JP2004011441A - Cylinder direct injection type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow good stratified charge combustion even when using an outside cavity 16 or an inside cavity 17, whichever. <P>SOLUTION: A fuel injection valve 11 is arranged on a piston reciprocating axis 14 for injecting a fuel directly into a combustion chamber 1. A spark plug 12 is arranged near the fuel injection valve 11. The outside cavity 16 in the form of an approximate axial rotor relative to the piston reciprocating axis 14 is recessed in a piston crown surface 15. Similarly, the inside cavity 17 in the form of an approximate axial rotor relative to the piston reciprocating axis 14 is recessed in the outside cavity 16. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a center injection type direct injection type internal combustion engine in which a fuel injection valve and a spark plug are arranged on or near a piston reciprocation axis, and more particularly to an improvement in a cavity shape recessed in a piston crown surface.
[0002]
[Prior art]
As a direct injection type internal combustion engine, Japanese Patent Application Laid-Open No. 2000-265841 discloses a center injection type engine in which a fuel injection valve and a spark plug are arranged on or near a piston reciprocating axis. A deep dish portion (inner cavity), which is substantially axially symmetric with respect to the reciprocating axis of the piston, is formed in the piston crown surface, and a plurality of shallow dish portions (outer cavities) are intermittently formed around the deep dish portion. It is concavely formed.
[0003]
[Problems to be solved by the invention]
The above-mentioned shallow plate portion has a valve recess shape for avoiding interference with the intake / exhaust valve, and is not axially symmetrical with respect to the piston reciprocating axis. 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. The present invention has been made in view of such a problem.
[0004]
[Means for Solving the Problems]
In the direct injection internal combustion engine of the present invention, the fuel injection valve and the spark plug are arranged on or near the piston reciprocating axis, and the fuel is directly injected from the fuel injection valve into the combustion chamber. The generated mixture is spark-ignited by the spark ignition plug. An outer cavity is formed in the piston crown surface and has an approximately axis-of-rotation body shape with respect to the piston reciprocating axis, and an inner cavity is formed in the outer cavity with an approximately-axis-rotation body shape with respect to the piston reciprocating axis. Is done. Typically, stratified combustion is realized using the outer cavity under stratified high load operation conditions, and stratified combustion is realized using the inner cavity under stratified low load operation conditions.
[0005]
【The invention's effect】
Since both the outer cavity and the inner cavity are substantially in the form of a rotating body with respect to the piston reciprocating axis, the stratified combustion is mainly performed using the outer cavity, and the stratified combustion is mainly performed using the inner cavity. In either case, stratified combustion with good fuel efficiency and sufficient suppression of unburned HC emissions can be realized.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0007]
FIG. 1 schematically shows a direct injection internal combustion engine according to the present invention. The combustion chamber 1 is defined by a cylinder head 2, a cylinder block 3, and a piston 4 fitted into a cylinder 3a of the cylinder block 3. An intake port 5 and an exhaust port 6 that open to the combustion chamber 1 are formed in the cylinder head 2. An intake valve 7 and an exhaust valve 8 that open and close these ports 6 and 7 are driven using an intake valve cam 9 and an exhaust valve cam 10.
[0008]
The cylinder head 2 includes a fuel injection valve 11 for directly injecting fuel into the combustion chamber 1 toward the crown surface 15 of the piston 4, and a spark plug 12 for spark-igniting a mixture in the combustion chamber 1. In the state facing the combustion chamber 1, they are arranged close to each other on or near the cylinder center axis, that is, the piston reciprocating axis 14. Here, in particular, the fuel injection valve 11 is arranged on the piston reciprocating axis 14, and the ignition plug 12 is arranged close to the fuel injection valve 11. As the fuel injection valve 11, a multi-hole type injection valve having strong directivity is used so that the change in the spray shape becomes small even when the in-cylinder pressure increases in the latter half of the compression stroke. The operations of the fuel injection valve 11 and the spark plug 12 are controlled by the engine control unit 13.
[0009]
The piston crown surface 15 has an upwardly convex (virtual) triangular pyramid shape, that is, a pent roof shape so as to follow the shape of the top surface of the pent roof type combustion chamber 1 formed in the cylinder head 2. An outer cavity 16 is recessed in the piston crown surface 15 so as to cut out a central portion thereof, and an inner cavity 17 is further recessed on the surface of the outer cavity 16. That is, the piston has a double cavity structure in which the two cavities 16 and 17 are formed concentrically on the piston crown surface 15.
[0010]
The outer cavity 16 has a substantially shaft-rotating body shape (axisymmetric shape, toroidal shape) with respect to the piston reciprocating axis 14. However, since the piston crown surface 15 in which the outer cavity 16 is recessed is not in the shape of a rotating shaft, when the piston crown surface 15 is viewed from above (combustion injection valve side) as shown in FIG. The opening 16k is not a perfect circle with the piston reciprocating axis 14 as the center. The inner cavity 17 has a shaft rotating body shape (axially symmetrical shape, toroidal shape) with respect to the piston reciprocating axis 14, and as shown in FIG. 2, the piston crown surface 15 is viewed from above (from the combustion injection valve side). In this case, the opening 17k forms a perfect circle with the piston reciprocating axis 14 as the center.
[0011]
FIG. 3 schematically shows the spraying behavior under the stratified high load operation condition. The wall surface of the outer cavity 16 includes a first outer wall surface 16a, a second outer wall surface 16b continuous to the outer peripheral side of the first outer wall surface 16a, and a third outer wall surface 16c continuous to the second outer wall surface 16b. Can be divided. The first outer wall surface 16a is an inclined surface that becomes higher toward the center piston reciprocating axis 14, and has an upwardly convex virtual conical shape as a whole. The inner cavity 17 is recessed so as to cut out the center of the first outer wall surface 16a. The second outer wall surface 16b includes an outer curved surface that smoothly curves toward the third outer wall surface 16c, and a part thereof is a flat surface 16d that is substantially orthogonal to the piston reciprocating axis 14. The third outer wall surface 16c constitutes the outer wall surface of the entire outer cavity 16, and has a reentrant shape that is inclined in a direction approaching the piston reciprocating axis 14 toward the upper side of the piston (upward in FIG. 3).
[0012]
The fuel spray injected from the fuel injection valve 11 has a hollow conical shape projecting downward around the piston reciprocating axis 14. As shown in FIG. 3A, the fuel spray F1 under the stratified high load operation condition is set so as to obliquely collide with the first outer wall surface 16a. The angle θ1 between the (center) injection direction F2 of the spray F1 and the portion of the first outer wall surface 16a on the spraying direction side (radially outward from the portion where the spray collides) is an obtuse angle (90 ° to 180 °). °). Therefore, the fuel spray F1 collides with the first outer wall surface 16a at a gentle angle, and the fuel spray F1 after the collision does not accidentally scatter, but along the first outer wall surface 16a, i.e., along the outer circumferential side. The guide is favorably guided toward the second outer wall surface 16b. By the outer curved surface of the second outer wall surface 16b, the spray is favorably guided along the third outer wall surface 16c.
[0013]
The third outer wall surface 16c is an inclined surface inclined at an angle close to the spray direction F2. Specifically, the angle θ2 between the extension line 16c ′ of the third outer wall surface 16c and the parallel line F2 ′ of the ejection direction F2 is sufficiently small. However, the reentrant angle d of the third outer wall surface 16c with respect to the piston reciprocating axis 14 is smaller than the angle of the injection direction F2 with respect to the piston reciprocating axis 14. The fuel spray is satisfactorily guided by the third outer wall surface 16c in the direction of the original injection. As a result, as shown in FIGS. 3B and 3C, a swirling flow F3 that swirls like a vortex in the vertical direction along the piston reciprocating axis 14 is generated. The surrounding air is entrained by the swirling flow F3, and the air-fuel mixture generated above the outer cavity 16 becomes a homogeneous air-fuel mixture K1 without concentration unevenness.
[0014]
FIG. 4 schematically shows the spraying behavior under the stratified low load operation condition. The wall surface of the inner cavity 17 includes a first inner wall surface 17a, a second inner wall surface 17b continuous to the outer peripheral side of the first inner wall surface 17a, and a third inner wall surface 17c continuous to the second inner wall surface 17b. Can be divided. The first inner wall surface 17a is an inclined surface that becomes higher toward the central piston reciprocating axis 14, and has an upwardly convex conical shape as a whole. The second inner wall surface 17b forms an inner curved surface that smoothly curves toward the third inner wall surface 17c. The third inner wall surface 17c constitutes the outer wall surface of the entire inner cavity 17, and has a reentrant shape that inclines in a direction approaching the piston reciprocating axis 14 toward the upper side of the piston (upward in FIG. 4).
[0015]
As shown in FIG. 4A, the fuel spray F4 under the stratified low load operation condition is set so as to obliquely collide with the first inner wall surface 17a. The angle θ3 between the (center) injection direction F5 of the spray F4 and a portion of the first inner wall surface 17a on the spray advancing direction side (radially outward from the portion where the spray collides) is an obtuse angle (90 ° to 180 °). °). Therefore, the fuel spray F4 collides with the first inner wall surface 17a at a gentle angle, and the fuel spray F4 after the collision does not accidentally scatter, but along the first inner wall surface 17a on the outer peripheral side, that is, along the first inner wall surface 17a. It is favorably guided to the second inner wall surface 17b side. Further, the spray is satisfactorily guided along the third inner wall surface 17c by the smoothly curved second inner wall surface 17b.
[0016]
The third inner wall surface 17c is an inclined surface inclined at an angle close to the injection direction F5. Specifically, the angle θ4 between the extension line 17c ′ of the third inner wall surface 17c and the parallel line F5 ′ of the ejection direction F5 is sufficiently small. However, the reentrant angle e of the third inner wall surface 17c with respect to the piston reciprocating axis 14 is smaller than the angle of the injection direction F5 with respect to the piston reciprocating axis 14. The fuel spray is satisfactorily guided by the third inner wall surface 17c in the original injection direction. As a result, as shown in FIGS. 4B and 4C, a swirling flow F6 that swirls like a vortex in the vertical direction along the piston reciprocating axis 14 is generated. The surrounding air is entrained by the swirling flow F6, and the air-fuel mixture generated above the cavity 17 becomes a homogeneous air-fuel mixture K2 without concentration unevenness. This mixture K2 is sufficiently smaller than the mixture K1 formed by the outer cavity 16 shown in FIG.
[0017]
Since the injection timing is set on the retard side as compared with the high load operation region, even if the injection directions F2 and F4 are the same in the low load operation region and the high load operation region, as described above, the high load region In this case, the spray collides with the first outer wall surface 16a, and in a low load region, the spray collides with the first inner wall surface 17a, so that the outer cavity 16 and the inner cavity 17 can be selectively used according to the load.
[0018]
For example, when using an injection valve capable of changing the injection direction as disclosed in JP-A-2000-303936, preferably, the fuel injection direction is directed to the outer cavity 16 close to the cylinder 3a in the stratified high load region, In the low load region, the injection direction is variably controlled so as to direct the inner cavity 17 near the center. Specifically, the angle of the injection direction with respect to the piston reciprocating axis 14 is relatively large in a stratified high load region and relatively small in a stratified low load region.
[0019]
With reference to FIG. 5, the specific shape of the piston and the operation and effect associated therewith will be described in further detail.
[0020]
The depth b of the inner cavity 17 with respect to the piston crown 15 is greater than the depth a of the outer cavity 16 with respect to the piston crown 15. As a result, in the low-load operation region in which the injection timing is set to the retard side, the crown wall flow can be effectively suppressed and prevented.
[0021]
The depth c of the inner cavity 17 itself is smaller than the depth a of the outer cavity 16 itself (the shallowest part). Thus, in the high load operation region, the spray is favorably introduced into the outer cavity 16 without being blocked by the inner cavity 17.
[0022]
Since both the third outer wall surface 16c of the outer cavity 16 and the third inner wall surface 17c of the inner cavity 17 have a reentrant shape that approaches the piston reciprocating axis 14 as the piston moves upward, the air-fuel mixture is favorably contained in the cavities 16, 17. Can be contained. In particular, the reentrant angle e of the inner cavity 17 is set to be larger than the reentrant angle d of the outer cavity 16. Thus, fuel spillage from the inner cavity 17 is positively prevented, and stable stratified combustion can be realized even in an extremely low load operation region such as idling.
[0023]
The angle g between the first inner wall surface 17a of the inner cavity 17 and the plane orthogonal to the piston reciprocating axis 14 is smaller than the angle f between the third outer wall surface 16c of the outer cavity 16 and the plane orthogonal to the piston reciprocating axis 14. Thereby, especially in the high-load stratified operation region where the crown wall flow tends to increase, the crown wall flow can be effectively suppressed and prevented. Incidentally, as shown in a second embodiment described later, the inclination angle g of the inner cavity 17 may be set to zero, and the first inner wall surface 17a may be a flat surface orthogonal to the piston reciprocating axis 14.
[0024]
The radius of curvature Ri of the second inner wall surface 17b, that is, the inner curved surface, is smaller than the radius of curvature Rh of the outer curved surface of the second outer wall surface 16b. Thereby, the stratified mixed gas mass K2 generated in the inner cavity 17 becomes compact, and the stratified combustion in the low load operation region is stabilized.
[0025]
FIG. 6 schematically shows a piston crown shape according to the second embodiment. It is to be noted that the same reference numerals are given to substantially the same components as those of the first embodiment, and the duplicate description will be omitted. In the second embodiment, the air-fuel mixture generated by the inner cavity 17 is smaller than in the first embodiment. That is, the piston shape is set so as to enhance stability in an extremely low load operation region such as idling even in a low load stratification operation region. Specifically, the first inner wall surface 17 a ′ of the inner cavity 17 is a flat surface orthogonal to the piston reciprocating axis 14. The depth b ′ of the inner cavity with respect to the piston crown 15 is smaller than the depth a ′ of the outer cavity 16 with respect to the piston crown 15. The reentrant angle of the third inner wall surface 17c with respect to the piston reciprocating axis 14 is set to be smaller than or equal to the reentrant angle of the third outer wall surface 16c with respect to the piston reciprocating axis 14. Thus, it is possible to prevent the air-fuel mixture in the inner cavity 17 from becoming excessively concentrated at low to medium loads, and to effectively suppress and prevent the generation of smoke and unburned HC.
[0026]
The technical ideas of the present invention that can be grasped from the above embodiments are listed together with their effects.
[0027]
(1) In a center injection type direct injection type internal combustion engine in which a fuel injection valve and a spark plug are arranged on or near a piston reciprocating axis, an outer cavity having a substantially shaft-rotating body shape with respect to the piston reciprocating axis. Is formed in the crown surface of the piston, and an inner cavity, which is also substantially in the form of a rotating shaft with respect to the piston reciprocating axis, is formed in the outer cavity. By adopting such a double-cavity structure, for example, stratified combustion is realized by using the inner cavity in a low-load region, and stratified combustion is realized by using the outer cavity in a high-load region. In a wide load range including the region, stratified combustion with stable fuel efficiency and low unburned HC can be realized.
[0028]
(2) A first outer wall surface on which fuel spray obliquely collides with a wall surface of the outer cavity, a second outer wall surface continuous with the outer peripheral side of the first outer wall surface, and a third outer wall continuous with the second outer wall surface. And a part or all of the second outer wall surface is formed as an outer curved surface that smoothly curves toward the third outer wall surface, and the third outer wall surface is close to an injection direction of the fuel spray. An inclined surface that is inclined at an angle. Thereby, for example, the fuel injected in the stratified high load region and colliding with the first outer wall surface is guided to the outer curved surface and the third outer wall surface of the second outer wall surface, and swirls vertically in the outer cavity and the space above the outer cavity. -A circulating swirl flow is generated. This makes it easy for the fuel to mix with the air and for the concentration to be uneven, so that a homogeneous mixture field (lump) can be formed in the outer cavity. Therefore, the emission of smoke is suppressed and prevented, and stable stratified combustion can be obtained even if a large amount of EGR is introduced, so that good stratified combustion with little emission of NOx can be realized. Further, since the stratified mixed air mass is formed by the outer cavity having a larger volume than the inner cavity, stable combustion can be realized in a high-load operation region where a relatively large load is applied.
[0029]
(3) A first inner wall surface on which fuel spray obliquely collides with a wall surface of the inner cavity, a second inner wall surface continuous with the outer peripheral side of the first inner wall surface, and a third inner wall continuous with the second inner wall surface. A wall surface, and a part or all of the second inner wall surface is an inner curved surface that smoothly curves toward the third inner wall surface, and the third inner wall surface is close to an injection direction of the fuel spray. An inclined surface that is inclined at an angle. Thereby, for example, the fuel injected in the stratified low load region and colliding with the first inner wall surface is guided to the inner curved surface and the third inner wall surface of the second inner wall surface, and swirls vertically in the inner cavity and the space above it. -A circulating swirl flow is generated. As a result, the fuel is easily mixed with the air and the concentration is hardly uneven, so that a homogeneous mixed gas field (lump) can be formed in the inner cavity. Therefore, the emission of smoke is suppressed and prevented, and stable stratified combustion can be obtained even if a large amount of EGR is introduced, so that good stratified combustion with little emission of NOx can be realized. Further, since the stratified mixed air mass is formed by the inner cavity having a smaller volume than the outer cavity, stable combustion can be realized in a relatively low load operation region.
[0030]
(4) The radius of curvature of the inner curved surface is made smaller than the radius of curvature of the outer curved surface. Thereby, under a low-load stratification condition using the inner cavity, a small air-fuel mixture is easily formed, and stable stratification combustion can be realized.
[0031]
(5) The third outer wall surface has a reentrant shape that approaches the piston reciprocating axis as it goes upward of the piston. As a result, the fuel injected into the outer cavity can be satisfactorily contained, and good stratified combustion with less unburned HC and good fuel economy can be realized.
[0032]
(6) The third inner wall surface has a reentrant shape that approaches the piston reciprocating axis as it goes upward of the piston. Thereby, the fuel injected into the inner cavity can be satisfactorily contained, and stratified combustion with low unburned HC and good fuel efficiency can be realized.
[0033]
(7) The inclination of the third inner wall surface with respect to the piston reciprocating axis is greater than the inclination of the third outer wall surface with respect to the piston reciprocating axis. Thereby, it is possible to more reliably prevent the fuel spray from spilling from the inside of the inner cavity, and realize stable stratified combustion at an extremely low load such as idling.
[0034]
(8) The inclination of the third inner wall surface with respect to the piston reciprocating axis is smaller than the inclination of the third outer wall surface with respect to the piston reciprocating axis. Thus, it is possible to prevent the air-fuel mixture in the inner cavity from becoming excessively rich, and to suppress and prevent the generation of smoke and unburned HC.
[0035]
(9) The depth of the inner cavity with respect to the piston crown is made smaller than the depth of the outer cavity with respect to the piston crown. Thereby, the stratified mixed air mass formed particularly in the inner cavity becomes compact, and stable stratified combustion can be realized in an extremely low load region such as idling.
[0036]
(10) The depth of the inner cavity with respect to the piston crown is made larger than the depth of the outer cavity with respect to the piston crown. In this case, the stratified mixed air mass formed in the inner cavity becomes relatively large, and stable stratified combustion can be realized in a low load region to a medium load region.
[0037]
(11) The depth of the inner cavity itself is made smaller than the depth of the outer cavity itself. As a result, the air-fuel mixture formed in the inner cavity is relatively small, and the air-fuel mixture formed in the outer cavity is relatively large. Stable stratified combustion can be realized in both load regions.
[0038]
(12) The first outer wall surface is an inclined surface that becomes higher toward the piston reciprocating axis. Thereby, the momentum of the fuel spray colliding with the first outer wall surface is moderated to prevent the wall flow, and the generation of smoke and the increase of unburned HC can be reduced and prevented.
[0039]
(13) The first inner wall surface is an inclined surface that becomes higher toward the piston reciprocating axis. Thus, the momentum of the fuel spray colliding with the first inner wall surface is moderated to prevent the wall flow, and the generation of smoke and the increase of unburned HC can be reduced and prevented.
[0040]
(14) The inclination of the first inner wall surface with respect to the orthogonal surface of the piston reciprocating axis is smaller than the inclination of the first outer wall surface with respect to the orthogonal surface. This ensures that wall flow in the outer cavity is reliably reduced and prevented, and in the stratified high-load operation region where the injection amount is large and smoke and unburned HC are likely to increase, the outer cavity is used to generate smoke and unburned HC. Can be effectively reduced or prevented.
[0041]
(15) By ensuring that the first inner wall surface is a flat surface substantially perpendicular to the piston reciprocating axis, combustion stability in an extremely low load stratified operation region such as idling where smoke and unburned HC are originally emitted is small is secured. In addition, workability can be improved and cooling loss can be reduced.
[0042]
(16) If the fuel injection valve is a multi-hole injection valve, even when the in-cylinder pressure in the latter half of the compression stroke is high, the spray directivity is strong and the spray swirl flow is easily generated, so that the uniformity is high. It is easy to generate a stratified mixed air mass.
[0043]
(17) When performing stratified charge combustion in which fuel is injected late in the compression stroke, the injection timing under a high load operation condition is advanced compared to the injection timing under a low load operation condition. Thus, a mixed gas mass having an appropriate size can be formed under both the low load operation condition and the high load operation condition, and stable stratified combustion can be realized at both the low load and the high load.
[0044]
(18) When the fuel injection valve can change the injection direction, the angle of the injection direction with respect to the reciprocating axis of the piston is made relatively large so as to point toward the inner cavity when the load is low, and the outer cavity when the load is high. Is relatively small so as to be oriented.
[0045]
(19) As described above, the injection direction of the fuel injector is directed toward the outer cavity under the high-load operation condition, and is directed toward the inner cavity under the low-load operation condition. A small air-fuel mixture is formed, and a relatively large air-fuel mixture can be formed by the outer cavity under high load operation conditions, and stable stratified combustion can be realized in both the low load region and the high load region.
[Brief description of the drawings]
FIG. 1 is a configuration diagram schematically showing a direct injection internal combustion engine according to the present invention.
FIG. 2 is a top view corresponding to a top view of a piston crown surface.
FIG. 3 is an explanatory diagram showing a spray shape under a piston shape and a stratified high load condition according to the first embodiment.
FIG. 4 is an explanatory view showing a spray shape under a piston shape and a stratified low load condition according to the first embodiment.
FIG. 5 is a sectional view showing the shape and various dimensions of the piston according to the first embodiment.
FIG. 6 is a sectional view showing the shape and various dimensions of a piston according to a second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Combustion chamber 4 ... Piston 11 ... Fuel injection valve 12 ... Spark plug 15 ... Piston crown surface 16 ... Outer cavity 16a ... First outer wall surface 16b ... Second outer wall surface 16c ... Third outer wall surface 17 ... Inner cavity 17a ... 1 inner wall surface 17b 2nd inner wall surface 17c 3rd inner wall surface

Claims (19)

A fuel injection valve arranged on or near the piston reciprocating axis and directly injecting fuel into the combustion chamber;
A spark plug arranged on or near the piston reciprocating axis and spark-igniting the air-fuel mixture in the combustion chamber;
An outer cavity recessed in the piston crown surface and having a substantially shaft-rotating body shape with respect to the piston reciprocating axis;
An in-cylinder direct injection internal combustion engine having an inner cavity recessed in the outer cavity and having a substantially shaft-rotating body shape with respect to the piston reciprocating axis. The outer cavity includes a first outer wall surface on which fuel spray collides obliquely, a second outer wall surface continuous with the outer peripheral side of the first outer wall surface, and a third outer wall surface continuous with the second outer wall surface. Have
The second outer wall surface includes an outer curved surface that smoothly curves toward the third outer wall surface,
2. The direct injection internal combustion engine according to claim 1, wherein the third outer wall surface is an inclined surface inclined at an angle close to an injection direction of the fuel spray. The inner cavity includes a first inner wall surface on which fuel spray collides obliquely, a second inner wall surface continuous with the outer peripheral side of the first inner wall surface, and a third inner wall surface continuous with the second inner wall surface. Have
The second inner wall surface includes an inner curved surface that smoothly curves toward the third inner wall surface,
The direct injection internal combustion engine according to claim 2, wherein the third inner wall surface is an inclined surface inclined at an angle close to an injection direction of the fuel spray. 4. The direct injection internal combustion engine according to claim 3, wherein a radius of curvature of the inner curved surface is smaller than a radius of curvature of the outer curved surface. The direct injection type internal combustion engine according to any one of claims 2 to 4, wherein the third outer wall surface has a reentrant shape that approaches the piston reciprocating axis as it goes upward of the piston. 5. The direct injection internal combustion engine according to claim 3, wherein the third inner wall surface has a reentrant shape that approaches the piston reciprocating axis as it goes upward of the piston. 7. The direct injection internal combustion engine according to claim 3, wherein the inclination of the third inner wall surface with respect to the piston reciprocating axis is greater than the inclination of the third outer wall surface with respect to the piston reciprocating axis. 7. The direct injection internal combustion engine according to claim 3, wherein the inclination of the third inner wall surface with respect to the piston reciprocating axis is smaller than the inclination of the third outer wall surface with respect to the piston reciprocating axis. The direct injection internal combustion engine according to any one of claims 1 to 8, wherein a depth of the inner cavity with respect to the piston crown surface is smaller than a depth of the outer cavity with respect to the piston crown surface. The direct injection internal combustion engine according to any one of claims 1 to 8, wherein a depth of the inner cavity with respect to the piston crown is larger than a depth of the outer cavity with respect to the piston crown. The direct injection internal combustion engine according to any one of claims 1 to 10, wherein the depth of the inner cavity itself is smaller than the depth of the outer cavity itself. The direct injection internal combustion engine according to any one of claims 1 to 11, wherein the first outer wall surface is an inclined surface that becomes higher toward the reciprocating axis of the piston. The in-cylinder direct injection internal combustion engine according to any one of claims 1 to 12, wherein the first inner wall surface is an inclined surface that becomes higher toward the reciprocating axis of the piston. 14. The direct injection internal combustion engine according to claim 12, wherein an inclination of the first inner wall surface with respect to a plane orthogonal to the piston reciprocation axis is smaller than an inclination of the first outer wall surface with respect to the orthogonal plane. The direct injection internal combustion engine according to any one of claims 1 to 12, wherein the first inner wall surface is a flat surface substantially orthogonal to a piston reciprocating axis. The direct injection internal combustion engine according to any one of claims 1 to 15, wherein the fuel injection valve is a multi-hole injection valve. 17. In the case of performing stratified charge combustion in which fuel is injected late in the compression stroke, the injection timing is changed according to the load, and the injection timing in the high load operation condition is advanced more than the injection timing in the low load operation condition. In-cylinder direct injection internal combustion engine according to any one of the above. The fuel injection valve is an injection valve capable of changing an injection direction,
The direct injection internal combustion engine according to any one of claims 1 to 17, wherein the angle of the injection direction with respect to the piston reciprocating axis is larger under a low load condition than under a high load condition. 19. The direct injection internal combustion engine according to claim 17, wherein the injection direction of the fuel injection valve is directed to the outer cavity under a high load operation condition and is directed to the inner cavity under a low load operation condition.

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