Internal combustion engine with direct injection

Abstract

This direct injection-type internal combustion engine includes, in a combustion chamber, a spark plug and a fuel injection nozzle. The fuel injection nozzle injects fuel toward the spark plug. A sub-chamber for accommodating the spark plug is provided in the combustion chamber. Formed in the sub-chamber is an injection port through which a flame generated in the sub-chamber by the spark plug is discharged to outside the sub-chamber. Formed on the piston top surface are: an inclined surface that inclines on the cylinder head side toward the fuel injection nozzle; and a pair of side guides that are disposed so as to sandwich the inclined surface and extend in a circular arc shape along the edge of the piston top surface. The top section of the inclined surface is disposed further toward the fuel injection nozzle in comparison to the top sections of the side guides in the fuel injection direction.

Description

Technical Field

[0001] The present invention relates to an in-cylinder injection type internal combustion engine provided with a fuel injection nozzle for injecting fuel into a combustion chamber.

Background Art

[0002] Conventionally, an in-cylinder injection type internal combustion engine has been proposed, which includes a cylinder, a cylinder head, a piston, a combustion chamber formed by these components, a spark plug disposed at the center of the cylinder head, and a fuel injection nozzle provided in the combustion chamber for supplying fuel. In such an in-cylinder injection type internal combustion engine, an air-fuel mixture is formed in the combustion chamber by the intake air supplied into the combustion chamber through an intake port in the intake stroke and the fuel supplied by the fuel injection nozzle, and the compressed air-fuel mixture in the compression stroke is ignited by the spark plug.

[0003] In the intake and compression strokes of an in-cylinder injection type internal combustion engine, an air-fuel mixture is efficiently formed by a tumble flow formed by the intake air supplied to the combustion chamber.

[0004] In order to efficiently form such a tumble flow, an in-cylinder injection type internal combustion engine described in Patent Document 1 is proposed, in which a central raised portion having a cylindrical surface curved upward in the intake direction and outer raised portions also having cylindrical surfaces and located on both sides of the central raised portion in the cylinder row direction are provided on the top surface of the piston.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, according to the in-cylinder injection type internal combustion engine described in Patent Document 1, multiple independent tumble flows are formed by the central and outer ridges. As the engine speed increases, depending on the combustion cycle, the airflow from the central ridge, which becomes the main flow, may weaken, disrupting the balance with the tumble flow from the outer ridges and potentially causing significant turbulence in the airflow within the combustion chamber.

[0007] This invention has been made in view of the aforementioned problems, and aims to provide an in-cylinder injection type internal combustion engine that stabilizes the tumble flow formed during the compression process. [Means for solving the problem]

[0008] The above objective of the present invention is achieved by the following configuration. [1] A cylinder formed by a cylinder block, A cylinder head covering one end of the cylinder, A piston having a top surface facing the cylinder head and reciprocating within the cylinder, In the combustion chamber formed between the cylinder, the cylinder head, and the piston, a spark plug is positioned in the center of the cylinder head. The intake port and exhaust port provided in the cylinder head, sandwiching the spark plug, Within the combustion chamber, there is a sub-chamber for housing the spark plug, A fuel injection nozzle is positioned on one side of the intake / exhaust direction connecting the intake port and the exhaust port within the combustion chamber, and injects fuel toward the sub-chamber. An internal combustion engine with in-cylinder injection, The aforementioned sub-chamber has an injection port that connects the combustion chamber and the sub-chamber, and ejects flames from the sub-chamber. The top surface of the piston is formed with an inclined surface that extends along the intake and exhaust direction and slopes toward the cylinder head as it approaches one side, and a pair of lateral guide portions that are arranged to sandwich the inclined surface in the crankshaft direction perpendicular to the intake and exhaust direction, and that extend along the intake and exhaust direction and protrude toward the cylinder head. The lateral guide portion has a lateral guide surface that inclins toward the cylinder head as it approaches one side. In the intake and exhaust direction, the top of the inclined surface is positioned to one side of the top of the lateral guide surface. Internal combustion engine with direct injection. [2] The inclined surface and the lateral guide surface are formed such that, when the piston is at least at the bottom dead center beyond the midpoint between the top dead center and the bottom dead center, the extensions of the inclined surface and the lateral guide surface intersect the cylinder wall surface on the bottom dead center side of the fuel injection nozzle. [1] The internal combustion engine with direct injection described in [1]. [3] The extension line of the lateral guide surface is formed such that it intersects the cylinder wall on the other side in the intake / exhaust direction than the position where the extension line of the inclined surface intersects the cylinder wall, and on the bottom dead center side in the cylinder axial direction than the position where the extension line of the inclined surface intersects the cylinder wall. [2] The internal combustion engine with direct injection described in [2]. [4] The lateral guide portion is formed such that when the extension line of the lateral guide surface is extended along the wall surface of the cylinder while maintaining the angle from the position where the extension line of the lateral guide surface contacts the wall surface of the cylinder, the extension line of the lateral guide surface contacts the wall surface of the cylinder at a point closer to the bottom dead center than the position where the extension line of the inclined surface intersects the wall surface of the cylinder, [3] The internal combustion engine with direct injection described in [3]. [5] The lateral guide portion has a passage portion that extends in a direction intersecting the extending direction of the lateral guide portion and connects the inner surface and the outer surface of the lateral guide portion. The passage portion is formed to be located on the extension of the injection nozzle. The in-cylinder injection type internal combustion engine according to any one of [1] to [4].

Advantages of the Invention

[0009] According to the in-cylinder injection type internal combustion engine of the present invention, the tumble flow formed during the compression process can be made more stable by an inclined surface formed on the piston top surface and a side guide portion arranged so as to sandwich the inclined surface and formed along the edge of the piston top surface.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a main part showing a schematic configuration of an internal combustion engine according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a plan view in the cylinder axis direction showing a schematic configuration of the internal combustion engine. [Figure 3] FIG. 3 is a perspective view of a piston showing the shape of the piston top surface. [Figure 4] FIG. 4 is a central cross-sectional view showing the piston. [Figure 5] FIG. 5(A) is a cross-sectional view of a main part of the internal combustion engine showing a state where the piston has risen to the intermediate point during the compression process, and FIG. 5(B) is a cross-sectional view of a main part of the internal combustion engine showing a state where the piston has risen to the top dead center during the compression process. [Figure 6] FIG. 6 is a perspective view of a main part of the piston showing the flow of the airflow guided by the piston top surface. [Figure 7] FIG. 7 is a plan view in the cylinder axis direction of the piston top surface showing the flame injected from the auxiliary chamber. [Figure 8] FIG. 8 is a perspective view of the piston top surface showing the groove portion provided in the side guide portion. [Figure 9] FIGS. 9(A) and 9(B) are perspective views of the piston top surface showing different embodiments 1 and 2 of the protruding portion.

Modes for Carrying Out the Invention

[0011] A pre-chamber type internal combustion engine to which the in-cylinder injection type internal combustion engine according to an embodiment of the present invention is applied (hereinafter, simply referred to as "internal combustion engine") will be described with reference to FIGS. 1 to 8. Note that the present invention is not limited to the embodiments described below, and various modifications are possible as long as they have substantially the same configuration as the present embodiment and exhibit the same operational effects.

[0012] Regarding the internal combustion engine 1, in this specification, the cylinder axis direction Z indicates the direction in which the piston slides along the cylinder. When referred to as the vertical direction, it indicates the cylinder axis direction Z, with the cylinder head side being "up" and the crankshaft side being "down". This configuration can be referred to in FIG. 1. Also, the intake and exhaust direction X indicates the direction connecting the intake port and the exhaust port. The "intake side" is the intake port side in the intake and exhaust direction X, and the "exhaust side" is the exhaust port side in the intake and exhaust direction X. The intake and exhaust direction X is also the fuel injection direction by the fuel injection nozzle. Further, the crankshaft direction Y is the extending direction of the crankshaft and indicates the direction orthogonal to the cylinder axis direction Z and the intake and exhaust direction X. The crankshaft direction Y is also the cylinder bank direction arranged side by side along the crankshaft. This configuration can be referred to in FIG. 2.

[0013] (Overall Configuration) FIG. 1 is a cross-sectional view of a main part showing the schematic configuration of an internal combustion engine according to an embodiment of the present disclosure, and FIG. 2 is a plan view in the cylinder axis direction Z showing the schematic configuration of the internal combustion engine. The internal combustion engine 1 includes a main chamber 10 and a pre-chamber 20 that form a combustion chamber, an ignition plug 4, and a fuel injection nozzle 5. The internal combustion engine 1 of the present embodiment is an in-line type internal combustion engine in which a plurality of cylinders including the main chamber 10 and the pre-chamber 20 are arranged in series along the crankshaft 2. The arrangement of the cylinders may be V-type or horizontal type.

[0014] The main chamber 10 is a space defined by a cylinder block 11 that forms a cylindrical cylinder 11a extending in the vertical direction, a cylinder head 12 that covers the upper end side of the cylinder 11a, and a piston 13 that reciprocates within the cylinder 11a. The sub-chamber 20 is a space defined by the sub-chamber wall 21 provided in the cylinder head 12. The sub-chamber 20 has the sub-chamber wall 21 and a connecting passage 22 (injection port) that connects the main chamber 10 and the sub-chamber 20. The spark plug 4 is supported in the center of the cylinder head 12, and its tip is positioned within the sub-chamber 20, separated by the sub-chamber wall 21.

[0015] The cylinder head 12 has a pair of intake ports 15 connected to one side in the intake / exhaust direction X, which are opened and closed by an intake valve 14, and a pair of exhaust ports 17 connected to the other side, which are opened and closed via an exhaust valve 16. A fuel supply nozzle 18 is located inside the intake port 15. The fuel supply nozzle 18 can supply fuel into the main chamber 10 when the intake valve 14 is open. This configuration can be seen in Figures 1 and 2. The intake port 15 is connected to an intake passage (not shown). The exhaust port 17 is connected to an exhaust passage (not shown).

[0016] The piston 13 has a piston top surface 30 that faces the cylinder head 12 and constitutes the lower part of the main chamber 10, and a pin hole 13a that is connected to the upper end of the connecting rod 3 via a piston pin 19, and is connected to the crankshaft 2 via the connecting rod 3. As a result, the piston 13 reciprocates between the bottom dead center and the top dead center in the vertical direction of the cylinder 11a. This configuration can be seen in Figure 1.

[0017] The sub-chamber wall 21 has a circular cross-section centered on the cylinder axis (the axis passing through the center of the piston 13 and extending in the cylinder axis direction Z) in a plan view in the cylinder axis direction Z. Refer to Figure 2 for this configuration. The lower part of the sub-chamber wall 21 is formed in a hemispherical shape in the intake / exhaust direction X and the crank axis direction Y. Refer to Figure 1 for this configuration.

[0018] Multiple connecting passages 22 are formed along the circumferential direction of the sub-chamber wall 21 in a plan view in the cylinder axis direction Z, and connect the main chamber 10 and the sub-chamber 20.

[0019] The fuel injection nozzle 5 is located outside the sub-chamber 20 and on the periphery of the cylinder head 12. The fuel injection nozzle 5 is located on the intake valve 14 side in the intake / exhaust direction X, more specifically, between the pair of intake valves 14, 14. This configuration can be seen in Figure 2. The fuel injection nozzle 5 injects fuel directly towards the spark plug 4 in the sub-chamber 20. One of the multiple connecting passages 22, the first connecting passage 22A, is located on the line of fuel injection from the fuel injection nozzle 5, that is, on the extension of the fuel injection port of the fuel injection nozzle 5. Therefore, fuel injected from the fuel injection nozzle 5 can be directly supplied into the sub-chamber 20 via the first connecting passage 22A. The extension of the first connecting passage 22A passes below the fuel injection nozzle 5. This configuration can be seen by referring to Figures 1 and 5(A). The amount of fuel injected by the fuel injection nozzle 5 and the timing of fuel injection are controlled by a control unit (not shown).

[0020] The internal combustion engine 1 described above can output power from the crankshaft 2 by repeatedly performing intake, compression, expansion, and exhaust strokes, causing the piston 13 to reciprocate along the inside of the cylinder 11a. In addition, the internal combustion engine 1 described above receives fuel from a fuel supply nozzle 18 in the intake port 15 into the main chamber 10 during the intake stroke.

[0021] At this time, the intake air introduced into the main chamber 10 from the intake port 15 during the intake stroke is guided by the piston crown surface 30, thereby forming a tumble flow, which is a vertical vortex airflow (rotating around the crankshaft axis Y), within the main chamber 10. In this embodiment, the shape of the piston crown 30 allows for the stable formation of a tumble flow that does not obstruct fuel injection to the spark plug 4 by the fuel injection nozzle 5 when the piston 13 moves upward during the compression stroke. The specific shape of the piston crown 30 will be described later.

[0022] Furthermore, during the compression stroke, while the piston 13 is rising, fuel is injected from the fuel injection nozzle 5 towards the spark plug 4 in the sub-chamber 20 at a predetermined timing, filling the sub-chamber 20 with fuel. This configuration can be seen in Figure 5(A).

[0023] During the compression process, the fuel and fuel mixture supplied to the sub-chamber 20 is ignited by the spark plug 4 and burned within the sub-chamber 20. As a result, the flame F generated in the sub-chamber 20 is injected from the communication passage 22 toward the main chamber 10. This configuration can be seen in Figure 7. The flame F injected from the sub-chamber 20 toward the main chamber 10 causes the fuel mixture formed in the main chamber 10 to burn.

[0024] Next, the specific shape of the piston crown will be explained based on Figures 2 to 7. Figure 3 is a perspective view of the piston showing the shape of the piston crown, Figure 4 is a central cross-sectional view of the piston, Figure 5(A) is a cross-sectional view of the main part of the internal combustion engine showing the state in which the piston has risen to the midpoint, which will be described later, during the compression stroke, Figure 5(B) is a cross-sectional view of the main part of the internal combustion engine showing the state in which the piston has risen to top dead center during the compression stroke, Figure 6 is a perspective view of the main part of the piston showing the airflow guided by the piston crown, and Figure 7 is a plan view of the piston crown in the direction of the cylinder axis Z showing the flame ejected from the sub-chamber.

[0025] In a plan view in the cylinder axis direction Z, the circular piston top surface 30 has an inclined surface 31 and a flat surface 32 provided on the central side in the crank axis direction Y and extending along the intake and exhaust direction X, a pair of lateral guide portions 33, 33 provided on both sides in the crank axis direction Y with respect to the inclined surface 31 and the flat surface 32, and a protruding portion 34 and a valve recess 39 provided on the intake side of the inclined surface 31.

[0026] The inclined surface 31 is formed on the intake port 15 side (intake side) in the intake and exhaust direction X, that is, on the side where the fuel injection nozzle 5 is located.

[0027] The inclined surface 31 extends in the intake / exhaust direction X and is inclined toward the cylinder head 12 as it approaches the fuel injection nozzle 5. In other words, the inclined surface 31 is a surface that slopes upward toward the intake side. Specifically, the inclined surface 31 consists of a first inclined surface 31a and a second inclined surface 31b, which are formed sequentially along the intake and exhaust direction X, starting from the exhaust side (opposite side from the fuel injection nozzle 5). The second inclined surface 31b, which is located on the intake side, has a shorter length in the intake and exhaust direction X and a steeper angle of upward inclination toward the cylinder head 12. This configuration can be seen in Figure 4. In the example shown in Figure 4, the inclined surface 31 is formed by a first inclined surface 31a and a second inclined surface 31b with different angles. However, the inclined surface 31 only needs to have an inclination angle that becomes steeper in multiple stages as it approaches the intake side (fuel injection nozzle 5 side), and the inclined surface 31 may be formed from three or more inclined surfaces with different angles.

[0028] In this embodiment, the angle at the top of the inclined surface 31, the angle of the second inclined surface 31b, is set such that when the vertical position of the piston 13 is within a predetermined range, the point where the extension line of the second inclined surface 31b parallel to the intake and exhaust direction X (hereinafter simply referred to as the extension line of the inclined surface 31) intersects with the wall surface of the cylinder 11a is lower (piston side) in the cylinder axis direction Z than the fuel injection nozzle 5. At this time, the intersection point of the extension line of the inclined surface 31 and the wall surface of the cylinder 11a is defined as the first contact point H1. This configuration can be seen in Figure 4. Specifically, the inclined surface 31 is formed such that, when the piston 13 is at least on the lower dead center side of the midpoint which is between the top dead center and the bottom dead center, the extension of the inclined surface 31 intersects with the wall surface of the cylinder 11a at the first contact point H1. This configuration can be seen in Figure 5(A). On the other hand, when the piston 13 is at top dead center, the inclined surface 31 is formed such that the extension of the inclined surface 31 passes between the fuel injection nozzle 5 and the spark plug 4 and intersects with the lower surface of the cylinder head 12. This configuration can be seen in Figure 5(B).

[0029] Furthermore, it is preferable that the inclined surface 31 be formed such that, as shown in Figure 5(A), the extension of the inclined surface 31 intersects the wall surface of the cylinder 11a at the first contact point H1 when fuel is injected from the fuel injection nozzle 5. In this case, the vertical position of the piston 13 at the timing when fuel is injected from the fuel injection nozzle 5 approaches the bottom dead center as the engine speed increases. For this reason, it is preferable to set the extension of the inclined surface 31 to intersect the wall surface of the cylinder 11a at the fuel injection timing when the engine speed is high, around 5,000 rpm.

[0030] Furthermore, the inclined surface 31 is formed such that, when the piston 13 reaches top dead center, its top is located below the center line extending from the nozzle 22a of the first communication passage 22A of the sub-chamber 20 in a Y-view along the crank axis. This configuration can be seen in Figure 5(B). With this configuration, it is possible to prevent the inclined surface 31 from deteriorating due to direct contact of the flame F ejected from the sub-chamber 20 toward the main chamber 10.

[0031] Furthermore, a downward-sloping surface 36 is formed on the intake side of the inclined surface 31, which slopes downward as it approaches the intake side. The downward-sloping surface 36 is connected to the top of the inclined surface 31.

[0032] The flat surface 32 extends in the intake / exhaust direction X from the exhaust side end of the piston crown surface 30 toward the intake side and is continuous with the inclined surface 31. In this embodiment, the flat surface 32 is formed as a plane that extends parallel to the intake / exhaust direction X and the crankshaft direction Y, perpendicular to the cylinder axis direction Z. Refer to Figure 4 for this configuration. The flat surface 32 can be any smooth surface capable of guiding the airflow toward the inclined surface, and is not limited to a plane perpendicular to the cylinder axis Z. For example, the flat surface 32 may be a surface that is gently inclined at an angle with the inclined surface 31. When the flat surface 32 is inclined in the same direction as the inclined surface 31, the inclined surface 31 is defined as the area on the intake side of the center of the piston 13. By making the area on the exhaust side of the inclined surface 31 the flat surface 32, it is possible to suppress the separation of the airflow flowing along the piston crown surface 30 from the piston crown surface 30 on the exhaust side of the inclined surface 31.

[0033] The lateral guide portion 33 has a lateral guide surface 33a that slopes toward the cylinder head 12 from the exhaust end, a lateral extension surface 33b that extends substantially parallel to the piston crown surface 30 from the intake end of the lateral guide surface 33a, and a lateral downward slope surface 33c that slopes downward toward the piston crown surface 30 from the intake end of the lateral extension surface 33b. In other words, the lateral guide portion 33 protrudes toward the cylinder head 12 in the cylinder axis direction Z when viewed in the crank axis direction Y, and extends along the intake and exhaust direction X, and is formed in a roughly mountain shape with the intake side end of the lateral guide surface 33a as the peak. This configuration can be seen in Figure 4. The lateral guide portion 33 may also have its lateral extension surface 33b inclined in the same way as the lateral downward surface 33c. In this case, the lateral extension surface 33b and the lateral downward surface 33c will be at the same location.

[0034] The angle of the lateral guide surface 33a is set such that, when the vertical position of the piston 13 is within a predetermined range, the point where the extension line of the lateral guide surface 33a parallel to the intake and exhaust direction X (hereinafter simply referred to as the extension line of the lateral guide surface 33a) intersects with the wall surface of the cylinder 11a is lower (piston side) in the cylinder axis direction Z than the first contact point H1. At this time, the intersection point of the extension line of the lateral guide surface 33a and the wall surface of the cylinder 11a is defined as the second contact point H2. Furthermore, the lateral guide surface 33a is formed with a gentler slope than the inclined surface 31. This is because the top of the lateral guide surface 33a is positioned closer to the wall surface of the cylinder 11a in the intake / exhaust direction X compared to the top of the inclined surface 31. By forming the lateral guide surface 33a with a gentler slope than the inclined surface 31, the second contact point H2 is positioned lower in the cylinder axis direction Z and on the exhaust side in the intake / exhaust direction X compared to the first contact point H1. Furthermore, as shown in Figure 6, the lateral guide surface 33a is formed such that, when the extension of the lateral guide surface 33a extends along the inner wall of the cylinder 11a towards the intake side in the intake / exhaust direction X while maintaining an angle in the vertical direction from the second contact point H2, it reaches a third contact point H3 below the first contact point H1 at the lower side of the fuel injection nozzle 5 (a position that overlaps with the fuel injection nozzle 5 in a view along the cylinder axis Z). This configuration can be seen by referring to Figures 4 and 6.

[0035] The lateral downward surface 33c slopes downward from the lateral extension surface 33b toward the intake side and smoothly connects with the downward surface 36 located on the intake side of the inclined surface 31. That is, the lateral downward surface 33c and the downward surface 36 are flush. With this configuration, it is possible to suppress turbulence on the intake side of the piston top surface 30 of the airflow that flows in the intake / exhaust direction X along the inclined surface 31 and the flat surface 32, specifically airflow that did not separate from the inclined surface 31 and airflow that did not separate from the lateral guide surface 33a. This configuration can be seen in Figures 2 and 6.

[0036] As described above, the first separation angle α between the extension of the inclined surface 31 and the downward surface 36 is made larger than the second separation angle β between the extension of the lateral guide surface 33a and the lateral extension surface 33b. With this configuration, the airflow guided by the inclined surface 31, where the flow is strongest, is more likely to separate from the top of the inclined surface 31, thus making the tumble flow guided by the piston top surface 30 more stable. This configuration can be seen in Figure 4. It is also preferable that the first separation angle α be made larger than the second separation angle β even when the lateral extension surface 33b is inclined.

[0037] The guide width, which is the width in the crankshaft axis direction Y of the inclined surface 31 and the flat surface 32, is formed so that it gradually narrows as it moves toward the intake side in the intake / exhaust direction X. Specifically, the inner surfaces of the lateral guide portions 33 (the surfaces facing the cylinder axis) are inclined in the crankshaft axis direction Y so that they move closer to each other as they move toward the intake side. In addition, the outer surfaces of the lateral guide portions 33 (the surfaces facing the wall surface of the cylinder 11a) are formed in an arc shape along the wall surface of the cylinder 11a in the intake / exhaust direction X. The lateral guide portions 33 extend from the exhaust side to the intake side of the cylinder axis in the intake / exhaust direction X. Therefore, the width in the crankshaft axis direction Y of each lateral guide portion 33 is largest at the point located at the center of the piston 13 in the intake / exhaust direction X. The inclination angle of the inner surfaces of the lateral guide portions 33 is determined so that the width in the crankshaft axis direction Y of each lateral guide portion 33 on the intake side of the point located at the center of the piston 13 in the intake / exhaust direction X is approximately constant.

[0038] The protruding portion 34 is a projection formed upward on the downward surface 36. The protruding portion 34 is formed such that its width in the crankshaft axis direction Y decreases as it moves toward the exhaust side in the intake / exhaust direction X. The width in the crankshaft axis direction Y at the intake-side end of the protruding portion 34 is larger than the width in the crankshaft axis direction Y at the tip of the fuel injection nozzle 5. This configuration can be seen in Figure 2. In this embodiment, the protruding portion 34 is located between a pair of intake valves 14, 14. Specifically, the protruding portion 34 is formed using the trapezoidal portion, as viewed from the cylinder axis direction Z, between the pair of recesses corresponding to each intake valve 14, 14 in the valve recess 39, which is a recess formed to match the shape of the pair of intake valves 14, 14. That is, the valve recess 39 is formed flush with the downward surface 36 and the lateral downward surface 33c, and the protruding portion 34 protrudes upward from the downward surface 36. Furthermore, the protruding portion 34 may be configured such that the surface in the crankshaft axis direction Y, viewed from the intake / exhaust direction X, slopes upward as it approaches the center of the protruding portion 34. Refer to Figure 9(A) for this configuration. This allows the airflow along the downward surface 36 and the lateral downward surface 33c to be guided upward. In addition, the shape of the protruding portion 34 may be a rhombic shape or the like, in addition to the trapezoidal shape in the cylinder axis direction Z view as shown in Figure 2. That is, the width in the crankshaft axis direction Y of the exhaust end of the protruding portion 34 should decrease as it approaches the exhaust side. Refer to Figure 9(B) for this configuration.

[0039] (Effects and Benefits) Next, we will explain the effects of the shape of the piston crown surface 30 described above. As shown in Figure 5(A), during the compression stroke of the internal combustion engine 1, when the piston 13 is on the bottom dead center side of the midpoint of the cylinder 11a, the airflow flowing from the piston crown 30 toward the fuel injection nozzle 5 can be guided to contact the intake side wall of the cylinder 11a at the first contact point H1, which is below the fuel injection nozzle 5. As a result, the tumble flow generated in the main chamber 10 causes the fuel injected from the fuel injection nozzle 5 towards the spark plug 4 to flow towards the cylinder head 12, thereby suppressing an upward shift in the target of the injection position.

[0040] Furthermore, by gradually narrowing the guide width of the inclined surface 31 toward the fuel injection nozzle 5, the flow velocity of the airflow on the fuel injection nozzle 5 side of the inclined surface 31 increases, making the tumble flow more stable. Furthermore, by making the inclination angle of the inclined surface 31 gradually increase toward the fuel injection nozzle 5, the airflow guided by the inclined surface 31 is more easily separated smoothly at the edges of the inclined surface 31. As a result, the tumble flow formed by the inclined surface 31 becomes more stable.

[0041] As described above, the flat surface 32 makes the downstream side of the airflow flowing along the piston crown 30 a flat surface, which suppresses the separation of the airflow flowing toward the inclined surface 31 from the piston crown 30, thus making the tumble flow more stable.

[0042] As shown in Figure 6, the lateral guide portion 33 described above can guide the airflow flowing towards the fuel injection nozzle 5 along the outer edge of the piston top surface 30 to the second contact point H2, which is below the first contact point H1. This prevents the airflow guided by the inclined surface 31 from being disturbed by the airflow guided by the lateral guide portion 33. As a result, the tumble flow formed in the main chamber 10 by the piston top surface 30 becomes more stable. Furthermore, the lateral guide portion 33 is formed such that when the extension of the lateral guide surface 33a extends along the inner wall of the cylinder 11a toward the fuel injection nozzle 5 while maintaining an angle in the vertical direction from the second contact point H2, it reaches the third contact point H3 which is below the first contact point H1. As a result, the airflow guided by the lateral guide portion 33 can push up the airflow guided by the inclined surface 31, making the tumble flow more stable. Furthermore, since the lateral guide portion 33 is formed such that the lateral downward surface 33c and the downward surface 36 are flush, it is possible to suppress turbulence in the airflow flowing along the lateral downward surface 33c and the downward surface 36 without separating from the lateral guide surface 33a and the inclined surface 31, thereby making the tumble flow more stable. Furthermore, by making the width of the lateral guide section 33 approximately constant from the point where the width in the crankshaft axis direction Y is widest towards the fuel injection nozzle 5, it is possible to suppress turbulence in the airflow along the lateral guide section 33 in the crankshaft axis direction Y, thereby making the tumble flow more stable.

[0043] As shown in Figure 7, the protruding portion 34 described above allows, in a plan view in the cylinder axis direction Z, the flame F1 injected from the first communication passage 22A toward the fuel injection nozzle 5 from the sub-chamber 20 toward the main chamber 10 to be split in the crank axis direction Y and deflected away from the fuel injection nozzle 5. This reduces the influence of the flame F1 injected from the first communication passage 22A toward the fuel injection nozzle 5.

[0044] (Another embodiment) Next, the configuration of the groove provided in the lateral guide portion 33 will be described based on Figure 8. Figure 8 is a perspective view of the piston top surface showing the groove provided in the lateral guide portion 33. As shown above, the lateral guide portion 33 may be configured to have a groove 35 that extends in a direction intersecting the direction of extension of the lateral guide portion 33 and serves as a passage connecting the inside and outside of the lateral guide portion 33.

[0045] The groove 35 is recessed in the cylinder axis direction Z, extends in a direction intersecting the extending direction of the lateral guide portion 33, i.e., in the crank axis direction Y, and opens on the inner and outer surfaces of the lateral guide portion 33. Furthermore, the depth of the groove 35 in the vertical direction (cylinder axis direction Z) is formed to gradually increase from the outside (towards the center of the piston 13) in the direction in which the groove 35 extends towards the inside. Furthermore, the width of the groove 35, which is in the direction of extension of the lateral guide portion 33 (intake / exhaust direction X), is formed so that it gradually widens from the inside to the outside in the direction of extension of the groove 35.

[0046] With the groove 35 of this configuration, by providing a pair of lateral guide portions 33 on the edge of the piston crown surface 30, the flame F injected from the sub-chamber 20 can be efficiently transmitted to the gap formed between the outer side of the lateral guide portion 33 in the width direction (crankshaft direction Y) and the wall surface of the cylinder 11a. Therefore, the lateral guide portion 33 provided on the piston crown surface 30 can suppress the obstruction of the combustion spread of the fuel mixture outside the lateral guide portion 33. Furthermore, as the vertical depth of the groove 35 increases toward the inward direction in which the groove 35 extends, the flame F ejected from the sub-chamber 20 is more easily guided into the groove 35. Furthermore, as the width of the groove 35 increases from the inside to the outside in the direction of extension of the groove 35, the flame F is more easily propagated over a wider area on the outside in the width direction of the lateral guide portion 33. As a result, the fuel-air mixture burns more easily on the outside of the lateral guide portion 33.

[0047] Furthermore, the groove 35 is a groove for guiding the flame F ejected from the nozzle 22a of the sub-chamber 20 from the inside to the outside of the lateral guide portion 33, and is therefore not limited to the position shown in Figure 8. Specifically, the groove 35 should be provided in a plan view in the cylinder axis direction Z, at a position where the extension lines from each nozzle 22a of the sub-chamber 20 intersect with the lateral guide portion 33, extending along the extension lines from the nozzle 22a, and multiple grooves may be provided. However, the groove 35 shall not be provided in a position adjacent to the top of the inclined surface 31 of the lateral guide portion 33. This prevents the flow of air guided along the inclined surface 31 from being disturbed by the groove 35.

[0048] The lateral guide portion 33 may be configured such that the width in the crankshaft axis direction Y on the exhaust side of the groove portion 35 is greater than the width in the crankshaft axis direction Y on the intake side of the groove portion 35. This suppresses airflow turbulence caused by the airflow along the lateral guide portion 33 passing through the groove portion 35.

[0049] Furthermore, the groove 35 described above is not limited to a groove recessed in the upper surface of the lateral guide portion 33, but may also be a through hole drilled in a direction intersecting the extending direction of the lateral guide portion 33.

[0050] This embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications or improvements can be made to this embodiment, and such modified or improved forms may also be included in the present invention. For example, the features of the present invention are not limited to an internal combustion engine 1 using a sub-chamber 20 housing a spark plug 4 within a main chamber 10, but similar effects can be expected from any internal combustion engine equipped with a fuel injection nozzle 5 that injects fuel toward the spark plug 4. Furthermore, while gasoline is used in the internal combustion engine of this disclosure, it is not limited to gasoline, and other fuels such as alcohol may also be used.

[0051] As described above, the following matters are disclosed in this specification: (1) A cylinder formed by a cylinder block, A cylinder head covering one end of the cylinder, A piston having a top surface facing the cylinder head and reciprocating within the cylinder, In the combustion chamber formed between the cylinder, the cylinder head, and the piston, a spark plug is positioned in the center of the cylinder head. The intake port and exhaust port provided in the cylinder head, sandwiching the spark plug, Within the combustion chamber, there is a sub-chamber for housing the spark plug, A fuel injection nozzle is positioned on one side of the intake / exhaust direction connecting the intake port and the exhaust port within the combustion chamber, and injects fuel toward the sub-chamber. An internal combustion engine with in-cylinder injection, The aforementioned sub-chamber has an injection port that connects the combustion chamber and the sub-chamber, and ejects flames from the sub-chamber. The top surface of the piston is formed with an inclined surface that extends along the intake and exhaust direction and slopes toward the cylinder head as it approaches one side, and a pair of lateral guide portions that are arranged to sandwich the inclined surface in the crankshaft direction perpendicular to the intake and exhaust direction, and that extend along the intake and exhaust direction and protrude toward the cylinder head. The lateral guide portion has a lateral guide surface that inclins toward the cylinder head as it approaches one side. In the intake and exhaust direction, the top of the inclined surface is positioned to one side of the top of the lateral guide surface. Internal combustion engine with direct injection. With this configuration, the tumble flow can be made more stable by the inclined surface formed on the piston crown and the lateral guide portion that is positioned on either side of the inclined surface and formed along the edge of the piston crown.

[0052] (2) The inclined surface and the lateral guide surface are formed such that, when the piston is at least at the bottom dead center beyond the midpoint between the top dead center and the bottom dead center, the extensions of the inclined surface and the lateral guide surface intersect the cylinder wall surface on the bottom dead center side of the fuel injection nozzle. (1) The internal combustion engine with direct injection described in (1). With this configuration, the fuel injected from the fuel injection nozzle 5 toward the spark plug 4 is prevented from being misdirected by the airflow guided by the piston crown surface 30.

[0053] (3) The extension line of the lateral guide surface is formed such that it intersects the cylinder wall on the other side in the intake / exhaust direction than the position where the extension line of the inclined surface intersects the cylinder wall, and on the bottom dead center side in the cylinder axial direction than the position where the extension line of the inclined surface intersects the cylinder wall. (2) The internal combustion engine with direct injection described in (2). In this configuration, since the lateral guide surface 33a is located outside the inclined surface 31 in the crankshaft axis direction Y, it is closer to the wall surface of the cylinder 11a in the intake / exhaust direction X. As a result, the airflow guided by the lateral guide surface 33a reaches the wall surface of the cylinder 11a on the exhaust side of the intake / exhaust direction X more than the airflow guided by the inclined surface 31. However, since the airflow guided by the lateral guide surface 33a passes above the airflow guided by the inclined surface 31, the airflow guided by the lateral guide surface 33a is less likely to disturb the airflow guided by the inclined surface 31.

[0054] (4) The lateral guide portion is formed such that when the extension line of the lateral guide surface is extended along the wall surface of the cylinder while maintaining the angle from the position where the extension line of the lateral guide surface contacts the wall surface of the cylinder, the extension line of the lateral guide surface contacts the wall surface of the cylinder at a point closer to the bottom dead center than the position where the extension line of the inclined surface intersects the wall surface of the cylinder. (3) The internal combustion engine with direct injection described in (3). With this configuration, the airflow guided by the lateral guide surface 33a flows along the wall surface of the cylinder 11a and merges with the airflow guided by the inclined surface 31. At this point, the airflow guided by the inclined surface 31 can be supported. As a result, the tumble flow formed on the piston crown surface 30 becomes more stable.

[0055] (5) The lateral guide portion has a passage portion that extends in a direction intersecting the extending direction of the lateral guide portion and connects the inner surface and the outer surface of the lateral guide portion. The passage portion is formed to be located on the extension of the injection nozzle. A direct-injection internal combustion engine as described in any one of (1) to (4). With this configuration, the flame injected from the sub-chamber can be efficiently guided into the gap between the lateral guide portion 33 and the wall surface of the cylinder 11a, thereby achieving both stable tumble flow formation during the compression process and high combustion efficiency. [Explanation of Symbols]

[0056] 1. Internal combustion engine 2 Crank Axle 3 Connecting rods 4 spark plugs 5. Fuel injection nozzle 10 Main room 11a Cylinder 11 Cylinder block 12 Cylinder head 13a Pin hole 13 pistons 14 Intake valves 15 Intake Ports 16 Exhaust valve 17 Exhaust Ports 18 Fuel supply nozzle 19 Piston pin 20 Antechamber 21 Antechamber wall 22A 1st communication passage (injection port) 22 Communication passage (injection port) 30 Piston crown 31a 1st slope 31b 2nd slope 31 Slope 32 Flat surface 33a Lateral guide surface 33b Lateral extension surface 33c Lateral downhill surface 33. Lateral guide section 34,41 Protruding section 35 groove 36 Downward slope 39 valve recesses H1 1st contact point H2 2nd contact point H H3 3rd contact point H

Claims

1. A cylinder formed by a cylinder block, A cylinder head covering one end of the cylinder, A piston having a top surface facing the cylinder head and reciprocating within the cylinder, In the combustion chamber formed between the cylinder, the cylinder head, and the piston, a spark plug is positioned in the center of the cylinder head. The intake port and exhaust port provided in the cylinder head, sandwiching the spark plug, Within the combustion chamber, there is a sub-chamber for housing the spark plug, A fuel injection nozzle is positioned on one side of the intake / exhaust direction connecting the intake port and the exhaust port within the combustion chamber, and injects fuel toward the sub-chamber. An internal combustion engine with in-cylinder injection, The aforementioned sub-chamber has an injection port that connects the combustion chamber and the sub-chamber, and ejects flames from the sub-chamber. The top surface of the piston is formed with an inclined surface that extends along the intake and exhaust direction and slopes toward the cylinder head as it approaches one side, and a pair of lateral guide portions that are arranged to sandwich the inclined surface in the crankshaft direction perpendicular to the intake and exhaust direction, and that extend along the intake and exhaust direction and protrude toward the cylinder head. The lateral guide portion has a lateral guide surface that inclins toward the cylinder head as it approaches one side. In the intake and exhaust direction, the top of the inclined surface is positioned to one side of the top of the lateral guide surface. Internal combustion engine with direct injection.

2. The inclined surface and the lateral guide surface are formed such that, when the piston is at least at the bottom dead center beyond the midpoint between the top dead center and the bottom dead center, the extensions of the inclined surface and the lateral guide surface intersect the cylinder wall surface on the bottom dead center side of the fuel injection nozzle. The in-cylinder injection type internal combustion engine according to claim 1.

3. The extension line of the lateral guide surface is formed such that it intersects the cylinder wall on the other side in the intake / exhaust direction than the position where the extension line of the inclined surface intersects the cylinder wall, and on the bottom dead center side in the cylinder axial direction than the position where the extension line of the inclined surface intersects the cylinder wall. The in-cylinder injection type internal combustion engine according to claim 2.

4. The lateral guide portion is formed such that, when the extension line of the lateral guide surface is extended along the cylinder wall while maintaining the angle from the position where the extension line of the lateral guide surface contacts the cylinder wall, the extension line of the lateral guide surface contacts the cylinder wall at a point closer to the bottom dead center than the position where the extension line of the inclined surface intersects the cylinder wall. The in-cylinder injection type internal combustion engine according to claim 3.

5. The lateral guide portion has a passage portion that extends in a direction intersecting the extending direction of the lateral guide portion and connects the inner surface and the outer surface of the lateral guide portion. The passage portion is formed to be located on the extension of the injection nozzle. An internal combustion engine with in-cylinder injection according to any one of claims 1 to 4.

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