JPH10339140A - Cylinder direct injection internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize combustion of layered and mixed gas, and improve combustion of homogeneously mixed gas. SOLUTION: A fuel injection valve 6 to directly inject fuel to a combustion chamber 4 is provided, fuel is injected in a compression process at least in a partial load range, and in a suction process in a high load range, and combustion is started by a spark plug 5. A cavity 15 is provided in a crown surface of a piston 1, and the fuel injection valve 6 disposed at a peripheral part of the combustion chamber 4 is set to face the spark plug 5 disposed around a center of the combustion chamber having the cavity 15 between them. A bottom surface 15a of the cavity 15 is formed as a flat surface roughly parallel to a combustion chamber wall surface facing it, and the bottom surface 15a is inclined to be deeper on the fuel injection valve side and shallower on the spark plug side. Fuel from the fuel injection valve 6 is partly reflected at the bottom surface 15a, while it is injected toward the ignition plug 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an internal combustion engine that injects fuel directly into a cylinder.

[0002]

2. Description of the Related Art A fuel injection valve is provided in a combustion chamber of an internal combustion engine,
Injecting fuel directly into the combustion chamber during the engine compression stroke,
An in-cylinder direct injection type internal combustion engine, which can realize stable combustion even with an ultra-lean mixture as a whole by forming a combustible mixture layer around the ignition plug at the time of ignition, It is proposed in Japanese Unexamined Patent Publication No. 8-35429.

[0003] As shown in FIGS. 4 and 5, a fuel injection valve 6 provided in a cylinder head 2 is provided in a combustion chamber 4 formed between a piston 1, a cylinder head 2 and a cylinder block 3. The fuel is directly injected, and the air-fuel mixture is ignited by the spark plug 5 and burned. In this case, in an operation region where the engine load is relatively small, the fuel injection timing is set in the latter half of the compression stroke. It prevents diffusion of the injected fuel, forms a combustible mixture layer near the ignition plug 5, enables stable stratified combustion even with an ultra-lean mixture as a whole, and in an operation region where the engine load is large. The fuel is injected in the intake stroke to promote the mixing with air in advance, so that the air-fuel mixture in the vicinity of the stoichiometric air-fuel ratio as a whole is surely burned, and high output is secured.

To stabilize stratified combustion, it is necessary to stably form a combustible mixture layer near the ignition plug. For this purpose, a cavity 21 is provided on the top surface of the piston 1, and The fuel injected toward the ignition plug 5 is guided toward the spark plug 5, and a swirl control valve 12 is provided in one of the pair of intake ports 10. Creates a swirl inside.

[0005] As a result, when the ignition plug 5 is ignited, combustion starts from the combustible air-fuel mixture layer in the vicinity, and the flame propagates on the swirl to the surrounding lean air-fuel mixture layer containing less fuel components. Even a lean air-fuel mixture is stably burned, reducing pumping loss and heat loss in a low load range, improving fuel efficiency and reducing CO ₂ emissions.

In the region where the engine load is large, the fuel injection valve 6
By setting the injection timing to the intake stroke, the injected fuel is sufficiently diffused before ignition, and the mixing of air is promoted by the vertical gas flow accompanying the rise of the piston. To ensure combustion. In this case, the swirl control valve 12 is fully opened in order to increase the intake efficiency.

[0007]

However, in this case,
Even in the low-load region where stratified mixture combustion is performed, in order to form a combustible mixture layer near the ignition plug in a region where the fuel injection amount is small, the depth of the cavity should be made shallow, and the ignition plug should be sufficiently close to the ignition plug during ignition. It is necessary to make the fuel spray easily accessible.

On the other hand, in the region where the fuel injection amount is large even in the case of stratified mixture combustion, the concentrated fuel spray becomes partially concentrated in the shallow cavity, thereby increasing the smoke or the ignitability. It worsens, and there is also a problem of contamination of the spark plug. If the injected fuel overflows from the shallower cavity, the combustion becomes slower, and there is a possibility that the amount of HC increases and the fuel efficiency deteriorates. Therefore, in this region, a mixture of moderate concentration is collected near the spark plug, and the fuel spray is contained in the cavity.
It is desirable to have a relatively deep cavity.

On the other hand, in the region where the engine load is large and the homogeneous mixture is burned near the stoichiometric air-fuel ratio, it is necessary to promote the diffusion of the injected fuel and to sufficiently mix the fuel and air before the ignition. The cavity hinders the tumble flow, which is a vertical vortex generated in the combustion chamber during the compression rising stroke of the piston, and does not promote the diffusion of fuel, leading to an increase in smoke and a decrease in output and fuel consumption.

Therefore, an object of the present invention is to improve the shape of the cavity and to solve these problems.

[0011]

According to a first aspect of the present invention, a combustion injection valve for directly injecting fuel into a combustion chamber is provided, and fuel is supplied at least during a compression stroke at a partial load range and at an intake stroke at a high load range. In an in-cylinder direct injection internal combustion engine in which the fuel is injected and ignited by an ignition plug, a cavity is provided on the top surface of a piston, and a fuel injection valve disposed around the combustion chamber is provided near the center of the combustion chamber with the cavity interposed therebetween. The bottom surface of the cavity is formed in a plane substantially parallel to the cylinder head side combustion chamber wall surface facing the ignition plug disposed in
And the bottom is inclined so that it is deep on the fuel injection valve side and shallow on the spark plug side.

According to a second aspect of the present invention, the inner peripheral surface of the cavity is formed to be substantially circular and substantially parallel to the piston axis.

According to a third aspect of the present invention, the wall of the combustion chamber on the cylinder head side is formed in a pent roof type, and the top surface of the piston is formed on an inclined surface substantially parallel to the pent roof surface.
The cavity was formed on one of the slopes facing the pent roof surface on which the intake valve was disposed.

According to a fourth aspect of the present invention, the ignition plug is disposed substantially at the center of the combustion chamber, the fuel injection valve is disposed at a cylinder head around the combustion chamber, and the fuel injection valve is opposed to the ignition plug with the cavity interposed therebetween. At the same time, the fuel spray was disposed obliquely toward the bottom surface of the cavity, and was formed so that a part of the fuel spray was reflected toward the bottom surface of the cavity toward the spark plug.

According to a fifth aspect of the present invention, the bottom surface of the cavity is gently curved so as to be convex toward the combustion chamber wall surface.

According to a sixth aspect of the present invention, the intake ports are formed in a pair of parallel straight ports, and a swirl control valve is interposed in one of the intake ports.

[0017]

According to the first aspect of the present invention, in the operation region where the load of the engine in which the stratified mixture combustion is performed is small,
Even when the fuel injection amount is small, the fuel spray from the fuel injection valve is sufficiently concentrated near the spark plug because the bottom of the cavity is flat and shallow on the spark plug side, and stable ignition performance is achieved. Secured. In addition, even though the depth of the cavity is shallow on the spark plug side, it is deep on the fuel injection valve side, so the cavity effective volume is larger than that of the entire shallower one, and therefore the fuel injection amount has increased. Even when the fuel spray does not escape outside the cavity,
It fits in the cavity, preventing deterioration of HC and fuel economy.

Further, in an operating region where the load of the engine in which the homogeneous mixture combustion is performed is large, the fuel spray injected in the intake stroke is stirred and mixed by the tumble flow generated as the piston descends and rises. However, the cavity is shallow on the side of the spark plug, and the tumble flow is hardly hindered, so that the diffusion of fuel is promoted, and a uniform gas mixture layer is formed at the time of ignition, so that uniform and rapid combustion can be realized.

In the second invention, since the inner periphery of the cavity is circular without irregularities, even if the air-fuel mixture is pushed into the cavity near the top dead center, the adhesion of fuel to the inner peripheral wall surface is small, and smoke and HC generation can be reduced.

According to the third aspect of the present invention, the gap between the pent roof surface on the cylinder head side and the piston top surface can be reduced near the piston top dead center, and the air-fuel mixture can be sufficiently sealed in the cavity, and the flame can be smoothly propagated. As a result, the combustion efficiency can be improved, and the fuel consumption and HC can be reduced.

According to the fourth aspect of the invention, during the stratified mixture combustion, the fuel spray injected from the fuel injection valve in the peripheral portion of the combustion chamber is reflected on the bottom surface of the cavity and heads toward the ignition plug at the center of the combustion chamber. It is easy to concentrate the combustible gas mixture layer on
In addition, since the combustion is started near the center of the combustion chamber, the flame is efficiently propagated, and the rapid combustion allows the fuel efficiency and H
C can be improved.

In the fifth invention, the bottom surface of the cavity is gently curved so as to be convex toward the combustion chamber wall surface side, so that the inner surface of the piston can be made closer to the top dead center side in the axial direction of the piston. The compression height of the piston can be shortened while avoiding interference with the small end of the connecting rod, and the weight and size of the piston can be reduced.

In the sixth aspect of the present invention, the intake port is formed in a pair of parallel straight ports, and the swirl control valve is interposed in one of the intake ports. Efficiency is increased, and high output can be achieved.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described with reference to the drawings.

1 and 2, 1 is a piston, 2 is a cylinder head, 3 is a cylinder block, 4 is a combustion chamber defined by them, 8 is an intake valve, 9 is an exhaust valve, 10
Denotes an intake port and 11 denotes an exhaust port.

On the top surface of the piston 1, there are inclined surfaces 1a, 1b opposed to the combustion chamber wall surfaces 2a, 2b of the pent roof type cylinder head 2 and inclined in the left-right direction so as to be substantially parallel thereto. The formed skirt 1c forms a horizontal plane perpendicular to the axis of the piston 1. A cavity 15 is formed on one of the slopes 1a facing the pent roof type combustion chamber wall surface 2a on which the intake valve 8 is disposed.

The cavity 15 is formed by a rotating body having a substantially constant depth with respect to the slope 1a. In other words, the cavity 15 is arranged substantially at the center of the slope 1a, but a part of the cavity 15 reaches the opposite slope 1b beyond the ridge line 1d of the piston top surface, and a part opposite to this reaches the skirt 1c. Formed. The cavity 15 has a bottom surface 15a.
Has a flat surface, and its inner peripheral surface 15b is formed as a vertical surface substantially parallel to the axis of the piston, and the bottom surface 15a and the inner peripheral surface 15b are connected by an arc surface 15c.

The tip end of the fuel injection valve 6 is located at a position where the cavity 15 extends over the skirt portion 1c, and a spark plug 5 is provided at a position located along the ridge line 1d, in other words, substantially at the center of the combustion chamber 4. The bottom surface 15a of the cavity 15 is the slope 1
Since the depth is substantially constant with respect to the piston a, the bottom surface 15a is inclined with respect to the piston axis, and when viewed from a plane orthogonal to the piston axis, the side of the fuel injection valve 6 is the deepest, and the ignition plug 5
Side is the shallowest.

The fuel injection valve 6 is provided to be inclined with respect to the piston axis, and the ignition plug 5 is arranged substantially coaxially, so that the fuel spray from the fuel injection valve 6 can be spread while spreading. A part of the light is reflected by the bottom surface 15a and is guided to the ignition plug 5 as a whole.

The pair of intake ports 10 are formed on both sides of the fuel injection valve 6 in parallel with each other, and are formed as straight ports having a substantially constant inflow angle with respect to the combustion chamber 4. A swirl control valve 12 is provided in one intake port 10, and by closing this swirl control valve 12, intake air is introduced only from the other intake port 10 and swirl is generated inside the combustion chamber 4.

The intake valve 8 and the exhaust valve 9 are provided in pairs.

The small end 7 of the connecting rod is connected to the piston 1 from the inner surface side of the piston, and the small end 7 of the connecting rod is brought as close as possible without interfering with the inner surface of the top surface of the piston.

The configuration is as described above. Next, the operation will be described.

First, in the operating region where the engine load is a partial load and stratified mixture combustion is performed, the swirl control valve 12 of the intake port 10 is closed, and intake swirl is formed in the cylinder during the intake stroke.

Fuel is injected from the fuel injection valve 6 in the latter half of the compression stroke. At the time of fuel injection, the piston 1 rises, and the fuel spray injected from the fuel injection valve 6 toward the cavity 15 of the piston 1
The light is reflected toward the ignition plug 5 at the center of the combustion chamber.

Since the fuel injection timing is in the latter half of the compression stroke,
The time until the piston 1 reaches the compression top dead center is short, the fuel spray does not spread evenly in the combustion chamber, and a rich mixture layer in the flammable range is formed and maintained near the ignition plug 5 at the time of ignition. .

The flammable mixture layer is ignited by the ignition action of the ignition plug 5, and the combustion is propagated to the surrounding lean mixture layer by swirling the gas flow around this portion. Therefore, the overall air-fuel ratio is, for example, A / F = 40 to
Even with a super-lean mixture such as 50, combustion is stably performed.

In this case, in the stratified mixture combustion, in a region where the engine load is relatively small and the fuel injection amount is relatively small, the fuel spray is concentrated in the vicinity of the ignition plug 5 and the combustible mixture However, since the bottom surface 15a of the cavity 15 is flat and inclined so as to be the shallowest on the side of the ignition plug 5, the fuel spray sprays forward and the bottom surface 15a of the cavity 15
As a result, the fuel is forcibly guided in the direction of the ignition plug 5, and even with a small amount of fuel, the fuel is efficiently concentrated near the ignition plug 5. As a result, a combustible mixture layer is reliably formed around the ignition plug 5, and stable ignition performance can be maintained.

On the other hand, in the region where the engine load is relatively large in the stratified mixture combustion, the fuel injection amount increases, and if the depth to the bottom surface 15a of the cavity 15 is small, the ignition plug 5 The mixture layer formed in the vicinity of the fuel cell becomes excessively thick, which causes an increase in smoke and fouling of the spark plug 5, and also does not allow all of the fuel spray to be contained in the cavity. And fuel economy is likely to increase.

However, although the cavity 15 becomes shallow on the side where the spark plug 5 is located, it is sufficiently deep on the side where the fuel injection valve 6 is located to secure a necessary combustion chamber volume.
The gap between the combustion chamber wall surfaces 2a, 2b on the cylinder head side and the piston top surface can be reduced, so that the fuel spray spreads over the ridgeline 1d of the piston top surface and diffuses around.
It easily advances along the inner periphery of the cavity 15 to the deep side of the bottom surface 15a, preventing excessive concentration of fuel near the ignition plug 5 and dispersing an air-fuel mixture including fuel spray into the cavity 15.
More enclosed inside.

Thus, the combustion flame ignited by the ignition plug 5 quickly propagates into the cavity, and realizes a stable lean mixture combustion without increasing smoke.
C and fuel economy can be maintained satisfactorily.

Since the inner periphery of the cavity 15 is circular without irregularities, even if the air-fuel mixture is pushed into the cavity near the top dead center, the adhesion of the fuel on the inner peripheral wall surface is small and the swirl sustainability is high. Good generation of smoke and HC can be reduced.

On the other hand, in the homogeneous mixture combustion operation region where the engine load is large, the fuel injection from the fuel injection valve 6 is advanced to the intake stroke, and the swirl control valve 12 of the intake port 10 is fully opened. The fuel spray is sufficiently agitated with the intake air as the piston 1 descends during the intake stroke and rises during the compression stroke.
A tumble flow, which is a longitudinal vortex in the axial direction of the piston, is generated in the combustion chamber 4 with the movement of the tumble flow. As the depth to the bottom surface of the cavity 15 increases, the tumble flow becomes stronger near the spark plug. Is difficult to maintain, and the gas flow at the time of ignition is easily attenuated. However, since the bottom surface 15a of the cavity 15 is inclined and becomes shallow near the center where the spark plug 15 is located, the tumble flow is not hindered. The injected fuel diffuses well by ignition and mixes uniformly.

As a result, the homogeneous mixture combustion with the mixture near the stoichiometric air-fuel ratio is performed very smoothly and quickly.
An increase in smoke can be suppressed, and good output and fuel economy characteristics can be maintained.

The intake port 10 is formed as a straight port, so that the flow of intake air into the cylinder is smooth even in the engine fully open operation range, the intake efficiency is increased, and a high output can be achieved.

Next, another embodiment shown in FIG. 3 will be described.

This is because the bottom surface 15a of the cavity 15 is curved toward the combustion chamber side so as to have a gentle convex surface, and the inner wall surface 1e of the top surface of the piston 1 is also curved upward by that amount. End 7 is attached to inner wall 1 of piston 1
e is moved upward as far as possible without interfering with e.

As a result, the compression height of the piston 1 can be shortened, which leads to a reduction in the weight of the piston 1, which contributes to increasing the allowable rotation speed of the engine and reducing friction loss, and the maximum output of the engine. And fuel efficiency can be improved.

[Brief description of the drawings]

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

FIG. 2 is a plan view mainly showing a piston top surface.

FIG. 3 is a longitudinal sectional view showing another embodiment.

FIG. 4 is a longitudinal sectional view of a conventional example.

FIG. 5 is a plan view of the same.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piston 1a Slope 1b Slope 1d Ridge 2 Cylinder head 3 Cylinder block 4 Combustion chamber 5 Spark plug 6 Fuel injection valve 8 Intake valve 9 Exhaust valve 15 Cavity 15a Bottom surface 15b Inner peripheral surface

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 69/04 F02M 69/04 P

Claims (6)

[Claims] A combustion injection valve for injecting fuel directly into a combustion chamber is provided, and in a compression stroke at least in a partial load range,
In a high-load region, fuel is injected during the intake stroke, and a direct injection internal combustion engine is designed to ignite and burn with a spark plug.A cavity is provided on the top surface of the piston, and a fuel injection valve arranged around the combustion chamber is provided. Facing the spark plug arranged near the center of the combustion chamber with the cavity interposed therebetween, the bottom surface of the cavity is formed in a plane substantially parallel to the opposed cylinder head side combustion chamber wall surface, and the bottom surface is deep on the fuel injection valve side, An in-cylinder direct injection internal combustion engine characterized by being inclined so as to be shallow on the side of the spark plug. 2. An in-cylinder direct injection internal combustion engine according to claim 1, wherein an inner peripheral surface of said cavity is substantially circular and formed substantially parallel to a piston axis. 3. A pent roof in which a combustion chamber wall surface on a cylinder head side is formed in a pent roof type, and a top surface of a piston is formed on a slope substantially parallel to the pent roof face, and an intake valve is disposed on the slope. 3. The direct injection internal combustion engine according to claim 1, wherein the cavity is formed on one slope facing the surface. 4. The ignition plug is disposed substantially at the center of the combustion chamber, the fuel injection valve is disposed in a cylinder head around the combustion chamber, and the fuel injection valve faces the ignition plug with the cavity interposed therebetween. Placed diagonally toward
The direct injection internal combustion engine according to any one of claims 1 to 3, wherein a part of the fuel spray is formed so as to reflect toward the ignition plug while being reflected on the bottom surface of the cavity. 5. The direct injection internal combustion engine according to claim 1, wherein the bottom surface of the cavity is gently curved so as to be convex toward the combustion chamber wall surface side. 6. An in-cylinder direct injection internal combustion engine according to claim 1, wherein the intake port is formed as a pair of parallel straight ports, and a swirl control valve is interposed in one of the intake ports. organ.