JPH08246877A - Combustion chamber structure for internal combustion engine - Google Patents

Abstract

PURPOSE: To realize stratified charge where the vicinity of a spark plug arranged in the cylinder center becomes a thick air-fuel mixture. CONSTITUTION: A pair of intake valves 7 and a pair of exhaust valves are provided with respective cylinders, and a spark plug is arranged in the cylinder center. A fuel injection valve 13 is arranged so that a thick air-fuel mixture is formed along the center of an intake air port 11. A tip part of the intake air port 11 can bend downward so that a tumble is generated in a combustion chamber 6. On a top surface of a piston 4, a recessed groove 15 is formed in the radial direction so as to run along the tumble. In this recessed groove 15, since a width of an exhaust valve side end part being the inlet side of the tumble flowing along here is wide and a width of an end part on the intake valve 7 side being the outlet side is narrow, the thick air-fuel mixture is gathered to the center by being carried on the tumble.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a combustion chamber structure of a spark ignition type internal combustion engine in which stratified charge is provided to an ignition plug located at the center of a cylinder.

[0002]

2. Description of the Related Art Mainly in order to reduce fuel consumption, a layer having a rich air-fuel mixture and a layer having a thin air-fuel mixture are formed in layers in a combustion chamber, and the air-fuel mixture having a low air-fuel ratio as a whole is ignited by igniting the layer. 2. Description of the Related Art A stratified charge type spark ignition internal combustion engine capable of being combusted is conventionally known. For example, in Japanese Unexamined Patent Publication No. 6-159076, a ridge having a ridgeline extending in the axial direction of the crankshaft is formed on the top surface of a piston arranged in the cylinder, and the cylinder is swung in the longitudinal direction. A configuration is shown that produces a stable flow or tumble. Further, in this example, the fuel is injected and supplied by the fuel injection valve along the portions on the inner sides of the intake ports that are opened and closed by the pair of intake valves. Further, the spark plug is located substantially at the center of the cylinder.

In this structure, when the intake valve is opened in the intake stroke, intake air flows in along the ceiling wall surface of the combustion chamber and moves downward along the cylinder wall surface opposite to the intake valve. The tumble is generated so that it is smoothly guided by the raised portion of the surface and goes upward along the cylinder wall surface near the intake valve. Then, a rich air-fuel mixture is provided in advance near the center of the intake air flow to secure an ignitable air-fuel mixture region near the spark plug.

In addition to this, Japanese Patent Laid-Open No. 5-240047 discloses an example of a configuration in which an inverse tumble that turns in the opposite direction to the above example is generated.

[0005]

However, in the conventional combustion chamber structure as described above, when the intake air passes through the opening of the intake valve, the rich air-fuel mixture is unevenly distributed near the center of the intake flow. Even after passing through the opening of the intake valve, the rich mixture easily diffuses in the circumferential direction in the combustion chamber by colliding with the valve head of the intake valve or the top surface of the piston, achieving sufficient stratification. Can not do it.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a combustion chamber is defined between a recess formed in the lower surface of a cylinder head and a piston, and an ignition plug is arranged substantially at the center of the cylinder. Combustion of an internal combustion engine in which one or more intake valves are arranged at a position deviated to one side, and an intake port is formed so that a tumble is generated in the combustion chamber by an intake flow flowing through the intake valves. In the chamber structure, the top surface of the piston is characterized in that a concave groove whose one end on the intake valve side has a narrow width and which widens toward the opposite side is formed in the radial direction.

According to a second aspect of the present invention, the concave groove is shallow at the peripheral portion of the piston and deep at the central portion of the piston.
Its bottom surface is characterized by a smooth concave surface that follows the tumble turning.

[0008]

The intake air flowing into the combustion chamber in the intake stroke travels from the intake valve portion, which is located at one side of the cylinder, toward the opposite side of the cylinder along the ceiling wall surface of the combustion chamber.
Further, it descends along the wall surface of the cylinder, is further inverted by the top surface of the piston, and rises along the wall surface of the cylinder near the intake valve to generate a swirling flow, that is, a tumble in the cylinder longitudinal direction.

At this time, on the piston top surface, the intake flow flows from the portion of the cylinder opposite to the intake valve toward the intake valve side, but the concave groove formed on the piston top surface is Since the width of the portion on the inlet side is wide and the width of the portion on the outlet side is narrow, it is possible to suppress the intake flow from being dispersed left and right. Therefore, if the air-fuel mixture that flows in from the intake valve is stratified, the stratified state is reliably held in the combustion chamber, and the rich air-fuel mixture is collected in the vicinity of the spark plug.

Further, according to the second aspect of the invention, the bottom surface of the concave groove forms a smooth concave surface along the swirling of the tumble, so that the tumble in the combustion chamber is further strengthened.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

1 to 3 show an embodiment of a combustion chamber structure of an internal combustion engine according to the present invention.
The cylinder head 3 is mounted and fixed on the upper surface of the cylinder block 2 in which the cylinder 1 is formed.
A piston 4 is slidably fitted and arranged therein. A so-called pent roof type recess 5 is formed on the lower surface of the cylinder head 3, and a combustion chamber 6 is defined between the recess 5 and the top surface of the piston 4. As shown in FIG. 2, a pair of intake valves 7 and a pair of exhaust valves 8 are arranged in the combustion chamber 6, more specifically, in the recess 5 that is the ceiling thereof. The intake valve 7 is arranged on one inclined surface of the pent roof, and the exhaust valve 8 is arranged on the other inclined surface. That is, the pair of intake valves 7 are arranged so as to be offset from one side of the cylinder 1. And these intake valve 7 and exhaust valve 8
A spark plug 9 is arranged substantially at the center of the combustion chamber 6 surrounded by. The intake port 11 opened and closed by the intake valve 7 and the exhaust port 12 opened and closed by the exhaust valve 8 are formed in the cylinder head 3 in a so-called cross-flow type.

Here, in the intake port 11 of each cylinder, the upstream side portion is gathered in one flat passage, and the downstream side portion is bifurcated. In particular, the intake ports 11 are formed symmetrically with a center line L passing between the pair of intake valves 7 and the center of the cylinder 1 as the center. Further, as shown in FIG. 3, the intake port 11 has its downstream end portion gently curved downward along the axial direction of the cylinder 1 so that tumble occurs in the combustion chamber 6 in the vertical direction. .

On the upstream side of the intake port 11, a fuel injection valve 13 for injecting and supplying fuel toward the intake port 11.
Are arranged for each cylinder. This fuel injection valve 13
The fuel is injected toward the partition wall 14 which is located slightly upstream of the bifurcated intake port 11 and which is located at the upstream side. That is, as shown in FIG.
In the plan view of the cylinder 1, fuel is injected along the above-mentioned center line L. Further, the spray angle θ is small, and the fuel spray is formed along the inner parts of the bifurcated intake ports 11, in other words, along the central partition wall 14 vicinity. .

On the other hand, the piston 4 is integrally cast from an aluminum alloy or the like, and its top surface 4
Basically, “a” forms a plane orthogonal to the axis of the cylinder 1, and at the center thereof, as shown in FIGS. 4 and 5, a concave groove 15 is formed along the radial direction. This groove 15 is
It is formed along the center line L from the intake valve 7 side to the opposite exhaust valve 8 side, that is, along the direction orthogonal to the crankshaft axial direction. And this groove 15 is
As shown in FIG. 4, the one end 15a on the intake valve 7 side is tapered in a plan view so that the width is gradually narrowed toward the opposite side. And the other end 1
5b has the largest width. Also, this groove 1
The bottom surface 15c of the groove 5 is shallow at both ends thereof, that is, at the peripheral edge of the piston 4 and deep at the central portion, and forms a smooth concave surface along the swirling of the tumble in the combustion chamber 6, as shown in FIG. .

In the structure of the above-described embodiment, the intake air flow that has flowed into the combustion chamber 6 from the intake port 11 in the intake stroke starts from the opening of the intake valve 7 which is located at one side of the cylinder 1 and ends at the ceiling of the combustion chamber 6. Heading toward the opposite side of the cylinder 1 along the wall surface, descending along the wall surface of the cylinder 1 on the exhaust valve 8 side, further inverted by the top surface 4a of the piston 4, and rising along the wall surface of the cylinder 1 near the intake valve 7. As a result, a swirl flow in the longitudinal direction of the cylinder 1, that is, a tumble, is generated as indicated by an arrow TF in FIG.

As described above, the intake flow flowing into the combustion chamber 6 is centered between the pair of intake valves 7 as fuel is injected along the inside of the bifurcated intake port 11. A rich air-fuel mixture (indicated by an arrow FU in FIG. 2) is unevenly distributed in a portion, and the flow on both sides thereof is mainly air (indicated by an arrow AR in FIG. 2). That is, the layers flow into the combustion chamber 6 in layers, but this flow collides with the valve head portion of the intake valve 11 and further collides with the top surface 4a of the piston 4, thereby exerting a force in a direction that spreads left and right. receive.

However, when the piston 4 moves up in the compression stroke and the tumble TF flows along the top surface 4a of the piston 4, the concentrated air-fuel mixture FU at the center is surely collected by the concave groove 15. That is, piston 4
At the top surface 4a, as shown by the arrow in FIG. 6, the tumble TF flows from the portion of the cylinder 1 opposite to the intake valve 7 toward the intake valve 7 side. Since the groove 15 formed at the end has a wide width at the end 15b on the inlet side and a narrow width at the end 15a on the outlet side, a thick mixture near the center where stratification is becoming ambiguous. FUs are collected in a thin stream and are suppressed from being dispersed left and right. Therefore, it is possible to surely maintain the stratification while turning to the spark plug 9 side, and to secure an air-fuel mixture region of ignitable air in the vicinity of the spark plug 9. Further, by making the bottom surface 15c of the concave groove 15 a smooth concave surface, the tumble TF on which the rich air-fuel mixture FU is mounted can be made even stronger.

Next, FIGS. 7 and 8 show different embodiments of the groove 15. In this embodiment, a straight portion is provided on the side of the narrow end 15a which is the exit side of the tumble TF flowing along the top surface 4a of the piston 4, and the concave groove 15 is formed in a substantially Y shape as a whole. . According to this embodiment, the flow of the air-fuel mixture narrowed by the concave groove 15 can be rectified by the straight portion on the outlet side, and the air-fuel mixture layer can be prevented from collapsing during the compression stroke.

9 and 10 show another embodiment of the groove 15. In this embodiment, the bottom surface 15c of the concave groove 15 is formed into a substantially Y shape having a straight line portion, the opening edge of the top surface 4a of the piston 4 is formed into a simple tapered shape, and both sides of the concave groove 15 are formed. The surface is an inclined surface. Also in this embodiment, the rectifying effect at the outlet side portion can be obtained.

[0021]

As is apparent from the above description, according to the combustion chamber structure of the internal combustion engine of the present invention, it is possible to suppress the spread of the intake air flow that has flowed in through the opening of the intake valve, and use the tumble. As a result, stable stratified air supply can be realized.

According to the second aspect of the invention, the tumble along the center of the cylinder toward the vicinity of the spark plug can be further strengthened.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a combustion chamber structure according to the present invention.

FIG. 2 is a plan view showing a configuration seen from above a cylinder.

FIG. 3 is a sectional view taken along the cylinder axis.

FIG. 4 is a plan view of the piston showing a groove on the top surface of the piston.

5 is a cross-sectional view taken along the line AA of FIG.

FIG. 6 is an explanatory view showing the flow of intake air on the top surface of the piston.

FIG. 7 is a plan view of a piston showing another embodiment of the groove.

8 is a sectional view taken along line BB of FIG.

FIG. 9 is a plan view of a piston showing another embodiment of the groove.

10 is a cross-sectional view taken along the line CC of FIG.

[Explanation of symbols]

 4 ... Piston 6 ... Combustion chamber 7 ... Intake valve 11 ... Intake port 15 ... Recessed groove

Claims (2)

[Claims] 1. A combustion chamber is defined between a recess formed in the lower surface of a cylinder head and a piston, an ignition plug is disposed substantially at the center of the cylinder, and a spark plug is provided at a position offset to one side of the cylinder. One or more intake valves are arranged,
In the combustion chamber structure of the internal combustion engine in which the intake port is formed so that the tumble is generated in the combustion chamber by the intake air flow that flows in through the intake valve, the top surface of the piston has one end on the intake valve side. A combustion chamber structure for an internal combustion engine, characterized in that a groove having a narrow width and widening toward the opposite side is formed in the radial direction. 2. The groove is shallow at the periphery of the piston,
2. The combustion chamber structure according to claim 1, wherein the piston is deepened in the center thereof, and the bottom surface thereof forms a smooth concave surface along the swirling of the tumble.