JP2004036461A - Cylinder injection type spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder injection type spark ignition internal combustion engine capable of sufficiently increasing the temperature of exhaust gas without requiring complicated fuel injection control. <P>SOLUTION: The cylinder injection type spark ignition internal combustion engine comprises a fuel injection valve 7 for injecting a fuel in the form of developing penetrating force stronger than that of conical fuel spray and an ignition plug 6. The fuel is injected in a compression stroke by the fuel injection valve to form a combustible mixture near the ignition plug for stratified charge combustion. When the temperature of exhaust gas is increased, the fuel is injected near the top dead center of compression by the fuel injection valve and the ignition timing of the ignition plug is set at the middle of an expansion stroke. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a direct injection spark ignition internal combustion engine.
[0002]
[Prior art]
By injecting fuel directly into the cylinder, an ignitable mixture (hereinafter, flammable mixture) is formed only in the vicinity of the ignition plug at the time of ignition, and combustion of the lean mixture as a whole in the cylinder Stratified combustion that allows for is known. In such stratified charge combustion cylinder injection type spark ignition internal combustion engine implementing, as with typical internal combustion engine, HC in the exhaust gas, CO, and, in order to purify NO _X, in the exhaust system A catalyst device is provided, and it is desired that the catalyst device be quickly warmed up so that these components can be purified immediately after the start of the engine.
[0003]
In the direct injection type spark ignition internal combustion engine disclosed in Japanese Patent Application Laid-Open No. H10-153138, a combustible air-fuel mixture is provided near an ignition plug in order to increase the temperature of the exhaust gas at the time of engine start and to quickly warm up the catalyst device. It has been proposed to inject fuel into the cylinder in the exhaust stroke in addition to the main fuel injection in the compression stroke for forming the fuel, and to retard the ignition timing. In this way, it is intended to delay the combustion by retarding the ignition timing to maintain the combustion until the exhaust stroke, and to further burn the fuel in the exhaust stroke injection in the exhaust stroke.
[0004]
In this prior art, the fuel injection valve is a general one that injects fuel in a conical shape, and the penetration force of the spray fuel is relatively weak. As a result, if the fuel injection timing is delayed in the main fuel injection at the time of engine startup, fuel with a low penetration force will be injected against an extremely high in-cylinder pressure, and the fuel atomized during flight will have a further penetration force. Are weakened and easily dispersed, and a combustible mixture cannot be formed near the ignition plug.
[0005]
Thus, the main fuel injection timing must be at the latest in the middle stage of the compression stroke before the in-cylinder pressure becomes extremely high. At the end of the compression stroke, a combustible mixture is formed near the ignition plug. In order to ensure that the combustible mixture is ignited and burned, it must be ignited before the combustible mixture is temporally dispersed, and the ignition timing cannot be greatly retarded. As a result, ignition must be carried out at the beginning of the expansion stroke at the latest.
[0006]
Due to this ignition timing retard, combustion can be barely sustained until the early stage of the exhaust stroke, and if the fuel is further injected at the beginning of the exhaust stroke, the combustion can be further sustained and the exhaust gas temperature can be raised, and the catalytic device Early warm-up can be realized.
[0007]
[Problems to be solved by the invention]
Thus, in the above-described prior art, in order to increase the temperature of the exhaust gas, the fuel injection at the early stage of the exhaust stroke is indispensable, and such fuel injection twice in one cycle complicates the fuel injection control.
[0008]
Accordingly, an object of the present invention is to provide an in-cylinder injection spark ignition internal combustion engine capable of sufficiently increasing exhaust gas temperature without complicating fuel injection control.
[0009]
[Means for Solving the Problems]
An in-cylinder injection spark ignition internal combustion engine according to claim 1, comprising a fuel injection valve for injecting fuel into a shape having a stronger penetration force than conical fuel spray, and a spark plug, In a cylinder injection type spark ignition internal combustion engine that injects fuel in a compression stroke by an injection valve and forms a combustible mixture near the ignition plug to perform stratified combustion, when the exhaust gas temperature is increased, the fuel injection valve Fuel is injected near the compression top dead center, and the ignition timing of the ignition plug is set to the middle stage of the expansion stroke.
[0010]
According to a second aspect of the present invention, there is provided the in-cylinder injection spark ignition internal combustion engine according to the first aspect, wherein the middle stage of the expansion stroke is 20 ° after the compression top dead center. It is characterized in that the crank angle is in the range from to 50 °.
[0011]
According to a third aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine according to the first or second aspect, wherein the exhaust gas temperature is increased when the engine is started. It is characterized by being.
[0012]
According to a fourth aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine according to the first or second aspect, wherein the NO _X storage reduction catalyst device is provided in the engine exhaust system. The time when the exhaust gas temperature is increased is when SO _X is released from the NO _X storage reduction catalyst device.
[0013]
A cylinder injection type spark ignition internal combustion engine according to claim 5 according to the present invention is the cylinder injection type spark ignition internal combustion engine according to any one of claims 1 to 4, wherein the compression top dead center is near the compression top dead center. Is characterized by a crank angle range from 30 ° before compression top dead center to compression top dead center.
[0014]
A cylinder injection type spark ignition internal combustion engine according to claim 6 of the present invention is the cylinder injection type spark ignition internal combustion engine according to any one of claims 1 to 4, wherein the compression top dead center is near the compression top dead center. Is characterized by a crank angle range from the compression top dead center to 30 ° after the compression top dead center.
[0015]
In addition, a direct injection type spark ignition internal combustion engine according to claim 7 according to the present invention is the direct injection type spark ignition internal combustion engine according to any one of claims 1 to 6, wherein the fuel injection valve comprises: It has a slit-shaped injection hole for injecting fuel in a thin fan shape.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic longitudinal sectional view showing a direct injection type spark ignition internal combustion engine according to the present invention, and FIG. 2 is a plan view of a piston in FIG. In these figures, 1 is an intake port, and 2 is an exhaust port. The intake port 1 communicates with the cylinder via an intake valve 3, and the exhaust port 2 communicates with the cylinder via an exhaust valve 4. Reference numeral 5 denotes a piston, and a concave cavity 8 is formed on the top surface of the piston. Reference numeral 6 denotes a spark plug arranged near the upper center of the cylinder. Reference numeral 7 denotes a fuel injection valve arranged on the intake port side around the upper part of the cylinder.
[0017]
The fuel injection valve 7 has a slit-shaped injection hole, and injects fuel as a substantially fan-shaped spray 10 having a relatively small thickness. In order to carry out stratified combustion, as shown in FIGS. 1 and 2, fuel is injected into a cavity 8 formed on the top surface of the piston 5 in the latter half of the compression stroke. The liquid fuel 10 indicated by the oblique lines injected into the cavity 8 in this manner is atomized by friction with the intake air in the cylinder during the flight, enters the cavity 8, and advances along the bottom wall 8a of the cavity 8. It is vaporized before being guided to the vicinity of the ignition plug 6 by the opposed side wall 8b facing the fuel injection valve of the cavity 8, and at the time of ignition, a combustible mixture is formed only near the ignition plug 6 as shown by a dot. By igniting and burning this combustible air-fuel mixture, lean air-fuel mixture can be burned as a whole in the cylinder as stratified combustion.
[0018]
The fan-shaped fuel spray having a small thickness spreads in the width direction when traveling along the bottom wall 8a of the cavity 8, so that heat can be favorably absorbed from a wide range of the bottom wall 8a of the cavity 8. In the fuel spread in the width direction on the bottom wall 8 a of the cavity 8, the central portion of the fuel is imparted with an upward velocity component by the opposing side wall 8 b of the cavity 8 and moves toward the vicinity of the ignition plug 6. The piston 8 collides at an acute angle with the opposed side wall 8b of the cavity 8 which is formed in an arc shape in a plan view of the piston, so that an upward velocity component and a velocity component toward the center are also imparted, and the vicinity of the ignition plug 6 Head to.
[0019]
In this manner, the fan-shaped fuel spray having a small thickness can form a lump of combustible mixture having a good degree of vaporization in the vicinity of the ignition plug 6 as compared with the conventional conical fuel spray. This makes it possible to increase the fuel injection amount during stratified combustion, and to expand stratified combustion with a low fuel consumption rate to a higher load side. At high engine load when the required fuel amount is large, fuel may be injected during the intake stroke to form a homogeneous mixture in the cylinder, and homogeneous combustion may be performed.
[0020]
Since the stratified combustion is a lean burn, a relatively large amount of NO _X is contained in the exhaust gas. In order to purify the NO _X , the exhaust system of the in-cylinder injection spark ignition internal combustion engine has a NO. _{An X} storage reduction catalyst device (not shown) is provided. This _the NO _X storage reduction catalyst device absorbs NO _X in the exhaust gas when a high concentration of oxygen in the exhaust gas, which is oxygen concentration in the exhaust gas to release NO _X absorbed to decrease, this time If the exhaust gas contains a reducing component such as HC or CO, the NO _X released by the reducing component is reduced and purified. Thus, NO _X can be purified before it is released to the atmosphere.
[0021]
As described above, the in-cylinder injection spark ignition internal combustion engine may perform not only stratified combustion at a lean air-fuel ratio but also homogeneous combustion at a stoichiometric air-fuel ratio or a rich air-fuel ratio. It is necessary to purify HC, CO, and the like contained in water. Since the NO _X storage reduction catalyst device also generally has an oxidation catalyst such as platinum, it can purify HC and CO in exhaust gas. However, it is preferable to provide the three-way catalyst device in the exhaust system separately from the NO _X storage reduction catalyst device.
[0022]
In the direct injection spark ignition internal combustion engine common internal combustion engine including, HC in the exhaust gas immediately after the engine starting, CO, and which it is desired to purify NO _X, in order that the engine start it is necessary to activate the catalyst supported by elevating the temperature of _the NO _X storage reduction catalyst device and a catalyst device such as a three-way catalytic converter immediately after. In order to easily raise the temperature of the catalyst device without using a special mechanism, it is necessary to retard the ignition timing and raise the exhaust gas temperature, but significantly retard the ignition timing and considerably reduce the exhaust gas temperature. Unless raised, the catalyst device cannot be warmed up early.
[0023]
FIGS. 3 and 4 show a fan-shaped spray (circle plot) and a conical spray (square plot) injected by a fuel injection valve 7 of a direct injection type spark ignition internal combustion engine. FIG. 3 is a graph showing the spray tip reaching distance with respect to the elapsed time in the case where the in-cylinder pressure is 0.1 MPa (absolute pressure), and FIG. 4 is a case where the in-cylinder pressure is 0.5 MPa (absolute pressure). As shown in these figures, the fan-shaped spray has a considerably larger penetration force than the conical spray.
[0024]
In the present embodiment, stratified charge combustion is performed at a retarded ignition timing when the engine is started, provided that the fuel injection timing is near the compression top dead center and the ignition timing is in the middle of the expansion stroke. If the ignition timing is retarded until the middle stage of the expansion stroke, the combustion can be continued up to the middle stage of the exhaust stroke, and the exhaust gas temperature can be sufficiently increased and the catalyst device can be quickly warmed up. In the stratified combustion at the time of engine start, the piston temperature is lower than in the normal stratified combustion, and the amount of fuel adhering to the cavity 8 increases. The fuel injection amount is increased so that the fuel ratio becomes stoichiometric or slightly lean.
[0025]
FIG. 5 shows the fuel injection timing and the ignition timing at the time of starting the engine in the present embodiment. Specifically, fuel injection is started and ended within the crank angle range INJ, that is, within the crank angle range from 30 ° before compression top dead center to compression top dead center (0 °), and ignition is performed at the crank angle range INJ. The operation is performed within a range IGN, that is, a crank angle range from 20 ° to 50 ° after the compression top dead center.
[0026]
The fuel injected into the cylinder from the fuel injection valve is atomized by friction with the intake air in the cylinder during flight, and the atomization is promoted as the in-cylinder pressure is increased and the intake density is increased. Further, as the penetrating force of the injected fuel increases, the frictional force with the intake air increases, and the atomization is promoted. As described above, the general conical spray has a weak penetration force, and when injected near the compression top dead center, atomization is not so much promoted by the penetration force, but atomization is promoted by high in-cylinder pressure, and The atomized fuel is further reduced in penetration force by the high in-cylinder pressure and dispersed. Thus, if the conical spray is injected near the compression top dead center, a combustible mixture cannot be formed near the ignition plug.
[0027]
In the present embodiment, the fuel injection valve 7 has a slit-shaped injection hole, and injects fuel in a thin fan shape. As described above, the fan-shaped spray thus injected is conical. It has a higher penetration force than shape spraying. Thus, even if the penetration force of the fuel injected and atomized near the compression top dead center is weakened by the high in-cylinder pressure, the atomized fuel still has a strong penetration force and does not disperse. As a result, the atomized fuel enters the cavity 8 formed on the top surface of the piston as intended, and reaches the vicinity of the spark plug 6 through the cavity 8 by its own penetrating force as described above. A flammable mixture can be formed in the vicinity of 6. The combustible air-fuel mixture formed here is increased in fuel injection amount as described above in order to ensure reliable ignitability as compared with the combustible air-fuel mixture during normal stratified combustion, and is made rich. ing.
[0028]
Thus, in this embodiment, since fuel injection near the compression top dead center is possible, the ignition timing can be retarded until the combustible mixture formed immediately thereafter is temporally dispersed, It is possible to retard the ignition timing to the middle stage of the expansion stroke. Further, when the engine is started, the temperature in the cylinder is low, and sufficient fuel is not supplied from the bottom wall 8a and the opposed side wall 8b of the fuel in the cavity 8 of the piston 5 from the bottom wall 8a. Therefore, if fuel injection is performed when the in-cylinder pressure before the vicinity of compression top dead center is not so high, as in normal stratified combustion, atomization is not sufficiently promoted during flight by the in-cylinder pressure. The injected fuel enters the cavity 8 as a large lump of liquid fuel, and most of the fuel easily remains attached to the cavity 8. As a result, the amount of unburned fuel emission increases.
[0029]
In the present embodiment, when the engine is started, the fuel is injected near the compression top dead center. Therefore, as described above, even if sufficient heat is not supplied from the cavity 8, the injected fuel reaches the inside of the cavity 8. Since the particles are sufficiently atomized during the previous flight, they are easily vaporized in the cavity 8, and the amount of fuel adhering to the cavity 8 is reduced, so that the amount of unburned fuel discharged can be reduced.
[0030]
FIG. 5 shows a fuel injection timing and an ignition timing at the time of starting the engine in another embodiment of the direct injection type spark ignition internal combustion engine according to the present invention. Specifically, the fuel injection is started and started within the crank angle range INJ ′ near the compression top dead center, that is, within the crank angle range from before compression top dead center (0 °) to after compression top dead center 30 °. The ignition is terminated and the ignition is performed within the crank angle range IGN, that is, within the crank angle range from 20 ° to 50 ° after the compression top dead center, as described above.
[0031]
When the fuel is injected within this crank angle range INJ ', the in-cylinder pressure is high as described above, whereby the fuel is atomized. However, the penetration force does not weaken until the fuel is dispersed, and the fuel is in the vicinity of the ignition plug 6. Can reliably form a combustible mixture that can be ignited and burned with respect to the ignition timing retarded in the middle stage of the expansion stroke.
[0032]
Incidentally, there is a case where the intake air sucked into the cylinder during the intake stroke generates a swirling flow that swirls in the cylinder in the vertical direction. This swirling flow attenuates during the compression stroke, and is completely crushed by the piston at the compression top dead center and disappears. However, at the end of the compression stroke, the combustible mixture formed near the ignition plug is slightly dispersed without completely disappearing. In the present embodiment, the fuel is injected not in the compression stroke in which the swirl flow exists but in the expansion stroke in which the swirl flow has completely disappeared as in the above-described embodiment. Even if the combustible air-fuel mixture formed in the vicinity is slightly dispersed, good stratified combustion can be realized.
[0033]
Further, the above-described NO _X storage reduction catalyst device absorbs SO _X in the exhaust gas by the same mechanism as NO _X. The absorbed SO _X is not released only by lowering the oxygen concentration in the atmosphere like NO _X , and the SO _X absorption amount in the NO _X storage reduction catalyst gradually increases. When the SO _X absorption amount increases in this manner, NO _X cannot be absorbed correspondingly, and therefore, when the SO _X absorption amount reaches a certain level, SO _X must be released. In order to release SO _X , it is necessary to lower the oxygen concentration in the atmosphere and to heat the NO _X storage reduction catalyst device. As described above, it is effective to increase the exhaust gas temperature by setting the fuel injection timing near the compression top dead center and setting the ignition timing to the middle stage of the expansion stroke.
[0034]
In the embodiments described so far, the cavity on the top surface of the piston is used to guide the injected fuel to the vicinity of the ignition plug. However, this is not a limitation of the present invention, and the cavity for guiding the injected fuel to the vicinity of the ignition plug is used. May be provided in the cylinder head, and the fuel injected from the fuel injector flies directly in the cylinder toward the vicinity of the spark plug without using the cavity, and the combustible air-fuel mixture The present invention is also applicable to a direct injection type spark ignition internal combustion engine that forms the following. Further, the present invention is applied to a direct injection type spark ignition internal combustion engine that realizes stratified combustion using a fuel injection valve that injects fuel into a shape having a stronger penetration force than a conical fuel spray at the same fuel injection pressure. The fuel injection valve is not limited to a fuel injection valve having a slit injection hole and injecting fuel in a fan shape, and may be, for example, a fuel injection valve having a columnar shape or the like.
[0035]
【The invention's effect】
As described above, the in-cylinder injection spark ignition internal combustion engine according to the present invention includes the fuel injection valve that injects the fuel into a shape having a stronger penetration force than the conical fuel spray, and the ignition plug. In a cylinder-injection spark ignition internal combustion engine that injects fuel in the compression stroke and forms a combustible mixture near the spark plug to perform stratified combustion, when the exhaust gas temperature is increased, the fuel injection valve closes the compression top dead center. To inject the fuel, and set the ignition timing by the spark plug to the middle stage of the expansion stroke. The fuel spray having a strong penetration force maintains a relatively strong penetration force even when sufficiently atomized against a high in-cylinder pressure near the compression top dead center, and reliably forms a combustible mixture near the ignition plug. I can do it. In this way, since the combustible mixture can be formed near the ignition plug after the fuel injection near the compression top dead center, the combustible mixture is temporally dispersed even if the ignition timing is retarded to the middle stage of the expansion stroke. This can be reliably ignited and burned before. As a result, combustion can be continued up to about the middle stage of the exhaust stroke, and the exhaust gas temperature can be sufficiently increased even with one fuel injection per cycle.
[Brief description of the drawings]
FIG. 1 is a schematic vertical sectional view showing a direct injection type spark ignition internal combustion engine according to the present invention.
FIG. 2 is a plan view of the piston of FIG. 1;
FIG. 3 is a graph showing a spray tip reaching distance with respect to an elapsed time in a fan-shaped spray and a cone-shaped spray when an in-cylinder pressure is 0.1 MPa.
FIG. 4 is a graph showing a spray tip reaching distance with respect to an elapsed time in a fan-shaped spray and a cone-shaped spray when an in-cylinder pressure is 0.5 MPa.
FIG. 5 is a diagram showing a fuel injection timing range and an ignition timing range at the time of engine start of the direct injection type spark ignition internal combustion engine according to the present invention.
[Explanation of symbols]
5 Piston 6 Spark plug 7 Fuel injection valve 8 Cavity

Claims (7)

A fuel injection valve for injecting fuel into a shape having a stronger penetration force than the conical fuel spray; and an ignition plug. The fuel injection valve injects fuel in a compression stroke, and a combustible mixture near the ignition plug is provided. When the exhaust gas temperature is increased in a direct injection type spark ignition internal combustion engine that performs stratified combustion by forming a fuel injection valve, fuel is injected near the compression top dead center by the fuel injection valve and the ignition timing by the ignition plug is expanded. An in-cylinder injection spark ignition internal combustion engine having a middle stroke. The in-cylinder injection spark ignition internal combustion engine according to claim 1, wherein the middle stage of the expansion stroke is a crank angle range from 20 to 50 after compression top dead center. The in-cylinder injection spark ignition internal combustion engine according to claim 1 or 2, wherein the temperature of the exhaust gas is increased when the engine is started. The engine exhaust system is arranged _the NO _X storage reduction catalyst device, to claim 1 or 2, characterized in when to increase the exhaust gas temperature is when releasing the SO _X from the _the NO _X storage reduction catalyst device An in-cylinder injection spark ignition internal combustion engine according to claim 1. The in-cylinder injection type according to any one of claims 1 to 4, wherein the vicinity of the compression top dead center is a crank angle range from 30 ° before the compression top dead center to the compression top dead center. Spark ignition internal combustion engine. The in-cylinder injection type according to any one of claims 1 to 4, wherein the vicinity of the compression top dead center is a crank angle range from the compression top dead center to 30 ° after the compression top dead center. Spark ignition internal combustion engine. The in-cylinder injection spark ignition according to any one of claims 1 to 6, wherein the fuel injection valve has a slit-shaped injection hole for injecting fuel in a fan shape having a small thickness. Internal combustion engine.

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