JP2004190530A - Direct injection type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To conduct a perfect stratified-charge combustion throughout a wide range of the engine load. <P>SOLUTION: The internal combustion engine includes a fuel-injection valve 11 for injecting fuel directly into a combustion chamber 1 formed above a piston 4, and an ignition plug 12 for conducting spark-ignition to an air-fuel mixture in the chamber 1. An external cavity 16 is made in a piston crown 15, and an internal cavity 17 is made in a bottom pace 16a of the external cavity 16. A normal 19, which is orthogonal to the bottom face 17a of the internal cavity 17, and extends to the combustion chamber, is inclined to the ignition plug 12 in relation to an injection center line 14 of the fuel-injection valve 11. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in a direct injection type internal combustion engine having a fuel injection valve for directly injecting fuel into a combustion chamber and an ignition plug, and having an outer cavity and an inner cavity formed in a piston crown surface.
[0002]
[Prior art]
Conventional direct injection type internal combustion engines include, for example, Patent Literature 1 and Patent Literature 2. Patent Literature 1 discloses a center injection type direct injection type internal combustion engine in which a fuel injection valve is disposed on a cylinder center line above a combustion chamber, and a spark plug is located closer to the exhaust side than the fuel injection valve. Is arranged. One bowl-shaped stratification cavity is recessed in the piston crown. The curved bottom surface of the cavity is set so that the spark plug side becomes deeper. Therefore, it is described that the fuel can be held for a relatively long time inside the cavity, particularly at a portion near the spark plug, and the stratified combustion can be performed in a wide operating range.
[0003]
In Patent Literature 2, in a center injection type direct injection type internal combustion engine in which a fuel injection valve is arranged on a cylinder center line and an ignition plug is arranged in the vicinity thereof, a piston is provided with a shaft substantially parallel to the cylinder center line. A deep dish portion (inner cavity) having a symmetrical shape is recessed, and a plurality of shallow dish portions (outer cavities) are intermittently recessed circumferentially around the deep dish portion.
[0004]
[Patent Document 1]
JP-A-2000-34925
[Patent Document 2]
JP 2000-265841 A
[Problems to be solved by the invention]
When there is only one piston cavity as in Patent Literature 1, it is difficult to perform good stratified combustion over a wide engine load range. For example, when performing stratified charge combustion in a region where the engine load is relatively high, the size and shape of the cavity are designed so that the mixture formed in and above the cavity has an appropriate concentration, for example, near the stoichiometric air-fuel ratio. In such a case, when the load is low, a good mixed air mass cannot be obtained, and there is a concern that the stability of combustion and ignition may be reduced.
[0007]
In the case where a plurality of cavities (deep plate portion and shallow plate portion) are recessed in the piston crown surface as in Patent Literature 2, the cavities are selectively used according to the engine load, so that the mixed air mass is determined according to the engine load. The stratified combustion can be performed in a wide operating range.
[0008]
However, in Patent Literature 2, the shallow plate portion has a valve recess shape for avoiding interference with the intake and exhaust valves, and is not axially symmetric with respect to the cylinder center line. That is, the shallow plate portion does not have a circular shape centered on the fuel injection valve when viewed in the cylinder axis direction. For this reason, when stratified charge combustion is performed using the shallow plate portion, the fuel spray injected into the shallow plate portion may spill from between adjacent shallow plate portions, leading to deterioration of fuel efficiency and increase in unburned HC. There is. Also, when stratified charge combustion is performed using the deep dish portion, the fuel spray injected into the deep dish portion is discharged from the deep dish portion because the side wall of the deep dish portion is smoothly connected to the shallow dish portion. The fuel is easily spilled into the fuel cell and there is a concern that fuel consumption may deteriorate and unburned HC may increase.
[0009]
Further, in Patent Document 2, since the deep dish portion has a symmetrical shape and a rotating body shape centered on the injection center line (cylinder center line) of the fuel injection valve, a low load region, particularly an extremely low load such as idling, is provided. In the region, a compact fuel mixture obtained using the deep dish tends to form near the center of the combustion chamber. On the other hand, the spark plug is arranged, for example, offset to the exhaust valve side in order to avoid interference with the fuel injection valve. Therefore, as long as the ignition plug, more specifically, the electrode portion or gap, which is the ignition position, does not protrude to the vicinity of the cylinder center line, the position where the mixture is formed and the position of the ignition plug are separated, or the mixture is not separated. Since the gap of the ignition plug is located near the boundary with the air layer, stable ignition may be difficult.
[0010]
Another problem is that even if the improvement of the fuel injection valve enables early homogenization of the air-fuel mixture, the squish flow generated in the latter half of the compression stroke by the lower surface of the cylinder head and the piston crown surface causes the vicinity of the spark plug gap Flow may be disturbed, resulting in leaning due to excessive diffusion, or blowing out of ignition due to a high-speed gas flow, which may hinder the stability of stratified combustion.
[0011]
The present invention has been made in view of such a problem, and has as its main object to provide a novel in-cylinder direct injection internal combustion engine that can stably perform stratified combustion in a wide engine load range. .
[0012]
[Means for Solving the Problems]
An in-cylinder direct injection internal combustion engine according to the present invention includes a fuel injection valve for directly injecting fuel into a combustion chamber formed above a piston, a spark plug for spark-igniting an air-fuel mixture in the combustion chamber, It has an outer cavity recessed in the crown surface of the piston, and an inner cavity recessed in the bottom surface of the outer cavity.
[0013]
The present invention is characterized in that a normal extending perpendicular to the bottom surface of the inner cavity toward the combustion chamber is inclined toward the ignition plug with respect to the injection center line of the fuel injection valve. Alternatively, such that the fuel injected from the fuel injection valve is directed toward the ignition plug via the bottom surface of the inner cavity, the bottom surface of the inner cavity is positioned with respect to a reference plane orthogonal to the injection center line of the fuel injection valve. It is characterized in that the side corresponding to the ignition plug is inclined so as to be deep.
[0014]
【The invention's effect】
According to the present invention, good stratified combustion can be performed in a wide engine load region by selectively using the inner cavity and the outer cavity according to the engine load and the like. Since the mixture formed using the inner cavity is smaller than the mixture formed using the outer cavity, when performing stratified combustion using the inner cavity, the mixture formed by the mixture and the spark plug The position is easily shifted. However, in the present invention, since the bottom surface of the inner cavity or its normal line is appropriately inclined, when performing the stratified combustion using the inner cavity, the fuel injected from the fuel injection valve passes through the bottom surface of the inner cavity. Thus, the mixture can be favorably directed to the spark plug, and a good mixed air mass can be formed around the spark plug, so that stable stratified combustion can be realized.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 schematically shows a direct injection internal combustion engine according to the present invention. A plurality of cylinders 3a (only one is shown in the figure) are formed in the cylinder block 3, and a piston 4 is slidably fitted to each cylinder 3a. The combustion chamber 1 is formed above the piston 4. Specifically, the combustion chamber 1 is defined by a crown surface of the piston 4, a lower surface of the cylinder head 2 fixed to an upper part of the cylinder block 3, and an inner wall surface of the cylinder 3a, that is, a cylinder bore. An intake port 5 and an exhaust port 6 that open to the combustion chamber 1 are formed in the cylinder head 2. The cylinder head 2 is provided with a pair of intake valves 7 for opening and closing the intake port 5 and a pair of exhaust valves 8 for opening and closing the exhaust port 6 for each cylinder. These intake and exhaust valves are respectively driven by well-known cams and the like.
[0017]
A fuel injection valve 11 for directly injecting fuel into the combustion chamber 1 and a spark plug 12 for spark-igniting an air-fuel mixture in the combustion chamber 1 are provided in the cylinder head 2 with the fuel injection valve 11 facing the combustion chamber 1. , On or near the cylinder center line 14 and close to each other. Here, in particular, the center injection type in which the fuel injection valve 11 is arranged such that the injection center line of the fuel injection valve 11 (the center line of the spray having a hollow conical shape) coincides with the cylinder center line 14. As described above, since the injection center line 14 coincides with the cylinder center line, the injected fuel does not directly collide with the cylinder bore, regardless of the fuel injection timing (piston position at the time of injection). , 17 are securely received by the piston crown including the bottom surface.
[0018]
An ignition plug 12 is arranged near the fuel injection valve 11. The ignition plug 12 is disposed on the exhaust valve side (left side in the figure) where there is a relatively large space, specifically, between the pair of exhaust valves 8. The fuel injection amount and injection timing of the fuel injection valve 11, the ignition timing of the ignition plug 12, and the like are controlled by a well-known control unit including a CPU and a memory.
[0019]
Referring to FIG. 2, piston crown 15 has an upwardly convex (virtual) triangular pyramid shape, that is, a pent roof shape, similarly to the lower surface of cylinder head 2. An outer cavity 16 is recessed in the piston crown surface 15 so as to cut out a center portion thereof, and an inner cavity 17 is further recessed in a bottom surface 16a of the outer cavity 16 so as to cut out the center portion. Have been. That is, it has a double cavity structure in which two cavities 16 and 17 are formed in the piston crown surface 15.
[0020]
The outer cavity 16 is constituted by a bottom surface 16a and a curved outer surface 16b rising upward from the periphery of the bottom surface 16a, and has a substantially shaft-rotating body shape as a whole with respect to a cylinder center line (piston center line) 14. (Axisymmetric shape, toroidal shape), almost thin plate type. Here, the bottom surface 16a has a flat cone shape slightly convex upward, but may be a flat surface or a curved surface. The outer wall surface 16b has a reentrant shape in which the upper side is inclined inward so as to satisfactorily contain fuel.
[0021]
The inner cavity 17 is constituted by a flat bottom surface 17a and a curved outer wall surface 17b rising upward from the peripheral edge of the bottom surface 17a. ing. The bottom surface 17a is inclined with respect to a reference surface 18 orthogonal to the injection center line 14. This inclination will be described later. The outer wall surface 17b has a reentrant shape in which the upper side is inclined inward so as to properly contain the fuel.
[0022]
As shown in FIG. 3, when the piston 4 is viewed from above in the cylinder axis direction, the center of the cylinder is adjusted so that the injected fuel can be favorably introduced into both the opening 16 k of the outer cavity 16 and the opening 17 k of the inner cavity 17. It has a substantially perfect circle centered on the line (injection center line) 14. However, the shape is not necessarily a perfect circle due to the fact that the piston crown surface 15 has a pent roof shape.
[0023]
Referring again to FIG. 2, the inclination of the bottom surface 17 a of the inner cavity 17 is such that the fuel injected from the fuel injection valve 11 toward the inner cavity 17 is the ignition position of the ignition plug 12 via the bottom surface 17 a. That is, it is set so as to favorably go to the gap 12a. Specifically, the bottom surface 17a of the inner cavity 17 has a predetermined angle with respect to the reference surface 18 orthogonal to the injection center line 14 such that the side corresponding to the spark plug, here the exhaust side (left side in FIG. 2), is deeper. (A sharp angle) is inclined by α. That is, the normal 19 extending to the combustion chamber 1 side orthogonal to the inner cavity bottom face 17a is inclined at a predetermined angle α toward the spark plug with respect to the injection center line 14. The inner cavity 17 may have a shape of a rotating shaft around the above-mentioned normal 19, or a shape in which the bottom of the rotating shaft shape with respect to the injection center line 14 is notched so that the exhaust side is deeper. There may be. In any case, the opening 16k is desirably circular with the injection center line 14 as the center so that the injected fuel can be introduced well.
[0024]
More specifically, at a predetermined time in the latter half of the compression stroke, the injection center line 14, the intersection point 20 where the injection center line 14 intersects the inner cavity bottom surface 17 a, and the gap 12 a of the ignition plug 12 with respect to the normal 19 The connecting line 21 is arranged substantially symmetrically. That is, the injection center line 14 and the above-mentioned line 21 are inclined at substantially the same angles α and β in directions different from each other with respect to the normal 19.
[0025]
The above-mentioned predetermined time is a compression top dead center where ignition is performed by the spark plug 12 from the latter half of the compression stroke in which fuel is injected toward the inner cavity 17 in a stratified low load region R2 in which stratified combustion is performed using the inner cavity 17 described later. This corresponds to a case where the injected fuel spray is well diffused inside the inner cavity 17 (when the spread diameter of the spray is substantially equal to the diameter of the inner cavity 17) within the period up to the vicinity.
[0026]
Since the inclination of the bottom surface 17a of the inner cavity 17 is defined in this manner, the ignition plug 12 eccentric from the injection center line 14 to the exhaust side in the stratified low load region R2 in which fuel is injected toward the inner cavity 17 The air-fuel mixture can be satisfactorily formed around the gap 12a, and stable stratified combustion can be realized.
[0027]
FIG. 4 shows the fuel injection timing according to the engine load. Stratified combustion is performed in a low / medium load range where the engine load is lower than the first threshold T1, and homogeneous combustion is performed in a homogeneous high load range R1 higher than the first threshold T1. In the stratified low load region R2 where the engine load is lower than the second threshold value T2 (T2 <T1), fuel is injected only once into the inner cavity 17. In the stratified high load region R3 in which the engine load is higher than the second threshold value T2 and lower than the first threshold value T1, fuel spray is well received by the inner cavity 17 in one injection toward the inner cavity 17. Since there is no injection, split injection is performed in which fuel is injected separately into two, a first injection toward the outer cavity 16 and a second injection toward the inner cavity 17.
[0028]
When adjusting the fuel injection period (injection amount) according to the engine load, in this embodiment, the injection start timing is advanced / retarded without changing the injection end timing. For example, if the load increases, the injection start timing is advanced. However, the present invention is not limited to this, and the end time may be changed according to the load, or both the start time and the end time may be changed.
[0029]
In the homogeneous high load region R1 in which homogeneous combustion is performed, fuel injection is performed during the intake stroke so that fuel is injected toward the piston crown surface 15 outside the outer cavity 16, and sufficient mixing time is ensured. Accordingly, the injected fuel is favorably diffused throughout the combustion chamber 1 without being accumulated in the cavities 16 and 17.
[0030]
In the stratified low load region R2, the injected fuel is injected toward the inner cavity 17. That is, the fuel injection start / end timing is set to the latter half of the compression top dead center so that the injected fuel can be received well in the inner cavity 17.
[0031]
In the stratified high load region R3, the fuel injection is performed twice as described above. The first fuel injection timing is set in the first half to the middle of the compression stroke so that the injected fuel is introduced into the outer cavity 16, and the second injection timing is when the injected fuel is injected into the inner cavity 17. In order to be introduced, it is set in the latter half of the compression stroke similarly to the above-described stratified low load region R2. In the stratified high load region R3, the first injection amount is adjusted according to the engine load, and the second fuel injection amount is a constant lower than the fuel injection amount in the stratified low load region R2 regardless of the load. The value is fixed. The second injection end timing is almost the same as the injection end timing in the stratified low load region R2.
[0032]
If the split injection is performed in the stratified low-load region R2, an unnecessarily lean air-fuel mixture is formed, which may cause a misfire or increase the amount of fuel discharged as unburned HC even if the ignition is performed. . Also, if the fuel injection is performed only once toward the inner cavity 17 in the stratified high load region R3, the concentration of the air-fuel mixture formed in the vicinity of the ignition plug becomes excessively rich, or the injected fuel becomes less dense. As a result, the mixture may not be received, and may protrude into the outer cavity, failing to form a good air-fuel mixture, which may lead to an increase in unburned HC.
[0033]
FIG. 5 shows the behavior of the fuel spray in the stratified low load region R2. As shown in (a), the fuel F0 injected in the shape of a hollow cone toward the inner cavity 17 in the latter half of the compression stroke first collides with the inner cavity bottom surface 17a. Thereafter, as shown in (b), the fuel spray is guided along the bottom surface 17 a and the outer wall surface 17 b of the appropriately inclined inner cavity 17, and heads toward the sky above the inner cavity 17. At this time, the inclination of the bottom surface 17a of the inner cavity is defined as described above, and the fuel spray is set so as to be directed toward the ignition plug 12, so that the fuel spray flows over the inner cavity 17 with the rise of the piston. By swirling the surrounding air while swirling, a homogeneous air-fuel mixture F0 ′ is generated above the cavity near the spark plug, as shown in FIG. That is, the mixed gas mass F0 ′ is formed around the vicinity of the spark plug 12 slightly offset from the injection center line 14 toward the exhaust side. Therefore, while the air-fuel mixture F0 'is relatively compact according to the size of the inner cavity 17, the air-fuel mixture F0' is positioned such that the gap 12a of the spark plug is located substantially at the center of the air-fuel mixture F0 '. Lump F0 'can be generated, and stable and favorable stratified combustion can be realized.
[0034]
FIG. 6 shows the behavior of the fuel spray in the stratified high load region R3. As shown in (a), the first injected fuel F1 injected into the outer cavity 16 in a substantially hollow conical shape first collides with the bottom surface 16a of the outer cavity. Thereafter, as shown in (b), the fuel spray is guided along the bottom surface 16a and the outer wall surface 16b of the outer cavity 16 to move upward of the outer cavity 16, and while entraining the surrounding air, (c) and (d). As shown in ()), a mixed gas mass F1 ′ is formed above the outer cavity 16. This mixed gas mass F1 ′ is relatively large according to the size of the outer cavity 16, and the outer cavity 16 has a substantially shaft-rotating body shape with respect to the cylinder center line 14, so that the cylinder center It is formed substantially at the center of the combustion chamber centered on the line 14. In addition, since the mixed fuel mass F1 ′ has a relatively small fuel injection amount due to the divided injection, the mixture has a substantially donut-shaped mixture distribution with a thin center portion.
[0035]
Further, a second fuel injection F2 is performed toward the inner cavity 17 in the latter half of the compression stroke. This second fuel injection F2 has the same injection angle as the first fuel injection, but is performed in the latter half of the compression stroke in which the piston is at a high position, so that it is reliably injected into the inner cavity 17 without spilling into the outer cavity 16. It is accepted. By the second fuel injection, a relatively small air-fuel mixture is formed around the ignition plug 12 as in the case of the stratified low load region R2, and this air-fuel mixture is substantially formed by the first fuel injection. By filling the hollow portion of the donut-shaped mixed gas mass F1 ', a substantially homogeneous mixed gas mass is generated from the inside of the outer cavity 16 to the sky as shown in (e). Therefore, good stratified combustion can be stably performed.
[0036]
As described above, in order to realize good stratified combustion in a wide load range, regardless of the injection timing, that is, the in-cylinder pressure, the fuel injection in the accurate direction and the injection amount toward the outer cavity 16 and the inner cavity 17 is performed. There is a need to do. Further, it is desired that the fuel spray has a hollow shape, more preferably a hollow conical shape, so that the injection amount to the cavity is not excessive.
[0037]
Therefore, the fuel injection valve 11 has a small change in the spray shape even when the in-cylinder pressure increases in the latter half of the compression stroke and has high directivity, such as a multi-hole injection valve 11A as shown in FIG. Such a swirl nozzle type injection valve 11B is used.
[0038]
As is well known, the multi-hole injection valve 11A has a large number of injection holes 22 formed intermittently in the circumferential direction along a hollow cone. Therefore, the spray 23 to be injected becomes an intermittent spray in the circumferential direction along the hollow conical shape as a whole, and the fuel injection angle hardly changes due to the injection back pressure.
[0039]
As disclosed in Japanese Patent Application Laid-Open No. 2000-329036, the swirl nozzle type injection valve 11B includes a swirler 24 for imparting a swirling component to fuel, and an injection hole 26 having a step 25 formed therein. Have. Due to the step 25 of the injection hole portion 26, the fuel spray 27 to be injected has a thin part in the circumferential direction 28 having a hollow conical shape. When this swirl nozzle type injection valve 11B is used, hollow cone-shaped fuel injection without changing the fuel spray angle due to the injection back pressure can be performed.
[0040]
As shown in FIG. 9, in the latter half of the compression stroke, a squish flow 31 toward the center of the cylinder is generated by the gap 30 between the piston crown surface 15 outside the outer cavity 16 and the lower surface of the cylinder head 2. In this embodiment, the gap between the outer wall surface 16b of the outer cavity 16 and the spark plug 12 is set so that the mixture 33 generated around the spark plug is not diffused by the squish flow 31. A space (gap) 35 larger than 30 is provided. Therefore, the strong squish flow 31 near the compression top dead center is released into the outer cavity 16 through the space 35 as shown by the arrow 31 ′, and the mixed air mass 33 once formed near the spark plug Are not diffused by the squish flow.
[0041]
In order to more reliably reduce and avoid the influence of the squish flow 31, the upper end 16c of the outer wall surface 16b of the outer cavity is set at a position higher than the upper end 17c of the outer wall surface 17b of the inner cavity. Further, the depth 36 of the outer cavity is set larger than the gap 30 described above. With these settings, in order to inject fuel toward the inner cavity 17, even if fuel injection is started relatively late, that is, in the latter half of the compression stroke, the fuel that has been wound up through the inner cavity 17 can be sufficiently removed. While mixing, it is possible to form the mixed gas mass 33 having an appropriate concentration near the ignition plug.
[0042]
In order to enable stable stratified combustion in a wide engine load region while reducing and avoiding the influence of the squish flow, the gap 12a of the ignition plug 12 is arranged inside the outer cavity outer wall surface 16b, The cylinder radial direction distance between the wall surface 16b and the gap 12a is set to be larger than the cylinder radial direction distance between the inner cavity outer wall surface 17b and the gap 12a.
[0043]
As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, but includes various modifications and changes. For example, in the above embodiment, the fuel injection valve is arranged on the cylinder center line, and the spark plug is offset to the exhaust side with respect to the cylinder center line. It may be offset with respect to the center line.
[0044]
Hereinafter, the technical background of the present invention will be described in detail with reference to the drawings.
[0045]
FIG. 10 shows the relationship between the equivalent ratio and the combustion performance in a homogeneous air-fuel mixture. As shown in the drawing, only in the short range 41 where the equivalence ratio is close to 1, both the fuel economy performance and the exhaust performance are compatible at a high level. The same applies to the case of stratified charge combustion. If there is a large variation in the air-fuel mixture distribution, the combustion performance deteriorates. In order to form a homogeneous mixture having an equivalent ratio of about 1 even in stratified combustion, it is necessary to mix the injected fuel after a sufficient time. If ignition is performed during the mixing process of the injected fuel, an inhomogeneous mixed air mass depending on the characteristics of the fuel injection valve will be ignited, leading to a reduction in fuel consumption and exhaust performance. Therefore, in order to perform good stratified combustion, it is necessary to form a homogeneous mixture, and it is desirable to change the size of the mixture according to the engine load. When a mixed gas mass is generated using a cavity, the size of the mixed gas mass mainly depends on the size of the cavity. Therefore, when there is only one cavity in the piston crown surface, the engine load for optimal combustion performance is limited to a certain region.
[0046]
FIG. 11 shows the relationship between the ratio between the cavity diameter and the bore diameter and the engine load capable of performing appropriate combustion, and FIG. 12 shows the load range in which appropriate combustion can be performed for each cavity. As can be seen from these figures, it is difficult to improve the combustion performance over a wide load range with one cavity diameter.
[0047]
As another problem, when the diameter of the cavity is increased, the air-fuel mixture formed by using the cavity tends to have a donut-shaped air-fuel mixture in which the vicinity of the center is thin as described above. On the other hand, in a spark ignition type internal combustion engine represented by a gasoline engine, considering full load performance, it is desirable that the flame propagation distance is isotropic, and the spark plug is installed near the center of the combustion chamber. It is desirable. Therefore, in the donut-shaped mixture distribution, there is a possibility that the ignition is not satisfactorily ignited by the spark plug installed near the center of the combustion chamber.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a direct injection type internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a sectional view showing a main part of the internal combustion engine according to the embodiment.
FIG. 3 is a top view of the crown surface of the piston according to the embodiment as viewed from the cylinder axis direction.
FIG. 4 is a characteristic diagram showing a fuel injection timing according to an engine load.
FIG. 5 is an explanatory diagram showing a state of a combustion chamber in a stratified low load region.
FIG. 6 is an explanatory diagram showing a state of a combustion chamber in a stratified high load region.
7A is a side view corresponding to the multi-hole fuel injection valve, and FIG.
8A is a cross-sectional view, FIG. 8B is a side view, and FIG. 8C is a cross-sectional view of a spray related to the swirl nozzle injection valve.
FIG. 9 is an operation explanatory view relating to a squish flow.
FIG. 10 is a characteristic diagram showing a relationship between an equivalent ratio and combustion performance.
FIG. 11 is a graph showing a relationship between a cavity size and an optimum engine load.
FIG. 12 is a characteristic diagram showing an optimum load range for each cavity diameter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Combustion chamber 4 ... Piston 11 ... Fuel injection valve 12 ... Spark plug 12a ... Gap 14 ... Cylinder center line (injection center line)
15 Piston crown surface 16 Outer cavity 17 Inner cavity 18 Reference surface 19 Normal line 20 Intersection 21 Line

Claims (11)

A fuel injection valve for directly injecting fuel into a combustion chamber formed above the piston,
A spark plug for spark-igniting the mixture in the combustion chamber,
An outer cavity recessed in the crown surface of the piston,
In an in-cylinder direct injection internal combustion engine having an inner cavity recessed at the bottom of the outer cavity,
An in-cylinder direct injection internal combustion engine, characterized in that a normal extending perpendicular to the bottom surface of the inner cavity toward the combustion chamber is inclined toward the ignition plug with respect to the injection center line of the fuel injector. A fuel injection valve for directly injecting fuel into a combustion chamber formed above the piston,
A spark plug for spark-igniting the mixture in the combustion chamber,
An outer cavity recessed in the crown surface of the piston,
In an in-cylinder direct injection internal combustion engine having an inner cavity recessed at the bottom of the outer cavity,
The bottom surface of the inner cavity is positioned on the reference plane orthogonal to the injection center line of the fuel injection valve so that the fuel injected from the fuel injection valve travels toward the spark plug via the bottom surface of the inner cavity. An in-cylinder direct injection internal combustion engine, characterized in that the side corresponding to the plug is inclined so as to be deeper. Between the outer wall surface of the outer cavity and the spark plug, a squish flow toward the center of the piston generated in the latter half of the compression stroke due to the gap between the piston crown surface outside the outer cavity and the lower surface of the cylinder head is released to the outer cavity. 3. The direct injection internal combustion engine according to claim 1, wherein a predetermined space is secured. In the latter half of the compression stroke, the gap between the outer wall surface of the outer cavity and the spark plug is set to be larger than the gap between the piston crown surface and the lower surface of the cylinder head. In-cylinder direct injection internal combustion engine according to any one of the above. The in-cylinder direct injection according to any one of claims 1 to 4, wherein the depth of the outer cavity is set to be larger than the gap between the piston crown surface and the lower surface of the cylinder head in the latter half of the compression stroke. Type internal combustion engine. The direct injection internal combustion engine according to any one of claims 1 to 5, wherein the spark plug is arranged inside an outer wall surface of the outer cavity. The injection center line of the fuel injection valve substantially coincides with the cylinder center line,
7. The direct injection internal combustion engine according to claim 1, wherein the spark plug is offset toward the exhaust side with respect to a cylinder center line. At a predetermined time in the latter half of the compression stroke, the injection center line and a line connecting the intersection where the injection center line intersects the bottom surface of the inner cavity and the ignition plug are substantially perpendicular to a normal line orthogonal to the bottom surface of the inner cavity. The direct injection internal combustion engine according to any one of claims 1 to 7, wherein the internal combustion engine is arranged symmetrically. In the stratified low load region, fuel is injected only once in the latter half of the compression stroke, and at least in the stratified high load region where the load is higher than the stratified low load region, fuel is injected twice during the compression stroke. An in-cylinder direct injection internal combustion engine according to any one of claims 1 to 8. In the stratified high load region, the first injection timing is set so that the first injected fuel enters the outer cavity, and the second injection timing is set such that the second injected fuel enters the inner cavity. The direct injection type internal combustion engine according to claim 9, wherein the internal combustion engine is set. The direct injection internal combustion engine according to claim 9 or 10, wherein the fuel injection timing is set so that the fuel enters the inner cavity in the stratified low load region.

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