in a closed state, When a tangent line is drawn that is parallel to the central axis of the umbrella portion and touches the guide portion on a virtual cross section that includes the guide portion, the angle between the central axis and the tangent line is set to a specific angle on the side where the tangent line has a tangent point and on the intake passage side. The specific tangent line is the tangent line that has the smallest specific angle among the tangent lines. Internal combustion engine.

2. The maximum dimension of the guide portion in a direction perpendicular to the central axis is equal to or greater than one-fourth of the outer diameter of the umbrella portion.

2. The internal combustion engine of claim 1.

3. On the virtual cross section, The outer surface of the shaft portion is straight, The bottom surface of the guide portion is formed in a convex arc shape toward the cylinder side and is continuous with the outer surface of the shaft portion.

2. The internal combustion engine of claim 1.

4. The guide portion has an annular shape centered on the central axis when viewed in a direction along the central axis.

2. The internal combustion engine of claim 1.

5. When the intake valve is in a certain range of opening degrees including the fully open state, the specific tangent line intersects one or more selected from a portion of the spark plug located in the cylinder and a portion of the exhaust valve located in the cylinder in a closed state.

2. The internal combustion engine of claim 1.

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