JP3365257B2 - In-cylinder direct injection spark ignition engine - Google Patents

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 combustion chamber in a direct injection spark ignition engine for a cylinder.

[0002]

2. Description of the Related Art In order to stratify an air-fuel mixture that collects fuel in the vicinity of a spark plug, an injector (fuel injection valve) is faced in the cylinder so that the fuel is directly injected into the cylinder. There is a direct injection type spark ignition engine that is designed to inject.

As a conventional in-cylinder direct injection type spark ignition engine, there is one in which an intake port is made to stand upright along a cylinder wall, as disclosed in, for example, Japanese Patent Application Laid-Open No. 6-81651.

The intake air that has flowed into the cylinder from the upright intake port descends along the cylinder wall and then causes a reverse tumble that swivels along the piston crown.

The fuel injected from the injector into the cylinder is atomized and vaporized in the process of being swirled by the reverse tumble, and the liquid fuel is prevented from adhering to the spark plug and misfire is prevented. Has become.

However, in such a conventional direct injection type spark ignition engine for a cylinder, since the upright intake port is provided so as to penetrate through the upper part of the cylinder head, the intake manifold is provided above the cylinder head. It is necessary to connect them, and there is a problem that the total height of the engine becomes large.

Since the cylinder head is provided with an upright intake port, there is a problem in that the degree of freedom in arranging the water jacket formed around the combustion chamber wall of the cylinder head is reduced.

Further, as a conventional direct injection type spark ignition engine for a cylinder, for example, the one disclosed in Japanese Patent Laid-Open No. 8-35429 has an intake port curved in a spiral shape.

The intake air that has flowed into the cylinder from the intake port curved in a spiral shape causes a strong swirl that swirls along the cylinder.

However, in such a conventional in-cylinder direct injection type spark ignition engine, since the pressure loss imparted to the flow of intake air by the intake port curved in a spiral shape is large, it is difficult to increase the output of the engine. There is a problem that it will be.

The present invention has been made in view of the above problems, and an object thereof is to provide a combustion chamber structure suitable for a direct injection spark ignition engine in a cylinder.

[0012]

According to a first aspect of the present invention, there is provided a direct injection type spark ignition engine for a direct injection type spark ignition engine, wherein an intake port is connected to a cylinder.
The intake air flowing into the cylinder swirls around the cylinder center line.
Swirl Initiator Producing Swirl Flow with Whirl Components
The step and the crown of the piston are formed with a convex portion protruding in the center
And is dented in a dish shape and is orthogonal to the cylinder center line.
A cavity with a circular cross section is eccentric from the cylinder centerline.
And the cavity is a flat circular cavitation.
B bottom and the cavity side of the outer periphery of this cavity bottom
The fuel spray form of the injector is defined as
Set in the shape of a hollow cone with spray, in the latter half of the compression stroke
When the center line of the fuel spray is the center of the bottom of the cavity
Fuel injection in compression stroke injection.
The spread of the fog was suppressed and the fuel spray collided with the side surface of the cavity.
Therefore, it is intended to suppress the adhesion.

According to another aspect of the present invention, there is provided an in-cylinder direct injection type spark ignition engine in which intake air flows into the cylinder through an intake port.
Has a swirl component that rotates around the cylinder center line.
Swirl generating means for generating a swirling flow and a piston crown
When a convex portion protruding like a roof is formed in the center of the part
In both cases, a cavity that is dish-shaped is formed,
I has a circular cross section perpendicular to the cylinder center line,
The bottom surface of the cavity with a flat circular shape
The side surface of the cavity expands from the outer periphery to the shape of an inverted cone,
The fuel spray form of the injector is
It is set to a hollow conical shape, and the fuel during the latter half of the compression stroke is
The center line of the material spray intersects the center of the bottom of the cavity.
And the spread of fuel spray in compression stroke injection
The fuel spray collides with the side surface of the cavity and adheres.
I tried to suppress it.

A cylinder direct injection type spark ignition engine according to a third aspect is the invention according to the first or second aspect,
The spark plug was arranged at a substantially central portion of the ceiling wall of the combustion chamber, and the protrusion height of the center electrode was set to be larger than 3.5 mm.

A cylinder direct injection type spark ignition engine according to a fourth aspect is the invention according to any one of the first to third aspects, wherein the fuel spray injected from the injector has a cone angle of 40 °. The configuration is such that it expands into a hollow conical shape in the range of up to 70 °, and 6% to 12% in the central portion of the fuel spray.
% Of fuel is distributed.

According to a fifth aspect of the present invention, there is provided a direct injection spark ignition engine for a direct injection type cylinder in which the depth of the cavity is set to 4 mm or more.

According to a sixth aspect of the present invention, there is provided a direct injection type spark ignition engine for a direct injection type cylinder in which the center line of the fuel spray injected from the injector is horizontal to the horizontal line. The depression angle is set to about 36 °.

A cylinder direct injection type spark ignition engine according to a seventh aspect is the invention according to any one of the first to sixth aspects, wherein the fuel injection timing of the injector is set to an intake stroke at a high load, The fuel injection timing of the injector is set to the compression stroke when the load is low.

An in-cylinder direct injection spark ignition engine according to an eighth aspect of the present invention is the invention according to any one of the first to seventh aspects, in which the two intake ports extend substantially linearly in a plan view. A straight port is provided, and a swirl control valve that restricts intake air introduced into the cylinder from one intake port is provided as a swirl generating means.

[0020]

In the cylinder direct injection spark ignition engine according to the first and second aspects of the present invention, the injector opens in the compression stroke in which the piston rises in the stratified charge combustion region operated at a lean air-fuel ratio, for example. Then, fuel is injected into the combustion chamber. In a state where the air sucked into the cylinder through the intake port is compressed by the piston, the fuel is ignited and burned through the spark plug.

The fuel spray injected from the injector in the compression stroke in which the piston rises is injected in the intake air flow direction in the intake port and is collected in the cavity by the swirl. The fuel spray collected in the cavity is heated by the piston, atomized and vaporized, and a high-concentration mixture is accumulated in the cavity. As the piston approaches the top dead center, the ignition plug approaches the high-concentration mixture in the cavity, and the mixture is stratified.

Even in the homogeneous combustion region where fuel is injected from the injector in the intake stroke in which the piston descends, it is required to suppress the spread of fuel spray under a low back pressure so as not to collide with the wall surface of the cavity.

By setting the fuel spray form of the injector to a hollow conical shape having an initial spray, the spray particle size is made small in the compression stroke injection with high back pressure, and
The spread of the fuel spray can be suppressed, and the fuel spray can be prevented from colliding with and adhering to the side surface of the cavity.

By thus concentrating the fuel in the vicinity of the spark plug, ignition can be reliably performed, and the limit value of the lean air-fuel ratio at which combustibility is ensured can be expanded. By reducing the air-fuel ratio of the air-fuel mixture supplied to the cylinder, pumping loss of the engine can be reduced and fuel consumption can be reduced. Further, it is not necessary to increase the fuel injection amount in the cold state, and the emission can be improved.

Since the fuel injected from the injector spreads into the cavity depressed in the crown of the piston, it is prevented from hitting the crown of the piston and bouncing back to the ignition plug, and the liquid fuel directly adheres to the ignition plug. It prevents the occurrence of misfire.

On the other hand, even in the homogeneous combustion region where the fuel is injected from the injector in the intake stroke in which the piston descends, the penetration of the fuel spray is short and the particle size is small so that the fuel spray does not collide with the crown or cylinder of the piston. Is required to be small.

By setting the fuel spray form of the injector to a hollow conical shape having an initial spray, the spray particle size is reduced in the intake stroke injection with low back pressure, and
The penetration of the fuel spray is shortened, and the fuel spray is prevented from colliding with and adhering to the piston crown portion and the cylinder wall surface, thereby improving the emission and increasing the output.

Since it is not necessary to make the intake port stand upright along the cylinder wall, it is possible to prevent the intake manifold from being mounted at a high position and to make the engine compact. Further, the degree of freedom in arranging the water jacket for circulating the cooling water around the combustion chamber wall of the cylinder head is increased, and the cooling performance of the engine can be improved.

Further , by making the cross section of the cavity orthogonal to the cylinder center line into a circular shape, the fuel spray can be collected in the cavity and the swirl force can be maintained. As a result, the limit value of the lean air-fuel ratio at which combustibility is ensured is expanded, and fuel consumption is reduced.

In the in-cylinder direct injection type spark ignition engine according to claim 3, the spark plug is arranged substantially in the center of the ceiling wall of the combustion chamber, and the protrusion height of the center electrode is set to be larger than 3.5 mm. The rich mixture is collected near the discharge gap of the spark plug through the cavity. As a result, the limit value of the lean air-fuel ratio at which combustibility is ensured is expanded, and fuel consumption is reduced.

In the in-cylinder direct injection spark ignition engine according to claim 4, the fuel spray injected from the injector spreads into a hollow conical shape having a cone angle in the range of 40 ° to 70 °. 6% to 12% of fuel is also distributed in the central portion to reduce the spray particle size in the compression stroke injection with a high back pressure, and to suppress the spread of the fuel spray, so that the fuel spray has a side surface of the cavity. It is possible to prevent the particles from colliding with and adhering to.

By thus concentrating the fuel in the vicinity of the spark plug, the limit value of the lean air-fuel ratio for ensuring the combustibility is expanded and the fuel consumption is reduced.

In the cylinder direct injection type spark ignition engine according to the fifth aspect, by setting the depth of the cavity to 4 mm or more, the fuel spray can be collected in the cavity and the swirl force can be maintained. As a result, the limit value of the lean air-fuel ratio that ensures combustibility is expanded,
Fuel consumption can be reduced.

In the cylinder direct injection type spark ignition engine according to the sixth aspect, by setting the depression angle formed by the center line of the fuel spray injected from the injector with respect to the horizontal line to about 36 °, the fuel spray is injected into the cavity. You can collect swarms and maintain swirl power. As a result, the limit value of the lean air-fuel ratio that ensures combustibility is expanded,
Fuel consumption can be reduced.

In the in-cylinder direct injection spark ignition engine according to claim 7, fuel is injected from the injector in the compression stroke in which the piston rises when the load is low, and the rich mixture is passed through the cavity to the vicinity of the spark plug. Effectively collected. As a result, the limit value of the lean air-fuel ratio at which combustibility is ensured is expanded, and fuel consumption is reduced.

At high load, fuel is injected from the injector during the intake stroke in which the piston descends, and a homogeneous mixture is formed in the combustion chamber by the ignition timing, ensuring stable combustion without being affected by cycle fluctuations. The output is improved.

In the in-cylinder direct injection type spark ignition engine according to claim 8, 2 which extends linearly with respect to the cylinder
By squeezing one of the straight ports of the book via the swirl control valve, the swirl ratio can be adjusted while maintaining high intake charge efficiency.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the combustion chamber 3 is defined between the combustion chamber ceiling wall 20 formed in the cylinder head and the piston 1. The reciprocating motion of the piston 1 in the cylinder 5 is converted into a continuous rotary motion of a crankshaft (not shown) via a connecting rod (not shown).

Combustion chamber ceiling wall 2 inclined to a pent roof type
At 0, an intake port 21 that branches into two and two exhaust ports (not shown) are opened facing each other. The combustion chamber ceiling wall 20 is composed of an intake port side inclined surface where each intake port 21 opens and an exhaust port side inclined surface where each exhaust port opens.

An ignition plug 4 is provided which faces the combustion chamber 3 from the central portion of the combustion chamber ceiling wall 20. The spark plug 4 is disposed coaxially with the center line of the cylinder 5, is located between each intake valve 7 and each exhaust valve 8, and faces the combustion chamber 3. Two intake valves 7 and two exhaust valves 8 are provided to face each other so as to sandwich the spark plug 4.

Each intake port 2 is used as a swirl generating means.
A swirl control valve 2 is a straight port that extends substantially linearly in a plan view and adjusts the amount of intake air introduced into the cylinder 5 from one intake port 21.
6 is provided.

A swirl control valve 26 is provided in the intake passage upstream of the branch point of each intake port 21. The butterfly type swirl control valve 26 rotates via a rotary shaft 27.

As shown in FIG. 2, the swirl control valve 26 in the shape of a semi-disc has a crescent-shaped notch 28. The cutout portion 28 is offset and opened in the same direction as the rotating shaft 27 so as to face the intake port 21 of the other side more largely at the closed position of the swirl control valve 26. As a result, the swirl control valve 26 throttles the intake flow that is taken into the cylinder 5 through the one intake port 21 when the swirl control valve is closed, and increases the ratio of the intake amount that flows into the cylinder 5 from the other intake port 21. 5 creates a swirling flow.

The swirl flow generated in the cylinder 5 swirls around an axis inclined at a predetermined angle with respect to the center line of the cylinder 5, and the swirl component swirling around the center line of the cylinder 5 and the swirl component of the cylinder 5. It has a tumble component that revolves around a horizontal line that is orthogonal to the center line. In the cylinder 5, a swirl that swivels in the counterclockwise direction is generated as shown by the white arrow in FIG.

An actuator (not shown) is connected to the rotary shaft 27 of the swirl control valve 26. A control unit (not shown) that controls the operation of the actuator closes the swirl control valve 26 in the stratified combustion region where the engine load and the rotational speed are equal to or less than a predetermined value based on a preset map, and excludes the stratified combustion region. Then, the swirl control valve 26 is opened.

An injector (fuel injection valve) 6 facing the combustion chamber 3 from the side of the combustion chamber ceiling wall 20 and an ignition plug 4 facing the combustion chamber 3 from the center are provided.

The valve opening timing and valve opening period (injection pulse width) of the injector 6 are controlled by the control unit according to the operating state.

The control unit calculates the basic injection amount Tp by the following equation based on the intake air amount Qa detected by each sensor (not shown) and the engine speed N.

Tp = K · Qa / N (1) where K is a constant, and in a predetermined homogeneous combustion region, the air-fuel ratio falls within a narrow range around the theoretical air-fuel ratio, while in a predetermined stratified combustion region. The final fuel injection amount Ti is calculated by the following equation so that the air-fuel ratio for achieving the stratified combustion by the lean air-fuel mixture is calculated, and the fuel injection amount is feedback-controlled.

Ti = Tp × α × COEF + Ts (2) where α is the air-fuel ratio feedback correction coefficient, COEF
Is a sum of various correction coefficients using parameters such as a cooling water temperature correction coefficient and a correction coefficient for stratified combustion, and Ts is an invalid injection pulse width.

A pulse signal corresponding to the calculated fuel injection amount Ti is output to the injector 6 to control the fuel injection.

The control unit adjusts the air-fuel ratio of the air-fuel mixture supplied to the cylinder 5 to a leaner side of the stoichiometric air-fuel ratio in the stratified combustion region where the engine load and engine speed are below a predetermined value. The air-fuel ratio of the air-fuel mixture supplied to the cylinder 5 is adjusted to the stoichiometric air-fuel ratio or the rich side in the homogeneous combustion region where the engine load or rotation speed rises above a predetermined value.

The fuel injected into the cylinder 5 as the injector 6 opens is mixed with the air taken in from the intake port 21 as each intake valve 7 is opened. The air-fuel mixture formed in the cylinder 5 is ignited and combusted through the ignition plug 4 while being compressed by the piston 1. The burned gas is discharged from each exhaust port as the exhaust valve 8 is opened during the exhaust stroke in which the piston 1 rises after the piston 1 is lowered and the rotational force is taken out via the crankshaft. Each of these steps is continuously repeated.

The fuel injection timing, which is the valve opening timing of the injector 6, is set based on a preset map in the latter half of the compression stroke in which the piston 1 rises in the stratified combustion region where the engine load and the rotational speed are below a predetermined value. The intake stroke is set so that the piston 1 descends in the homogeneous combustion region where the engine load or engine speed rises above a predetermined value.

In the crown portion 10 of the piston 1, a convex portion 31 protruding in a roof shape is formed in the central portion thereof, and a cavity 11 recessed in a dish shape is formed.

The cavity 11 has a circular cross section perpendicular to the center line of the cylinder 5, and is defined by a planar circular cavity bottom surface 15 and a cavity side surface 16 extending from the outer periphery of the cavity bottom surface 15 into an inverted conical surface shape. To be done. The inclination angle of the cavity side surface 16 with respect to the vertical line is 1
It is set to about 0 °.

The cavity 11 has a circular cross section that is eccentric to the injector 6 side with respect to the center line of the cylinder 5, and is arranged so as to be close to the injector 6. The depth Dc of the cavity 11 is set to 4 mm or more.

The spark plug 4 faces the cavity 11 at a position farthest from the injector 6. The discharge gap of the spark plug 4 is composed of a tip end surface of a cylindrical center electrode 41 and side electrodes facing the end surface. Normally, the protrusion height Hp of the center electrode 41 is set to about 3.5 mm. In the present embodiment, the protrusion height Hp of the center electrode 41 corresponds to the deepening of the cavity 11.
Is set to be larger than 3.5 mm to bring the discharge gap closer to the cavity 11.

The crown portion 10 of the piston 1 is inclined along the combustion chamber ceiling wall 20 by the convex portion 31. Thereby, when the piston 1 reaches the top dead center, the volume of the combustion chamber 3 defined between the piston 1 and the combustion chamber ceiling wall 20 is concentrated in the cavity 11, and a high compression ratio is obtained.

The injectors 6 are located laterally of the intake valves 7 and between the intake valves 7 and face the combustion chamber 3. The fuel injection direction of the injector 6 is the cavity 1
1, the fuel spray is arranged so as to face the spark plug 4
The configuration does not hit. The depression angle θf formed by the center line F of the fuel spray injected from the injector 6 with respect to the horizontal line L
Is set to about 36 °, and as shown in FIG. 1, when the piston 1 is in the latter half of the compression stroke, the piston 1 intersects the central portion of the bottom surface 15 of the cavity 11.

As the injector 6 is opened, the fuel spray injected from its nozzle is in the form of a hollow cone having an initial spray, the cone angle of which is in the range of 40 ° to 70 ° and the central portion thereof. In addition, 6% to 12% of fuel is distributed. A swirl injection valve is used as the injector 6, and atomization can be achieved while suppressing the penetration force of the fuel spray.

With the above construction, the operation will be described below.

As each intake valve 7 is opened, air is taken into the cylinder 5 from each intake port 21. In the homogeneous combustion region, the injector 6 opens in the intake stroke in which the piston 1 descends, and in the stratified combustion region, the injector 6 opens in the latter half of the compression stroke in which the piston 1 rises, and fuel spray from the injector 6 into the combustion chamber 3 Is jetted.

In a state where the air sucked into the cylinder 5 through each intake port 21 is compressed by the piston 1, the fuel is ignited and burned through the spark plug 4. The burned gas is discharged from each exhaust port as the exhaust valve 8 is opened during the exhaust stroke in which the piston 1 rises after the piston 1 is lowered and the rotational force is taken out via the crankshaft. Each of these steps is continuously repeated.

In the homogeneous combustion region where the engine load or engine speed rises above a predetermined value, the swirl control valve 26 is fully opened, and the intake air is divided into the two intake ports 21 substantially evenly and sucked into the cylinder 5. To be done. Therefore,
The port area is expanded and the intake charge efficiency of the engine can be improved.

In the homogeneous combustion region, the intake flows flowing into the cylinder 5 through the intake ports 21 collide with each other and the swirl force generated in the cylinder 5 weakens, but the mixture supplied to the cylinder 5 is weakened. Is adjusted to the stoichiometric air-fuel ratio or to the rich side, and fuel is injected from the injector 6 in the intake stroke in which the piston 1 descends, so that the piston 1 rises and is homogeneous in the combustion chamber 3 by the ignition timing. An air-fuel mixture is formed, ignition is reliably performed, and flame propagation is promoted.

The swirl control valve 26 is closed in a stratified combustion region where the engine load or engine speed is below a predetermined value, and most of the intake air passes through one intake port 21 as each intake valve 7 is opened. Is swirled into the cylinder 5 and swirls along the side surface 16 of the cylinder 5 and the cavity 11.

By narrowing one of the two straight ports extending linearly with respect to the cylinder 5 via the swirl control valve 26, the swirl ratio can be adjusted while maintaining a high intake charging efficiency.

Most of the fuel spray injected from the injector 6 in the latter half of the compression stroke in which the piston 1 rises goes into the cavity 11 and is collected in the cavity 11 by the swirl. The fuel spray collected in the cavity 11 is heated by the piston 1, atomized and vaporized, and a high-concentration mixture is accumulated in the cavity 11. As the piston 1 approaches the top dead center, the spark plug 4
Approaching, stratification of the air-fuel mixture is achieved, and ignition is reliably performed.

By forming the cavity 11 in a circular cross section, setting the inclination angle of the cavity side surface 16 with respect to the vertical line to about 10 °, and setting the depth of the cavity 11 to 4 mm or more, it is possible to avoid an increase in the size of the engine. It is possible to collect the fuel spray in the cavity 11 and maintain the swirl force.

FIG. 3 is a characteristic diagram showing the relationship between the depth of the cavity 11, the unburned HC concentration of exhaust gas, and the engine height. The unburned HC emission amount decreases as the depth of the cavity 11 increases. This is cavity 11
As the fuel depth increases, the fuel spray becomes
This is because it is possible to prevent the wall surface of No. 1, particularly the bottom surface 15, from colliding and adhering. However, as the depth of the cavity 11 increases, the wall thickness of the crown portion of the piston 1 increases and the engine height increases.

Even if the cavity 11 is deepened to 4 mm or more, the discharge gap of the spark plug 4 is separated from the annular side electrode by 3.5 mm or more, so that the piston 1 collects in the cavity 11 near the top dead center. The high-concentration air-fuel mixture thus generated approaches the discharge gap of the spark plug 4, and the fuel can be concentrated near the discharge gap of the spark plug 4.

Even in the homogeneous combustion region where fuel is injected from the injector 6 in the intake stroke in which the piston 1 descends,
It is required to suppress the spread of the fuel spray under a low back pressure so as not to collide with the wall surface of the cavity 11.

On the other hand, even in the homogeneous combustion region where the fuel is injected from the injector 6 in the intake stroke in which the piston 1 descends, the penetration of the fuel spray is carried out so that the fuel spray does not collide with the crown portion 10 of the piston 1 or the cylinder 5. It is required to be short and have a small particle size.

By setting the fuel spray form of the injector 6 to a hollow conical shape having the initial spray, the spray particle size can be made small in the compression stroke injection with a high back pressure, and the spread of the fuel spray can be suppressed and the fuel spray Are prevented from colliding with and adhering to the side surface 16 of the cavity 11.

FIG. 4 is a characteristic diagram showing the relationship between the back pressure of the injector 6 and the cone angle of the fuel spray. Compared to the solid cone fuel spray form, the hollow cone fuel spray form suppresses the spread of the fuel spray under high back pressure, and the hollow cone fuel spray with the initial spray is compared to the hollow cone fuel spray form. The spray form can further suppress the spread of fuel spray under high back pressure. This is because the inertial mass of the spray group that spreads to the central portion of the fuel spray is large at the initial stage of injection, so that a negative pressure is generated inside the liquid film and the spread of the fuel spray can be suppressed. And, the hollow cone-shaped spray form having the initial spray does not have a blister due to collision of the tip with air,
It is possible to prevent collision and interference with the wall surface of the cavity 11.

FIG. 5 is a characteristic diagram showing the relationship of the combustion performance to the cone angle of the fuel spray. From this, when the cone angle of the fuel spray is in the range of 40 ° to 70 °, the HC concentration in the exhaust gas decreases and the engine stability C
It can be seen that Pi is improved.

FIG. 6 is a characteristic diagram showing how the exhaust performance changes with respect to the cone angle of the fuel spray according to the depth of the cavity 11. From this, it can be seen that the deeper the cavity 11, the smaller the cone angle of the fuel spray required.

FIG. 7 shows the shape of fuel spray under high back pressure. From this, it is understood that the spray tip of the hollow jet expands, and the hollow jet having the initial injection suppresses the spread of the spray tip.

FIG. 8 shows the fuel distribution measured under high back pressure by the receiving method in which the fuel spray is received by the divided dish. From this, it can be seen that the cone angle in which the fuel is most distributed is smaller in the hollow injection having the initial injection than in the hollow injection. In the hollow injection having the initial injection, 6% to 12% of fuel is also distributed in the central portion where the cone angle is 0 ° to 10 °.

By thus concentrating the fuel in the vicinity of the spark plug 4, ignition can be reliably performed, and the limit value of the lean air-fuel ratio at which the combustibility is ensured can be expanded. By leaning the air-fuel ratio of the air-fuel mixture supplied to the cylinder 5, pumping loss of the engine is reduced and fuel consumption is reduced. Further, it is not necessary to increase the fuel injection amount in the cold state, and the emission can be improved.

The fuel injected from the injector 6 spreads into the cavity 11 recessed in the crown portion 10 of the piston 1 and hits the crown portion 10 of the piston 1 to make the spark plug 4
Therefore, it is possible to prevent the liquid fuel from directly adhering to the ignition plug 4 and causing misfire.

Since each intake port 2 extends linearly, the output during full-open output operation is not impaired. Further, by opening / closing the swirl control valve 26, a flow field according to operating conditions can be supplied. For example, since it is possible to operate with the same air-fuel ratio when switching between stratified combustion and homogeneous combustion, it is possible to eliminate the torque step during this switching.

Since each intake port 21 is provided so as to be largely inclined with respect to the center line of the cylinder 5, it is possible to prevent the intake manifold (not shown) from being mounted at a high position and to make the engine compact. . Further, the degree of freedom of arrangement of the water jacket (not shown) formed around the combustion chamber wall of the cylinder head is increased, and the cooling performance of the engine can be improved.

[Brief description of drawings]

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

FIG. 2 is a schematic plan view of a piston.

[Fig. 3] Similarly, cavity depth and unburned H of exhaust gas
The characteristic view which shows the relationship between C concentration and engine height.

FIG. 4 is a characteristic diagram showing the relationship between the back pressure of the injector and the cone angle of the fuel spray.

FIG. 5 is a characteristic diagram showing the relationship between combustion performance and cone angle of fuel spray.

FIG. 6 is a characteristic diagram showing how the exhaust performance changes with the cone angle of the fuel spray according to the depth of the cavity.

FIG. 7 is a view showing the shape of fuel spray under the same high back pressure.

FIG. 8 is a diagram showing a fuel distribution under a high back pressure by a receiving method in which the fuel spray is similarly received by a divided dish.

[Explanation of symbols]

1 piston 3 Combustion chamber 4 spark plugs 5 cylinders 6 injectors 7 intake valve 10 Piston crown 11 cavities 15 Cavity bottom 16 Cavity side 20 Combustion chamber ceiling wall 21 intake port 26 swirl control valve 28 Notch 31 convex 41 Center electrode

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI // F02F 3/26 F02F 3/26 A (56) References JP-A-7-102976 (JP, A) JP-A-1- 203613 (JP, A) JP-A-8-35429 (JP, A) JP-A-60-95188 (JP, A) JP-A-60-56118 (JP, A) JP-A-10-299539 (JP, A) JP 10-281039 (JP, A) JP 7-63061 (JP, A) JP 9-144543 (JP, A) JP 10-339139 (JP, A) JP 6-81651 (JP, A) JP 5-79337 (JP, A) JP 8-200116 (JP, A) JP 9-79038 (JP, A) JP 7-286520 (JP, A) Kaihei 7-217436 (JP, A) Actual Kaihei 1-124040 (JP, U) International Publication 96/36808 (WO, A1) (58) Fields investigated ( Int.Cl. ⁷ , DB name) F02B 23/10 F02M 61/18 F02B 17/00

Claims (8)

(57) [Claims] 1. Intake that flows into a cylinder from an intake port
Has a swirl component that rotates around the cylinder center line.
Swirl generating means for generating a swirling flow, and a convex portion protruding in the central portion is formed on the crown portion of the piston
At the same time, the dish-shaped depressions and the cross section orthogonal to the cylinder center line
Circular cavity formed off-center from the cylinder centerline
The cavity has a flat circular cavity bottom and
It is defined by the bottom of the cavity and the outer side of the cavity.
Is, the fuel spray form of the injector, the hollow having an initial spray
It is set to a conical shape so that the fuel spray
So that the center line intersects the center of the bottom of the cavity.
Composed to suppress spread of fuel spray in compression stroke injection
That the fuel spray collides with and adheres to the side of the cavity.
In- cylinder direct injection spark ignition engine characterized by suppressing . 2. An intake air flowing into a cylinder from an intake port
Has a swirl component that rotates around the cylinder center line.
The swirl generating means for generating the swirling flow and the convex portion protruding in the roof shape in the center of the piston crown
Is formed and a dish-shaped cavity is formed, and the cavity has a circular cross section orthogonal to the cylinder center line.
The bottom surface of the cavity, which has a circular shape, and the
Cavity side that spreads from the outer periphery of the bottom of the vity to the shape of an inverted cone
Defined by the plane, the fuel spray form of the injector, the hollow having an initial spray
It is set to a conical shape so that the fuel spray
So that the center line intersects the center of the bottom of the cavity.
Composed to suppress spread of fuel spray in compression stroke injection
That the fuel spray collides with and adheres to the side surface of the cavity.
In- cylinder direct injection spark ignition engine characterized by suppressing . 3. The in-cylinder direct cylinder according to claim 1 or 2, wherein the spark plug is arranged substantially in the center of the ceiling wall of the combustion chamber, and the protrusion height of the center electrode is set to be larger than 3.5 mm. Injection spark ignition engine. 4. The fuel spray injected from the injector is configured to spread into a hollow conical shape having a cone angle in the range of 40 ° to 70 °, and 6% to 12% of fuel is also contained in the center of the fuel spray. The in-cylinder direct injection spark ignition engine according to any one of claims 1 to 3, characterized in that 5. The direct injection spark ignition engine for a cylinder according to claim 1, wherein the depth of the cavity is set to 4 mm or more. 6. The in-cylinder according to claim 1, wherein a depression angle formed by a center line of the fuel spray injected from the injector with respect to a horizontal line is set to about 36 °. Direct injection spark ignition engine. 7. The fuel injection timing of the injector is set to an intake stroke when the load is high, and the fuel injection timing of the injector is set to a compression stroke when the load is low. In-cylinder direct injection type spark ignition engine described in. 8. The intake port is provided with two straight ports extending substantially linearly in a plan view, and the swirl generating means is provided with a swirl control valve for restricting intake air introduced into the cylinder from one intake port. In-cylinder direct injection spark ignition engine according to any one of claims 1 to 7.