JP2009121251A - Cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable generation of strong turbulence throughout a cylinder at an ignition timing by forming two tumble flows with almost the same strength in the cylinder by a fuel jetted out in the latter half of a compression stroke without deteriorating exhaust emission. <P>SOLUTION: This cylinder injection type spark ignition internal combustion engine is provided with a fuel injection valve 1 arranged around the upper part of the cylinder, and two cavities 3b and 3c formed in a piston top face approximately symmetrically with a protrusion 3a extended along a central vertical plane P passing the central axis line of the cylinder as a border. The fuel injection valve jets out the fuel F approximately in a fan shape expanded in a width direction while having a slit injection hole, or jets out the fuel approximately in the fan shape expanded in the width direction on the whole from an injection hole row in place of the slit injection hole. The width direction of the injection fuel is approximately in parallel with a horizontal plane orthogonal to the central axis line of the cylinder and a central vertical plane. In the latter half of the compression stroke, the fuel injection valve jets out the fuel so that the center C of the injection fuel approximately in the fan shape is almost directed to the boundary B between a piston top face and a cylinder bore. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a direct injection spark ignition internal combustion engine.

  A homogeneous combustion is known in which fuel is directly injected into a cylinder to form a homogeneous mixture in the cylinder, and this homogeneous mixture is ignited and combusted at the ignition timing at the end of the compression stroke. In order to improve such homogeneous combustion, it is preferable to increase the combustion speed by causing strong turbulence in the cylinder at the ignition timing.

  To that end, it is conceivable to inject fuel at the end of the intake stroke, and to increase the tumble flow in the cylinder with this injected fuel. However, even if the tumble flow is strengthened in this way, a relatively long time from the end of the intake stroke to the end of the compression stroke Thus, the tumble flow is attenuated, and there may be a case where strong turbulence cannot exist in the cylinder at the ignition timing.

  By injecting the fuel in an appropriate direction in the latter half of the compression stroke, the intake air around the injected fuel moves together with the injected fuel and a tumble flow is generated in the cylinder. It does not disappear in a short time and can be crushed by the piston to generate a strong turbulence in the cylinder. However, the fuel injected in the latter half of the compression stroke is atomized and swirled in the cylinder together with a single tumble flow and gradually vaporized. However, the fuel cannot be sufficiently vaporized by the ignition timing. Since a good homogeneous mixture is not formed in the cylinder, good homogeneous combustion cannot be realized even if strong turbulence exists in the cylinder.

  A fuel injection valve is arranged at the approximate center of the cylinder top, and two cavities are formed on the top surface of the piston approximately symmetrically with the central ridge as a boundary. The latter half of the compression stroke follows the cylinder center axis from the fuel injection valve. It has been proposed to inject fuel (see, for example, Patent Document 1).

  The fuel injected in such a configuration travels along the two cavities with the surrounding intake air being drawn by the ridges on the top surface of the piston, and thus the intake flow drawn by the injected fuel is Are two tumble flows that swirl in the longitudinal direction in the cylinder in opposite directions.

  Since these two tumble flows swirl in substantially the same cylinder space, the strengths of the two tumble flows are approximately equal and balance each other and continue swirling in the cylinder until they are crushed by the piston just before the ignition timing at the end of the compression stroke. In this way, if the injected fuel is divided into two tumble flows and swirls in the cylinder together, and the liquid fuel atomized in each tumble flow gradually vaporizes, the two tumble flows are made by the piston immediately before the ignition timing. Almost all liquid fuel can be vaporized before being crushed, and at the ignition timing, turbulence can be generated in the cylinder, and a good homogeneous air-fuel mixture can be formed in the cylinder. Good homogeneous combustion with a high speed can be realized.

JP-A-2005-194942 JP-A-9-256853

  However, when fuel is injected from the fuel injection valve arranged substantially at the center of the cylinder in this way toward the raised portion at the center of the piston top surface in the latter half of the compression stroke, the injected fuel reaches the raised portion at a short flight distance. As a result, the atomization due to friction with the liquid becomes insufficient, and a relatively large amount of liquid fuel collides with the ridges, so that liquid fuel adheres to the ridges and both cavities and vaporizes in the expansion stroke and burns. Exhaust emissions are exacerbated because they are discharged as unburned fuel without contributing.

  Therefore, an object of the present invention is to generate a tumble flow having two equal strengths in the cylinder by the fuel injected in the latter half of the compression stroke without deteriorating the exhaust emission, and sufficiently evaporate the fuel by the ignition timing. An in-cylinder injection spark ignition internal combustion engine that can form a good homogeneous mixture in a cylinder and generate strong turbulence in the entire cylinder at the ignition timing.

  According to a first aspect of the present invention, there is provided a direct injection spark ignition internal combustion engine having a fuel injection valve disposed around a cylinder upper portion and a raised portion extending along a central vertical plane passing through a cylinder central axis. The fuel injection valve has a slit injection hole and injects fuel in a substantially fan shape extending in the width direction or is injected from an injection hole array. The fuel is injected into a substantially fan shape that spreads in the width direction as a whole by the plurality of injected fuels, and the width direction of the injected fuel is substantially parallel to a horizontal plane perpendicular to the cylinder center axis and the center vertical plane, In the latter half of the compression stroke, the fuel injection valve is characterized in that the fuel is injected so that the center of the substantially fan-shaped injected fuel is substantially directed to the boundary between the piston top surface and the cylinder bore.

  According to a second aspect of the present invention, the direct injection spark ignition internal combustion engine according to the first aspect is the direct injection spark ignition internal combustion engine according to the first aspect, wherein the piston of the fuel injection valve is approximately a third of the piston stroke. The fuel is injected so that the center of the substantially fan-shaped injected fuel is substantially directed to the boundary between the piston top surface and the cylinder bore when it is raised by two.

  A direct injection spark ignition internal combustion engine according to claim 3 of the present invention is the direct injection spark ignition internal combustion engine according to claim 1, wherein the ignition plug is disposed substantially at the center of the upper part of the cylinder, and The raised portion is characterized in that a depression is formed in the vicinity of the ignition plug at the ignition timing.

  According to the in-cylinder injection spark-ignition internal combustion engine of the first aspect of the present invention, in the latter half of the compression stroke, the fuel injection valve has a substantially fan-shaped center of the injected fuel almost to the boundary between the piston top surface and the cylinder bore. In order to inject the fuel to face, the injected fuel is sufficiently atomized by friction with the intake air at a relatively long flight distance until reaching this boundary, sufficiently reducing the liquid fuel impinging on the piston and cylinder bore The increase in unburned fuel does not exacerbate exhaust emissions. The intake air drawn by the injected fuel collides with the vaporized and atomized fuel, collides with the boundary between the piston top surface and the cylinder bore, and splits up and down to generate two tumble flows that turn vertically in opposite directions. . At this time, the upper and lower cylinder volumes of the substantially fan-shaped injected fuel are substantially equal, so the strengths of the two tumble flows are substantially equal. As the piston rises, these two equal strength tumble flows are brought into contact with the ridges extending along the central longitudinal plane substantially parallel to the width direction of the injected fuel and along the two cavities on the top surface of the piston. The two tumble flows still have the same volume in the cylinder, and the strength of the two tumble flows is maintained approximately the same, depending on the difference in strength. Since the weak tumble flow is not extinguished by the strong tumble flow, it is reliably maintained until immediately before the ignition timing. The liquid fuel atomized until the two tumble flows are crushed by the piston is almost vaporized in each tumble flow, causing turbulence throughout the cylinder at the ignition timing and a good homogeneous mixture in the cylinder. Formed and good homogeneous combustion can be achieved.

  According to the in-cylinder injection spark ignition internal combustion engine of claim 2 according to the present invention, in the in-cylinder injection spark ignition internal combustion engine of claim 1, the fuel injection valve has a piston whose piston stroke is approximately equal to the piston stroke. When it rises by two-thirds, it is designed to inject fuel, so that the two tumble flows generated when the injection timing is too early disappears before being crushed by the piston just before the ignition timing, Also, there is no increase in the amount of unburned fuel due to the injection timing being too late and the flight distance of the injected fuel being shortened so that much liquid fuel adheres to the piston top surface or cylinder bore. The atomized liquid fuel that swirls in the cylinder with two tumble flows due to the timing being too late will shorten the time until just before the ignition timing and will not vaporize sufficiently. Not be or not to gas formation.

  According to the in-cylinder injection spark ignition internal combustion engine of the third aspect of the present invention, in the in-cylinder injection spark ignition internal combustion engine of the first aspect, the ignition plug is disposed substantially at the upper center of the cylinder, and the piston top A depression is formed in the vicinity of the spark plug at the ignition timing in the raised portion of the surface. Thereby, combustion can be reliably started from the air-fuel mixture disturbed in the depression, and the combustion speed can be increased from the early stage of combustion.

  FIG. 1 is a schematic longitudinal sectional view showing an embodiment of an in-cylinder injection spark ignition internal combustion engine according to the present invention, and FIG. 2 is an in-cylinder plan view. 1 and 2 show the fuel injection timing in the latter half of the compression stroke for homogeneous combustion. In these drawings, reference numeral 1 denotes a fuel injection valve that is arranged around the upper part of the cylinder and directly injects fuel into the cylinder, and 2 is an ignition plug that is arranged substantially at the center of the upper part of the cylinder. Reference numeral 3 denotes a piston, 4 denotes a pair of intake ports, and 5 denotes a pair of exhaust ports.

  As shown by a solid line in FIG. 2, the fuel injection valve 1 injects the fuel F into a substantially fan shape having slit-shaped injection holes and extending in the width direction w, or as shown by a one-dot chain line in FIG. In addition, the fuel is injected in a substantially fan shape that spreads in the width direction w as a whole by a plurality of injected fuels f injected from the nozzle hole rows instead of the slit nozzle holes. As shown in FIG. 1, the fuel injected from the fuel injection valve 1 does not spread so much in the thickness direction t.

  1 and 2, P is a central vertical plane passing through the cylinder center axis, and in this embodiment is located between two intake ports 4 and two exhaust ports 5. The fuel injection valve 1 is located in the middle of the two intake ports 4 around the cylinder top, and the width direction w of the fuel injected from the fuel injection valve 1 is a horizontal plane and a central vertical plane P perpendicular to the cylinder central axis. And substantially parallel.

This in-cylinder spark-ignition internal combustion engine forms a homogeneous air-fuel mixture that is leaner than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio in the cylinder, and performs homogeneous combustion in which this homogeneous air-fuel mixture is ignited and burned by the spark plug 2. is there. The lean air-fuel ratio in the case where homogeneous combustion leaner than the stoichiometric air-fuel ratio is performed is set so that the amount of NO _x generated is relatively small (for example, about 20). A required fuel amount is set for each engine operating state determined by the engine speed, the engine load, and the like. When the required fuel amount is greater than or equal to the set amount and a high engine output is required, homogeneous combustion at a rich air-fuel ratio (for example, about 12.5) may be performed.

  In particular, in homogeneous combustion at a stoichiometric air-fuel ratio or lean air-fuel ratio, since there is not much injected fuel, it is necessary to sufficiently vaporize the injected fuel to form a good homogeneous mixture in the cylinder. In order to realize good homogeneous combustion, it is preferable to increase the combustion speed by generating strong turbulence in the cylinder at the ignition timing at the end of the compression stroke.

  In the in-cylinder injection spark ignition internal combustion engine of the present embodiment, as shown in FIGS. 1 and 2, in the latter half of the compression stroke, the center C of the substantially fan-shaped injected fuel substantially faces the boundary B between the piston top surface and the cylinder bore. Thus, the fuel injection valve 1 injects fuel. In actual fuel injection timing control, for example, when the center of the injection hole of the fuel injection valve 1 is directed to the boundary B, the fuel injection start timing, the fuel injection end timing, or the fuel injection intermediate timing is set.

  According to such fuel injection, the injected fuel F is sufficiently atomized by friction with the intake air at a relatively long flight distance until reaching the boundary B, and the liquid fuel that collides and adheres to the piston and cylinder bore is sufficiently reduced. can do. Thus, a large amount of attached fuel is vaporized in the expansion stroke and discharged without contributing to combustion, and the exhaust emission does not deteriorate due to the increase in unburned fuel.

  Further, as indicated by arrows in FIG. 1, the intake air drawn by the injected fuel F collides with the vaporized and atomized fuel and collides with the boundary B between the piston top surface and the cylinder bore and splits up and down, opposite each other. Two tumble streams T are generated that swirl in the direction. At this time, the upper and lower cylinder volumes of the substantially fan-shaped injected fuel F are substantially equal, so the strengths of the two tumble flows T are substantially equal.

  As shown in FIGS. 1 and 2, a first cavity 3 b and a second cavity 3 c are formed on the top surface of the piston 3 approximately symmetrically with a raised portion 3 a extending along the central vertical plane P as a boundary. . The first cavity 3b far from the fuel injection valve 1 is formed so as to suppress the attenuation of the tumble flow T formed on the upper side of the injected fuel F, and the second cavity 3c on the fuel injection valve 1 side is formed of the injected fuel F. It is formed so as to suppress the attenuation of the tumble flow T formed on the lower side.

  As a result, as shown in FIG. 3, the two tumble flows T formed in the cylinder as described above come into contact with the raised portion 3a by the rising of the piston 3, and the two cavities 3b on the piston top surface respectively. 3c and 3c, and the two tumble flows T remain substantially equal because the cylinder volumes in which the two tumble flows T rotate are substantially equal. In addition, since the weak tumble flow is not extinguished by the strong tumble flow due to the difference in strength, it is reliably maintained until immediately before the ignition timing.

  When only one tumble flow is formed in the cylinder, the atomized fuel swirling in the cylinder together with the tumble flow contacts only a part of the intake air in the cylinder, and from the fuel injection timing in the latter half of the compression stroke. In contrast to the fact that the tumble flow cannot be sufficiently vaporized until it is crushed by the piston, in this embodiment, since the injected fuel is divided into two tumble flows T and swirls in the cylinder, the atomized fuel Are in contact with a part of the intake air in the cylinder in each tumble flow T, and contact with a relatively large amount of intake air in the cylinder as a whole. Until T is crushed by the piston 3, the atomized liquid fuel can be almost vaporized in each tumble flow T. Accordingly, the entire cylinder is disturbed at the ignition timing, and a good homogeneous mixture is formed in the cylinder, so that good homogeneous combustion can be realized.

  In this embodiment, the fuel injection valve is configured such that when the piston 3 rises by about two thirds of the piston stroke in the latter half of the compression stroke, the center C of the substantially fan-shaped injected fuel is the boundary between the piston top surface and the cylinder bore. The fuel injection valve 1 injects fuel so as to be substantially directed to B. In other words, the center of the injection hole of the fuel injection valve 1 is directed to the boundary B between the piston top surface and the cylinder bore when the piston 3 is raised by about two thirds of the piston stroke. When the fuel valve rises by about two thirds, the fuel injector 1 injects fuel.

  As a result, the two tumble flows T generated when the injection timing is too early disappears before being crushed by the piston immediately before the ignition timing, or the flight distance of the injected fuel is shortened because the injection timing is too late. A large amount of liquid fuel does not adhere to the top surface of the piston or the cylinder bore, so that the amount of unburned fuel discharged does not increase. Also, the atomized liquid fuel that swirls in the cylinder with two tumble flows T due to the injection timing being too late will shorten the time until just before the ignition timing and will not vaporize sufficiently. Qi will not be formed.

  In the present embodiment, a depression 3d is formed in the raised portion 3a of the piston top surface in the vicinity of the ignition plug 2 at the ignition timing. If such a recess 3d is not formed in the raised portion 3a, the turbulence of the air-fuel mixture tends to disappear in a slight gap between the raised portion 3a and the cylinder head, and combustion at the initial stage of combustion becomes slow. There is. However, in the present embodiment, at the ignition timing, combustion can be reliably started from the air-fuel mixture disturbed in the recess 3d, and the combustion speed can be increased from the beginning of combustion.

  The flame thus generated in the recess 3d propagates to the air-fuel mixture on the raised portion 3a and the air-fuel mixture on the two cavities 3b, and the air-fuel mixture on the raised portion 3a is a small amount even if the turbulence disappears. The air-fuel mixture on the two cavities 3b in which strong turbulence exists suddenly burns, and good homogeneous combustion with a high combustion speed is realized.

  In the present embodiment, the required fuel amount determined by the engine operating state may be divided and injected. The fuel thus divided and injected is easily vaporized and atomized during the flight until reaching the boundary B between the cylinder bore and the piston top surface.

  By further retarding the fuel injection timing, the injected fuel collides with the second cavity 3c on the fuel injection valve 1 side and moves toward the vicinity of the spark plug 1. Thereby, the stratified combustion which forms a combustible air-fuel mixture only in the vicinity of the spark plug 1 can be performed. In such stratified combustion, the combustible air-fuel mixture can be ignited and combusted even if the ignition timing is greatly retarded, for example, until the middle of the expansion stroke. It can be used to sufficiently increase the gas temperature.

  In the in-cylinder injection spark ignition internal combustion engine, in order to reliably generate the two tumble flows T, the penetration force of the injected fuel F is strong so that, for example, the fuel tip after 1 ms from the start of injection reaches 60 mm or more. It is preferable to do.

1 is a schematic longitudinal sectional view showing an embodiment of an in-cylinder injection spark ignition internal combustion engine according to the present invention, and shows a fuel injection timing in the latter half of a compression stroke. FIG. 2 is a plan view in a cylinder of the cylinder injection type spark ignition internal combustion engine of FIG. 1. It is a schematic longitudinal cross-sectional view which shows embodiment of the cylinder injection type spark ignition internal combustion engine by this invention, and has shown the time just before two tumble flows are crushed by a piston.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel injection valve 2 Spark plug 3 Piston 4 Intake port 5 Exhaust port F Injection fuel T Tumble flow

Claims (3)

  A fuel injection valve disposed around the upper part of the cylinder, and two cavities formed on the piston top surface approximately symmetrically with a raised portion extending along a central vertical plane passing through the cylinder central axis, The fuel injection valve has a slit injection hole and injects the fuel in a substantially fan shape that spreads in the width direction or injects the fuel in a substantially fan shape that spreads in the width direction as a whole by a plurality of injected fuels injected from the nozzle hole array The width direction of the injected fuel is substantially parallel to a horizontal plane perpendicular to the cylinder center axis and the central vertical plane, and in the latter half of the compression stroke, the fuel injection valve is the center of the substantially fan-shaped injected fuel. An in-cylinder injection spark ignition internal combustion engine characterized by injecting fuel so that is substantially directed to the boundary between the piston top surface and the cylinder bore.   The fuel injection valve is configured to inject fuel so that the center of the substantially fan-shaped injection fuel is substantially directed to the boundary between the piston top surface and the cylinder bore when the piston is raised by about two thirds of the piston stroke. The in-cylinder injection spark ignition internal combustion engine according to claim 1,   The in-cylinder injection spark according to claim 1, wherein a spark plug is disposed substantially at the center of the upper part of the cylinder, and a depression is formed in the vicinity of the spark plug at an ignition timing in the raised portion of the piston top surface. Ignition internal combustion engine.

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