JP3781537B2 - Combustion chamber structure of in-cylinder injection engine - Google Patents

Description

[0001]
BACKGROUND 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 cylinder.
[0002]
[Prior art]
Conventionally, as a method for improving the fuel efficiency of an engine, improvement of theoretical thermal efficiency, reduction of pumping loss, reduction of friction, and the like have been proposed. Among them, in order to improve the theoretical thermal efficiency and reduce the pumping loss, there are methods of performing lean combustion control, high EGR (exhaust gas recirculation) combustion control, etc. in addition to the method of increasing the compression ratio or expansion ratio in the combustion chamber. . In these lean combustion control and high EGR control, gas flow such as tumble, swirl, and squish is generated in the cylinder to improve the combustibility of the air-fuel mixture in the combustion chamber.
[0003]
Such an engine is based on the formation of a uniform air-fuel mixture in the combustion chamber during the intake stroke, but on the other hand, the air-fuel ratio of the air-fuel mixture in the combustion chamber is adjusted by adjusting the fuel injection direction and timing. It was intentionally performed to change the locality.
[0004]
That is, a stratified combustion method has been proposed in which the entire combustion chamber is burned with a lean air-fuel ratio, for example, by locally enriching the air-fuel ratio in the combustion chamber or by forming an air-fuel mixture only at a local portion. It was.
[0005]
However, in the conventional stratified combustion system, formation of the local air-fuel mixture in the combustion chamber is not sufficient, and a great improvement in the degree of freedom of air-fuel mixture formation has been desired. Therefore, as a countermeasure, various in-cylinder injection engines that directly inject fuel into the cylinder have been proposed.
[0006]
For example, in Japanese Patent Application Laid-Open No. 5-1544, a mask wall for directing the flow of intake air passing through an intake port is provided in a part around an intake valve, and a reverse tumble flow is forcibly generated in a cylinder to compress it. The fuel injected obliquely with respect to the cylinder axial direction from the injection means (injector) provided on the lower side of the intake port during the stroke is put on the reverse tumble flow, and the air-fuel mixture is supplied to the top of the combustion chamber. An example of a configuration that guides in the direction is shown.
[0007]
Japanese Patent Laid-Open No. 6-146886 discloses that the injection means is attached to the lower position of the intake port in the same manner as the technique of the above-mentioned Japanese Patent Laid-Open No. 5-1544, and the intake port has a cross-sectional shape whose one half is widened The configuration is made. Then, the center of the intake air flow is decentered to promote the generation of a reverse tumble flow, the fuel is injected obliquely with respect to the cylinder axial direction to be placed on the reverse tumble flow, and the air-fuel mixture is provided at the top of the combustion chamber A configuration example is shown in which it is guided in the direction of.
[0008]
Furthermore, in Japanese Patent Laid-Open No. 6-42352, the injection means is attached toward the cylinder axial direction at the center of the top of the combustion chamber, and ignition is performed by projecting a spark plug from between the two intake ports into the combustion chamber. An example of such a configuration is shown.
[0009]
[Problems to be solved by the invention]
However, the in-cylinder injection internal combustion engine disclosed in JP-A-5-11544 employs an intake port that forcibly generates a reverse tumble flow by means of a mask wall. May become excessive. As a result, an insufficient amount of intake air occurs, which may affect the output performance.
[0010]
Next, in the technique disclosed in Japanese Patent 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 this reverse tumble flow is generated by the curved portion on the upper surface of the piston. Try to promote. However, since only the curved portion is configured to form the combustion chamber space, the compression ratio may become excessively high. As a result, it is difficult to set a compression ratio suitable for a fuel used in a normal engine, so-called regular gasoline.
[0011]
In addition, since there is a distance between the injection port of the fuel injection valve and the electrode of the spark plug, it is difficult to control the local air-fuel ratio in the vicinity of the electrode in detail, and the stability and ignitability of combustion are low.
[0012]
Furthermore, the above-mentioned two publications disclose technologies that the injection means performs fuel injection obliquely with respect to the cylinder axis direction. However, if the fuel is injected in an oblique direction, the fuel will wash away the lubricating oil on the inner wall surface of the cylinder, reducing the lubricity and causing functional problems such as uneven wear on the inner surface of the cylinder and compression leakage due to this. There is a problem that occurs.
[0013]
Next, in the combustion chamber structure of an internal combustion engine disclosed in Japanese Patent Application Laid-Open No. 6-42352, the spark plug is installed in the center of the top of the combustion chamber and directly below, and the ignition portion of the spark plug is the injection region of the injection means. Is placed inside. However, this conventional example ignites the rear end side of the injected fuel rather than igniting the fuel reflected on the upper surface of the piston, and the rich air-fuel mixture after ignition goes to the center of the combustion chamber. The main purpose is to perform combustion at the center position.
[0014]
However, with this method, good stratified combustion can be obtained in the low injection amount region, but when the injection amount increases, it becomes difficult to suppress the occurrence of smoke.
[0015]
The present invention has been made in order to solve the above-described problems in the prior art, and the object thereof is to always achieve good stratified combustion by utilizing the reflection of fuel on the piston upper surface in various operating states of the engine. An object of the present invention is to provide an in-cylinder injection engine having a simple configuration that can be secured.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, a combustion chamber structure of a direct injection type engine according to claim 1 includes a cylinder head having a combustion chamber ceiling formed in a pent roof type, and a cylinder from a substantially central position of the combustion chamber ceiling. An injector that injects fuel at a predetermined timing toward the upper surface of the axial piston, and a peripheral region on the upper surface of the piston is formed in a plane perpendicular to the cylinder axis, and a central region of the upper surface of the piston moves from the peripheral region to the center of the piston. And a piston having a piston head formed in a substantially caldera volcano shape in which a cavity having a predetermined depth is recessed at a substantially central portion thereof so as to protrude toward the combustion chamber ceiling.
[0017]
The spark plug is provided so as to project obliquely with respect to the cylinder axial direction from the intake side of the ceiling portion of the combustion chamber into the combustion chamber, and when the piston is substantially at the top dead center position, An ignition part is provided at a position displaced from the center of the cavity toward the intake side. The cavity has a substantially arc shape composed of a compound curve centered at the position where the concave shape of the cavity is offset from the injection center axis of the injector toward the spark plug and the upper position of the cavity. that having a inclined surface which is inclined to the ignition plug side by the ignition plug facing sides via injection center axis between.
[0018]
According to the above configuration, when the piston rising to the cylinder head side in the engine compression stroke reaches a predetermined position before top dead center, the fuel is injected from the injector, and the injected fuel (hereinafter simply referred to as “injected fuel”). ) Spreads toward the cavity, is received in the cavity, and diffuses by reflection, crawling, and splashing.
[0019]
The diffused fuel is prevented from diffusing into the peripheral region of the upper surface of the piston due to the shape of the piston head, and a part of the fuel stays in the cavity while colliding with the ceiling of the combustion chamber. At that time, the fuel colliding with the inclined surface portion in the cavity is reflected to the spark plug side and diffused in the peripheral region of the ignition portion. Therefore, a part of the stratified mixture is surely applied to the ignition part, and as a result, a stratified mixture that can be ignited around the ignition part of the spark plug can be led, and stable ignitability can be obtained.
[0020]
In addition, by properly controlling the direction and extent of fuel diffusion according to the shape of the piston head, that is, the caldera volcano shape, there is no breakage of the air-fuel mixture that makes flame propagation impossible, the occurrence of an over-lean region, and rapid growth. Combustion can be obtained, and partial burn can be prevented. Thus, good ignitability and combustion stability can be obtained in a wide operation region, and as a result, good drivability, reduction of HC, and improvement of fuel consumption can be achieved. And since it has combustion chamber space other than a cavity, a compression ratio does not become high and can use regular gasoline.
[0021]
Further, since fuel is injected toward the piston in the cylinder axial direction, deterioration of engine combustion due to a cooling action caused by a part of the injected fuel directly colliding with the inner peripheral wall surface of the cylinder, smoldering of the plug, It is possible to prevent deterioration of lubricity with the piston.
[0022]
The combustion chamber structure of the direct injection type engine according to claim 2 has a piston pin direction of a piston pin arranged in a direction in which the opening shape of the cavity is orthogonal to the intake / exhaust side of the ceiling portion of the combustion chamber as a short axis. It has a substantially elliptical shape with the suction / exhaust side as the major axis in the direction perpendicular to the piston pin direction, and when the piston is in the vicinity of the top dead center, it is at the inner upper position of the cavity and the suction side from the center of the cavity It is characterized by having a shape in which the ignition part of the spark plug is arranged at a position displaced to the right. Thereby, the spread of the air-fuel mixture in the combustion chamber in the piston pin direction can be suppressed, and the ignitability when the fuel injection amount is small with a low load can be ensured. In addition, at a high load, a large space in which the air-fuel mixture can diffuse (hereinafter simply referred to as “air-fuel mixture diffusion volume”) can be secured, and lean combustion can be performed. Therefore, good stratified combustion can be obtained in a wide operating region.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is an explanatory cross-sectional view schematically illustrating an in-cylinder injection engine 10 according to an embodiment of the present invention, and FIG. 2 is an explanatory view of a piston 18 in FIG. 2A is a top view of the piston 18, and FIG. 2B is a cross-sectional view taken along the line XX of FIG.
[0028]
As shown in FIG. 1, the in-cylinder injection engine 10 is formed in a predetermined shape with a cylinder head 14 having a combustion chamber ceiling portion (hereinafter simply referred to as a “ceiling portion”) 12 formed in a pent roof shape. A piston 18 having a piston head 16 and a cylinder portion 22 having a cylinder 20 into which the piston 18 is removably fitted are used as basic components.
[0029]
As shown in FIG. 1, the ceiling portion 12 has two slope portions 12 a and 12 b that gradually expand away from the top portion, and has a shape similar to a gable roof as a whole. The inclined surface portion 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. Further, two exhaust valves (not shown) for communicating and blocking between the exhaust port (not shown) and the combustion chamber 24 are provided on the inclined surface portion 12b. Hereinafter, for convenience of explanation, the intake valve side is referred to as the intake IN side, and the exhaust valve side is referred to as the exhaust EX side.
[0030]
As shown in FIG. 1, the spark plug 30 is provided on the intake IN side of the cylinder head 14 so as to be inclined with respect to the axial direction of the cylinder 20, and has an ignition portion at one end protruding toward the combustion chamber 24. A certain electrode part 32 is provided.
[0031]
Further, an injector 34 is provided substantially above the center of the ceiling 12. The injector 34 injects the fuel f toward the axial piston head 16 side of the cylinder 20, and the injection center shaft 35 is offset by a predetermined distance from the center axis line 21 of the cylinder 20 to the exhaust EX side. Is set. The fuel injection shape by the injector 34 forms a substantially conical hollow shape that gradually spreads around the injection center axis 35.
[0032]
The substantially conical hollow shape of the injected fuel can be easily formed, for example, by setting the injection spread angle to be about 40 to 80 degrees and injecting the fuel f while giving a rotational component. is there. Specifically, it can be formed by hollow cone spraying by an injector 34 using a swirl nozzle.
[0033]
The shape of an intake port (not shown) that is communicated with or cut off from the combustion chamber 24 via the intake valve is configured so that a weak tumble gas flow in the positive direction is generated in the combustion chamber 24. The tumble ratio is set to be about 0.5 to 2.
[0034]
As shown in FIG. 1, the piston 18 is disposed so that the piston pin 42 extends in a direction orthogonal to the intake / exhaust side. As shown in FIGS. 1 and 2, the piston head 16 has a peripheral portion 38 that forms a plane orthogonal to the cylinder central axis 21 and a central portion 41 based on a convex shape corresponding to the combustion chamber ceiling portion 12. Therefore, it is formed in the shape of a so-called caldera volcano.
[0035]
As the central portion 41 moves from the peripheral portion 38 to the center of the piston head 16, the inclination angle with respect to the peripheral portion 38 gradually increases, and the convex portion 36 whose longitudinal cross-sectional shape forms a quadratic curve shape, and the piston head 16. A cavity 37 is formed in a recess at a predetermined depth so as to form an approximately elliptical shape in which the opening shape extends in a direction orthogonal to the piston pin 42 at approximately the center.
[0036]
As shown in FIG. 1, the concave shape of the cavity 37 has a substantially arc shape made up of a relatively large radius curve or compound curve, and the center point of the compound curve is the spark plug from the axial center position of the injector 34. It is arranged above the 30 side by a predetermined offset. An inclined surface portion 40 that is inclined toward the electrode portion 32 side of the spark plug 30 is provided on the exhaust EX side of the cavity 37.
[0037]
Further, as shown in FIG. 2 (B), the inclined surface portion 40 has a vertical cross-sectional shape formed in parallel with the peripheral edge portion 38, and both end sides are formed so as to rise smoothly toward the upper side of the piston. . The opening diameter of the cavity 37 is set to about 30 to 70% with respect to the diameter D of the cylinder 20, and the depth of the cavity 37 from the piston head peripheral portion 38 is the deepest portion of the diameter D of the cylinder 20. The limit is set to about 15%.
[0038]
The electrode portion 32 of the spark plug 30 is set so that when the piston 18 is in the vicinity of the top dead center, the position is offset inside the cavity 37 and offset from the center of the piston 18 toward the intake IN side. It is arranged so as not to be directly exposed to the spray from.
[0039]
The injection spread angle of the injector 34 is set so that the injection range is within the cavity 37 at a predetermined timing (substantially near the top dead center position) when the piston 18 reciprocates.
[0040]
Below, operation | movement of the cylinder injection engine 10 which has the said structure is described. The in-cylinder injection engine 10 according to the present embodiment controls the fuel injection amount, the injection timing, and the ignition timing so that stratified combustion is performed during low / medium load operation and uniform combustion is performed during high load operation. . The uniform combustion performed at the time of high-load operation is that fuel is injected into the combustion chamber 24 during the intake stroke, and is substantially the same operation as a conventional engine that injects fuel into the intake port during the intake stroke. Therefore, the detailed description is abbreviate | omitted and only the stratified combustion at the time of the low and medium load operation | movement which is the characteristics of this invention is demonstrated here.
[0041]
First, when the piston 18 rises to a predetermined position near the top dead center in the compression stroke, the fuel f is injected from the injector 34 into the hollow cone shape toward the cylinder head 21 in the direction of the cylinder shaft 21 by a predetermined injection amount. Then, the fuel f is received by a cavity 37 provided substantially at the center of the piston head 16 of the piston 18 that continues to rise, and diffuses in the cavity 37 by reflection, scooping, jumping, and the like.
[0042]
The diffused fuel is prevented from diffusing into the peripheral portion 38 due to the shape of the cavity 37 and the convex portion 36, and a part of the fuel collides with the ceiling portion 12 and stays in the cavity. In particular, the fuel that has collided with the inclined surface portion 40 is reflected to the spark plug side and diffused in the peripheral region of the ignition portion. After the injection is completed, ignition is performed at an appropriate timing to ignite and burn the stratified mixture. Therefore, it is possible to form a stratified mixture in which a part of the stratified mixture is reliably applied to the ignition part.
[0043]
Further, due to the opening shape of the cavity 37 having a substantially elliptical shape having a minor axis in the direction of the piston pin 42, the spread of the stratified mixture in the direction of the piston pin 42 is suppressed, and the mixture diffusion volume in which the mixture diffuses is large. Secured.
[0044]
Therefore, it is possible to achieve both improvement in ignitability when the injection amount is small at low load and achievement of lean combustion that effectively uses the diffusion volume at high load, and good combustion can be obtained in a wide operating range. As a result, good operability, the reduction of HC, can also be achieved improvement in reduction further fuel consumption of NO _X. In addition, since the combustion chamber 24 has a combustion space other than the cavity 37, the compression ratio is not increased, and ordinary fuel, so-called regular gasoline can be used.
[0045]
Furthermore, the injected fuel riding on the weak tumble flow in the combustion chamber flows to the spark plug 30 side. At this time, the surface of the cavity 37 is formed with a smooth curve, so that the tumble flow is disturbed. Therefore, a stratified air-fuel mixture that is gradually homogeneous and suitable for stratified combustion can be formed in the cavity 37. As a result, it is possible to prevent the mixture from being broken and the occurrence of an overlean region, in which flame propagation is impossible, and to achieve appropriate and rapid combustion with a lean air-fuel ratio as a whole, and to prevent the occurrence of partial burn. it can.
[0046]
Further, since the injected fuel is difficult to diffuse to the cylinder 20 side due to the injection direction and the action of the central portion 41, it is possible to prevent the fuel f from adhering to the cylinder 20 and to reduce the lubricity of the cylinder 20 and the function in the piston operation. The occurrence of a failure can be effectively prevented. Further, since the fuel f is injected toward the piston 18 in the cylinder axial direction, the deterioration of the combustion state and the smoldering of the spark plug 30 caused by the cooling action caused by a part of the injected fuel directly colliding with the inner peripheral wall surface of the cylinder. Can be prevented.
[0047]
In addition, this invention is not limited to the structure of each above-mentioned embodiment, A various deformation | transformation is possible within the range of the summary of invention. For example, in the above embodiment, the case where the gas flow by the weak tumble flow exists has been described, but a weak swirl flow may be added.
[0048]
【The invention's effect】
As described above, according to the combustion chamber structure of the direct injection engine according to the present invention, the injected fuel injected from the injector and colliding with the inclined surface portion in the cavity is reflected and diffused to the spark plug side. Therefore, a stratified mixture that can be easily ignited can be guided around the ignition part of the spark plug, and stable ignitability can be obtained.
[0049]
Also, since the opening shape of the cavity is formed in a substantially elliptical shape having a minor axis in the piston pin direction, the mixture diffusion volume in which the spread of the stratified mixture in the piston pin direction is suppressed and the mixture is diffused It is possible to secure a large amount of fuel, and to achieve both improved ignitability when the injection amount is low at low load and the achievement of lean combustion that effectively uses the diffusion volume at high load. Obtainable.
[Brief description of the drawings]
FIG. 1 is an explanatory cross-sectional view schematically illustrating an in-cylinder injection engine according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of the piston of FIG.
[Explanation of symbols]
12 Combustion chamber ceiling part 14 Cylinder head 16 Piston head 18 Piston 20 Cylinder 22 Cylinder part 24 Combustion chamber 30 Spark plug 32 Electrode part (ignition part)
34 Injector 36 Convex part 37 Cavity 38 Peripheral part 40 Inclined surface part f Fuel

Claims (2)

A cylinder head having a combustion chamber ceiling formed in a pent roof type;
An injector that injects fuel at a predetermined timing from the substantially central position of the ceiling portion of the combustion chamber toward the upper surface of the piston in the cylinder axial direction;
The peripheral area of the upper surface of the piston is formed in a planar shape perpendicular to the cylinder axis, and the central area of the upper surface of the piston protrudes toward the combustion chamber ceiling as it moves from the peripheral area to the center of the piston. And a piston having a piston head formed in a substantially caldera volcano shape in which a cavity having a predetermined depth is recessed substantially in the center thereof;
Protruding obliquely with respect to the cylinder axial direction from the intake side of the combustion chamber ceiling to the combustion chamber, and when the piston is substantially at the top dead center position, and a spark plug having an ignition portion at a position offset from the center of the cavity to the intake side,
The cavity has a substantially circular arc shape composed of a compound curve centered at a position where the concave shape of the cavity is offset to the spark plug side of the injection center axis of the injector and above the cavity. in and the combustion chamber structure for a direct injection type engine according to claim Rukoto which have a inclined surface which is inclined to said spark plug side at the side facing the spark plug through between the injection central axis of the injector. The cavity has an opening shape in which the piston pin direction of the piston pin arranged over the direction orthogonal to the suction / exhaust side of the combustion chamber ceiling is a short axis, and the suction / intake direction is orthogonal to the piston pin direction. The spark plug has a substantially elliptical shape with the exhaust side as the major axis, and the spark plug is located at an inwardly upper position of the cavity and a position displaced from the center of the cavity toward the intake side when the piston is in a position near the top dead center. The combustion chamber structure of a direct injection type engine according to claim 1, characterized in that the ignition part of the cylinder is arranged.

Images