JP2004019480A - In-cylinder direct injection internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enlarge a stratified charge combustion region by enlarging a control range in a fuel injection time when stratified air-fuel mixture of a cylinder direct injection type internal combustion engine is produced. <P>SOLUTION: In the cylinder direct injection type internal combustion engine, an ignition plug is disposed near a cylinder axis, and a cavity 11 having a bottom wall and a side wall is recessed in a substantially center of a crown surface of a piston 4. The tip of a fuel injection valve is disposed above the side wall of the cavity 11, and fuel is injected from the fuel injection valve toward the side wall of the cavity 11. Much fuel is advanced downward from the above part of the side wall of the cavity 11 along the cylinder axis, and collided with the side wall of the cavity always keeping the same positional relation even when a piston position (crank angle) at the collision is different. Thus, influence of the fuel injection time to the formation of the stratified air-fuel mixture is reduced, a settable range of the fuel injection time is extended, and stratified charge combustible operation region is enlarged. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an in-cylinder direct injection internal combustion engine that directly injects fuel into a combustion chamber.
[0002]
[Prior art]
As a conventional in-cylinder direct injection internal combustion engine disclosed in Japanese Patent Application Laid-Open No. H11-82028, a hollow conical fuel is injected from a fuel injection valve provided in an upper portion of a combustion chamber toward a cavity provided in a piston crown surface. Configuration. The cavity is composed of a cylindrical peripheral wall, a bottom wall, and a conical ridge, and the substantially hollow conical fuel spray injected from above collides with the peripheral wall of the cavity at an acute angle, and the fuel that has collided with the peripheral wall has a bottom. It is intended to form a stratified mixture around the spark plug by ascending via the wall surface and the conical ridge toward the spark plug provided above the conical ridge.
[0003]
[Problems to be solved by the invention]
However, in the above-described conventional in-cylinder direct injection type internal combustion engine, the fuel spray advances while spreading, and the piston sliding direction and the fuel advancing direction or the fuel spreading direction are greatly different. As a result, the engine rotation speed and the engine load are reduced. If the fuel injection timing changes accordingly, the degree of spread of the fuel spray when colliding with the piston, the position of collision with the piston, and the like greatly differ, so that a desired stratified mixture cannot always be formed as intended.
[0004]
That is, since fuel injection can be performed only for a certain limited period, the operation range in which stratified combustion can be performed is limited, and the fuel consumption rate cannot be improved and the exhaust emission cannot be sufficiently reduced.
[0005]
[Means for Solving the Problems]
Therefore, according to the present invention, an ignition plug is disposed near the cylinder axis and a cavity having a bottom wall surface and a side wall surface is formed substantially at the center of the piston crown surface, while a fuel injection valve is provided above the cavity side wall surface. A tip is disposed, and fuel is injected from the fuel injection valve toward the side wall surface of the cavity.
[0006]
In this way, the spray of the fuel injected from the fuel injection valve increases the proportion of the fuel traveling along the cylinder axis from above to below the cavity side wall surface, and the fuel traveling in this direction impinges. Even if the piston position (crank angle) at the time is different, it always collides with the cavity side wall surface while maintaining the same positional relationship, so that the influence of the fuel injection timing on the formation of the stratified mixture becomes small, and the settable fuel injection timing The range can be expanded. As a result, the operating region in which stratified combustion can be performed is expanded, so that the fuel consumption rate can be improved and the exhaust emission can be sufficiently reduced.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
1 and 2 show the configuration of the first embodiment of the present invention. The combustion chamber 1 is defined by a cylinder head 2, a cylinder block 3, and a piston 4, and communicates with an intake port 5 and an exhaust port 6 via an intake valve 7 and an exhaust valve 8, respectively. A fuel injection valve 9 and a spark plug 10 are arranged in the upper part of the combustion chamber 1 together with the intake valve 7 and the exhaust valve 8, and the spark plug 10 is installed substantially at the center of the combustion chamber 1. A cavity 11 for receiving fuel spray is provided on the crown surface of the piston 4. As shown in FIG. 2, the cavity 11 has a substantially circular shape in a plan view, and has a gentle gradient from the side wall surface to the bottom wall surface.
[0008]
FIG. 3 shows a form of fuel spray of the first embodiment. The tip of the fuel injection valve 9, that is, the injection hole 9 a, is located above the side wall surface of the cavity 11, and the center axis and the cylinder axis of the spray cone of the fuel injected from the fuel injection valve 9 toward the side wall surface 11 of the cavity 11. The fuel injection valve 9 is attached to the cylinder head 2 so that the angle β is approximately の of the spray cone angle α.
[0009]
Further, the fuel spray is formed in a semi-conical shape in which a half on the cylinder center side is cut off from the hollow conical shape due to the shape of the injection hole 9a or the like.
Here, the fuel injection is performed by opening the fuel injection valve for a predetermined period during each cycle, and the fuel injection amount is changed by changing the fuel injection period because the injection rate of a general fuel injection valve is constant. It is adjusted, and in that case, the injection start timing or the end timing will be changed. When the engine rotation speed changes, fuel injection is performed for a predetermined period based on the required load.However, even if the injection period is the same, if the injection start timing is fixed, or if the rotation speed is high, the injection is calculated in terms of crank angle. The end time is delayed. Conversely, when the injection end timing is fixed, the injection start is relatively early. Also, when the engine load changes, the injection end timing or the injection start timing naturally changes with the change of the injection period. As a result, as described above, in the conventional spray mode, when the injection end timing or the injection start timing fluctuates according to the change in the load or the rotation speed of the engine, the piston position when the fuel spray collides with the piston crown surface. Greatly changed, and it was difficult to stably obtain a good stratified mixture.
[0010]
On the other hand, in the present embodiment, the tip of the fuel injection valve 9 is arranged above the side wall surface of the cavity 11 and the fuel is injected from the fuel injection valve 9 toward the side wall surface of the cavity 11. Most of the fuel spray proceeds along the cylinder axis from above to below the side wall surface of the cavity 11 and collides with the side wall surface of the cavity 11 while always maintaining the same positional relationship even when the piston position (crank angle) at the time of collision is different. Therefore, the influence of the fuel injection timing on the formation of the stratified mixture is reduced, the range of the fuel injection timing that can be set is expanded, the operation region where stratified combustion can be performed is expanded, and the fuel consumption rate is improved and the exhaust emission is reduced. Is done.
[0011]
The effect of the present embodiment will be described in more detail with reference to FIG. FIG. 4 shows the movement of fuel in the cylinder when the compression stroke injection is performed to perform stratified combustion. Since the fuel injected from the fuel injection valve 9 is injected in the cylinder axis direction, that is, in the sliding direction of the piston, the fuel is received at substantially the same position in the cavity 11 regardless of the fuel injection timing.
[0012]
Since the center portion of the fuel injection valve 9 and the slope portion 11a of the peripheral wall of the cavity 11 are arranged at the same position in the cylinder axis projection direction, the fuel spray collides with the slope portion 11a facing the peripheral wall of the cavity 11. Since the fuel spray is injected at a high pressure of 10 Mpa or more, after once colliding with the slope portion 11a, the direction of the fuel spray is changed by the slope of the slope portion 11a by the penetrating force, and the bottom of the cavity 11 is provided below the ignition plug 10 in the cylinder. Proceed toward the opposite slope section across the axis.
[0013]
At this time, since the fuel spray atomized by the high-pressure injection collides with the slope at an obtuse angle, a thick liquid film is not formed on the crown surface, and the spray and the liquid film moving along the bottom surface of the cavity 11 are Vaporization and mixing are performed sequentially. Thereafter, the fuel spray is jumped up to the upper side of the combustion chamber 1 by the slope portion of the peripheral wall of the cavity 11 below the ignition plug 10, and a good mixture is formed near the ignition plug 10. Since the fuel mixture is sprayed in the sliding direction of the piston 4 as described above, the fuel mixture is substantially the same even if the fuel injection timing and the fuel injection period are changed depending on the engine load and the rotational speed. An air-fuel mixture can be formed around the spark plug 10.
[0014]
Further, in the present embodiment, the fuel injection valve is attached to the cylinder head so that the angle formed by the central axis of the spray cone and the cylinder axis is approximately の of the spray cone angle, and the hollow cone is used to move the fuel injection valve from the cylinder center to the cylinder center. Is formed so as to form a semi-conical spray in which a part is cut out, the following effects can be obtained.
That is, as in the conventional general case, when the fuel spray is formed into a continuous hollow conical shape and fuel injection is performed in the latter half of the compression stroke for stratified combustion, the inside of the cone has a low pressure with respect to the high atmospheric pressure in the latter half of the compression stroke. As a result, the spray is moved inward, resulting in a smaller spray angle. However, as in the present embodiment, by spreading the spray in a semi-conical shape, no differential pressure is generated inside and outside the spray, so that the spray angle does not greatly change depending on the in-cylinder pressure, that is, the injection timing. Therefore, it is possible to prevent the fuel from colliding with a part of the cavity 11 and to suppress generation of smoke and combustion chamber deposit.
[0015]
FIG. 5 shows a cavity shape according to the second embodiment. In the second embodiment, the cavity 11 has a gentle inclination from the side wall surface to the bottom wall surface, but from the direction corresponding to the fuel injection valve 9 toward the position of the cavity 11 corresponding to the ignition plug 10, The opening is set to be narrow in a fan shape. As a result, the once received fuel can be more concentrated and guided toward the spark plug 10.
[0016]
FIG. 6 is a schematic diagram of a fuel spray shape according to the third embodiment. Here, the fuel injection valve 9 is a multi-injection hole nozzle, and the directing direction of each injection hole is substantially directed to the cylinder center axis direction so that the center of gravity of the spray substantially matches the cylinder axis direction. Are arranged so that the fuel spray injected from each injection hole forms a semicircle.
As described above, in the present embodiment, the fuel spray injected from the fuel injection valve 9 is asymmetric with respect to the center axis of the fuel injection valve 9, and the center of gravity of the fuel spray is substantially parallel to the cylinder axis direction. Therefore, the fuel can be reliably received in the cavity 11 irrespective of the fuel injection timing, and the stratified combustion can be performed by arranging the air-fuel mixture having good properties in the ignition plug 10 in a wide operating region.
[0017]
FIG. 7 is a schematic diagram of a fuel spray shape according to the fourth embodiment. As in the third embodiment, the fuel injection valve 9 is a multi-injection hole nozzle, and the fuel spray shape is the same in that the fuel spray injected from each of the injection holes is arranged to form a semicircle. The semicircular center portion is arranged so as to be directed parallel to the cylinder axis.
In this embodiment, the fuel spray injected from the fuel injection valve is configured so that the ridge line closest to the cylinder peripheral wall is substantially parallel to the cylinder axis, so that the fuel spray flies in a direction different from the piston sliding direction. The amount of fuel spray can be reduced, and a good air-fuel mixture can be distributed to the ignition plug 10 in a wide operating range as in the third embodiment.
[0018]
FIG. 8 shows a piston shape according to the fifth embodiment. In the present embodiment, the shape of the piston cavity below the fuel injection valve 9 is substantially straight in a plan view. As schematically shown in FIG. 9, the fuel spray in the fifth embodiment has a configuration in which a flat fuel spray is injected using a fuel injection valve having an injection hole opened in a slit shape. The flat fuel spray shown in FIG. 9 is injected in the cylinder axial direction with respect to the piston crown surface shown in FIG. 8, and once the spray is received by a linear slope, the fuel injection timing and the fuel injection period change. Also, a good air-fuel mixture is formed near the ignition plug via the cavity, and a good air-fuel mixture can be formed around the ignition plug in a wide operating range.
[0019]
In the present embodiment, the fuel spray injected from the fuel injection valve 9 has a flat plate shape, and the injection direction of the fuel spray is configured to be substantially parallel to the cylinder axis direction. In addition to the fact that the fuel spray is easily received in the cavity 11, the direction in which the fuel spray once received advances in the cavity 11 can be easily controlled, and a stratified mixture can be formed more reliably.
[0020]
In addition, a configuration in which at least half of the fuel spray injected from the fuel injection valve 9 collides with the wall surface of the cavity 11 on the cylinder axis side at an obtuse angle is common to each embodiment. Therefore, the colliding fuel spray changes its traveling direction in the cavity 11 and moves toward the spark plug 10, so that a thick liquid film is not formed in the cavity 11. Once thinly deposited, the fuel liquid film is quickly vaporized and mixed, so that stratified combustion can be performed without generating smoke and combustion chamber deposits.
[0021]
Similarly, since the cavity 11 is configured so as to have a gentle gradient from the side wall surface to the bottom wall surface in common to each embodiment, while the fuel received by the cavity 11 on the piston 4 crown surface is vaporized, By climbing up the gradient and soaring toward the spark plug 10, it is possible to reliably arrange the stratified mixture around the spark plug 10.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a first embodiment of the present invention.
FIG. 2 is a plan view and a longitudinal sectional view showing the piston of the embodiment.
FIG. 3 is a view showing a form of fuel spray according to the embodiment.
FIG. 4 is a view showing movement of fuel in a cylinder according to the embodiment.
FIG. 5 is a plan view and a longitudinal sectional view showing a piston according to the second embodiment.
FIG. 6 is a diagram showing a form of fuel spray according to a third embodiment.
FIG. 7 is a view showing a form of fuel spray according to a fourth embodiment.
FIG. 8 is a plan view and a longitudinal sectional view showing a piston according to the fifth embodiment.
FIG. 9 is a view showing a form of fuel spray according to a fifth embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Combustion chamber 4 ... Piston 9 ... Fuel injection valve 9a ... Injection hole 10 ... Spark plug 11 ... Cavity

Claims (9)

An in-cylinder direct injection internal combustion engine in which a spark plug is disposed near the cylinder axis and a cavity having a bottom wall surface and a side wall surface is provided substantially at the center of the piston crown surface,
An in-cylinder direct injection internal combustion engine, wherein a tip of a fuel injection valve is arranged above the cavity side wall surface, and fuel is injected from the fuel injection valve toward the cavity side wall surface. The fuel injection valve is attached to a cylinder head such that an angle formed between a central axis of a spray cone of fuel injected from the fuel injection valve and a cylinder axis is approximately の of a spray cone angle. An in-cylinder direct injection internal combustion engine according to claim 1. The in-cylinder direct injection internal combustion engine according to claim 2, wherein the fuel injection valve forms a semi-conical spray in which a part on the cylinder center side is cut away from the hollow conical shape. The cylinder according to claim 1, wherein the fuel spray injected from the fuel injection valve is asymmetric with respect to the center axis of the fuel injection valve, and the center of gravity of the fuel spray is substantially parallel to the cylinder axis direction. Internal direct injection type internal combustion engine. 2. The direct injection internal combustion engine according to claim 1, wherein a ridge line of the fuel spray injected from the fuel injection valve closest to the cylinder peripheral wall is substantially parallel to the cylinder axis. 3. 2. The direct injection type internal combustion engine according to claim 1, wherein the fuel spray injected from the fuel injection valve has a flat plate shape, and an injection direction of the fuel spray is substantially parallel to a cylinder axis direction. 7. The fuel injection valve according to claim 1, wherein at least half of the fuel spray injected from the fuel injection valve collides at an obtuse angle with the cylinder center side wall surface of the cavity. An in-cylinder direct injection internal combustion engine according to any one of the preceding claims. The direct injection internal combustion engine according to any one of claims 1 to 7, wherein the cavity has a gentle gradient from a side wall surface to a bottom wall surface. The direct injection type internal combustion engine according to any one of claims 1 to 8, wherein the cavity has a gentle gradient from a bottom wall surface toward an upper portion of the cavity below the spark plug.

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