JPH11280478A - Piston for cylinder injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve combustion performance with a piston of a cylinder injec tion type internal combustion engine which can provide an intake valve with a lift even near the top dead center. SOLUTION: A projection 21 on the top of a piston 4 is provided with an intake valve side inclined surface 11, and an exhaust valve side inclined surface 23, parallely to two inclined surfaces of a cylinder head. A bowl 12 is recessed on an eccentric position to the side of the intake valve in respect to a piston outer circle. A pair of valve recesses 31, 32 are formed correspondingly to a valve head of the intake valve. The bowl has a dish-like form in which a side wall surface 12 is widened in a taper shape upward. A bottom surface 12a of the bowl 12 has a continuous same lane with bottom surfaces 31a, 31b of the valve recesses 31, 32.

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.

[0003] As a piston of a direct injection internal combustion engine capable of stratified lean combustion, for example, Japanese Patent Application Laid-Open No. 8-3542 is disclosed.
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. Further, in order to generate a strong swirl in this bowl, 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, during stratified lean combustion, 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 igniting at an appropriate time, ignition and combustion will result.

[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 formed in the piston crown.

[0007] 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 with an intake valve, the bowl and the valve recess partially overlap. That is, the valve recess facing the outer peripheral portion of the bowl is relatively shallow compared to the bowl, and is a narrow area particularly near the compression top dead center. As a result, part of the fuel injected into the bowl enters the narrow valve recess, making it difficult for the flame to propagate, leading to an increase in unburned fuel and a decrease in combustion performance such as deterioration of fuel efficiency and exhaust performance. There is a risk of doing so.

An object of the present invention is to further improve the combustion performance of a piston of a direct injection internal combustion engine capable of giving a lift to an intake valve even near the intake top dead center.

[0009]

An in-cylinder injection type 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 in the center. 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.

According to the first aspect of the present invention, the intake valve-side inclined surface and the 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 are provided on the piston top. A substantially dish-shaped bowl recessed at a position eccentric to the intake valve side with respect to the piston outer circle, and the intake valve side corresponding to the valve head of the intake valve so as to partially overlap the bowl. And a pair of valve recesses recessed on the inclined surface, wherein the bottom surface of the bowl and the bottom surface of the valve recess are formed on the same continuous surface.

The invention according to a second aspect of the present invention provides an intake valve-side inclined surface and an exhaust valve-side inclined surface which are inclined on the top of the piston so as to be substantially parallel to the two inclined surfaces constituting the pent roof type combustion chamber. A substantially dish-shaped bowl recessed at a position eccentric to the intake valve side with respect to the piston outer circle, and the intake valve side corresponding to the valve head of the intake valve so as to partially overlap the bowl. And a pair of valve recesses recessed in the inclined surface, wherein the bottom surface of the valve recess is formed as an inclined surface connected to the bottom surface of the bowl.

A third aspect of the present invention provides an intake valve-side inclined surface and an exhaust-valve-side inclined surface which are inclined on the top of the piston so as to be substantially parallel to the two inclined surfaces constituting the pent roof type combustion chamber, respectively. A bowl recessed at a position eccentric to the intake valve side with respect to the outer circle, and the bowl has
In order to avoid interference with the valve head of the intake valve, the opening is formed in a substantially bowl-like shape that is elongated in the axial direction of the piston pin.

More preferably, a variable valve mechanism for variably controlling a valve lift characteristic of the intake valve is provided.

With the above configuration, swirl is generated in the cylinder during stratified charge combustion, for example, by closing one intake port. Here, the configuration is such that the space between the combustion chamber on the cylinder head side and the top of the piston at the piston top dead center is as small as possible.
Therefore, the swirl generated in the cylinder is well contained in the bowl (and the valve recess) with the rise of the piston. Then, the fuel is injected toward the bowl near the top dead center, so that good stratified combustion can be realized.

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 the valve recess), and achieves homogeneous combustion with a homogeneous mixture.

According to the first and second aspects of the present invention, a pair of valve recesses are formed in the intake valve-side inclined surface corresponding to the valve head of the intake valve. It is possible to give a lift to the valve, which is advantageous in improving the output during homogeneous combustion.

According to the first aspect of the present invention, since the bottom surface of the bowl and the bottom surface of the valve recess are formed on the same continuous surface, the valve recess does not locally become narrow unlike the conventional example. Thus, the entire flame spreads from the bowl to the valve recess. As a result,
In particular, the combustion performance during stratified combustion is improved. Specifically, the emission of unburned fuel is suppressed, and the fuel efficiency and exhaust performance are improved.

According to the second aspect of the present invention, since the bottom surface of the valve recess is formed as an inclined surface connected to the bottom surface of the bowl, the flame can propagate well from the bowl to the valve recess particularly during stratified combustion. As a result, combustion performance is improved, and more specifically, emission of unburned fuel is suppressed, and fuel efficiency and exhaust performance are improved.

On the other hand, in the third aspect of the present invention, since the bowl is recessed so as to avoid interference with the valve head of the intake valve, a lift can be given to the intake valve near the intake top dead center. It is.

The bowl according to the third aspect of the invention is formed in a substantially bowl shape having an elliptical opening, and has a smooth shape with no corner portions. As a result, the gas flow in the combustion chamber becomes smoother, heat spots are less likely to be generated, the full-opening performance during homogeneous combustion is improved, and the flame propagates well in the bowl during stratified combustion, resulting in combustion. The characteristics can be further improved.

[0021]

As described above, according to the present invention, it is possible to give a lift to the intake valve even near the intake top dead center, which is particularly advantageous for increasing the output during high-load operation.

According to the first and second aspects of the present invention, the flame propagates from the bowl to the valve recess as a whole during stratified combustion, thereby suppressing the discharge of unburned fuel and improving the fuel efficiency and exhaust performance. Can be planned.

According to the third aspect of the present invention, the gas flow in the combustion chamber is smooth, heat spots are less likely to occur, and the full opening performance during homogeneous combustion is improved.
The flame propagates favorably in the bowl during stratified combustion, and the combustion characteristics can be further improved.

[0024]

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 to which the piston 4 according to the present invention is applied will be described with reference to FIGS. As shown, the cylinder block 1
, A plurality of cylinders 3 are arranged in series, and the 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 is provided on one inclined surface 11a, and a pair of exhaust valves 6 are provided on the other inclined surface 11b. Are arranged respectively. 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. Although not shown in detail, a well-known variable valve mechanism is provided for the intake valve 5 so that the valve lift characteristic can be variably controlled according to the engine operating conditions.

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 comprises:
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
As described later, a bowl 12 is recessed at a position eccentric to the intake valve 5 side, and when the piston 4 is near the top dead center, the spray axis of the fuel injection valve 10 The bowl 12 is oriented.

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. In addition, a butterfly valve type air control valve 15 that opens and closes the intake passage 14b is interposed 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 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 positively diffused in the cylinder 3 by the tumble flow, and the fuel is diffused into the bowl 12 and valve recesses 31 and 3 described later.
2 (FIGS. 3 to 5), and homogenization is promoted.

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 toward the bowl 12 in the latter half of the compression stroke. This injected fuel is stored in the piston 4
Top bowl 12 and valve recesses 31 and 32 (Figs.
5) Riding on the swirl flow enclosed in the spark plug 7, it moves to the spark plug 7 side to form an ignitable air-fuel mixture around the spark plug 7, so that ignition is performed at an appropriate timing to enable ignition combustion. .

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.

The projection 21 forming the top of the piston 4 has a plane substantially parallel to the two inclined surfaces 11a and 11b (FIGS. 1 and 2) constituting the pent roof type combustion chamber 11 on the cylinder head 2 side. An intake valve side inclined surface 22 and an exhaust valve side inclined surface 23 are formed, and the bowl 12 is recessed at a position eccentric to the intake valve side. And
A pair of valve recesses 31 and 32 are formed in the intake valve side inclined surface 22 so as to partially overlap the bowl 12, corresponding to the valve head of the intake valve 5.

The bowl 12 has a substantially circular shape in plan view and has a diameter larger than the radius of the piston 4, and is recessed from the intake valve side inclined surface 22 to the exhaust valve side inclined surface 23. ing. The bowl 12 has a bottom surface 12a formed in a circular flat surface, and a side wall surface 12b formed in a dish shape in which the side surface surface 12b gently expands in a tapered shape, and
Both sides are partially cut away by the valve recesses 31 and 32. 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.

The valve recesses 31 and 32 are provided with the intake valve 5.
However, since they are recessed in a columnar shape along the direction of inclination, they overlap with the bowl 12 and therefore appear in a substantially semicircular shape.

In this embodiment, the valve recess 3 is used.
The bottom surfaces 31a and 32a of the bowls 12 and
It is formed on the same plane continuous with 2a. In other words, the bowl 12 and the valve recesses 31, 32 are set to the same depth, and the valve recess bottom surfaces 31a, 32a,
The bowl bottom surface 12a is the same plane that is substantially parallel to the intake valve side inclined surface 22.

As shown in FIG. 5, a sufficient gap is secured between the intake valve 5 and the valve recess bottom surfaces 31a, 32a, so that the intake valve 5 does not interfere with the piston 4. As a result, a lift can be given to the intake valve 5 even near the intake top dead center.

FIG. 6 shows the behavior of the piston 4 and fuel spray during stratified charge combustion. The fuel spray F injected toward the bowl 12 in the latter half of the compression stroke as shown in (a) moves on the swirl swirling in the bowl 12 as shown in (b) and moves to the spark plug 7 side. A combustible mixture F is formed around the ignition plug 7. When the mixture F is ignited at an appropriate timing, the bottom surface 12
Since the “a” and the valve recess bottom surfaces 31 a and 32 a are formed on the same plane, the flame G propagates well from the bowl 12 to the valve recesses 31 and 32 as shown in FIG. Finally, as shown in (d), the flame G spreads well throughout the bowl 12 and the valve recesses 31 and 32, and good combustion is performed without leaving unburned fuel.

Since the valve recesses 31 and 32 are recessed inside the intake valve side inclined surface 22, a part of the intake valve side inclined surface 22 remains on the outer peripheral portions of the valve recesses 31 and 32. Therefore, when the piston 4 approaches the top dead center,
Since each surface of the convex portion 21 is close to the corresponding surface on the cylinder head 2 side, the bowl 12 and the valve recess 3
1 and 32 are in a state of being sealed well over the entire circumference. Therefore, the swirl and the mixture in the bowl 12 and the valve recesses 31 and 32 do not leak to the outside, and the combustion proceeds favorably.

On the other hand, 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 is located above the center line (line AA in FIG. 3) of the pair of intake ports 8 where the tumble flows are concentrated, and the bowl 12 and the valve recesses 31 and 32 have a thin bottom and substantially dish shape. So that the bowl 12, valve recess 31,
The fuel that has entered the inside 32 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, the second embodiment of the present invention will be described with reference to FIGS.
A piston according to the embodiment will be described. In the second and third embodiments to be described later, 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 omitted as appropriate.

In the second embodiment, the bottom surfaces 41a and 42a of the pair of valve recesses 41 and 42 are inclined surfaces connected to the outer peripheral edge of the bottom surface 12a of the bowl 12. That is, the bottom surfaces 41a and 42a are substantially semicircular arc-shaped planes inclined along the intake valve side inclined surface 22 in the direction of the center line L1 orthogonal to the piston pin. The inner peripheral surfaces 41b, 42b of the valve recesses 41, 42 are peripheral wall surfaces along the inclination direction of the intake valve 5 corresponding to the valve head of the intake valve 5, as in the first embodiment.

As shown in FIG. 9, the shortest depth D1 of the valve recesses 41 and 42 is set so that the intake valve 5 does not interfere with the crown surface of the piston 4. Therefore,
It is possible to give a lift to the intake valve 5 even near the compression top dead center.

According to the structure of the second embodiment, the bottom surfaces 41a and 42a of the valve recesses 41 and 42 are
Since the inclined surface is connected to the bottom surface 12a of the second member, the flame propagates well from the bowl 12 to the valve recesses 41 and 42 during stratified combustion, as in the first embodiment, so that good combustion is achieved. .

Also, the valve recesses 41, 4 of this embodiment
2, the volume is substantially reduced by the area R shown by the hatched line in FIG. 9 as compared with the valve recesses 31 and 32 of the first embodiment, and the output reduction caused by the compression ratio reduction is reduced. Can be suppressed.

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

The opening 50a of the bowl 50 of this embodiment has a substantially bowl-like shape that is elongated in the axial direction of the piston pin so that the intake valve 5 does not interfere with the crown surface of the piston 4. Has been established. That is, the surface of the bowl 50 is one smooth hemispherical curved surface. That is, the bowl 50 is recessed so as to substantially accommodate the valve head of the intake valve 5, and also serves the function of the valve recess of the first and second embodiments. Therefore, even if the intake valve 5 lifts near the compression top dead center, the intake valve 5 does not interfere with the piston 4 crown surface as shown in FIG.

According to the third embodiment, since there is no valve recess in the crown surface of the piston 4 and the bowl 50 has a smooth curved shape, the gas flow becomes good during homogeneous combustion, Heat spots are less likely to occur, abnormal combustion is suppressed, and further improvement in full-open performance can be achieved. Further, since the bowl 50 has a smooth curved shape, during stratified combustion, the flame propagates well in the bowl 50, and the combustion proceeds well without fuel stagnation.

Further, in the third embodiment, the valve recess does not need to be formed separately from the bowl as in the first and second embodiments, so that the manufacturing thereof is further facilitated.

[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 sectional view taken along line A1-A1 of FIG. 4;

FIG. 6 is an explanatory diagram showing the behavior of fuel injected into the bowl of the first embodiment.

FIG. 7 is a perspective view showing a second embodiment of the piston according to the present invention.

FIG. 8 is a plan view of a piston according to a second embodiment.

9 is a sectional view taken along line A2-A2 in FIG.

FIG. 10 is a perspective view showing a third embodiment of the piston according to the present invention.

FIG. 11 is a plan view of a piston according to a second embodiment.

FIG. 12 is a sectional view taken along line A3-A3 in FIG. 11;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 4 ... Piston 5 ... Intake valve 12 ... Bowl 21 ... Convex part 22 ... Intake valve side inclined surface 23 ... Exhaust valve side inclined surface 31, 32 ... Valve recess 31a, 32a ... Bottom 41, 42 ... Valve recess 41a, 42a ... Bottom 50 ... bowl

Claims (4)

[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 a cylinder injection type internal combustion engine in which stratified combustion is realized by injecting fuel near a compression stroke in a state where a swirl component is added, two inclinations constituting the pent roof type combustion chamber are provided at the top of the piston. An intake valve-side inclined surface and an exhaust-valve-side inclined surface which are inclined so as to be substantially parallel to the respective surfaces; a substantially dish-shaped bowl 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 so as to partially overlap with the bottom surface of the bowl and the valve recess. The piston of the direct injection internal combustion engine, characterized in that formed in the same plane continuous and a bottom surface of Ruburisesu. 2. 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 a cylinder injection type internal combustion engine in which stratified combustion is realized by injecting fuel near a compression stroke in a state where a swirl component is added, two inclinations constituting the pent roof type combustion chamber are provided at the top of the piston. An intake valve-side inclined surface and an exhaust-valve-side inclined surface which are inclined so as to be substantially parallel to the respective surfaces; a substantially dish-shaped 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 in the intake valve side inclined surface corresponding to the valve head of the intake valve so as to partially overlap the bottom surface of the valve recess. A piston for a cylinder injection internal combustion engine, characterized in that formed on the inclined surface connecting the bottom surface of the bowl. 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 injecting fuel near the compression stroke in a state where a swirl component is applied, two inclinations constituting the pent roof type combustion chamber are provided at the top of the piston. An intake valve-side inclined surface and an exhaust valve-side inclined surface which are respectively inclined so as to be substantially parallel to the surfaces, and a bowl recessed at a position eccentric to the intake valve side with respect to the piston outer circle. Is characterized in that its opening is formed in a substantially bowl shape that is elongated in the axial direction of the piston pin so as to avoid interference with the valve head of the intake valve. The piston of the direct injection internal combustion engine. 4. 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.