JP3743895B2 - In-cylinder injection engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion chamber 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 theoretical thermal efficiency and reduce pumping loss, there is a method of performing lean combustion control, high EGR (exhaust gas recirculation) combustion control, etc. in addition to a 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. On the other hand, the air-fuel ratio of the air-fuel mixture is locally adjusted by adjusting the fuel injection direction and timing. Changes were also made on purpose. That is, a stratified combustion method has been proposed in which the entire combustion chamber is burned with a lean air-fuel ratio as a whole by locally enriching the air-fuel ratio or forming an air-fuel mixture only at a local portion.
[0004]
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. Accordingly, various in-cylinder injection engines that directly inject fuel into the cylinder have been proposed as countermeasures.
[0005]
For example, in Japanese Patent 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 the intake valve, and a reverse tumble flow is forcibly generated in the cylinder, thereby compressing the compression stroke. Sometimes fuel injected obliquely with respect to the cylinder axial direction from the injection means provided below the intake port is put on the reverse tumble flow, and the air-fuel mixture is guided in the direction of the spark plug provided at the top of the combustion chamber An example of the configuration is shown.
[0006]
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 flow is decentered to promote the generation of the reverse tumble flow, the fuel is injected obliquely with respect to the cylinder axial direction to be put on the reverse tumble flow, and the mixture is ignited at the top of the combustion chamber. A configuration example is shown in which it is guided in the direction of the plug.
[0007]
Furthermore, in Japanese Patent Laid-Open No. 6-42352, the injection means is attached downward to the center position of the top of the combustion chamber, and an ignition plug is projected from between the two intake ports into the combustion chamber for ignition. The configuration is shown.
[0008]
[Problems to be solved by the invention]
However, the in-cylinder injection internal combustion engine disclosed in JP-A-5-1544 employs an intake port that forcibly generates a reverse tumble flow by a mask wall, so that an intake resistance in a high-speed and high-load region is adopted. May become excessive. As a result, the intake air amount may be insufficient and output performance may be affected.
[0009]
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 commensurate with the fuel required for a normal practical engine, so-called regular gasoline.
[0010]
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 finely control the local air-fuel ratio in the vicinity of the electrode, and the stability and ignitability of combustion are low.
[0011]
Furthermore, the above-mentioned two publications disclose technologies that the injection means performs fuel injection obliquely with respect to the cylinder axis direction. However, when the fuel is injected in an oblique direction, the lubricant is washed away from the lubricating oil on the inner peripheral wall surface of the cylinder. And so on.
[0012]
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.
[0013]
However, with this method, good stratified combustion can be obtained in the low injection region, but it is difficult to suppress the occurrence of smoke in a situation where the injection amount increases.
[0014]
The present invention has been made in order to solve the above-mentioned problems in the prior art, and its purpose is to always ensure good stratified combustion by utilizing the reflection of fuel on the piston upper surface in various operating states of the engine. It is an object of the present invention to provide an in-cylinder injection type engine having a simple configuration.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, a direct injection engine according to claim 1 includes a combustion chamber ceiling formed in a pent roof type , an intake means and an exhaust means capable of generating a tumble flow in the combustion chamber in the intake stroke. a cylinder head having a piston and injection means for injecting fuel into the cylinder axial direction at a predetermined timing provided substantially at the center position, the upper surface portion facing the cylinder head is formed in a planar shape of the combustion chamber ceiling, the piston A recess having an opening formed in a substantially central position of the upper surface portion of the cylinder and having a combination of a small-diameter arc provided on the intake side and a large-diameter arc provided on the exhaust side facing each other, and a combustion chamber A position that protrudes obliquely with respect to the cylinder axial direction from the air intake side of the ceiling to the combustion chamber, and is located in the vicinity of the small-diameter arc of the recess and the position where the fuel injected from the injection means does not adhere directly Ignition means having an ignition part, a convex wall part projecting from the upper surface part toward the combustion chamber ceiling part on the outer periphery of the opening part of the concave part corresponding to the shape of the combustion chamber ceiling part, and formed on the ignition means side of the convex wall part And a notch that avoids interference between the convex wall and the ignition means at a position where the piston is raised near the top dead center.
[0016]
According to the above configuration, the fuel injected by the injection means is diffused by movements such as reflection, scooping and jumping up in the recess. The fuel diffused in the recess is directed by the recess shape and the weak tumble flow existing in the combustion chamber, guided to the intake means side, that is, the arc of the small diameter of the recess, and jumped up to the piston by the recess. It is done.
[0017]
Therefore, the rich air-fuel mixture can be concentrated in the vicinity of the ignition part located in the vicinity of the center position of the small-diameter arc, and the ignitability by ignition and stable stratified combustion can be performed.
[0018]
In particular, a convex wall portion is provided so as to protrude from the upper surface portion toward the combustion chamber ceiling portion along the outer periphery of the opening portion of the concave portion, corresponding to the shape of the combustion chamber ceiling portion, and the piston is raised near the top dead center Since the notch that avoids the interference between the convex wall and the ignition means is provided on the ignition means side of the convex wall, it is possible to suppress the diffusion of fuel to other than the ignition means, and the mixture cannot be propagated through the flame. You can reduce tearing.
[0019]
Further, by providing the ignition part of the ignition means at a position where the fuel injected by the fuel injection means does not directly adhere, it is possible to avoid smoldering and fogging of the ignition means and to generate sparks generated by the injected fuel passing through the ignition part. Discharge instability can be avoided.
[0020]
Furthermore, the deterioration of combustion due to the cooling action caused by a part of the injected fuel directly colliding with the inner peripheral wall surface of the cylinder, and the adhering part of the injected fuel to the inner peripheral wall surface of the cylinder It is possible to prevent deterioration in lubricity between the cylinder and the piston due to washing away the lubricating oil film.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a diagram showing a reference example 1 for explaining an embodiment of the present invention , and more specifically, a cross-sectional view for explaining the configuration of a direct injection type engine 10 in the reference example 1. FIG . As shown in the figure, the in-cylinder injection engine 10 is a so-called cylinder head 14 having a pent roof type combustion chamber ceiling portion (hereinafter simply referred to as “ceiling portion”) 12 and an upper surface portion 16 basically having a planar shape. A flat piston 18 and a cylinder 22 having a cylinder bore 20 into which the piston 18 is fitted so as to be able to reciprocate are used as basic components.
[0034]
FIG. 2 is a schematic explanatory view of the ceiling portion 12 of FIG. 1 viewed from the cylinder 22 side. As shown in FIGS. 1 and 2, the ceiling portion 12 has two inclined surfaces 12a and 12b, and has a shape similar to a gable roof shape in which these inclined surfaces 12a and 12b are formed in a roof shape. And the ceiling part 12 is formed in the position eccentric from the central axis z of the cylinder bore 20 to the exhaust valve 28 side mentioned later.
[0035]
As shown in FIG. 2, the two inclined surfaces 12 a and 12 b of the ceiling portion 12 communicate with an intake port and an exhaust port (not shown) provided in the cylinder head 14 and the combustion chamber 24. Two intake valves 26 and two exhaust valves 28, which are intake means and exhaust means to be shut off, are provided.
[0036]
A spark plug 30 as ignition means is screwed into the cylinder head 14 so as to protrude from between the intake valves 26 with respect to the central axis z of the cylinder bore 20 and protrude into the combustion chamber 24. The spark plug 30 has an electrode portion 32 that is an ignition portion at a tip portion protruding toward the combustion chamber 24, and the electrode portion 32 is in a state where the spark plug 30 is screwed to the cylinder head 14. The fuel f injected by the fuel injection means, which will be described later, is positioned so as not to be directly applied.
[0037]
An injector 34 as fuel injection means is provided at a position substantially above the center of the ceiling portion 12. The injector 34 injects the fuel f in the direction of the central axis z of the cylinder bore 20, and the injection shape forms a substantially conical hollow shape that gradually spreads around the injection central axis fm.
[0038]
The formation of the substantially conical hollow shape of the fuel f can be easily formed by setting an injection angle such that the injection spread angle is about 40 to 80 degrees and injecting the fuel while giving a rotational component. . Specifically, it can be formed by hollow cone spraying by an injector 34 using a swirl nozzle. The injection divergence angle is set so that the piston 18 is within the piston recess 36 described later at a predetermined position.
[0039]
Then, due to the shape of an intake port (not shown) that is communicated with or cut off from the combustion chamber 24 by the intake valve 26, a positive weak tumble gas flow (arrow G in the figure) is generated in the combustion chamber 24. The tumble ratio is set to be approximately 0.5-2.
[0040]
Next, the shape of the piston 18 will be described with reference to FIG. FIG. 3 is an explanatory top view of the piston 18 of FIG. As shown in the drawing, the piston 18 is based on a planar shape in which the shape of the upper surface portion 16 is orthogonal to the central axis z direction of the cylinder bore 20. Then, on the upper surface portion 16, an arc formed with a small diameter R1 and an arc formed with a large diameter R2 are opposed to each other on the intake valve 26 side and the exhaust valve 28 side, respectively, and a straight line between the two is a straight line s. A recess 36 having a generally teardrop-shaped opening 35 connected thereto is provided.
[0041]
The recess 36 has a bottom 38 that is substantially the same type (substantially teardrop-shaped) as the opening 35 that is parallel to the top surface 16 and at a predetermined depth h, and has a smooth curved surface from the periphery of the bottom 38. It has a peripheral wall portion 40 that rises substantially perpendicularly (90 to 150 degrees) to the upper surface portion 16 through a continuous curved surface 38a.
[0042]
The center position (cavity center: hereinafter simply referred to as “kc1”) of the concave portion 36 on the small diameter R1 side (hereinafter simply referred to as “small diameter R1 side”) is the center axis z passing through the electrode portion 32 of the spark plug 30. The central position (hereinafter simply referred to as “kc2”) on the large diameter R2 side (hereinafter simply referred to as “large diameter R2 side”) is provided on the parallel axis, and is located on the exhaust valve 28 side relative to the central axis z of the cylinder bore 20. Is provided so as to be substantially coaxial with the injection center axis fm of the injector 34.
[0043]
The diameter d2 of the large diameter R2 of the recess 36 is set to about 30 to 70% with respect to the diameter D of the cylinder bore 20, and the diameter d1 of the small diameter R1 is 10 to 50% with respect to the diameter D of the cylinder bore 20. It is set to a size of about. The depth h of the recess 36 is set to a limit of about 15% of the diameter D of the cylinder bore 20.
[0044]
Next, the operation and effects in the low / medium load operation region of the direct injection engine having the above-described configuration will be described. In the in- cylinder injection engine 10 of Reference Example 1 , in the high load operation region, the fuel f is injected into the cylinder during the intake stroke to perform high output operation, but the detailed description thereof is omitted. To do.
[0045]
First, in the compression stroke in the engine operating state, when the piston 18 rises to a predetermined position, the fuel f is injected from the injector 34 into a hollow cone shape. The fuel f collides with the bottom 38 of the recess 36 of the piston 18 that continues to rise. At that time, the formed hollow cone shape is collapsed, and the fuel f is efficiently diffused by reflection, creeping, jumping, etc. in the recess 36.
[0046]
In the peripheral wall 40, the momentum of the fuel f diffused by the reflection or the like is suppressed, and the spreading direction of the fuel f is controlled. That is, the fuel f is diffused so as to gather on the small diameter R1 side because the recess 36 is formed in a substantially teardrop shape and the weak tumble flow generated in the intake stroke exists in the combustion chamber 24. The piston is pushed up above the piston 18 by the peripheral wall 40 on the R1 side.
[0047]
Therefore, the fuel f is guided to the side of the spark plug 30 positioned above the small diameter side, and forms a mixture having good ignitability and suitable for stratified combustion around the electrode portion 32 at a predetermined ignition timing. Can do. As a result, it is possible to prevent the mixture from being broken and the overlean region from being interrupted by flame propagation, and to obtain appropriate and rapid combustion with a lean air-fuel ratio as a whole, and to prevent the occurrence of partial burn. Can do. Therefore, it is possible to obtain good stratified combustion as described above under wide operating conditions in the low / medium load region.
[0048]
The inclined surfaces 12a and 12b of the pent roof type ceiling portion 12 maintain a weak tumble flow even in the compression stroke, and moderate tumble flow turbulence that contributes to fuel diffusion occurs near the top dead center to improve combustion. Can contribute.
[0049]
Due to the various actions described above, stratified combustion performed in a low load and medium load region can be performed better, and as a result, good drivability, reduction of HC, reduction of NOx, and improvement of fuel consumption are also achieved. In addition, since the compression ratio does not increase by securing the compact combustion chamber 24 formed by the recess 36 and the pent roof type ceiling portion 12, ordinary fuel, so-called regular gasoline can be used.
[0050]
Further, since the fuel f is less likely to diffuse to the cylinder inner peripheral wall surface 42 due to the injection direction and the action of the recess 36, it is possible to prevent a decrease in lubricity due to the fuel f adhering to the cylinder inner peripheral wall surface 42. In addition, it is possible to effectively prevent the occurrence of functional failure in the piston operation.
[0051]
Next, Reference Example 2 for explaining the embodiment of the present invention will be described below. Figure 4 is a sectional view illustrating the configuration of a cylinder injection type engine in Reference Example 2, FIG. 5 is a top illustration of the piston 18. In the figure, the same components as those in Reference Example 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
[0052]
A characteristic configuration of the reference example 2 that is different from that of the reference example 1 described above is the shape of the recess 36 provided in the upper surface part 16. That is, an arc formed with a small diameter R1 and a circular arc formed with a large R2 diameter d2 are provided opposite to each other on the intake valve 26 side and the exhaust valve 28 side, and a large diameter R2 is provided therebetween. In other words, a concave portion 36 having a substantially egg-shaped opening 35 smoothly connected by a curve c1 having a diameter d3 (d3>d1> d2) larger than the diameter d2 is provided.
[0053]
According to the above configuration, the fuel f injected from the injector 34 into the recess 36 is efficiently diffused by reflection, scooping, jumping, and the like. Therefore, the diffusion operation as described above is obtained without stopping the momentum with a certain regularity as a whole, and good stratified combustion can be achieved. Therefore, the air-fuel mixture G formed by the diffusion of the fuel f can be made more homogeneous as compared with the reference example 1 .
[0054]
Next, described below with the reference example 3 for illustrating an embodiment of the present invention. Figure 6 is a sectional view illustrating the configuration of a cylinder injection type engine in Reference Example 3, FIG. 7 is a top illustration of the piston 18. In the figure, the same components as those in Reference Example 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
[0055]
A characteristic configuration of the reference example 3 different from the above-described reference examples 1 and 2 is the shape of the recess 36. The concave portion 36 has an arc formed with a small diameter R1 and an arc formed with a large diameter R2 opposed to each other on the intake valve 26 side and the exhaust valve 28 side, and has a small diameter smaller than the diameter d2 of the large diameter R2. And having a substantially daruma-shaped opening 35 connected by a curve c2 having a radius d4 (d1>d4> d2) larger than the diameter d1 of R1. As for the shape of the bottom portion of the concave portion 36, the large diameter R2 side has a bottom portion 38 substantially parallel to the upper surface portion 16 as in the first embodiment. The connecting portion between the large diameter R2 and the small diameter R1 is folded such that the depth h1 on the small diameter R1 side is shallower than the depth h2 on the large diameter R2 side, thereby forming a stepped portion v.
[0056]
According to the above configuration, the fuel f injected from the injector 34 to the large-diameter R2 side of the recess 36 causes efficient diffusion of the fuel f due to reflection, creeping, jumping, and the like. That is, the fuel f scoops up the peripheral wall portion 40a on the small diameter R1 side by the substantially dull shape of the concave portion 36 and the weak tumble flow existing in the combustion chamber 24, is guided to the small diameter R1 side, and runs up the stepped portion v. . The air-fuel mixture always passes through the vicinity of the electrode portion 32 positioned above the small diameter side of the recess 36. Therefore, compared with the first and second embodiments, the air-fuel mixture can be more concentratedly formed on the electrode part 32, and the ignitability can be further improved.
[0057]
Next, it will be described below embodiments of the present invention. Figure 8 is a sectional view illustrating the configuration of the direct injection engine of the embodiment, FIG. 9 is a top explanatory view of a piston 18 used in this embodiment. In the figure, the same components as those in Reference Example 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
[0058]
In the present embodiment, the characteristic configuration different from the above-described Reference Example 1 is a position that protrudes toward the ceiling portion 12 so as to surround the periphery of the opening portion 35 of the recess 36 and the piston 18 is raised near the top dead center. Thus, a convex wall portion 54 for avoiding interference with the spark plug 30 is provided, and the spark plug 30 is arranged so that the electrode portion 32 faces the concave portion 36 side.
[0059]
As shown in FIG. 8, the convex wall portion 54 has two inclined surface portions 54a and 54b so that the shape in the height direction substantially corresponds to the inclined surfaces 12a and 12b of the ceiling portion 12. The top portion is formed with a flat portion 60 so as to be parallel to the upper surface portion 16 and has a substantially trapezoidal shape. Further, as shown in FIG. 9, the convex wall portion 54 is provided so that the center thereof is substantially coaxial with the central axis kc2 of the large diameter R2, and the outer wall portion 54b is directed toward the ceiling portion 12 side. Therefore, it is formed so as to gradually narrow in the direction of the central axis kc2 of the large diameter R2.
[0060]
And the convex wall part 54 has the notch part 66 from which the convex wall part 54 was removed by predetermined width on the ignition plug 30 side. Further, as is apparent from FIG. 8, cross-sectional shape of the recess 36, the direction of the intake valve 26 side is formed lower.
[0061]
Therefore, according to the above configuration, it is possible to sufficiently suppress the diffusion of fuel in the direction other than the electrode portion 32 of the spark plug 30 as compared with the above-described embodiment, and further reduce the air-fuel mixture tearing. be able to. Thereby, reduction of HC (hydrocarbon) can be aimed at and the improvement of a fuel consumption can be obtained.
[0062]
In addition, this invention is not limited to each above-mentioned reference examples 1-3 and the structure of this Embodiment , A various deformation | transformation is possible within the range of the summary of invention. For example, in each of the reference examples 1 to 3 and the present embodiment , the shape of the concave portion 36 provided on the upper surface portion 16 of the piston 18 has been described in various ways. However, the shape is not limited to the above shape, and the concave portion 36 is not limited thereto. Various shapes can be adopted as long as the fuel f injected into the compact combustion chamber formed by the above can smoothly diffuse.
[0063]
【The invention's effect】
As described above, according to the direct injection engine according to the present invention, a locally rich air-fuel mixture can be more appropriately formed at a predetermined position in the combustion chamber of the engine. That is, it is possible to achieve an air-fuel mixture state suitable for performing stratified combustion while ensuring a lean air-fuel ratio as a whole under a wide range of operating conditions in the low / medium load region. Thereby, it is possible to contribute to improvement of exhaust emission, improvement of drivability and improvement of fuel consumption.
[Brief description of the drawings]
1 is a cross-sectional view illustrating a configuration of a direct injection type engine in Reference Example 1. FIG .
FIG. 2 is a schematic explanatory view of the ceiling portion of FIG. 1 viewed from the cylinder bore side.
FIG. 3 is an explanatory top view of the piston of FIG. 1;
4 is a cross-sectional view illustrating a configuration of a direct injection type engine in Reference Example 2. FIG .
5 is an explanatory top view of the piston of FIG. 4. FIG.
6 is a cross-sectional view illustrating a configuration of a direct injection engine in Reference Example 3. FIG .
7 is an upper surface explanatory view of the piston of FIG. 6. FIG.
FIG. 8 is a cross-sectional view illustrating the configuration of a direct injection engine in the present embodiment.
9 is an upper surface explanatory view of the piston of FIG. 8. FIG.
[Explanation of symbols]
12 Combustion chamber ceiling 14 Cylinder head 18 Piston 22 Cylinder 24 Combustion chamber 26 Intake valve (intake means)
28 Exhaust valve (exhaust means)
30 Spark plug (ignition means)
32 Electrode part (ignition part)
34 Injector
36 Recess 42 Cylinder inner peripheral wall surface f Fuel

Claims (1)

A cylinder head having a combustion chamber ceiling formed in a pent roof type and an intake means and an exhaust means capable of generating a tumble flow in the combustion chamber in the intake stroke;
Injection means provided at substantially the center position of the combustion chamber ceiling and injecting fuel in the cylinder axial direction at a predetermined timing;
A piston top surface facing the cylinder head is formed in a planar shape,
A recess having an opening formed in a substantially central position on the upper surface of the piston and having a combination of a small-diameter arc provided on the intake side and a large-diameter arc provided on the exhaust side facing each other. When,
The fuel is injected from the injection means directly at a position in the vicinity of the small-diameter arc of the concave portion provided in an oblique direction with respect to the cylinder axial direction from the intake side of the combustion chamber ceiling to the combustion chamber. Ignition means having an ignition part at a position where it does not adhere;
A convex wall portion projecting from the upper surface portion toward the combustion chamber ceiling portion corresponding to the shape of the combustion chamber ceiling portion on the outer periphery of the opening of the recess;
A cylinder formed on the ignition means side of the convex wall portion, and having a notch for avoiding interference between the convex wall portion and the ignition means at a position where the piston is raised near the top dead center. Internal injection engine.

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