JP2002115549A - Cylinder direct injection spark ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a gas flow from being obstructed by a squish flow generated when a piston approaches the top dead center of compression, and ensure stable combustion at the time of stratified and homogeneous combustion. SOLUTION: In this cylinder direct injection spark ignition engine, injection fuel from a fuel injection valve toward into a cavity 6 formed in a piston crown surface to guide the injected fuel in the vicinity of a spark plug 3 by utilizing a flow of gas in a cylinder so as to generate a stratified mixture to perform combustion by a lean mixture as a whole, a clearance L2 between an exhaust side slope 16 of the piston crown surface and a cylinder head 4 is constituted so as to be larger than a clearance L1 between a suction side slope 15 of the piston crown surface and the cylinder head 4. In this way, a squish flow generated when a piston 5 approaches the top dead center of compression is suppressed, the gas flow in the cylinder can be prevented from being obstructed, and stability of combustion can be ensured at the time of stratified and homogenous combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In-cylinder direct injection spark ignition engines generally perform a stratified combustion operation at a low load. In the stratified combustion operation, the injected fuel is ignited by utilizing the gas flow in the cylinder. The mixture is guided to the plug so that an air-fuel mixture ignitable is formed near the ignition plug.

Here, as a method for collecting the injected fuel in the vicinity of the ignition plug, Japanese Patent Application Laid-Open Nos. 8-35429 and 10-33
The "wall guide method" disclosed in JP-A-9138 and the "air guide method" disclosed in JP-A-4-112931 and JP-A-11-257078 are known.

The wall guide method is shown in FIG.
As shown in (b), a pent-roof combustion chamber recessed in the cylinder head, a cavity recessed in the piston crown surface, and a diagonally downwardly facing lower pent-roof combustion chamber disposed below the intake port. A high-pressure fuel injection valve that injects fuel directly into the cylinder in a certain direction, a spark plug arranged substantially at the center of the pent roof combustion chamber, and a tumble flow generating means for generating a swirl flow in the cylinder. And using a swirl flow generated by the gas flow generation means and a shape of a cavity recessed in the piston crown surface to guide the fuel to the vicinity of the ignition plug and perform stratified combustion.

On the other hand, the air guide system is shown in FIG.
(A) and (b), a pentroof-shaped combustion chamber recessed in a cylinder head, a shallow dish-shaped cavity recessed in a piston crown surface, and the pentroof-shaped cavity disposed below an intake port. A high-pressure fuel injection valve that injects fuel directly into the cylinder in a direction obliquely downward with respect to the combustion chamber,
An ignition plug disposed substantially at the center of the pent roof combustion chamber, and gas flow generating means for generating a forward tumble flow in the cylinder, utilizing the forward tumble flow generated by the gas flow generating means. This method introduces fuel to the vicinity of the spark plug to perform stratified combustion.

[0006] In any method, an ignitable air-fuel mixture is formed in the vicinity of the ignition plug, so that the ignition plug can ignite even with an ultra-lean air-fuel ratio that cannot be ignited as a whole. . After ignition by the ignition plug, the combustion is expanded to the whole area in the cylinder using the gas flow.

[0007]

[Problems to be solved by the invention]
The former wall guide type engine had a cavity near the intake side of the piston crown, so the squish flow ejected from the gap between the exhaust slope of the piston crown and the cylinder head at the end of the compression stroke There is a problem that the swirl flow is hindered by the squish flow. If the swirl flow is obstructed, it becomes impossible to collect a rich air-fuel mixture in the vicinity of the spark plug, which causes deterioration of combustion stability. Furthermore, even during homogeneous combustion, the squish flow impedes the flow of gas toward the spark plug, so that the formation of an air-fuel mixture in the cylinder becomes non-uniform, which causes deterioration of the combustion state.

FIG. 29 and FIG. 30 show how the swirl flow in the cylinder is obstructed by the squish flow. When the piston is located before the compression top dead center, as shown in FIG. Even if swirl flow is formed,
When the piston approaches the compression top dead center, a squish flow from the exhaust side to the intake side is generated as shown in FIG. 30, and the swirl flow toward the spark plug is obstructed.

Also, the latter air guide type direct injection type spark ignition engine has a cavity at the center of the piston crown surface or near the intake side so that the injected fuel can be collected under the ignition plug. Therefore, the squish flow ejected from the gap between the exhaust side slope of the piston crown surface and the cylinder head is strong, and the squish flow hinders the tumble flow during stratified combustion, and similarly degrades combustion stability. Was. Further, even during homogeneous combustion, there is a problem that, although not as effective as the above-mentioned wall guide method, the uniformity of the air-fuel mixture in the cylinder is hindered by the influence of the squish flow, and combustion deteriorates.

FIGS. 31 and 32 show how the squish flow impedes the tumble flow. When the piston is located before the compression top dead center, the tumble flow is generated in the cylinder as shown in FIG. Even if it is generated, when the piston approaches the compression top dead center, the squish flow from the exhaust side to the intake side weakens the tumble flow as shown in FIG.

In FIGS. 31 (b) and 32 (b),
The tumble flow is drawn so as to rise while spreading from the bottom of the cavity, but this is to make it easier to see the tumble flow, which is a vertical vortex, and means that the actual tumble flow is generated with such inclination This is not the case (the same applies to other drawings).

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned technical problems of the prior art. In a direct injection type spark ignition engine, a squish flow generated when the piston approaches a compression top dead center is used. An object of the present invention is to prevent gas flow in the inside from being hindered and to ensure stable combustion during stratified combustion and homogeneous combustion.

[0013]

According to a first aspect of the present invention, fuel directly injected into a cylinder from a fuel injection valve is collected near an ignition plug by utilizing gas flow in the cylinder to enable ignition. In a direct injection type spark ignition engine that performs combustion at a lean air-fuel ratio, the gap between the exhaust side slope of the piston crown and the cylinder head is larger than the gap between the intake side slope of the piston crown and the cylinder head. It is characterized by having comprised in.

According to a second aspect of the present invention, in the first aspect, the gap between the exhaust-side slope of the piston crown surface and the cylinder head is within a range in which fuel injected into the cavity does not overflow from the cavity and flow into the exhaust side. It is characterized in that it is configured to be larger than the gap between the intake side slope of the piston crown surface and the cylinder head.

According to a third aspect of the present invention, in the second aspect, a gap between the exhaust-side slope of the piston crown surface and the cylinder head is located at the piston position when the upper end of the fuel spray reaches the cavity. The angle formed between the horizontal plane and the straight line connecting the upper end on the exhaust side and the fuel injection point is set to be smaller than the angle formed between the upper end of the fuel spray and the horizontal plane.

In a fourth aspect based on the second aspect, the clearance between the exhaust-side slope of the piston crown surface and the cylinder head is represented by the following equation: α <θ−γ / 2, where α: the upper end of the fuel spray At the position of the piston when it reaches the cavity, the angle between the horizontal plane and the straight line connecting the upper end of the cavity on the exhaust side and the fuel injection point is set so as to satisfy the following: θ: Mounting angle of the fuel injection valve γ: Spray angle of the fuel injection valve It is characterized by that.

In a fifth aspect based on the second aspect, the clearance between the exhaust-side slope of the piston crown and the cylinder head is such that the height of the exhaust-side surface of the cavity is higher than the height of the intake-side surface. It is characterized by being set.

According to a sixth aspect of the present invention, the fuel directly injected into the cylinder from the fuel injection valve is collected near the ignition plug by utilizing the in-cylinder gas flow so that the fuel can be ignited, and the entire combustion is performed at a lean air-fuel ratio. In a direct injection type spark ignition engine, a concave portion is provided on an exhaust-side slope of a piston crown surface.

According to a seventh aspect of the present invention, in the first to fifth aspects, a recess is provided on the exhaust-side slope of the piston crown.

An eighth invention is characterized in that, in the sixth or seventh invention, the recess is formed so as to extend from the end on the exhaust side in the circumferential direction of the piston.

According to a ninth aspect, in the sixth to eighth aspects, the engine uses the tumble flow generated in the cylinder to guide the injected fuel to the vicinity of the spark plug and perform stratified combustion. It is a direct injection type spark ignition engine,
The concave portion communicates with an upper end portion on the exhaust side of the cavity.

According to a tenth aspect of the present invention, fuel directly injected into a cylinder from a fuel injection valve is collected near an ignition plug by utilizing in-cylinder gas flow so as to be ignitable, and combustion is performed at a lean air-fuel ratio as a whole. In a direct injection type spark ignition engine,
The exhaust-side slope of the piston crown is further provided with a slope that becomes lower outward from a center line from the exhaust side to the intake side.

In an eleventh aspect based on the first to fifth aspects, the exhaust-side slope of the piston crown is further provided with a slope that becomes lower from the center line from the exhaust side to the intake side toward the outside. It is characterized by having.

A twelfth invention is characterized in that, in the tenth or eleventh invention, the top of the piston crown surface is inclined so as to become lower toward the outside.

According to a thirteenth aspect, fuel directly injected into a cylinder from a fuel injection valve is collected near a spark plug by utilizing in-cylinder gas flow to enable ignition, and combustion is performed at a lean air-fuel ratio as a whole. In a direct injection type spark ignition engine,
The engine uses a swirl flow generated in a cylinder and a shape of a cavity recessed in a piston crown surface to direct fuel injected near a spark plug to perform stratified combustion, and to perform in-cylinder direct injection spark ignition. The engine is characterized in that an exhaust-side slope of the crown surface of the piston is further provided with a slope that becomes lower as it goes in the direction of the swirl flow.

According to a fourteenth invention, in the first invention, the engine is a direct injection in-cylinder system in which the fuel is injected into the vicinity of a spark plug by utilizing the tumble flow generated in the cylinder to perform stratified combustion. A spark ignition engine, characterized in that a groove communicating with the cavity is provided on an exhaust-side slope of the piston crown.

According to a fifteenth aspect, in the fourteenth aspect,
The groove is provided on both sides with respect to a center line from the exhaust side to the intake side.

[0028]

According to the first aspect, the gap on the exhaust side is larger than the gap on the intake side.
When the piston approaches the compression top dead center, generation of a squish flow from the exhaust side to the intake side can be suppressed.

The squish flow from the exhaust side to the intake side impedes the gas flow that collects the injected fuel near the ignition plug during stratified charge combustion, and provides a uniform mixture even during homogeneous combustion. The gas flow is hindered, which causes deterioration of combustion stability during stratified combustion and homogeneous combustion. However, by applying the present invention, generation of a squish flow from the exhaust side to the intake side is suppressed. Therefore, it is possible to prevent the squish flow from deteriorating the combustion stability during the stratified combustion and the homogeneous combustion.

Further, if the exhaust side clearance is increased, the injected fuel overflows from the cavity and flows into the exhaust side, causing deterioration of combustion stability. However, by applying the second to fifth aspects of the present invention, This can prevent such a problem from occurring.

According to the sixth and seventh aspects of the present invention, since a recess is formed in the exhaust-side slope of the piston crown surface, a space is formed between the exhaust-side slope and the cylinder head at the compression top dead center, and squish The generation of flow can be suppressed. Here, if the recess is formed as in the eighth invention, the volume of the recess can be increased, and the occurrence of squish flow can be further suppressed. Applying the ninth invention,
If the recess and the cavity are partially communicated, the compressed gas does not pass through the narrow gap, and the generation of the squish flow can be further suppressed.

According to the eleventh and twelfth aspects, the squish flow is generated in a direction perpendicular to the direction from the exhaust side to the intake side, and the squish flow hinders gas flow in the cylinder. Can be suppressed.

According to the thirteenth to fifteenth aspects,
Since the squish flow is generated in the direction that enhances the gas flow in the cylinder, the injected fuel can be reliably collected near the ignition plug during stratified combustion, and the mixture is more homogeneous during homogeneous combustion. It is possible to improve the combustion stability during stratified combustion and homogeneous combustion.

[0034]

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

First, the case where the present invention is applied to a wall guide type direct injection type spark ignition engine will be described.

FIG. 1 shows a schematic configuration of an engine to which the present invention is applied. In the engine 1, a swirl flow (lateral vortex) generated in a combustion chamber 2 is injected into a cavity 6. The fuel is guided to the vicinity of the ignition plug 3 and the ignition plug 3
This is a so-called wall guide type direct injection type spark ignition engine that forms a ignitable mixture in the vicinity and enables lean combustion.

A pent roof type combustion chamber 2 is formed in the cylinder head 4, and a cavity 6 is formed in the crown surface of the piston 5 on the intake side corresponding to the pent roof type combustion chamber 2. Further, a high-pressure fuel injection valve 7 for injecting fuel into the cavity 6 obliquely downward with respect to the cavity 6 is disposed below the intake port 11, and a spark plug is provided substantially at the center of the pent roof type combustion chamber 2. 3 are arranged.

In the figure, 9 is an intake valve, 10 is an exhaust valve, and two intake ports 1 corresponding to the two intake valves.
Two exhaust ports 12 corresponding to one and two exhaust valves
(See FIG. 2). Here, intake port 1
In order to generate a tumble flow (vertical vortex) at the time of homogeneous combustion, 1 is provided at an angle higher than an intake port of an engine performing normal premixed combustion.

One of the two intake ports 11 has
A swirl control valve 13 is provided as a swirl flow generating means. When the swirl control valve 13 is closed, a swirl flow is generated in the cylinder by intake air flowing only from the other intake port 11. When the engine 1 performs stratified charge combustion, if the swirl control valve 13 is closed and fuel is injected in the compression stroke, the fuel spray injected into the cavity 6 is swirled by the swirl flow and the shape of the cavity 6.
The mixture is guided in the direction, and an ignitable rich air-fuel mixture can be formed near the ignition plug 3.

On the other hand, when the swirl control valve 13 is opened, a tumble flow as a vertical vortex is generated in the cylinder because the angle of the intake port 11 is raised. When the engine 1 performs the homogeneous combustion operation,
By opening the swirl control valve 13 in the intake stroke and injecting fuel while creating a tumble flow in the cylinder, a homogeneous air-fuel mixture is generated in the entire combustion chamber, and a homogeneous combustion operation can be performed.

Now, consider a situation in which the piston 5 approaches the compression top dead center.

In such a situation, the gap between the piston 5 and the cylinder head 4 decreases, and the gas in this gap is compressed and pushed out, and a squish flow is generated. However, when this squish flow is generated from the exhaust side toward the intake side, the swirl flow during stratified combustion is disturbed by the influence of the squish flow, and the injected fuel does not collect near the spark plug 3 and the combustion stability Causes a decrease. Further, even during homogeneous combustion, the tumble flow is obstructed, so that the mixing of the injected fuel and air does not proceed sufficiently, and the air-fuel mixture becomes non-uniform, which causes a reduction in combustion stability.

For this reason, in the engine shown in FIG. 1, the formation of the crown surface of the piston 5 as described below suppresses the generation of a squish flow from the exhaust side to the intake side, and the stratification occurs. The swirl flow during combustion and the tumble flow during homogeneous combustion are not hindered.

The shape of the piston 5 will be specifically described. As shown in FIG. 3, the piston 5 is left as a protrusion around the cavity 6 formed in the piston crown. Each of the projections is a flat inclined surface 15 on the intake side and an inclined surface 16 on the exhaust side, each of which is a flat surface, and a top portion 17 where both surfaces intersect.
(Ridge line or horizontal plane) and a conical surface 18 surrounding the periphery. As shown in FIG. 4, the exhaust side slope 16 of the piston crown surface and the upper surface of the combustion chamber 2 (cylinder head 4)
Of the piston 5 is set so that the gap L2 between the piston 5 and the cylinder head 4 is wider than the gap L1 between the intake side slope 15 and the cylinder head 4.

However, in this case, if the exhaust side gap L2 is too large, the fuel injected into the cavity 6 overflows outside the cavity 6. Therefore, the gap L2 is set to be larger than the gap L1 within a range where the fuel injected into the cavity 6 does not overflow. Specifically, the injection at the time of high rotation in the stratified combustion operation in which the fuel spray is most likely to spill. At the timing (injection timing set on the advance side), at the piston position when the upper end of the fuel spray reaches the cavity 6, a straight line L connecting the point where the side surface height of the cavity 6 is the highest and the fuel injection point is The angle α between the horizontal plane H and the horizontal plane H is set to be smaller than the angle β between the upper end of the spray and the horizontal plane H.

Α <β (1) Here, assuming that the mounting angle of the fuel injection valve 7 is θ and the spray angle is γ, the angle β between the upper end of the spray and the horizontal plane H is β = θ −γ / 2 (2) Therefore, the exhaust-side gap L2 is set to be α that satisfies α <θ−γ / 2 (3).

By forming the piston 5 in such a shape, the squish flow generated by the exhaust-side squish area is weakened, so that the gas flow is not hindered. Therefore, the combustion spray can easily reach the vicinity of the ignition plug under the stratified combustion condition, and under the homogeneous combustion condition, the air-fuel mixture can be evenly distributed to the exhaust side by the gas flow, and the combustion stability can be improved.

Since the exhaust side gap L2 is set so as to satisfy the above relational expression (1) or (3),
The injected fuel does not overflow to the exhaust side, so that the amount of fuel collected near the spark plug is reduced and the combustion stability is not deteriorated.

Here, the exhaust-side gap L2 is made larger than the intake-side gap L1 by changing the shape of the piston crown surface, but the exhaust-side gap L2 is changed by changing the shape on the cylinder head side. It may be larger than the intake side gap L1. In this case as well, the generation of a squish flow that inhibits gas flow in the cylinder can be similarly suppressed.

Further, the piston 5 may have the following shape.

In the example shown in FIG. 6, a concave portion (volume) 21 is provided between the exhaust side slope 16 of the piston crown surface and the cylinder head 4, leaving a ridgeline at the boundary with the cavity 6. By providing such a concave portion 21, when the piston 5 reaches the compression top dead center, the exhaust side slope 1 on the exhaust side.
Since a space is formed between the cylinder head 6 and the cylinder head 4, it is difficult to generate a squish flow, and the same operation and effect as in the previous embodiment can be obtained.

In the example shown in FIG.
1 is provided in parallel with the top portion 17 of the piston crown surface, but as shown in FIG. 7, extends in the circumferential direction of the piston 5 from the end on the exhaust side, not in parallel with the ridge line, and extends to the side of the cavity 6. It may be formed. Thereby, the volume of the concave portion 21 'can be made larger than that of the example shown in FIG.
The squish flow can be further suppressed.

In the piston shown in FIG. 8, the slope S on the exhaust-side slope 16 of the piston crown surface decreases from the center line C from the intake side to the exhaust side toward the outside.
1 is further provided. Further, in the example shown in FIG. 9, a slope S <b> 1 that becomes lower from the center line C going from the intake side to the exhaust side toward the outside is provided.
Further, a slope S2 is provided so that 7 becomes lower toward the outside, and both end portions of the top portion 17 are dropped.

With such a shape, the squish flow generated by the exhaust side squish area is, as shown in FIG. 10, a center line C from the intake side to the exhaust side.
, The squish flow toward the cavity 6 can be weakened. In particular, in the example shown in FIG. 9, the squish flow toward the inside of the cavity 6 is further suppressed by positively flowing the squish flow toward the outside of the cavity 6 by the inclination S2.

Further, in the piston shown in FIG. 11, the slope S which becomes lower in the same direction as the swirl direction is provided between the exhaust-side piston crown surface and the pent roof surface on the head upper surface.
3 are provided. Thereby, as shown in FIG. 12, the squish flow F generated by the exhaust side squish area
2 goes in the same direction as the swirl flow F1,
The squish flow enhances the swirl flow created at the intake port. Therefore, under the stratified combustion condition, the fuel spray easily reaches the vicinity of the spark plug, and the combustion stability is improved. Under the homogeneous combustion condition, the squish flow is directed laterally with respect to the center line C from the intake side to the exhaust side. As a result, since the tumble flow is not hindered, it is possible to generate a homogeneous mixture in which the mixture can be distributed to the exhaust side.

Next, the case where the present invention is applied to an in-cylinder direct injection type spark ignition engine of the air guide type will be described.

FIGS. 13 and 14 show a schematic configuration of another engine to which the present invention is applied.
Unlike the engine shown in FIG. 2, the so-called air-guide direct injection spark ignition of the so-called air guide system which directly guides the fuel to the vicinity of the ignition plug by the tumble flow generated by the intake port and the piston cavity shape to improve the stratified combustion stability. Engine.

The same components as those of the engine shown in FIGS. 1 and 2 are denoted by the same reference numerals and description thereof will be omitted. Only different components will be described. Tumble control valves 20 as tumble flow generating means
Is provided. This tumble control valve 2
When 0 is closed, the lower half of the intake port 11 is closed,
When the intake air flows only from the upper half of the intake port 11, a tumble flow is generated in the cylinder. Then, the injected fuel spray is collected in the vicinity of the ignition plug 3 by the tumble flow, and a stable stratified combustion operation can be performed.

As shown in FIG. 15, the piston 5 has a convex portion around the cavity 6 formed in the piston crown, and the convex portion is formed on the inclined surface 15 on the intake side and on the exhaust side. It is composed of an inclined surface 16, an apex 17 (ridgeline or horizontal plane) where the two intersect, and a conical surface 18 surrounding the periphery.

Here, in order to suppress the squish flow generated at the compression top dead center and prevent the tumble flow from being disturbed by the influence of the squish flow, as shown in FIG. The gap L2 between the side slope 16 and the cylinder head 4 is set to be larger than the gap L1 between the intake slope 15 and the cylinder head 4. Here, if the exhaust-side gap L2 is too large, the effect of receiving the fuel spray in the combustion chamber of the piston concave portion is reduced, so that the height of the exhaust-side surface of the cavity 6 is limited to a value at which the fuel spray does not overflow from the cavity 6. Specifically, as shown in FIG.
The height H2 of the exhaust side surface (the height of the exhaust side end E2 of the cavity 6 viewed from the bottom B of the cavity 6) is equal to the height of the intake side surface (the exhaust end E1 of the cavity 6 viewed from the bottom B of the cavity 6). Is set to be larger than H1) H1.

H2> H1 (4) By forming the piston crown surface in this way, the squish flow generated by the exhaust-side squish area is weakened, and the tumble flow is not hindered. In this case, the combustion spray easily reaches the vicinity of the ignition plug, and the combustion stability is improved. Further, under the homogeneous combustion conditions, the air-fuel mixture can be evenly distributed to the exhaust side by the tumble flow, and a homogeneous air-fuel mixture can be generated, thereby improving the combustion stability. Since L2 is set so as to satisfy the above relational expression (4), the injected fuel does not overflow from the cavity 6 and collect near the spark plug, so that the combustion stability does not deteriorate.

Although the exhaust-side gap L2 is made larger than the intake-side gap L1 by changing the shape of the piston crown surface, the exhaust-side gap L2 is changed by changing the shape on the cylinder head side. It can be made larger than the intake side gap L1, and in this case also, the generation of squish flow can be suppressed.

The piston may be constructed as follows.

In the piston shown in FIG. 18, a concave portion 22 is provided on the exhaust side slope 16 of the piston crown surface so that the exhaust side end of the cavity 6 remains. In the piston shown in FIG. 19, a recess 22 ′ having the same width as the cavity 6 and connecting to the upper end of the cavity 6 on the exhaust side is provided.

By providing such recesses 22 and 22 ', a space is created between the inclined surface 16 and the cylinder head 4 on the exhaust side, so that a squish flow is less likely to be generated, as in the previous embodiment. Combustion stability can be ensured. In particular, in the example shown in FIG. 19, since the cavity 6 communicates with the concave portion 22 ′, the gas compressed on the exhaust side does not pass through the narrow gap, so that generation of a strong squish flow is suppressed. Can be. FIG.
Also in the example shown in FIG. 9, the height H2 ′ on the exhaust side of the cavity 6 is set so as to be higher than the height H1 on the intake side, and the injected fuel overflows from the cavity 6 to the recess 22 ′. It does not flow.

In the examples shown in FIGS. 20 and 21, the exhaust-side slope 16 of the piston crown is further provided with a slope S4.
It becomes lower as going outward from the center line C from the intake side to the exhaust side. Further, in the example shown in FIG. 21, the top 17 of the piston crown surface has an inclination S5,
Is set lower as going outward.

As a result, the squish flow generated by the exhaust-side squish area is directed outward with respect to the center line C from the intake side to the exhaust side as shown in FIG. The flow can be weakened. In particular, in the example shown in FIG. 21, the squish flow can be positively guided to the outside of the cavity 6 by dropping both side ends of the top 17, and the squish flow directly flowing into the cavity 6 can be further suppressed. .

In the example shown in FIG. 23, grooves G communicating with the cavity 6 are provided on both sides of a center line C from the intake side to the exhaust side on the exhaust side slope 16 of the piston crown.
By providing such a groove G, as shown in FIG. 24, the squish flow F3 generated by the exhaust-side squish area is directed in the same direction as the tumble flow F4, and is formed at a port or the like by the squish flow. Tumble flow is enhanced. Therefore, under the stratified combustion condition, the fuel spray easily reaches the vicinity of the spark plug 3, and under the homogeneous combustion condition, the generation of the homogeneous air-fuel mixture is promoted by the enhanced tumble flow. Can be secured.

Here, the groove is provided in parallel with the center line C. However, as shown in FIG. 25, the groove is
You may provide so that the space | interval of one groove | channel may become wide. This allows the squish flow F3 'to act on the tumble flow F4 so as to be directed to the spark plug, as shown in FIG. 26, and the injected fuel can be more effectively collected near the spark plug. .

Although the embodiments of the present invention have been described above, the above-described configuration shows only a part of the configuration to which the present invention is applied, and the scope of the present invention is not limited to the above-described configuration. For example, the configuration for generating the swirl flow or the tumble flow in the cylinder is not limited to the above configuration, and may be generated by another configuration.

It is also possible to adopt a configuration in which the above configurations are combined. For example, the gap L2 on the exhaust side is made larger than the gap L1 on the intake side, and a recess is provided on the exhaust side. It is also possible to have a slope that regulates the direction of the camera. Thereby, the interference between the squish flow and the in-cylinder gas flow can be further prevented, and the combustion stability can be further improved.

[Brief description of the drawings]

FIG. 1 is a view of a wall-guided direct-injection spark ignition engine to which the present invention is applied, as viewed from the side of a cylinder.

FIG. 2 is a view of the engine as viewed from above a cylinder.

3A and 3B show a piston shape of the engine, wherein FIG. 3A is a plan view and FIG. 3B is a longitudinal sectional view.

FIG. 4 is a view for further explaining the shape of the piston.

FIG. 5 is a view for further explaining the shape of the piston.

FIGS. 6A and 6B show another example of a piston shape according to the present invention, wherein FIG. 6A is a longitudinal sectional view and FIG. 6B is a plan view.

7A and 7B show another example of the piston shape according to the present invention, wherein FIG. 7A is a longitudinal sectional view and FIG. 7B is a plan view.

8A and 8B show another example of the piston shape according to the present invention, wherein FIG. 8A is a plan view, and FIG. 8B is a sectional view taken along line XX of FIG.

FIGS. 9A and 9B show another example of the piston shape according to the present invention, wherein FIG. 9A is a plan view and FIG. 9B is a sectional view taken along the line YY of FIG. 9A.

FIG. 10 is a diagram for explaining a state of a squish flow generated by the piston shape.

11A and 11B show another example of the piston shape according to the present invention, wherein FIG. 11A is a plan view, and FIG. 11B is a ZZ of FIG.
3 shows a cross section.

FIG. 12 is a view for explaining a state of a squish flow generated by the piston shape.

FIG. 13 is a diagram of an in-cylinder direct injection type spark ignition engine of an air guide type to which the present invention is applied, as viewed from the side of the cylinder.

FIG. 14 is a view of the engine as viewed from above a cylinder.

FIG. 15 shows the shape of the piston.
(A) is a plan view, and (b) is a longitudinal sectional view.

FIG. 16 is a view for further explaining the shape of the piston.

FIG. 17 is a view for further explaining the piston shape.

FIGS. 18A and 18B show another example of the piston shape according to the present invention, wherein FIG. 18A is a longitudinal sectional view and FIG.

19A and 19B show another example of a piston shape according to the present invention, wherein FIG. 19A is a longitudinal sectional view, and FIG. 19B is a plan view.

FIGS. 20A and 20B show another example of the piston shape according to the present invention, wherein FIG. 20A is a plan view, and FIG.
It is XX sectional drawing.

FIGS. 21A and 21B show another example of the piston shape according to the present invention, wherein FIG. 21A is a plan view, and FIG.
It is a YY sectional view.

FIG. 22 is a view for explaining a state of a squish flow generated by the piston shape.

FIGS. 23A and 23B show another example of the piston shape according to the present invention, wherein FIG. 23A is a plan view, and FIG.
It is a ZZ sectional view.

24A and 24B are views for explaining a state of a squish flow generated by the piston shape, where FIG.
(B) is a longitudinal sectional view.

25A and 25B show another example of a piston shape according to the present invention, wherein FIG. 25A is a plan view, and FIG.
It is a ZZ sectional view.

26A and 26B are views for explaining a state of a squish flow generated by the piston shape, where FIG.
(B) is a longitudinal sectional view.

27A and 27B are diagrams for explaining the wall guide method, wherein FIG. 27A is a diagram viewed from the side of the cylinder, and FIG. 27B is a diagram viewed from above the cylinder.

FIGS. 28A and 28B are views for explaining the air guide system, wherein FIG. 28A is a view from the side of the cylinder, and FIG. 28B is a view from above the cylinder.

FIG. 29 shows a swirl flow generated in the combustion chamber.

FIG. 30 shows a state in which a swirl flow and a squish flow interfere with each other.

FIG. 31 shows a tumble flow generated in a combustion chamber.

FIG. 32 shows how a tumble flow and a squish flow interfere with each other.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Combustion chamber 3 Spark plug 4 Cylinder head 5 Piston 6 Cavity 7 Fuel injection valve 8 Combustion chamber 11 Intake port 13 Swirl control valve 15 Intake side slope 16 Exhaust side slope 20 Tumble control valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02F 1/24 F02F 1/24 D 3/26 3/26 A F02M 61/14 310 F02M 61/14 310A 61 / 18 360 61/18 360J

Claims (15)

[Claims] An in-cylinder direct injection system in which fuel directly injected into a cylinder from a fuel injection valve is collected near an ignition plug by utilizing in-cylinder gas flow and ignitable, and combustion is performed at a lean air-fuel ratio as a whole. In the spark-ignition engine, a gap between the exhaust-side slope of the piston crown and the cylinder head is configured to be larger than a gap between the intake-side slope of the piston crown and the cylinder head. Injection spark ignition engine. 2. A gap between the exhaust-side slope of the piston crown and the cylinder head is provided within a range in which fuel injected into the cavity does not overflow from the cavity and flow into the exhaust side. 2. The apparatus according to claim 1, wherein the gap is larger than a gap with the head.
In-cylinder direct-injection spark ignition engine according to item 1. 3. A gap between the exhaust side slope of the piston crown surface and the cylinder head is formed by a straight line connecting the upper end of the exhaust side of the cavity and the fuel injection point at the piston position when the upper end of the fuel spray reaches the cavity. 3. An in-cylinder direct injection spark ignition engine according to claim 2, wherein an angle formed between the fuel spray and the horizontal plane is set to be smaller than an angle formed between the upper end of the fuel spray and the horizontal plane. 4. The clearance between the exhaust side slope of the piston crown surface and the cylinder head is represented by the following equation: α <θ−γ / 2, where α: piston position when the upper end of the fuel spray reaches the cavity. The angle formed between a horizontal plane and a straight line connecting the upper end of the cavity on the exhaust side to the fuel injection point and the horizontal plane are set so as to satisfy: θ: mounting angle of the fuel injection valve γ: spray angle of the fuel injection valve. An in-cylinder direct injection spark ignition engine as described in the above. 5. The clearance between the exhaust-side slope of the piston crown and the cylinder head is set such that the height of the exhaust-side surface of the cavity is higher than the height of the intake-side surface. 3. The in-cylinder direct injection spark ignition engine according to 2. 6. In-cylinder direct injection in which fuel directly injected from a fuel injection valve into a cylinder is collected near an ignition plug by utilizing in-cylinder gas flow and ignitable, and combustion is performed at a lean air-fuel ratio as a whole. An in-cylinder direct injection type spark ignition engine, characterized in that a recess is provided on the exhaust side slope of the piston crown surface. 7. An in-cylinder direct injection spark ignition engine according to claim 1, wherein a concave portion is provided on an exhaust-side slope of said piston crown surface. 8. The in-cylinder direct injection spark ignition engine according to claim 6, wherein the recess is formed so as to extend in a circumferential direction of the piston from an end on the exhaust side. 9. An in-cylinder direct injection spark ignition engine of a type in which fuel injected by utilizing a tumble flow generated in a cylinder is guided to a vicinity of an ignition plug to perform stratified combustion, and wherein the recess is provided. The in-cylinder direct injection spark ignition engine according to any one of claims 6 to 8, wherein the in-cylinder direct injection type spark ignition engine communicates with an upper end portion on the exhaust side of the cavity. 10. In-cylinder direct injection in which fuel directly injected from a fuel injection valve into a cylinder is collected near an ignition plug by using in-cylinder gas flow and ignitable, and combustion is performed at a lean air-fuel ratio as a whole. An in-cylinder direct-injection engine, wherein the exhaust-side slope of the piston crown is further provided with a slope that becomes lower outward from a center line from the exhaust side toward the intake side. Spark ignition engine. 11. The exhaust-side slope of the piston crown is further provided with a slope which becomes lower from the center line from the exhaust side to the intake side toward the outside.
6. The in-cylinder direct injection spark ignition engine according to any one of claims 1 to 5. 12. The in-cylinder direct injection spark ignition engine according to claim 10, wherein the top of the crown surface of the piston is inclined so as to become lower toward the outside. 13. In-cylinder direct injection in which fuel directly injected from a fuel injection valve into a cylinder is collected near an ignition plug by using in-cylinder gas flow and ignitable, and combustion is performed at a lean air-fuel ratio as a whole. In the spark ignition engine, the engine uses a swirl flow generated in the cylinder and a shape of a cavity recessed in a piston crown surface to guide fuel injected near the ignition plug to perform stratified combustion. An in-cylinder direct injection spark ignition engine, characterized in that the exhaust-side slope of the piston crown surface is further provided with a slope that becomes lower as it proceeds in the direction of swirl flow. . 14. An in-cylinder direct injection spark ignition engine of a type in which fuel injected by utilizing a tumble flow generated in a cylinder is guided to a vicinity of an ignition plug to perform stratified combustion. The in-cylinder direct injection spark ignition engine according to claim 1, wherein a groove communicating with the cavity is provided on an exhaust-side slope of the surface. 15. The groove according to claim 1, wherein said groove is provided on both sides of a center line from the exhaust side to the intake side.
5. A direct injection type spark ignition engine according to item 4.