JP2003328759A - Direct injection, spark ignition type internal-combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct injection, spark ignition type internal-combustion engine capable of forming a stratified mixture gas in a proper condition in the neighborhood of a spark plug by injecting a fuel to a projecting part formed in a cavity at the crown surface of a piston. <P>SOLUTION: The cavity 31 is formed at the crown surface of the piston 7, and the side face 35 of the cavity is formed in a curved surface continued smoothly to the bottom surface 33 of the cavity, and the projecting part 37 protrusive in the axial direction of the cylinder is formed at the bottom surface 33 of the cavity. A top face 39 confronting the fuel atomization from a fuel injection valve 19 is formed at the tip of the projecting part 37, and it is arranged so that the extension surface of the top face 39 intersects the cavity bottom surface 33 at an obtuse angle. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection spark ignition type internal combustion engine that directly injects fuel into a cylinder.

[0002]

2. Description of the Related Art Conventionally, in a direct injection spark ignition type internal combustion engine, fuel is directly injected from a fuel injection valve into a cylinder to form a stratified air-fuel mixture, thereby performing a large lean combustion. There is. This has the advantage that the fuel consumption can be significantly reduced, especially when the internal combustion engine is under medium load or low load.

In such a direct injection spark ignition type internal combustion engine, since it is necessary to steadily ignite and burn the air-fuel mixture, an appropriate size and empty space are provided in the cylinder according to the rotational speed and load of the internal combustion engine. It is important to form a stratified mixture having a fuel ratio at the ignition position of the spark plug. For this purpose, it is important to atomize the fuel spray from the fuel injection valve and control the mixing of the spray and air by the combination of the spray and the shape of the piston crown surface to form a desired stratified mixture.

On the other hand, in a diesel engine in which fuel is directly injected into a cylinder to perform compression ignition combustion, Japanese Patent Laid-Open No. 9-4943
As described in Japanese Unexamined Patent Publication (Kokai) No. 1, there is provided a direct injection internal combustion engine in which a protrusion is formed in a cavity formed on a crown surface of a piston and fuel sprayed from a fuel injection valve is collided with the protrusion and diffused into the cavity. It is disclosed. The invention described in the publication is applied to a diesel engine in which atomized fuel is collided with projections in a cavity to be atomized and compressed to ignite and burn.

[0005]

However, the invention described in the publication is effective for a direct injection spark ignition type internal combustion engine as a technique for achieving good mixing of fuel spray and air, but a diesel internal combustion engine As a premise, the fuel is diffused to the lower part of the cavity. Therefore, it is difficult to apply the method directly to a direct-injection spark ignition internal combustion engine in which it is necessary to stratify the air-fuel mixture in the vicinity of an ignition plug arranged in the upper part of the combustion chamber.

[0006]

Therefore, in a direct injection spark ignition type internal combustion engine according to the present invention, a cavity is formed in the crown surface of the piston, and the side surface of the cavity is formed by a curved surface that is smoothly continuous with the bottom surface of the cavity. A protrusion protruding from the bottom surface of the cavity in the cylinder axial direction was provided at substantially the center. Then, a top surface facing the fuel spray from the fuel injection valve is formed at the tip of this protrusion, and an extension surface of this top surface is configured to intersect the cavity bottom surface at an obtuse angle.

[0007]

According to the present invention, since the top surface is provided at the tip of the projection protruding from the bottom surface of the cavity in the cylinder axial direction, the fuel sprayed from the fuel injection valve collides with the top surface and atomizes the spray. Can be made. Since the side surface of the cavity is formed by a curved surface that is smoothly continuous with the bottom surface, a circulating flow of atomized fuel spray is formed in the cavity and in the region above it. The atomized fuel spray evaporates and diffuses into the inside of the circulating flow to form a homogeneous air-fuel mixture, and the outside diffusion of the fuel spray is suppressed outside the circulating flow. As a result, there is an effect that a stratified mixture in a proper state is formed in the vicinity of the spark plug.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings, but the scope of the present invention is not limited to the embodiments described below. FIG. 1 is a system configuration diagram showing a configuration of a direct injection spark ignition type internal combustion engine according to a first embodiment of the present invention.

The internal combustion engine 1 has a combustion chamber 9 defined by a cylinder head 3, a cylinder block 5 and a piston 7. Fresh air is introduced into the combustion chamber 9 by an intake valve 11 and an intake port 13, and an exhaust valve 15 is provided. And exhaust port 17
The exhaust gas is discharged from the combustion chamber 9 by. A fuel injection valve 19 and a spark plug 21 are arranged in the center of the upper portion of the combustion chamber 9.

The internal combustion engine 1 is integrally controlled by an engine control unit (hereinafter referred to as ECU) 23. The ECU 23 controls the fuel injection valve 19, the spark plug 21 and the like by performing necessary processing and calculation based on signals sent from sensors such as the accelerator opening sensor 25, the water temperature sensor 27 and the crank angle sensor 29. FIG. 2 is an enlarged sectional view showing the combustion chamber. In the present embodiment, the combustion chamber 9 is formed in a pent roof shape, a fuel injection valve 19 is arranged in the center of the upper part of the combustion chamber 9, and an ignition plug 21 is arranged in the vicinity of the fuel injection valve 19.

The piston 7 has a crown shape corresponding to the pent roof shape of the combustion chamber 9, and a cavity (bowl) 31 is recessed in the center of the crown surface. Cavity 31
Is composed of a bottom surface 33 and a side surface 35, and the side surface 33 is composed of a curved surface that is smoothly continuous with the bottom surface 35, and the curved surface is directed toward the spark plug 21 at the opening of the cavity 31. A protrusion 37 is formed so as to protrude from the center of the bottom surface 33 in the axial direction of the cylinder.

The projection 37 has a fuel injection valve 19 at its tip.
Has a top surface 39 opposite to. In the present embodiment, the top surface 39 is a surface that is substantially perpendicular to the central axis of the spray from the fuel injection valve 19. The extension surface P of the top surface 39 intersects the bottom surface 33 of the cavity 31 at an obtuse angle. Here, the obtuse angle means that the angle θ shown in FIG. 2 is between 135 and 180 degrees.

Regarding the internal combustion engine 1 having the above structure,
The case where fuel is injected will be described. When the piston 7 approaches the compression top dead center, the fuel is injected from the fuel injection valve 19 toward the protrusion 37 of the cavity 31. Almost the entire amount of the injected fuel collides with the top surface 39 of the protrusion 37, and the spray is atomized. The atomized spray is the projection 3
7 travels radially outward from the top surface 39 and re-diffuses while entraining ambient air.

At this time, the re-dispersed spray collides with the bottom surface 33 at an obtuse angle and advances to the side surface 35 along the curved surface, as shown in FIG.
A circulating flow is formed from the cavity 31 toward the upper part of the combustion chamber 9 as indicated by the arrow. The fuel spray is vaporized and mixed in this circulation flow to form a stratified mixture. The stratified air-fuel mixture is in a state where its inside is mixed substantially homogeneously and excessive diffusion to the outside is suppressed.

According to the present embodiment, the entire amount of fuel injected from the fuel injection valve is configured to collide with the top surface 39 of the projection 37, so that a large-diameter spray does not remain and a more uniform spray is obtained. There is an effect that a stratified air-fuel mixture can be formed. Further, according to the present embodiment, since the curved surface forming the side surface 35 of the cavity 31 is directed toward the spark plug 21 at the opening of the cavity 31, a stratified mixture is formed in the vicinity of the spark plug 21. Then, the stratified air-fuel mixture can be satisfactorily burned, stable combustion can be realized, and at the same time, the emission amount of exhaust harmful components can be reduced, and good fuel efficiency can be obtained.

Further, according to this embodiment, since the top surface 39 of the projection 37 is constituted by a surface substantially perpendicular to the center axis of the spray of the fuel injection valve, when the spray collides with the top surface 39. Since the impact is large and atomization of the spray is promoted, there is an effect that a more homogeneous stratified mixture can be formed.
According to the present embodiment, the fuel injection valve 19 is installed in the combustion chamber 9
Since it is arranged in the center of the cylinder, the sprayed fuel can be prevented from adhering to the cylinder wall surface, and the positional relationship between the axis of the fuel injection valve 19 and the axis of the protrusion 37 is substantially the same with respect to the injection timing. It does not change as it is on a straight line. Therefore, there is an effect that a favorable stratified air-fuel mixture can be formed at a wider engine rotation speed and load.

Next, a second embodiment will be described.
FIG. 3 is a sectional view showing a combustion chamber of the internal combustion engine according to the second embodiment. In FIG. 3, the same parts as those described above are designated by the same reference numerals, and the description thereof will be omitted. In the present embodiment, as shown in the drawing, a depression 41 is formed around the protrusion 37 so as to be lower than the line of intersection between the extension surface P of the top surface 39 and the bottom surface 33 of the cavity 31.

The fuel injected from the fuel injection valve 19 collides with the top surface 39 of the projection 37, atomizes the spray, and is re-diffused outward in the radial direction. At this time, air can be entrained from the lower side of the spray flow re-diffusing in the depression 41, and vaporization and mixing can be promoted from both the upper side and the lower side of the re-diffusing spray. Therefore, according to the present embodiment, a more homogeneous stratified mixture can be formed, and more stable combustion can be performed,
There is an effect that emission of HC, NOx and the like can be suppressed.

FIG. 4 is a sectional view showing a combustion chamber of an internal combustion engine according to the third embodiment. Note that, also in FIG. 4, the same portions as those described above are denoted by the same reference numerals, and description thereof will be omitted. In the present embodiment, the tip portion of the protrusion 37 is formed in a conical shape as shown in the drawing, and the top surface 39a is formed as a conical surface. Also in this embodiment, the conical surface 39a and the bottom surface 3
The angle θ formed by 3 is an obtuse angle.

The fuel injected from the fuel injection valve 19 collides with the conical surface 39a and atomizes the spray. Since the conical surface 39a is formed with a slight inclination from the horizontal direction, the fuel spray advances radially outward at an angle slightly below the vertical with respect to the spray direction, and from the bottom surface 33 to the side surface 35. And a circulating stream of spray is formed. In the present embodiment, the fuel spray smoothly advances to the bottom surface 33 as compared with the case where the top surface 39 is formed as a flat surface, so that a more homogeneous stratified mixture can be formed in the vicinity of the spark plug 21. And, more stable combustion can be performed, and HC and NO
There is an effect that the discharge of x and the like can be suppressed.

FIG. 5 is a sectional view showing a combustion chamber of an internal combustion engine according to the fourth embodiment. FIG. 6 is a trihedral view showing a combustion chamber of an internal combustion engine according to a fourth embodiment, (a) is a sectional view thereof, (b) is a plan view taken along the line AA of (a),
(C) is a sectional view taken along line BB of (b). In the present embodiment, the tip portion of the protrusion 37 is formed in a pent roof shape composed of two planes. The apex angle of the pent roof at the tip of the protrusion 37 is formed as an obtuse angle because it is convenient for the sprayed fuel to form a stratified mixture, as described above.

Here, the symbol R shown in FIG. 6 indicates the position of the ridgeline of the pent roof of the combustion chamber 9. In the present embodiment, the ridgeline T of the protrusion 37 and the ridgeline R of the pent roof of the combustion chamber 9 are formed parallel to each other in the cylinder axis direction. The crown surface of the piston 7 is also formed in a pent roof shape, and its ridgeline Q is formed parallel to the ridgeline R of the pent roof of the combustion chamber 9 (see FIG. 6C).

Here, in the first to third embodiments, the fuel spray diffuses to the entire outer circumference of the projection 37 in the radial direction, but in the present embodiment, the fuel spray is perpendicular to the ridgeline T of the pent roof of the projection 37. Spread in any direction. Therefore, it becomes possible to form a small stratified small air-fuel mixture, and it is possible to obtain good fuel efficiency at a lower load. And
It is not necessary to form a curved surface from the bottom surface 33 of the cavity 31 to the opening over the entire circumference, and there is an advantage that the degree of freedom in designing the combustion chamber 9 is increased.

FIG. 7 is a trihedral view showing a combustion chamber of an internal combustion engine according to the fifth embodiment, and (a) is a sectional view thereof.
(B) is a plan view taken along the line AA of (A), and (C) is a cross-sectional view taken along the line BB of (B). Also in this embodiment, the tip of the protrusion 37 is formed in a pent roof shape composed of two planes, as in the above-described embodiments. However, in the present embodiment, the ridge line T of the pent roof of the protrusion 37 and the ridge line R of the pent roof of the combustion chamber 9 are formed so as to be orthogonal to each other.

According to the present embodiment, a large curved surface can be formed from the bottom surface 33 of the cavity 31 to the opening, and when atomized fuel is atomized and rediffused toward the ridge of the pent roof of the combustion chamber 9. In addition, there is an effect that a more homogeneous stratified mixture can be formed. Figure 8
FIG. 4 is a diagram showing a relationship between an engine rotation speed and a load in switching combustion modes of an internal combustion engine. FIG. 9 is a cross-sectional view showing a combustion chamber when fuel injection is performed during the intake stroke of the internal combustion engine. The system configuration of the internal combustion engine 1 is as shown in FIG.

The ECU 25 of the internal combustion engine 1 comprehensively judges the operating condition of the internal combustion engine 1 based on signals sent from the accelerator opening sensor 25, the water temperature sensor 27, the crank angle sensor 29, etc., and stratified combustion and homogeneous combustion. Switch. In the present invention, when the load is relatively low, fuel is mainly injected in the compression stroke to form a stratified mixture in the combustion chamber 9 for spark ignition combustion, and when the load is relatively high, the intake stroke is mainly used. The fuel is injected to form a homogeneous air-fuel mixture in the combustion chamber for spark ignition combustion.

Therefore, by switching between the two combustion methods of stratified combustion and homogeneous combustion according to the operating conditions of the internal combustion engine 1, there is an effect that both low fuel consumption and high output can be achieved at the same time. The fuel injection valve 19 used in the embodiment of the present invention is a so-called swirl type. The swirl type injection valve has a characteristic that the spray angle is narrow under high back pressure and wide under low back pressure. Therefore, when performing stratified combustion, that is, when injecting fuel in a compression stroke with a high back pressure, the entire spray can be made to collide with the top surface 39 of the protrusion 37 of the cavity 31. When performing homogeneous combustion, that is, when fuel is sprayed in the intake stroke with a low back pressure, it is preferable in the internal combustion engine 1 that the spray needs to be diffused throughout the combustion chamber 9 and uniformly mixed.

By using a swirl type injection valve, preferable spray characteristics can be obtained in both stratified charge combustion and homogeneous combustion, and both low fuel consumption and high output can be realized.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing a configuration of a direct injection spark ignition type internal combustion engine according to a first embodiment.

FIG. 2 is an enlarged sectional view showing a combustion chamber.

FIG. 3 is a sectional view showing a combustion chamber of a direct injection spark ignition type internal combustion engine according to a second embodiment.

FIG. 4 is a sectional view showing a combustion chamber of a direct injection spark ignition type internal combustion engine according to a third embodiment.

FIG. 5 is a sectional view showing a combustion chamber of a direct injection spark ignition type internal combustion engine according to a fourth embodiment.

FIG. 6 is a three-sided view showing a combustion chamber, (a) is a sectional view,
(B) is a plan view taken along the line AA of (B), and (C) is a cross-sectional view of (B).

FIG. 7 is a three-sided view showing the combustion chamber, (a) is a sectional view,
(B) is a plan view taken along the line AA of (B), and (C) is a cross-sectional view of (B).

FIG. 8 is a diagram showing a relationship between an engine rotation speed and a load in switching the combustion mode of the engine.

FIG. 9 is a sectional view showing a combustion chamber when fuel is injected during an intake stroke of an internal combustion engine.

[Explanation of symbols]

1 Direct injection spark ignition internal combustion engine 7 pistons 9 Combustion chamber 19 Fuel injection valve 21 spark plug 31 cavity (bowl) 33 Bottom 35 side 37 Projection 39 top 41 hollow

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 61/18 310 F02M 61/18 310Z F term (reference) 3G023 AA01 AA04 AA07 AB01 AB03 AC05 AD02 AD09 AG01 3G066 AA02 AB02 AD12 BA14 BA16 BA17 BA25 BA26 CC34 CC41 DB08 DB09 DC04 DC05 DC14 3G301 HA04 HA16 JA21 JA23 KA08 KA09 KA24 KA25 LB04 MA19 PE01Z PE03Z PE08Z PF03Z

Claims (11)

[Claims] 1. A fuel injection valve and an ignition plug are arranged substantially in the center of the upper part of a combustion chamber, and a cavity defined by a bottom surface and a side surface is formed as a recess in the crown surface of a piston that reciprocates in a cylinder. In the spark ignition internal combustion engine, the side surface of the cavity is formed by a curved surface that is smoothly continuous with the bottom surface of the cavity, and a projection portion that protrudes in the cylinder axial direction from the bottom surface of the cavity is provided substantially at the center of the cavity. A direct injection spark ignition type internal combustion engine, characterized in that a top surface facing the fuel spray from the fuel injection valve is formed at a tip, and an extension surface of the top surface intersects the bottom surface of the cavity at an obtuse angle. 2. The direct injection spark ignition type internal combustion engine according to claim 1, wherein the entire amount of fuel injected from the fuel injection valve is configured to collide with the top surface of the protrusion. 3. The direct injection spark ignition type internal combustion engine according to claim 1, wherein the curved surface forming the side surface of the cavity is directed toward the spark plug at the opening of the cavity. 4. The cavity is formed with a recess around the protrusion that is lower than a line of intersection between the extension surface of the top surface and the bottom surface of the cavity. The direct injection spark ignition type internal combustion engine according to claim 3. 5. The top surface of the protrusion is formed by a surface substantially perpendicular to the central axis of the spray from the fuel injection valve. Direct injection spark ignition internal combustion engine. 6. The direct injection spark ignition type internal combustion engine according to any one of claims 1 to 4, wherein a top surface of the projection is a conical surface. 7. The top surface of the protrusion is formed as a pent roof by two flat surfaces.
The direct injection spark ignition type internal combustion engine according to claim 4. 8. The direct injection spark ignition according to claim 7, wherein the pent roof-shaped ridgeline of the top surface of the protrusion and the pent roof-shaped ridgeline of the combustion chamber are oriented in directions orthogonal to each other. Internal combustion engine. 9. The direct injection device according to claim 1, wherein the fuel injection valve is arranged in the center of the upper part of the combustion chamber, and the spark plug is arranged in the vicinity thereof. Spark ignition internal combustion engine. 10. The direct injection spark ignition type internal combustion engine according to claim 1, wherein the fuel injection valve is a swirl type injection valve. 11. At a relatively low load, fuel is mainly injected in a compression stroke to form a stratified mixture in a combustion chamber for spark ignition combustion, and at a relatively high load, fuel is mainly used in an intake stroke. The direct injection spark ignition internal combustion engine according to any one of claims 1 to 10, characterized in that a homogeneous air-fuel mixture is formed in the combustion chamber to perform spark ignition combustion.