JP3775038B2 - In-cylinder injection spark ignition internal combustion engine piston - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark ignition internal combustion engine typified by a gasoline engine, and more particularly to an improvement in a piston of a direct injection spark ignition internal combustion engine in which fuel is directly injected into a cylinder.
[0002]
[Prior art]
In a spark ignition internal combustion engine typified by a gasoline engine, a so-called homogeneous combustion is performed by forming a substantially homogeneous air-fuel ratio mixture in the cylinder at the time of fully open output, and in a low load region, Various types of in-cylinder spark-ignition internal combustion engines that perform stratified combustion in which a relatively rich air-fuel mixture is formed only in the vicinity of the spark plug and an average air-fuel ratio is very large have been proposed.
[0003]
The piston can with the direct injection spark ignition internal combustion engine the stratified lean burn, for example, are known those described in Japanese Patent Laid-open flat 5-71383. In the internal combustion engine described in this publication, a circular bowl (cavity) eccentric to the piston outer circle is formed on the top surface of the piston, and the cylinder head side is directed to the bowl near the top dead center of the piston. A fuel injection valve for injecting and supplying fuel is disposed. In addition, one of the pair of intake ports is configured as a helical port, and an air control valve that opens and closes the other intake port is provided. At the time of lean combustion, the air control valve is closed and fresh air is introduced only from one helical port to generate a strong swirl in the cylinder. Since this swirl is introduced into the bowl as the piston rises, fuel is injected into the bowl near the compression top dead center, so that a combustible air-fuel mixture is formed in the bowl and carried to the vicinity of the spark plug. It is. Therefore, ignition is performed by igniting at an appropriate timing.
[0004]
[Problems to be solved by the invention]
In the cylinder-injected spark ignition internal combustion engine piston capable of stratified combustion as described above, the bowl is recessed at a position eccentric to the piston outer circle on the top surface of the piston, and in the stratified combustion, Since the combustion proceeds at this point, there is a problem that the outer peripheral portion of the piston adjacent to the bowl is likely to become a heat spot that is locally heated, and that this portion is likely to cause knocking during high load operation.
[0005]
In order to alleviate the occurrence of such knocking, it is conceivable that an R chamfered portion is formed in a curved shape over the entire circumference of the piston at the corner portion between the piston top surface and the piston outer peripheral surface. However, if the radius of curvature of the R chamfered portion is increased too much, the volume of the piston clevis defined by the cylinder wall surface, the piston outer peripheral surface and the piston ring increases, and the amount of unburned HC remaining in the piston clevis is discharged. Will increase.
[0006]
This invention is a heat spot that is particularly likely to occur at the corner portion of the piston that forms a bowl at an eccentric position on the top surface while minimizing an increase in the amount of unburned HC emissions due to an increase in the volume of the piston clevis. An object of the present invention is to provide a piston for a cylinder injection spark ignition internal combustion engine having a novel structure that effectively suppresses the occurrence of knocking.
[0007]
[Means for Solving the Problems]
Accordingly, the invention of claim 1 has a fuel injection valve for directly injecting fuel into the cylinder, an ignition plug is disposed at the center of the cylinder, and a substantially round bowl is formed on the piston outer surface. In a piston of an in-cylinder spark ignition internal combustion engine recessed at a position eccentric with respect to a circle, an R chamfer is formed over the entire circumference of the piston at the corner portion between the top surface of the piston and the outer peripheral surface of the piston. The radius of curvature of the first section that is relatively close to the bowl is set to be larger than the curvature radius of the second section other than the first section in the R chamfer around the entire circumference of the piston. It is said.
[0008]
Further, in the invention of claim 2, which further embodies the invention of claim 1, the first section is within a predetermined range centered on a position closest to the bowl in an R chamfered portion over the entire circumference of the piston. Is set.
[0009]
According to a third aspect of the present invention, at least the range in which the fuel spray from the fuel injection valve directly interferes is set in the second section in the R chamfered portion over the entire circumference of the piston .
[0010]
According to a fourth aspect of the present invention, the center of the bowl as viewed on the piston plane is arranged on a line connecting the fuel injection valve and the center of the piston and at a position eccentric to the fuel injection valve side.
[0011]
【The invention's effect】
According to the first or second aspect of the present invention, an R chamfered portion is formed over the entire circumference of the piston at the corner portion between the piston top surface and the piston outer peripheral surface, and the bowl easily forms a heat spot in the R chamfered portion. Since the radius of curvature of the adjacent first section is set to be relatively large, the occurrence of knocking can be effectively suppressed.
[0012]
In addition, since the radius of curvature of the second section other than the first section is set to be relatively small in the R chamfered portion, in this second section, there is a gap between the piston outer peripheral surface, the cylinder wall surface, and the piston ring. The volume of the formed piston clevis becomes relatively small, and the discharge amount of unburned HC staying in the piston clevis can be reduced.
[0013]
That is, knocking can be effectively suppressed while minimizing the amount of unburned HC discharged.
[0014]
Further, according to the third aspect of the present invention, the region where the fuel spray directly interferes, that is, the region where the temperature is relatively low due to the fuel cooling and the unburned HC is easily discharged is the region where the radius of curvature is relatively small. Since there are two sections, the amount of unburned HC emissions can be further effectively reduced.
[0015]
According to the invention of claim 4, the first section close to the bowl is disposed on the fuel injection valve side, and the second section faces the fuel injection valve. As a result, the region where the fuel spray from the fuel injection valve directly interferes, that is, the region where the temperature is relatively low due to fuel cooling and the unburned HC is easily discharged becomes the second section having a small curvature radius. Similarly to the invention of Item 3, the amount of unburned HC emitted can be reduced more effectively.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
First, the configuration of a direct injection spark ignition internal combustion engine in which the piston 4 of the present invention is used will be described with reference to FIGS. A plurality of cylinders 3 are arranged in series on the cylinder block 1, and the cylinder head 2 is fixed via a cylinder gasket 17 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 has a so-called pent roof type, and a pair of intake valves 5 is provided on one inclined surface 11a and a pair of exhaust valves 6 is provided on the other inclined surface 11b. Are arranged respectively. A spark plug 7 is disposed at a substantially central position of the cylinder 3 surrounded by the pair of intake valves 5 and the pair of exhaust valves 6.
[0018]
The cylinder head 2 is formed with a pair of intake ports 8 corresponding to the pair of intake valves 5 independently of each other. That is, the pair of intake ports 8 do not merge in the cylinder head 2 and open independently on the side surfaces of the cylinder head 2. An exhaust port 9 is formed corresponding to the exhaust valve 6.
[0019]
The electromagnetic fuel injection valve 10 having a substantially cylindrical shape is disposed on the lower surface portion of the cylinder head 2 near the side wall of the cylinder 3 on the intake valve 5 side, and is attached in such a posture that its central axis is directed obliquely downward. The fuel injection valve 10 is disposed between the two intake valves 5, and the spray axis is directed to the center X1 (FIG. 1) of the cylinder 3 and the piston 4 where the spark plug 7 is located.
[0020]
As will be described later, a circular bowl 12 is formed at a position eccentric to the intake valve 5 side on the top surface of the piston 4 disposed in the cylinder 3, and the piston 4 is in the vicinity of the top dead center. Sometimes, the spray axis of the fuel injection valve 10 is directed to the bowl 12.
[0021]
The pair of intake ports 8 are connected to a pair of intake passages 14a and 14b that are independently formed on the intake manifold 13 side. A butterfly valve type air control valve 15 for opening and closing the intake passage 14b is interposed in the one intake passage 14b. The air control valve 15 is controlled to open and close according to engine operating conditions by a drive mechanism (not shown) via a shaft 16. 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, the intake port 8 is not a helical port but a substantially straight port. It has a shape.
[0022]
The basic operation of the internal combustion engine will be briefly described. First, a homogeneous air-fuel mixture is formed in the cylinder 3 at the time of full load of the engine or in a region where the air-fuel ratio is relatively small in the lean combustion region. Homogeneous combustion is performed. During the homogeneous combustion, the air control valve 15 is controlled to be in an open state, and fresh air is introduced into the cylinder 3 from both the pair of intake ports 8. Thereby, 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 homogenization is promoted without staying in the bowl 12.
[0023]
On the other hand, in a lean combustion region where the air-fuel ratio is very large in a low load region, stratified lean combustion is performed that enables reliable ignition by stratification of the air-fuel mixture. During this stratified lean combustion, the air control valve 15 is closed, and fresh air flows into the cylinder 3 from only one intake port 8. Thereby, in the cylinder 3, the tumble component is relatively weakened and a swirl flow along the horizontal direction is generated strongly. During this 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 rides on the swirl flow confined in the bowl 12 at the top of the piston 4 and moves toward the spark plug 7 to form an ignitable air-fuel mixture around the spark plug 7. Ignition combustion is possible by igniting.
[0024]
Next, based on FIGS. 1-3, the structure of the piston 4 which concerns on 1st Example is demonstrated in detail.
[0025]
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 convex portion 21 is basically composed of four surfaces. That is, the intake valve side inclined surface 22 and the exhaust valve side inclined surface 23 which are substantially parallel to the two inclined surfaces 11a and 11b constituting the pent roof type combustion chamber 11 on the cylinder head 2 side, and the outer circle of the piston 4 The convex portion 21 is constituted by a pair of conical side surfaces 24 and 25 having conical surfaces concentric with each other.
[0026]
An annular horizontal surface 26 is formed on the outer periphery of the convex portion 21. The annular horizontal plane 26 is composed of a single plane orthogonal to the center line of the piston 4, and is continuous in a thin annular shape over the entire circumference of the piston 4. Further, a part of the annular horizontal plane 26 on the suction and exhaust valve side is a substantially crescent-shaped horizontal plane, which is not shown here, but remains as a flat surface on both sides of the combustion chamber 11 on the cylinder head 2 side. It contributes to the formation of squish together with the squish area.
[0027]
Further, the bowl 12 is recessed in a range centering on the intake valve side inclined surface 22, and a part of the bowl 12 approaches the exhaust valve side inclined surface 23. The bowl 12 has a true circle shape when viewed on the plane of the piston 4, and its center X2 is a line connecting the center X1 of the piston 4 and the fuel injection valve 10, that is, the line AA in FIG. And it is arrange | positioned in the position eccentric to the fuel injection valve 10 side (namely, intake valve side). The bottom surface of the bowl 12 is along a plane perpendicular to the center line of the piston 4, and the inner peripheral wall surface rises upward. As shown in FIG. 2, when the piston 4 is at the top dead center, the spark plug 7 is disposed in the bowl 12 and positioned on the outer periphery thereof.
[0028]
By the way, a plurality of ring grooves 30 (or even one) may be provided in the outer circumferential surface of the piston 4 so as to extend in the circumferential direction at appropriate intervals in the axial direction. An annular piston ring 32 that seals between them is fitted. Accordingly, a piston clevis 36 is defined between the outer peripheral surface of the top land 34 of the piston 4, the wall surface of the cylinder 3, and the uppermost piston ring 32, and this piston clevis 36 is a combustion formed in the cylinder 3. It faces the room.
[0029]
Here, a so-called R chamfered portion 40 is curvedly formed over the entire circumference of the piston 4 at a corner portion between the annular horizontal surface 26 on the top surface of the piston 4 and the outer peripheral surface of the top land 34 of the piston 4. In the R chamfered portion 40, the curvature radius R1 of the first section 42 that is relatively close to the bowl 12 is set to be larger than the curvature radius R2 of the second section 44 other than the first section 42. Yes.
[0030]
More specifically, the first section 42 is set to a predetermined range centered on a position 46 closest to the outer peripheral edge of the bowl 12 in the R chamfered portion 40. In this embodiment, the outer periphery of the piston 4 is set. The region is set to include the intake valve side half circumference and the exhaust valve side part. Further, in the R chamfered portion 40, a region where the fuel spray injected from the fuel injection valve 10 directly interferes during the intake stroke, that is, a region located within the range of the spray angle θ1 in FIGS. It is set in the second section 44. In other words, in the R chamfered portion 40, the range located within the fuel spray angle θ1 is set in the second section 44, and the other range is set in the first section 42.
[0031]
As an example, the curvature radius R1 of the first section 42 is set to about 0.5 mm, and the curvature radius R2 of the second section 44 is set to about 0.1 mm.
[0032]
As described above, the R chamfered portion 40 is formed over the entire circumference of the piston 4 at the corner portion between the top surface of the piston 4 and the outer peripheral surface of the piston 4, and the bowl that easily becomes a heat spot in the R chamfered portion 40. Since the radius of curvature R1 of the first section 42 close to 12 is set to be relatively large, the occurrence of knocking can be effectively suppressed.
[0033]
In addition, since the radius of curvature R2 of the second section 44 other than the first section 42 is set to be relatively small in the R chamfered portion 40, the volume of the piston clevis 36 is relatively small in the second section 44. As a result, the amount of unburned HC remaining in the piston clevis 36 is effectively reduced. That is, the occurrence of knocking can be effectively suppressed while suppressing an increase in the amount of unburned HC emissions to a minimum.
[0034]
In particular, in this embodiment, the center X2 of the bowl 12 is located on the spray axis along the line AA in FIG. 1 and is arranged at a position eccentric to the fuel injector 10 side. A region where the fuel spray from the fuel directly interferes, that is, a region within the fuel injection angle θ1 inevitably becomes the second section 44. As a result, the region where the temperature is relatively low due to the fuel cooling and the unburned HC is easily discharged becomes the second section 44 having a relatively small curvature radius R2, and the amount of unburned HC discharged can be further effectively reduced. .
[0035]
4 and 5 show a second embodiment of the piston 4 according to the present invention. In the second and third embodiments, which will be described later, the same components as those in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted as appropriate.
[0036]
In the second embodiment, as in the first embodiment, an R chamfered portion 40 is formed over the entire circumference of the piston 4 at the corner portion of the piston 4 top surface and the piston 4 outer peripheral surface. The curvature radius of the first section 42 adjacent to the bowl 12 is set larger than the curvature radius of the second section 44.
[0037]
Here, the spray angle of the fuel spray injected from the fuel injection valve 10 is deflected downward from the intended spray angle θ1 (FIG. 5) by the gas flow generated in the cylinder 3, and actually, FIG. The spray angle θ2 shown in FIG. Therefore, in the second embodiment, the second section 44 is set to be relatively larger than the first embodiment in consideration of the deflection and expansion of the spray angle due to the gas flow in the cylinder 3. That is, a region located within the spray angle θ <b> 2 is set within the second section 44. More specifically, the first section 42 occupies about a half circumference on the intake valve side, and the second section 44 occupies about a half circumference on the exhaust valve side.
[0038]
According to the second embodiment, since the second section 44 is enlarged in consideration of the gas flow in the cylinder 3, the unburned HC emission amount is reduced to the first while effectively suppressing the occurrence of knocking. It becomes possible to reduce more than an example.
[0039]
6 and 7 show a third embodiment of the piston 4 according to the present invention.
[0040]
In this embodiment, the center X2 of the bowl 12 as viewed on the plane of the piston 4 is shifted upward in FIG. 6 with respect to a line (CC line in FIG. 6) connecting the piston 4 center X1 and the fuel injection valve 10. I have a heart. The first section 42 is set only within a predetermined range centering on the position 46 closest to the outer peripheral edge of the bowl 12 in the R chamfered portion 40, and the rest is the second section 44. Specifically, the second section 44 is set to be larger than the first section 42.
[0041]
Also in the third embodiment, the radius of curvature of the first section 42 adjacent to the bowl 12 in the R chamfered portion 40 is relatively large, and the occurrence of knocking is effectively suppressed and remains. Since the radius of curvature of the second section 44 is set to be relatively small, the volume of the piston clevis 36 is minimized, and the amount of unburned HC discharged in the piston clevis 36 can be effectively reduced. it can.
[Brief description of the drawings]
FIG. 1 is a plan view showing a configuration of a direct injection spark ignition internal combustion engine to which a piston according to a first embodiment of the present invention is applied.
FIG. 2 is a longitudinal sectional view taken along line AA in FIG.
FIG. 3 is an enlarged view of a main part of FIG. 2;
FIG. 4 is a plan view showing the configuration of a direct injection spark ignition internal combustion engine to which a piston according to a second embodiment of the present invention is applied.
5 is a longitudinal sectional view taken along line BB in FIG.
FIG. 6 is a plan view showing the configuration of a direct injection spark ignition internal combustion engine to which a piston according to a third embodiment of the present invention is applied.
7 is a longitudinal sectional view taken along the line CC in FIG. 6;
[Explanation of symbols]
3 ... Cylinder 4 ... Piston 7 ... Spark plug 10 ... Fuel injection valve 12 ... Bowl 40 ... R chamfer 42 ... First section 44 ... Second section

Claims (4)

It has a fuel injection valve that directly injects fuel into the cylinder, a spark plug is arranged at the center of the cylinder, and a substantially round bowl is recessed at a position eccentric to the piston outer circle on the top surface of the piston. In the in-cylinder injection spark ignition internal combustion engine piston,
An R chamfered portion is formed over the entire circumference of the piston at a corner portion between the top surface of the piston and the outer peripheral surface of the piston, and the first portion that is relatively close to the bowl in the R chamfered portion over the entire circumference of the piston . A piston for a direct injection spark ignition internal combustion engine, wherein a radius of curvature of a section is set to be larger than a radius of curvature of a second section other than the first section. 2. The in-cylinder injection type according to claim 1, wherein the first section is set to a predetermined range centering on a position closest to the bowl in an R chamfered portion over the entire circumference of the piston. A piston for a spark ignition internal combustion engine. 3. The range in which at least the fuel spray from the fuel injection valve directly interferes within the R chamfered portion over the entire circumference of the piston is set in the second section. 4. Piston for an in-cylinder injection spark ignition internal combustion engine.   The center of the bowl as viewed on a piston plane is arranged on a line connecting the fuel injection valve and the center of the piston and at a position eccentric to the fuel injection valve side. The piston of the cylinder injection type spark ignition internal combustion engine in any one of 3.

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