JP2000008863A - Piston for cylinder injection internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To introduce a swirl, on the outer peripheral side turning around the outer peripheral part of a cylinder, effectively into a bowl. SOLUTION: An intake valve side slope 22 and an exhaust valve side slope 23 in parallel to a slope of a pent roof type combustion chamber are formed in a protruded part 21 in a top part of a piston 4. A plate-shaped bowl 12 is hollowly provided in a position eccentric to an intake valve side in the protruded part, also a swirl guide part 40 is hollowly provided in a cylinder swirl downstream position of the bowl 12. A guide side wall surface 40b of the swirl guide part 40 is smoothly connected to a peripheral wall surface 12b of the bowl 12, also extended to an outer peripheral part of the protruded part. At stratified charge combustion time, a swirl component in an outer peripheral side turning around the outer peripheral part of a cylinder is well introduced in the bowl 12 along the guide side wall surface 40b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston of a direct injection internal combustion engine represented by a gasoline engine, and more particularly, to homogeneous combustion and 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 internal combustion engine capable of performing 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. 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 disclosed in this publication, at the time of 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 around 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]

In the swirl generated in the cylinder, the flow component on the outer peripheral side tends to be stronger than the flow component on the inner peripheral side. However, in the conventional piston structure, although the swirl component on the inner peripheral side is relatively easily introduced into the bowl, the swirl component on the outer peripheral side has a pent roof inclined surface on the cylinder head side near the compression top dead center,
It is easily damped by being sandwiched between the inclined surface of the piston crown and
Not well introduced into the bowl. As a result, a sufficient swirl component cannot be ensured in the bowl, and there is a possibility that the combustion efficiency is reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel piston of a direct injection type internal combustion engine capable of effectively introducing in-cylinder swirl rotating around the outer periphery of a cylinder into a bowl.

[0007]

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 identical 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 addition to realizing homogeneous combustion, stratified combustion is realized by performing fuel injection near the compression stroke with a swirl component provided in the cylinder.

According to the first aspect of the present invention, 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 are provided on the piston top. A protruding portion having a swirl guide is formed at a position eccentric to the intake valve side with respect to the outer diameter of the piston. The swirl guide is characterized in that the side wall surface of the swirl guide portion is smoothly connected to the peripheral wall surface of the bowl and extends to the outer peripheral portion of the convex portion.

That is, an intake valve side inclined surface and an exhaust valve side inclined surface are formed on the top surface of the convex portion formed on the piston top portion, and the space between the piston top dead center and the combustion chamber on the cylinder head side is formed. Is configured to be as small as possible.

During stratified combustion, in-cylinder swirl is generated in the cylinder by, for example, closing one intake port. Here, the swirl on the outer peripheral side that rotates around the outer peripheral portion of the cylinder comes into a shape that abuts against the side wall surface of the swirl guide portion with the rise of the piston, and is smoothly introduced into the bowl using the side wall surface as a guide. Accordingly, the swirl on the outer peripheral side is sufficiently introduced into the bowl, and is well sealed in the bowl near the piston top dead center. As a result, good stratified combustion can be realized by injecting the fuel toward the bowl near the top dead center.

In 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.

More preferably, the flat bottom surface of the swirl guide is formed at a position shallower in the axial direction of the piston than the bottom surface of the bowl, which is a circular flat surface.

That is, a step is provided between the bowl and the swirl guide, so that the air-fuel mixture or the swirl component introduced into the bowl is securely contained in the bowl without leaking to the swirl guide. .

According to a third aspect of the present invention, a pair of valve recesses are formed in the inclined surface on the intake valve side so as to correspond to a valve head of the intake valve, and the swirl guide portion is provided in the cylinder swirl of the bowl. One of the valve recesses located on the downstream side is also used.

When the valve recess is recessed in this way, it is possible to give a lift to the intake valve even near the intake top dead center, which is advantageous in improving the output during homogeneous combustion.

According to a fourth aspect of the present invention, the peripheral wall surface of the bowl and the side wall surface of the swirl guide portion are formed in a smoothly continuous curved surface, and the bottom surface of the bowl and the bottom surface of the swirl guide portion are formed. Are formed on a smooth continuous flat surface.

That is, since the bowl and the swirl guide are formed as one smoothly continuous recess,
The processing is easy and the unevenness of the piston crown surface is reduced, which is advantageous in terms of thermal efficiency.

[0018]

As described above, according to the piston of the in-cylinder injection type internal combustion engine according to the present invention, the swirl component on the outer peripheral side revolving around the outer peripheral portion of the cylinder is smoothly performed using the side wall surface of the swirl guide section as a guide. Since it is introduced into the bowl, a swirl of sufficient strength can be ensured in the bowl, so that its combustion characteristics are improved.

[0019]

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 according to the present invention 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 1 recessed in the cylinder head 2
Reference numeral 1 is a so-called pent roof type, in which a pair of intake valves 5 is 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.

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,
It is open independently on the side. 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. Further, the fuel injection valve 10
Is arranged between the two intake valves 5 as shown in FIG.

At the top of the piston 4 disposed in the cylinder 3, a substantially dish-shaped bowl 12 is recessed 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. In addition,
The ignition plug 7 is arranged so as to enter the bowl 12 when the piston 4 is at the top dead center and to be located on the outer periphery thereof.

A pair of intake ports 8 are respectively formed on a pair of intake passages 14 formed independently on the intake manifold 13 side.
a, 14b. 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. In addition,
When the air control valve 15 is closed, the other intake passage 14
Fresh air flows in only through the intake port 8 connected to a, but this intake port 8 is not a helical port, but has a loosely curved substantially straight port shape.

The basic operation of the internal combustion engine will be described. When the engine is fully loaded or in a lean combustion region where the air-fuel ratio is relatively small, a homogeneous mixture is formed in the cylinder 3 for ignition. Homogeneous combustion takes place. At the time of 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,
Homogenization is promoted without stagnation in 2.

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. At the time of 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. The injected fuel moves toward the spark plug 7 on the swirl flow trapped in the bowl 12 at the top of the piston 4 and forms an ignitable mixture around the spark plug 7. Ignition enables ignition combustion.

Next, referring to FIGS. 3 to 5, the first embodiment of the present invention will be described.
The configuration of the piston 4 according to the embodiment, particularly the configuration of the top portion thereof, will be described in detail.

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. The projection 21 is basically composed of four surfaces. In other words, the convex portion 21 has the intake valve-side inclined surface 22 and the exhaust valve-side inclined surface which are 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. It is constituted by a surface 23 and a pair of conical side surfaces 24 and 25 formed of conical surfaces concentric with the outer circle of the piston 4.

When the piston 4 is at the top dead center, the clearance generated between the surfaces 22 to 25 of the projection 21 and the combustion chamber 11 of the cylinder head 2 becomes very small. Most of the remaining volume is
1 is occupied by the bowl 12 and the swirl guide 40 described later.

The squish areas 2a, 2 left as flat surfaces on both sides of the combustion chamber 11 on the cylinder head 2 side are provided on the thrust and anti-thrust side portions of the top surface of the piston 4.
b (FIG. 1), a pair of horizontal surfaces 26 are formed.

The bowl 12 has a bottom surface 12a formed in a circular flat surface and a peripheral wall surface 12a.
b has a dish shape which is gently tapered upward. The opening edge (upper edge) 12c of the bowl 12
4 and 5, the piston 4 has a circular shape when viewed in the axial direction of the piston 4, and slightly protrudes toward the exhaust valve side inclined surface 23 side.

In the present embodiment, a swirl guide portion 40 is provided at a position downstream of the bowl 12 in the swirl direction in the direction of flow of the in-cylinder swirl S rotating in the cylinder 3. The swirl guide portion 40 is formed from two surfaces, that is, a flat guide bottom surface 40a formed at a position shallower in the piston axial direction than the bottom surface 12a of the bowl 12, a guide bottom surface 40a and a convex portion. 21 and a guide side wall surface 40b that is gently inclined upward so as to connect to the top surface.

The guide side wall surface 40b is capable of satisfactorily supporting the outer swirl S1 rotating around the outer periphery of the cylinder 3 in the bowl
And is formed so as to face the outer swirl S1 so as to guide the inside of the bowl 1 more specifically.
2 and smoothly connected to the peripheral wall 12b
The projection 21 extends to the outer peripheral side up to the outer peripheral portion, that is, the conical side surface 25.

The guide side wall surface 4 extending substantially linearly
The upper edge 40c of the bowl 0b is smoothly connected to the opening edge 12c of the bowl 12, that is, extends in the tangential direction of the bowl opening edge 12c.

Next, the operation of this embodiment will be described with reference to FIGS.

At the time of stratified lean combustion, a strong swirl S is generated in the cylinder 3 by closing one intake valve 5 as described above.

FIG. 4A shows a state in which the piston 4 is located at the bottom dead center of the intake air. When the piston 4 rises from this state (a) to the position shown in FIG. The swirl S2 on the inner peripheral side, which has a relatively weak flow component, is introduced into the bowl 12 with the peripheral wall surface 12b of the bowl 12 located at a higher position in the piston axial direction as a guide.

When the piston 4 rises from this state (b) to the state shown in (c) (a state near ignition), the inclined surfaces 11a and 11b of the cylinder 3 and the inclined surfaces 22 and 23 of the piston 4 The space between is becoming very narrow. At this time, the swirl S1 on the outer peripheral side, which has a relatively strong flow component and revolves around the outer peripheral portion of the cylinder 3, collides with the guide side wall surface 40b of the swirl guide portion 40, and
Along the inside of the bowl 12.

In the latter half of the compression stroke, the bowl 12
When the piston 4 approaches the top dead center as shown in FIG.
1 are close to the corresponding surfaces on the side of the cylinder head 2, respectively, and the bowl 12 is in a state of being sealed well over the entire circumference, and the swirls S1 and S2 of sufficient strength are placed inside the bowl 12. Is contained in Therefore, the swirl and the mixture in the bowl 12 do not leak to the outside, and the combustion proceeds well in the bowl 12.

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 shaped like a dish with a tapered shape with a gentle upper part, and the bowl 12 is located on the center line of a pair of intake ports 8 where the tumble flows are concentrated. The fuel that has entered inside 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.

As described above, in the present embodiment, the swirl S1 on the outer peripheral side that rotates around the outer peripheral portion of the cylinder 3 can be smoothly introduced into the bowl 12 by using the side wall surface 40b of the swirl guide section 40 as a guide. The swirl can be secured in the bowl 12, and its combustion characteristics are improved.

Further, in the first embodiment, the guide bottom surface 40a of the swirl guide portion 40 is
Is formed at a shallower position in the axial direction of the piston, and a step is provided between the bowl 12 and the swirl guide section 40. Therefore, the swirl or the air-fuel mixture introduced into the bowl 12 is removed by the swirl guide section 40. Can be securely contained in the bowl 12 without leaking out.

Next, referring to FIGS. 6 to 8, the second embodiment of the present invention will be described.
A piston according to the embodiment will be described. Note that, in the embodiments described later, the same reference numerals are given to the portions already described, and the overlapping description will be appropriately omitted.

In the second embodiment, a known variable valve mechanism is provided for the intake valve 5 shown in FIGS. 1 and 2, so that the valve lift characteristic can be variably controlled in accordance with the engine operating conditions. ing. A pair of valve recesses 31 and 32 are formed in the intake valve-side inclined surface 22 of the convex portion 21 so as to correspond to the valve head of the intake valve 5.

As in the first embodiment, the bowl 12
A swirl guide section 40 is formed at a position on the swirl downstream side of the swirl.
The two downstream swirl valve recesses 32 also serve as one downstream valve recess 32.

More specifically, the upstream valve recess 31 located upstream of the bowl 12 in the flow direction of the in-cylinder swirl S
Is formed in a relatively shallow circular recess along the valve inclination angle, and appears in a substantially crescent shape because it partially overlaps the bowl 12. This upstream valve recess 31
The flat bottom surface 12a is formed at a position shallower than the bowl bottom surface 12a in the piston axial direction, and the side wall surface 31b is formed in an arc shape corresponding to the valve head of the intake valve 5. It has a curved surface.

On the other hand, in the flow direction of the swirl S,
Although the bottom surface 32a of the downstream valve recess 32 located on the downstream side is formed at substantially the same depth as the bottom surface 31a of the upstream valve recess 31, the side wall surface 32b
(40b) is the swirl guide section 40 of the first embodiment.
The peripheral wall surface 12 of the bowl 12 is similar to the guide side wall surface 40b of FIG.
b and is extended outwardly to the outer peripheral portion of the convex portion 21. That is, the side wall surface 32
b has a shape retreated to the exhaust valve side (downstream of the swirl S) as compared with the side wall surface 31b of the upstream valve recess 31.

That is, in this embodiment, the swirl downstream portion of the bowl 12 includes the swirl guide portion 40 and the downstream valve recess 32 so that the upstream valve recess 3 is formed.
It is recessed over a wider area than one.

In the second embodiment, since the pair of valve recesses 31 and 32 are formed in the inclined surface 22 on the intake valve side, a lift can be given to the intake valve 5 even near the intake top dead center. This is advantageous in improving the output during homogeneous combustion.

Further, since the swirl guide portion 40 is recessed so as to serve also as the downstream valve recess 32, the swirl component S1 on the outer peripheral side can be efficiently introduced into the bowl 12, and the first embodiment The same effect as the example can be obtained.

FIGS. 9 to 11 show a piston according to a third embodiment of the present invention.

In the third embodiment, a portion 42 corresponding to the swirl guide portion 40 of the first embodiment has a shape that is smoothly integrated with the bowl 12. In other words, in this embodiment, the non-circular 1 in which the peripheral wall surface 12b of the bowl 12 and the side wall surface 42b of the swirl guide portion 42 smoothly continue.
The bottom surface 12a of the bowl 12 and the bottom surface 42a of the swirl guide portion 42 are formed as one smoothly non-circular flat surface.

In other words, the bowl 12 itself is recessed so as to protrude downstream of the swirl so as to serve also as the swirl guide 42.

According to the third embodiment, the first
As in the embodiment, a swirl of sufficient strength can be introduced into the bowl 12 using the side wall surface 42b of the swirl guide portion 42 as a guide, and the combustion characteristics are improved.

In the third embodiment, the bowl 12
And the swirl guide portion 42 are formed as one smoothly continuous recess, so that the number of processing steps during casting of the piston is reduced, the manufacture thereof is facilitated, and the unevenness of the piston crown surface is reduced, so that the thermal efficiency is reduced. It is economically advantageous.

[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 an operation explanatory view of the first embodiment, wherein the upper part is a plan view and the lower part is a sectional view.

FIG. 5 is an operation explanatory view of the first embodiment, similarly to FIG. 4;

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

FIG. 7 is an operation explanatory view of the second embodiment, in which the upper part is a plan view and the lower part is a sectional view.

FIG. 8 is an operation explanatory view of the second embodiment, similarly to FIG. 7;

FIG. 9 is a perspective view showing a third embodiment of the piston according to the present invention.

FIG. 10 is an operation explanatory view of the third embodiment, wherein the upper part is a plan view,
The lower section is a sectional view.

FIG. 11 is an explanatory view of the operation of the third embodiment, similarly to FIG. 10;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 4 ... Piston 12 ... Bowl 12b ... Peripheral wall surface 22 ... Intake valve side inclined surface 23 ... Exhaust valve side inclined surface 31, 32 ... Valve recess 40, 42 ... Swirl guide part 40b, 42b ... Side wall surface S1 ... Outer side swirl S2 ... Inner swirl

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) F02F 3/26 F02F 3/26 A F term (reference) 3G023 AA01 AA18 AB03 AC05 AD02 AD07 AD09 AG01 3G024 AA09 DA01 DA06 DA08 DA18 FA14 GA01

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 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. A convex portion having an intake valve side inclined surface and an exhaust valve side inclined surface inclined so as to be substantially parallel to the surface is formed, and a dish-shaped bowl is eccentric to the intake valve side with respect to the piston outer circle on this convex portion. The swirl guide portion is recessed at a position downstream of the in-cylinder swirl of the bowl, and the side wall surface of the swirl guide portion is Smoothly with connecting the piston in cylinder injection type internal combustion engine, characterized in that it has extended to the outer periphery of the convex portion. 2. A flat bottom surface of the swirl guide section,
2. The piston of a direct injection internal combustion engine according to claim 1, wherein the piston is formed at a position shallower in the axial direction of the piston than a bottom surface of the bowl having a circular flat surface. 3. A pair of valve recesses are formed on the intake valve side inclined surface corresponding to a valve head of the intake valve, and the swirl guide portion is located on a downstream side of the in-cylinder swirl of the bowl. 3. The piston of a direct injection internal combustion engine according to claim 1, wherein one of the valve recesses is also used. 4. A peripheral wall surface of the bowl and a side wall surface of the swirl guide portion are formed into a smoothly continuous curved surface, and a bottom surface of the bowl and a bottom surface of the swirl guide portion are smoothly continuous. The piston of a direct injection internal combustion engine according to claim 1, wherein the piston is formed on a flat surface.