JPH05214940A - Direct injection spark ignition engine - Google Patents

Abstract

PURPOSE:To improve the combustion chamber shape of a direct-injection type spark ignition engine for allowing lean combustion. CONSTITUTION:Two intake valves 9 and two exhaust valves 10 are provided face to face across an ignition plug 8 on a combustion chamber ceiling wall 11, and a fuel injection valve 3 is provided on the side of the intake valves 9. An inclined face 22 reflecting and diffusing fuel sprays toward the exhaust valves 10 is formed on a piston top face 21, and a squish area 12 generating the gas facing the diffused fuel is formed on the side of the exhaust valves 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a direct injection spark ignition engine.

[0002]

2. Description of the Related Art A premixed spark ignition engine equipped with a carburetor and a fuel injection valve in its intake pipe has a problem of delay in fuel transportation, especially during transient operation. A direct injection spark ignition engine in which a fuel injection valve faces a combustion chamber has been considered.

As this direct injection type spark ignition engine, the one disclosed in Japanese Patent Laid-Open No. 57-62915 has been disclosed.
Fuel was injected into the combustion chamber during the intake stroke, and an intake swirl was generated in the combustion chamber to promote the mixing of fuel and air.

The uniform mixing of fuel and air contributes to stable combustion, but in the case of combustion with an ultra-lean mixture, smooth ignition by a spark plug becomes very difficult with such a uniform mixing method. In order to stabilize the ignition performance, stratification of the air-fuel mixture that enriches the air-fuel ratio in the vicinity of the spark plug is effective, but in an engine in which fuel and air are mixed from the intake stroke like this, in the vicinity of the spark plug. It is difficult to collect the fuel in the first place, and there is a problem that stable ignition performance cannot be obtained when performing ultra-lean combustion with a mixture much thinner than the theoretical air-fuel ratio.

In view of the above problems, the present invention aims to improve the shape of the combustion chamber of a direct injection spark ignition engine in order to enable lean combustion.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a direct injection type spark ignition engine in which a combustion chamber faces an ignition plug and a fuel injection valve, and an intake valve and an exhaust valve are opposed to each other with the ignition plug interposed between the ceiling walls of the combustion chamber. The fuel injection valve is provided on the side of the intake valve, and an inclined surface for reflecting and diffusing the fuel spray injected from the fuel injection valve toward the exhaust valve is formed on the piston top surface, and the exhaust gas is also provided. A squish area that causes a gas flow facing the diffusion fuel is formed on the side of the valve, and the fuel injection timing of the fuel injection valve is set during the compression stroke.

Further, a swirl control valve for opening and closing the intake port according to the operating condition is provided, and a sub-port is formed which bypasses the swirl control valve and guides intake air just before one intake valve.

[0008]

The fuel spray injected during the compression stroke hits the inclined surface and diffuses toward each exhaust valve. As a result, the fuel spray hits the top surface of the piston and the exhaust valve, which become relatively hot, and promotes atomization and vaporization of the fuel spray.

A squish occurs from the side of the exhaust valve near the top dead center of the piston, and the squish transports a large amount of fuel distributed in the vicinity of the exhaust valve to the vicinity of the spark plug, and a large amount of fuel near the spark plug. Realizes stratification of the distributed air-fuel mixture. Since the fuel injection is in the compression stroke, the stratified state of this air-fuel mixture is maintained even at the time of ignition, which ensures stable ignition performance even when the air-fuel mixture is diluted, and reduces fuel consumption and emissions. Higher output can be achieved.

In the region far from the spark plug of the combustion chamber, the air-fuel ratio becomes extremely lean, and the self-ignition reaction leading to knocking is suppressed, and as a result, the compression ratio is increased, and the thermal efficiency and output are improved.

Further, during partial load operation, etc., each intake port is closed by the swirl control valve, and a strong swirl is generated in the combustion chamber by the intake air flow introduced from the auxiliary port, so that the flame propagation speed is further increased. It is possible to realize stable lean combustion.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a direct injection type spark ignition type 4-stroke engine will be described below with reference to the accompanying drawings.

As shown in FIGS. 1 and 2, the combustion chamber ceiling wall 11 of the cylinder head 1 is inclined in a pent roof type, and an ignition plug 8 faces the center thereof, and the ignition plug 8 is sandwiched therebetween.
Two intake valves 9 and two exhaust valves 10 are provided so as to face each other.

As a means for generating swirl in the combustion chamber 5, a swirl control valve 7 for opening and closing both intake ports 13 branched in a siamese shape is provided, and the swirl control valve 7 is bypassed at the bottom of one intake port 13. An auxiliary port 15 for guiding intake air is provided.

The intake port 15a of the sub port 15 is opened immediately upstream of the swirl control valve 7 at the fully closed position, and the blow port 15b of the sub port 12 is opened immediately upstream of the valve seat 6. Swirl control valve 7
When the valve is fully closed, most of the intake air is sucked into the combustion chamber 5 through the auxiliary port 15 through one intake valve 9 at a low inflow angle, and is introduced at a high speed from the auxiliary port 15 having a small cross-sectional area. As indicated by arrow S in FIG. 2, a strong swirl is generated in the combustion chamber 5.

The swirl control valve 7 is rotated about a shaft 19 by a drive device (not shown) so as to be fully closed during partial load operation and fully open during high load operation.

A fuel injection valve 3 is provided on the combustion chamber ceiling wall 11 beside the intake valve 9 and in this embodiment between the intake valves 9. The fuel injection timing should be as close as possible to the ignition timing during the compression stroke (for example, 30 degrees before top dead center).
And the fuel injection direction is directed slightly obliquely downward from the horizontal, so that the fuel spray hits the center of the piston 4 at a predetermined stroke position near the compression top dead center.

As shown in FIG. 3, the top surface 2 of the piston 4 is
A diffusion table 20 is formed at a substantially central position of 1 and an inclined surface 22 facing the fuel spray from the fuel injection valve 3 is formed on the diffusion table 20. The inclination angle of the inclined surface 22 is determined by a predetermined angle with respect to the direction of fuel spray from the fuel injection valve 3, and the fuel spray reflected on the inclined surface 22 is indicated by a two-dot chain line in FIGS. 10 head portion 10a.

On the combustion chamber ceiling wall 11, a squish area 12 is provided on the side of both exhaust valves 10,
A squish area 24 is formed on the top surface 21 of the piston 4 laterally of the diffusion table 20. Both of them are formed in parallel with each other, and generate a squish (gas flow) facing the center of the combustion chamber 5 near the top dead center of the piston 4, in other words, facing the fuel spray.

The diffusion table 20 is raised from the top surface 21 of the piston 4 in a triangular pyramid shape, and behind the inclined surface 22, a pair of inclined surfaces 23 facing the squish areas 12 and 24 is formed.
The inclination angle and the inclination direction of each inclined surface 23 are determined so that the squish is reflected by each inclined surface 23 and guided to the vicinity of the spark plug 8.

Next, the operation will be described.

FIG. 4A shows a state in which the piston 4 has reached the crank angle of 90 ° before the compression top dead center.
Fuel injection has not yet been performed here.

In FIG. 4, FIG. 4b shows a state in which the piston 4 has reached 30 ° before the compression top dead center, where fuel injection is performed. Most of the fuel sprayed from the fuel injection valve 3 is reflected by the inclined surface 22 and guided to the head portion 10a of each exhaust valve 10. By colliding the fuel spray with the diffusion table 20 and the exhaust valve 10 having a relatively high temperature, or by diffusing the fuel spray in the vicinity thereof, atomization and vaporization of the fuel spray are promoted. On the other hand, this fuel spray cools the piston 4 and the exhaust valve 10, which have a high thermal load.

On the other hand, as shown by the white arrow in FIG. B, as the piston 4 rises, a squish toward the center of the combustion chamber 5 is generated, and this squish is reflected and diverted to each inclined surface 23 of the diffusion table 20. By moving toward the spark plug 8, a large amount of fuel distributed in the vicinity of each exhaust valve 10 is pushed back to the vicinity of the spark plug 8 in the center of the combustion chamber.

In FIG. 4, FIG. 4c shows a state in which the piston 4 has reached the compression top dead center, in which most of the fuel is collected in the vicinity of the spark plug 8 and the mixture in the vicinity of the spark plug 8 is stratified. Turn into. The rich mixture layer formed in the vicinity of the spark plug 8 is injected into the combustion chamber ceiling wall 11 by the piston 4 rising in the compression stroke of fuel injection and the subsequent stroke until ignition. The air-fuel mixture layer does not diffuse, a good ignition atmosphere is generated and maintained in the vicinity of the spark plug 8, and the ignition is surely ignited to generate an initial flame kernel.

During the partial load operation, the swirl control valve 7 is closed, and the intake air introduced from one intake valve 9 through the auxiliary port 15 in the intake stroke forms a strong swirl (swirl flow) along the inner circumference of the cylinder. Since the flame propagation speed is increased by the swirl, stable lean combustion is realized, fuel consumption is reduced, emissions are reduced, and high output is achieved.

During high load operation in which the swirl control valve 7 is opened, intake air is evenly introduced from each intake port 13 and swirl does not occur in the combustion chamber 5, but the fuel injection amount increases, so sufficient ignition performance is obtained. And reliable flame propagation is maintained.

Further, due to the stratification of the air-fuel mixture, the air-fuel ratio becomes relatively large in the region far from the spark plug 8 of the combustion chamber 5, that is, the air-fuel ratio becomes extremely lean, which leads to knocking which tends to occur at the end of the combustion chamber. The self-ignition reaction is less likely to occur, so that the compression ratio can be substantially increased, and thermal efficiency and output can be improved.

[0029]

As described above, according to the present invention, in a direct injection spark ignition engine, an intake valve and an exhaust valve are provided to face each other with a spark plug sandwiched in a ceiling wall of a combustion chamber, and a fuel is provided on a side of the intake valve. Since the injection valve is faced, a sloped surface for reflecting and diffusing the fuel spray in the direction of the exhaust valve is formed on the top surface of the piston, and a squish area for causing gas flow facing the diffusion fuel is formed on the side of the exhaust valve. It is possible to collect fuel near the spark plug immediately before ignition, secure stable ignitability by stratification even with a lean mixture, and improve fuel economy and exhaust emission based on lean combustion.

Further, by generating a swirl at the time of partial load, the flame propagation speed can be increased, and the stability of lean burn can be further improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention.

FIG. 2 is a plan view of a combustion chamber ceiling wall.

FIG. 3 is a plan view of the same piston.

FIG. 4 is a diagram showing the flow of fuel and gas.

[Explanation of symbols]

 3 Fuel injection valve 4 Piston 5 Combustion chamber 7 Swirl control valve 8 Spark plug 9 Intake valve 10 Exhaust valve 11 Combustion chamber ceiling wall 12 Squish area 13 Intake port 15 Sub-port 20 Diffusion table 22 Slope 23 Slope 24 Squish area

Claims (2)

[Claims] 1. In a direct injection spark ignition engine in which a spark plug and a fuel injection valve face a combustion chamber, an intake valve and an exhaust valve are provided to face each other with a spark plug sandwiched on a ceiling wall of the combustion chamber. A fuel injection valve is faced to the side, and an inclined surface for reflecting and diffusing the fuel spray injected from the fuel injection valve toward the exhaust valve is formed on the top surface of the piston, and the diffusion fuel is provided to the side of the exhaust valve. A direct-injection spark ignition engine, characterized in that a squish area that causes a gas flow that opposes is formed, and the fuel injection timing of the fuel injection valve is set during the compression stroke. 2. A swirl control valve for opening and closing an intake port according to operating conditions is provided, and a sub-port that bypasses the swirl control valve and guides intake air immediately before one intake valve is formed. 1. A direct injection spark ignition engine according to 1.