JPH11182247A - Combustion chamber structure for direct injection type engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide combustion chamber structure of a direct injection type engine of simple constitution that can always ensure excellent stratified combustion using reflection of fuel on the upper face of a piston. SOLUTION: The direct injection type engine has a cylinder head 14 with a bent-roof type combustion chamber top part 12, and a piston 18 provided with a piston head formed in protruding shape in correspondence with the combustion chamber top part 12. The cylinder head 14 is provided with an injection means for injecting fuel in the axial direction of a cylinder toward the piston 18, and a spark plug 30 protruded obliquely to the axial direction of the cylinder from the intake means side. The piston head has a cavity recessed being opened in almost circular shape with the bottom face inclined onto the intake side. A squish area toward the center of the piston head is formed between the piston head and the combustion chamber top part 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber structure of a direct injection type engine in which fuel is directly injected into a combustion chamber and a stratified mixture is formed in the combustion chamber to perform stratified combustion.

[0002]

2. Description of the Related Art Conventionally, techniques for improving fuel efficiency of an engine include improving theoretical thermal efficiency, reducing pumping loss,
Reduction of friction has been proposed. Over time, to improve theoretical thermal efficiency and reduce pumping loss,
In addition to the method of increasing the compression ratio or the expansion ratio in the combustion chamber, lean combustion control and high EGR (exhaust gas recirculat
ion) There is a method of performing combustion control or the like. In these lean burn control and high EGR control, tumble,
A gas flow such as swirl or squish is generated to improve the combustibility of the air-fuel mixture in the combustion chamber.

[0003] Such an engine is basically based on forming a uniform mixture in the combustion chamber during the intake stroke. On the other hand, the mixture in the combustion chamber is adjusted by adjusting the fuel injection direction and the injection timing. It was also intentionally performed to locally change the air-fuel ratio of the fuel cell.

[0004] That is, a stratified combustion system in which combustion is performed at a lean air-fuel ratio as a whole in the entire combustion chamber by making the air-fuel ratio locally rich in the combustion chamber, or forming an air-fuel mixture only in a local portion, or the like. Had been proposed.

However, in the conventional stratified combustion system,
Such local formation of an air-fuel mixture in the combustion chamber is not sufficient, and it has been desired to greatly improve the degree of freedom of the air-fuel mixture formation. Therefore, various in-cylinder injection engines that directly inject fuel into the cylinder have been proposed as a countermeasure.

For example, Japanese Patent Application Laid-Open No. H5-1544 discloses that
A mask wall that directs the flow of intake air passing through the intake port is provided in a part around the intake valve, forcibly generating a reverse tumble flow in the cylinder, and the injection provided below the intake port during the compression stroke. A configuration example is shown in which fuel injected obliquely from the means (injector) with respect to the cylinder axis direction is placed on a reverse tumble flow, and the air-fuel mixture is guided toward a spark plug provided at the top of the combustion chamber. I have.

In Japanese Patent Application Laid-Open No. 146886/1994, an injection means is mounted at a lower position of an intake port in the same manner as in the technique of Japanese Patent Application Laid-Open No. 5-1544, and the sectional shape of the intake port is changed to one side. A half is widened. Then, the center of the intake air flow is eccentric to promote the generation of the reverse tumble flow, the fuel is injected obliquely to the cylinder axis direction, and the fuel is placed on the reverse tumble flow, and the air-fuel mixture is provided at the top of the combustion chamber at the spark plug. Is shown in the figure.

[0008]

However, the in-cylinder injection type internal combustion engine disclosed in the above-mentioned Japanese Patent Application Laid-Open No. H5-1544 employs an intake port for forcibly generating a reverse tumble flow by a mask wall. Therefore, the suction resistance may be excessive in a high-speed and high-load region. As a result, an insufficient intake air amount occurs, which may affect the output performance.

Next, according to the technique disclosed in Japanese Patent Application Laid-Open No. 6-146886, a reverse tumble flow is generated by adjusting the cross-sectional shape of the intake port as described above, and the reverse tumble flow is generated by the curved portion on the piston upper surface. To promote the generation of However, since only the inside of the curved portion forms the combustion chamber space, the compression ratio may be excessively high. Therefore, it is difficult to set a compression ratio suitable for a fuel used in a normal engine, that is, a regular gasoline.

In order to secure a sufficient volume of the combustion chamber by enlarging the curved portion and the cavity so as to obtain a normal compression ratio, the distance between the injection port of the fuel injection valve and the electrode of the ignition plug is increased. It is difficult to guide the air-fuel mixture to the spark plug side due to an increase, it is difficult to accurately generate a stratified air-fuel mixture, and there is a problem that combustion stability and ignitability are low.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a cylinder having a simple structure capable of precisely producing a stratified air-fuel mixture produced by reflection of fuel on a piston upper surface. An object of the present invention is to provide a combustion chamber structure of an injection engine.

[0012]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a combustion chamber structure for a direct injection type engine, wherein an injector supplies fuel from a substantially center position of a ceiling of the combustion chamber at a predetermined timing. The ignition plug is arranged so as to be injected toward the piston head in the cylinder axial direction, the ignition plug protrudes from the intake side of the combustion chamber ceiling into the combustion chamber, and the ignition portion of the ignition plug is substantially inward of the cavity at the top dead center position of the piston. It is arranged so as to be located at an upper position and at a position deviated from the center of the cavity toward the intake side.

[0013] The cavity has a slope at the bottom inclined at an angle at which fuel injected from the injector is reflected toward the ignition portion. In addition, the combustion chamber ceiling and the piston have a configuration in which a squish flow, which is a flow of an air-fuel mixture, is generated from the peripheral side to the center of the piston upper surface during the compression stroke.

The in-cylinder injection type engine having the above-described configuration includes:
When the piston rising to the cylinder head reaches a predetermined position before the top dead center, fuel is injected from the injector, and the injected fuel (hereinafter simply referred to as “injected fuel”) spreads toward the cavity. And is received in the cavity and diffuses by reflection, crawling, and jumping to form an air-fuel mixture.

Here, the injected fuel that has collided with the inclined surface inclined toward the intake side at the bottom of the cavity is reflected toward the ignition portion, and the injected fuel that is likely to protrude from the cavity due to the momentum of the reflection is pushed back into the cavity by the squish flow. In addition, diffusion outside the cavity is suppressed. As a result, it is possible to form an air-fuel mixture at a position near the ignition portion of the ignition plug.

Therefore, the direction in which the injected fuel spreads can be precisely controlled, and the air-fuel mixture can be generated at an appropriate timing in the vicinity of the ignition portion of the ignition plug deviated to the intake side. That is, the position where the mixture is generated in the combustion chamber can be accurately and easily controlled.

As a result, the position where the mixture is generated can be accurately controlled even in a wide combustion chamber space, and good ignitability and combustion stability can be ensured in a wide operation range.
The compression ratio can be set to a value suitable for the fuel used in a normal engine, so-called regular gasoline.

The combustion chamber structure of the direct injection engine according to the second aspect is characterized in that a gas flow of a weak forward tumble exists in the combustion chamber during the compression stroke. As a result, good turbulence due to collision of the squish flow and the weak tumble flow is generated in the combustion chamber at the time of ignition. As a result, combustion of the air-fuel mixture is promoted, and good driving performance, reduction of HC, and improvement of fuel efficiency can be achieved.

According to a third aspect of the present invention, the in-cylinder injection engine is formed such that the inclined surface of the cavity is a concave curved surface centered on a position offset from the injection center axis of the injector toward the spark plug and above the upper surface of the piston. It is characterized by being. This makes it possible to accurately and easily control the position where the air-fuel mixture is generated in the combustion chamber, as in the case of the first or second aspect. In particular, since the inclined surface has a concave curved surface shape, the concave volume space of the cavity is further enlarged. Therefore, the combustion region of the air-fuel mixture can be expanded, and the fuel efficiency can be further improved.

According to a fourth aspect of the present invention, there is provided a combustion chamber structure of an in-cylinder injection type engine, in which the injected fuel is injected so as to form a substantially conical hollow shape which gradually spreads in the injection direction about the injection center axis of the injector. The conical spread angle of the fuel is set so that the spread range of the injected fuel falls within the cavity during injection. Therefore, a stratified mixture can be easily and reliably formed in the cavity.

According to a fifth aspect of the present invention, there is provided a combustion chamber structure of a direct injection type engine, wherein an injector has an injection nozzle for injecting fuel by giving a spiral movement to the fuel. By the injection of the injection nozzle, the fuel injection shape can be formed into a substantially conical hollow shape.

[0022]

Embodiments of the present invention will be described below in detail. FIG. 1 is a cross-sectional explanatory view schematically illustrating a direct injection engine 10 according to a first embodiment of the present invention, and FIG. 2 is a top view of a piston 18 in FIG.

As shown in FIG. 1, the in-cylinder injection engine 10 includes a cylinder head 14 having a combustion chamber ceiling (hereinafter simply referred to as a “ceiling”) 12 formed in a pent roof shape, and a piston head 16. Has a piston 18 formed in a convex shape corresponding to the ceiling portion 12 and a cylinder portion 22 having a cylinder 20 into which the piston 18 is reciprocally fitted.

As shown in FIG. 1, the ceiling portion 12 has two sloped portions 12a, 1a that gradually separate from each other from the top and expand.
2b, and is generally shaped like a gable roof. The slope 12 a is provided with two intake valves (not shown) for communicating and blocking between an intake port (not shown) provided in the cylinder head 14 and the combustion chamber 24. The slope 12b is provided with two exhaust valves (not shown) for communicating and shutting off between an exhaust port (not shown) and the combustion chamber 24. Hereinafter, for convenience of explanation, the intake valve side is the intake IN side, and the exhaust valve side is the exhaust E
Called the X side. The ceiling 12 is provided at a position offset from the center of the cylinder 20 to the exhaust side.

The spark plug 30 is, as shown in FIG.
The cylinder 2 provided on the intake IN side of the cylinder head 14
The combustion chamber 24 is provided so as to be inclined with respect to the axial direction 0 and to project into the combustion chamber 24 at the end. Further, the spark plug 30 has an electrode portion 32 as an ignition portion at an end protruding toward the combustion chamber 24.

Further, an injector 34 is provided substantially above the center of the ceiling 12. The injector 34 supplies fuel to the axial piston head 1 of the cylinder 20.
6 and the injection center axis 35 of the cylinder 2
It is set at a position offset toward the exhaust EX side from the central axis 21 of 0. The injection shape of the fuel by the injector 34 forms a substantially conical hollow shape gradually expanding around the injection center axis 35 (indicated by a dotted line f in FIG. 1).

The substantially conical hollow shape of the injected fuel can be easily formed by, for example, setting the injection angle so that the divergence angle of the injection is about 40 to 80 degrees, and injecting the fuel while giving a rotational component. Is possible. Specifically, it can be formed by hollow cone spraying by the injector 34 using a swirl nozzle.

The shape of an intake port (not shown) that is communicated with and shut off from the combustion chamber 24 via an intake valve is configured so that a forward weak tumble gas flow is generated in the combustion chamber 24. I have. Tumble ratio is about 0.5
２2 is set. The tumble flow in the forward direction refers to a gas flow in a direction of rolling on the piston head 16 from the intake IN side to the exhaust EX side.

As shown in FIG. 1, the piston 18 corresponds to a peripheral portion 17 of the piston head 16 formed in a plane shape perpendicular to the cylinder center axis 21 and the pent roof type ceiling portion 12 from the peripheral portion 17. Convex part 1
9.

When the piston 18 moves up to just before the top dead center in the compression stroke in cooperation with the cylinder head 14, the air-fuel mixture flows from the peripheral portion 17 toward the center of the piston head 16. It has a structure that produces a so-called squish flow (compression turbulence).

The piston head 16 is provided with a cavity 36 having a substantially circular opening 39 whose center is offset by a predetermined amount from the injection center axis 35 toward the intake IN side. . When the fuel injected from the injector 34 collides, the cavity 36
It has a bottom 37 that is inclined at an angle that reflects light to two sides.

The exhaust side of the bottom 37 is connected to the wall 38 facing the rising electrode 32 at a predetermined angle via a smooth curved surface from the bottom 37. Therefore, even when the fuel injected from the injector collides with the wall 38, the fuel is reflected toward the electrode 32.

The electrode portion 32 of the ignition plug 30 is set so as to be located above the cavity 36 and offset from the center of the cavity 36 toward the intake IN when the piston 18 is located near the top dead center. In the embodiment, it is arranged at a position where the injected fuel from the injector 34 does not directly collide.

The injection divergence angle of the injector 34 is set such that the injection range falls within the cavity 36 at a predetermined timing when the piston 18 moves up and down (just before the top dead center).

The opening diameter d of the opening 39 of the cavity 36
Is set to about 30 to 70% of the diameter D of the cylinder 20 as shown in FIG.
Of the cylinder diameter D from the peripheral portion 17 at the deepest portion.
% Is set as the limit.

Next, the operation and operation of the in-cylinder injection engine 10 having the above configuration will be described below. The in-cylinder injection engine 10 according to the present embodiment performs the stratified combustion operation only at the time of low / medium load operation, and performs the uniform combustion operation at the time of high load operation. Controlled.

The uniform combustion performed during the high load operation is as follows:
The fuel is injected into the combustion chamber 24 during the intake stroke during the intake stroke. Since the operation is substantially the same as that of a conventional engine that injects fuel into the intake port during the intake stroke, detailed description is omitted, and the features of the present invention are described herein. The stratified combustion operation at the time of low / medium load operation will be described.

First, in the compression stroke, when the piston 18 rises to a predetermined position near top dead center from the injector 34 toward the piston head 16 at a predetermined timing set according to the operating state of the engine. As a result, a predetermined amount of fuel is injected in a hollow cone shape. The injected fuel is supplied to the piston 18 which continues to rise.
And is diffused by reflection, crawling around, and jumping up in the cavity 36. Part of the fuel that has jumped up collides with the ceiling portion 12 and diffuses.

Since the ceiling portion 12 is formed in a pent roof shape, the fuel that jumps up in the cavity 36 and collides with the ceiling portion 12 with its momentum is reflected so as to gather at the center of the combustion chamber. Further, the injected fuel that has collided with the bottom 37 of the cavity 36 is reflected toward the spark plug 30 due to its inclination, and diffuses near the electrode 32.

When the piston 18 is further raised, the space between the ceiling 12 and the piston head 16 becomes sufficiently narrow, and a squish flow flows from the peripheral edge 17 of the piston head 16 toward the cavity 36. The light is reflected in the cavity 36 by the squish flow, and the opening 3
The fuel which is about to jump out from 9 toward the peripheral portion 17 is forcibly pushed back toward the center of the piston 18 and diffuses in the cavity 36 and the upper region thereof. In addition, at this time, the squish flow and the weak tumble flow existing in the combustion chamber 24 collide with each other, so that a turbulence of the air-fuel mixture that promotes combustion is generated in the combustion chamber 24.

Thus, a stratified mixture suitable for ignition is formed near the electrode portion 32 at an appropriate timing. Here, for example, when the fuel injection amount during the medium load operation is relatively large, the injected fuel reflected by the cavity 36 is diffused into the cavity 36 and the upper region thereof, and a stratified mixture having a large diffusion volume and uniformly diffused. Is formed.

When the fuel injection amount during idling or the like is small, a stratified mixture partially applied to the electrode portion 32 is reliably formed due to the inclination of the bottom portion 37 of the cavity 36. Therefore, in a wide operating region, a good mixture having good ignitability and suitable for stratified combustion can be formed around the electrode portion 32, and has a cavity forming a wide combustion chamber space, that is, a large volume. Even in the cavity, the generation position of the air-fuel mixture can be accurately controlled.

Thus, the engine can be operated using regular gasoline with the compression ratio set to the normal compression ratio. Also, good driving performance, reduction of HC, NO
X can be reduced and fuel efficiency can be improved.

Further, since the injected fuel is diffused in the cavity and in the upper region thereof, it is possible to prevent the mixture from being unable to propagate the flame and to prevent the generation of the air-fuel mixture and the over-lean region. Appropriate and rapid combustion can be obtained with a lean air-fuel ratio, and partial burn can be prevented.

Further, since the injected fuel is injected in the cylinder axial direction, it is difficult to diffuse to the cylinder 20 side.
It is possible to prevent the injected fuel from adhering to the cylinder 20, deteriorate the lubricity between the cylinder 20 and the side surface of the piston 18, and perform combustion caused by a cooling effect caused by a part of the injected fuel directly colliding with the inner peripheral wall of the cylinder 20. Deterioration of the state can be prevented.

Next, a second embodiment of the present invention will be described below. FIG. 3 is an explanatory sectional view of the second embodiment, and FIG. 4 is an explanatory top view of a piston 18 used in the second embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the present embodiment, a characteristic configuration different from the above-described first embodiment lies in the concave shape of the cavity 36. The concave shape of the cavity 36 is basically formed in a hemispherical shape as shown in FIG.
The exhaust side wall portion 37 a of 7 is formed in a concave curved surface centered on an upper position offset toward the ignition plug 30 from the injection center axis 35 of the injector 34. Therefore, of the injected fuel injected from the injector 34,
What collides with the exhaust side wall portion 37a of the bottom portion 37 is the electrode portion 3
The light is reflected in two directions and locally forms an appropriate mixture in the vicinity of the electrode portion 32.

Here, since the bottom 37 has a hemispherical shape, a larger volume of the cavity than in the first embodiment is ensured. As a result, the diffusion volume of the fuel injected into the cavity can be further increased, and the fuel consumption can be improved by expanding the combustion region of the air-fuel mixture. In addition, since the hemispherical shape is used as the basic shape, the tumble flow existing in the combustion chamber can be maintained without being disturbed.

It should be noted that the present invention is not limited to the configuration of each of the above embodiments, and various modifications can be made within the scope of the invention. For example, in each of the above-described embodiments, a case has been described in which a gas flow due to a weak tumble flow exists, but a weak swirl flow may be generated by changing the shape of an intake port or the like, and may be used in combination with the weak tumble flow.

[0050]

As described above, according to the combustion chamber structure of the direct injection engine according to the present invention, the direction in which the injected fuel is diffused is precisely controlled by the inclined portion in the cavity and the squish flow generated on the upper surface of the piston. , And an air-fuel mixture can be generated at an appropriate timing near the electrode portion of the ignition plug. Therefore, good ignitability and combustion stability can be ensured in a wide operating range, and the compression ratio can be set to a normal value.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view schematically illustrating a direct injection engine according to a first embodiment of the present invention.

FIG. 2 is an explanatory top view of the piston of FIG. 1;

FIG. 3 is a sectional view schematically illustrating a direct injection engine according to a second embodiment of the present invention.

FIG. 4 is an explanatory top view of the piston of FIG. 3;

[Explanation of symbols]

 12 ceiling part of combustion chamber 14 cylinder head 16 piston head 18 piston 19 convex part 20 cylinder 22 cylinder part 24 combustion chamber 30 spark plug 32 electrode part 34 injector 36 cavity f fuel

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 61/14 310 F02M 61/14 310S

Claims (5)

[Claims] 1. A pent roof type combustion chamber ceiling, an injector for directly injecting fuel into the combustion chamber,
A cylinder head having an ignition plug for igniting an air-fuel mixture in the combustion chamber; a piston upper surface having a basic shape corresponding to a shape of a ceiling portion of the combustion chamber of the cylinder head; and a substantially central position of the piston upper surface. Piston having a cavity recessed in and against which fuel injected from the injector collides;
In a combustion chamber structure of a direct injection type engine that forms a stratified mixture in the combustion chamber and performs stratified combustion, the injector is configured to supply fuel from a substantially central position of a ceiling of the combustion chamber at a predetermined timing to a cylinder shaft. Wherein the ignition plug protrudes into the combustion chamber from the intake side of the combustion chamber ceiling, and the ignition portion of the ignition plug is located substantially at the top dead center of the piston. In the upper part of the cavity, it is arranged so as to be located at a position deviated from the center of the cavity toward the intake side, the fuel injected from the injector at the bottom in the direction of the ignition part The combustion chamber ceiling and the piston have a slope inclined at an angle of reflection, and the combustion chamber ceiling portion and the piston are spaced from the periphery of the piston upper surface during the compression stroke. A combustion chamber structure for a direct injection type engine, wherein a squish flow has a configuration that is generated is the flow of the mixture towards the central. 2. The combustion chamber structure for a direct injection engine according to claim 1, wherein a gas flow of a weak forward tumble exists in the combustion chamber during the compression stroke. 3. The inclined surface of the cavity is formed in a concave curved shape whose center is offset from the injection center axis of the injector toward the spark plug and above the piston upper surface. The in-cylinder injection type engine combustion chamber structure according to claim 1 or 2. 4. The injector performs injection such that the injected fuel forms a substantially conical hollow shape that gradually expands in an injection direction about an injection center axis of the injector, and a divergence angle of the injected fuel is determined by the piston. The combustion chamber structure of a direct injection engine according to any one of claims 1 to 3, wherein the spread range of the injected fuel is set to fall within the cavity at a predetermined timing during the vertical operation. 5. The combustion chamber structure of a direct injection engine according to claim 4, wherein said injector has an injection nozzle which gives fuel in a spiral rotation direction to inject the fuel.