JP3781536B2 - 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 an in-cylinder injection 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]
[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]
[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 output performance.
[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 suitable for a fuel used in a normal engine, so-called regular gasoline.
[0010]
If the curved portion or the cavity is enlarged so as to obtain a normal compression ratio to secure a sufficient combustion chamber volume, the distance between the injection port of the fuel injection valve and the electrode of the spark plug increases. It is difficult to guide the air-fuel mixture to the spark plug side, it is difficult to accurately produce a stratified air-fuel mixture, and there are problems such as low combustion stability and low ignitability.
[0011]
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide an in-cylinder injection engine having a simple configuration capable of precisely generating a stratified mixture generated by reflection of fuel on the upper surface of a piston. It is to provide a combustion chamber structure.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the combustion chamber structure of a direct injection type engine according to claim 1 is a cylinder having a pent roof type combustion chamber ceiling portion having a pair of inclined surfaces each having an intake side and an exhaust side. A head, an injector provided on the cylinder head, for injecting fuel at a predetermined timing from a substantially center position of the combustion chamber ceiling to the upper surface of the piston in the cylinder axial direction, and a protrusion corresponding to the shape of the combustion chamber ceiling of the cylinder head A piston head having a basic shape as a shape, provided in a cylinder head, a piston that generates a squish flow from the peripheral side of the piston head toward the center of the piston head by cooperating with the combustion chamber ceiling during the compression stroke, A spark plug that protrudes obliquely from the inclined surface on the intake side of the ceiling of the combustion chamber into the combustion chamber in the direction of the cylinder axis, and the piston head And a cavity having a bottom portion inclined toward the spark plug side, and the spark plug is located at an upper position inside the cavity when the piston is located near the top dead center and on the intake side from the center of the cavity. The electrode portion is arranged at a position offset to the position.
[0013]
The cavity has a bottom portion that is inclined toward the spark plug. Further, the combustion chamber ceiling and the piston have a configuration in which a squish flow, which is a flow of air-fuel mixture from the peripheral side of the upper surface of the piston toward the center, is generated during the compression stroke.
[0014]
In the cylinder injection engine having the above-described configuration, when the piston rising to the cylinder head reaches a predetermined position before top dead center, fuel is injected from the injector, and the injected fuel (hereinafter simply referred to as “injection”). Fuel ”) spreads toward the cavity, is received in the cavity, and diffuses by reflection, scooping and jumping to form an air-fuel mixture.
[0015]
Here, the injected fuel collides with the bottom of the cavity is Ru is reflected on the electrode portion side. The fuel that seems to protrude from the cavity due to the momentum of reflection is pushed back into the cavity by the squish flow, and diffusion outside the cavity is suppressed. Thereby, the mass of the air-fuel mixture can be formed in the vicinity of the electrode portion of the spark plug.
[0016]
Therefore, the direction in which the injected fuel diffuses can be precisely controlled, and the air-fuel mixture can be generated in the vicinity of the electrode portion of the spark plug that is displaced to the intake side. That is, the generation position of the air-fuel mixture in the combustion chamber can be controlled accurately and easily.
[0017]
As a result, it is possible to accurately control the generation position of the air-fuel mixture even in a wide combustion chamber space, to ensure good ignitability and combustion stability in a wide operation region, and to reduce the compression ratio to a fuel used in a normal engine. It can be set to a value suitable for so-called regular gasoline.
[0018]
In the combustion chamber structure of the direct injection engine according to claim 2, the cavity rises at a predetermined angle from the bottom inclined to the spark plug side and a smooth curved surface from the bottom, and the injection central axis of the injector is interposed therebetween. And a wall portion facing the electrode portion of the spark plug.
[0019]
According to a third aspect of the present invention, there is provided a combustion chamber structure for an in-cylinder injection engine in which a cavity is formed in a concave shape so that a bottom portion has a hemispherical shape as a basic shape, and is opposed to a spark plug through an injection center axis of an injector The exhaust side portion of the bottom portion has a concave curved surface shape centered on the upper position of the piston upper surface at a position offset toward the spark plug side from the injection center axis of the injector.
[0022]
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 a direct injection type engine 10 according to the first embodiment of the present invention, and FIG. 2 is a top view of the piston 18 of FIG.
[0023]
As shown in FIG. 1, the in-cylinder injection engine 10 includes a cylinder head 14 having a combustion chamber ceiling portion (hereinafter simply referred to as “ceiling portion”) 12 formed in a pent roof shape, and a piston head 16 having a ceiling portion. The piston 18 formed into a convex shape corresponding to 12 and the cylinder portion 22 having the cylinder 20 into which the piston 18 is removably fitted are used as basic components.
[0024]
As shown in FIG. 1, the ceiling portion 12 has two slope portions 12 a and 12 b that are gradually separated from the top portion and expand, 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. Further, the ceiling portion 12 is provided at a position offset to the exhaust side from the center of the cylinder 20.
[0025]
As shown in FIG. 1, the spark plug 30 is provided on the intake IN side of the cylinder head 14, is inclined with respect to the axial direction of the cylinder 20, and is provided so that the end protrudes into the combustion chamber 24. Further, the spark plug 30 has an electrode portion 32 that is an ignition portion at an end portion protruding toward the combustion chamber 24.
[0026]
Further, an injector 34 is provided substantially above the center of the ceiling 12. The injector 34 injects fuel toward the axial piston head 16 of the cylinder 20, and the injection center axis 35 is set at a position offset from the center axis 21 of the cylinder 20 to the exhaust EX side. The fuel injection shape by the injector 34 forms a substantially conical hollow shape that gradually spreads around the injection central axis 35 (indicated by a dotted line f in FIG. 1).
[0027]
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 while giving a rotational component to the fuel. is there. Specifically, it can be formed by hollow cone spraying by an injector 34 using a swirl nozzle.
[0028]
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. The tumble flow in the positive direction refers to a gas flow in a direction that rolls on the piston head 16 from the intake IN side to the exhaust EX side.
[0029]
As shown in FIG. 1, the piston 18 protrudes from the peripheral edge 17 of the piston head 16 formed in a planar shape orthogonal to the cylinder center axis 21 and protrudes from the peripheral edge 17 corresponding to the pent roof type ceiling 12. It has the convex part 19 which does.
[0030]
When the piston 18 rises to just before the top dead center in the compression stroke due to the cooperation with the cylinder head 14, the air-fuel mixture flows from the peripheral edge 17 side toward the center of the piston head 16, so-called squish flow. It has a structure that generates (compression turbulence).
[0031]
Further, 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 to the intake IN side and having a recess. The cavity 36 includes a bottom portion 37 that is inclined at an angle that reflects toward the electrode portion 32 when fuel injected from the injector 34 collides.
[0032]
The exhaust side of the bottom portion 37 is connected to a wall portion 38 facing the rising electrode portion 32 at a predetermined angle through a smooth curved surface between the bottom portion 37. Therefore, even when the fuel injected from the injector collides with the wall portion 38, it is reflected to the electrode portion 32 side.
[0033]
The electrode portion 32 of the spark plug 30 is set to be positioned above the cavity 36 and offset from the center of the cavity 36 toward the intake IN side when the piston 18 is located near the top dead center. Then, it arrange | positions in the position where the injection fuel from the injector 34 does not collide directly.
[0034]
The injection spread angle of the injector 34 is set so that the injection range is within the cavity 36 at a predetermined timing (position just before top dead center) when the piston 18 moves up and down.
[0035]
As shown in FIG. 2, 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, and the depth of the cavity 36 is the deepest part. The limit is set from the peripheral edge 17 to about 15% of the cylinder diameter D.
[0036]
Next, the operation and action of the in-cylinder injection engine 10 having the above configuration will be described below. The in-cylinder injection engine 10 in the present embodiment performs the stratified charge combustion operation only during the low / medium load operation, and the fuel injection amount, the injection timing, and the ignition timing so as to perform the uniform combustion operation during the high load operation. Be controlled.
[0037]
The uniform combustion performed at the time of the high load operation is such that fuel is injected into the combustion chamber 24 during the intake stroke, and is the same operation as a conventional engine that injects fuel into the intake port during the intake stroke. The explanation is omitted, and here, the stratified combustion operation at the time of low / medium load operation, which is a feature of the present invention, will be described.
[0038]
First, in the compression stroke, fuel is delivered from the injector 34 toward the piston head 16 at a predetermined timing set according to the engine operating state, in other words, when the piston 18 rises to a predetermined position near the top dead center. A predetermined injection amount is injected into a hollow cone shape. The injected fuel is received by the cavity 36 of the piston 18 that continues to rise, and diffuses in the cavity 36 due to reflection, scooping, jumping, and the like. A part of the jumped fuel collides with the ceiling portion 12 and diffuses.
[0039]
And since the ceiling part 12 is formed in the pent roof type | mold, the fuel which jumped up in the cavity 36 and collided with the ceiling part 12 with the momentum is reflected so that it may gather on the combustion chamber center side. The injected fuel that collides with the bottom 37 of the cavity 36 is reflected toward the spark plug 30 by the inclination and diffuses in the vicinity of the electrode portion 32.
[0040]
As the piston 18 further rises, the space between the ceiling 12 and the piston head 16 becomes sufficiently narrow, and a squish flow that flows from the peripheral edge 17 side of the piston head 16 toward the cavity 36 is generated. The fuel reflected in the cavity 36 by this squish flow and trying to jump out from the opening 39 toward the peripheral edge 17 is forcibly pushed back toward the center of the piston 18 and in the cavity 36 and its upper range. Spread. Further, at this time, the squish flow and the weak tumble flow existing in the combustion chamber 24 collide with each other, so that the air-fuel mixture is turbulent in the combustion chamber 24 so as to promote combustion.
[0041]
Thereby, a stratified mixture suitable for ignition is formed in the vicinity of the electrode portion 32 at an appropriate timing. Here, for example, when the fuel injection amount at the time of medium load operation is relatively large, the injected fuel reflected by the cavity 36 diffuses in the cavity 36 and in the upper region thereof, and the stratified mixture has a wide diffusion volume and is uniformly diffused. Is formed.
[0042]
Further, when the fuel injection amount is small at the time of idling or the like, a stratified air-fuel mixture in which a part is reliably applied to the electrode portion 32 is formed by the inclination of the bottom portion 37 of the cavity 36. Therefore, in a wide operation region, a good air-fuel mixture having good ignitability and suitable for stratified combustion can be formed around the electrode portion 32, and a cavity forming a wide combustion chamber space, that is, having a large volume. Even in the cavity, the generation position of the air-fuel mixture can be accurately controlled.
[0043]
Thereby, the engine operation using regular gasoline can be performed with the compression ratio set to a normal compression ratio. In addition, good drivability, HC reduction, NOX reduction, and fuel efficiency improvement can be achieved.
[0044]
In addition, since the injected fuel diffuses in the cavity and in the upper part of the cavity, it is possible to prevent the air-fuel mixture from being broken and the occurrence of an overlean region where flame propagation is impossible. Appropriate and rapid combustion can be obtained at the fuel ratio, and partial burn can be prevented.
[0045]
In addition, since the injected fuel is injected in the cylinder axial direction, it is difficult to diffuse to the cylinder 20 side, the adhesion of the injected fuel to the cylinder 20 can be prevented, and the lubricity between the cylinder 20 and the side surface of the piston 18 is deteriorated. In addition, it is possible to prevent the deterioration of the combustion state caused by the cooling effect caused by a part of the injected fuel directly colliding with the inner peripheral wall surface of the cylinder 20.
[0046]
Next, a second embodiment of the present invention will be described below. FIG. 3 is an explanatory cross-sectional view of the second embodiment, and FIG. 4 is an upper surface explanatory view of the 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 is omitted.
[0047]
In the present embodiment, a characteristic configuration different from that of the first embodiment described above is the concave shape of the cavity 36. As shown in FIG. 3, the concave shape of the cavity 36 is basically formed in a hemispherical shape, and the exhaust side portion 37 a of the bottom portion 37 is closer to the spark plug 30 than the injection center shaft 35 of the injector 34. It is formed in a concave curved surface shape centered on the upper position offset to. Therefore, of the injected fuel injected from the injector 34, the fuel that collides with the exhaust side portion 37 a of the bottom portion 37 is reflected toward the electrode portion 32 and locally forms an appropriate air-fuel mixture in the vicinity of the electrode portion 32.
[0048]
Here, since the bottom portion 37 has a hemispherical shape, a larger volume of the cavity is ensured than in the first embodiment. As a result, the diffusion volume of the fuel injected into the cavity can be further increased, and fuel efficiency can be improved by expanding the combustion region of the air-fuel mixture. Further, since the hemispherical shape is used as a basic shape, the tumble flow existing in the combustion chamber can be maintained without being disturbed.
[0049]
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 each of the above-described embodiments, the case where the gas flow due to the weak tumble flow exists has been described. However, the shape of the intake port or the like may be changed to generate a weak swirl flow, which may be used in combination with the weak tumble flow.
[0050]
【The invention's effect】
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 diffuses can be precisely controlled by the inclined portion in the cavity and the squish flow generated on the upper surface of the piston. The air-fuel mixture can be generated at an appropriate timing near the electrode portion of the spark plug. Therefore, it is possible to ensure good ignitability and combustion stability in a wide operation region, and to set the compression ratio to a normal value.
[Brief description of the drawings]
FIG. 1 is an explanatory cross-sectional view schematically illustrating an in-cylinder injection engine according to a first embodiment of the present invention.
FIG. 2 is a top view for explaining the piston of FIG. 1;
FIG. 3 is an explanatory cross-sectional view schematically illustrating a direct injection engine according to a second embodiment of the present invention.
4 is an upper surface explanatory view of the piston of FIG. 3. FIG.
[Explanation of symbols]
12 Combustion chamber ceiling 14 Cylinder head 16 Piston head 18 Piston 19 Protruding portion 20 Cylinder 22 Cylinder portion 24 Combustion chamber 30 Spark plug 32 Electrode portion 34 Injector 36 Cavity f Fuel

Claims (3)

A cylinder head having a pent roof type combustion chamber ceiling portion having a pair of inclined surfaces formed of an intake side and an exhaust side;
An injector that is provided in the cylinder head and 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;
A piston head having a convex shape corresponding to the shape of the combustion chamber ceiling of the cylinder head, and the piston head from the peripheral side of the piston head by the cooperation with the combustion chamber ceiling during the compression stroke; A piston that generates a squish flow toward the center;
An ignition plug that is provided in the cylinder head and protrudes in an oblique direction with respect to the cylinder axial direction into the combustion chamber from an inclined surface on the intake side of the ceiling portion of the combustion chamber;
A cavity that is recessed substantially at the center of the piston head and has a bottom portion that is inclined toward the spark plug,
In the cylinder, the spark plug has an electrode portion disposed at an upper position inside the cavity when the piston is located near the top dead center and at a position offset from the center of the cavity toward the intake side. Combustion chamber structure of an injection engine. The cavity is
A bottom portion inclined toward the spark plug;
The wall portion that rises from the bottom portion through a smooth curved surface at a predetermined angle and faces the electrode portion of the spark plug with the injection center axis of the injector interposed therebetween. The combustion chamber structure of an in-cylinder injection engine. The cavity is
The bottom portion is formed in a concave shape so as to have a hemispherical shape as a basic shape, and the exhaust side portion of the bottom portion facing the spark plug with the injection center axis of the injector interposed therebetween is an injection center axis of the injector The in-cylinder injection engine according to claim 1, wherein the in-cylinder injection engine has a concave curved surface shape centered on a position offset from the spark plug side and above the upper surface of the piston.

Images