JP2009185688A - Direct-injection spark-ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve combustion stability by improving a degree of concentration (degree of homogeneity) of a stratified air-fuel ratio when performing stratified combustion during a cold period including an engine start period. <P>SOLUTION: A fuel injection valve (outward valve) 5 forming hollow conical fuel spray is arranged in the upper center of a combustion chamber 4. During the cold period including the engine start period, fuel injection for stratified combustion from the fuel injection valve 5 is divided into a plurality of times, and subsequent injection is performed at timing with fuel spray injected later brought in fuel spray injected in first. After engine start, injection timing is delayed to a TDC (compression top dead center) or later together with ignition timing to ensure expansion stroke injection; meanwhile, an injection interval of divided injection is shortened in comparison with an injection interval of compression stroke injection. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a direct-injection spark-ignition internal combustion engine, and more particularly, to fuel injection control during cold including the engine start.

  In Patent Document 1, in a direct injection spark ignition internal combustion engine, at the time of stratified combustion in which fuel is injected in a compression stroke, the fuel injection is divided into a plurality of times, and the fuel that has been divided and injected is injected first On the other hand, the fuel injected thereafter is injected so as to overlap in the vicinity of the spark plug.

  That is, of the divided fuels, the previously injected fuel forms an air-fuel mixture in a region determined by the injection characteristics of the fuel injection valve, the injection direction, the influence of gas flow in the combustion chamber, and the like. The fuel injected after this injection has a flow along the injection direction due to the influence of the previous injection, so that the fuel injected later forms a spray of the same form. Then, it proceeds through the combustion chamber at a higher speed than the previously injected fuel. Accordingly, the fuel injected later is caught up with the previously injected fuel and overlapped to form an air-fuel mixture with an appropriate concentration degree at that position.

However, when the engine is cold, the engine wall surface temperature is low, and the adverse effect on the combustion performance due to the fuel wall adhesion is large, so split injection is prohibited and single injection is performed only once.
JP 2002-115593 A

  In the technique described in Patent Document 1, since the split injection is prohibited and the injection is performed only once in the cold including the start of the engine, the concentration (homogeneity) of the stratified mixture is reduced. As a result, the combustion stability deteriorates.

In addition, in the single injection, since the penetration of the fuel spray is stronger than in the split injection, there is a possibility that the amount of adhesion to the wall surface is increased.
The present invention has been made in view of such a situation, and an object of the present invention is to make it possible to perform stratified combustion more stably during cold including the start of the engine.

  For this reason, in the present invention, during cold including the start of the engine, fuel injection is performed immediately before the ignition timing and fuel spray is ignited to cause stratified combustion, and the fuel injection is divided into a plurality of times. It is set as the structure which performs subsequent fuel injection at the timing at which the fuel spray injected later is drawn into the fuel spray injected previously.

  According to the present invention, at the time of stratified combustion in the cold state including when the engine is started, the concentration (homogeneity) of the air-fuel mixture can be increased by the above-described divided injection, and the combustion stability can be improved. it can.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram of a direct injection spark ignition internal combustion engine showing an embodiment of the present invention.
In FIG. 1, a pent roof type combustion chamber 4 is formed by a cylinder head 1, a cylinder bore 2, and a piston 3, and a fuel injection valve 5 is disposed downward in the center of the upper part thereof.

  The fuel injection valve 5 is an outward valve as shown in FIG. 2, and a fuel passage 51 is formed along the axis at the tip of the fuel injection valve body 50. The fuel passage 51 is tapered at the tip. An opening 52 is formed.

  A poppet-type valve element 54 is provided at the tip of a rod 53 that penetrates the fuel passage 51 in the direction of the passage, and the tapered surface of the poppet-type valve element 54 is opposed to the tapered opening 52.

  Accordingly, when the valve body 54 is lifted to the outside, an outward annular jet 55 is formed between the tapered opening 52 and the tapered surface of the valve 54, and fuel is injected from the jet 55. The fuel spray has a hollow conical shape.

  The spark plug 6 is disposed obliquely at a position eccentric from the upper center of the combustion chamber 4, and is thereby disposed to ignite the outer edge of the hollow conical fuel spray injected from the fuel injection valve 5. Yes.

  More specifically, a part of the outer edge of the hollow conical fuel spray injected from the fuel injection valve 5 is swelled (swelled) by shearing with the surrounding air. Are arranged to be.

  The operation of the fuel injection valve 5 and the spark plug 6 is controlled by an engine control unit (ECU) 7, which includes an engine speed Ne detected by an engine speed sensor, a fuel pressure Pf detected by a fuel pressure sensor, and a water temperature sensor. A signal such as the water temperature Tw detected by is input.

The operation mode (combustion mode) of the internal combustion engine includes a homogeneous operation mode and a stratified operation mode.
In the homogeneous operation mode, fuel injection of the fuel injection valve 5 is performed in the intake stroke, and a homogeneous air-fuel mixture is formed in the entire combustion chamber 4 by the ignition timing by the spark plug 6, so that the stoichiometric air-fuel ratio or lean Homogeneous combustion is performed at an air-fuel ratio (A / F = 20 to 30).

  On the other hand, in the stratified operation mode, the fuel injection of the fuel injection valve 5 is performed in the compression stroke, and the stratified mixture is formed in a part of the combustion chamber 4 (the central portion of the combustion chamber 4 that can be ignited by the spark plug 6). By forming an air mass, stratified combustion is performed at a very lean air-fuel ratio (A / F = 30 to 40) as a whole.

  By the way, when stratified combustion is performed during cold including the start of the engine, in other words, when starting with stratified combustion and reducing the amount of HC emissions at the start and immediately after start, the mixture is simply stratified. Instead, it is necessary to make the air-fuel mixture compact.

  In addition, during warm-up immediately after starting, the ignition timing is retarded from the top dead center to promote warm-up (early activation of the exhaust purification catalyst due to the exhaust temperature rise), so the injection timing is also from the top dead center Since it is retarded, it becomes expansion stroke injection. In the expansion stroke injection, since the piston advances downward, the mixture is more easily diffused than in the compression stroke injection. Therefore, the mixture needs to be made more compact.

  Therefore, in the present invention, fuel injection for stratified combustion is divided into a plurality of times during cold including the start of the engine. And this division | segmentation injection (multistage injection) is set as the structure which performs subsequent injection at the timing at which the fuel spray injected later is drawn into the fuel spray injected previously.

This will be described with reference to FIG.
In the case of a single injection (when the required injection amount is injected at a time), as shown in FIG. 3A, the penetration is large, and the inside of the hollow conical spray has a large space.

On the other hand, in the case of divided injection (when the required injection amount is divided into two injections; in the case of two injections), it is as follows.
As shown in FIG. 3 (b-1), in the first injection of the second injection, the amount of injection per injection is reduced as compared with the case of a single injection, so the penetration is reduced. Therefore, the spread is also reduced.

  In other words, the fuel spray of the outward valve has a low penetration in the first place, but by dividing the injection amount, the momentum is further reduced and the spray stays near the spray point.

And the negative pressure area | region by the flow velocity of injection generate | occur | produces behind the spray of the 1st injection.
As shown in FIG. 3B-2, the second injection of the second injection is performed toward the negative pressure region behind the spray of the first injection. Accordingly, since the spray of the second injection is attracted by negative pressure, the flow velocity is higher than that of the spray of the first injection, catching up with the spray of the first injection, and the spray of the second injection enters the spray of the first injection.

  In other words, the rear end of the spray has a negative pressure, and normally ambient air flows in. However, by performing the second injection there, the second spray is drawn into the first spray. It is.

  Thus, finally, as shown in FIG. 3 (b-3), the spray of the second injection enters the spray of the first injection, and diffusion prevention and improvement in uniformity are expected. Moreover, vaporization is also accelerated | stimulated by the collision with the surrounding air at the time of drawing.

  In this way, when stratified combustion is performed during cold including engine start, fuel is injected in multiple times, not only increasing the concentration, but also reducing fuel spray penetration and compact In addition, a homogeneous stratified mixture can be formed, the flame propagation stability can be improved and the combustion speed can be shortened, the combustion stability can be improved, and the amount of gas quench due to diffusion can be reduced.

  Also, when the expansion stroke is injected during warm-up immediately after starting, the piston advances downward, so that the air-fuel mixture is more easily diffused than the compression stroke injection, and the rear end of the spray by the previous injection Since the generation time of the negative pressure also becomes earlier, the injection interval of the divided injection (interval from the start timing of the previous injection to the start timing of the subsequent injection) is narrowed compared to the compression stroke injection.

FIG. 4 is a flowchart of the fuel injection control in the cold state including when the engine is started.
In S1, the water temperature Tw detected by the water temperature sensor is read, and it is determined whether or not the water temperature Tw is lower than a predetermined value Tw1, that is, when it is cold.

  When the water temperature Tw is less than the predetermined value Tw1 (when cold), the process proceeds to S2. On the other hand, when the water temperature Tw is equal to or higher than the predetermined value Tw1 (in the case of hot restart or the like), this routine is terminated and the normal control is started.

  In S2, it is determined whether or not the engine speed Ne is less than a predetermined value Ne1, that is, at the time of starting. The predetermined value Ne1 is set to be equivalent to the fast idle rotation speed (for example, 700 to 800 rpm).

If the engine speed Ne is less than the predetermined value Ne1 (when starting), the process proceeds to S3. On the other hand, if the engine speed Ne is greater than or equal to the predetermined value Ne1, the process proceeds to S5.
In S3, stratified combustion is performed by split injection, and the engine is started. This is called mode A. Specifically, the control is performed as follows.

・ Ignition timing is set before TDC (compression top dead center).
-The injection timing is set immediately before the ignition timing before TDC.
The injection interval of divided injection (interval from the injection start timing of the previous injection to the injection start timing of the subsequent injection) τ is a predetermined value τA.

The required injection amount at the time of starting is constant, and the injection pulse width (injection time) is set according to the fuel pressure Pf.
In next S4, it is determined whether or not the engine speed Ne has become equal to or greater than a predetermined value Ne1, and in the case of NO, the process returns to S3 and continues the mode A. Thereafter, when the answer is YES (when the fast idle speed is reached), the process proceeds from S4 to S5.

In S5, stratified charge combustion is performed by split injection, and warm-up operation is performed. This is called mode B. Specifically, the control is performed as follows.
・ Ignition timing is set after TDC. This is to promote warm-up by ignition timing retard (early activation of the exhaust purification catalyst due to an increase in exhaust temperature).

-The injection timing is set after TDC and immediately before the ignition timing. This is because it is necessary to similarly retard the ignition timing in order to enable stratified combustion.
The injection interval τ of the divided injection is set to a predetermined value τB, which is shorter than the injection interval τA in mode A (τB <τA). This is because the injection interval of the divided injection is shortened from the time of the compression stroke injection to further prevent diffusion.

-Increase the throttle opening TVO. This is because torque correction is performed so as to compensate for the torque drop due to the ignition timing retard.
In next S6, it is determined whether or not the water temperature Tw has become equal to or higher than the predetermined value Tw1, and in the case of NO, the process returns to S5 and continues the mode B. Thereafter, when the answer is YES (when the warm-up is completed), this routine is terminated and the routine proceeds to normal control.

  After shifting to the normal control, the homogeneous combustion and the stratified combustion are switched according to the operating conditions (mainly engine speed and load). That is, stratified combustion is performed in a low rotation / low load region, and homogeneous combustion is performed in a high rotation / high load region.

FIG. 6 is a time chart of the above control.
At the start (until the fast idle speed is reached), the ignition timing and the injection timing are set before TDC, and the injection interval of the divided injection is set relatively long.

  When the fast idle rotation speed is reached and the warm-up operation is started, the ignition timing and the injection timing are set after TDC, and the injection interval of the divided injection is set relatively short. In addition, the throttle opening is corrected to increase to compensate for the torque drop due to the ignition timing retardation.

  In addition, according to the present embodiment, after the engine is started, the injection interval τB of the divided injection is set to the injection interval τB in the compression stroke injection when the injection timing is retarded to TDC and later after the ignition is started to perform the expansion stroke injection. By making it shorter, since the piston is moving downward during the expansion stroke injection, the concentration of the air-fuel mixture can be kept high even though the air-fuel mixture is likely to diffuse, and Corresponding to the earlier generation timing of the negative pressure at the rear end of the spray due to the previous injection, an effect is obtained that the post injection can be performed at an appropriate timing.

  Further, according to the present embodiment, as the fuel injection valve 5, an outward valve that is provided downward in the center of the upper portion of the combustion chamber and that forms a hollow conical fuel spray by an outward annular jet outlet is used. The spark plug 6 is arranged so as to directly ignite the outer edge of the hollow conical fuel spray, so that the fuel spray from the low-penetration outward valve is reduced to a lower penetration by split injection in the first place. The concentration (homogeneity) of the fuel can be further increased, and the fuel spray can be ignited and burned without reaching the piston crown surface or the cylinder wall surface, thereby reducing the HC emission amount at the time of starting.

  In the above description, the number of divided injections is two. However, if possible, the number of divided injections is divided into three or more to further suppress penetration, thereby improving the homogeneity of the stratified mixture. Also good.

The block diagram of the direct-injection spark-ignition internal combustion engine which shows one Embodiment of this invention Illustration of fuel injection valve (outward valve) Illustration of split injection Flow chart of cold fuel injection control including engine start Fuel injection control time chart

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Cylinder bore 3 Piston 4 Combustion chamber 5 Fuel injection valve 50 Fuel injection valve main body 51 Fuel passage 52 Tapered opening 53 Rod part 54 Poppet-like valve body 55 Annular jet 6 Spark plug 7 ECU

Claims (3)

In a direct-injection spark-ignition internal combustion engine having a fuel injection valve and an ignition plug in the combustion chamber,
At the time of cold including when the engine is started, fuel injection is performed immediately before the ignition timing to ignite the fuel spray, and stratified combustion is performed.
A direct-injection spark-ignition internal combustion engine characterized by dividing a fuel injection into a plurality of times and performing a subsequent injection at a timing at which a fuel spray injected later is drawn into a previously injected fuel spray.   After the engine is started, the injection timing is retarded from the top dead center together with the ignition timing to make the expansion stroke injection, while the injection interval of the divided injection is made shorter than the injection interval in the compression stroke injection. Item 5. A direct-injection spark-ignition internal combustion engine according to Item 1. The fuel injection valve is an outward valve provided downward in the upper center of the combustion chamber to form a hollow conical fuel spray,
The direct-injection spark-ignition internal combustion engine, wherein the spark plug is disposed so as to ignite an outer edge of the hollow conical fuel spray.

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