JPH11193722A - Direct injection type spark-ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the stratified combustion by suppressing generation of smoke and unburned hydrocarbon and suppressing or reducing deposition on the top of the piston. SOLUTION: A land 20 that gradually becomes wider by the top view from the side where an intake valve 5 is located to the side where an exhaust valve 6 is located is formed by protruding on the top of the piston 1. This allows the intake tumble flow a to be divided to both sides of the land 20 on the side where the exhaust valve is located, and to flow to the side where the intake valve is located. Then, it is diverted upward on that side where the intake valve is located, and directed inward near a fuel injection valve 13 for the center of a combustion chamber 4. Because the intake tumble flow a becomes the above-mentioned symmetric whirls of a generally spiral shape, the fuel injected in the compression stroke is diverted upward by the tumble flow a. As a result, deposition on the top of the piston 1 is prevented, Also, the fuel can be transferred toward an ignition plug 12. Thus, generation of smoke, unburned hydrocarbon and deposits due to adhesion of the fuel is suppressed, and the stratified combustion can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a direct injection type spark ignition engine.

[0002]

2. Description of the Related Art As is well known, in a direct injection type spark ignition engine, fuel is directed toward a cavity combustion chamber provided on a piston crown surface during a compression stroke in a state where a swirl flow is given to intake air in a low load operation range. Injection and stratified combustion at an ultra-lean air-fuel ratio by forming a relatively rich mixture only around the spark plug, but among such in-cylinder injection type spark ignition engines For example, see JP-A-6-816.
As shown in Japanese Patent Publication No. 51, the swirling flow applied to the intake air flows from substantially below the intake valve toward the piston crown surface, and reverses at the piston crown surface toward the ignition plug in the center of the combustion chamber. There has been known an arrangement in which a so-called reverse tumble flow is provided.

[0003]

As described above, in the case where the reverse tumble flow is applied to the intake air during stratified charge combustion, in the compression stroke, the air flows from the side of the combustion chamber near the opening of the intake port toward the cavity combustion chamber. When the fuel is injected, the fuel rides on the reverse tumble flow and collides with the cavity combustion chamber, and the fuel adheres to the cavity combustion chamber in the form of a liquid film, which causes smoke and unburned HC, and causes the adhered fuel. May be deposited as a deposit.

Accordingly, the present invention provides an in-cylinder injection type spark ignition engine which can suppress the generation of smoke and unburned HC, and can also suppress the accumulation of deposits on the piston crown surface and perform stable stratified combustion. To provide.

[0005]

According to the first aspect of the present invention, two intake valves, a spark plug disposed at the center of the combustion chamber, and the combustion chamber between the two intake valves from the side of the combustion chamber. A fuel injection valve for directly injecting fuel into the chamber, and a cylinder injection type spark ignition engine in which stratified combustion is performed by performing fuel injection during a compression stroke with a tumble flow applied to intake air. A land portion that gradually widens in plan view from the intake valve arrangement side to the other exhaust valve arrangement side is formed at the center of the crown surface so as to protrude.

According to a second aspect of the invention, the upper surface of the land portion according to the first aspect is formed so as to be inclined upward from the intake valve arrangement side to the exhaust valve arrangement side.

[0007] In the invention of claim 3, claims 1 and 2
At the end of the land portion on the exhaust valve arrangement side described in the above, has a ridge line on a center line in a direction from the intake valve arrangement side to the exhaust valve arrangement side of the land portion in plan view, and oppose each other with the ridge line as a boundary. It is characterized in that a raised portion inclined in the direction is formed.

In the invention of claim 4, claims 1 and 2
At the end of the land portion on the exhaust valve arrangement side described in the above, the ridge line in a direction orthogonal to the center line in the direction from the intake valve arrangement side to the exhaust valve arrangement side of the land portion in plan view at a position substantially below the exhaust valve. And the ridges are formed with ridges inclined in opposite directions to each other with the ridgeline as a boundary.

In the invention of claim 5, claims 1 to 4 are provided.
A concave curved portion which is smoothly connected to the upper surface of the land portion is formed substantially below the intake valve at the end of the land portion on the side where the intake valve is disposed.

According to the invention of claim 6, claims 1 to 5 are provided.
The tumble strengthening means is provided on the upstream side of the intake valve described in (1).

In the invention according to claim 7, the tumble strengthening means according to claim 6 is a partial shielding valve that shields a substantially lower half of the intake passage during stratified combustion and opens the intake passage during homogeneous combustion. It is characterized by having.

According to the invention of claim 8, the tumble reinforcing means according to claim 6 is a subport having one end opened upstream of the throttle valve and the other end opened almost immediately above the intake valve. Features.

[0013]

According to the first aspect of the present invention, the land at the center of the crown surface of the piston is formed gradually wider in plan view from the intake valve arrangement side to the exhaust valve arrangement side. In the compression stroke, the tumble flow is diverted to both sides of the large-volume land portion on the exhaust valve arrangement side to the intake valve arrangement side, and is reversed upward to the intake valve arrangement side to inward in the vicinity of the fuel injection valve. As a result, a substantially spiral symmetric vortex is directed toward the center of the combustion chamber.

Therefore, during the stratified charge combustion, the fuel injected from the fuel injection valve during the compression stroke is inverted upward from the piston crown side to form a tumble flow having an inward substantially spiral symmetric vortex. The piston is deflected upward to suppress and reduce the adhesion to the piston crown surface, and rides on the flow of the substantially spiral symmetrical vortex to form a relatively rich mixture, which is a spark plug at the center of the combustion chamber. It is transferred to.

As a result, it is possible to suppress the generation of smoke and unburned HC and the accumulation of deposits due to the adhesion of fuel to the piston crown surface, and to stabilize the gas flow and reliably transfer the fuel toward the spark plug. By performing stable stratified combustion, the cycle fluctuation of combustion can be suppressed and the output can be increased.

According to the invention described in claim 2, according to claim 1
In addition to the effect of the invention, since the upper surface of the land is inclined upward from the intake valve arrangement side to the exhaust valve arrangement side, the fuel injected from the fuel injection valve in the compression stroke during stratified combustion is The fuel spray scattered in the direction of the piston crown can be collected along the slope of the upper surface of the land in the direction of the spark plug in the central portion of the upper combustion chamber, so that more stable stratified combustion can be performed.

According to the third aspect of the present invention, in addition to the effects of the first and second aspects of the present invention, the end of the land on the side where the exhaust valve is disposed is disposed at the end of the land in the plan view. Has a ridgeline on the center line in the direction from the side toward the exhaust valve arrangement side, and has formed ridges inclined in opposite directions from the ridgeline, so that the tumble flow of intake air in the compression stroke by the ridges. Dividing to both sides of the land can be enhanced, and the gas flow of the substantially spiral symmetric vortex can be further stabilized.

According to the fourth aspect of the present invention, in addition to the effects of the first and second aspects of the present invention, the end of the land on the exhaust valve arrangement side is located substantially below the exhaust valve in plan view. The land has a ridge line in a direction perpendicular to the center line in the direction from the intake valve arrangement side to the exhaust valve arrangement side, and the ridges form ridges that are inclined in opposite directions from the ridge line. Sometimes, the fuel spray injected from the fuel injection valve in the compression stroke and scattered in the direction of the piston crown is jumped up along the slope of the ridge in a state where the fuel spray is further urged toward the spark plug toward the center of the upper combustion chamber. In addition to being able to collect, the fuel film on the piston crown surface can be positively peeled off, and the generation of smoke, unburned HC and the accumulation of deposits can be suppressed more reliably, and stable stratified combustion can be performed. be able to.

According to the invention of claim 5, according to claim 1,
In addition to the effects of the inventions of (1) to (4), a concavely curved portion which is smoothly connected to the upper surface of the land portion is formed substantially below the intake valve at the end of the land portion on the side where the intake valve is disposed, so that the fuel in the compression stroke The fuel spray injected from the injection valve and scattered substantially in the direction of the piston crown below the intake valve is bounced up along the curved surface of the concave portion while being further urged toward the spark plug toward the center of the upper combustion chamber. The fuel film on the piston crown surface can be aggressively peeled off, and the generation of smoke, unburned HC and the accumulation of deposits can be suppressed more reliably, resulting in a more stable stratified combustion. Can be performed.

According to the invention of claim 6, according to claim 1,
In addition to the effects of the fifth to fifth aspects, a tumble strengthening means is provided on the upstream side of the intake valve, so that a strong tumble flow can be given to the intake air, and the stratified combustion operation region can be widened.

According to the invention of claim 7, according to claim 6,
In addition to the effects of the invention, the tumble reinforcing means is constituted by a partial shielding valve, so that the structure is simple and the cost can be advantageously obtained.

According to the invention of claim 8, according to claim 6,
In addition to the effect of the invention, the tumble strengthening means is configured as a subport whose one end is opened upstream of the throttle valve and the other end is opened almost immediately above the intake valve. The tumble flow can be formed, and therefore, even at a low rotation speed where the tumble flow is difficult to form, the tumble flow can be reliably formed, and the stratified combustion can be stabilized.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

1 to 4, 1 is a cylinder block, 2 is a piston, 3 is a cylinder head, 4 is a cylinder block 1, a piston 2 and a cylinder head 3
And shows the combustion chamber formed by.

The cylinder head 3 includes two intake valves 5 and two exhaust valves 6 disposed opposite to the intake valves 5, and takes in air from one intake port 7 and exhausts it from the other exhaust port 8. It has a cross flow port structure.

The intake port 7 is formed in a substantially horizontal direction similarly to the exhaust port 8 so that a tumble flow can be easily formed in the intake air in the combustion chamber 4.

Further, on the upstream side of the intake valve 5, specifically, on the intake manifold 9, there is provided a tumble flow enhancing means 10 for forcibly applying a tumble flow during stratified combustion.

In this embodiment, a partial shielding valve 11 is used as the tumble strengthening means 10 to shield a substantially lower half of the intake manifold 9 as an intake passage during stratified combustion and to open the intake manifold 9 during homogeneous combustion. I have.

The cylinder head 3 is provided with an ignition plug 12 substantially at the center of the combustion chamber 4, and the fuel is injected into the side of the combustion chamber 4 near the opening between the two intake ports 7. A valve 13 is provided to inject fuel directly from the fuel injection valve 13 into the combustion chamber 4.

On the other hand, a land portion 20 having a gradually increasing width in plan view is formed at the center of the crown surface of the piston 2 from the intake valve arrangement side to the exhaust valve arrangement side at the center thereof.

The land portion 20 has a flat upper surface. In this embodiment, both sides of the land portion 20 are connected to a general reference surface of the crown surface of the piston 2 by a gentle curved surface. It may be formed so as to be continuous with the general reference surface on an inclined surface.

According to the structure of the above embodiment, as shown in FIG. 5A, when the intake valve 5 is opened in the intake stroke, air is sucked into the combustion chamber 4 from the intake port 7 near the center of the combustion chamber. To form a tumble flow a going downward.
Since the land portion 20 of the crown surface of the piston 2 is formed to have a gradually wide width in plan view from the intake valve arrangement side to the exhaust valve arrangement side, this tumble flow a is generated during the compression stroke as shown in FIG. On the arrangement side, the air flows to both sides of the land portion 20 having a large volume and flows toward the intake valve arrangement side, and at the intake valve arrangement side, turns upward and turns inward in the vicinity of the fuel injection valve 13 so that the combustion chamber 4 It becomes an almost spiral symmetrical vortex toward the center.

Therefore, during stratified combustion, the compression stroke shown in FIG.
(B), (c) and as shown in FIG.
3 is deflected upward by the tumble flow which is turned upward from the crown side of the piston 2 and turned into an inward substantially spiral symmetrical vortex. Is prevented from adhering to the crown surface, and is transferred toward the spark plug 12 in the central portion of the combustion chamber along the substantially spiral symmetric vortex flow as shown in FIG. A mixture having a relatively rich air-fuel ratio can be distributed around the ignition plug 12, and stratified combustion can be performed with an ultra-lean air-fuel ratio as a whole.

As a result, it is possible to suppress the generation of smoke, unburned HC and the accumulation of deposits due to the adhesion of fuel to the crown surface of the piston 2, to stabilize the gas flow and to ensure the fuel is directed toward the spark plug 12. The stable stratified combustion can be performed by the transfer to suppress the fluctuation of the combustion cycle and increase the output.

In particular, in the present embodiment, the intake manifold 9
Since the tumble strengthening means 10 for forcibly applying the tumble flow during stratified combustion is provided, a strong tumble flow can be applied to the intake air, and the stratified combustion operation area can be widened.

Further, as described above, the tumble strengthening means 10 shields the substantially lower half of the intake manifold 9 during stratified charge combustion and allows the intake air to flow from the substantially upper half of the intake manifold 9, thereby achieving homogeneous combustion. Sometimes, the intake manifold 9 is constituted by the partial shielding valve 11 that opens, so that the structure is simple and the cost can be advantageously obtained.

On the other hand, when the engine is started or the engine is cold, such as in a high load range, fuel is injected from the fuel injection valve 13 during the intake stroke to promote vaporization and homogenize the mixture to perform homogeneous combustion. However, at the time of this homogeneous combustion, as described above, the arrangement of the intake port 7 causes the tumble flow a to be drawn downward from the intake port 7 near the center of the combustion chamber of the intake port 7 and formed downward. When fuel is injected from the fuel injection valve 13 in the intake stroke, the fuel spray rides on a downward tumble flow, so that it is possible to avoid fuel clogging of the ignition plug 12, prevent smoldering, and suppress emission of unburned HC. Of course, in the compression stroke, the tumble flow a is turned into an inward spiral substantially symmetric vortex by the land portion 20 of the piston 2 crown surface, so that the air-fuel mixture can be favorably homogenized. , It is possible to stabilize the homogeneous combustion.

6 to 12 show land portions 20 on the piston crown surface.
In the embodiment shown in FIG. 6, land portions 2 protruding from the crown surface of the piston 2 are shown.
The upper surface of 0 is inclined upward from the intake valve arrangement side to the exhaust valve arrangement side.

Therefore, according to the structure of this embodiment, the fuel injected from the fuel injection valve 13 in the compression stroke during the stratified charge combustion becomes a tumbling symmetrical vortex inward, as described above. Although the flow a tends to be deflected as a whole to the spark plug 12 side, the fuel spray scattered toward the piston crown surface of the injected fuel is not
Due to the inclination of the upper surface of 0, the fuel can be positively collected toward the spark plug 12 in the central portion of the upper combustion chamber 4, and more stable stratified combustion can be performed.

In the embodiment shown in FIGS. 7 and 8, a direction from the intake valve arrangement side of the land portion 20 to the exhaust valve arrangement side in a plan view is provided at the end of the land portion 20 on the exhaust valve arrangement side. Have a ridge line on the center line of the, and in the opposite direction from the ridge line,
That is, a raised portion 21 inclined in the front-rear direction of the engine is formed.

According to the structure of this embodiment, since the tumble flow a of the intake air is diverted to the left and right sides of the land portion 20 in the compression stroke by the ridge 21, the wing-shaped twin vortex is formed. Can further stabilize the gas flow, and can greatly contribute to the improvement of the output during stratified combustion.

In the embodiment shown in FIGS. 9 and 10, the land portion 20 has an end on the side where the exhaust valve is disposed, and a plan view at a position substantially below the exhaust valve 6 from the side where the intake valve is disposed on the land 20. A ridge is formed in a direction perpendicular to the center line in the direction toward the exhaust valve arrangement side, and a ridge 22 is formed in the opposite direction to the ridge, that is, inclined in the engine left-right direction.

According to the structure of this embodiment, during the stratified charge combustion, the fuel spray injected from the fuel injection valve 13 in the compression stroke and scattered in the direction of the piston crown surface is inclined by the inclination of the left side surface of the raised portion 22 shown in the drawing. Along with the upper part of the combustion chamber 4 toward the spark plug 12 in a state of being urged toward the spark plug 12, and the fuel film on the piston crown surface can be positively peeled off. Thus, generation of unburned HC and accumulation of deposits can be suppressed more reliably, and stable stratified combustion can be performed.

In the embodiment shown in FIGS.
At a position substantially below the intake valve at the end of the land portion 20 on the side where the intake valve is disposed, a concave curved portion 23 smoothly connected to the upper surface of the land portion 20 is provided.
Is formed.

According to the structure of this embodiment, of the fuel injected from the fuel injection valve 13 in the compression stroke during stratified charge combustion, the fuel spray scattered substantially in the direction of the piston crown surface below the intake valve 5 is removed from the recessed portion. Along the curved surface of the curved portion 23, the upper part of the combustion chamber 4 can be further urged toward the spark plug 12 in the central portion to jump up and collect the fuel. It is possible to positively perform, and it is possible to more reliably suppress smoke, generation of unburned HC, and deposition of deposits, and to perform stable stratified combustion.

The structure of the land portion 20 of the piston crown surface is not limited to those of the above embodiments, and can be arbitrarily combined within the scope described in the claims.

FIGS. 13 and 14 show different embodiments of the tumble enhancing means 10.

In this embodiment, one end of the throttle valve 1 extends from the intake manifold 9 to the intake port 7.
The sub port 24 is provided upstream of the intake port 4 and has the other end opened at a position substantially immediately above the intake valve 5. The sub port 24 is used as the tumble strengthening means 10.

According to the structure of this embodiment, in a low load region in which stratified charge combustion is performed, a relatively large differential pressure generated between the upstream of the throttle valve 14 and the vicinity of the intake valve 5 of the intake port 7 causes the intake valve 5 Subport 24 opened almost directly above
, A strong tumble flow a can be formed in the combustion chamber 4, so that the tumble flow a can be reliably formed even at a low rotation speed where the tumble flow a is difficult to form. Stratified combustion can be stabilized. The same effect can be obtained even when the upstream opening of the subport 24 is set to the throttle valve downstream, and each of the intake ports on the downstream side of the upstream opening of the subport is provided with a very common on-off valve for opening and closing the passage. Is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an in-cylinder injection spark ignition engine according to the present invention.

FIG. 2 is a view taken along the line AA of FIG. 1;

FIG. 3 is a plan view showing a first embodiment of a land portion provided on a piston crown surface.

FIG. 4 is a sectional view taken along the line BB in FIG. 3;

FIG. 5 is a schematic diagram showing the behavior of fuel spray during stratified charge combustion in the embodiment, where (A) shows the intake stroke, (B),
(C) shows the fuel injection timing in the compression stroke, and (d) shows the ignition timing.

FIG. 6 is a sectional view showing a second embodiment of a land portion.

FIG. 7 is a plan view showing a third embodiment of a land portion.

FIG. 8 is a sectional view taken along line CC of FIG. 7;

FIG. 9 is a plan view showing a fourth embodiment of a land portion.

FIG. 10 is a sectional view taken along the line DD in FIG. 9;

FIG. 11 is a plan view showing a fifth embodiment of a land portion.

FIG. 12 is a sectional view taken along the line EE in FIG. 11;

FIG. 13 is a sectional view showing a different embodiment of the tumble strengthening means.

FIG. 14 is a view taken along line FF of FIG. 13;

[Explanation of symbols]

 2 Piston 4 Combustion chamber 5 Intake valve 6 Exhaust valve 7 Intake port (intake path) 9 Intake manifold (intake path) 10 Tumble reinforcing means 11 Shielding valve 12 Spark plug 13 Fuel injection valve 14 Throttle valve 20 Land part 21 Engine front and rear direction Inclined protrusion 22 Projection inclined in engine left-right direction 23 Concave portion 24 Subport

Claims (8)

[Claims] 1. A fuel supply system comprising: two intake valves; a spark plug disposed in a central portion of a combustion chamber; and a fuel injection valve for directly injecting fuel from a side of the combustion chamber into the combustion chamber between the two intake valves. In a cylinder injection type spark ignition engine in which stratified combustion is performed by performing fuel injection during a compression stroke in a state where a tumble flow is given to intake air, a central portion of a piston crown surface is provided on the other side from an intake valve arrangement side. An in-cylinder injection spark ignition engine, characterized in that a land portion gradually widening in plan view is formed so as to protrude toward the exhaust valve arrangement side. 2. The in-cylinder injection spark ignition engine according to claim 1, wherein an upper surface of the land is inclined upward from an intake valve arrangement side to an exhaust valve arrangement side. 3. A ridge line is provided at an end of the land portion on the exhaust valve arrangement side on a center line in a direction from the intake valve arrangement side to the exhaust valve arrangement side of the land portion in plan view, and the ridge line is a boundary. The in-cylinder injection type spark ignition engine according to claim 1 or 2, wherein raised portions inclined in opposite directions are formed. 4. A direction perpendicular to a center line of a direction from the intake valve arrangement side of the land to the exhaust valve arrangement side in a plan view at an end of the land on the exhaust valve arrangement side at a position substantially below the exhaust valve. The in-cylinder injection spark ignition engine according to claim 1 or 2, wherein ridges are formed at the ridges, and ridges which are inclined in directions opposite to each other with respect to the ridges are formed. 5. The method according to claim 1, wherein a concavely curved portion is formed at an end of the land on the side where the intake valve is disposed, substantially below the intake valve, so as to be smoothly connected to the upper surface of the land. The in-cylinder injection spark ignition engine as described in the above. 6. The in-cylinder injection spark ignition engine according to claim 1, wherein a tumble enhancing means is provided upstream of the intake valve. 7. The in-cylinder according to claim 6, wherein the tumble strengthening means is a partial shielding valve that shields a substantially lower half of the intake passage during stratified combustion and opens the intake passage during homogeneous combustion. Injection spark ignition engine. 8. The in-cylinder injection type spark according to claim 6, wherein the tumble enhancing means is a subport having one end opened upstream of the throttle valve and the other end opened almost immediately above the intake valve. Ignition engine.