JP2005171814A - Direct cylinder injection internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably form air-fuel mixture at an ignition position of an ignition plug 14 while maintaining a stratification degree of the air-fuel mixture, in injection in a compression stroke. <P>SOLUTION: A cylindrical first cavity 7 and a second cavity 8 of a bottom face of the first cavity 7 are formed to a piston crown surface 5a. The center B of the second cavity 8 is shifted from the center A of the first cavity 7. A swirl control valve forms swirl flows S1, S2 in the first cavity 7 and the second cavity 8, respectively, and fuel is carried to the ignition plug by an upward flow U. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a direct injection type internal combustion engine.

  An example of a gasoline direct injection internal combustion engine is described in Patent Document 1. This comprises a fuel injection valve that injects fuel in parallel with the cylinder axis from the center of the cylinder head, and an ignition plug is disposed at a position adjacent to the fuel injection valve. And a fuel injection valve implement | achieves highly efficient combustion by injecting fuel in the latter half of a compression stroke at the time of partial load.

In such an internal combustion engine, a bowl-like cavity is formed at the center position of the piston crown surface, and a generally conical ridge is formed at the center position of the cavity. It is known that fuel spray from the fuel injection valve collides with the peripheral wall of the cavity at an acute angle and circulates in the bowl to form an air-fuel mixture at the ignition position of the spark plug.
JP 2000-34925 A

However, since the load with good fuel consumption is determined by the size of the bowl only by the air-fuel mixture formation by circulation in the bowl, the load with poor fuel consumption can be made depending on the size of the bowl.
The present invention has been made paying attention to such problems, and an object thereof is to stably form an air-fuel mixture at an ignition position of a spark plug while maintaining the stratification degree of the air-fuel mixture during compression stroke injection. .

  Therefore, in the present invention, in a direct injection type internal combustion engine that forms a swirl flow in a cylinder, a cylindrical first cavity and a second cavity in the first cavity are formed on the piston crown surface, The center of the cavity was shifted from the center of the first cavity.

  According to the present invention, by shifting the center of the first cavity and the center of the second cavity, the center position of the swirl flow generated in the cavity is shifted, thereby generating an upward flow of the fuel spray and the spark plug. Thus, the air-fuel mixture can be stably formed at the ignition position, and stable and highly efficient operation can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a configuration of an internal combustion engine 1 according to the first embodiment of the present invention.
A combustion chamber 2 of the internal combustion engine 1 is formed by a cylinder head 3, a cylinder block 4 and a piston 5.
An intake port 10 and an exhaust port 11 formed in the cylinder head 3 communicate with the combustion chamber 2. In order to perform intake air from the intake port 10 or exhaust air from the exhaust port 11, an intake valve 12 and an exhaust valve 13 are provided. The intake valve 12 and the exhaust valve 13 are driven to open and close by an intake valve cam and an exhaust valve cam (not shown), respectively.

A fuel injection valve 14 is disposed downward in the cylinder axial direction substantially at the upper center of the combustion chamber 2. On the exhaust side near the fuel injection valve 14 (substantially the center at the top of the combustion chamber 2), a spark plug 15 is disposed obliquely, and the ignition gap is disposed at the combustion chamber center position (on the cylinder center axis).
A cavity 6 is formed in the crown surface 5 a of the piston 5. The cavity 6 includes a first cavity 7 formed on the piston crown surface 5 a and a second cavity 8 formed on the bottom surface of the cavity 7. The first cavity 7 and the second cavity 8 are formed such that the center A of the first cavity 7 and the center B of the second cavity 8 are shifted from each other in the radial direction of the piston (left-right direction in the figure). Yes.

The first cavity 7 is formed in a substantially cylindrical shape with a predetermined depth in the cylinder axial direction. The outer peripheral side wall of the cavity 7 is expanded from the piston crown surface 5a toward the cylinder shaft downward. The center A of the first cavity 7 is in the vicinity of a straight line parallel to the cylinder axis and passing through the ignition position of the spark plug 15.
The second cavity 8 is formed in the first cavity 7 and is formed in a cylindrical shape with a predetermined depth in the cylinder axial direction. The outer periphery (side wall) 8 a of the second cavity 8 is formed so that the center A of the first cavity 7 is located slightly inside the second cavity 8 on the axial center side of the piston 5. The bottom surface 8 b of the second cavity 8 is formed to face the fuel injection valve 14 and is formed perpendicular to the axis of the fuel injection valve 14. The center B of the second cavity 8 is in the vicinity of an extension line of the axis of the fuel injection valve 14.

The internal combustion engine 1 controls the fuel injection timing (fuel injection amount) of the fuel injection valve 14 and the ignition timing of the spark plug 15 based on a signal from an engine control unit (not shown).
Further, in the internal combustion engine 1, as a combustion mode, a stratified operation mode that realizes operation at a lean air-fuel ratio by performing fuel injection during the compression stroke and improves fuel consumption, and fuel injection during the intake stroke. And a homogeneous operation mode in which operation is performed at a stoichiometric air-fuel ratio. These operation modes are appropriately selected according to the current operation state with reference to an operation region map or the like determined in advance from the operation state (rotation speed, load).

Hereinafter, the stratified operation mode will be described.
A swirl control valve 17 is disposed in the intake passage 16 upstream of the intake port 10. When the swirl control valve 17 has two intake valves 12 for each cylinder and has an intake port 10 independent for each intake valve 12, one intake port 10 can be opened and closed. This valve 17 generates and strengthens swirl flow in the cylinder (inside the combustion chamber 2). This is a means to enhance swirl flow. In addition, when there are two intake valves 12 in each cylinder, the swirl flow enhancing means may enhance the swirl flow in the combustion chamber 2 by shifting the opening timing of each intake valve. Further, the swirl flow in the combustion chamber 2 may be enhanced by making the intake port 10 a helical port.

When a swirl flow is generated in the combustion chamber 2, as shown in FIG. 2, a first swirl flow S1 swirling in the first cavity 7 of the piston 5 and a second swirl flow S2 swirling in the second cavity 8 are obtained. And are formed respectively.
In the swirl flow field, the pressure in the vicinity of the turning center decreases, and the pressure increases toward the outer peripheral side. For this reason, if two swirl flows are piled up and down and the center of rotation is shifted, an upward flow and a downward flow are partially generated. In the present embodiment, since the outer peripheral portion (side wall 8a of the second cavity 8) of the second swirl flow S2 is disposed in the vicinity of the turning center of the first swirl flow S1 (center A of the first cavity 7), the first An upward flow U is generated near the center A of the cavity 7.

  When operating in a predetermined stratified combustion operation region, the first swirl flow S1 and the second swirl flow S2 are strengthened by the swirl control valve 17 and directed from the fuel injection valve 14 to the second cavity 8 in the latter half of the compression stroke. Inject fuel. The fuel that has reached the second cavity 8 is well mixed with air by the second swirl flow S2. By raising the air-fuel mixture on the upward flow U, the air-fuel mixture can reliably reach the ignition position of the spark plug 15.

The spark plug 15 performs combustion by igniting the transported fuel (air mixture). Exhaust gas after combustion is discharged from the combustion chamber 2 to the exhaust port 11 via the exhaust valve 13.
According to the present embodiment, the fuel injection valve 14 that directly injects fuel from the upper part of the combustion chamber 2, the ignition plug 15 disposed substantially at the center of the upper part of the combustion chamber 2, and the swirl flows S1 and S2 in the cylinder are strengthened. Means (for example, a swirl control valve 17), and has a cylindrical first cavity 7 in the piston crown surface 5a, a second cavity 8 in the first cavity 7, and a second cavity 8 The first cavity 7 and the second cavity 8 are formed so as to shift the center B of the first cavity 7 from the center A of the first cavity 7. For this reason, the center positions of the swirl flows S1 and S2 generated in the first cavity 7 and the second cavity 8 are shifted from each other. As a result, an upward flow U is generated and the fuel injected from the fuel injection valve 14 is generated. Can be stably supplied to the spark plug 15.

  Further, according to the present embodiment, the outer periphery (wall surface 8 a) of the second cavity 8 is formed at the approximate center A of the first cavity 7 on the axial center side of the piston 5. For this reason, there may be a field where the swirl flow S1 in the first cavity 7 is very weak in the direction from the piston 5 to the cylinder head 3 where the swirl flow S2 in the second cavity 8 is very strong. Due to this effect, a strong upward flow U from the second cavity 8 toward the first cavity 7 is generated, and the supplied fuel can be stably supplied to the spark plug.

According to the present embodiment, the center A of the first cavity 7 is parallel to the cylinder axis and below the ignition position of the spark plug 15. For this reason, it becomes possible to stably ignite the fuel transported by the upward flow U.
According to the present embodiment, the second cavity 8 is on an extension line of the axis of the fuel injection valve 14. Therefore, the fuel can be stably supplied into the second cavity 8, and the supplied fuel can be transported to the spark plug 15 by the generated upward flow U. This effect makes it possible to stably ignite the transported fuel.

Further, according to the present embodiment, the center B of the second cavity 8 is on an extension line of the axis of the fuel injection valve 14. For this reason, the fuel can be supplied into the second cavity 8 in a more stable state.
Further, according to the present embodiment, the fuel injection valve 14 is disposed substantially at the center of the upper portion of the combustion chamber 2. For this reason, fuel can be disposed in the cavities 7 and 8 while maintaining a high degree of stratification. This effect not only provides stable combustion, but also enables combustion with good exhaust performance.

  Further, according to the present embodiment, in a predetermined operation region (operation region based on the rotation speed and load), operation is performed with stratified combustion in which fuel is injected during the compression stroke, and swirl flow enhancement means (for example, The swirl control valve 17) strengthens the swirl flow S1, S2. Therefore, it is possible not only to generate a uniform fuel in the cavities 7 and 8 while maintaining the stratification degree, but also to increase the upward flow U from the second cavity 8 toward the first cavity 7. It becomes possible. This effect not only provides stable combustion, but also enables combustion with good exhaust performance.

Further, according to the present embodiment, in a predetermined stratified combustion operation region, the fuel injection valve 14 injects fuel into the second cavity 8 and the swirl flow enhancing means 17 enhances the swirl flow. For this reason, stable combustion with even better exhaust performance is possible.
Further, according to the present embodiment, in a predetermined stratified combustion operation region, the fuel injection valve 14 performs a plurality of times of fuel injection in one stroke, and injects the fuel to be injected last into the second cavity 8. Then, the swirl flow enhancing means 17 enhances the swirl flow S1, S2. For this reason, fuel can be stably supplied to the spark plug 15 by the upward flow U from the second cavity 8 even under conditions where the total supply fuel increases. This effect not only provides stable combustion, but also enables combustion with good exhaust performance.

Next, a second embodiment will be described with reference to FIG.
4A and 4B are views showing the positional relationship of the fuel injection valve 14 with respect to the second cavity 8, where FIG. 4A is a cross-sectional view and FIG. 4B is a plan view.
As shown in (a), the fuel injection valve 14 is disposed in a state in which this axis has a predetermined angle α with the cylinder axis. As shown in (b), the center B of the second cavity 8 is on the center line of the fuel spray injected from the fuel injection valve 14 in plan view. For this reason, the fuel from the fuel injection valve 14 is stably injected toward the second cavity 8.

As described above, the fuel from the fuel injection valve 14 is injected during the compression stroke, and the fuel is transported to the spark plug 15 by the swirl flows S1 and S2 formed in the first cavity 7 and the second cavity 8, respectively. .
Next, a third embodiment will be described with reference to FIG.
FIG. 5 is a view showing a state in which the fuel from the fuel injection valve 14 is injected in a plurality of times.

The volume of the second cavity 8 is smaller than the volume of the first cavity 7. Therefore, it is desirable to supply the fuel in a plurality of times under the condition on the high load side where the fuel injection amount increases in accordance with the required load in the stratified combustion region.
In the present embodiment, the first fuel is injected into the first cavity 7 and the second fuel is injected into the second cavity 8. Due to the effects of the swirl flows S1 and S2, the fuel injected into the second cavity 8 is transported to the spark plug 15.

Next, a fourth embodiment will be described with reference to FIG.
6A and 6B are views showing a state in which fuel injection is performed using a multi-hole type fuel injection valve 18 having a spiral angle, where FIG. 6A is a cross-sectional view and FIG. 6B is a plan view.
When this fuel injection valve 18 is used, since a spiral angle is added to the injection valve 18, a stronger swirl flow S <b> 2 is generated in the second cavity 8. As a result, the fuel is stably transported to the ignition position of the spark plug 15.

The fuel injection valve 18 is an injection valve in which four injection holes are formed, but the same effect can be obtained regardless of the number of injection holes.
Next, a fifth embodiment will be described with reference to FIG.
FIG. 7 is a view showing a state in which fuel injection is performed using the injection valve 19 that realizes hollow spraying by the swirl flow S3 formed in the nozzle 19a.

By setting the swirl flow S3 in the nozzle 19a in the same rotational direction as the swirl flows S1 and S2 in the cavities 7 and 8, a stronger swirl flow is generated. As a result, the fuel is stably transported to the ignition position of the spark plug 15.
FIG. 8 is a diagram showing a fifth embodiment in which the arrangement of two cavities is changed with respect to the first embodiment. In this embodiment, the center A of the first cavity 7 is parallel to the cylinder axis and ignition is performed. The first cavity 7 is positioned on a straight line passing through the ignition position of the plug 15, the center B of the second cavity 8 is positioned on the extension line of the axial center of the fuel injection valve 14, and directly above the side wall 8 a of the second cavity 8. The center A is located.

Sectional drawing which shows the structure of the internal combustion engine which concerns on 1st Embodiment. The figure which shows the state which generated the swirl flow in the combustion chamber The figure which shows the state in which air-fuel mixture is conveyed to a spark plug The figure which shows the positional relationship of the fuel injection valve with respect to a 2nd cavity. The figure which shows the state which injected the fuel in multiple times The figure which shows the state which injected the fuel using the multi-hole type fuel injection valve which arranged the spiral angle The figure which shows the state which injected the fuel using the injection valve which implement | achieves a hollow spray by the swirl flow formed in a nozzle Sectional drawing which shows the structure of the internal combustion engine which concerns on 5th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Combustion chamber 3 Cylinder head 4 Cylinder block 5 Piston 6 Cavity 7 1st cavity 8 2nd cavity 10 Intake port 11 Exhaust port 12 Intake valve 13 Exhaust valve 14, 18, 19 Fuel injection valve 15 Spark plug

Claims (11)

  A fuel injection valve for directly injecting fuel from the upper part of the combustion chamber, a spark plug disposed substantially at the center of the upper part of the combustion chamber, and means for enhancing the swirl flow in the cylinder, the piston crown surface having a cylindrical shape The first cavity has a first cavity, and the second cavity is provided in the first cavity, and the first cavity and the second cavity are formed so as to shift the center of the second cavity from the center of the first cavity. In-cylinder direct injection internal combustion engine.   2. The direct injection internal combustion engine according to claim 1, wherein an outer periphery of the second cavity is formed at a substantially center of the first cavity on the axial center side of the piston.   3. The direct injection type internal combustion engine according to claim 1, wherein the center of the first cavity is parallel to the cylinder axis and below the ignition position of the spark plug.   The in-cylinder direct injection internal combustion engine according to claim 1 or 2, wherein the second cavity is on an extension line of the axis of the fuel injection valve.   The in-cylinder direct injection internal combustion engine according to claim 1 or 2, wherein the center of the second cavity is on an extension line of the axis of the fuel injection valve.   The direct injection type internal combustion engine according to any one of claims 1 to 5, wherein the fuel injection valve is disposed substantially at the center of the upper portion of the combustion chamber.   7. A stratified combustion operation in which fuel is injected during a compression stroke is performed in a predetermined operation region, and the swirl flow enhancement means enhances swirl flow during this operation. An in-cylinder direct injection internal combustion engine according to any one of the above.   The fuel injection valve injects fuel into the second cavity in a predetermined stratified combustion operation region, and the swirl flow enhancement means enhances swirl flow. An in-cylinder direct injection internal combustion engine according to claim 1.   In a predetermined stratified combustion operation region, the fuel injection valve performs a plurality of times of fuel injection in one stroke, injects the fuel to be injected last into the second cavity, and the swirl flow enhancing means The direct injection type internal combustion engine according to any one of claims 1 to 6, wherein swirl flow is enhanced.   The said fuel injection valve is a multi injection hole injection valve provided with the injection hole which added the spiral angle of the same rotation direction as a swirl flow, It is any one of Claims 1-9 characterized by the above-mentioned. In-cylinder direct injection internal combustion engine.   The in-cylinder direct injection according to any one of claims 1 to 9, wherein the fuel injection valve is a swirl injection valve that realizes a hollow spray by a flow in the same rotational direction as a swirl flow. Internal combustion engine.

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