JPH10317973A - Piston of direct injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stratified lean combustion without using a helical port by forming slopes on the exhaust valve side and on the intake valve side on the top face of a piston, and recessedly providing a circular cavity combustion chamber on the slope on the intake valve side and a pair of valve recesses positioned on both sides of it. SOLUTION: On the top face of a piston, an exhaust valve side slope 23 nearly in parallel with the slope on the exhaust valve side of a pent roof type combustion chamber is formed, and similarly an intake valve side slope nearly in parallel with the slope on the intake valve side of the pent roof type combustion chamber is formed. The respective upper edges of the intake valve side slope and the exhaust valve side slope 23 are formed into a top horizontal face 30, and an intake valve side horizontal face 26 and an exhaust valve side horizontal face 27 of nearly crescent shape are formed outside the respective slopes for defining a squish area. On the position eccentric to the intake valve side against the outer circle of piston, a circular cavitay combustion chamber 12 is recessedly provided, and a pair of valve recesses 31, 32 are recessedly provided on the intake valve side slope corresponding to the valve head parts of the intake valves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder of a cylinder injection type internal combustion engine represented by a gasoline engine, and more particularly to a homogeneous combustion and a stratified combustion utilizing a tumble component and a swirl component generated in a cylinder. The present invention relates to an improvement in a piston of a direct injection type internal combustion engine that can perform both.

[0002]

2. Description of the Related Art At the time of full-open output or the like, a so-called homogeneous combustion is performed by forming a mixture having a substantially homogeneous air-fuel ratio in a cylinder, and in a low load range, a relatively small portion of the cylinder, that is, only in the vicinity of a spark plug, is relatively formed. 2. Description of the Related Art Various direct injection internal combustion engines that perform stratified combustion so as to obtain a very large average air-fuel ratio by forming a rich air-fuel mixture have been conventionally proposed.

As a piston of a direct injection type internal combustion engine capable of stratified lean combustion, for example, Japanese Patent Publication No. 8-3542
No. 9 is known. In the internal combustion engine described in this publication, a non-circular cavity combustion chamber eccentric to the piston outer circle is formed at the top of the piston, and fuel is injected toward the cavity combustion chamber near the piston top dead center. A fuel injection valve is arranged to be able to supply. The cavity combustion chamber is of a reentrant type so as to contain fuel and swirl therein. In addition, in order to generate a strong swirl in the cavity combustion chamber, one of the pair of intake ports is configured as a helical port, and an air control valve for opening and closing the other intake port is provided.

That is, in the internal combustion engine of this publication, at the time of lean burn, the air control valve is closed and fresh air is introduced only from one of the helical ports to generate a strong swirl in the cylinder. Since this swirl is introduced into the cavity combustion chamber as the piston rises, by injecting fuel into the cavity combustion chamber near the compression top dead center, a combustible mixture is formed in the cavity combustion chamber, and the spark plug is formed. It is carried nearby. Therefore, by performing ignition at an appropriate timing, ignition combustion is reached.

There have been proposed various variable valve mechanisms for variably controlling valve lift characteristics such as opening and closing timings and operating angles of intake and exhaust valves of an internal combustion engine in accordance with engine operating conditions. It is already in practical use. For example, Japanese Unexamined Utility Model Publication No. 57-198306 and Japanese Unexamined Patent Publication No. 6-185321 disclose a variable valve mechanism capable of changing a valve operating angle by unequal-speed rotation of a camshaft. In addition, a type in which two types of cams are selectively used, a type in which the phase of a camshaft with respect to a crankshaft is advanced, and the like are known.

[0006]

However, in the above-described conventional piston configuration, the cavity combustion chamber at the top of the piston is formed in a non-circular, substantially triangular, squid-shaped shape, so that a swirl of sufficient strength is stored here. To do so, a very strong swirl must be created in the cylinder using the helical port as described above.

Therefore, the use of such a helical port has a drawback that the intake resistance is large and the maximum output is suppressed at the time of full-open output.

In addition, by making the cavity combustion chamber a reentrant type as described above, swirl and air-fuel mixture can be reliably held in the cavity combustion chamber at the time of stratified lean combustion, but fuel is supplied during the intake stroke at a high load or the like. Even if an attempt is made to perform homogeneous combustion by injection, fuel tends to stay in the cavity combustion chamber, and sufficient performance cannot be ensured.

That is, stratified lean combustion and homogeneous combustion under a high load cannot be sufficiently compatible.

Furthermore, when an attempt is made to apply a variable valve mechanism to, for example, the intake valve side of the above-described in-cylinder injection type internal combustion engine, a valve recess is formed at the top of the piston to avoid interference between the intake valve and the piston. However, if a valve recess is simply added to the above-described conventional piston, the inside and outside of the cavity combustion chamber communicate with each other through the valve recess, so that performance during stratified combustion cannot be secured at all.

The present invention provides a piston for a direct injection type internal combustion engine which can realize stratified lean combustion without using a helical port and can sufficiently achieve both stratified lean combustion and homogeneous combustion. The purpose is to:

[0012]

SUMMARY OF THE INVENTION A piston of a direct injection internal combustion engine according to the present invention has two intake valves and two exhaust valves in a pent roof type combustion chamber recessed in a cylinder head, and has a cylinder substantially similar to that of the first embodiment. A fuel injection valve that has a spark plug in the center and directly injects fuel into the cylinder is arranged on the intake valve side, and performs fuel injection near the intake stroke with the tumble flow component provided in the cylinder. In the piston of a direct injection type internal combustion engine, which realizes stratified combustion by realizing homogeneous combustion and performing fuel injection near the compression stroke with a swirl component provided in the cylinder, the pent roof type combustion chamber The exhaust valve side inclined surface consisting of a plane inclined so as to be substantially parallel to the exhaust valve side inclined surface, and the intake valve side inclination of the pent roof type combustion chamber An intake valve-side inclined surface formed of a plane or a virtual plane inclined so as to be substantially parallel to an upper surface of the intake valve-side inclined surface and an upper edge of the exhaust valve-side inclined surface, and A top horizontal plane consisting of a plane perpendicular to the line, and an intake valve-side horizontal plane and an exhaust valve-side horizontal plane formed in a substantially crescent shape outside the intake valve-side inclined surface and the exhaust valve-side inclined surface so as to form a squish area. A pair of side surfaces forming side portions of the convex portion formed by the two inclined surfaces and the top horizontal surface, and a true circular cavity combustion chamber recessed at a position eccentric to the intake valve side with respect to the piston outer circle. And a pair of valve recesses formed in the intake valve side inclined surface corresponding to the valve head of the intake valve. The piston of the present invention is suitable for an internal combustion engine having a variable valve mechanism for variably controlling a valve lift characteristic of an intake valve.

[0013] In the second aspect of the present invention, the convex portion and the cavity combustion chamber are formed symmetrically with respect to a diameter line in a direction orthogonal to the piston pin.

In the above configuration, the intake valve side inclined surface, the exhaust valve side inclined surface, the top horizontal surface, and the pair of conical side surfaces provide:
A projection at the top of the piston is formed. The projection is configured such that the space between the piston and the combustion chamber on the cylinder head side at the top dead center is as small as possible.
During stratified combustion, swirl is generated in the cylinder by, for example, closing one intake port. This swirl is confined in the cavity combustion chamber as the piston rises, but since the cavity combustion chamber is a perfect circle, a sufficient swirl can be secured in the cavity combustion chamber without depending on the helical port. Then, the fuel is injected toward the cavity combustion chamber near the top dead center, so that good stratified combustion can be realized. Here, a valve recess is formed in the intake valve side inclined surface, and a part of the outer peripheral edge of the cavity combustion chamber is cut out by the valve recess. Since a top horizontal surface exists in a belt shape between the two, the gas flow to and from the exhaust valve side is suppressed, so that stratified combustion is not impaired.

During homogeneous combustion, fresh air flowing into the cylinder via a pair of intake valves generates a tumble flow, and fuel is injected near the intake stroke. This tumble flow prevents the fuel from remaining in the cavity combustion chamber, and realizes homogeneous combustion with a homogeneous mixture. In particular, since the cavity combustion chamber is a simple perfect circle, fuel does not easily stay.

According to the third aspect of the present invention, the outer peripheral edge of the cavity combustion chamber does not intersect the exhaust valve side top ridgeline between the top horizontal surface and the exhaust valve side inclined surface. The top horizontal surface remains between the valve-side portion and the ridgeline.

In particular, in the fourth aspect, the width of the top horizontal surface in the axial direction of the piston pin is set so as to cover substantially the entirety of the pair of valve recesses. That is, the length between both ends of the pair of valve recesses in the piston pin axial direction,
The width of the top horizontal surface in the axial direction of the piston pin is relatively similar.

According to the third and fourth aspects of the present invention,
The outer peripheral edge of the cavity combustion chamber does not protrude to the exhaust valve side inclined surface, and the outer peripheral edge does not have a shape cut off toward the exhaust valve side. Therefore, the cavity combustion chamber is separated from the exhaust valve side inclined surface together with the valve recess, and when the piston is near the top dead center, gas flow between the cavity combustion chamber and the space on the exhaust valve side is suppressed.
That is, at the time of stratified charge combustion, the swirl and the air-fuel mixture can be reliably contained in the cavity combustion chamber, and stratified charge combustion is improved.

According to the fifth aspect of the present invention, a step is provided between a lower edge of the exhaust valve side inclined surface and the exhaust valve side horizontal surface. This step is used for adjusting the compression ratio.

According to the sixth aspect of the present invention, the cavity combustion chamber has a dish shape in which the inner peripheral side wall surface is tapered upward. Thereby, at the time of homogeneous combustion, the fuel in the cavity combustion chamber is more easily washed away by the tumble flow, and the mixture is homogenized.

[0021]

According to the piston of the direct injection internal combustion engine according to the present invention, the swirl flow generated in the cylinder can be sufficiently stored in the cavity combustion chamber without using means such as a helical port. And stable stratified combustion can be realized. In particular, by providing the top flat surface between the intake valve side and the exhaust valve side, it is possible to suppress a decrease in performance during stratified combustion due to the formation of the valve recess. In addition, since the cavity combustion chamber does not have a complicated shape, fuel can be prevented from staying in the cavity combustion chamber during homogeneous combustion using a tumble flow, and favorable homogeneous combustion can be achieved. In other words, stratified lean combustion at low load and homogeneous combustion at high load can be made compatible at a very high level.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

First, the configuration of a direct injection internal combustion engine using the piston 4 of the present invention will be described with reference to FIGS. As shown in the drawing, a plurality of cylinders 3 are arranged in series in a cylinder block 1, and a cylinder head 2 is fixed so as to cover the upper surface thereof.
A piston 4 is slidably fitted in the cylinder 3. The combustion chamber 11 recessed in the cylinder head 2 is configured as a so-called pent roof type.
A pair of intake valves 5 are arranged on one inclined surface 11a, and a pair of exhaust valves 6 are arranged on the other inclined surface 11b. An ignition plug 7 is arranged at a substantially central position of the cylinder 3 surrounded by the pair of intake valves 5 and the pair of exhaust valves 6. For the intake valve 5,
Although not shown in detail, a known variable valve operating mechanism is provided, and the valve lift characteristic can be variably controlled according to the engine operating conditions. 9 and 10
FIG. 9 shows an example of a valve lift characteristic obtained by this variable valve mechanism. In FIG. 9, the opening / closing timing is delayed while the operating angle is constant, and in FIG. The operating angle is configured to increase and decrease.

In the cylinder head 2, a pair of intake ports 8 respectively corresponding to the pair of intake valves 5 are formed independently of each other. That is, the pair of intake ports 8 do not merge in the cylinder head 2, and are independently opened on the side surface of the cylinder head 2. An exhaust port 9 is formed corresponding to the exhaust valve 6.

The substantially cylindrical electromagnetic fuel injection valve 10 has:
It is arranged on the lower surface of the cylinder head 2 near the side wall of the cylinder 3 on the side of the intake valve 5, and is mounted with its central axis directed obliquely downward. In particular, as shown in FIG. 2, the fuel injection valve 10 is disposed between two intake valves 5.

The piston 4 disposed in the cylinder 3
As described later, a circular cavity combustion chamber 12 is formed at a position eccentric to the intake valve 5 side.
When the piston 4 is near the top dead center, the spray axis of the fuel injection valve 10 is directed toward the cavity combustion chamber 12.

The pair of intake ports 8 are connected to a pair of intake passages 14a and 14b independently formed on the intake manifold 13 side. A butterfly valve type air control valve 15 for opening and closing the intake passage 14b is provided in one intake passage 14b. The opening and closing of the air control valve 15 is controlled by a drive mechanism (not shown) via a shaft 16 in accordance with engine operating conditions. When the air control valve 15 is closed, fresh air flows only through the intake port 8 connected to the other intake passage 14a. However, this intake port 8 is not a helical port, but a gently curved substantially straight line. It is shaped like a port.

The basic operation of the internal combustion engine will be briefly described. First, when the engine is fully loaded or in a region where the air-fuel ratio is relatively small in the lean combustion region, a homogeneous air-fuel mixture is formed in the cylinder 3. Homogeneous ignition is performed. During this homogeneous combustion, the air control valve 15 is controlled to be open, and fresh air is introduced into the cylinder 3 from both the pair of intake ports 8. As a result, a strong tumble flow (longitudinal vortex) is generated in the cylinder 3. The fuel is injected and supplied into the cylinder 3 during the intake stroke. This fuel is actively diffused in the cylinder 3 by the tumble flow, and the homogenization is promoted without staying in the cavity combustion chamber 12.

On the other hand, in the lean load region where the air-fuel ratio is extremely large in the low load region, stratified lean combustion is performed that enables reliable ignition by stratification of the air-fuel mixture. During the stratified lean combustion, the air control valve 15 is closed, and fresh air flows into the cylinder 3 from only one of the intake ports 8. Thereby, in the cylinder 3, the tumble component is relatively weakened, and the swirl flow along the horizontal direction is strongly generated. During the stratified lean combustion, fuel is injected from the fuel injection valve 10 to the cavity combustion chamber 12 in the latter half of the compression stroke. This injected fuel is
The piston 4 moves toward the spark plug 7 on the swirl flow sealed in the cavity combustion chamber 12 at the top of the piston 4 and forms an ignitable air-fuel mixture around the spark plug 7. Ignition combustion becomes possible.

Next, the piston 4 will be described with reference to FIGS.
, In particular, the configuration of the top portion will be described in detail.

In the piston 4, a projection 21 is provided on the top surface so that the cavity combustion chamber 12 occupies most of the space in the cylinder 3 at the top dead center.
The projection 21 is basically composed of five surfaces. That is, the intake valve side inclined surface 22 and the exhaust valve side inclined surface 23, which are planes substantially parallel to the two inclined surfaces 11a and 11b constituting the pent roof type combustion chamber 11 on the cylinder head 2 side, and the intake valve side inclined surface A top horizontal plane 30 formed of a plane that is formed in a band shape so as to connect the upper edge of the surface 22 and the upper edge of the exhaust valve-side inclined surface 23 and that is orthogonal to the center line of the piston 4, and concentric with the outer circle of the piston 4 The convex portion 21 is constituted by a pair of conical side surfaces 24 and 25 each having a slightly inclined conical surface. In this embodiment, the intake valve side inclined surface 22 is not finally left as a flat surface due to the formation of the valve recesses 31 and 32 and the cavity combustion chamber 12, which will be described later. As shown by, it is a virtual plane.

Outside the intake valve-side inclined surface 22 and the exhaust valve-side inclined surface 23, a substantially crescent-shaped intake valve-side horizontal surface 26 and an exhaust valve-side horizontal surface 27 are formed, respectively. The intake valve side horizontal surface 26 and the exhaust valve side horizontal surface 27 are formed of one plane orthogonal to the center line of the piston 4 and are left as flat surfaces on both sides of the combustion chamber 11 on the cylinder head 2 side. Squish areas 2a and 2b (see FIG. 1). A very narrow horizontal surface 28, 2 is provided between the lower edge of the conical side surfaces 24, 25, which forms an arc, and the outer peripheral edge of the piston 4.
9 are left (see FIG. 5). These horizontal planes 26,
27, 28 and 29 are located at the same height as one plane. Further, in this embodiment, due to the compression ratio, a step 34 exists between the lower edge 23a of the exhaust valve side inclined surface 23 and the exhaust valve side horizontal surface 27, and the step 34 is , And a flat surface that is larger than the exhaust valve side inclined surface 23.

The cavity combustion chamber 12 is recessed over the top horizontal surface 30, the intake valve side inclined surface 22, and the intake valve side horizontal surface 26. The cavity combustion chamber 12 has a true circular shape when viewed on the plane of the piston 4 and has a diameter larger than the radius of the piston 4. The bottom surface is along a plane perpendicular to the center line of the piston 4, and the inner peripheral side wall surface is formed in a dish shape which is gently tapered upward. The outer peripheral edge of the cavity combustion chamber 12 is located inside a pair of virtual side ridges generated between the conical side surfaces 24 and 25 and the intake valve side inclined surface 22. That is, the intake valve side inclined surface 22 is larger than the cavity combustion chamber 12 in the axial direction of the piston pin. Similarly, the portion of the outer peripheral edge of the cavity combustion chamber 12 closer to the exhaust valve is located slightly closer to the intake valve than the exhaust valve side top ridgeline 33 between the top horizontal surface 30 and the exhaust valve side inclined surface 23. The top horizontal plane 30 remains between the ridge 33 and the outer peripheral edge of the cavity combustion chamber 12 though the width is narrow. In other words, the outer peripheral edge of the cavity combustion chamber 12 does not intersect the exhaust valve side top ridge line 33 and is not notched.
Further, as shown in FIG. 2, when the piston 4 is at the top dead center, the ignition plug 7 is disposed so as to enter the cavity combustion chamber 12 and to be located on the outer peripheral portion thereof.

A pair of valve recesses 31 and 32 are formed in the intake valve side inclined surface 22 so as to correspond to the valve head of the intake valve 5. Although the valve recesses 31 and 32 are formed in a relatively shallow circular shape along the valve inclination angle, since they overlap with the cavity combustion chamber 12, they each appear in a crescent shape. In the present embodiment, a part of the outer periphery of each of the valve recesses 31 and 32 slightly approaches the top horizontal plane 30, the conical side surfaces 24 and 25, and the intake valve side horizontal plane 26.

The conical side surface 2 of the projection 21
The apex angle θ of the 4 and 25 cones (see FIG. 5) is
The positions of the ridgelines 35, 36 between the fourth horizontal plane 25 and the top horizontal plane 30 are set as small as possible so as to be on the outer peripheral side of the piston 4. Thereby, when the piston 4 is at the top dead center, the clearance generated between the conical side surfaces 24 and 25 and the combustion chamber 11 on the cylinder head 2 side is very small, and remains in the cylinder 3. Most of the volume is occupied by the cavity combustion chamber 12. Further, since the ridge lines 35 and 36 are located near the outer periphery of the piston 4, the width of the top horizontal surface 30 in the piston pin axial direction is
The pair of valve recesses 31 and 32 cover substantially the entire formation range in the axial direction of the piston pin.

The structure of the top of the piston 4 configured as described above is symmetrical about the diameter line (that is, line AA in FIG. 3) in the direction perpendicular to the piston pin. In addition, the fuel injection valve 10 has a symmetrical axis A-
It is arranged to inject fuel along line A.

In the above configuration, the swirl generated in the cylinder 3 at the time of stratified combustion causes the swirl generated in the cylinder combustion chamber 12 because the cavity combustion chamber 12 has a simple perfect circular shape.
It is smoothly guided inside and stored with sufficient strength. Then, after the fuel is injected toward the cavity combustion chamber 12 in the latter half of the compression stroke, when the piston 4 approaches the top dead center, the top horizontal surface 30 surrounding the cavity combustion chamber 12 and the intake valve side inclined surface 22 (actually, Valve recess 3
1 and 32) and the horizontal surface 26 on the intake valve side, as shown by imaginary lines in FIG. 1, respectively, come close to the corresponding planes on the cylinder head 2 side. A good seal is obtained over the entire circumference. Therefore, the swirl and the mixture in the cavity combustion chamber 12 do not leak to the outside, and the combustion proceeds in the cavity combustion chamber 12. Therefore, stable stratified lean combustion can be performed without using the intake port 8 as a helical port, and a decrease in the maximum output due to the use of the helical port can be avoided. In particular, the valve recesses 31 and 32 are recessed so as to overlap with the cavity combustion chamber 12, and the cavity combustion chamber 12, the valve recesses 31 and 32, and the exhaust valve side inclined surface 2 are formed.
Since the top horizontal surface 30 exists between the valve recess 3 and the valve 3, the adverse effects due to the formation of the valve recesses 31 and 32 are extremely small, and sufficiently favorable stratified combustion can be secured.

At the time of homogeneous combustion, fresh air flowing from the pair of intake ports 8 forms a tumble flow in the cylinder 3 and fuel is injected during the intake stroke.
The cavity combustion chamber 12 has a dish shape in which the upper portion is gently expanded in a tapered shape, and is positioned above a center line (A-A line in FIG. 3) of a pair of intake ports 8 where the tumble flows are concentrated. Since the circular cavity combustion chamber 12 is located, the fuel entering the cavity combustion chamber 12 is easily washed away by the tumble flow and does not stay. Therefore, a homogeneous air-fuel mixture can be formed even under a high load, and good homogeneous combustion can be achieved.

FIGS. 6 and 7 show a second embodiment of the piston 4 according to the present invention. In this embodiment, the step 34 between the exhaust-valve-side inclined surface 23 and the exhaust-valve-side horizontal surface 27 is removed, and the lower edge 23a of the exhaust-valve-side inclined surface 23 becomes the exhaust-valve-side horizontal surface 27. Has reached.

In the configuration of the second embodiment, as shown in FIG. 8, at the time of homogeneous combustion in which fresh air is introduced from both intake ports 8, a tumble flow indicated by an arrow is generated on the exhaust valve side horizontal surface 2 as shown in FIG.
7 to the exhaust valve side inclined surface 23 to flow more smoothly. In other words, the attenuation of the tumble flow due to the unevenness such as the step portion 34 in the above-described embodiment is reduced, and the tumble component can be stored for a long time during the compression stroke. Therefore, it is possible to improve HC in the exhaust gas particularly when the engine is fully opened.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a direct injection internal combustion engine according to the present invention.

FIG. 2 is a bottom view showing a state where the cylinder head is viewed from a lower surface side.

FIG. 3 is a plan view showing a first embodiment of the piston according to the present invention.

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

FIG. 5 is a sectional view taken along the line BB in FIG. 3;

FIG. 6 is a plan view showing a second embodiment of the piston according to the present invention.

FIG. 7 is a sectional view taken along the line CC of FIG. 6;

FIG. 8 is an explanatory diagram showing a flow of a tumble flow in a cylinder by the piston.

FIG. 9 is a characteristic diagram showing an example of a valve lift characteristic of an intake valve.

FIG. 10 is a characteristic diagram showing another example of the valve lift characteristics of the intake valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 4 ... Piston 12 ... Cavity combustion chamber 21 ... Convex part 22 ... Intake valve side inclined surface 23 ... Exhaust valve side inclined surface 24, 25 ... Conical side surface 26 ... Intake valve side horizontal surface 27 ... Exhaust valve side horizontal surface 30 ... Top horizontal surface 31 , 32: valve recess 34: step

Claims (7)

[Claims] 1. A pent-roof type combustion chamber recessed in a cylinder head has two intake valves and two exhaust valves, has a spark plug substantially at the center of the cylinder, and
A fuel injection valve that injects fuel directly into the cylinder is arranged on the intake valve side, and achieves homogeneous combustion by performing fuel injection near the intake stroke with a tumble flow component added to the cylinder, In a piston of an in-cylinder injection type internal combustion engine in which stratified combustion is realized by performing fuel injection near a compression stroke in a state where a swirl component is added, substantially parallel to an inclined surface on the exhaust valve side of the pent roof type combustion chamber. An exhaust valve side inclined surface consisting of a plane inclined so as to be;
Similarly, an intake valve side inclined surface formed of a plane or a virtual plane inclined so as to be substantially parallel to the intake valve side inclined surface of the pent roof type combustion chamber, an upper edge of the intake valve side inclined surface, and the exhaust valve side inclined surface. And a top horizontal plane which is a plane orthogonal to the piston center line, and a substantially crescent shape outside the intake valve side inclined surface and the exhaust valve side inclined surface so as to constitute a squish area. The intake valve side horizontal surface and the exhaust valve side horizontal surface, a pair of side surfaces constituting a side portion of the convex portion formed by the two inclined surfaces and the top horizontal surface, and a position eccentric to the intake valve side with respect to the piston outer circle. And a pair of valve recesses recessed in the intake valve side inclined surface corresponding to the valve head of the intake valve. Internal injection type internal combustion engine Piston. 2. The piston of a direct injection internal combustion engine according to claim 1, wherein the projection and the cavity combustion chamber are formed symmetrically with respect to a diameter line in a direction orthogonal to the piston pin. . 3. An outer peripheral edge of the cavity combustion chamber does not intersect an exhaust valve side top ridgeline between the top horizontal surface and the exhaust valve side inclined surface, and a portion of the outer peripheral edge near the exhaust valve. The piston of a cylinder injection type internal combustion engine according to claim 1 or 2, wherein the top horizontal surface remains between the ridge and the ridge. 4. The piston of a cylinder injection type internal combustion engine according to claim 3, wherein the width of the top horizontal surface in the axial direction of the piston pin is set so as to cover substantially the entirety of the pair of valve recesses. 5. The in-cylinder injection according to claim 1, wherein a step portion is provided between a lower edge of the exhaust valve side inclined surface and the exhaust valve side horizontal surface. Pistons for internal combustion engines. 6. The in-cylinder injection type according to claim 1, wherein the cavity combustion chamber has a dish shape in which an inner peripheral side wall surface is tapered upward. Internal combustion engine piston. 7. The piston of a direct injection internal combustion engine according to claim 1, further comprising a variable valve mechanism for variably controlling a valve lift characteristic of the intake valve.