JP2002038957A - Combustion chamber for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a combustion chamber structure for an internal combustion engine. SOLUTION: In a pent roof type combustion chamber having a cavity 8 on an intake side of a top wall of a piston 7, a part 9a crossing a valve seat face 10 of an exhaust valve of an exhaust side peripheral part of a top wall 9 of a cylinder is extendedly formed in a direction flush with the valve seat face 10 and a part 9b without crossing the valve seat face 10 is formed so as to reduce space volume formed between the part 9b and the top wall of the piston 7 by bringing the part 9b close to the top wall of the piston 7 from the direction flush with the valve seat face 10 as the part 9b approaches toward a peripheral end part of the top wall 9 of the cylinder. As a result, masking by the top wall 9 of the cylinder when lifting an exhaust valve is prevented to excellently maintain output and fuel consumption and flame propagation delay is suppressed to prevent abnormal combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber of an internal combustion engine provided with a valve operating mechanism, and more particularly to a technique for avoiding abnormal combustion while maintaining engine performance in an engine that performs stratified combustion.

[0002]

2. Description of the Related Art In recent years, in a spark ignition type engine such as a gasoline engine, fuel is directly injected into a combustion chamber, and fuel is injected in a compression stroke in a low / medium load region so that a combustible air-fuel mixture is formed only in the vicinity of a spark plug. A technology has been developed in which stratified combustion is performed by producing a stratified gas, thereby enabling combustion with a significantly lean air-fuel ratio to greatly improve fuel efficiency and exhaust gas purification performance.

As a combustion chamber of an engine that performs stratified combustion, a cavity is formed on the top wall of the piston near the intake port in order to efficiently generate a dense layered mixture around the spark plug. A vortex flow, i.e., a tumble flow, due to the intake air flow is formed therein, and a stratified mixture layer is generated in the cavity by the tumble flow to perform stratified combustion. Also, if the exhaust side wall of the cavity is formed high to confine the fuel spray in the cavity,
In order to secure a compression ratio, it is required that the exhaust side be convex. Therefore, in order to satisfy these requirements, the piston top wall is a so-called pent roof type having an inclined surface which is inclined upward and downward from the central portion to the intake side and the exhaust side,
The combustion chamber structure has a cavity formed on the inclined surface on the intake side.

Incidentally, the cylinder top wall is also formed in a pent roof type according to the shape of the piston top wall (Japanese Patent Application Laid-Open No. 200-200200).
0-97031).

[0005]

However, in the combustion chamber structure formed in combination with the above-mentioned convex piston, the volume of the periphery of the combustion chamber is large, so that the flame propagation is delayed, and the end unburned air-fuel mixture is formed. There has been a problem that abnormal combustion such as knocking due to self-ignition and pre-ignition due to hot surface ignition in a high temperature portion in the combustion chamber is likely to occur. In particular, in the combustion chamber structure in which the stratified combustion is performed, the combustion flame from the ignition plug may get over the convex portion on the exhaust side, so that the propagation distance is increased and the flame propagation delay is increased, thereby promoting the above tendency.

In view of the above problem, by providing a squish area in which the distance between the cylinder top wall and the piston top wall is narrowed in the peripheral portion, and pushing the unburned mixture into the center of the combustion chamber,
In some cases, the flame propagation delay is suppressed to avoid the occurrence of abnormal combustion. However, if a large squish area is to be provided over the entire circumference of the combustion chamber, a step is generated between the valve seat surface on which the valve element (intake / exhaust valve) of the valve mechanism is seated and the squish area surface. At the time of low lift, the flow resistance of intake and exhaust increases due to the masking by the stepped portion, which causes a decrease in engine output and a deterioration in fuel efficiency.

The present invention has been made in view of such conventional problems, and simultaneously prevents the masking and the occurrence of abnormal combustion, thereby obtaining stable combustion performance while securing output performance and fuel efficiency. It is an object of the present invention to provide a combustion chamber of an internal combustion engine adapted to be used.

[0008]

SUMMARY OF THE INVENTION Accordingly, the invention according to claim 1 is a combustion chamber of an internal combustion engine provided with a valve operating mechanism, wherein a peripheral portion of a cylinder top wall is provided with a valve body of the valve operating mechanism. The portion that intersects with the valve seat surface on which the seat is seated is formed to extend in the same plane direction as the valve seat surface, and the portion that does not intersect with the valve seat surface is formed as the valve seat surface approaches the peripheral end of the cylinder top wall. And a space formed between the piston top wall and the piston top wall is reduced so as to be closer to the piston top wall direction than the same plane direction.

According to the first aspect of the present invention, the portion of the peripheral portion of the cylinder top wall that does not intersect with the valve seat surface decreases as the space volume formed between the piston top wall and the peripheral end of the cylinder top wall approaches. As a result, the unburned air-fuel mixture present in the peripheral portion having a long flame propagation distance can be reduced, and the volume of the peripheral portion of the combustion chamber is reduced near the end of the piston compression stroke. The unburned air-fuel mixture is pushed to the center by the airflow toward the center. As a result, the diffusion region of the unburned air-fuel mixture is narrowed, the delay in flame propagation is suppressed, and abnormal combustion such as knocking and pre-ignition is suppressed.

[0010] Further, a portion of the periphery of the cylinder top wall that intersects with the valve seat surface on which the valve body of the valve operating mechanism is seated is formed so as to be smoothly connected to the same surface as the valve seat surface. Since the valve body is not masked by the cylinder top wall around the valve seat surface when the valve lift is low, an increase in flow path resistance can be prevented, so that the output performance and fuel efficiency of the engine can be maintained satisfactorily.

The invention according to a second aspect of the present invention is provided with a valve mechanism, and has an inclined surface in which fuel is directly injected into the combustion chamber, and a piston top wall is inclined downward from the center toward the intake side and the exhaust side. And a combustion chamber of the internal combustion engine having a cavity on the intake-side inclined surface, wherein an exhaust-side peripheral portion of the cylinder top wall intersects a valve seat surface on which the exhaust valve of the valve train is seated. The portion extends in the same plane direction as the valve seat surface, and the portion that does not intersect with the valve seat surface is closer to the peripheral end of the cylinder top wall than in the same direction as the valve seat surface toward the piston top wall. , So that the volume of the space formed between the piston and the top wall is reduced.

According to the second aspect of the invention, the effect obtained by the first aspect of the invention is similarly exhibited, and
The following unique effects can be obtained. That is, since the space volume of the exhaust-side peripheral portion is formed sufficiently small, the amount of the unburned air-fuel mixture in the exhaust-side peripheral portion is reduced, and the unburned air is generated from the exhaust-side peripheral portion near the end of the compression stroke. The air-fuel mixture is pushed back to the intake side.

Thus, it is possible to sufficiently suppress the spread of the flame propagation and prevent abnormal combustion while promoting the combustion in the cavity to secure stable combustion (particularly stratified combustion). Further, masking of the exhaust valve at the time of low lift can be prevented, and the output performance and fuel efficiency of the engine can be maintained satisfactorily. Further, in the invention according to claim 3, the intake side peripheral portion of the cylinder top wall approaches the peripheral end of the cylinder top wall from a portion farther from the cylinder center than a portion where the space volume of the exhaust side peripheral portion starts to decrease. Accordingly, the piston is moved closer to the piston top wall from the same plane direction as the valve seat surface of the intake valve of the valve operating mechanism, so that the volume of the space formed between the piston top wall and the piston top wall is reduced.

According to the third aspect of the invention, since the cavity is formed on the intake side, the propagation distance of the flame generated by the main combustion of the air-fuel mixture in the cavity to the peripheral part on the intake side is reduced to the peripheral part on the exhaust side. Is shorter than the propagation distance of
By reducing the space volume from a portion farther from the cylinder center than the exhaust side peripheral portion, the flame propagation distance to the intake side peripheral portion can be set to an appropriate size.

[0015]

1 to 4 show an embodiment of the present invention. In the figure, a direct injection spark ignition type internal combustion engine 1 is shown.
Has a cylinder block 20 and a cylinder head 21, and each cylinder 22 formed in the cylinder block 20
, Two intake ports 2A and 2B and two exhaust ports 3A and 3B are formed in the cylinder head 21. An ignition plug 6 is arranged at a substantially central portion of each cylinder 22 so as to be surrounded by two intake ports 2A and 2B and two exhaust ports 3A and 3B, and performs spark ignition.

A fuel injection valve 5 is disposed between the two intake ports 2A and 2B near the peripheral wall of the combustion chamber 4, and fuel is injected obliquely downward into the combustion chamber 4 from the fuel injection valve 5. . The fuel injection valve 5 is accommodated in a hole 23 opened in the combustion chamber 4 formed in the cylinder head 21, and fuel is injected from the fuel injection valve 5 into a cavity 8 formed in the piston 7, which will be described later. Hole 2 so as not to hinder the progress of
An escape groove 24 for spray is provided near the opening 3.

The cylinder head 21 has a flat surface 25 extending in a crescent shape with respect to the cylindrical cylinder 22.
The squish area is formed on the exhaust side and the intake side of the combustion chamber 4 in cooperation with the piston 7. The top wall (crown surface) of the piston 7 is defined as a ridgeline at a position slightly offset from the center of the cylinder 22 toward the exhaust side.
The intake side and the exhaust side have inclined surfaces 7a and 7b which are inclined downward. The inclined surface 7a on the intake side is provided with a cavity 8 for promoting a tumble flow and holding a fuel spray mass during stratified combustion. .

At the periphery of the top wall of the piston 7, both inclined surfaces 7 are provided.
An annular reference horizontal plane 27 surrounding a and 7b is formed. On the exhaust side and the intake side of the reference horizontal plane 27, the cylinder head 2 is formed in a crescent shape on the same plane.
An intake-side horizontal surface 28 and an exhaust-side horizontal surface 29 that form a squish area between the first flat surfaces 25 and 26 are formed.

The cylinder head 21 faces the cylinder 22.
The cylinder top wall 9 formed on the lower surface of the piston 7 is formed in a so-called pent roof type in which the center is recessed substantially corresponding to the convex shape of the top wall (crown surface) of the piston 7 and is inclined downward on the intake side and the exhaust side. However, the peripheral portion is formed with the configuration according to the present invention as described below. That is, a portion 9a intersecting with the valve seat surface 10 on which the exhaust valve is seated is formed in the peripheral portion on the exhaust side of the cylinder top wall 9 so as to extend in the same plane direction as the valve seat surface 10. Is formed with a tilt angle close to vertical (see FIGS. 2 and 3).

Specifically, a top wall extends from the valve seat surface 10 to the peripheral portion of the cylinder 22 in the same inclination direction as the exhaust side inclined surface 12, and the flat surface 25 forming the squish area is formed. In the vicinity, a draft 30 having a near vertical inclination angle is formed. As described above, since the draft 30 is formed at a position away from the valve seat surface 10, the flow path of the exhaust gas discharged from the combustion chamber 4 to the exhaust port is not masked when the exhaust valve is at a low lift.

A portion 9b of the cylinder top wall which does not intersect with the valve seat surface 10 at the periphery of the exhaust side, that is, 2
The portion between the valve seats is formed closer to the piston 7 top wall than to the same surface direction as the valve seat surface 10 as the cylinder peripheral end is approached, and formed between the piston 7 top wall. The end volume (space volume) V is formed so as to decrease. Specifically, one end extends from the ridgeline 31 to the periphery of the cylinder 22 at one end.
It is formed so as to have a radius of curvature R so that it smoothly contacts the same plane as 0 so as to have a tangent line and the other end is connected to the peripheral edge (flat surface 25) (see FIGS. 2 and 4).

On the other hand, the peripheral portion 9c on the intake side of the cylinder top wall 9
The piston is moved from the valve seat surface 11 of the intake valve toward the cylinder peripheral end from a portion (ridge 32) farther from the cylinder center than a portion (ridge 31) where the end volume V of the exhaust side peripheral portion starts to decrease. The space formed between the piston 7 and the top wall is reduced so as to approach the top wall of the piston 7. Specifically, the intake valve is formed so as to be connected to the peripheral end of the cylinder at a lower inclination angle than the valve seat surface 11 of the intake valve.

Next, the operation will be described. The fuel injected from the fuel injection valve 5 rides on the tumble flow returning to the fuel injection valve 5 side along the cavity 8 to form a stratified mixture in the cavity 8, but a part of the fuel mixture passes over the cavity 8 and is exhausted. Spills to the side. Here, the flame ignited by the ignition plug 6 reaches the peripheral portion of the fuel chamber 4, particularly the peripheral portion on the exhaust side, beyond the exhaust-side inclined surface 7 b of the piston 7, and the flame propagation distance is reduced to the intake side. Larger than. Therefore, in order to avoid knocking and pre-ignition, it is necessary to reduce the exhaust-side end volume V. Therefore,
A squish area is formed from a position closer to the center of the cylinder than the intake side, that is, a position indicated by a ridgeline 31, between the two valve seats (portion not intersecting with the valve seat) on the exhaust side peripheral portion of the cylinder top wall. Flat surface 25
The end volume V is narrowed down by giving a curvature radius R to. In addition, the terminal end of the radius of curvature R is continuous with the flat surface 25 forming the squish area, and cooperates with the exhaust-side horizontal surface 29 of the piston 7 at the end of the compression stroke to flow the airflow from the peripheral portion of the cylinder toward the center ( As a result, unburned air-fuel mixture present at the peripheral edge of the cylinder is pushed back toward the center of the cylinder.

In this manner, the diffusion region of the unburned air-fuel mixture is narrowed, and the delay in flame propagation is suppressed. As a result, abnormal combustion such as knocking and pre-ignition is suppressed. Further, the valve seat surface 1 around the exhaust side of the cylinder top wall 9.
The portion 9a that intersects 0 is formed so as to extend in the same plane direction as the valve seat surface 10 without narrowing down to a position close to the flat surface 25. 9, the flow resistance of the exhaust gas to the exhaust port can be reduced without masking, so that the output and the fuel efficiency can be maintained satisfactorily (see FIG. 3).

On the other hand, since the cavity 8 is formed on the intake side, the propagation distance of the flame generated by the main combustion of the air-fuel mixture in the cavity to the peripheral part on the intake side is larger than the propagation distance to the peripheral part on the exhaust side. Therefore, the flame propagation distance to the intake-side peripheral portion can be made appropriate by reducing the spatial volume of the intake-side peripheral portion from a portion farther from the cylinder center than the exhaust-side peripheral portion.

[Brief description of the drawings]

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

FIG. 2 is a view of the cylinder top wall of the embodiment as viewed from below.

FIG. 3 is a sectional view taken along the line AA of FIG. 2;

FIG. 4 is a sectional view taken along the line BB of FIG. 2;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2A, 2B Intake port 3A, 3B Exhaust port 4 Combustion chamber 5 Fuel injection valve 6 Spark plug 7 Piston 8 Cavity 9 Cylinder top wall 9a Cylinder top wall Intersecting part with valve seat surface of exhaust side peripheral part 9b Cylinder top Portion of the wall exhaust side periphery that does not intersect with the valve seat surface 10 Valve seat surface where the exhaust valve sits 11 Valve seat surface where the intake valve sits

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02F 1/24 F02F 1/24 D 3/00 3/00 Z 3/26 3/26 C F term (reference 3G016 AA02 AA06 AA15 AA19 BA03 BA06 CA36 CA37 CA45 CA46 CA57 CA60 3G023 AA02 AA03 AA06 AA07 AB03 AC05 AD03 AD04 AD06 AD07 AD08 AD09 AD29 AG01 AG02 3G024 AA02 AA04 AA05 AA14 AA15 DA03 DA01 DA03 DA

Claims (3)

[Claims] A combustion chamber of an internal combustion engine provided with a valve operating mechanism, wherein a portion intersecting a peripheral portion of a cylinder top wall with a valve seat surface on which a valve body of the valve operating mechanism is seated is a valve seat. A portion that does not intersect with the valve seat surface is formed so as to extend in the same plane direction as the surface, and the piston is moved closer to the piston top wall direction from the same plane direction as the valve seat surface as approaching the peripheral end of the cylinder top wall. A combustion chamber of an internal combustion engine, wherein a space volume formed between the combustion chamber and the top wall is reduced. A fuel injection means for injecting fuel directly into the combustion chamber; a piston top wall having an inclined surface inclined downward from a central portion to an intake side and an exhaust side; A combustion chamber of an internal combustion engine having a cavity on an inclined surface,
A portion that intersects the exhaust side peripheral portion of the cylinder top wall with a valve seat surface on which the exhaust valve of the valve mechanism is seated is formed to extend in the same plane direction as the valve seat surface, and intersects with the valve seat surface. The portion not to be formed is formed so as to approach the piston top wall direction from the same plane direction as the valve seat surface as approaching the peripheral end portion of the cylinder top wall, so that the volume of space formed between the piston top wall and the piston seat is reduced. A combustion chamber of an internal combustion engine. 3. A valve operating mechanism according to claim 1, further comprising: a portion on the intake side of the cylinder top wall which is farther from the center of the cylinder than a portion on the exhaust side where the space volume starts to decrease, approaches the peripheral end of the cylinder top wall. A combustion chamber of an internal combustion engine, wherein the combustion chamber is formed so as to approach the piston top wall from the same surface direction as the valve seat surface of the intake valve to reduce a space volume formed between the piston top wall and the piston top wall.