JP2002004864A - Cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize proper stratified charge combustion, even when a strong squish is generated at high-speed rotation of an engine. SOLUTION: This cylinder injection type spark ignition internal combustion engine has a cavity 8, formed on a top face of a piston 5 for having a facing sidewall 8b facing a fuel injection valve for guiding fuel injected in the cavity in a later half of compressing process from the fuel injection valve upwards along the facing sidewall, ultimately in the neighborhood of an ignition plug 6. A squish area for generating a squish flow bound for the neighborhood of the ignition plug in the later half of compressing process is formed on a part between the top face of piston and a cylinder head. The facing sidewall of the cavity has a pointing face P, to direct fuel to the neighborhood of the ignition plug. A Coanda operating face Q for directing a part of the fuel flowing on the pointing face to a neighboring region near to the squish area for a neighboring region of the ignition plug using Coanda effect is formed on a part of the open end of the pointing face.

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 internal combustion engine.

[0002]

2. Description of the Related Art An in-cylinder injection spark ignition internal combustion engine having a fuel injection valve for directly injecting fuel into a cylinder injects fuel into a cavity formed on a piston top surface in the latter half of a compression stroke. With this, the fuel is vaporized using the high-temperature air and the heat of the piston, and is guided to the vicinity of the spark plug,
At the ignition timing, a flammable mixture having good ignitability is formed only in the vicinity of the ignition plug, and stratified combustion capable of burning a lean mixture as a whole in the cylinder is realized.

In a general cylinder injection type spark ignition internal combustion engine, fuel injected into a cavity travels along a bottom wall in the cavity and a side wall facing the fuel injection valve and is guided to the vicinity of a spark plug. . The opposite side wall of the cavity is provided with a return portion for finally deflecting the fuel near the spark plug located above the inside of the cavity.

The direct injection type spark ignition internal combustion engine disclosed in Japanese Patent Application Laid-Open No. 2000-27652 discloses that all fuels are provided by partially changing the length of the return portion in the cavity on the opposing side wall of the cavity. Are not allowed to reach the vicinity of the ignition plug at the same time, but the arrival times of the respective parts of the fuel are provided with a difference so that the combustible mixture formed by the respective parts of the fuel continuously passes through the vicinity of the ignition plug.
Thus, near the ignition timing, the combustible mixture formed by any of the fuel portions is always in contact with the ignition plug, and the combustible mixture can be reliably ignited and burned.

[0005]

However, in a direct injection type spark ignition internal combustion engine, if a cavity is formed on the piston top surface, a squish flow flowing into the cavity may be generated at the end of the compression stroke. This squish flow is directed toward the vicinity of the spark plug, and becomes stronger as the engine speed increases.

In the above-described prior art, if stratified combustion is limited to a low engine speed, the squish flow generated is weak, so that the combustible mixture can be ignited and burned without any particular problem. However, when the stratified combustion operation region is expanded to the high rotation side, at the ignition timing, the combustible mixture near the ignition plug is deformed by a strong squish flow, and the ignition gap of the ignition plug comes into contact with the peripheral portion of the combustible mixture. It will be. The periphery of the combustible mixture has a large concentration gradient with respect to the surrounding air. As a result, even if the ignition gap is in contact with such a peripheral portion whose concentration is unstable, the combustible air-fuel mixture may not be ignited and satisfactorily burned in some cases.

Accordingly, an object of the present invention is to form a combustible air-fuel mixture in the vicinity of a spark plug and perform stratified charge combustion, so that fuel injected into a cavity formed on the top surface of the piston is finally converted to a gas in the cavity. An object of the present invention is to enable good stratified combustion to be realized even when a strong squish flow is generated at a high engine speed in an in-cylinder injection spark ignition internal combustion engine guided to the vicinity of a spark plug by an opposed side wall.

[0008]

According to the first aspect of the present invention, there is provided a direct injection type spark ignition internal combustion engine having a spark plug disposed on an upper wall of a cylinder and a fuel for directly injecting fuel into the cylinder. An injection valve, and a cavity formed on a piston top surface, wherein the cavity has an opposite side wall facing the fuel injection valve, and is injected into the cavity in the latter half of the compression stroke from the fuel injection valve. In a direct injection type spark ignition internal combustion engine in which fuel is finally directed upward along the opposed side wall and near the spark plug, a part of the compression stroke is provided between the piston top surface and the cylinder head. A squish area for generating a squish flow toward the vicinity of the ignition plug is formed in the latter half, and the opposed side wall of the cavity has a directing surface for directing fuel to a region near the ignition plug. At a part of the open end of the directing surface, a part of the fuel traveling on the directing surface is directed to an adjacent area adjacent to the squish area side with respect to the area near the ignition plug by using a Coanda effect. It is characterized in that a Coanda working surface is provided.

According to a second aspect of the present invention, there is provided a cylinder injection type spark ignition internal combustion engine, comprising: a spark plug disposed on an upper wall of a cylinder; a fuel injection valve for directly injecting fuel into the cylinder; A cavity formed on the top surface of the piston, the cavity having an opposing side wall facing the fuel injection valve, and the fuel injected from the fuel injection valve into the cavity in the latter half of the compression stroke. In the direct injection type spark ignition internal combustion engine which is guided upwardly along the opposed side wall to the vicinity of the ignition plug, a part between the piston top surface and the cylinder head includes the ignition in the second half of the compression stroke. A squish area for generating a squish flow toward the vicinity of the plug is formed, and the opposite side wall of the cavity has a directing surface for directing fuel to a region near the ignition plug, The squish area portion at the open end, characterized in that the inclined surface inclined outward of the cavity with respect to the directional surface is provided.

[0010]

FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a direct injection type spark ignition internal combustion engine according to the present invention. FIG. 2 is a plan view of the piston of FIG. In these figures, 1 is an intake port, and 2 is an exhaust port.
The intake port 1 communicates through the intake valve 3 and the exhaust port 2 communicates through the exhaust valve 4 into the cylinder. The in-cylinder injection spark ignition internal combustion engine in the present embodiment is an intake / exhaust two-valve engine having two intake ports 1 and intake valves 3 and two exhaust ports 2 and exhaust valves 4, in particular. ,
It does not limit the invention. 5 is a piston,
The top surface has a concave cavity 8 unevenly distributed on the intake valve 3 side.
Are formed. Reference numeral 6 denotes an ignition plug disposed substantially at the center of the upper portion of the cylinder, and reference numeral 7 denotes a fuel injection valve for directly injecting fuel from the periphery of the upper portion of the cylinder into the cylinder. The fuel injection valve 7 is disposed on the side of the intake port 1 where the temperature becomes relatively low due to the intake flow in the cylinder in order to prevent fuel vapor.

The fuel injection valve 7 has a slit-shaped injection hole, and injects fuel in a thin fan shape.
In order to perform stratified combustion, fuel is injected into a cavity 8 formed on the top surface of the piston 5 in the latter half of the compression stroke, as shown in FIG. The cavity 8 has a bottom wall 8a against which the fuel injected from the fuel injection valve 7 collides, and an opposing side wall 8b facing the fuel injection valve 7. Although the fuel 10 immediately after the injection indicated by hatching is liquid, the cavity 8
At the time of ignition, and becomes a flammable mixture having good ignitability indicated by dots at the time of ignition. In this way, a combustible mixture is formed only in the vicinity of the ignition plug 6 to realize stratified charge combustion in which a lean mixture can be burned as a whole in the cylinder.

Since the fan-shaped fuel spray having a small thickness spreads in the width direction when traveling along the bottom wall 8a of the cavity 8, the fuel spray in the cavity 8 has a smaller thickness than a general conical fuel spray.
The heat can be well absorbed from a wide range of the bottom wall 8a of the base member 8 and easily vaporized. This makes it possible to inject a relatively large amount of fuel in the latter half of the compression stroke, and to expand the stratified charge combustion operation region where the fuel consumption rate is low toward the high rotation and high load side. Since the opposing side wall 8b of the cavity 8 has an arc shape in a plan view, the central portion of the fuel in the width direction is such that the velocity vector traveling on the bottom wall 8a is changed to an upward velocity vector by the opposing side wall 8b. It is converted and can be directed to the vicinity of the ignition plug 6. Further, both sides of the fuel in the width direction collide with the opposing side wall 8b at an acute angle, and the velocity vector traveling on the bottom wall 8a is increased by the opposing side wall 8b and the velocity vector in the center direction. This is converted into a combined speed vector with the vector, and it is possible to move toward the vicinity of the ignition plug 6. Thus, a lump of combustible air-fuel mixture can be formed near the ignition plug.

By the way, in order to locate the ignition plug 6 disposed substantially at the center of the upper part of the cylinder near the opposing side wall 8b of the cavity 8, the cavity 8 must be unevenly distributed on the top surface of the piston. (If the cavity is unevenly located on the intake valve side of the piston top surface as in the present embodiment, it will be on the exhaust valve side of the piston top surface). The squish area S is easily formed. Thus, at the end of the compression stroke, which is the ignition timing, a squish flow is generated from the squish area S into the cavity 9, that is, toward the vicinity of the spark plug 6.

The squish flow is weak when the engine is running at a low speed, and does not cause a problem such as deformation of the combustible air-fuel mixture. However, when the stratified combustion is to be performed on the high engine speed side, the squish flow becomes strong, and FIG.
As shown by the arrow in FIG. 5, the combustible mixture M at the ignition timing is deformed, and the ignition gap of the ignition plug 6 comes into contact with the peripheral portion of the combustible mixture. The peripheral portion of the combustible mixture has a large concentration gradient with respect to the surrounding air, that is,
In this peripheral portion, the concentration of the air-fuel mixture rapidly decreases toward the surrounding air (air-fuel concentration is zero). In particular, when the engine is running at high speed, since the time from the end of fuel injection to the ignition timing is short, the degree of dispersion in the combustible air-fuel mixture is low, and the concentration gradient in the surrounding area is further increased. It is difficult to ignite the combustible mixture even if the ignition gap is in contact with the surrounding portion of the combustible mixture which is unstable in concentration. Thus, misfire is likely to occur due to the squish flow.

In the direct injection type spark ignition internal combustion engine of the present embodiment, as shown in FIG.
Has a directional surface P for directing the main fuel to the region near the spark plug, and at a part of the open end of the directional surface P, a part of the fuel traveling on the directional surface P is partially It has a Coanda action surface Q directed to an adjacent area adjacent to the squish area S with respect to the adjacent area. The Coanda working surface Q is an inclined surface that is inclined outward of the cavity 8 with respect to the directing surface P. As a result, as shown in FIG. 3, most of the fuel guided by the directional surface P on the opposed side wall 8b of the cavity 8 forms a combustible mixture M1 near the ignition plug, and some of the fuel has a Coanda effect. The air-fuel mixture M2 is formed in the region adjacent to the squish area S with respect to the vicinity of the ignition plug by the Coanda effect of the surface Q.

In practice, the combustible mixture M1 and the mixture M2
Is a lump and cannot be clearly distinguished, but for the sake of simplicity, will be described below in a distinguished manner. If the air-fuel mixture M2 is formed by the Coanda action surface Q as described above, the concentration around the boundary of the combustible air-fuel mixture M1 with the air-fuel mixture M2 gradually decreases the air-fuel mixture concentration toward the air around the air-fuel mixture M2. Therefore, the mixture has a substantially uniform mixture concentration with good ignitability.

As a result, when the squish flow is generated as shown in FIG. 4 at the ignition timing at the end of the compression stroke, the combustible air-fuel mixture M1 is deformed substantially in the same manner as described above, and the periphery of the boundary contacts the ignition gap. As described above, the concentration of the air-fuel mixture around the boundary is substantially uniform and good ignitability is guaranteed as described above, so that the combustible air-fuel mixture M1 can be ignited and burnt well.

Further, the presence of the air-fuel mixture M2 also has an effect of slightly suppressing the deformation of the combustible air-fuel mixture M1 due to the squish flow.
Is improved as compared with the prior art shown in FIG. Further, the concentration of the air-fuel mixture M2 is generally lean, but at the ignition timing, the air-fuel mixture is compressed in the direction of the combustible air-fuel mixture M1 by the squish flow, so that the concentration becomes sufficiently combustible, and the air-fuel mixture M2 becomes unburned It is not emitted as fuel.

Thus, by providing the Coanda working surface Q, good stratified combustion can be realized at the time of high engine speed. Also, when the engine is running at low speed, the combustible air-fuel mixture M1 near the spark plug is similar to when the engine is running at high speed.
Then, the combustible mixture M1 is formed with the mixture M2 adjacent to the squish area S side. At this time, the time from fuel injection to ignition timing is long, and in ignition timing,
The combustible air-fuel mixture M1 near the spark plug is dispersed to some extent and overlaps with the air-fuel mixture M2, so that the overall combustible air-fuel mixture has good ignitability. Also, at this time, the squish flow is weak, and the overall combustible mixture is not deformed, but is ignited and burned well by reliable contact of the spark plug 6 with the ignition gap.

However, when the engine is running at a low speed, there is a relatively long time from the fuel injection to the ignition timing. At this time, the air-fuel mixture M2 is also easy to disperse. If the space side angle with the surface Q is too large, dispersion of the air-fuel mixture M2 to the squish area S side is promoted, and unburned fuel is increased. Need to be set appropriately.

Further, when the Coanda working surface Q is formed on the entire open end of the directing surface P, a relatively lean air-fuel mixture is provided not only in the area adjacent to the squish area with respect to the area near the spark plug but also in other adjacent areas. Which merely increases the unburned fuel. Accordingly, as described above, the Coanda working surface Q is formed so that the air-fuel mixture M2 is formed only in the region between the vicinity of the ignition plug 6 and the squish area S, and the open end of the directing surface P is the squish area side portion. Only, that is, at the open end of the directivity plane P, it is preferable to provide only the range corresponding to the width of the strong squish flow at the time of high engine rotation. In the present embodiment, the Coanda action surface Q is formed as a part of a cylindrical shape inclined toward the squish area S with respect to the cylinder center axis. Thereby, at the open end of the directivity plane P,
Both sides of the Coanda working surface Q smoothly disappear.

In the above-described embodiment, the cavity 8 on the top surface of the piston 5 distinguishes the bottom wall 8a against which the fuel collides and the opposed side wall 8b which guides the fuel traveling on the bottom wall 8a to the vicinity of the ignition plug. It is possible. However, this is not a limitation of the present invention. For example,
Even if the bottom wall and the opposing side wall cannot be distinguished in shape as in the case where the cavity has a substantially hemispherical shape, the present invention provides a structure in which a portion where fuel collides is used as the bottom wall, It is clear that the portion that directs the fuel traveling upwards near the spark plug is intended as the opposing side wall of the cavity.

In the present embodiment, the opposing side wall 8b of the cavity 8 has, in a longitudinal section, an arc-shaped portion extending smoothly from the bottom wall 8a, and a linear directing surface extending in a tangential direction of the arc-shaped portion. P. However, this does not limit the invention,
The radius of the arc-shaped portion may be increased, and the tip of the arc-shaped portion may be used as the directivity plane P for directing the fuel to the region near the ignition plug.

[0024]

As described above, according to the in-cylinder injection spark ignition internal combustion engine according to the first aspect of the present invention, fuel is directly injected into the cylinder with the spark plug disposed on the upper wall of the cylinder. A fuel injection valve, and a cavity formed on the piston top surface, the cavity has an opposing side wall facing the fuel injection valve, and the fuel injected from the fuel injection valve into the cavity in the latter half of the compression stroke. In a direct injection type spark ignition internal combustion engine that finally leads upward along the opposing side wall to the vicinity of the spark plug, a part between the piston top surface and the cylinder head has a portion near the spark plug in the latter half of the compression stroke. A squish area for generating a squish flow directed toward the ignition plug is formed, and the opposing side wall of the cavity has a directing surface for directing fuel to a region near the spark plug, and a part of the open end of the directing surface advances on the directing surface. Coanda effect surfaces to direct to the adjacent areas partially utilizing Coanda effect adjacent to the squish area side with respect to the spark plug near the area of the fuel is provided for. Thereby, at the time of high engine speed, the squish flow toward the vicinity of the spark plug in the latter half of the compression stroke increases,
The squish flow deforms the combustible mixture formed in the region near the ignition plug by the fuel along the directional surface of the cavity-facing side wall, and the ignition gap of the ignition plug comes into contact with the squish area side peripheral portion of the combustible mixture. In other words, the surrounding portion is adjacent to the air-fuel mixture formed in the adjacent region by a part of the fuel along the Coanda working surface, thereby causing a concentration gradient with respect to the surrounding air. It has a substantially uniform mixture concentration with good properties. Thus, even if a strong squish flow is generated, the combustible air-fuel mixture in the vicinity of the ignition plug reliably ignites and burns, and good stratified combustion can be realized.

Further, according to the cylinder injection type spark ignition internal combustion engine according to the second aspect of the present invention, there is provided a spark plug disposed on an upper wall of a cylinder, and a fuel for directly injecting fuel into the cylinder. An injection valve, and a cavity formed on a piston top surface, the cavity having an opposing side wall facing the fuel injection valve, and the fuel injected from the fuel injection valve into the cavity in the second half of the compression stroke. In an in-cylinder injection spark ignition internal combustion engine that is guided upward along the opposing side wall to the vicinity of the spark plug, a portion between the piston top surface and the cylinder head is directed toward the vicinity of the spark plug in the latter half of the compression stroke. A squish area for generating a squish flow is formed, and the opposing side wall of the cavity has a directing surface for directing fuel to a region near the ignition plug, and a squish area side portion at an open end of the directing surface. The inclined surface is provided which is inclined outwardly of the cavity relative to oriented surfaces. Thereby,
At high engine speed, the squish flow toward the vicinity of the spark plug intensifies in the latter half of the compression stroke.
The fuel along the directional surface of the cavity-facing side wall deforms the combustible mixture formed in the region near the ignition plug, and the ignition gap of the ignition plug comes into contact with the squish area side peripheral portion of the combustible mixture. This peripheral portion is adjacent to an air-fuel mixture formed by a part of fuel along an inclined surface provided on a squish area side portion at an open end of the directing surface, so as to cause a concentration gradient with respect to surrounding air. The surroundings will have a substantially uniform mixture concentration with good ignitability. Thus, even if a strong squish flow is generated, the combustible air-fuel mixture in the vicinity of the ignition plug reliably ignites and burns, and good stratified combustion can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a direct injection spark ignition internal combustion engine according to the present invention.

FIG. 2 is a plan view of the piston of FIG. 1;

3 is an enlarged cross-sectional view of the vicinity of a cavity-facing side wall of the in-cylinder injection spark ignition internal combustion engine of FIG. 1 in a latter half of a compression stroke.

FIG. 4 is an enlarged sectional view of the vicinity of a cavity-facing side wall of the in-cylinder injection spark ignition internal combustion engine of FIG. 1 at an ignition timing.

FIG. 5 is an enlarged sectional view showing the vicinity of a cavity-facing side wall of a conventional direct injection type spark ignition internal combustion engine at an ignition timing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Intake port 2 ... Exhaust port 3 ... Intake valve 4 ... Exhaust valve 5 ... Piston 6 ... Spark plug 7 ... Fuel injection valve 8 ... Cavity 8a ... Bottom wall 8b ... Opposite side wall P ... Directional surface Q ... Coanda working surface S ... Squish area

Claims (2)

[Claims] A spark plug disposed on an upper wall of the cylinder;
A fuel injection valve for directly injecting fuel into the cylinder, and a cavity formed on the top surface of the piston, wherein the cavity has an opposing side wall facing the fuel injection valve, from the fuel injection valve In the cylinder injection type spark ignition internal combustion engine, the fuel injected into the cavity in the latter half of the compression stroke is finally directed upward along the opposite side wall and guided to the vicinity of the ignition plug. A squish area for generating a squish flow toward the vicinity of the ignition plug in the latter half of the compression stroke is formed in a part between the head and the head, and the opposed side wall of the cavity has a directing surface for directing fuel to a region near the ignition plug. A part of the open end of the directing surface has a part of the fuel that travels on the directing surface, utilizing a Coanda effect to the spark plug vicinity region. Injection spark ignition internal combustion engine, characterized in that the Coanda effect surfaces to direct to the adjacent region adjacent to the serial squish area side. 2. A spark plug disposed on an upper wall of the cylinder,
A fuel injection valve for directly injecting fuel into the cylinder, and a cavity formed on the top surface of the piston, wherein the cavity has an opposing side wall facing the fuel injection valve, from the fuel injection valve In the cylinder injection type spark ignition internal combustion engine, the fuel injected into the cavity in the latter half of the compression stroke is finally directed upward along the opposite side wall and guided to the vicinity of the ignition plug. A squish area for generating a squish flow toward the vicinity of the ignition plug in the latter half of the compression stroke is formed in a part between the head and the head, and the opposed side wall of the cavity has a directing surface for directing fuel to a region near the ignition plug. Having a squish area side portion at an open end of the directing surface,
An in-cylinder injection spark ignition internal combustion engine, wherein an inclined surface inclined outward of the cavity with respect to the directing surface is provided.