JP3800727B2 - In-cylinder fuel injection internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct injection internal combustion engine, and more particularly to an improvement of a direct injection internal combustion engine that operates at a lean air-fuel ratio.
[0002]
[Prior art]
A conventional in-cylinder internal combustion engine is described in, for example, Japanese Patent Application Laid-Open No. 8-35429. The purpose of this is to enable stable stratified combustion regardless of the large load range, that is, the amount of fuel injection. The shape of the concave combustion chamber provided on the upper surface of the piston is approximately the wall near the spark plug. A straight space and a space in which fuel and air diffuse and mix are formed behind the straight wall surface. For this reason, even when the load is high, that is, in a state where the amount of fuel is large, a combustible air-fuel ratio mixture can be formed without stagnating excess fuel near the spark plug.
[0003]
Japanese Patent Laid-Open No. 8-260986 discloses that a step portion is provided in a wall surface portion which is an upstream region of a swirl (swirl flow) with respect to the spark plug of the concave combustion chamber, and this step portion is located at the piston position in the latter half of the compression stroke. Has been proposed in which the fuel injected from the engine to the combustion chamber is directed upward to improve the combustion under a medium engine load.
[0004]
[Problems to be solved by the invention]
However, in such a conventional cylinder injection internal combustion engine, the concave combustion chamber on the upper surface of the piston has a non-circular shape having a linear portion or an irregular shape in which the stepped portion faces the wall surface of the concave combustion chamber. Therefore, in order to transport and diffuse the fuel injected into the concave combustion chamber, it is necessary to generate a strong swirling flow in the cylinder. For this reason, the shape of the intake port is a so-called helical type, or an intake control valve with a small opening area is provided in the port. However, in the case of a helical port, the intake resistance at high loads increases and the generated torque decreases. Invite. Further, in the case of an intake control valve having a small opening area, there is a problem in that the effect of improving the fuel efficiency is impaired because the pump loss increases even at the same suction negative pressure at the partial load.
[0005]
An object of the present invention is to eliminate such conventional problems.
[0006]
[Means for Solving the Problems]
The invention according to claim 1 is an injection valve for injecting fuel into a cylinder, a spark plug that protrudes from a position close to a wall surface of a concave combustion chamber formed on the upper surface of a piston, and a swirl of intake air in the combustion chamber and the cylinder. A spark ignition engine having a means for generating a flow, the cross-sectional shape of the wall surface of the concave combustion chamber is substantially circular, the bottom surface portion is formed by a shallow bottom portion and a deep bottom portion deeper than this, and The deep bottom portion is formed so as to be located on the downstream side of the swirling flow generated in the concave combustion chamber with respect to the spark plug.
[0007]
The invention according to claim 2 forms a concave pocket portion on the wall surface near the deep bottom while keeping the wall surface substantially circular by projecting the upper surface of the piston in the side wall portion near the deep bottom portion of the concave combustion chamber into the concave combustion chamber. To do.
[0008]
According to a third aspect of the present invention, an inclined portion is formed on the bottom surface of the deep bottom portion of each of the inventions so that the depth gradually increases from the portion close to the spark plug toward the downstream side of the swirling flow.
[0009]
In the invention of claim 4, the cross-sectional shape of the deep bottom portion of each of the above inventions is substantially semicircular.
[0010]
[Action / Effect]
According to each of the above inventions, the swirling flow generated in the concave combustion chamber has a substantially circular wall surface in the combustion chamber. It is possible to mix the transportation of fresh and fresh air. For this reason, it is not necessary to make the intake port helical type, or to provide an intake control valve in the intake manifold to strengthen the swirl flow generated in the cylinder. The fuel efficiency improvement effect in stratified combustion is not impaired.
[0011]
Further, the injection injected from the injection valve rides on the swirling flow in the concave combustion chamber, passes under the spark plug while being diffused and mixed, and is transported to the deep bottom portion of the concave combustion chamber. At low load, the fuel is ignited in a state where it is concentrated around the spark plug. Therefore, the deep bottom located on the downstream side of the fuel does not have a significant effect at this time, that is, the bottom of the combustion chamber directly below the spark plug is shallow. Since it is bottom-shaped, it is not necessary to make the spark plug protrude more than necessary, and good ignition performance can be obtained.
[0012]
On the other hand, a lot of fuel is injected at the time of high load, and this fuel is distributed from directly under the spark plug to the deep bottom of the downstream region. At this time, a large amount of fuel is introduced into the deep bottom portion by the swirling flow and held at the deep bottom portion, so that a spatial margin for mixing with fresh air is obtained. Also, near the bottom of the deep bottom, when swirl flows from the shallow bottom to the deep bottom, a vortex is generated due to the step, and swells are increased, further promoting diffusion and better It becomes possible to make a simple mixture. The ignition is performed on the fuel remaining below the spark plug as in the case of a low load, the ignition flame propagates to the deep bottom, and the entire fuel is combusted. In this way, it is possible to create a good mixture state from low load to high load.
[0013]
By the way, when the depth of the combustion chamber cannot be sufficiently obtained, fuel overflows from the concave combustion chamber to the upper surface of the piston, which may cause an increase in the amount of discharged unburned fuel. On the other hand, according to the invention of claim 2, by projecting the upper surface of the piston in the side wall portion near the deep bottom portion of the concave combustion chamber into the concave combustion chamber, the wall surface near the deep bottom portion is maintained while maintaining a substantially circular wall surface. Since the concave pocket portion is formed, even if the depth of the shallow bottom portion of the concave combustion chamber is not large, the deep bottom portion substantially coincides with the protruding position of the fuel. Can be held in the concave combustion chamber, and the injected fuel can be reliably burned.
[0014]
In the invention of claim 3, the inclined portion is formed on the bottom surface of the deep bottom portion so that the depth gradually increases from the portion close to the spark plug toward the downstream side of the swirling flow. In this way, by gradually changing the bottom surface of the deep bottom portion of the concave combustion chamber near the spark plug, it is possible to prevent the air-fuel ratio around the spark plug from becoming excessively thin at low load, and to obtain more steady ignition performance. .
[0015]
In the invention of claim 4, since the cross-sectional shape of the deep bottom portion is substantially semicircular, interference with the small end of the connecting rod can be avoided, thereby suppressing the overall piston height while ensuring a large deep bottom volume. The piston weight can be reduced and the overall engine height can be reduced.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, some embodiments of the present invention will be described with reference to the drawings.
[0017]
1 and 2 show an embodiment of the present invention. First, the structure will be described. 1 is a piston, 2 is an injection valve for directly injecting fuel into the cylinder 4, 3 is a spark plug, 4 is a cylinder, 5 is a cylinder head, and 6 is a concave combustion chamber formed on the upper surface of the piston. Show. Reference numeral 7 denotes an intake valve, and reference numeral 8 denotes an exhaust valve. In the present embodiment, the intake valve 7 and the exhaust valve 8 are each a four-valve type provided with two each.
[0018]
The upper surface of the piston is formed in a raised shape composed of an intake side inclined surface 1a and an exhaust side inclined surface 1b, and these inclined surfaces 1a and 1b are formed on the cylinder head 5 side with an intake side wall surface 5a that forms a pent roof type combustion chamber and an exhaust side. Each is formed substantially parallel to the wall surface 5b. As shown by the one-dot chain line in FIG. 1, the space above the piston 1 is extremely narrow near the compression top dead center. At this time, the concave combustion chamber 6 is substantially sealed with the cylinder head 5. It has become.
[0019]
FIG. 2 shows a planar configuration of the piston 1, and intake manifolds 10a and 10b are connected to the intake ports 9a and 9b, respectively, and an intake control valve 11 is provided in one intake manifold 10b. In order to generate a swirl flow, opening / closing control is performed in accordance with the load and the rotational speed of the engine.
[0020]
FIG. 3 shows a cross-sectional shape of the combustion chamber 6. The planar shape of the combustion chamber 6 has a substantially circular wall surface 6c as shown in FIG. 2, and a shallow bottom portion 6a and a deep bottom portion 6b having different depths are formed on the inner bottom surface portion thereof. The shallow bottom portion 6a has a substantially flat shape from a position close to the injection valve 2 to the vicinity of the spark plug 3 along the swirl flow (S) generated in the combustion chamber. On the other hand, the deep bottom portion 6b is formed so as to be positioned on the downstream side of the swirling flow (S) from the vicinity of the spark plug 3 and to have a substantially semicircular planar shape. The shallow bottom part 6a, the deep bottom part 6b, and the side wall part 6c are smoothly connected by the curved surface.
[0021]
Note that the fresh air during stratified combustion is an intake port formed in a substantially straight pipe shape in order that the intake control valve 11 provided in the intake manifold 10b suppresses the introduction of fresh air from the intake port 9b during the intake stroke. The gas flows selectively from 9a, and a swirling flow is generated in the cylinder 4 with the inflow resistance at the intake manifold 10a and the intake port 9a being small. The swirl flow (S) in the combustion chamber 6 is generated by introducing the swirl flow in the cylinder into the combustion chamber 6 through the intake and compression strokes. Further, the fuel (F) at the time of stratified combustion is injected by the injection valve 2 so as to be directed to the bottom surface of the combustion chamber 6 in the compression stroke.
[0022]
Next, the operation will be described.
[0023]
First, the swirling flow (S) generated in the combustion chamber 6 is attenuated even if it is a relatively weak swirling flow or the compression stroke because the wall surface 6c of the combustion chamber 6 has a substantially circular shape. In addition, the transportation of the fuel (F) and the fresh air are sufficiently mixed. Also, in the vicinity of the compression top dead center, the space above the combustion chamber 6 is extremely narrow as described above, so that the combustion chamber 6 is substantially sealed at this time, and the swirl flow in the combustion chamber 6 Can be saved effectively. For this reason, it is not necessary to make the intake port 9a a helical type or to provide an intake control valve having a notch in the intake manifold 10a to strengthen the swirl flow generated in the cylinder. There is no reduction in torque, and there is no reduction in fuel efficiency improvement effect in stratified combustion.
[0024]
On the other hand, in order to perform stratified combustion, the injection (F) injected from the injection valve 2 in the compression stroke is diffused almost toward the spark plug 3 as shown in FIG. As shown in (b) or (c) of FIG. 4, it rides on the swirling flow (S) and passes below the spark plug 3 and is transported to the deep bottom 6b while being diffused and mixed.
[0025]
When the load is low even in the region where homogeneous combustion is performed, the fuel (F) is ignited in the state of FIG. At this time, since the bottom surface of the combustion chamber directly below the spark plug 3 is relatively shallow, it is not necessary to project the gap portion of the spark plug 3 more than necessary, and good ignitability can be obtained.
[0026]
On the other hand, when the load is relatively high in the region where homogeneous combustion is performed, that is, when the amount of injected fuel is relatively large, the fuel (F) is ignited substantially in the state shown in FIG. At this time, a large amount of fuel (F) is introduced into the deep bottom portion 6b by the swirling flow (S) and is held by the deep bottom portion 6b, and a space capable of mixing with fresh air is secured by the volume of the deep bottom portion 6. The In addition, when the swirling flow flows from the shallow bottom portion 6a near the bottom surface of the deep bottom portion 6b, a vortex is generated due to the step, and the swell increases. It becomes possible to make a mixture. Ignition is performed on the fuel remaining below the spark plug 3 as in the case of a low load, the flame propagates to the deep bottom portion 6b, and the entire fuel is combusted. In this way, good mixture characteristics and combustion can be obtained from low load to high load.
[0027]
5 and 6 show a second embodiment of the present invention. In this embodiment, a projecting portion 6d is added into the concave combustion chamber 6 from the upper surface of the piston 1 on the downstream side of the swirl flow with respect to the spark plug 3, and a concave pocket portion 6e is formed on the wall surface near the deep bottom portion 6b. It is.
[0028]
In general, when the depth of the combustion chamber 6 is not sufficient, there is a problem that unburnt fuel increases due to the occurrence of fuel overflow as shown by the hatched portion in FIG. Therefore, it is conceivable to make the side wall concave to prevent the protrusion, but in a combustion chamber having a certain depth, the protrusion suppression effect cannot be sufficiently exhibited.
[0029]
On the other hand, in the second embodiment, even when the depth of the combustion chamber shallow bottom portion 6b is not large, the position of the deep bottom portion 6c substantially coincides with the protruding position. The fuel trapping action at 6e acts effectively, and the injected fuel can be reliably burned in the combustion chamber 6.
[0030]
8 to 10 show a third embodiment of the present invention. As shown in FIGS. 7 (a)-(b)-(c), this is because the depth d of the bottom surface of the deep bottom portion 6b is from the portion close to the spark plug 3 to the downstream side of the swirl flow. Inclined portions that gradually become larger are formed. In this way, by gradually changing the bottom surface of the deep bottom portion 6b in the vicinity of the spark plug 3, it is possible to prevent the air-fuel ratio of the air-fuel mixture around the spark plug from becoming too thin at a low load and to further improve the ignitability. it can.
[0031]
As shown in each of the above embodiments, by making the cross-sectional shape of the deep bottom portion 6b substantially semicircular, interference with the small end of the connecting rod on the piston structure is avoided. The total height and weight of the piston can be reduced while ensuring.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a first embodiment of an in-cylinder injection engine according to the present invention.
FIG. 2 is a plan view of the piston according to the first embodiment.
3A and 3B are explanatory views showing changes in the piston cross-sectional shape of the first embodiment, wherein FIG. 3A is a cross-sectional view taken along line AA in FIG. 2, and FIG. 3B is a cross-sectional view taken along line BB in FIG. ing.
FIG. 4 is an explanatory diagram showing fuel behavior in the first embodiment.
FIG. 5 is a plan view of a piston according to a second embodiment of the present invention.
6A and 6B are explanatory views showing changes in the piston cross-sectional shape of the second embodiment, wherein FIG. 6A is a cross-sectional view taken along the line AA in FIG. 5, FIG. ) Similarly shows a CC cross section.
FIG. 7 is a plan view of a piston for explaining a fuel overflow phenomenon from a concave combustion chamber.
FIG. 8 is a plan view of a piston according to a third embodiment of the present invention.
9A and 9B are explanatory diagrams showing changes in the piston cross-sectional shape of the third embodiment, wherein FIG. 9A is a cross-sectional view taken along the line AA in FIG. 8, FIG. ) Similarly shows a CC cross section.
10 is a cross-sectional view showing a cross-section along the line AA in FIG. 8;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piston 2 Fuel injection valve 3 Spark plug 4 Cylinder 5 Cylinder head 6 Recessed combustion chamber 6a Bottom bottom part 6b Bottom deep part 6c Side wall part 6d Upper surface protrusion part 6e Pocket part 7 Intake valve 8 Exhaust valve 9 Intake port 10 Intake manifold 11 Intake Control valve F Fuel spray S Swirling flow

Claims (4)

An injection valve that injects fuel into the cylinder, an ignition plug that protrudes from a position close to the wall surface of the concave combustion chamber formed on the upper surface of the piston, and means for generating a swirling flow of intake air in the combustion chamber and the cylinder. In the spark ignition engine provided, the concave combustion chamber has a substantially circular cross-sectional shape of the wall surface, a bottom portion is formed by a shallow bottom portion and a deep bottom portion deeper than the bottom portion, and the deep bottom portion is the spark plug. On the other hand, an in-cylinder fuel injection internal combustion engine characterized in that it is positioned downstream of the swirl flow generated in the concave combustion chamber. A concave pocket portion is formed on the wall surface near the deep bottom while keeping the wall surface substantially circular by projecting the upper surface of the piston in the side wall portion near the deep bottom portion of the concave combustion chamber into the concave combustion chamber. Item 2. The in-cylinder fuel injection internal combustion engine according to Item 1. The inclined portion is formed on the bottom surface of the deep bottom portion so that the depth gradually increases from the portion close to the spark plug toward the downstream side of the swirling flow. An in-cylinder fuel injection internal combustion engine as described in 1. The in-cylinder fuel injection internal combustion engine according to any one of claims 1 to 3, wherein a cross-sectional shape of the deep bottom portion is substantially semicircular.

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