JP2000282920A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the warming performance of a catalyst in an internal combustion engine of inner cylinder injection type. SOLUTION: When a catalyst 33 is not activated, additional fuel injection in one or more runs is made in expansion stroke or exhaust stroke after ignition, and the exhaust temp. is raised for activation of the catalyst 33 by post- combustion the added fuel by the flames of the main combustion. At this time, the exhaust gas SCV21 is controlled to the close side, and the valve opening timing of the exhaust valve is controlled to the advance side, while swirls are produced in the gas flow in the cylinder in the exhaust stroke, and part of the combustion gas in the cylinder is allowed to flow toward one of the exhaust ports 19b. Thereby the gas flow in the cylinder is promoted, and turning the added fuel in particulates is promoted, and also the mixing ad agitation of the added fuel with inner cylinder gas are promoted, and thereby the injected additional fuel is completely combusted to preclude generation of smokes, and the exhaust temp. is raised to make smoke prevention and early activation of catalyst compatible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection type internal combustion engine control apparatus for directly injecting fuel into a cylinder and burning the fuel.

[0002]

2. Description of the Related Art In recent years, the demand for an in-cylinder injection engine having features of low fuel consumption, low exhaust emission, and high output has been rapidly increasing. Many of these in-cylinder injection engines generally adopt a stratified combustion system. In the stratified combustion system, fuel is injected late in the compression stroke, the mixture of fuel and air is stratified to form a relatively rich mixture near the spark plug, and this mixture is ignited to form the entire mixture. This enables combustion at a significantly lean air-fuel ratio.

[0003] Such a stratified combustion system has high thermal efficiency, reduces heat loss to exhaust gas, and has a large amount of intake air per unit fuel. Therefore, such a stratified combustion system is compared with a conventional engine (intake port injection engine). The exhaust temperature drops significantly. Therefore, particularly in a low load region including idling, the exhaust gas temperature becomes lower than the activation lower limit temperature of the catalyst designed based on the exhaust gas temperature of the conventional engine, and as a result, the exhaust gas purification performance deteriorates. A situation may occur.

As a countermeasure against this, Japanese Patent Laid-Open Publication No. Hei 8-100638
As shown in the publication, in addition to fuel injection before ignition (injection of main fuel), additional fuel is injected from the initial stage to the middle stage of the expansion stroke after ignition, and the additional fuel is used for combustion of main fuel by ignition (main fuel injection). There has been proposed a technique of activating a catalyst by raising the exhaust gas temperature by post-combustion by flame propagation of (combustion).

[0005]

However, in the technique disclosed in the above-mentioned publication, the additional fuel injection is performed from the initial stage of the expansion stroke to the middle stage. However, when the fuel is injected in the early stage of the expansion stroke, the flame of the main combustion is generated. Since the additional fuel is injected under the remaining high temperature and high pressure, the additional fuel starts to ignite immediately after the injection. As a result, before the additional fuel is sufficiently atomized, the outer periphery of the fuel droplet starts burning and the inside of the fuel droplet carbonizes,
There is a problem that smoke is generated.

Although the above-mentioned publication does not mention the injection amount of the additional fuel at all, there is an optimum value for the injection amount of the additional fuel. Therefore, unburned gas (hydrocarbon) is exhausted to deteriorate exhaust emission or increase exhaust temperature. Conversely, when the amount of additional fuel injected is large, the excess injection is discharged as unburned HC without burning, relative to the amount of residual oxygen in the in-cylinder gas after main combustion, and exhaust emissions are reduced. It also causes deterioration, generation of smoke, and deterioration of fuel efficiency due to excessive fuel injection.

Further, in the above-mentioned publication, additional fuel is injected in a low load region including idling. However, stratification is performed in a state where engine friction is high such as in a cold state where the engine is not warmed up. When the combustion is performed, the fuel injected in the compression stroke is ignited before being sufficiently vaporized, so that the combustion is not stabilized and the engine vibration is increased.

In the cylinder injection engine, since the air-fuel ratio of the air-fuel mixture is made lean and the air-fuel mixture is burned in an excessive oxygen state, the amount of NOx (nitrogen oxide) in the exhaust gas tends to increase. As a countermeasure, a NOx storage type lean NOx catalyst is often installed in the exhaust pipe. This lean NOx catalyst stores NOx in the exhaust gas during lean operation in which the oxygen concentration in the exhaust gas is high, and when the air-fuel ratio is switched to a rich or stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas decreases. Then, the NOx stored so far is reduced and purified. Therefore, in order to maintain the NOx purification performance of the lean NOx catalyst, it is necessary to switch to the rich operation (or the stoichiometric operation) from time to time during the lean operation. However, when switching from the lean operation to the rich operation, if the fuel injection amount is increased, torque shock occurs and drivability is reduced.

[0009] It has been studied to mount a supercharger (turbocharger) driven by exhaust pressure on an in-cylinder injection engine for the purpose of further increasing output and reducing fuel consumption.
When the turbocharger is installed, due to the poor response of the turbocharger,
The great advantage of the in-cylinder injection engine, the good acceleration response, is impaired.

The present invention has been made in view of these circumstances, and a first object of the present invention is to post-burn additional fuel without generating smoke to raise the exhaust gas temperature and activate the catalyst early. It is to make it.

A second object of the present invention is to activate the catalyst at an early stage by injecting the additional fuel at an appropriate timing and at an appropriate injection amount, thereby preventing deterioration of fuel efficiency and exhaust emission. That is.

A third object is to achieve both a reduction in engine vibration (roughness) during idling and an early activation of the catalyst.

A fourth object is to prevent the occurrence of torque shock when switching from lean operation to rich operation in order to reduce and purify NOx stored in the lean NOx catalyst.

A fifth object of the present invention is to improve the acceleration response of a direct injection internal combustion engine equipped with a supercharger.

[0015]

In order to achieve the first object, according to the first aspect of the present invention, the additional fuel injection control means is provided for controlling the post-ignition expansion stroke or the exhaust stroke when the catalyst is not activated. The additional fuel is injected one or more times during the stroke, and the additional fuel is post-combusted with the main combustion flame by ignition, thereby raising the exhaust gas temperature and activating the catalyst. On this occasion,
The gas flow promoting means promotes the gas flow in the cylinder, thereby promoting the atomization of the injected additional fuel by the gas flow and the mixing and stirring of the additional fuel and the gas containing oxygen in the cylinder. This makes it possible to raise the exhaust gas temperature without causing the injected additional fuel to completely combust and generate smoke, thereby achieving both smoke prevention and early catalyst activation.

In this case, an exhaust swirl control valve disposed at one of a plurality of exhaust ports provided in each cylinder is used as the gas flow promoting means, and additional fuel injection is performed. During the control, the exhaust swirl control valve may be controlled to close. By controlling the exhaust swirl control valve to the closed side, during the exhaust stroke, before additional fuel starts to burn,
Swirl is generated in the gas flow in the cylinder, and this swirl promotes atomization of the additional fuel and promotes mixing and stirring of the additional fuel and the in-cylinder gas.

Alternatively, the gas flow in the cylinder may be promoted by controlling the valve opening timing of the exhaust valve to the advanced side during the additional fuel injection control.
In other words, when the valve opening timing of the exhaust valve is controlled to the advanced side, the timing at which the combustion gas in the cylinder is discharged is advanced, and a portion of the combustion gas in the cylinder is discharged to the exhaust port before the additional fuel starts burning. It starts to flow toward. Thereby, the gas flow in the cylinder is promoted, the atomization of the additional fuel is promoted, and the mixing and stirring of the additional fuel and the in-cylinder gas are promoted.

In order to achieve the second object,
According to a fourth aspect of the present invention, one or both of the additional fuel injection amount and the injection timing are determined by the injection amount of the main fuel injected before ignition, the engine speed, the engine load, the engine temperature, the exhaust temperature, and during the exhaust stroke. The control may be performed based on at least one of the in-cylinder combustion state and the oxygen concentration in the exhaust gas. That is, these parameters all affect the combustibility of the additional fuel (for example, the higher the oxygen concentration in the exhaust gas, the larger the amount of additional fuel that can be combusted). Further, the period during which the flame of the main combustion by ignition continues, that is, the period during which the additional fuel can be burned, also changes according to these parameters. Therefore, if one or both of the injection amount and the injection timing of the additional fuel are controlled by at least one of these parameters, the injection of the additional fuel can be performed at a proper timing and a proper injection amount, and the fuel consumption can be improved. The catalyst can be activated at an early stage while preventing deterioration and deterioration of exhaust emission.

Attention is also paid to the point that ions are generated when fuel is burned in the cylinder, and ions generated by combustion in the cylinder are detected through a spark plug as described in claim 5, and based on the ion current, The in-cylinder combustion state during the exhaust stroke may be determined by the combustion state determination means, and one or both of the injection amount and the injection timing of the additional fuel may be controlled based on the in-cylinder combustion state during the exhaust stroke. . This makes it possible to optimize the additional fuel injection control while detecting the in-cylinder combustion state during the exhaust stroke using the ignition plug.

In order to achieve the third object,
According to a sixth aspect, the combustion mode switching means may switch the combustion mode during idling between stratified combustion and homogeneous combustion based on at least one of the engine temperature, the exhaust gas temperature, and the catalyst temperature. . By doing so, for example, when the engine friction is high, such as during a cold time when the engine is not warmed up, by switching to the homogeneous combustion method, fuel is injected in the intake stroke to perform homogeneous combustion, The combustion state can be stabilized, and engine vibration (roughness) during idling can be reduced.

Further, the in-cylinder exhaust residual amount (internal EGR amount) may be controlled by controlling the opening of the exhaust swirl control valve by the exhaust residual amount control means. In this way, by controlling the opening of the exhaust swirl control valve, the internal E
GR (internal exhaust gas recirculation) can be realized.
Exhaust gas purification performance can be improved by combining R and a catalyst, and an external EGR device can be eliminated,
It also leads to cost reduction.

In order to achieve the fourth object,
When reducing and purifying NOx stored in the lean NOx catalyst, one or more times of additional fuel is injected during the expansion stroke or the exhaust stroke after ignition to cause the additional fuel to be ignited. The air-fuel ratio of the exhaust gas may be switched to a rich or stoichiometric air-fuel ratio by post-combustion with the main combustion flame. In other words, the additional fuel injected after the ignition does not change much when the engine is burned.
If the operation is switched to the rich operation by the injection of the additional fuel at the time of the reduction purification, the operation can be switched from the lean operation to the rich operation without a torque shock, and the drivability can be improved.

In order to achieve the fifth object,
According to a ninth aspect of the present invention, a supercharger driven by exhaust pressure is mounted, and at the time of acceleration, one or more times of additional fuel is injected during an expansion stroke or an exhaust stroke after ignition to ignite the additional fuel. The post-combustion with the flame of the main combustion may raise the exhaust pressure to improve the responsiveness of the supercharger. In this manner, the turbocharger can further increase the output and reduce the fuel consumption without deteriorating the acceleration response, which is a great advantage of the direct injection internal combustion engine.

[0024]

[Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of an intake pipe 12 of a direct injection engine 11 which is a direct injection internal combustion engine, and an air flow meter 14 for measuring an intake air amount is provided downstream of the air cleaner 13. Have been. A throttle body 15 having a built-in throttle valve (not shown) is provided at an intermediate portion of the intake pipe 12. The throttle body 15 has a throttle opening sensor 16 for detecting a throttle opening and a drive for the throttle valve. Actuator 17 is provided.

Each cylinder of the engine 11 has two intake ports 18a, 18b and two exhaust ports 19a, 19b.
Is provided. One of the intake ports 18a
Has an intake swirl control valve (hereinafter referred to as "intake SC
V), and an exhaust port 19a is provided with an exhaust swirl control valve (hereinafter, referred to as “exhaust SCV”) 21.
Further, each cylinder of the engine 11 is provided with a fuel injection valve 22 and a spark plug 23, a crank angle sensor 24 for detecting a crank angle, a cylinder discrimination sensor 25 for detecting a reference position for discriminating a cylinder, A water temperature sensor 26 for detecting an engine cooling water temperature and an exhaust valve opening timing changing device 27 for changing the opening timing of an exhaust valve (not shown) of each cylinder are provided.

The ignition plug 23 is connected to the secondary winding side of the ignition coil 28, and the primary winding side of the ignition coil 28
An igniter 29 controlled by an electronic control unit 36 described later is connected. During engine operation, the igniter 29 cuts off the primary current of the ignition coil 28 at each ignition timing, thereby generating a high voltage on the secondary side of the ignition coil 28, and applying this high voltage to the ignition plug 23, Generates spark discharge.

On the other hand, the exhaust pipe 30 is provided with an exhaust gas temperature sensor 31 for detecting the temperature of the exhaust gas and an oxygen sensor 32 for detecting the concentration of oxygen in the exhaust gas.
A NOx storage type lean NOx catalyst 33 is provided downstream of the NOx catalysts 1 and 32. The lean NOx catalyst 33 is provided with a catalyst temperature sensor 34 for detecting a catalyst temperature. A muffler 35 is provided downstream of the lean NOx catalyst 33.
Is attached.

The output signals of the various sensors described above are taken into an electronic control unit (hereinafter referred to as “ECU”) 36. The ECU 36 includes a CPU 37, a RAM 3
8, ROM39 (storage medium), input interface 4
0, a microcomputer having an output interface 41 and the like.
Drive circuits 42 and 43 for driving various actuators such as 2 are built in. This ECU 36
The CPU 37 executes the fuel injection control program and the ignition control program stored in M39 to perform the fuel injection control and the ignition control.

When the lean NOx catalyst 33 is not activated (that is, when the catalyst temperature is lower than the activation lower limit temperature α), the ECU 36 executes the program shown in FIGS. When low)
In addition, additional fuel is injected in the expansion stroke or the exhaust stroke after ignition, and the additional fuel is post-combusted with the flame of the main combustion by ignition to raise the exhaust gas temperature and activate the lean NOx catalyst 33. In addition to functioning as a control means, the exhaust SCV 21 is controlled to be closed during the additional fuel injection control, and at the same time, the opening timing of an exhaust valve (not shown) is controlled to be advanced by the exhaust valve opening timing changing device 27. This also functions as a gas flow promoting unit that promotes gas flow in the cylinder and promotes post combustion of the additional fuel. In the present embodiment (1), the exhaust SCV 21 is fully opened during normal operation and performs two-stage control of switching to fully closed when performing additional fuel injection, and the exhaust valve opening timing is normally the most retarded. When the additional fuel injection is performed, two-stage control for switching to the most advanced angle is performed.

Hereinafter, the processing contents of the programs shown in FIGS. 2 to 4 for performing these controls will be described. The idle control program shown in FIGS. 2 and 3 is repeatedly executed at predetermined time intervals during a period in which the idle state is determined based on the throttle opening VA, the engine speed NE, and the like. When the program is started, first, in step 101, the engine speed NE, the throttle opening VA, the intake air amount QA, the cooling water temperature Thw, and the exhaust gas temperature Th detected by various sensors.
e) Read the detection signal of the engine operating state such as the catalyst temperature Thc.

Thereafter, in step 102, the lean NO is determined based on the catalyst temperature Thc detected by the catalyst temperature sensor 34.
The activation state of the x catalyst 33 is determined, and if the catalyst temperature Thc is equal to or lower than the activation lower limit temperature α, it is determined that the lean NOx catalyst 33 cannot sufficiently purify the exhaust gas, that is, an inactive state. In this case, it is determined that the temperature of the exhaust gas needs to be increased by the additional fuel injection, and the routine proceeds to step 103, where the additional fuel injection execution flag Fwpi is set to "1" meaning "additional fuel injection", and the combustion is performed. Method flag Fco
m is set to “S” meaning stratified combustion, and the combustion mode is switched to stratified combustion. Here, when performing the additional fuel injection, the reason for switching the combustion method to the stratified charge combustion is that oxygen is left at the end of the main combustion in order to post-burn the additional fuel injected after the ignition with the flame of the main combustion. Therefore, the main combustion is performed by stratified combustion using a lean air-fuel mixture so that oxygen is left at the end of the main combustion.

Further, when performing additional fuel injection,
Since the combustion tends to be unstable, it is determined that the idle-up is necessary, and the routine proceeds to step 107, where the idle target rotational speed Nltarget is switched to the higher idle rotational speed Na.

On the other hand, at step 102, the catalyst temperature T
When hc is higher than the activity lower limit temperature α, the lean NO
When it is determined that the x catalyst 33 is activated,
In step 04, the additional fuel injection execution flag Fwpi is set to "0" which means "no additional fuel injection is performed". Thereafter, in step 105, the engine warm-up state is determined based on the cooling water temperature Thw detected by the water temperature sensor 26.
If the cooling water temperature Thw is equal to or lower than the predetermined temperature β1 set to a relatively low temperature, it is determined that the engine is in a cold state, and the routine proceeds to step 106, where the combustion mode flag Fcom is set to “H” meaning homogeneous combustion. In addition, the combustion method is switched to homogeneous combustion that facilitates stable combustion even in a cold state. Even in this case,
As in the case of performing the additional fuel injection, it is determined that the idle-up is necessary, and the routine proceeds to step 107, where the target idle speed N
Switch ltarget to the higher idle speed Na.

In step 105, the cooling water temperature T
If hw is determined to be higher than the predetermined temperature β1,
If it is determined that the combustion is relatively stable, step 108
The target idle speed Nltarget is switched to the lower idle speed Nb (where Nb <Na). Then, in the next step 109, the engine warm-up state is determined again based on the cooling water temperature Thw, and if the cooling water temperature Thw is equal to or higher than a predetermined temperature β2 (where β2> β1) set to a relatively high temperature, the engine is started. 11 is determined to be in a completely warmed-up state, the routine proceeds to step 110, and the combustion mode flag Fcom
Is set to “S” meaning stratified combustion, and the combustion method is switched to stratified combustion with good fuel efficiency.

On the other hand, at step 109, the cooling water temperature T
hw is determined to be lower than the predetermined temperature β2 (β1
If <Thw <β2), it is determined that the engine 11 is in the process of warming up, and the routine proceeds to step 111, where the combustion mode flag Fcom is set to “H” meaning homogeneous combustion, and the combustion mode is set to the warm-up mode. Switch to homogeneous combustion for stable combustion even in the middle of the machine. These steps 103, 106, 110, 1
The process of switching the combustion mode in step 11 serves as the combustion mode switching means in the claims.

As described above, the lean NOx catalyst 33
Of the additional fuel injection, the combustion method, the idle target rotation speed Nltar
After setting get, the process proceeds to step 112 in FIG. 3, and the main fuel injection amount (main injection amount) to be injected before ignition, the main fuel injection timing (main injection timing), and the ignition timing are calculated.

Here, when calculating the main injection amount Ti1, first, the basic fuel injection amount Tp is calculated from a map or the like according to the engine operating state such as the engine speed NE and the engine load.
Is calculated using various correction coefficients Fc such as a cooling water temperature correction coefficient and an air-fuel ratio feedback correction coefficient, and an invalid injection amount Tv for correcting a response delay time of the fuel injection valve 22 that changes according to a battery voltage. From the formula, the main injection amount Ti
1 is calculated. Ti1 = Tp × Fc + Tv

When calculating the main injection timing, the engine speed NE and the basic fuel injection amount T are determined according to the combustion method.
The main injection timing is calculated based on p and a map or the like. This main injection timing is set as the injection end timing in the case of stratified combustion, and is set as the injection start timing in the case of homogeneous combustion.

When calculating the ignition timing, first,
The basic ignition timing is calculated by a map or the like according to the engine speed NE and the basic fuel injection amount Tp, and the basic ignition timing is corrected by the cooling water temperature or the like to calculate the final ignition timing.

As described above, the main injection amount, the main injection timing,
After calculating the ignition timing, the routine proceeds to step 113, where it is determined whether or not the additional fuel injection execution flag Fwpi is “1” meaning “additional fuel injection is performed”, and Fwpi = “0”.
In the case of (no additional fuel injection is performed), step 117
Then, the valve opening of the exhaust SCV 21 is set to 100% (fully open), the valve opening timing of the exhaust valve is set to the most retarded angle, and the control is performed with priority given to the exhaust performance.

On the other hand, at step 113, Fwpi =
If “1” (additional fuel injection is performed), step 11
4 and execute the additional fuel injection amount / injection timing calculation program of FIG. 4 to execute the additional fuel injection amount (additional injection amount Ti
2) and the additional fuel injection timing (additional injection timing θ2) are calculated as follows. First, in step 201, the basic additional injection amount Qbase is calculated by map interpolation using the main injection amount Ti1. In this case, considering that the main injection amount Ti1 decreases and the remaining amount of oxygen at the end of the main combustion increases, the basic additional injection amount Qbase increases as the main injection amount Ti1 decreases.

Thereafter, at step 202, the oxygen sensor 3
Based on the exhaust oxygen concentration O2 detected in step 2, the residual oxygen amount correction amount Qco for the basic additional injection amount Qbase is calculated by the following equation. Qco (i) = Qco (i-1) + (O2 -Ko) .times.Co

In the above equation, Qco (i) is the current residual oxygen amount correction amount, Qco (i-1) is the previous residual oxygen amount correction amount,
Ko is a reference oxygen concentration, and Co is a correction coefficient. For example,
When the exhaust oxygen concentration O2 is higher than the reference oxygen concentration Ko, the residual oxygen amount correction amount Qco is increased by a correction amount (O2-Ko) × Co according to the difference between the exhaust oxygen concentration O2 and the reference oxygen concentration Ko. . Conversely, when the exhaust oxygen concentration O2 is lower than the reference oxygen concentration Ko, the correction amount (O2 -Ko) corresponding to the difference between the exhaust oxygen concentration O2 and the reference oxygen concentration Ko
The residual oxygen amount correction amount Qco is reduced by × Co.

In the next step 203, the basic additional injection amount Q
The additional injection amount Ti2 is obtained by adding the residual oxygen amount correction amount Qco to the base. Ti2 = Qbase + Qco, where Qbase + Qco is the minimum injection quantity Qm at which ignition is possible
If it is less than in, the additional injection amount Ti2 is subjected to guard processing with the minimum ignitable injection amount Qmin, and Ti2 =
Qmin, and Qbase + Qco is the minimum injection amount Qm
In the case of in or more, Ti2 = Qbase + Qco.

After calculating the additional injection amount Ti2, step 20
4, the basic additional injection timing θbase is changed to the main injection amount Ti
1 is calculated by map interpolation. In this case, considering that the flame of main combustion lasts longer as the main injection amount Ti1 increases, the basic additional injection timing θbase is retarded as the main injection amount Ti1 increases.

In the next step 205, the ion remaining timing Ti in the cylinder during the exhaust stroke is detected, and the ion remaining timing correction amount θc for the basic additional injection timing θbase is calculated based on the ion remaining timing Ti. Detection of ions in the cylinder during the exhaust stroke is performed by applying a constant voltage to the ignition plug 23 after ignition, collecting ions in the gas present in the gap between the electrodes of the ignition plug 23 at the plug electrode, and detecting ions flowing through the plug electrode. Detect the current. Then, the last time at which ions can be detected is defined as the ion remaining time Ti, and the ion remaining time correction amount θc is calculated by the following equation. θc (i) = θc (i−1) + (Ti−Ki) × Ci

In the above equation, θc (i) is the current ion remaining time correction amount, θc (i-1) is the previous ion remaining time correction amount, Ki is the reference ion remaining time, and Ci is the correction coefficient. For example, when the ion remaining time Ti is later than the reference ion remaining time Ki, the correction amount (Ti-Ki) according to the difference between the ion remaining time Ti and the reference ion remaining time Ki.
The amount of correction of remaining ion timing θc is increased by × Ci (the additional injection timing θ2 is thereby retarded). On the other hand, when the ion remaining time Ti ends before the reference ion remaining time Ki, the correction amount (Ti−Ki) × the difference according to the difference between the ion remaining time Ti and the reference ion remaining time Ki.
The amount of correction of the ion remaining timing θc is reduced by Ci (the additional injection timing θ2 is advanced).

After calculating the ion residual timing correction amount θc, the routine proceeds to step 206, where the ion residual timing correction amount θc is added to the basic additional injection timing θbase to calculate the additional injection timing θ2. θ2 = θbase + θc

After calculating the additional injection amount Ti2 and the additional injection timing θ2 as described above, the routine returns to step 115 in FIG. 3, and the valve opening of the exhaust SCV 21 is calculated to obtain the exhaust SCV.
21 is controlled to the closing side (for example, fully closed). This allows
In the exhaust stroke, before the additional fuel starts burning, swirl is generated in the gas flow in the cylinder, and this swirl promotes atomization of the additional fuel and promotes mixing and stirring of the additional fuel and the in-cylinder gas. Is done.

Further, in the next step 116, the valve opening timing of the exhaust valve is calculated, and the valve opening timing is controlled to the advanced side (for example, the most advanced angle). As a result, the timing at which the combustion gas in the cylinder is discharged is advanced, and before the additional fuel starts burning, a part of the combustion gas in the cylinder starts flowing toward one exhaust port 19b, and the above-described exhaust SCV 21 The gas flow in the cylinder is effectively promoted in combination with the swirl generation effect by the above, and the atomization of the additional fuel is promoted, and the mixing and stirring of the additional fuel and the gas in the cylinder are promoted.

An example of the main fuel and additional fuel injection control performed by the idle control program described above will be described with reference to FIG. The ignition timing is set to a timing near the end of the compression stroke regardless of the combustion method. In homogeneous combustion,
As in Example 1, the main fuel is injected in the intake stroke to form a homogeneous mixture in the cylinder by the ignition timing. In the stratified combustion, as in Example 2, the main fuel is injected in the compression stroke. A stratified mixture is formed in which a portion near the spark plug 23 has a locally high mixture ratio. Example 3 is an example in which the injection of the main fuel is divided into two times, and the main fuel is injected once each in the intake stroke and the compression stroke. The main fuel injection may be performed three or more times.

On the other hand, as shown in Examples 4, 5, and 6, the additional fuel may be injected one or more times in the expansion stroke or the exhaust stroke after ignition. In addition, in the program of FIGS. 2 to 4, the injection of the additional fuel is performed only once in the expansion stroke or the exhaust stroke (Examples 4 and 5).

In the embodiment (1) described above, when the lean NOx catalyst 33 is not activated (that is, when the catalyst temperature is lower than the activation lower limit temperature α), additional fuel is added in the expansion stroke or the exhaust stroke after ignition. The fuel is injected and the additional fuel is post-combusted with the main combustion flame to raise the exhaust gas temperature and activate the lean NOx catalyst 33.

During the additional fuel injection control, the exhaust SCV 21 is controlled to the closed side, and while the gas flow in the cylinder is swirled during the exhaust stroke, the exhaust valve opening timing is advanced. By controlling the flow of a part of the combustion gas in the cylinder toward one exhaust port 19b, the gas flow in the cylinder can be effectively promoted before the additional fuel starts to be burned. The atomization of the additional fuel can be promoted by the gas flow, and the mixing and stirring of the additional fuel and the in-cylinder gas can be promoted. This makes it possible to raise the exhaust gas temperature without causing the injected additional fuel to completely combust and generate smoke, thereby achieving both smoke prevention and early catalyst activation.

In this embodiment (1), during the additional fuel injection control, the exhaust SCV 21 is controlled to be closed and the exhaust valve opening timing is controlled to be advanced. Only one of them may be performed. Even in this case, the gas flow in the cylinder can be promoted, and the combustibility of the additional fuel can be improved.

In this embodiment (1), the main injection amount,
Considering that the amount of additional fuel that can be completely combusted and the appropriate injection timing will change depending on the amount of residual oxygen in the cylinder gas and the ion remaining timing, the injection amount and injection timing of the additional fuel are determined by the main injection amount, Control is performed based on the amount of oxygen remaining in the cylinder gas and the timing of remaining ions, so that additional fuel can be injected at the right time with the right amount of injection, preventing fuel consumption deterioration and exhaust emission deterioration. While lean NOx
The catalyst 33 can be activated at an early stage.

Incidentally, the main injection amount is set according to the engine operating state such as the engine speed and the engine load.
If the main injection amount is reflected when calculating the injection amount and the injection timing of the additional fuel, the engine operation state such as the engine speed and the engine load can also be reflected indirectly. In addition, since the cooling water temperature (engine temperature) and the exhaust temperature also affect the combustibility of the additional fuel, these may be reflected in the injection amount and the injection timing of the additional fuel. However, in the present invention, one or both of the injection amount and the injection timing of the additional fuel may be set to a fixed value.

In the present embodiment (1), the exhaust SCV 21 is held in the fully open state except when additional fuel injection is performed. However, by controlling the opening of the exhaust SCV 21 during operation of the engine, In-cylinder exhaust residual amount (internal EGR amount)
May be controlled (this function corresponds to the residual exhaust gas amount control means in the claims). In this way, by controlling the opening of the exhaust SCV 21, internal EGR (internal exhaust gas recirculation) can be realized.
Exhaust gas purification performance can be improved by combining the GR and the lean NOx catalyst 33, and an external EGR device can be eliminated, leading to cost reduction.

[Embodiment (2)] By the way, lean NO
The x catalyst 33 stores NOx in the exhaust gas during the lean operation in which the oxygen concentration in the exhaust gas is high, and when the air-fuel ratio is switched to the rich or stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas decreases, The NOx stored so far is reduced and purified. Therefore, in order to maintain the NOx purification performance of the lean NOx catalyst 33, it is necessary to occasionally switch to the rich operation (or the stoichiometric operation) during the lean operation. However, when switching from the lean operation to the rich operation, if the injection amount of the main fuel is increased, a torque shock occurs and drivability is disadvantageously reduced.

Therefore, in the embodiment (2) of the present invention shown in FIG. 6, every time the lean operation time reaches a certain time,
The air-fuel ratio of the exhaust gas is increased or reduced by temporarily injecting additional fuel one or more times in an expansion stroke or an exhaust stroke after ignition and post-burning the additional fuel with a main combustion flame by ignition. Switching to the air-fuel ratio, the lean NOx catalyst 33
To reduce and purify the NOx stored in the tank.

Hereinafter, the processing contents of the program of FIG. 6 for executing the NOx reduction purification control will be described. This program is repeatedly executed at predetermined time intervals. When the present program is started, first, in step 101, it is determined whether or not the NOx reduction / purification control flag Fnox is “1” meaning “under execution of the NOx reduction / purification control”.
If “0”, that is, if the NOx reduction purification control is not being performed, the process proceeds to step 302, where it is determined whether the lean operation time has reached a certain time or not. It is determined that the NOx reduction purification of the catalyst 33 is unnecessary, and this program is ended without performing the subsequent processing.

Thereafter, when the lean operation time reaches a predetermined time, it is determined that the NOx reduction purification of the lean NOx catalyst 33 is necessary, and the routine proceeds to step 303, where the NOx reduction purification control flag Fnox is set to "NOx reduction purification control execution". It is set to "1" which means "medium", and one or more times of additional fuel is injected in the expansion stroke or the exhaust stroke after ignition, and the additional fuel is post-combusted with the main combustion flame by ignition to exhaust. The air-fuel ratio of the gas is switched to the rich or stoichiometric air-fuel ratio to reduce and purify the NOx stored in the lean NOx catalyst 33.

During execution of the NOx reduction / purification control, "Yes" is determined in step 301, and the routine proceeds to step 304, where it is determined whether or not the execution time of the NOx reduction / purification control has reached a predetermined time. If not, the process of ending this program is repeated. And NO
When the execution time of the x reduction purification control reaches a predetermined time,
The process proceeds from step 304 to step 305, where the NOx reduction / purification control flag Fnox is set to "0" meaning "no NOx reduction / purification control is performed", and the NOx reduction / purification control is terminated. Thus, every time the lean operation time reaches a certain time, the NOx reduction / purification control by the additional fuel injection is performed for a predetermined time.

During the execution of the additional fuel injection, the exhaust SCV 21 is controlled to the closed side as in the first embodiment (1).
A swirl is generated in the gas flow in the cylinder during the exhaust stroke, and / or the opening timing of the exhaust valve is controlled to the advanced side, so that a part of the combustion gas in the cylinder is discharged to one exhaust port 1.
9b to promote gas flow in the cylinder,
The combustibility of the additional fuel may be improved.

In the embodiment (2) described above, attention is paid to the point that the engine output of the additional fuel injected after the ignition does not change much even if it is burned.
When the NOx stored in the fuel cell 3 is reduced and purified, the operation is switched to the rich operation by the injection of the additional fuel, so that the operation can be switched from the lean operation to the rich operation without a torque shock, and the drivability is improved. be able to.

In this embodiment (2), every time the lean operation time reaches a certain time, NOx by additional fuel injection
The reduction purification control is executed. For example, a NOx concentration sensor is installed downstream of the lean NOx catalyst 33, and N2 in the exhaust gas flowing out of the lean NOx catalyst 33 is reduced.
The Ox concentration is detected by the NOx concentration sensor, and when the NOx concentration in the exhaust gas flowing out from the lean NOx catalyst 33 increases and exceeds the determination value, the NOx reduction / purification control by additional fuel injection is executed for a predetermined time. You may do it.

[Embodiment (3)] In general, an in-cylinder injection engine has features of low fuel consumption and high output, but in order to further increase output and save fuel, the in-cylinder injection engine is provided with an exhaust pressure. Attachment of a supercharger (turbocharger) driven by is considered. However, when the supercharger is mounted, the poor response of the supercharger itself impairs the good acceleration response characteristic of the direct injection engine.

Therefore, in the embodiment (3) of the present invention, a supercharger driven by exhaust pressure is mounted on the in-cylinder injection engine, and the program shown in FIG. 7 is executed every predetermined time or every predetermined crank angle. This ensures good acceleration response, a feature of the direct injection engine. In this program, first, in step 401, it is determined whether or not the vehicle is accelerating, for example, based on the amount of change in the accelerator opening. Unless the vehicle is accelerating, the exhaust pressure increase control by additional fuel injection is not performed. For example, the routine proceeds to step 402, where exhaust pressure increase control is performed by additional fuel injection. During this exhaust pressure increase control, the exhaust pressure is increased by injecting additional fuel one or more times in the expansion stroke or the exhaust stroke after ignition and post-combustion of the additional fuel by the flame of the main combustion by ignition. This improves the responsiveness of the turbocharger.

During the execution of the additional fuel injection, the exhaust SCV 21 is controlled to the closed side as in the first embodiment (1).
A swirl is generated in the gas flow in the cylinder during the exhaust stroke, and / or the opening timing of the exhaust valve is controlled to the advanced side, so that a part of the combustion gas in the cylinder is discharged to one exhaust port 1.
9b to promote gas flow in the cylinder,
The combustibility of the additional fuel may be improved.

In the above-described embodiment (3), during the acceleration, the exhaust pressure rise control is performed by the additional fuel injection, so that the supercharger can be used without deteriorating the acceleration response which is a great advantage of the in-cylinder injection engine. As a result, it is possible to further increase the output and reduce fuel consumption.

The above three embodiments (1) to (3)
(3) may be combined, or two embodiments may be combined.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an entire engine control system showing an embodiment (1) of the present invention.

FIG. 2 is a flowchart showing a flow of processing of an idle control program (part 1);

FIG. 3 is a flowchart showing a flow of processing of an idle control program (part 2);

FIG. 4 is a flowchart showing the flow of processing of an additional fuel injection amount / injection timing calculation program;

FIG. 5 is a time chart exemplarily showing ignition timing, main fuel injection, and timing of additional fuel injection;

FIG. 6 is a flowchart showing a processing flow of a NOx reduction purification control program used in the embodiment (2) of the present invention.

FIG. 7 is a flowchart showing a processing flow of an exhaust pressure rise control program used in the embodiment (3) of the present invention.

[Explanation of symbols]

11. In-cylinder injection engine (in-cylinder injection internal combustion engine), 1
2 ... intake pipe, 18a, 18b ... intake port, 19a, 1
9b ... exhaust port, 20 ... intake swirl control valve (intake SCV), 21 ... exhaust swirl control valve (exhaust SCV), 22 ... fuel injection valve, 23 ... spark plug, 26 ... water temperature sensor, 27 ... exhaust valve opening timing Change device, 30 ... exhaust pipe, 31 ... exhaust temperature sensor, 3
2. Oxygen sensor, 33: lean NOx catalyst, 34: catalyst temperature sensor, 36: ECU (additional fuel injection control means, gas flow promotion means, combustion mode switching means, exhaust residual amount control means, combustion state determination means).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 7/08 F01N 7/08 Z 3G301 F02B 37/00 302 F02B 37/00 302G F02D 9/04 F02D 9 / 04 AC 41/02 301 41/02 301F 41/34 41/34 E 43/00 301 43/00 301J 301T 45/00 368 45/00 368Z (72) Inventor: Kimitaka Saito 14 Iwatani, Shimowasukamachi, Nishio City, Aichi Prefecture. Address Japan Auto Parts Research Institute, Inc. (72) Inventor Shingo Morishima 14 Iwatani, Shimoba Kakucho, Nishio City, Aichi Prefecture Japan Auto Parts Research Institute, Inc. No. 1 F-term in Denso Corporation (reference) 3G004 AA01 BA06 DA03 DA24 DA25 3G005 DA01 EA04 EA16 FA04 GD02 HA05 HA09 JB01 JB02 3G065 AA03 AA04 AA06 AA07 AA10 CA12 CA13 CA14 DA04 DA15 EA02 EA03 GA05 GA08 GA09 GA10 GA17 GA41 HA02 HA21 HA22 KA02 KA12 3G084 AA04 BA13 BA15 BA24 CA02 CA03 CA04 DA02 DA10 DA11 FA23 FA19 FA23 AA02 AA10 AA11 AA12 AA17 AA24 AB06 BA03 BA32. HA16 HA19 JA02 JA04 JA24 KA05 KA07 KA12 LA00 LA01 LB04 MA11 MA19 MA26 NA08 NB02 ND01 NE11 NE13 NE14 NE15 NE19 PA01Z PA17Z PC00Z PD01Z PD03A PD11Z PD12Z PE01A PE01Z PE03Z PE04Z PE05Z PE08Z PE10Z

Claims (9)

[Claims] 1. An in-cylinder injection type internal combustion engine in which fuel is directly injected into a cylinder and an air-fuel mixture is ignited by an ignition plug, wherein an exhaust gas purification catalyst installed in an exhaust passage of the internal combustion engine; When the catalyst is not activated, one or more times of additional fuel is injected during the expansion stroke or the exhaust stroke after ignition, and the additional fuel is post-combusted with the main combustion flame by ignition to raise the exhaust gas temperature. Additional fuel injection control means for activating the catalyst, and gas flow promotion means for promoting gas flow in the cylinder during additional fuel injection control by the additional fuel injection control means to promote post-combustion of additional fuel. An internal combustion engine control device, comprising: 2. The gas flow promoting means includes an exhaust swirl control valve disposed in one of a plurality of exhaust ports provided in each cylinder, and additional fuel injection by the additional fuel injection control means. The internal combustion engine control device according to claim 1, wherein the exhaust swirl control valve is controlled to be closed during the control. 3. The internal combustion engine according to claim 1, wherein the gas flow promoting unit controls the opening timing of the exhaust valve to the advanced side during the additional fuel injection control by the additional fuel injection control unit. Engine control device. 4. The additional fuel injection control means determines whether one or both of the additional fuel injection amount and the injection timing is the main fuel injection amount to be injected before ignition, the engine speed, the engine load, the engine temperature, 4. The internal combustion engine control device according to claim 1, wherein the control is performed based on at least one of an exhaust temperature, an in-cylinder combustion state during an exhaust stroke, and an oxygen concentration in the exhaust gas. 5. An additional fuel injection control means, comprising: combustion state determination means for detecting ions generated by combustion in a cylinder through the spark plug, and determining a combustion state in the cylinder during an exhaust stroke based on the ion current. 5. The internal combustion engine according to claim 4, wherein one or both of the injection amount and the injection timing of the additional fuel are controlled based on the in-cylinder combustion state during the exhaust stroke determined by the combustion state determination means. Engine control device. 6. A combustion mode switching means for switching a combustion mode during idling between stratified combustion and homogeneous combustion based on at least one of an engine temperature, an exhaust gas temperature, and a catalyst temperature. An internal combustion engine control device according to any one of claims 1 to 5. 7. An internal combustion engine control system according to claim 2, further comprising: an exhaust residual amount control means for controlling an in-cylinder residual exhaust amount by controlling an opening degree of said exhaust swirl control valve. . 8. An in-cylinder injection type internal combustion engine in which fuel is directly injected into a cylinder and an air-fuel mixture is ignited by an ignition plug, wherein: a lean NOx catalyst installed in an exhaust passage of the internal combustion engine; When reducing and purifying NOx occluded in the combustion chamber, one or more additional fuels are injected in an expansion stroke or an exhaust stroke after ignition, and the additional fuel is post-combusted by a flame of main combustion by ignition. An internal combustion engine control device comprising: an additional fuel injection control unit that switches an air-fuel ratio of exhaust gas to a rich or stoichiometric air-fuel ratio. 9. A direct injection type internal combustion engine in which fuel is directly injected into a cylinder and an air-fuel mixture is ignited by an ignition plug, a supercharger driven by exhaust pressure, and a post-ignition expansion during acceleration. One or more additional fuels are injected in a stroke or an exhaust stroke, and the additional fuel is post-combusted by a flame of main combustion by ignition, thereby increasing exhaust pressure and improving responsiveness of the supercharger. An internal combustion engine control device comprising: a fuel injection control unit.