JP2016094925A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize combustion during cold operation, in a direct injection spark ignition type internal combustion engine which generates a normal tumble flow in a combustion chamber.SOLUTION: Grooves 14a, 14b are formed at a front side and a rear side of a top face of a piston 14. A small-capacity recess 14c is formed at the inner side relative to the grooves 14a, 14b. By forming the recess 14c, an air-fuel mixture, which is relatively higher in fuel concentration than the surroundings, can be collected into the recess 14c, and be introduced to an ignition plug 22 by rise of the piston 14, and thus, the ignitability of the air-fuel mixture can be enhanced. Accordingly, combustion can be stabilized during cold operation. Furthermore, in the combustion chamber 18, an intensity of a tumble flow, which is generated by the grooves 14a, 14b, from an exhaust side to an intake side can be increased, which can suppress the attenuation of the tumble flow caused by its collision with fuel, securing a disturbance intensity necessary for combustion after ignition.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an internal combustion engine, and more particularly to a direct injection spark ignition internal combustion engine including an injector that directly injects fuel into a combustion chamber.

  Conventionally, for example, Japanese Patent Application Laid-Open No. 2000-104550 discloses a direct injection spark ignition type internal combustion engine including an injector that directly injects fuel into a combustion chamber. This internal combustion engine has two intake ports and two exhaust ports, and fuel is injected from the injector provided in the vicinity between the openings of the two intake ports toward the center of the top surface of the piston in the latter half of the compression stroke. Is configured to do. In addition, this internal combustion engine is directed toward the top surface of the piston from the exhaust side through the lower side of the spark plug by the intake air flowing into the combustion chamber from the two intake ports during the intake stroke, and is inverted at this top surface. Thus, a positive tumble flow from the intake side toward the spark plug is generated. Further, at the center of the top surface of the piston of the internal combustion engine, there are provided two side wall-shaped standing walls extending from the exhaust side to the intake side. According to the conventional internal combustion engine configured as described above, the fuel from the injector can be atomized by causing a frontal collision with the tumble flow. Further, the two standing walls can suppress the diffusion of the fuel collided with the tumble flow in the front direction (that is, the direction orthogonal to the intake / exhaust direction).

JP 2000-104550 A JP 2009-04-7006 A

  By the way, in lean burn combustion, which contributes to improving the thermal efficiency of an internal combustion engine, the above-described normal tumble flow is used to compensate for the slowing of the combustion speed accompanying the leaning of the concentration of the mixture of fuel and intake air. The flow of the intake air is strengthened to improve the flame propagation speed. On the other hand, during the cold operation immediately after the start of the internal combustion engine, it is desirable to raise the exhaust gas temperature by slowly burning the air-fuel mixture in the expansion stroke in order to warm up the exhaust catalyst early. However, since the ignitability of the air-fuel mixture is low in the expansion stroke during cold operation, it is necessary to concentrate the air-fuel mixture more closely on the spark plug near the ignition timing in order to stabilize the combustion during cold operation. There is. In this regard, in the above-described conventional internal combustion engine, the air-fuel mixture can be guided to the spark plug in the vicinity of the ignition timing, but the fuel concentration in the air-fuel mixture is made uniform by causing the tumble flow and the fuel to collide head-on. Therefore, the ignitability may be reduced during cold operation.

  The present invention has been made in view of the above-described problems. That is, an object of the present invention is to stabilize combustion during cold operation in a direct-injection spark-ignition internal combustion engine that generates a normal tumble flow in the combustion chamber.

The present invention is an internal combustion engine,
A combustion chamber constituted by at least the wall surface of the cylinder bore, the bottom surface of the cylinder head, and the top surface of the piston;
A spark plug that faces the combustion chamber from substantially the center of the bottom surface constituting the combustion chamber;
A first intake port and a second intake port formed on the bottom surface constituting the combustion chamber;
A first exhaust port and a second exhaust port formed in a substantially symmetric place with respect to the first intake port and the second intake port on the bottom surface constituting the combustion chamber, with the installation location of the ignition plug as a center;
An injector for directly injecting fuel into the combustion chamber, from an intake side where the first intake port and the second intake port are formed, to an exhaust side where the first exhaust port and the second exhaust port are formed An injector for injecting fuel toward
The intake air that has flowed into the combustion chamber from the first intake port and the second intake port is directed from the exhaust side to the top surface via the lower side of the spark plug, and reversed from the top surface to be reversed from the intake side. A tumble flow generating means directed toward the spark plug;
A central groove having a substantially U-shaped cross section formed at a location facing the spark plug on the top surface;
A first outer groove portion having a substantially U-shaped cross section formed from the first exhaust port side toward the first intake port side outside the formation position of the central groove portion on the top surface, A first outer groove portion in which an end portion on the intake side of the outer groove portion curves toward an installation location of the injector;
A second outer groove portion having a substantially U-shaped cross section formed from the second exhaust port side toward the second intake port side outside the formation position of the central groove portion on the top surface; A second outer groove portion in which an end portion on the intake side of the outer groove portion curves toward an installation location of the injector;
It is characterized by providing.

  According to the present invention, the air-fuel mixture having a relatively higher fuel concentration than the surroundings can be collected in the central groove and guided to the spark plug as the piston rises, so that the ignitability of the air-fuel mixture can be improved. Therefore, combustion during cold operation can be stabilized. In addition, since the flow strength of the tumble flow generated in the combustion chamber in the direction from the exhaust side to the intake side can be increased by the first outer groove portion and the second outer groove portion, the tumble flow is attenuated by the collision with the fuel. It is also possible to suppress the turbulence intensity necessary for the combustion after ignition. Therefore, it is possible to warm up the exhaust catalyst early by causing the air-fuel mixture to burn slowly during the expansion stroke during the cold operation.

It is a cross-sectional schematic diagram of the combustion chamber of the engine of embodiment of this invention. It is the top view which looked at the combustion chamber 18 of FIG. 1 from the cylinder head 16 side. It is sectional drawing of the hollow 14c of FIG. It is a figure which shows the measurement result of the flow intensity | strength of a tumble flow. It is a figure which shows the piston of the cross-sectional structure for a comparison of this invention. It is a figure which shows the piston of the cross-sectional structure for a comparison of this invention.

  An internal combustion engine according to an embodiment of the present invention is a direct-injection spark ignition engine that is mounted as a drive source for a moving body such as a vehicle. FIG. 1 is a schematic sectional view of a combustion chamber of an engine according to an embodiment of the present invention. As shown in FIG. 1, the cylinder 12 of the engine 10 is provided with a piston 14 that reciprocates within the cylinder 12. A cylinder head 16 is disposed above the cylinder 12. A combustion chamber 18 is defined by at least the bore wall surface of the cylinder 12 (the wall surface of the cylinder bore), the top surface of the piston 14, and the bottom surface of the cylinder head 16.

  The cylinder head 16 is provided with an injector 20 for directly injecting fuel into the combustion chamber 18. The cylinder head 16 is also provided with an ignition plug (ignition plug) 22 for igniting the air-fuel mixture in the combustion chamber 18. Two intake ports 24 and two exhaust ports 26 are formed on the lower surface of the cylinder head 16. The combustion chamber 18 communicates with the intake passage 28 via the intake port 24 and communicates with the exhaust passage 30 via the exhaust port 26. In the intake port 24, the direction indicated as “tumble direction” in FIG. 1, that is, the lower side of the spark plug 22, the exhaust side is directed to the top surface of the piston 14, and the top surface is reversed. An airflow control valve (not shown) for generating a positive tumble flow from the intake side toward the ignition plug 22 is provided.

FIG. 2 is a plan view of the combustion chamber 18 of FIG. 1 viewed from the cylinder head 16 side. Note that “front side” shown in FIG. 2 means the front side of the moving body on which the engine 10 is mounted, and “rear side” means the rear side of the moving body. As shown in FIG. 2, grooves 14 a and 14 b are formed on the front side and the rear side of the top surface of the piston 14. The grooves 14a and 14b have a substantially U-shaped cross section. Center line C _14a of the groove 14a extends toward the intake port 24a from the exhaust port 26a at the exhaust side and central portion, at the end of the intake side is curved toward the injection hole side of the injector 20. Centerline C _14b of the groove 14b extends toward the exhaust port 26b to the intake port 24b in the exhaust side and central portion is curved toward the injection hole side of the injector 20 at the intake side.

  A small volume recess 14c is formed inside the grooves 14a and 14b. The recess 14 c is formed at the center of the top surface of the piston 14. The reason why it is formed in the central portion of the top surface of the piston 14 is to avoid the interference with the grooves 14a and 14b and to suppress the dispersion of the air-fuel mixture retained in the recess 14c. The recess 14c is formed so that the width in the front-rear direction is narrower than the width in the intake-exhaust direction. The reason for this is to suppress the intrusion of the tumble flow into the recess 14c. The width of the recess 14c in the front-rear direction is about the plug diameter of the spark plug 22. Moreover, as shown in FIG. 3, the cross section of the dent 14c is substantially U-shaped, and the surface of the dent 14c is processed so as not to provide a sharp bend to prevent separation and attenuation of the tumble flow.

  As described above, in lean burn combustion, the flow of the intake air in the cylinder is strengthened using a positive tumble flow in order to compensate for the slowing of the combustion speed accompanying the lean concentration of the mixture, thereby improving the flame propagation speed. ing. Further, during cold operation immediately after the start of the engine that performs lean burn combustion, it is desirable to raise the exhaust gas temperature by slowly burning the air-fuel mixture in the expansion stroke in order to warm up the exhaust catalyst early.

  Although the fuel injected from the injector 20 in the compression stroke is directed to the exhaust side, the penetration force is weakened by the collision with the opposing tumble flow, so that the progress of the fuel to the exhaust side is suppressed to some extent. Therefore, by appropriately setting the injection timing of the injector 20, it is possible to secure a mixture concentration that can be ignited even in the expansion stroke in the vicinity of the spark plug 22 near the top dead center of the piston 14. However, since the tumble flow is attenuated by the collision with the fuel, the flow intensity in the direction from the exhaust side to the intake side is reduced, and the turbulence intensity required for the combustion after ignition is likely to be reduced. Further, the air-fuel mixture is also dispersed by the tumble flow, and the stratification degree at the time of ignition tends to be low. Therefore, in order to stabilize the combustion during the cold operation, it is necessary to secure a certain degree of stratification during ignition while suppressing the attenuation of the tumble flow.

  In this regard, according to the top surface structure of the piston 14 shown in FIG. 2, the air-fuel mixture having a higher fuel concentration than the surroundings can be collected in the recess 14 c and guided to the spark plug 22 as the piston 14 rises. As a result, the ignitability of the air-fuel mixture can be improved. Therefore, combustion during cold operation can be stabilized. Further, since the flow strength of the tumble flow generated in the combustion chamber 18 from the exhaust side to the intake side can be increased by the grooves 14a and 14b, the attenuation of the tumble flow due to the collision with the fuel is suppressed, and the ignition is performed. The turbulence intensity required for subsequent combustion can also be ensured. Therefore, it is possible to warm up the exhaust catalyst early by causing the air-fuel mixture to burn slowly during the expansion stroke during the cold operation.

  FIG. 4 is a diagram showing measurement results of the flow strength (tumble strength) of the tumble flow. The “present invention” shown in FIG. 4 shows the flow strength when the piston 14 having the top structure shown in FIG. 2 is used. Further, “shape with cavity” and “normal shape” shown in the same figure show flow strengths when the pistons having the comparative sectional structure shown in FIGS. 5 and 6 are used, respectively. The data shown in FIG. 4 is the flow intensity of the tumble flow at 90 ° before the bottom dead center measured by PIV (Particle Image Velocimetry). It can be seen from FIG. 4 that by using the piston 14 having the top structure shown in FIG. 2, the flow strength equivalent to the normal shape, that is, the smooth shape having no protrusions can be secured. Therefore, according to the present invention, attenuation of the tumble flow due to the collision with the fuel can be suppressed.

  In the above embodiment, the intake ports 24a and 24b are the "first intake port" and "second intake port" of the present invention, and the exhaust ports 26a and 26b are the "first exhaust port" and " In the “second exhaust port”, the airflow control valve is in the “tumble flow generating means” of the present invention, the recess 14 c is in the “central groove portion” of the present invention, and the grooves 14 a and 14 b are “first exterior portion” of the present invention and It corresponds to “second exterior part”, respectively.

DESCRIPTION OF SYMBOLS 10 Engine 12 Cylinder 14 Piston 14a, 14b Groove 14c Depression 16 Cylinder head 18 Combustion chamber 22 Spark plug 24 Intake port 26 Exhaust port

Claims (1)

A combustion chamber constituted by at least the wall surface of the cylinder bore, the bottom surface of the cylinder head, and the top surface of the piston;
A spark plug that faces the combustion chamber from substantially the center of the bottom surface constituting the combustion chamber;
A first intake port and a second intake port formed on the bottom surface constituting the combustion chamber;
A first exhaust port and a second exhaust port formed in a substantially symmetric place with respect to the first intake port and the second intake port on the bottom surface constituting the combustion chamber, with the installation location of the ignition plug as a center;
An injector for directly injecting fuel into the combustion chamber, from an intake side where the first intake port and the second intake port are formed, to an exhaust side where the first exhaust port and the second exhaust port are formed An injector for injecting fuel toward
The intake air that has flowed into the combustion chamber from the first intake port and the second intake port is directed from the exhaust side to the top surface via the lower side of the spark plug, and reversed from the top surface to be reversed from the intake side. A tumble flow generating means directed toward the spark plug;
A central groove having a substantially U-shaped cross section formed at a location facing the spark plug on the top surface;
A first outer groove portion having a substantially U-shaped cross section formed from the first exhaust port side toward the first intake port side outside the formation position of the central groove portion on the top surface, A first outer groove portion in which an end portion on the intake side of the outer groove portion curves toward an installation location of the injector;
A second outer groove portion having a substantially U-shaped cross section formed from the second exhaust port side toward the second intake port side outside the formation position of the central groove portion on the top surface; A second outer groove portion in which an end portion on the intake side of the outer groove portion curves toward an installation location of the injector;
An internal combustion engine comprising:

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