JP2004324563A - Direct-injection internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct-injection internal combustion engine which conducts a favorable combustion. <P>SOLUTION: A cylinder head 2a, a cylinder block 2b, an intake valve 7, an exhaust valve 8, a fuel-injection valve 11, a spark plug 12, and a piston 3 having a cavity 4 on the crown are provided in the internal combustion engine. Shape of the injected fuel from the fuel-injection valve 11 is made almost invariant under conditions of a stratified light-load operation, and a stratified heavy-load operation. In the condition of the stratified light-load operation, injected fuel is directly ignited, while in the condition of the stratified heavy-load operation, the fuel is ignited after being shot to the cavity 4. Thus, a favorable combustion is performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to a direct injection type internal combustion engine.
[0002]
[Prior art]
Fuel is injected in a hollow conical shape from the fuel injection valve arranged at the center of the cylinder toward the piston, and the spray collides with the side surface of the cavity provided in the piston, and rises above the cavity via the bottom surface of the cavity. Patent Literature 1 discloses a direct injection internal combustion engine that performs stratified combustion operation by igniting fuel.
[0003]
[Patent Document 1]
JP-A-11-82028
[0004]
[Problems to be solved by the invention]
However, in the above invention, since the size of the stratified mixture formed on the cavity is always constant irrespective of the size of the load, the range of the load condition in which a good stratified combustion operation can be performed is narrow. There's a problem.
[0005]
An object of the present invention is to expand the load condition range in which stratified charge combustion operation can be favorably performed at low cost.
[0006]
[Means for solving the problem]
For this reason, in the present invention, the fuel spray during the stratified charge combustion operation has a substantially constant hollow conical shape, and the injected fuel is directly ignited under the stratified low load operation condition, and the piston cavity is formed under the stratified high load operation condition. It ignites the fuel that has risen via.
[0007]
The “substantially constant hollow cone shape” means that the opening angle of the injection, that is, the apex angle of the cone is substantially constant. That is, the present invention does not include a special variable mechanism for changing the opening angle of the injection, and the fuel injection in which the opening angle of the injection hardly changes even by the fuel injection amount or the fuel injection timing (in-cylinder pressure during fuel injection). Use a valve.
[0008]
[Action and effect]
According to the present invention, a stratified low-load operation for burning a relatively small air-fuel mixture and a stratified high-load operation for burning a relatively large air-fuel mixture are realized by a fuel injection valve having a fixed spray shape. Can be expanded at low cost.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows the configuration of the first embodiment of the present invention. The combustion chamber 1 is defined by a cylinder head 2a, a cylinder block 2b, and a piston 3. A gasket 14 is interposed between the cylinder head 2a and the cylinder block 3. A circular cavity 4 is provided in the center of the crown surface of the piston 3. The inner peripheral surface (side surface) 4a of the cavity 4 and the flat bottom surface 4c are smoothly connected by a curved surface 4b, and the inner peripheral surface 4a of the cavity is inclined inward. The cavity bottom surface 4c is a flat surface having no irregularities, and is perpendicular to the piston axial direction. Thus, the cavity 4 has a conical shape with the top cut off. The intake port 5 sends air necessary for combustion to the combustion chamber 1 through an intake valve 7 operated by an intake valve cam 9. The exhaust port 6 discharges exhaust gas burned in the combustion chamber 1 via an exhaust valve 9 operated by an exhaust valve cam 10. The fuel injection valve 11 provided in the cylinder head 2a is disposed substantially coaxially with the piston 4 (on the cylinder center axis) above the combustion chamber 1 and has a plurality of injection holes of the same shape for injecting fuel. . The fuel injected from the plurality of injection holes toward the piston 3 forms one hollow conical spray as a whole. The ignition plug 12 ignites the fuel injected by the combustion injection valve 11. The engine control unit 13 controls the timing of fuel injection from the combustion injection valve 11 and the timing of ignition of fuel by the spark plug 12 according to operating conditions.
[0010]
FIG. 4 shows the relationship between the operating conditions based on the load and the rotation and the combustion method used in the first embodiment. Among all the operating conditions, the region of relatively low load and low rotation is set as the stratified combustion operation region, and in this region, the stratified combustion that generates the air-fuel mixture in a part of the combustion chamber 1 is performed. In the stratified combustion operation region, stratified low-load operation is performed with a short interval from fuel injection to ignition during low load operation conditions, and stratified with a long interval from fuel injection to ignition during high load operation conditions. Perform high-load operation. The higher load and higher rotation side than the stratified combustion operation region is a homogeneous combustion operation region. In this region, fuel is injected from the fuel injection valve 11 in an intake stroke of sucking air from the intake port 5 into the combustion chamber 1, Homogeneous combustion that produces a homogeneous mixture of air and fuel is performed in the entire combustion chamber 1.
[0011]
First, the injection and the air-fuel mixture under the above-described stratified low-load operation condition will be described with reference to FIG.
[0012]
The fuel injection pressure under the stratified low load operation condition is set to a relatively low pressure, and the fuel injection timing is set in the latter half of the compression stroke and near the compression top dead center. Since the amount of fuel injected at this time is small, the injection ends before the tip of the hollow conical spray reaches the piston 3, and immediately thereafter, the ignition by the spark plug 12 is performed. More specifically, the ignition timing is set so that the ignition is performed before the tip of the hollow conical spray reaches the piston 3. With the above settings, the size of the air-fuel mixture at the ignition timing is relatively small.
[0013]
Note that the injection opening angle of the fuel injection valve 11 is set to a relatively wide angle, for example, about 60 to 80 degrees, and the fuel spray passes through the discharge gap position of the ignition plug 12 or in the vicinity of the discharge gap. The timing can be set (immediately after the end of fuel injection). On the other hand, in order to set the above ignition timing using a fuel injection valve having a narrow injection opening angle, it is necessary to protrude the tip of the ignition plug into the combustion chamber for a long time, and to ensure the durability of the ignition plug. Becomes difficult.
[0014]
Next, the injection and the air-fuel mixture under the stratified high-load operation condition will be described with reference to FIG.
[0015]
The fuel injection pressure in the stratified high load operation condition is set to a relatively high pressure, and the fuel injection timing is set in the latter half of the compression stroke and more advanced than the fuel injection timing in the stratified low load operation condition. Since the spray shape at this time is substantially the same as the spray shape under the stratified low load operation condition (that is, the injection opening angle is wide), the fuel that has reached the piston 3 collides with the cavity inner peripheral surface 4a. The fuel after the collision proceeds below the cavity 4 along the cavity inner peripheral surface 4a, the traveling direction is bent by the cavity curved surface 4b, and proceeds radially inward of the cavity 4 along the cavity bottom surface 4c. It collides at the center of 4 c and rises above the cavity 4. Such a flow of the fuel proceeds while entraining the surrounding air, and a circulating flow of the air-fuel mixture is generated in a space between the cylinder head 2a and the piston 3. Due to this circulation flow, mixing of the fuel and air is promoted, and a substantially homogeneous mixed air mass is formed inside the cavity 4 and in the space above the cavity. The ignition plug 12 ignites the mixture. With the above settings, the size of the air-fuel mixture at the ignition timing becomes relatively large.
[0016]
When a fuel injection valve having a narrow injection opening angle is used, the fuel that has reached the piston 3 collides with the cavity bottom surface 4c, and a circulating flow that turns in a direction opposite to the above-described circulating flow is generated. In this case as well, an air-fuel mixture is formed inside the cavity 4 and in the space above the cavity 4, and the air-fuel ratio of the air-fuel mixture at the center (near the ignition plug 12) tends to be lean. In contrast, in the air-fuel mixture of the present embodiment, a distribution is obtained in which the internal air-fuel ratio is almost uniform or the air-fuel ratio in the center is slightly deeper and the air-fuel ratio is thinner in the peripheral portion, and good ignition and stable combustion are obtained. For this reason, for example, a large amount of EGR can be introduced, and operation with less generation of NOx can be performed.
[0017]
Next, the injection and the mixture in the homogeneous mixture combustion will be described.
[0018]
In the homogeneous operation, fuel is injected from the fuel injection valve 11 at a relatively wide angle in the latter half of the intake stroke as in the stratified operation, so that the injected fuel also diffuses outside the cavity 4 and the air and fuel are sufficiently mixed. A homogeneous air-fuel mixture near the stoichiometric air-fuel ratio is generated in the combustion chamber 1. For this reason, combustion with good fuel efficiency and low exhaust emission is possible.
[0019]
The effects of the first embodiment will be described.
[0020]
Under the stratified low load operation condition, the fuel injected from the fuel injection valve 11 is directly ignited. Under the stratified high load operation condition, the fuel collides with the cavity inner peripheral surface 4a and then rises above the cavity 4 via the cavity bottom surface 4c. The fuel injection valve 11 has a fixed spray shape (fixed injection opening angle) between a stratified low-load operation for burning a relatively small air-fuel mixture and a stratified high-load operation for burning a relatively large air-fuel mixture. , And the stratified combustion operation range can be expanded at low cost.
[0021]
Further, under the stratified low load operation condition, the ignition is performed before the tip of the fuel injection mist contacts the crown surface of the piston 3, so that the fuel can be burned without adhering to the piston 3, and the unburned HC is generated. The amount can be reduced. In addition, since the air-fuel mixture is burned in a state in which a heat insulating layer (air layer) is interposed between the air-fuel mixture and the piston 3, cooling loss can be reduced. In the stratified high-load operation condition, the fuel adheres to the cavity 4 of the piston 3. At this time, a circulating flow of the air-fuel mixture is generated in the cavity 4, and the gas flow vaporizes the adhered fuel. Is promoted, so that the unburned HC generation amount does not increase rapidly during stratified high load operation.
[0022]
Further, the fuel injection valve 11 has a plurality of injection holes each forming a solid spray, and the fuel injected from the plurality of injection holes forms a hollow conical spray. The spray shape hardly changes depending on the fuel injection amount and the fuel injection timing (in-cylinder pressure at the time of fuel injection). Therefore, the fuel spray can reliably reach a desired position (at or very near the discharge gap position of the ignition plug 12 under the stratified low load operation condition, and the cavity inner peripheral surface 4a under the stratified high load operation condition).
[0023]
Also, since the cavity inner peripheral surface 4a is inclined inward so that the cavity 4 has a substantially conical shape, the collision angle between the cavity inner peripheral surface 4a and the fuel spray during stratified high load operation becomes small (a sharp angle). , Most of the fuel travels below the cavity 4. When the inner circumferential surface 4a of the cavity is inclined parallel or slightly outward to the cylinder center axis, the amount of fuel spilled from the cavity 4 slightly increases, but the machining of the cavity 4 becomes easier.
[0024]
Further, since the cavity bottom surface 4c is formed on a surface having no irregularities, the fuel (air-fuel mixture) collides with each other at the center of the cavity bottom surface 4c during the stratified high load operation, and the flow rising above the cavity 4 is effectively performed. Is raised. Further, when the air-fuel mixture collides with each other, an appropriate turbulence occurs, and the air and the fuel are mixed well.
[0025]
Further, since the fuel injection timing in the stratified high-load operation condition is more advanced than the fuel injection timing in the stratified low-load operation condition, the combustion start timing in the stratified low-load operation is set near the compression top dead center to reduce the fuel consumption. On the other hand, at the time of stratified high-load operation, a sufficient mixing time of air and fuel by circulating flow can be secured.
[0026]
In addition, since the combustion injection pressure under the stratified high-load operation condition is higher than the combustion injection pressure under the stratified low-load operation condition, the penetration of the fuel spray during the stratified low-load operation is reduced to reduce the mixed air mass. On the other hand, a strong circulating flow can be created by increasing the penetration of the fuel spray during stratified high load operation. It is more preferable to increase the fuel injection pressure as the load increases within the stratified high load operation condition.
[0027]
FIG. 5 shows a second embodiment. Here, differences from the first embodiment will be described. When the spark plug 12 cannot be installed near the fuel injection valve 11 due to the structural limitation of the cylinder head 2, the spark plug 12 is mounted at a position distant from the fuel injection valve 11, and the bottom surface of the cavity far from the spark plug 12. The cavity bottom surface 4c is inclined so that the bottom of the cavity 4c2 is shallower than the cavity bottom surface 4c1 close to the spark plug 12, and the inclination of the cavity inner peripheral surface 4a2 far from the ignition plug 12 is changed to the cavity inner peripheral surface 4a1 close to the ignition plug 12. And the inner peripheral surfaces 4a1 and 4a2 are smoothly connected. In the stratified high-load operation condition, a fuel-air mixture suitable for combustion is generated near the ignition plug 12 by injecting fuel into the cavity inner peripheral surface 4a.
[0028]
Effects in the second embodiment will be described.
[0029]
In the second embodiment, even when the ignition plug 12 cannot be installed in the vicinity of the fuel injection valve 11 in the first embodiment, the operation becomes stable even when a large amount of EGR is introduced under the stratified high load operation condition as in the first embodiment. The combustion can be performed, and the combustion with low NOx and good fuel efficiency can be performed.
[0030]
FIG. 6 shows a third embodiment. Here, differences from the first embodiment will be described. In the third embodiment, when the fuel injection valve 11 cannot be set substantially parallel to the axial direction of the piston 3, the fuel injection valve 11 is attached with an inclination to the axial direction of the piston 3, A multi-hole injection valve capable of injecting fuel injection asymmetrically with respect to the axial direction of the fuel injection valve 11 is used. Thereby, the fuel injected from the fuel injection valve 11 has a hollow conical shape that is substantially symmetric with respect to the piston 3.
[0031]
The effect of the third embodiment will be described.
[0032]
In the third embodiment, even when the fuel injection valve 11 cannot be set substantially parallel to the axial direction of the cylinder 4 in the first embodiment, the shape of the fuel injection is substantially symmetric with respect to the piston 3. Since the conical shape can be used, the unburned HC and the cooling loss can be reduced under the stratified low-load operation condition as in the first embodiment, and the combustion with good fuel efficiency and low exhaust emission can be realized. Under the conditions, stable combustion can be performed even when a large amount of EGR is introduced, and combustion with low NOx and high fuel efficiency can be performed.
[0033]
FIG. 7 shows a fourth embodiment. Here, differences from the first embodiment will be described. When the increase control of the fuel injection pressure according to the increase in the load is not performed under the stratified high load operation condition, the fuel injection period is extended with the increase in the load, so that all the sprays may collide with the cavity inner peripheral surface 4a. May not be possible. In this case, the spray in the latter half of the period collides with the cavity curved surface 4b, and the collision angle becomes close to a right angle, so that the fuel after collision does not proceed in a certain direction. In such a state, the motion of the spray is not converted into a circulating flow.
[0034]
Therefore, in the fourth embodiment, when all the sprays cannot collide with the inner surface 4a of the cavity, the fuel injection is divided into two times, and the spray by the first injection is made to collide with the inner surface 4a of the cavity. While the same circulating flow as in the first embodiment is generated, the spray generated by the second injection is caused to collide with the cavity bottom surface 4c to generate the circulating flow in the opposite direction. As a result, an air-fuel mixture is generated near the center of the cavity by the first half injection, and an air-fuel mixture is generated near the inner peripheral surface of the cavity by the second half injection. As a result, one large air-fuel mixture is generated in the cavity as a whole. . Gas flows in different directions are generated to promote mixing of fuel and air, resulting in a good combustible gas mixture. In the fourth embodiment, two injections are performed from the fuel injection valve. However, a plurality of injections may be performed in order to generate an air-fuel mixture optimal for combustion.
[0035]
FIG. 8 shows the relationship between the operating conditions for the load and rotation and the combustion method used in the fourth embodiment. The high-load side of the stratified high-load operation condition in which all sprays cannot collide with the cavity inner peripheral surface 4a is defined as a multiple injection operation region.
[0036]
The effect of the fourth embodiment will be described.
[0037]
According to the fourth embodiment, even when the fuel injection pressure increase control according to the load increase is not performed under the stratified high load operation condition, a large mixed air mass is formed in the cavity by performing the injection multiple times. Can be generated. In addition, since circulating flows in different directions can be generated by a plurality of fuel injections, turbulence occurs in the cavity, and the mixing of the injected fuel and air can be promoted, as in the first embodiment. Even when a large amount of EGR is introduced, stable combustion can be performed, and combustion with low NOx and good fuel efficiency can be performed.
[0038]
The present invention is not limited to the above-described embodiment, but includes various modifications and improvements that can be made within the scope of the technical idea.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a first embodiment of the present invention.
FIG. 2 shows injection and air-fuel mixture behavior under a stratified low-load operation condition of the first embodiment.
FIG. 3 shows injection and mixture behavior under a stratified high load operation condition of the first embodiment.
FIG. 4 is a relationship diagram between operating conditions and a combustion method according to the first embodiment.
FIG. 5 shows injection and mixture behavior of the second embodiment.
FIG. 6 shows the injection and air-fuel mixture behavior of the third embodiment.
FIG. 7 shows the injection and air-fuel mixture behavior on the high load side under the stratified high load operation condition of the fourth embodiment.
FIG. 8 is a diagram illustrating a relationship between operating conditions and a combustion method according to a fourth embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Combustion chamber 2a Cylinder head 2b Cylinder block 3 Piston 4 Cavity 5 Intake port 6 Exhaust port 7 Intake valve 8 Exhaust valve 9 Intake cam 10 Exhaust cam 11 Fuel injection valve 12 Ignition plug 13 Engine control unit 14 Gasket

Claims (9)

A fuel injection valve disposed on or near the cylinder center axis,
A spark plug for igniting the fuel,
A piston provided with a cavity defined by a bottom surface and side surfaces substantially at the center of the crown surface,
The fuel injection valve injects fuel into a substantially constant hollow conical shape during the compression stroke in the stratified combustion operation region,
The ignition plug directly ignites the fuel injected from the fuel injector under a stratified low-load operation condition in the stratified combustion operation region, and ignites the cavity under a stratified high-load operation condition in the stratified combustion operation region. An in-cylinder direct injection internal combustion engine, which ignites fuel rising above the cavity via a bottom surface of the cavity after colliding with a side surface. The in-cylinder direct injection internal combustion engine according to claim 1, wherein, under the stratified low load operation condition, the ignition is performed before the tip of the fuel injection mist contacts the piston crown surface. The fuel injection valve has a plurality of injection holes each forming a solid spray, and fuel injected from the plurality of injection holes forms the hollow conical spray. Item 3. An in-cylinder direct injection internal combustion engine according to item 1 or 2. The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 3, wherein a side surface of the cavity is inclined inward so that the cavity has a substantially conical shape. The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 4, wherein the bottom surface of the cavity is formed on a surface without irregularities. The in-cylinder direct injection type according to any one of claims 1 to 5, wherein the fuel injection timing in the stratified high load operation condition is more advanced than the fuel injection timing in the stratified low load operation condition. Internal combustion engine. The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 6, wherein a combustion injection pressure under the stratified high load operation condition is higher than a combustion injection pressure under the stratified low load operation condition. On the relatively high-load side of the stratified high-load operation condition, at least two fuel injections are performed, the first being the injection that impinges the fuel spray on the piston cavity side surface, and the second is the injection that impinges the fuel spray on the piston cavity bottom surface. An in-cylinder direct injection internal combustion engine according to any one of claims 1 to 7, characterized in that: The in-cylinder according to any one of claims 1 to 8, wherein the fuel injection valve sprays fuel during an intake stroke in a homogeneous combustion operation region on a higher load side than the stratified combustion operation region. Direct injection internal combustion engine.

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