JP2013024171A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of knocking by promoting the scavenging of exhaust gas in a cylinder in an exhaust stroke, and by reducing exhaust gas remaining in the cylinder.SOLUTION: In a 4-cycle internal combustion engine 1 including a piston 10 disposed inside the cylinder 22 and a cylinder head 24 where an inlet valve 28 and an exhaust valve 29 are arranged at a position on a circumferential side of a piston top face 18, at least one flow path 12 having an opening end at positions on a center side and the circumferential side of the piston top face 18 respectively is formed in the piston top face 18, comprising a hole or a groove, or a hole and a groove formed curved or bent so as to divert in a predetermined direction with respect to a line L connecting the opening end 12a on the center side and the opening end 12b on the circumferential side in a planar view.

Description

  The present invention relates to an internal combustion engine, and more particularly to a piston top surface shape that generates a swirl flow (lateral vortex) in a cylinder during an exhaust stroke.

  In recent years, in internal combustion engines, measures have been pursued to improve combustion efficiency by increasing the compression ratio in order to improve fuel efficiency. However, when the compression ratio is increased, knocking is likely to occur. Therefore, how to suppress the knocking is the biggest problem in increasing the compression ratio.

Patent Document 1 (Japanese Patent Laid-Open No. 2007-278095) discloses an invention relating to an internal combustion engine that suppresses the occurrence of knocking by devising the shape of the piston top surface.
Hereinafter, the internal combustion engine disclosed in Patent Document 1 will be described with reference to FIGS. 11 and 12. FIG. 11 is a schematic sectional view showing the internal combustion engine of Patent Document 1, and FIG. 12 is a perspective view showing the piston top surface.

  As shown in FIG. 11, the internal combustion engine 100 of Patent Document 1 includes a cylindrical cylinder 122, a piston 110 disposed in a reciprocating manner inside the cylinder 122, and a piston top surface 118 side of the piston 110. And a cylinder head 124 that defines a combustion chamber 120 with respect to the piston top surface 118. In the cylinder head 124, an ignition device 126 is installed above the center of the combustion chamber 120, and an intake valve 128 and an exhaust valve 129 are installed around the ignition device 126, respectively.

  On the piston top surface 118, as shown in FIG. 12, four serrated surfaces 119 are formed along the circumferential direction. The serrated surface 119 includes a gently inclined surface portion 119a that is gently inclined in the circumferential direction, and a steeply inclined surface portion 119b that is abruptly inclined in the circumferential direction. The gently inclined surface portion 119a and the steeply inclined surface portion 119b are formed on the top surface portion 118a. It is also gently inclined in the radial direction toward the center. An inner peripheral side surface portion 119c and an outer peripheral side surface portion 119d are formed on the radial side surfaces of the gently inclined surface portion 119a and the steeply inclined surface portion 119b.

  In the internal combustion engine 100 of Patent Document 1 configured as described above, a serrated surface 119 including a gently inclined surface portion 119a and a steeply inclined surface portion 119b is formed along the circumferential direction of the piston top surface 118. The air-fuel mixture in the combustion chamber 120 flows from the top of the serrated surface 119 toward the valley, and a swirl flow (lateral vortex) is generated inside the cylinder 122. According to Patent Document 1, near the top dead center at the end of the compression stroke, the swirl flow that reaches the valley from the top of the serrated surface 119 moves upward along the steeply inclined surface 119b of the serrated surface 119. The swirl flow approaches the ignition device 126 provided above the piston top surface 118, so that the ignition of the air-fuel mixture by the ignition device 126 is promoted and the occurrence of knocking is suppressed.

  Further, according to Patent Document 1, the gently inclined surface portion 119a of the serrated surface 119 is gently inclined in the radial direction toward the top surface portion 118a, and therefore, toward the top surface portion 118a along the gently inclined surface portion 119a. It is said that a clockwise twisted flow is generated, the air-fuel mixture in the combustion chamber 120 is three-dimensionally agitated, and the occurrence of knocking is further suppressed.

  In short, the internal combustion engine 100 according to Patent Document 1 has the shape of the piston top surface 118 in which the air-fuel mixture easily collects toward the top surface portion 118a surrounded by the serrated surface 119 in the compression stroke. In the vicinity of the top dead center at the final stage, the air-fuel mixture is guided toward the ignition device 126 provided above the center of the piston top surface 118 to promote the ignition of the air-fuel mixture, thereby suppressing the occurrence of knocking. It is.

JP 2007-278095 A

  By the way, the same thing can be said in the exhaust stroke which is the upward stroke of the piston as in the compression stroke. That is, in the piston 110 of Patent Document 1 described above, exhaust gas tends to gather toward the top surface portion 118a even in the exhaust stroke. High pressure state.

In order to make scavenging in the exhaust stroke smooth, it is necessary to increase the pressure of the exhaust gas in the vicinity of the exhaust valve 129. In the internal combustion engine 100 of Patent Document 1, the cylinder 122 in which the exhaust valve 129 is installed is used. Since the pressure on the inner peripheral wall side becomes low, scavenging is not sufficiently performed in the exhaust stroke, and the exhaust gas tends to remain. If the exhaust gas is not sufficiently scavenged during the exhaust stroke, the remaining exhaust gas causes the temperature of the air-fuel mixture to rise during the intake stroke of the next stroke, which is a major factor in promoting knocking.
Recent research has shown that reducing residual exhaust gas during the exhaust stroke is particularly important in reducing knocking.

  The present invention has been made in view of such a conventional problem, and in an internal combustion engine, the scavenging of exhaust gas in the cylinder during the exhaust stroke is promoted, and the occurrence of knocking is suppressed by reducing the residual exhaust gas. It aims at realizing the means to do.

The present invention was invented in order to solve the problems of the prior art as described above,
An internal combustion engine according to the present invention includes a piston disposed in a cylinder and a cylinder head that defines a combustion chamber between the piston and a top surface of the piston. In an internal combustion engine in which an intake valve and an exhaust valve are arranged at positions on the outer peripheral side, the piston top surface has opening ends at the center side and outer peripheral side positions, respectively, and the center side opening in plan view That at least one flow path formed by bending or bending so as to detour in a predetermined direction with respect to a straight line connecting the end and the opening end on the outer peripheral side is formed on the top surface of the piston. Features.
Preferably, the flow path is formed on the top surface of the piston by a hole shape, a groove shape, or a hole and groove shape.

  If the internal combustion engine of this invention is comprised in this way, it will have an opening edge part in the position of the center side of a piston top surface, and an outer peripheral side, and the opening edge part of the said center side and the opening edge part of the said outer periphery side in planar view In order to form at least one flow path that is curved or bent so as to detour in a predetermined direction with respect to a straight line that connects to the exhaust line, the exhaust located on the center side of the cylinder during the exhaust stroke is formed. The gas flows through the flow path to the inner peripheral wall side of the cylinder, and an upward swirl flow around the predetermined side is generated in the cylinder.

  For this reason, the pressure in the vicinity of the exhaust valve on the outer peripheral side of the piston top surface in a plan view can be increased, and the scavenging of the exhaust gas during the exhaust stroke is promoted. Accordingly, it is possible to prevent the temperature of the air-fuel mixture from rising during the intake stroke of the next stroke due to the exhaust gas remaining in the cylinder, and it is possible to suppress the occurrence of knocking.

Further, in the above invention, the position where the opening end on the outer peripheral side of the flow path is shifted from the opening end on the center side of the flow path by a predetermined angle around the predetermined side with the center of the piston top surface as a base point It is desirable to form.
With this configuration, the streamline direction in plan view of the exhaust gas flowing out from the opening end on the outer peripheral side can be made parallel to the flow direction of the swirl flow, so that a strong swirl upward during the exhaust stroke It is possible to generate a flow.

Further, in the above invention, the flow path is constituted by a hole extending from the opening end on the central side toward the opening end on the outer peripheral side, and the cross section of the flow path of the flow path is formed on the outer periphery from the opening end on the central side. It is desirable to configure so as to gradually decrease toward the opening end on the side.
If configured in this way, the exhaust gas flowing in from the opening end on the center side of the gas flow path flows out from the opening end on the outer peripheral side without leaking in the middle of the gas flow path. A stronger swirl flow can be generated.

  Further, the flow passage cross section of the flow passage is configured so as to gradually become smaller from the opening end on the center side toward the opening end on the outer peripheral side, so that the exhaust gas flows from the opening end on the center side of the gas flow passage. In addition to facilitating inflow, the flow rate of the exhaust gas flowing out from the opening end on the outer peripheral side can be increased, so that a stronger upward swirl flow can be generated during the exhaust stroke.

Further, in the above invention, the flow preventing portion that protrudes toward the combustion chamber along the outer peripheral edge located upstream of the swirl flow around the predetermined side in the outer peripheral edge of the opening of the intake valve. It is desirable to form.
If such a flow preventing portion is formed, it is possible to prevent the exhaust gas from flowing in from the intake valve at the time of overlap at the end of the exhaust stroke.

  According to the present invention, with respect to a straight line that has opening end portions at positions on the center side and outer periphery side of the piston top surface and connects the opening end portion on the center side and the opening end portion on the outer periphery side in plan view. Since at least one flow path that is curved or bent so as to detour in a predetermined direction is formed on the top surface of the piston, an upward swirl flow is generated in the cylinder during the exhaust stroke. Can do.

  For this reason, the pressure in the vicinity of the exhaust valve on the outer peripheral side of the piston top surface in a plan view can be increased, and the scavenging of the exhaust gas during the exhaust stroke is promoted. Therefore, it is possible to prevent the temperature of the air-fuel mixture from rising during the intake stroke of the next stroke due to the exhaust gas remaining in the cylinder, so that the occurrence of knocking can be suppressed.

1 is a schematic sectional view showing an internal combustion engine of the present invention. It is the top view which showed the piston top surface of the internal combustion engine of this invention. It is the top view which showed the planar shape of the swirl flow production | generation flow path concerning the internal combustion engine of this invention. It is the top view which showed the other planar shape of the swirl flow production | generation flow path concerning the internal combustion engine of this invention. It is sectional drawing which showed the vertical shape of the swirl flow production | generation flow path concerning the internal combustion engine of this invention. FIG. 5 is an explanatory diagram for explaining a swirl flow generated in a cylinder during an exhaust stroke in the internal combustion engine of the present invention. In the internal combustion engine of the present invention, it is an explanatory diagram for explaining the pressure distribution in the cylinder radial direction during the exhaust stroke. In the internal combustion engine of this invention, it is the top view which visually recognized from the piston top surface side the cylinder head which formed the flow prevention part (shroud) in the outer periphery of an intake valve. It is the top view which showed the piston top surface of the internal combustion engine of the 2nd Embodiment of this invention. It is sectional drawing which showed the vertical shape of the swirl flow production | generation flow path concerning the internal combustion engine of the 2nd Embodiment of this invention. 1 is a schematic sectional view showing an internal combustion engine of Patent Document 1. FIG. 6 is a perspective view showing a piston top surface of an internal combustion engine of Patent Document 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
However, the scope of the present invention is not limited to the following embodiments, and the dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments are the same unless otherwise specified. It is not intended to limit the scope of the invention only, but merely an explanation.

<First Embodiment>
The internal combustion engine 1 of the present invention is a four-cycle internal combustion engine that completes one cycle by four strokes of suction, compression, explosion, and exhaust. FIG. 1 is a schematic cross-sectional view showing a four-cycle internal combustion engine of the present invention, and is a schematic cross-sectional view showing a state in which the internal combustion engine is in an exhaust stroke. FIG. 2 is a plan view showing a piston top surface of the four-cycle internal combustion engine of the present invention.

  As shown in FIG. 1, the internal combustion engine 1 of the present invention includes a cylindrical cylinder 22, a piston 10 that is reciprocally disposed inside the cylinder 22, an upper portion of the cylinder 22 (a piston top surface of the piston 10). 18) and a cylinder head 24 arranged on the 18th side.

  The piston 10 is rotatably connected to a connecting rod 40 connected to a crankshaft (not shown), and reciprocates in the cylinder 22 in the axial direction as the connecting rod 40 moves up and down. In addition, the piston top surface 18 of the piston 10 is formed in a mortar shape with a central portion gently recessed, and a squish surface 19 that is inclined toward the inner peripheral wall 22a side of the cylinder 22 is formed on the outer periphery thereof. Yes. Also, a plurality of swirl flow generation channels 12 described later are formed from the concave portion 17 of the piston top surface 18 to the squish surface 19.

  The cylinder head 24 is connected and fixed to the upper portion of the cylinder 22, and defines a combustion chamber 20 with the piston top surface 18 of the piston 10 at the top dead center. In the present invention, the shape of the combustion chamber 20 is not particularly limited, and various shapes such as a multispherical type, a wedge type, and a pent roof type may be employed in addition to the hemispherical type combustion chamber shown in FIG. Can do.

  In addition, the cylinder head 24 is provided with an ignition device 26 that is positioned substantially at the center of the piston top surface 18 and protrudes toward the center of the combustion chamber 20 in the plan view shown in FIG. Two intake valves 28, 28 and two exhaust valves 29, 29 are installed on the outer peripheral side of the piston top surface 18. In the exhaust stroke shown in FIG. 1, the exhaust valve 29 is opened, and the exhaust gas inside the cylinder 22 is discharged from the exhaust port 29a.

  Although not particularly shown, at the end of the exhaust stroke when the piston 10 is near top dead center, the intake valve 28 is opened with the exhaust valve 29 opened, and the exhaust valve 29 and the intake valve are temporarily opened. 28 is opened at the same time, so-called overlapping state.

As shown in FIG. 2, the swirl flow generation channel 12 extends in a clockwise direction from the center side of the piston top surface 18 toward the outer peripheral side.
That is, as shown in FIG. 2, the piston top surface 18 has an open end 12a on the center side and an open end 12b on the outer peripheral side, and the open end 12a on the central side and the open end on the outer peripheral side in plan view. In FIG. 2, for example, the straight line connecting the portion 12 b is curved so as to detour in the left direction with respect to the straight line L.
In the present embodiment, the eight swirl flow generation channels 12 are each formed at a position shifted by a predetermined angle with respect to the center of the piston top surface 18.

  In the exhaust stroke, the exhaust gas in the vicinity of the inner peripheral wall 22a of the cylinder 22 is less likely to flow than the exhaust gas on the center side of the cylinder 22 due to the viscous resistance of the inner peripheral wall 22a. Therefore, the internal pressure of the cylinder 22 at the beginning of the exhaust stroke when the piston 10 starts to rise is relatively higher on the center side than in the vicinity of the inner peripheral wall 22a of the cylinder 22. Further, if the central portion of the piston top surface 18 is recessed, the exhaust gas tends to collect, so that the pressure in this portion is higher than in other portions.

  Therefore, by forming a flow path (swirl flow generation flow path 12) extending from the center side of the piston top face 18 toward the outer peripheral side on the piston top face 18, the exhaust gas at the center side of the cylinder 22 is swirled. It flows to the inner peripheral wall 22 a side of the cylinder 22 through the generation flow path 12.

  Further, since the swirl flow generation flow path 12 extends in a clockwise direction from the center side of the piston top surface 18 toward the outer peripheral side, the swirl flow generation flow 12 is enlarged as shown in FIG. The exhaust gas outflow direction line (streamline 12h) flowing out from the opening end 12b on the outer peripheral side of the passage 12 collides with the inner peripheral wall 22a of the cylinder 22 at an acute angle, and enters the inside of the cylinder 22 in the clockwise direction. A swirl flow s is generated.

  In this way, if a flow path (swirl flow generation flow path 12) extending in the clockwise direction from the center side toward the outer peripheral side is formed on the piston top surface 18, the swirl flow generation flow path during the exhaust stroke is formed. The exhaust gas flows from the opening end portion 12 a on the center side of 12 to the opening end portion 12 b on the outer peripheral side, and an upward swirl flow s in the clockwise direction can be generated inside the cylinder 22.

  Further, as shown in an enlarged view in FIG. 3, the opening end 12b on the outer peripheral side of the swirl flow generation channel 12 is based on the center O of the piston top surface 18 with respect to the opening end 12a on the center side. , And are formed at positions shifted by a predetermined angle α in the clockwise direction. Therefore, for example, the swirl flow generation flow path 12 can be gently curved as compared with the case where the opening end 12a on the center side and the opening end 12b on the outer peripheral side are formed on the same radius. In addition, the streamline direction 12h in plan view of the exhaust gas flowing out from the opening end 12b on the outer peripheral side can be made parallel to the flow direction of the swirl flow s, and a strong swirl flow upward can be generated during the exhaust stroke. Can be generated.

  The planar alignment of the swirl flow generation channel 12 is such that the streamline direction 12h of the exhaust gas flowing out from the opening end 12b on the outer peripheral side collides with the inner peripheral wall 22a of the cylinder 22 at an acute angle, Any shape may be used as long as the upward swirl flow s is generated, and the shape is not necessarily limited to the curved shape described above. For example, as shown in FIG. 4A, a planar shape bent in the clockwise direction by combining the linear portion 12s and the bent portion 12c may be used, as shown in FIG. Thus, the planar shape bent clockwise may be sufficient as the straight part 12s is folded many times. However, in order to make the exhaust gas flow smooth and generate a strong swirl flow s, a planar shape that minimizes the pressure loss is preferable, and a gentle curved shape as shown in FIG. 3 is most suitable. .

  In addition, the swirl flow generation channel 12 of the present embodiment is formed by drilling between the opening end 12a on the center side and the opening end 12b on the outer peripheral side, and the channel cross section has a hole shape. Is formed. In this way, if the cross section of the swirl flow generation flow path 12 is formed in a hole shape, the exhaust gas flowing in from the opening end 12a on the center side does not leak in the middle of the flow path and opens on the outer peripheral side. Since it flows out from the end portion 12b, a strong swirl flow s can be generated inside the cylinder 22.

  Moreover, it is preferable that the longitudinal shape of the swirl flow generation flow path 12 is formed in a gently curved shape as shown in an enlarged view in FIG. 5 for the same reason as the planar shape described above. Further, the inflow direction line (stream line 12v1) at the opening end portion 12a on the center side of the swirl flow generation flow path 12 is close to be parallel to the axial line v of the piston so that exhaust gas can be taken in as much as possible. Is preferably formed. On the other hand, the outflow direction line (stream line 12v2) at the opening end 12b on the outer peripheral side of the swirl flow generation channel 12 is such that the exhaust gas is hardly taken in and a strong upward swirl flow s is generated. Preferably, it is formed slightly upward with respect to the perpendicular to the axial line v. Therefore, the opening end 12b on the outer peripheral side is preferably formed so as to be positioned on the squish surface 19 formed on the outer periphery of the piston top surface 18, as shown in FIG.

  In view of the above, in the swirl flow generation flow path 12, in order to make the exhaust gas easily flow from the opening end 12a on the central side toward the opening end 12b on the outer peripheral side, at least the opening end 12b on the outer peripheral side. It is preferable to form the streamline 12v2 in the cylinder so as to be closer to the axis line v of the piston than the streamline 12v1 in the opening end 12a on the center side.

  Further, as shown in enlarged views in FIGS. 3 and 5, the flow path cross section of the swirl flow generation flow path 12 is gradually reduced from the center side of the piston top surface 18 toward the outer peripheral side. By forming the exhaust gas, it becomes easier for the exhaust gas to flow from the opening end 12a on the center side of the swirl flow generation channel 12 toward the opening end 12b on the outer peripheral side, and a stronger swirl flow s is generated in the exhaust stroke. Is possible.

  In the present invention, when at least one swirl flow generation channel 12 as described above is formed on the piston top surface 18, an upward swirl flow s is generated inside the cylinder 22 during the exhaust stroke. However, in order to generate a stronger upward swirl flow s, it is preferable that a plurality of swirl flow generation channels 12 are formed on the piston top surface 18 as in the above-described embodiment.

Next, the effect | action of the swirl flow production | generation flow path 12 mentioned above is demonstrated.
As described above, the exhaust gas in the vicinity of the inner peripheral wall 22a of the cylinder 22 is less likely to flow relative to the exhaust gas at the center side of the cylinder 22 due to the viscous resistance of the inner peripheral wall 22a. Therefore, when the piston 10 is lifted, the exhaust gas on the center side of the cylinder 22 flows in from the opening end portion 12a on the center side of the swirl flow generation flow path 12 as shown in a sectional view in FIG. Then, the inside of the swirl flow generation flow path 12 flows toward the inner peripheral wall 22a side of the cylinder 22 and flows out from the opening end 12b on the outer peripheral side.

  As described above, since the swirl flow generation flow path 12 extends in a clockwise direction from the center side of the piston top surface 18 toward the outer peripheral side, the exhaust gas flowing out from the opening end 12b on the outer peripheral side. The gas collides with the inner peripheral wall 22a of the cylinder 22 at an acute angle in plan view, and as shown in FIGS. 6 (a) and 6 (b), a clockwise upward swirl flow s is generated inside the cylinder 22. Is generated.

Thus, when the swirl flow s is generated inside the cylinder 22, the radial pressure distribution inside the cylinder 22 is more relative to the inner peripheral wall 22 a side than to the center side of the cylinder 22, as shown in FIG. 7. High pressure state. Therefore, the pressure in the vicinity of the exhaust valve 29 located on the outer peripheral side of the piston top surface 18 in a plan view is increased, and the scavenging of the exhaust gas in the exhaust stroke is promoted. In addition, since the generated swirl flow s is upward, scavenging to the exhaust valve 29 installed at the upper part of the combustion chamber 20 is further promoted.
Therefore, it is possible to prevent the temperature of the air-fuel mixture from rising during the intake stroke of the next stroke due to the remaining exhaust gas, and the occurrence of knocking is suppressed.

  Note that the upward swirl flow s generated during the exhaust stroke described above also occurs during the compression stroke, which is also the upward stroke of the piston 10. Therefore, the radial pressure distribution in the cylinder 22 during the compression stroke is basically the same as that in FIG. 7 described above, and is relatively higher on the inner peripheral wall 22a side than on the center side of the cylinder 22. It becomes a pressure state. Therefore, the pressure of the air-fuel mixture in the vicinity of the ignition device 26 located on the center side of the piston top surface 18 in a plan view is reduced, and the ignitability of the air-fuel mixture is inferior to the internal combustion engine 100 of Patent Document 1 described above. You might also say that.

  However, the air-fuel mixture is ignited by the ignition device 26 at the end of the compression stroke, that is, when the piston 10 reaches top dead center. In this state, since the swirl flow s is also attenuated to a considerable extent, the pressure distribution in the combustion chamber 20 does not become a pressure distribution that adversely affects the ignitability of the air-fuel mixture. In particular, as shown in FIG. 1, if the ignition device 26 is installed at the top of the combustion chamber 20, the air-fuel mixture easily gathers toward the ignition device 26 when the piston 10 reaches the top dead center. It has excellent ignitability of air-fuel mixture.

  Further, as shown in FIG. 8, along the outer peripheral edge located upstream from the flow direction of the clockwise swirl flow s generated during the exhaust stroke, out of the outer peripheral edge of the opening of the intake valve 28. In the overlap state in which the exhaust valve 29 and the intake valve 28 are temporarily opened at the end of the exhaust stroke by forming a shroud (flow prevention portion 30) that protrudes toward the combustion chamber 20, the intake valve It is possible to prevent the exhaust gas from entering the opening 28.

  At this time, as shown in FIG. 8, in addition to the above-described flow prevention portion 30 (or separately from the flow prevention portion 30), it is generated during the exhaust stroke within the outer peripheral edge of the opening of the exhaust valve 29. By forming a shroud (flow guide portion 32) that protrudes toward the combustion chamber 20 along the outer peripheral edge located downstream of the flow direction of the swirl flow s, the exhaust gas is introduced into the opening of the exhaust valve 29. It can be guided smoothly, and scavenging of exhaust gas during the exhaust stroke is further promoted.

  8 and 9 are plan views of the cylinder head 24 viewed from the piston top surface 18 side. The flow direction of the swirl flow s and the installation positions of the intake valve 28 and the exhaust valve 29 are shown in FIGS. And in the opposite direction to that shown in FIG.

<Second Embodiment>
Next, a four-cycle internal combustion engine 1 according to a second embodiment of the present invention will be described with reference to FIGS.
This will be explained based on the above.
The 4-cycle internal combustion engine 1 of the second embodiment is basically the same as the 4-cycle internal combustion engine 1 of the first embodiment described above, and the same components are the same. Reference numerals are assigned and detailed description thereof is omitted.

  In the four-cycle internal combustion engine 1 of the second embodiment, as in the above-described embodiment, the swirl flow generation flow path 12 is from the center side of the piston top surface 18 toward the outer peripheral side, as shown in FIG. Curved and extends in the clockwise direction. However, the swirl flow generation flow path 12 is formed by grooving between the opening end 12a on the center side and the opening end 12b on the outer peripheral side, and as shown in FIG. The point that the road section is formed in a groove shape is different from the first embodiment described above.

  As described above, even if the flow path cross section of the swirl flow generation flow path 12 is a groove shape, the embodiment described above may be used as long as the planar alignment is curved and extends in the clockwise direction from the center side toward the outer peripheral side. Similarly, during the exhaust stroke, the exhaust gas flows from the opening end 12a on the central side of the swirl flow generation channel 12 to the opening end 12b on the outer peripheral side, and the upward swirling flow s in the clockwise direction is generated inside the cylinder 22. Can be generated. In addition, it is easier to form the swirl flow generation flow path 12 as compared with the case of the hole shape described above.

Further, the vertical shape of the swirl flow generation flow channel 12 when the flow channel cross section is formed in a groove shape is a uniform upward gradient from the center side of the piston top surface 18 toward the outer peripheral side, as shown in FIG. It is good to form. By doing in this way, since the direction of the exhaust gas in the longitudinal direction does not change in the middle of the flow path, the exhaust gas flowing in from the center side can smoothly flow to the outer peripheral side.
Note that the streamline v1 in the longitudinal direction of the opening end 12a on the center side is preferably formed so as to be nearly parallel to the axial line v of the piston, as in the above-described embodiment.
Also, the streamline v2 in the longitudinal direction of the opening end 12b on the outer peripheral side is preferably formed slightly upward with respect to the perpendicular to the axial line v of the piston, as in the above-described embodiment.

  In addition, when the cross section of the flow path is formed in a groove shape, for example, a dovetail groove shape or the like, the exhaust gas is formed by a cross sectional shape in which the opening width of the groove is narrower than the bottom width or the central width of the groove. Leakage in the middle of the flow path can be suppressed, and a strong swirl flow s can be generated inside the cylinder 22.

As mentioned above, although preferable embodiment of this invention was described, the scope of the present invention is not limited to the said embodiment. Various modifications can be made without departing from the object of the present invention.
For example, in the above-described embodiment, the flow path cross section of the swirl flow generation flow path has been described as having a hole shape or a groove shape, but the present invention is not limited to this, for example, the center side of the piston top surface 18 is In a single swirl flow generation flow path, such as a groove shape and a hole shape on the outer peripheral side, a hole shape and a groove shape can be used together. It is also possible to have a shape.

  According to the present invention, since an upward swirl flow is generated inside the cylinder during the exhaust stroke, the pressure in the vicinity of the exhaust valve can be increased, and the scavenging of the exhaust gas during the exhaust stroke is promoted. Therefore, it is possible to prevent the temperature of the air-fuel mixture from rising during the intake stroke of the next stroke due to the remaining exhaust gas, and to suppress the occurrence of knocking. It is suitable for a four-cycle internal combustion engine.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 10 Piston 12 Swirl flow generation flow path 12a Center side opening end part 12b Outer peripheral side opening end part 12c Curved part 12s Straight line part 17 Concave part 18 Piston top surface 19 Squish surface 20 Combustion chamber 22 Cylinder 22a Inside of the cylinder Peripheral wall 24 Cylinder head 26 Ignition device 28 Intake valve 29 Exhaust valve 29a Exhaust port 30 Shroud (flow prevention part)
32 shroud
40 connecting rod s swirl flow v piston axial line

Claims (5)

A piston disposed in the cylinder, and a cylinder head defining a combustion chamber between the piston and a top surface of the piston, and the cylinder head has an intake air at a position on an outer peripheral side of the piston top surface in a plan view. In an internal combustion engine in which a valve and an exhaust valve are arranged,
A direction on a predetermined side with respect to a straight line connecting the opening end on the center side and the opening end on the outer periphery side in a plan view, having opening end portions at positions on the center side and the outer periphery side of the piston top surface. An internal combustion engine characterized in that at least one flow path that is curved or bent so as to bypass the piston is formed on the top surface of the piston. 2. The internal combustion engine according to claim 1, wherein the flow path is formed in the top surface of the piston by a hole shape, a groove shape, or a hole and groove shape.   The opening end on the outer peripheral side of the flow path is formed at a position shifted by a predetermined angle in a direction around a predetermined side with respect to the opening end on the center side of the flow path, with the center of the piston top surface as a base point. The internal combustion engine according to claim 1 or 2, characterized by the above.   The flow path is configured by a hole extending from the opening end on the center side toward the opening end on the outer peripheral side, and the channel cross section of the flow path is changed from the opening end on the center side to the opening end on the outer peripheral side. The internal combustion engine according to any one of claims 1 to 3, wherein the internal combustion engine is configured to gradually become smaller toward the engine.   A flow-proof portion that protrudes toward the combustion chamber is formed along the outer peripheral edge located upstream of the outer peripheral edge of the opening portion of the intake valve with respect to the swirl flow around the predetermined side. An internal combustion engine according to any one of claims 1 to 4.

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