JPH11218026A - Piston for cylinder injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid worsening of stratified charge lean-burning due to formation of valve recesses. SOLUTION: An exhaust valve side inclined face 23 parallel to the inclined face of a pent roof type combustion chamber, and an intake valve side inclined face 22 are formed on a protruded part 21 of the top face of a piston 4. A bowl 12 is about circular, and valve recesses 31, 32 are dented-provided so that they are overlapped with the bowl. A step part 40 or an inclined-face connecting the top face of a protruded part 21 to the bottom face 31a of a valve recess is formed so that it will be connected to the outer peripheral side of the valve recess side wall face 31b facing cylinder swirl S1 turning along the outer paripheral part of a cylinder, and the step part 40 is extended up to the side face 25 of the protruded part 21. Since the component S1 of swirl escapes above the piston 4 along the step part 40, the swirl does not flow into the bowl 12.

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 bowl eccentric to the piston outer circle is formed at the top of the piston,
A fuel injection valve is arranged near the top dead center of the piston so that fuel can be injected and supplied toward the bowl. The bowl is of a reentrant type so as to contain fuel and swirl therein. Also, in order to generate a strong swirl in this bowl, one of the pair of intake ports is configured as a helical port,
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 bowl as the piston rises, by injecting fuel into the bowl near the compression top dead center, a combustible mixture is formed in the bowl, and the swirl is transported to the vicinity of the spark plug. It is. Therefore, by performing ignition at an appropriate timing, ignition combustion is reached.

[0005]

By the way, in order to improve the output during high-load operation, it is necessary to improve the charging efficiency of the intake air. For example, it is conceivable to increase the maximum lift of the intake valve. In this case, it is preferable to start opening the intake valve as early as possible. Also, during low to medium speed operation, filling efficiency is improved by closing the intake valve early, and during high speed operation, charging efficiency is improved by delaying the closing timing of the intake valve.For example, the phase of the intake side camshaft with respect to the crankshaft is changed. It is conceivable to variably control the valve lift characteristics by using a variable valve mechanism that retards the movement. In this case, when the intake valve is closed early, the opening timing is advanced accordingly.

As described above, it is often necessary to advance the opening timing of the intake valve in order to improve the output during high-load operation. In this case, the intake valve starts to lift even near the intake top dead center. Therefore, it is conceivable that a valve recess for avoiding interference between the intake valve and the piston is recessed in the piston top surface.

However, if a valve recess is added to the conventional piston for an in-cylinder injection type internal combustion engine in order to avoid interference between the intake valve and the piston, the bowl and the valve recess are partially overlapped. The outer peripheral edge of the bowl is partially cut away by the valve recess. Therefore, after the fuel is injected and supplied to the bowl near the compression top dead center, the in-cylinder swirl component that turns around the outer periphery of the cylinder flows into the bowl using the side wall of the valve recess as a guide, and turns inside the bowl. The swirl component in the combustion chamber is weakened, and the fuel in the bowl is easily taken out of the bowl. As a result, stratified lean combustion becomes unstable, leading to deterioration of fuel efficiency and an increase in HC.

The present invention provides a piston of an in-cylinder injection type internal combustion engine capable of achieving both stratified lean combustion and homogeneous combustion and giving a lift to an intake valve even near the intake top dead center by a valve recess. The purpose is to do.

[0009]

SUMMARY OF THE INVENTION In a cylinder injection type internal combustion engine according to the present invention, a pent roof type combustion chamber recessed in a cylinder head has two intake valves and two exhaust valves, and is provided substantially at the center of the cylinder. A fuel injection valve that has a spark plug and directly injects fuel into the cylinder is arranged on the intake valve side, and performs homogeneous fuel combustion by performing fuel injection near the intake stroke with a tumble flow component added to the cylinder. And stratified combustion is achieved by injecting fuel near the compression stroke with a swirl component provided in the cylinder.

[0010] The piston according to the present invention comprises a projection having an intake valve side inclined surface and an exhaust valve side inclined surface which are inclined so as to be substantially parallel to the two inclined surfaces constituting the pent roof type combustion chamber. A substantially circular bowl recessed at a position eccentric to the intake valve side with respect to the piston outer circle, and a pair of valve recesses recessed on the intake valve side inclined surface corresponding to the valve head of the intake valve. , Is provided.

That is, in the configuration of the present invention, the intake valve side inclined surface and the exhaust valve side inclined surface are formed on the top surface of the convex portion formed on the piston top portion, and the combustion chamber on the cylinder head side at the piston top dead center. Is designed to be as small as possible.

During stratified combustion, swirl is generated in the cylinder by, for example, closing one intake port. This swirl is sealed in the bowl with the rise of the piston, but since the bowl is substantially circular, sufficient swirl can be secured in the bowl. And
Good stratified combustion can be realized by injecting fuel toward the bowl near the top dead center.

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 bowl and achieves homogeneous combustion with a homogeneous mixture.

Since a pair of valve recesses is formed in the intake valve side inclined surface, a lift can be given to the intake valve even near the intake top dead center, and the output during homogeneous combustion can be improved. It is advantageous.

According to the first aspect of the present invention, the inclined surface smoothly continues to the outer peripheral side of the side wall surface of the one valve recess facing the swirl flow, and connects the bottom surface of the valve recess and the top surface of the convex portion. Is formed to extend to the side surface of the projection.

According to the second aspect of the present invention, the upper edge of the step is formed in a straight line parallel to the piston pin.

According to the configuration of the first and second aspects,
On the outer peripheral side of the side wall surface of one of the valve recesses facing the swirl flow, a step portion composed of an inclined surface connecting the bottom surface of the valve recess and the top surface of the convex portion is smoothly continuous, and this step portion is formed by the convex portion. Since it is extended to the side surface, the swirl component in the cylinder that rotates around the cylinder outer periphery and passes above the valve recess is appropriately released above the piston along the slope of the step, and enters the bowl. Never do. As a result, the swirl component swirling in the bowl is weakened and the stratified combustion is effectively prevented from being impaired.

According to a third aspect of the present invention, there is provided a steep inclined surface which is connected to an outer peripheral side of a side wall surface of one of the valve recesses facing the swirl flow and connects a bottom surface of the valve recess and a top surface of the convex portion. Is formed to extend up to the side surface of the convex portion in parallel with the piston pin on the piston plane.

According to the configuration of the third aspect, the swirl component that turns in the cylinder and passes above the valve recess collides with the steep step portion and is weakened here. As a result, the swirl component entering the bowl through the valve recess is effectively suppressed, and the stratified combustion is not impaired as in the first and second aspects.

According to a fourth aspect of the present invention, the side surface of the convex portion located on the outer peripheral side of one valve recess whose side wall surface faces the swirl flow is more than the side surface of the convex portion located on the outer peripheral side of the other valve recess. It is characterized in that it is arranged on the inner peripheral side of the piston.

According to a fifth aspect of the present invention, a piston reference horizontal plane consisting of a plane orthogonal to the center axis of the piston in the cylinder axial direction is provided on the outer peripheral portion of the projection. The piston reference horizontal plane is formed continuously around the entire circumference, and a region located on the outer peripheral side of the one valve recess is set wider than a region located on the outside of the other valve recess. .

According to the fourth and fifth aspects of the present invention, the side surface of the convex portion located on the outer peripheral side of the one valve lift whose side wall faces the swirl flow is formed relatively toward the inner peripheral side of the piston. In this part, the space between the side surface of the projection and the inner wall surface of the cylinder becomes relatively large. As a result, the swirl component that turns in the cylinder and passes above the valve recess appropriately flows into the space on the outer peripheral side of the relatively large convex portion. Therefore, the swirl component entering the bowl is effectively suppressed, and the stratified combustion is not impaired.

In addition, according to the configuration of the fourth and fifth aspects, the in-cylinder swirl component rotating around the cylinder outer periphery is sufficiently preserved even near the piston top dead center, so that the piston retreats from the top dead center. At this time, the rise of the air-fuel mixture from the bowl is promoted, and the accumulation of fuel in the bowl is more effectively suppressed.

According to the piston of the present invention,
As described above, the present invention is particularly suitable for an internal combustion engine provided with a variable valve mechanism for variably controlling a valve lift characteristic of an intake valve.

[0025]

According to the piston of the direct injection internal combustion engine according to the present invention, it is possible to give a lift to the intake valve even near the intake top dead center by forming the valve recess.
This is advantageous for improving the output during homogeneous combustion, and effectively suppresses the swirl component swirling around the outer periphery of the cylinder from flowing into the bowl through the valve recess when the piston is near the compression top dead center. Therefore, performance degradation during stratified combustion due to the formation of the valve recess can be suppressed. In other words, stratified lean combustion at low load and homogeneous combustion at high load can be made compatible at a very high level.

[0026]

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.

A pair of intake ports 8 respectively corresponding to the pair of intake valves 5 are formed in the cylinder head 2 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 includes:
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 arranged in the cylinder 3
A circular bowl 12 is formed on the top of the piston 4 at a position eccentric to the intake valve 5 side, as described later.
Is near the top dead center, the spray axis of the fuel injection valve 10 is directed toward the bowl 12.

The pair of intake ports 8 are connected to a pair of intake passages 14a and 14b formed independently 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 above-mentioned 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 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 bowl 12.

On the other hand, in the low-load region and in the lean-burn region where the air-fuel ratio is extremely large, stratified-lean combustion that enables reliable ignition by stratification of the air-fuel mixture is performed. 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 toward the bowl 12 in the latter half of the compression stroke. This injected fuel is stored in the piston 4
It moves on the side of the spark plug 7 on the swirl flow sealed in the bowl 12 at the top, and forms an ignitable mixture around the spark plug 7, so that ignition and combustion can be performed by igniting at an appropriate timing. Becomes

Next, the first embodiment of the present invention will be described with reference to FIGS.
The configuration of the piston 4 according to the embodiment, particularly the configuration of the top portion thereof, will be described in detail. 6 and 7 correspond to A in FIG.
It is sectional drawing which follows the -A line and the BB line.

In the piston 4, a convex portion 21 is provided on the top surface so that the bowl 12 occupies most of the space in the cylinder 3 at the top dead center. This projection 21
Is basically composed of five surfaces. That is, the recess 21 has two inclined surfaces 11 a and 11 b (FIG. 1) that constitute the pent roof type combustion chamber 11 on the cylinder head 2 side.
2) connecting the intake valve side inclined surface 22 and the exhaust valve side inclined surface 23, which are planes substantially parallel to 2), the upper edge of the intake valve side inclined surface 22 and the upper edge of the exhaust valve side inclined surface 23, It is composed of a band-shaped top horizontal surface 30 formed of a plane orthogonal to the center line of the piston 4 and a pair of conical side surfaces 24 and 25 formed of conical surfaces concentric with the outer circle of the piston 4. The pair of conical side surfaces 24 and 25 form side portions of the convex portion 21.

In this embodiment, the intake valve-side inclined surface 22 is provided with valve recesses 31 and 32,
Due to the formation of the 0 and the bowl 12, only a small amount actually remains near the top, and most of them are virtual planes. In this embodiment, the conical side surfaces 24 and 25 are integrally connected to each other through the lower edge of the exhaust valve side inclined surface 23.

The conical side surfaces 24, 2 of the convex portion 21
The apex angle of the cone of No. 5 is very small, and as shown in FIG.
The conical side surfaces 24 and 25 are steep. 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 (FIGS. 1 and 2) on the cylinder head 2 side is very small, and the bowl 12 occupies most of the volume remaining in the cylinder 3. Occupy.

A piston reference horizontal surface 26 is formed on the outer periphery of the projection 21. The piston reference horizontal plane 26 is constituted by one plane orthogonal to the center line of the piston 4 in the cylinder axial direction, and is continuous over the entire circumference of the piston 4 crown surface. The thrust and anti-thrust portions of the piston reference horizontal surface 26 correspond to the squish areas 2a and 2b (FIG. 1) left as flat surfaces on both sides of the combustion chamber 11 on the cylinder head 2 side.

The bowl 12 is recessed from the intake valve side inclined surface 22 to the top horizontal surface 30 and the exhaust valve side inclined surface 23. This bowl 12 has a 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 (upper edge) of the bowl 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, in the piston pin axial direction, the intake valve side inclined surface 22 is larger than the bowl 12.
On the other hand, the portion of the outer peripheral edge of the bowl 12 near the exhaust valve slightly protrudes closer to the exhaust valve than the exhaust valve side top ridge between the top horizontal surface 30 and the exhaust valve side inclined surface 23.
This is because the present embodiment uses the piston 4 having a relatively small diameter, and when the piston 4 has a large diameter, it is preferable that the piston 4 does not protrude from the top ridge line on the exhaust valve side. As shown in FIG. 2, when the piston 4 is at the top dead center, the spark plug 7 enters the bowl 12,
And it is arrange | positioned so that it may be located in the outer peripheral part.

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 the bowl 12, each of the valve recesses 31 and 32 appears in a substantially crescent shape. That is, valve recess 3
The inner edges of the bowls 1 and 32 are the upper edges of the bowl 12. The valve recesses 31 and 32 are set so that the depth does not become deeper than the piston reference horizontal plane 26 in the axial direction of the piston. That is, as is clear from FIG. 5, the shape is not concave below the piston reference horizontal plane 26.

Here, the valve recess 3 shown in the lower part of FIG.
In the vicinity of 1, the valve recess 31 is recessed in the intake valve side inclined surface 22 of the protrusion 21, so that the protrusion outer edge 21 a remains along the outer edge of the valve recess 31 in an arc-shaped weir shape. doing. In other words, the convex outer edge 21a remains between the arcuately curved valve recess side wall surface 31b connecting the valve recess bottom surface 31a and the top surface of the convex portion 21 and the side surface 24 of the convex portion 21. , A part of the intake valve side inclined surface 22 remains. This convex outer edge 21a
4 gradually decreases toward the intake valve side of the piston 4 toward the intake valve, that is, toward the right side in FIG. 4 according to the inclination of the intake valve side inclined surface 22, and in this embodiment, decreases abruptly on the way to reduce the valve recess 31. It disappears at the same height as the bottom surface 31a. The valve recess side wall surface 31b
Has a relatively steep slope along the center line of the intake valve 5 (FIG. 1).

On the other hand, the valve recess 3 shown in the upper part of FIG.
2. More specifically, the valve recess 32 whose side wall surface 32b connecting the bottom surface 32a of the valve recess and the top surface of the convex portion 21 faces the in-cylinder swirl flow S1 rotating in the cylinder 3.
Is in a shape in which the above-mentioned outer peripheral portion 21a of the convex portion does not substantially exist.

That is, a step portion 40 composed of an inclined surface connecting the valve recess bottom surface 32a and the top surface of the convex portion 21 is smoothly and continuously formed on the outer peripheral side of the valve recess side wall surface 32b. The protrusion 21 is formed to extend in the radial direction of the piston to the side surface 25. In other words, the step portion 40 connecting the valve recess bottom surface 32a and the top surface of the convex portion 21 extends from the outer peripheral edge of the bowl 12 to the side surface 25 of the convex portion 21, and a part of the step portion 40 is provided on the valve recess side. It constitutes the wall surface 32b.

That is, the structure of the top of the piston 4 is as follows:
The diameter line in the direction perpendicular to the piston pin (that is, A in FIG. 4)
−A line). In addition, the fuel injection valve 10 is arrange | positioned so that fuel may be injected along this AA line.

The upper edge 41 of the step portion 40 is connected to the top horizontal surface 30 of the convex portion 21 and is formed linearly in parallel with the piston pin direction (pent roof ridge line direction). On the other hand, the lower edge 42 of the step portion 40 has an arc shape on the inner peripheral side overlapping the valve recess side wall surface 32b, and extends in a straight line parallel to the piston pin on the outer peripheral side. For this reason, in the step portion 40, the region on the inner peripheral side is relatively steep,
The area on the outer peripheral side is one relatively gentle curved surface. More specifically, as shown in FIGS.
0 indicates that the ridge line 43 with the bowl 12 is relatively steep, and the ridge line 44 with the convex side surface 25 is relatively gently inclined.

In the above configuration, since the bowl 12 has a simple substantially circular shape, the swirl generated in the cylinder 3 during stratified combustion is smoothly guided into the bowl 12 and maintains sufficient strength. Saved as is. Then, after the fuel is injected toward the bowl 12 in the latter half of the compression stroke, when the piston 4 approaches the top dead center, each surface of the convex portion 21 having the bowl 12 becomes as shown by imaginary lines in FIG. Because they are close to the corresponding surfaces on the cylinder head 2 side,
The bowl 12 is in a state of being sealed well over the entire circumference. Therefore, the swirl and the mixture in the bowl 12 do not leak to the outside, and the combustion proceeds in the bowl 12.

Here, the valve recesses 31 and 32 are recessed so as to overlap with the bowl 12. However, since the bottom surface 32 a of one of the valve recesses 32 and the top surface of the convex portion 21 are smoothly connected by the step portion 40, The in-cylinder swirl component S1 that turns around the outer periphery of the cylinder 3 is, as shown by the reference numeral S2 in FIG.
The water flows upward from the top surface of the piston 4 along the step portion 40 and does not enter the bowl 12. Therefore, the swirl flow in the bowl 12 is not disturbed by the gas flow flowing from the outside of the bowl 12, and the adverse effect due to the formation of the valve recesses 31 and 32 is greatly reduced.
A sufficiently good 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 bowl 12 has a dish shape in which the upper portion is gently expanded in a tapered shape, and has a substantially circular shape on the center line (the A-A line in FIG. 3) of the pair of intake ports 8 where the tumble flows are concentrated. Since the bowl 12 is located, the fuel entering the bowl 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.

Next, a piston according to a second embodiment of the present invention will be described with reference to FIGS. In the embodiments described below, the same components as those in the first embodiment are denoted by the same reference numerals, and the description of the overlapping configurations and the functions and effects will be appropriately omitted.

In the second embodiment, the in-cylinder swirl flow S
A step portion 50 having a steep slope is formed on the outer peripheral side of the side wall surface 32b of the one valve recess 32 opposite to the step 1 in place of the step portion 40 of the first embodiment. That is, the step portion 50 is connected to the outer peripheral side of the valve recess side wall surface 32b at a slight angle, and connects the bottom surface 32a of the valve recess 32 and the top surface of the convex portion 21. The step portion 50 is an inclined surface that is parallel to the piston pin and substantially perpendicular to the piston reference horizontal plane 26, and extends to the side surface 25 of the projection 21.

More specifically, the upper edge 51 of the step portion 50 is connected to the top horizontal surface 30 of the projection 21 and extends linearly in parallel with the piston pin direction (pent roof ridge line direction). It is connected to the upper edge of the valve recess side wall surface 32b curved in an arc shape on the side. The lower edge 52 of the step portion 50 also extends linearly in parallel with the piston pin, and has a valve recess side wall surface 32 curved in an arc shape on the inner peripheral side.
b is connected to the lower edge. Further, the inner peripheral edge 5 of the step portion 50
3 is connected to the valve recess side wall surface 32b, and the outer peripheral edge 54 is connected to the side surface 25 of the projection 21.

According to the configuration of the second embodiment, the in-cylinder swirl component S that rotates along the outer periphery of the cylinder 3
1 collides with the steep step 50, where it is weakened.
As a result, the swirl component entering the bowl 12 via the valve recess 32 is effectively suppressed. Therefore, the swirl flow and the fuel in the bowl 12 are not disturbed by the gas flow flowing from the outside of the bowl 12, and the adverse effects due to the formation of the valve recesses 31 and 32 are extremely reduced, and a sufficiently good stratified combustion is achieved. Can be secured.

Next, the structure of a piston according to a third embodiment of the present invention will be described with reference to FIGS.

The piston of the third embodiment has basically the same construction as that of the first embodiment. That is, on the outer peripheral side of the side wall surface 32b of the valve recess 32 facing the in-cylinder swirl S1, the valve recess bottom surface 32a and the projection 21 are formed.
A step portion 40 composed of an inclined surface connecting to the top surface of the projection 21 is smoothly and continuously formed, and the step portion 40 is formed to extend in the piston radial direction to the side surface 25 of the projection 21.

Here, in the piston of the third embodiment, the side surface 62 of the convex portion 21 whose side wall surface 32b is located on the outer peripheral side of the valve recess 32 facing the in-cylinder swirl flow S1, is connected to the other side. It is arranged on the inner peripheral side of the piston with respect to the side surface 61 of the convex portion 21 located on the outer peripheral side of the valve recess 31. More specifically, the side surface 6 on the valve recess 32 side
2 is a slope that is steeper than the side surface 61 on the valve recess 31 side.

In other words, in the piston reference horizontal plane 26 continuously formed over the entire outer periphery of the convex portion 21, the region 6 located on the outer periphery side of the one valve recess 32.
4 is an area 6 located outside the other valve recess 31.
It is set wider than 3. That is, as is clear from FIG. 15, the space formed between the convex side surface 62 on the valve recess 32 side and the inner wall surface of the cylinder 3 is formed between the convex side surface 61 on the valve recess 31 side and the inner wall surface of the cylinder 3. Is relatively larger than the space defined by

According to the configuration of the third embodiment, the same effects as those of the first embodiment can be obtained. In addition, the area 64 of the piston reference horizontal surface 26 located on the outer peripheral side of the valve recess 32 and the space above the same. Is relatively large, so that the in-cylinder swirl component S1 that turns around the outer periphery of the cylinder
Flows into the space on the outer peripheral side of the convex portion 21 satisfactorily.
As a result, the swirl component entering the bowl 12 through the valve recess 32 is effectively suppressed, and the stratified combustion is not impaired.

Further, a swirl of sufficient strength can be stored in the space above the piston reference horizontal plane 26 even near the piston top dead center, so that the air-fuel mixture in the bowl 12 is generated by the central negative pressure of the in-cylinder swirl. Is obtained up to the spark plug 7, and the stratified combustion can be performed more stably.

[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 perspective view showing a first embodiment of the piston according to the present invention.

FIG. 4 is a plan view of a piston according to the first embodiment.

FIG. 5 is a front view of the piston according to the first embodiment.

FIG. 6 is a sectional view taken along the line AA of FIGS. 4 and 14;

FIG. 7 is a sectional view taken along the line BB in FIGS. 4 and 14;

FIG. 8 is a perspective view showing a second embodiment of the piston according to the present invention.

FIG. 9 is a plan view of a piston according to a second embodiment.

FIG. 10 is a front view of a piston according to a second embodiment.

FIG. 11 is a sectional view taken along the line CC of FIG. 9;

FIG. 12 is a sectional view taken along the line DD in FIG. 9;

FIG. 13 is a perspective view showing a third embodiment of the piston according to the present invention.

FIG. 14 is a plan view of a piston according to a third embodiment.

FIG. 15 is a front view of a piston according to a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 4 ... Piston 12 ... Bowl 21 ... Convex part 22 ... Intake valve side inclined surface 23 ... Exhaust valve side inclined surface 24, 25 ... Conical side surface 26 ... Piston reference horizontal surface 31, 32 ... Valve recess 40, 50 ... Stepped portion 61, 62 … Conical side

Claims (6)

[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 applied, each of the two inclined surfaces forming the pent roof type combustion chamber is substantially A convex portion having an intake valve side inclined surface and an exhaust valve side inclined surface inclined so as to be parallel, a substantially circular bowl recessed at a position eccentric to the intake valve side with respect to the piston outer circle, and the intake valve A pair of valve recesses recessed in the intake valve side inclined surface corresponding to the valve head of the valve, and the outer periphery of the side wall surface of one of the valve recesses facing the swirl flow is provided. And a stepped portion formed by an inclined surface connecting the bottom surface of the valve recess and the top surface of the convex portion, extending to the side surface of the convex portion. piston. 2. The piston for a direct injection internal combustion engine according to claim 1, wherein an upper edge of the step portion is formed in a straight line parallel to a piston pin. 3. A pent roof type combustion chamber recessed in a cylinder head has two intake valves and two exhaust valves, and has a spark plug substantially at the center of the cylinder.
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 applied, each of the two inclined surfaces forming the pent roof type combustion chamber is substantially A convex portion having an intake valve side inclined surface and an exhaust valve side inclined surface inclined so as to be parallel, a substantially circular bowl recessed at a position eccentric to the intake valve side with respect to the piston outer circle, and the intake valve A pair of valve recesses formed in the inclined surface on the intake valve side corresponding to the valve heads, and contacting the outer peripheral side of the side wall surface of one of the valve recesses facing the swirl flow. In addition, a step portion consisting of a steep inclined surface connecting the bottom surface of the valve recess and the top surface of the convex portion, in parallel with the piston pin on the piston plane, is formed to extend to the side surface of the convex portion. Piston of a direct injection internal combustion engine. 4. A pent roof type combustion chamber recessed in a cylinder head has two intake valves and two exhaust valves, has a spark plug substantially in 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 applied, each of the two inclined surfaces constituting the pent roof type combustion chamber is substantially A convex portion having an intake valve side inclined surface and an exhaust valve side inclined surface inclined so as to be parallel, a substantially circular bowl recessed at a position eccentric to the intake valve side with respect to the piston outer circle, and the intake valve A pair of valve recesses recessed in the intake valve side inclined surface corresponding to the valve head of the outer periphery of one valve recess whose side wall faces the swirl flow The side surface of the protrusion located, other than the side surface of the protrusion located on the outer peripheral side of the valve recess, a piston for a cylinder injection internal combustion engine, characterized in that arranged in the piston periphery. 5. A piston reference horizontal plane, which is a plane perpendicular to the center line in the cylinder axial direction of the piston, is formed continuously around the entire circumference of the piston crown surface on the outer peripheral portion of the projection. The piston of the direct injection internal combustion engine according to claim 4, wherein a region located on the outer peripheral side of the valve recess is set wider than a region located on the outside of the other valve recess. 6. 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 said intake valve.