JP2002089340A - Exhaust emission control method of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent flameout at the time of discharging NOx from an NOx absorbent in a stratified combustion type internal combustion engine. SOLUTION: An air-fuel mixture is stratified in a state where an average air-fuel ratio is lean at the time of engine low load driving, and NOx generated at this time is absorbed by the NOx absorbent 26 arranged in an exhaust passage. The average air-fuel ratio is changed from lean to rich at the time of making the average air-fuel ratio rich to discharge NOx from the NOx absorbent 26, and a degree of stratification at this time is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art An inflowing exhaust gas has a lean air-fuel ratio.
NO when_x And reduce the air-fuel ratio of the inflowing exhaust gas.
NO absorbed when stoichiometric air-fuel ratio or rich_x Emit
NO _x Place the absorbent in the engine exhaust passage
The air-fuel ratio of the mixture supplied to the
NO emitted from Seki_x NO_x Absorbed by absorbent, NO
_x NO absorbed by the absorbent_x Release the engine
Internal combustion engine that makes the mixture supplied to the engine rich
Has already been proposed by the applicant (PCT International Publication).
WO93 / 07363).

[0003]

However, a stratified-combustion internal combustion engine in which an air-fuel mixture formed in a combustion chamber is stratified to form an ignitable air-fuel mixture in a limited area of a part of the combustion chamber. in some from lean average air-fuel ratio in the combustion chamber so as to release the NO _x from the NO _x absorbent and the combustion chamber simply increasing the fuel supply to switch to rich when is being performed such stratified effect There is a problem that the air-fuel mixture formed in the limited area becomes excessively rich, and as a result, the air-fuel mixture cannot be satisfactorily ignited by the spark plug, thereby causing misfiring.

Further, as in the above-described internal combustion engine, NO
problem shock occurs to when the air-fuel mixture simply supplied to the engine in order to release the NO _x from _x absorbent rich, the output torque of the engine increases rapidly also occur.

[0005]

According to the present invention, in order to solve the above-mentioned problems, when the air-fuel ratio of the inflowing exhaust gas is lean, NO _x is absorbed, and the air-fuel ratio of the inflowing exhaust gas is theoretically reduced. in the air-fuel ratio or an exhaust purifying method for an internal combustion engine arranged to _the NO _x absorbent in the engine exhaust passage that releases the absorbed NO _x to be a rich air-fuel mixture is burned in the average air-fuel ratio is lean state in the combustion chamber The lean mixture combustion operation region is predetermined, and when the operating state of the engine is in the lean mixture combustion operation region, the mixture formed in the combustion chamber is stratified to form a stratified mixture in a part of the combustion chamber. the NO _x generated at this time to form the ignitable air-fuel mixture is taken up in _the NO _x absorbent, to release the NO _x from the NO _x absorbent when the operating state of the engine is in lean mixture combustion operating region Should In the meantime, the average air-fuel ratio in the combustion chamber is temporarily reduced from lean to the stoichiometric air-fuel ratio or rich, and the degree of stratification of the air-fuel mixture formed in the combustion chamber is reduced. The stoichiometric air-fuel ratio is switched from rich to lean, and the degree of stratification of the air-fuel mixture formed in the combustion chamber is increased.

In the second invention, in the first invention,
Air-fuel mixture when the average air-fuel ratio in the combustion chamber so as to release the NO _x from the NO _x absorbent is switched from lean to the stoichiometric air-fuel ratio or rich is substantially homogeneous mixture.

[0007] In the third invention, in the first invention,
NO _x fuel supply timing from the absorbent average air-fuel ratio in the combustion chamber so as to release the NO _x from lean into the combustion chamber when it is switched to the stoichiometric air-fuel ratio or rich is advanced.

[0008] In the fourth invention, in the third invention,
The average air-fuel ratio in the combustion chamber so as to release the NO _x from the NO _x absorbent is varied during the intake stroke to supply timing of the fuel from the compression stroke when it is switched from lean to the stoichiometric air-fuel ratio or rich.

In a fifth aspect, in the third aspect,
Selectively to allow the fuel injection to the into the combustion chamber into the intake port, the mean air in the combustion chamber by the when releasing the NO _x from the NO _x absorbent is to increase the fuel injection quantity into the intake port The fuel ratio is switched from lean to stoichiometric or rich.

In the sixth invention, in the third invention,
Selectively fuel injection into the combustion chamber into the intake port and the so performed, it is determined that it should be released the NO _x from the NO _x absorbent when the actual fuel into the combustion chamber is supplied Sometimes, when the fuel injection timing into the combustion chamber is advanced and the fuel injection amount into the combustion chamber is increased, the average air-fuel ratio in the combustion chamber is switched from lean to the stoichiometric air-fuel ratio or rich, and fuel is supplied into the intake port. NO _x
When it is determined that NO _x should be released from the absorbent, the amount of fuel injected into the intake port is increased to switch the average air-fuel ratio in the combustion chamber from lean to stoichiometric or rich.

In a seventh aspect, in the first aspect,
The air-fuel mixture in the combustion chamber is in a strong stratified state according to the operating state of the engine, and a weak stratified state in which the degree of stratification is lower than in the forced stratified state,
Is switched to a substantially uniform state, NO from _the NO _x absorbent
When the state is switched from the strong stratification state to a substantially uniform state when _x is to be released, the state is switched to a substantially uniform state after passing through the weak stratification state.

In an eighth aspect, in the first aspect,
The air-fuel mixture in the combustion chamber is in a strong stratified state according to the operating state of the engine, and a weak stratified state in which the degree of stratification is lower than in the forced stratified state,
Is switched to a substantially uniform state, NO from _the NO _x absorbent
_{When x} is to be released, when it is switched from the strong stratified state to the almost uniform state, it can be switched to a substantially uniform state after passing through the weak stratified state according to the operating state of the engine, or directly from the strong stratified state to the almost uniform state. Either of the switching methods is used.

[0013]

1 to 18 show a first embodiment in which the present invention is applied to a direct injection type internal combustion engine. First, referring to FIGS. 1 to 10, the direct injection type internal combustion engine will be described. The basic operation of the internal combustion engine will be described.

Referring to FIGS. 1 to 5, reference numeral 1 denotes an engine body, 2 denotes a cylinder block, 3 denotes a piston which reciprocates in the cylinder block 2, 4 denotes a cylinder head fixed on the cylinder block 2, and 5 denotes a cylinder head. A combustion chamber formed between the piston 3 and the cylinder head 4, 6a is a first intake valve, 6b
Represents a second intake valve, 7a represents a first intake port, 7b represents a second intake port, 8 represents a pair of exhaust valves, and 9 represents a pair of exhaust ports. As shown in FIG. 3, the first intake port 7a is a helical intake port, and the second intake port 7b is a straight port extending substantially straight. Further, as shown in FIG. 3, an ignition plug 10 is disposed at the center of the inner wall surface of the cylinder head 4, and the first intake valve 6a and the second
A fuel injection valve 11 is arranged around the inner wall surface of the thin head 4 between the intake valves 6b. On the other hand, a cavity 3a is formed on the top surface of the piston 3, as shown in FIGS. The cavity 3a has a substantially circular contoured shallow plate portion 12 extending from below the fuel injection valve 11 to below the ignition plug 10, and a hemispherical deep plate portion formed at the center of the shallow plate portion 12. 13 In addition, ignition plug 1
A recess 14 having a substantially spherical shape is formed at a connection portion between the shallow plate portion 12 and the deep plate portion 13 below the zero.

As shown in FIGS. 1 to 3, a first intake port 7a and a second intake port 7b of each cylinder are respectively provided with a first intake passage 15a and a second intake passage 15b formed in each intake branch pipe 15. The intake control valve 17 is connected to the inside of the surge tank 16 through the second intake passage 15b. These intake control valves 17 are connected via a common shaft 18 to an actuator 19 composed of, for example, a step motor. The step motor 19 is controlled based on an output signal of the electronic control unit 30. The surge tank 16 is connected to the air cleaner 2 via the intake duct 20.
1, a throttle valve 23 driven by, for example, a step motor 22 is disposed in the intake duct 20. This step motor 22 is also used by the electronic control unit 30
Is controlled based on the output signal of

[0016] On the other hand, the exhaust port 9 of each cylinder is connected to an exhaust manifold 24, the casing 2 the exhaust manifold 24 with a built-in _the NO _x absorbent 26 via an exhaust pipe 25
7 is connected. Exhaust manifold 24 and surge tank 1
Reference numeral 6 denotes a recirculated exhaust gas (hereinafter referred to as EGR gas) passage 2
An EGR valve 29 that controls the amount of EGR gas is disposed in the EGR gas passage 28. The EGR valve 29 is controlled based on an output signal of the electronic control unit 30. When the EGR valve 29 is closed, only air is supplied into the combustion chamber 5 via the intake ports 7a and 7b, and when the EGR valve 29 is opened, air and EGR gas flow through the intake ports 7a and 7b. The fuel is supplied into the combustion chamber 5 via the fuel cell.

The electronic control unit 30 is composed of a digital computer, and is connected to a random access memory (RAM) 32 and a ROM via a bidirectional bus 31.
(Read only memory) 33, CPU (microprocessor) 34, input port 35 and output port 36. A load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 is provided to the accelerator pedal 40.
Is connected, and the output voltage of the load sensor 41 is
7 to the input port 35. The top dead center sensor 42 generates an output pulse when the first cylinder reaches the intake top dead center, for example, and this output pulse is input to the input port 35. The crank angle sensor 43 generates an output pulse every time the crankshaft rotates by, for example, 30 degrees, and the output pulse is input to the input port 35. In the CPU 34, the output pulse of the top dead center sensor 42 and the crank angle sensor 4
The current crank angle is calculated from the output pulse of No. 3 and the engine speed is calculated from the output pulse of the crank angle sensor 43. On the other hand, the output port 36 is connected to each fuel injection valve 11 and each step motor 19,
22.

In the embodiment shown in FIGS. 1 to 5, a fuel injection valve is provided.
11 from the swirl valve which injects while giving the swirling force to the fuel
3 and FIG.
The fuel is conically injected as indicated by F in FIG. FIG.
Is the fuel injection amount and fuel injection timing from the fuel injection valve 11
FIG. 7 shows the same fuel injection amount as in FIG.
The opening of the throttle valve 23, the opening of the EGR valve 29, and the fuel
The average air-fuel ratio A / F in the firing chamber 5 is shown. What
In FIGS. 6 and 7, L represents the accelerator pedal 40.
This shows the amount of depression. As can be seen from FIG.
When the depression amount L of the pedal 40 is L₁ Engine low load less than
During operation, the injection amount Q at the end of the compression stroke_Two Only fuel injection
Will be On the other hand, when the depression amount L of the accelerator pedal 40 is L₁ 
And L_Two During the intake stroke during engine middle load operation during
Q₁ Fuel injection is performed only at the end of the compression stroke._Two 
Only fuel is injected. That is, when the engine is operating at medium load,
Fuel injection is performed in two stages, the air stroke and the end of the compression stroke.
You. Further, the depression amount L of the alcel pedal 40 is L_Two Than
During high engine load operation, the injection amount Q during the intake stroke ₁ 
Only fuel is injected. In FIG. 6, θS1 and
And θE1 represent the fuel injection Q performed during the intake stroke.₁ Injection opening
The start timing and the injection completion timing are shown respectively, and θS2 and θE
2 is the fuel injection Q performed at the end of the compression stroke_Two At the start of injection
And the injection completion timing, respectively.

Meanwhile, the opening degree of the throttle valve 23 is so small engine low and medium during load operation than the amount of depression L of the accelerator pedal 40 is L ₂ as shown in FIG. 7 is quite small and the opening degree at this time the throttle valve 23 Is the accelerator pedal 40
Is smaller as the stepping amount L of is smaller. On the other hand, the amount of depression L of Aruserupedaru 40 becomes large when the opening of the throttle valve 23 than L ₂ is fully opened growing rapidly. Further, the opening degree of the EGR valve 29 for small engine low and medium during load operation than the amount of depression L of the accelerator pedal 40 is L ₂ is quite large, the amount of depression L of the accelerator pedal 40 is L ₂
When it becomes larger, the opening degree of the EGR valve 29 rapidly decreases and becomes fully open. The average air-fuel ratio in the combustion chamber 5 switching switched from lean at some point L ₀ of the high-load operation region (L> L ₂₎ rich. That is, in a range where the depression amount L of the accelerator pedal 40 is smaller than L ₀ , the average air-fuel ratio A / F
Becomes lean, and at this time, the average air-fuel ratio A / F becomes lean as the depression amount L of the accelerator pedal 40 decreases. On the other hand, the average air-fuel ratio A / F and the amount of depression L of the accelerator pedal 40 is larger than L ₀ is made rich.

FIG. 8 shows the relationship between the opening degree of the intake control valve 17 and the depression amount L of the accelerator pedal 40. Intake control valve 17 to the small engine low load operation than the amount of depression L is L ₁ of the accelerator pedal 40 as shown in FIG. 8 is held in the fully closed state, the amount of depression L of the accelerator pedal 40 is higher than L ₁ Also increases, the intake control valve 17 is opened as the depression amount L of the accelerator pedal 40 increases. When the intake control valve 17 is fully closed, the intake air flows into the combustion chamber 5 while swirling through the helical first intake port 7a. A strong swirling flow is generated as shown by. On the other hand, when the intake control valve 17 is opened, the intake air also flows into the combustion chamber 5 from the second intake port 7b.

Next, the combustion method will be described with reference to FIGS. FIG. 9 shows a combustion method at the time of engine low load operation, and FIG. 10 shows a combustion method at the time of engine medium load operation.

As shown in FIG. 6, the accelerator pedal 40
During the amount of depression L is smaller engine load operation than L ₁ fuel is injected into the end of the compression stroke. At this time, the injected fuel F collides with the peripheral wall surface of the deep dish portion 13 as shown in FIGS. 9 (A) and 9 (B). Injection quantity Q ₂ at this time increases as the amount of depression L of the accelerator pedal 40 becomes larger as shown in FIG. The fuel that has collided with the peripheral wall surface of the deep dish portion 13 is diffused while being vaporized by the swirling flow S, and as a result, as shown in FIG. Combustible mixture G
Is formed. At this time, the inside of the combustion chamber 5 other than the concave portion 14 and the deep dish portion 13 is filled with air and EGR gas. Next, the mixture G is ignited by the spark plug 10.

On the other hand, the amount of depression L of the accelerator pedal 40 is in the engine during the time of load operation is between L ₁ and L ₂ first fuel injection Q ₁ is performed during the intake stroke in FIG. 6, then the end of the compression stroke fuel injection Q ₂ of the second round is performed.
That is, first, as shown in FIG. 10A, fuel injection F is performed toward the inside of the cavity 3a at the beginning of the intake stroke, and a lean mixture is formed in the entire combustion chamber 5 by the injected fuel. Next, as shown in FIG. 10 (B), fuel injection F is performed toward the inside of the cavity 3a at the end of the compression stroke, and as shown in FIG. A combustible air-fuel mixture G serving as a fire is formed in the fuel cell. The combustible air-fuel mixture G is ignited by an ignition plug 10 and is ignited by the ignition flame.
The entire lean mixture is burned. In this case, since the fuel injected at the end of the compression stroke is sufficient to produce a spark, as shown in FIG. ₂ is kept constant. The beginning of the intake stroke of the fuel injection amount Q ₁ contrast increases as the amount of depression L of the accelerator pedal 40 increases.

The amount of depression L of the accelerator pedal 40 in FIG. 6 is the larger engine high load operation than L ₂ is only fuel injection once the beginning of the intake stroke, whereby combustion chamber 1
A homogeneous mixture is formed in 5. At this time, the fuel injection amount at the beginning of the intake stroke is determined by the accelerator pedal 4
It increases as the stepping amount L of 0 increases.

The basic combustion method of the direct injection internal combustion engine shown in FIG. 1 has been described above. Next, a method of purifying exhaust gas suitable for the in-cylinder injection internal combustion engine will be described.

Referring first to FIG. 11, FIG.
4 schematically shows the relationship between the concentration of typical components in the exhaust gas discharged from the combustion chamber 5 and the average air-fuel ratio A / F in the combustion chamber 5. As can be seen from FIG.
The concentration of unburned HC and CO in the exhaust gas discharged from the combustion chamber increases as the average air-fuel ratio A / F in the combustion chamber 5 becomes rich, and the oxygen O ₂ in the exhaust gas discharged from the combustion chamber 5 increases.
Increases as the average air-fuel ratio A / F in the combustion chamber 5 becomes leaner.

On the other hand, the _the NO _x absorbent 26, for example, alumina, which is housed in a casing 27 shown in FIG. 1 with a carrier, for example, potassium K on the carrier, sodium Na,
At least one selected from alkali metals such as lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt are carried. Have been. The ratio of the total amount of air supplied to the engine intake passage, the combustion chamber 5 and the exhaust passage upstream of the NO _x absorbent 26 to the total amount of fuel (hydrocarbon) is determined by the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 26. It referred the air-fuel ratio of the _the NO _x absorbent 26 is the inflow exhaust gas is absorbed NO _x when the lean performs absorbing and releasing action of the NO _x concentration of oxygen in the inflowing exhaust gas to release NO _x absorbed to decrease. The NO _x absorbent 2
6 When no fuel (hydrocarbon) or air is supplied into the exhaust passage upstream, the air-fuel ratio of the inflowing exhaust gas matches the average air-fuel ratio A / F in the combustion chamber 5, and in this case, NO _x absorption The agent 26 has an average air-fuel ratio A in the combustion chamber 5.
/ F absorbs NO _x when the lean, the oxygen concentration in the gas in the combustion chamber 5 will release the NO _x absorbed to decrease.

If the above-mentioned NO _x absorbent 26 is arranged in the engine exhaust passage, the NO _x absorbent 26 actually performs the NO _x absorbing and releasing action, but the detailed mechanism of this absorbing and releasing action is not clear. There is also. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking platinum Pt and barium Ba supported on a carrier as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.

That is, the average air-fuel ratio A /
F is lean, therefore the oxygen concentration in the inflowing exhaust gas when the inflow exhaust gas is lean is increased, these oxygen O ₂ as shown in FIG. 12 (A) this time is O ₂
^- or O ^2- shape is deposited on the surface of the platinum Pt. On the other hand, NO in the inflowing exhaust gas becomes O ₂ ^- or O ₂ on the surface of platinum Pt.
Reacts with ^2- to form NO ₂ (2NO + O ₂ → 2NO
₂ ). Next, a part of the generated NO ₂ is absorbed in the absorbent while being oxidized on the platinum Pt, and is combined with the barium oxide BaO to be absorbed in the form of nitrate ion NO ₃ ⁻ as shown in FIG. Diffuses into agent. Thus N
O _x is absorbed into the NO _x absorbent 26.

As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ⁻ Is generated. On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent. There are released from the absorbent in the form of NO _2. Namely, when the oxygen concentration in the inflowing exhaust gas is released NO _x from the NO _x absorbent 26 when lowered. As can be seen from FIG. 11, when the degree of lean of the inflowing exhaust gas decreases, the oxygen concentration in the inflowing exhaust gas decreases. Therefore, when the degree of leanness of the inflowing exhaust gas decreases, the air-fuel ratio of the inflowing exhaust gas becomes lean. even if _the NO _x absorbent 2
6 will release NO _x .

On the other hand, at this time, the average empty space in the combustion chamber 3
The fuel ratio A / F is made rich and the air-fuel ratio of the inflow exhaust gas is
As shown in FIG. 11, a large amount of
Unburned HC and CO are discharged, and these unburned HC and CO are white.
Oxygen O on gold Pt_Two ^- Or O ^2-Reacts with and oxidizes
It is. Also, when the air-fuel ratio of the inflowing exhaust gas becomes rich,
The oxygen concentration in the exhaust gas is extremely low,
From NO_Two Is released and this NO_Two Is shown in FIG.
And react with unburned HC and CO to reduce
You. In this way, NO on the surface of platinum Pt_Two Exists
When exhausted, NO from the absorbent one after another_Two Is released
You. Therefore, if the air-fuel ratio of the inflow exhaust gas is made rich,
NO in between_x NO from absorbent 26_x Is released
And

That is, the air-fuel ratio of the inflowing exhaust gas is made rich.
First, unburned HC and CO are converted to O on platinum Pt._Two ^- or
Is O^2-Immediately oxidized and then platinum
O on Pt_Two ^- Or O^2-Is consumed but unburned HC,
If CO remains, the unburned HC and CO make it an absorbent
NO released from_x And NO emitted from the engine _x 
Is reduced. Therefore, the air-fuel ratio of the inflow exhaust gas is reset.
NO in a short time_x Absorbed by absorbent 26
NO_x Is released, and the released NO
_x NO in the atmosphere due to reduction_x Is discharged
It can be blocked. NO_x Absorbent
26 has the function of a reduction catalyst, so that
NO even if the air-fuel ratio is stoichiometric_x Released from absorbent 26
NO_x Is reduced. However, inflow and exhaust
NO if the air-fuel ratio of the gas is the stoichiometric air-fuel ratio_x absorption
NO from agent 26_x Is released only gradually
_xTotal NO absorbed in absorbent 26_x To release
Takes a little longer.

As described above, the average empty space in the combustion chamber 5
NO when fuel ratio A / F is lean_x Is NO_x absorption
Is absorbed by the agent 26. However, NO_x Of absorbent 26
NO _x Absorption capacity is limited, NO_x N of absorbent 26
O_x NO if absorption capacity is saturated_x Absorbent 26 is no longer N
O_x Can not be absorbed. Therefore NO_x N of absorbent 26
O_x NO before absorption capacity is saturated_x NO from absorbent 26
_x Must be released, which requires NO_x Absorbent
26 how much NO_x Estimate if is absorbed
There is a need. Then, this NO_x How to estimate absorption
explain about.

The average air-fuel ratio A / F in the combustion chamber 5 is lean
In some cases, the higher the engine load, the more the engine per unit time
NO emitted from_x Per unit time to increase the volume
NO _x NO absorbed by the absorbent 26_x The amount increases,
The higher the engine speed, the higher the emissions from the engine per unit time.
NO_x NO per unit time due to increased amount_x absorption
Absorbed by agent 26_x Increase. Therefore the unit time
Hit NO_x NO absorbed by the absorbent 26_x Quantity is engine load
And the engine speed. In this case, the engine load
It can be represented by the amount of depression L of the cell pedal 40.
NO per unit time_x N absorbed by the absorbent 26
O_x The amount is the amount of depression L of the accelerator pedal 40 and the engine speed.
N. Therefore, in the embodiment shown in FIG.
Hit NO _x NO absorbed by the absorbent 26_x Access amount A
Function L of the pedal 40 and the engine speed N
This NO_x A is L and N
In advance in the form of a map shown in FIG.
It is stored in M33.

On the other hand, the average air-fuel ratio A /
F is but NO _x is released from the NO _x absorbent 26 becomes the stoichiometric air-fuel ratio or rich affected average air-fuel ratio _the NO _x releasing amount from the main exhaust gas amount of this time. Ie, N the amount of NO _x amount exhaust gas is discharged from the unit time per _the NO _x absorbent 26 as to increase is increased, the average air-fuel ratio is discharged from the higher per unit time _the NO _x absorbent 26 becomes rich
The O _x amount increases. In this case, the exhaust gas amount, that is, the intake air amount is determined by the depression amount L of the accelerator pedal 40 and the engine speed N.
The average air-fuel ratio A / F is also a function of the accelerator pedal 40
Is a function of the stepping amount L and the engine speed N. Thus _the amount of NO _x D released from per unit time _the NO _x absorbent 26 becomes a depression amount function of L and the engine rotational speed N of the accelerator pedal 40, FIG. 1 as a function of the amount of NO _x D is L and N
The information is stored in the ROM 33 in advance in the form of a map shown in FIG.

As described above, when the average air-fuel ratio A / F in the combustion chamber 5 is lean, the NO _x absorption amount per unit time is represented by A, and the average air-fuel ratio A / F in the combustion chamber 5 is represented by A.
When F is the stoichiometric air-fuel ratio or rich, N per unit time
O _x emissions is _the amount of NO _x ΣNOX is estimated to be absorbed in _the NO _x absorbent 26 so represented by D will be can be calculated using the following equation.

ΣNOX = ΣNOX + AD FIG. 13 shows this NO_x The amount of NOx and the flatness in the combustion chamber 5
The relationship with the air-fuel ratio A / F is shown. It can be seen from FIG.
As shown in FIG.₀ Lower than the inside of the combustion chamber 5
The average air-fuel ratio A / F at is lean,
Sometimes NO_xIs NO_x As it is absorbed by the absorbent 26,
NO as shown in 13_x The amount ΣNOX increases. one
On the other hand, as shown in FIG.₀ Higher than
Then, the average air-fuel ratio A / F in the combustion chamber 5 becomes rich.
NO to become_x NO from absorbent 26_x Is released.
Therefore, as shown by X in FIG.
L ₀ And the average air-fuel ratio A / F becomes rich
And NO_x The quantity ΣNOX decreases.

On the other hand, the average air-fuel ratio A / F is the average air-fuel ratio A / F in the continuous combustion chamber 5 as is lean and the amount of NO _x ΣNOX shown in FIG. 13 exceeds the allowable value MAX at Y Is forcibly made rich. When the average air-fuel ratio A / F is made rich, NO _x is rapidly released from the NO _x absorbent 26, and thus, as shown in FIG.
The amount of O _x ΣNOX decreases rapidly. Next, the amount of NO _x ΣN
When OX decreases to the lower limit value MIN, the average air-fuel ratio A / F is returned from rich to lean.

By the way, for example, as shown in FIG.
The air-fuel mixture formed in the combustion chamber 5 is stratified and
Can be ignited in a limited area of the part, that is, in the cavity 3a
If a mixture is formed, such stratification
NO when operation is being performed _x NO from absorbent 26_x To
Increase the average air-fuel ratio in the combustion chamber 5 from lean to rich to release
Simply increasing the injection amount in the compression stroke to switch to
In a partly limited area in the firing chamber 5, that is, the cavity 3a
The air-fuel mixture formed inside becomes too rich. The result
As a result, the air-fuel mixture in the cavity 3a can be improved by the ignition plug 10.
The problem of misfiring due to inability to ignite
Will happen.

Generally, when the average air-fuel ratio A / F in the combustion chamber 5 is switched from lean to rich, a shock occurs because the engine output torque sharply increases. However, such a shock causes the driver to feel uncomfortable, so that the occurrence of such a shock must be prevented. Therefore, in the embodiment according to the present invention, the combustible air-fuel mixture formed in the cavity 3a is prevented from becoming excessively rich, and the average air-fuel ratio A / F is switched from lean to rich so that the above-mentioned shock does not occur. Next, this will be described with reference to FIGS.

In FIG. 15, broken lines indicate the fuel injection amount Q, the opening of the throttle valve 23, and the average air-fuel ratio A / F in the combustion chamber 5 during the normal operation shown in FIG.
First the engine load L is explained when switching from lean to rich the average air-fuel ratio A / F in order to release the NO _x from the NO _x absorbent 26 at the time of low engine low load operation than L _1. During low engine load operation, the engine load L
Is less than or equal to a predetermined lower limit load L _min
X> MAX switching action from lean average air-fuel ratio A / F be turned (Fig. 13) to rich is not performed, the average air-fuel ratio if the .SIGMA.NOX> MAX when the engine load L is equal to or greater than the lower limit load L _min The A / F is switched from lean to rich. That is, as the engine load L is illustrated in L _min <L <16 becomes the .SIGMA.NOX> MAX when L ₁ NO
_{x The} emission flag is set, and the average air-fuel ratio A in the combustion chamber 5 is set.
/ F is switched from lean to rich. Referring to FIG. 15, at this time, the average air-fuel ratio A / F is switched from lean indicated by a broken line to rich indicated by a solid line.

[0042] Add the average air-fuel ratio A / F of the switching action for from lean to rich intake stroke injection Q ₁ in addition to the compression stroke injection Q ₂ as shown in FIGS. 15 and 16 at this time,
Normal normal operation indicated by the dashed line the sum of the compression stroke injection amount Q ₂ and the intake stroke injection amount Q ₁ while decreasing as compared to during operation which indicates the compression stroke injection amount Q ₂ as shown in FIG. 15 by dashed lines This is performed by increasing the injection amount. Therefore, in this case, usually the sum of the intake stroke injection amount Q ₁ divided by a broken line to the injection amount portions Qa in the boundary and the injection amount portion Qb and the compression stroke injection amount Q ₂ and the injection amount portions Qa is indicated by a broken line The injection amount Q becomes equal to the injection amount Q during the operation, and the injection amount portion Qb becomes an increase in the supplied fuel.

By the way in this case, the cavity 3 by a fuel by compression stroke injection Q ₂ and the fuel injection amount portions Qa
If an air-fuel mixture is formed in a and the fuel in the injection amount portion Qb is dispersed in a region other than the cavity 3a, the air-fuel ratio of the air-fuel mixture formed in the cavity 3a becomes the same as in the normal operation. That is, even if the total injection amount is increased, the cavity 3a
The air-fuel mixture formed therein does not become rich, and thus the air-fuel mixture formed in the cavity 3a is ignited by the ignition plug 10 without misfiring.

On the other hand, in this case, the fuel in the compression stroke injection Q ₂ and the fuel in the injection portion Qa are burned, and the injection amount portion Qa
If the fuel b is not burned, the amount of fuel to be burned becomes the same as the fuel amount during normal operation indicated by the broken line, so that the output torque of the engine does not change and the injection amount portion Qb
Is simply used to switch the average air-fuel ratio A / F from lean to rich. Therefore, in this embodiment of the present invention to form a combustible air-fuel mixture to be combusted by the fuel of the fuel and the injection amount portions Qa by the compression stroke injection Q _2, non combustible mixture by the fuel of which is the amount of increase in the supply amount of fuel injection portion Qb In addition to preventing the occurrence of misfire by forming air, the average air-fuel ratio A /
And so as to release the NO _x from the NO _x absorbent 26 is switched to F from lean to rich.

That is, when the intake stroke injection Q ₁ is performed, this injected fuel is dispersed throughout the combustion chamber 5, but the intake stroke injection amount Q ₁ is an amount that can form a lean mixture in which the flame cannot propagate. It is said. However combustible mixture G formed by the compression stroke injection Q ₂ a such lean mixtures
(See FIG. 9 (C)), it will burn if mixed.
In this case, the combustible gas mixture G formed by the compression stroke injection Q ₂ is an intake stroke injection amount Q ₁ to substantially the entire occupied in the combustion injection quantity portion Qa since almost all the occupied cavities 3a of the cavity 3a Once determined, the amount of fuel burned is the same as during normal operation. Therefore, even if the average air-fuel ratio A / F is switched from lean to rich, no misfire occurs and the output torque of the engine does not change. Become.

Next, this will be described using specific numerical values (not actual numerical values). For example, the average air-fuel ratio during normal operation is lean, and the air amount at this time is 17 (g). Assume that the fuel amount is 1 (g). The average air-fuel ratio A / F is formed by the compression stroke injection Q ₂ 55% of the combustible mixture in the cavity 3a when switched from lean to rich, 45% of the remaining intake stroke injection Q
_{If the} compression stroke injection quantity Q ₂ is 0.5
5 (g), and the injection amount portion Qa of the intake stroke injection amount Q ₁
Is 0.45 (g). On the other hand, if the volume of the cavity 3a is 65% of the total volume of the combustion chamber 5, the total intake stroke injection amount (Qa + Qb) is 0.45 (g) /0.65°.
0.7 (g). Thus the air-fuel ratio of the lean mixture formed by the intake stroke injection Q ₁ is 17 (g) /0.7
(G) It becomes $ 24.3 and becomes an incombustible mixture. on the other hand,
The average air-fuel ratio A / F in the combustion chamber 5 is 17 (g) /
[0.55 (g) +0.7 (g)] = 13.6,
Be rich. At this time, the fuel contained in the combustible mixture formed in the cavity 3a is 1 (g), which is the same as that in the normal operation.

By properly setting the intake stroke injection amount Q ₁ and the compression stroke injection amount Q ₂ in this manner, the air-fuel ratio of the air-fuel mixture formed in the cavity 3 a is not changed, and the amount of fuel that is combusted is changed. Therefore, the average air-fuel ratio A / F can be switched from lean to rich. Note that FIG.
The intake stroke injection amount Q ₁ (Qa + Qb) and the compression stroke injection amount Q _{2 shown} in FIG.
And in the form of a function of the engine speed N in the ROM 33 in advance.

[0048] Then the engine load L is described in the case where switching to rich average air-fuel ratio A / F in order to release the NO _x from the NO _x absorbent 26 when lower than larger L ₀ than L ₁ from the lean . At this time, the throttle valve 23 is closed by a predetermined opening as shown by the solid line in FIG. When the throttle valve 23 is closed, the amount of air supplied into the combustion chamber 5 decreases, so that the average air-fuel ratio A / F in the combustion chamber 5 decreases. At this time, the throttle valve 23 is closed so that the average air-fuel ratio A / F becomes a predetermined rich air-fuel ratio indicated by a solid line in FIG. And in the form of a function of the engine speed N in the ROM 33 in advance.

When the throttle valve 23 is closed, the pumping loss increases, and the output torque of the engine decreases. Therefore, in the embodiment according to the present invention, the intake stroke injection amount Q _{1 is set} so that the output torque of the engine does not decrease at this time.
Is increased by Qc (only the portion above the broken line in FIG. 15). Incidentally, increment Qc of the intake stroke injection Q ₁ is stored in advance in the ROM33 in the form of depression amount function of L and engine speed N of the accelerator pedal 40. Note that so as to increase the intake stroke injection amount Q ₁ without increasing the compression stroke injection amount Q ₂ At this time the compression stroke injection amount Q ₂ is has an optimal amount of fuel to form the flame source .

Next, a fuel injection control routine will be described with reference to FIGS. This routine is executed by interruption every predetermined time.

Referring to FIGS. 17 and 18, first,
NO in step 100_x Absorbed by the absorbent 26
NO estimated to be_x The amount ΣNOX is the allowable value MAX
It is determined whether it is greater than ΣNOX ≦ MAX
Proceeds to step 101 and proceeds to NO_x If the release flag is set
It is determined whether or not it has been turned on. Normally NO_x Release
Since the lag has been reset, the process proceeds to step 102.
In step 102, the amount of depression L of the accelerator pedal 40 is determined.
And stored in advance in the ROM 33 based on the engine speed N.
From the relationship shown in FIG.₁ And pressure
Reduction stroke injection amount Q _Two Is calculated, and then in step 103
Is the depression amount L of the accelerator pedal 40 and the engine speed N
6 previously stored in the ROM 33 based on the
The injection timing is calculated from the relationship, and then at step 104
Is the depression amount L of the accelerator pedal 40 and the engine speed N
FIG. 7 is stored in advance in the ROM 33 based on
The opening of the throttle valve 23 is calculated from the relationship.

Next, at step 105, the RO is determined in advance based on the depression amount L of the accelerator pedal 40 and the engine speed N.
The degree of opening of the EGR valve 29 is calculated from the relationship shown in FIG. 7 stored in M33, and then in step 106, the relationship shown in FIG. From this, the opening degree of the intake control valve 17 is calculated. Next, at step 107, it is determined whether or not the depression amount L of the accelerator pedal 40 is lower than L ₀ (FIG. 7). L <NO _x emissions A from the map shown in FIG. 14 (A) proceeds to step 108 when the L ₀ is calculated. Next, at step 109 NO _x emissions D
Is set to zero, and then the routine proceeds to step 112. On the other hand, NO _x emissions D is calculated from the map shown in FIG. 14 (B) proceeds to step 110 when it is judged that L ≧ L ₀ in step 107. Then step 111
In absorption of NO _x amount A is made zero, then step 112
Proceed to.

[0053] amount of NO _x ΣNOX is estimated to be absorbed in _the NO _x absorbent 26 in step 112 (= ΣNO
X + AD). Next, at step 113, it is determined whether or not ΣNOX has become negative, and ΣNOX <0
When it has reached, the routine proceeds to step 114, where ΣNOX is made zero. Next, at step 115, it is determined whether or not ΣNOX has become smaller than the lower limit value MIN.
If <MIN, proceed to step 116 and NO
_{The x} release flag is reset.

On the other hand, in step 100 ΣNOX>
_The NO _x releasing flag proceeds to step 117 when it is determined to have become the MAX is set. When the NO _x release flag is set, steps 101 to 11 are performed.
Proceeding to 8, it is determined whether the engine load L is lower than the lower limit load _Lmin . Step L when L <L _min
Proceed to. Therefore, at this time, even if ΔNOX> MAX, the average air-fuel ratio A / F in the combustion chamber 5 is maintained lean.

On the other hand, when L≥L _min , the routine proceeds to step 119, where the intake stroke injection is performed based on the depression amount L of the accelerator pedal 40 and the engine speed N from the relationship shown in FIG. The amount Q ₁ and the compression stroke injection amount Q ₂ are calculated.
The injection timing is calculated from the relationship stored in the ROM 33 in advance based on the equation (1). Next, in step 121, the injection timing is stored in the ROM 33 based on the depression amount L of the accelerator pedal 40 and the engine speed N as shown in FIG. The opening of the throttle valve 23 is calculated from the relationship.

Next, at step 122, the RO is determined in advance based on the depression amount L of the accelerator pedal 40 and the engine speed N.
The opening degree of the EGR valve 29 is calculated from the relationship stored in the M33, and then in step 123, based on the depression amount L of the accelerator pedal 40, the intake control valve is stored in the ROM 33 from the relationship shown in FIG. 17 is calculated. The average air-fuel ratio in the combustion chamber 5 at this time is made rich, NO _x is released from the NO _x absorbent 26.

[0057] Fuel only end of the compression stroke is the amount of depression L of the accelerator pedal 40 is small engine low load operation than L ₁ as described above is injected. At this time, an air-fuel mixture is formed only in the cavity 3a, and a region other than the cavity 3a is substantially filled with air and EGR gas, so that a stratified state having a very high stratification degree is obtained.

On the other hand, during the engine middle load operation in which the depression amount L of the accelerator pedal 40 is between L ₁ and L ₂ , a lean mixture is formed entirely in the combustion chamber 5 by the intake stroke injection,
A mixture richer than the lean mixture is formed in the cavity 3a by the compression stroke injection. Therefore, at this time, a weak stratification state is obtained in which the degree of stratification is lower than that in the strong stratification state at the time of engine low load operation.

When the engine is operated under a high load in which the depression amount L of the accelerator pedal 40 is larger than L _2, only the intake stroke injection is performed.

By the way, in the embodiments described so far, when the engine is under low load operation, that is, when NO
_When NO _x is to be released from the _x absorbent 26, the average air-fuel ratio A / F is switched from lean to rich without causing misfire and maintaining a strong stratified state so that the output torque does not fluctuate. .

[0061] switched to stratified charge state or homogeneous mixture state from the strong stratification state when it becomes necessary to release the NO _x from the NO _x absorbent 26 in the strongly stratified state in the following described embodiment the contrary, weak are from _the NO _x absorbent 26 and the average air-fuel ratio a / F to stoichiometric air-fuel ratio or rich so as to release the NO _x by increasing the intake stroke injection amount in the stratified state or homogeneous mixture state. If the average air-fuel ratio A / F is increased to the stoichiometric air-fuel ratio or rich by increasing the intake stroke injection amount in this way, the air-fuel ratio of the air-fuel mixture formed in the cavity 3a does not change much as compared with the time of strong stratification. Thus, occurrence of misfire can be prevented.

[0062] In the following described embodiment allowed to burn all the fuel injected in the combustion chamber 5 when the average air-fuel ratio A / F in order to release the NO _x from the NO _x absorbent 26 to the stoichiometric air-fuel ratio or rich has manner, therefore _the NO _x absorbent 26
The average air-fuel ratio A / F in order to release the NO _x output torque of the engine will increase when it is the stoichiometric air-fuel ratio or rich from. This increase in output torque is suppressed by reducing the amount of intake air supplied into the combustion chamber 5, and
If the output torque still increases, the output torque is prevented from increasing by, for example, retarding the ignition timing.

Next, a basic routine for controlling fuel injection will be described first with reference to FIGS. 19 and 20.

FIG. 19 shows a routine for controlling the NO _x release flag, and this routine is executed by interruption every predetermined time. _The amount of NO _x ΣNOX Figure, first, at step 120 and referring to FIG. 19 13
It is determined whether or not the maximum value MAX has been exceeded.
.SIGMA.NOX> NO _x releasing flag proceeds to step 121 when it is MAX is set.

FIG. 20 shows a routine for performing the injection control. This routine is executed, for example, by interruption every predetermined time.

Referring to FIG. 20, first, in step 1
_The NO _x releasing flag is whether it is set is determined at 30. Accelerator pedal 40 proceeds to step 131 when _the NO _x releasing flag is not set
ROM3 based on the stepping amount L and the engine speed N
Intake stroke injection amount from the relationship shown in FIG. 6, which is stored in a 3 Q ₁ and compression stroke injection amount Q ₂ are calculated. Next, at step 132, the injection timing is calculated from the relationship shown in FIG. 6 previously stored in the ROM 33 based on the depression amount L of the accelerator pedal 40 and the engine speed N, and then at step 133, the injection amount L of the accelerator pedal 40 is calculated. 7, the opening degree of the throttle valve 23 is calculated from the relationship shown in FIG.
ROM3 based on the stepping amount L and the engine speed N
3, the opening degree of the EGR valve 29 is calculated, and then in step 135, the accelerator pedal 40
The opening degree of the intake control valve 17 is calculated from the relationship shown in FIG.

Next, at step 136, it is determined whether or not the depression amount L of the accelerator pedal 40 is lower than L ₀ (FIG. 7). L <NO _x emissions A from the map shown in FIG. 14 (A) proceeds to step 137 when the L ₀ is calculated. Next, at step 138 NO _x emissions D is made zero, then the routine proceeds to step 141. Step 1
When it is determined at 36 that L ≧ L ₀ , the routine proceeds to step 139, where NO is determined from the map shown in FIG.
_{The x} release amount D is calculated. Next, at step 140, N
The O _x absorption amount A is set to zero, and then the routine proceeds to step 141. _The amount of NO _x .SIGMA.NOX which is estimated to be absorbed in _the NO _x absorbent 26 in step 141 (= ΣNOX + A-
D) is calculated. Next, at step 142 ΣNOX
Is determined to be negative, and if ΣNOX <0, the routine proceeds to step 143, where ΣNOX is made zero.

On the other hand, if it is determined in step 130 that the NO _x release flag has been set, then step 1
The amount of depression L of the accelerator pedal 40 proceeds to 44 whether smaller is determined than L _1. When L <the L ₁ is rich processing I for the average air-fuel ratio A / F rich proceeds to step 146 is performed. In contrast when the L ≧ L ₁ the amount of depression L of the accelerator pedal 40 proceeds to step 145 is determined whether or not smaller than L _2. L <L
_{In the case of 2,} the routine proceeds to step 147, where the average air-fuel ratio A / F
Is performed, and when L ≧ L ₂ , the routine proceeds to step 148, where a rich process III for enriching the average air-fuel ratio A / F is performed.

That is, the rich processing I is performed at the time of engine low load operation.
In other words, NO in a strongly stratified state_x From absorbent 26
NO_x Indicates a rich process for releasing
In the middle load operation of the engine,
NO in state_x NO from absorbent 26_x Release
Rich processing III shows that the engine height
NO during load operation, i.e., in a homogeneous mixture state
_x NO from absorbent 26 _x Processing to release
Is shown. Then, these rich processing I, II, II
I will be described in order.

FIG. 21 is a time chart of one embodiment of the rich processing I. As shown in FIG. 21 NO _x
In the engine low load operation state before the release flag is set, that is, in the strong stratification operation state, the intake stroke injection is not performed,
Only the compression stroke injection is performed and the average air-fuel ratio A in the combustion chamber 5 is increased.
/ F is lean. At this time, the throttle valve 23 and the EGR valve 29 are opened.

[0071] Then, when _the NO _x releasing flag so as to release the NO _x from the NO _x absorbent 26 is set EGR valve 29
Is completely closed. At this time, the average air-fuel ratio A in the combustion chamber 5 is
Throttle valve 23 so that / F does not become extremely lean.
Is also closed to the set opening determined by the operating state of the engine. When the throttle valve 23 is closed to the set opening, the compression stroke injection amount is slightly increased so that the engine output torque does not decrease.

Next, when the time t ₁ elapses after the NO _x release flag is set, the compression stroke injection is stopped, and the intake stroke injection is started. That is, the state is switched from the strong stratified state to the uniform mixture state. At this time, the injection amount does not change, and therefore the average air-fuel ratio A / F in the combustion chamber 5 does not change. In addition,
At this time, the fuel injection amount is small, and when such a small amount of fuel is burned in a homogeneous mixture state, the risk of misfiring increases if a large amount of EGR gas is supplied. Therefore, in this embodiment, as shown in FIG. 21, the EGR valve 29 is fully closed before shifting to the homogeneous mixture combustion.
In this case, the EGR valve 29 does not necessarily need to be fully closed, and it may be sufficient to reduce the opening of the EGR valve 29 to some extent.

Next, when the time t ₂ elapses after the NO _x release flag is set, the intake stroke injection amount is increased to enrich the average air-fuel ratio A / F in the combustion chamber 5, and the throttle valve 23 operates the engine. The valve is further closed to the set opening determined by the state. At this time, the throttle valve 23 is closed to reduce the amount of intake air supplied into the combustion chamber 5, to make the average air-fuel ratio A / F rich with as little fuel as possible, and to reduce the average air-fuel ratio A / F. This is to prevent the output torque of the engine from increasing as much as possible when is made rich. At this time, when the output torque of the engine increases and a shock occurs, the average air-fuel ratio A /
It is necessary to take measures such as delaying the ignition timing while making F rich.

If the average air-fuel ratio A / F is made rich, NO
_x NO from absorbent 26_x The release action is started. Next
NO_x NO from absorbent 26_x Complete the release action of
Then, it returns to the strong stratification state again through the reverse order. That is,
NO_x When the discharge operation of the intake is completed, the intake stroke injection amount decreases.
And the throttle valve 23 is opened.
You. Then NO_x T after the release action of₁ Time
If it exceeds, the intake stroke injection is stopped and the compression stroke injection starts.
And NO_x T after the release action of_Two Passing time
Then, the throttle valve 23 and the EGR valve 29 are opened.
NO _x The release flag is reset.

FIG. 22 shows a routine of the rich process I for executing the NO _x release control shown in FIG. Referring to FIG. 22, first, at step 150, N
It is determined whether or not the release completion flag indicating that the release of O _x has been completed is set. Immediately after the start of the rich process I, since the release completion flag is not set, the process proceeds to step 151, where a pre-process until the average air-fuel ratio A / F is made rich is performed. This pretreatment in the embodiment shown in FIG. 21, a process of closing the throttle valve 23 and EGR valve 29 when _the NO _x releasing flag when set, i.e. rich processing I is started, the rich processing The process includes a process of switching from the compression stroke injection to the intake stroke injection after a lapse of t ₁ from the start of I, and a process of closing the throttle valve 23 after a lapse of t ₂ from the start of the rich process I.

Next, at step 152, it is determined whether or not this preprocessing has been completed. When the pre-processing is completed, the routine proceeds to step 153, where rich processing for making the average air-fuel ratio A / F rich is performed. In this embodiment, the rich process is performed by increasing the intake stroke injection amount. Then _the NO _x releasing amount D 'in the _the NO _x releasing action at step 154 is calculated. This _the NO _x releasing amount D 'is stored in advance in the ROM33 in the form of a map as shown in FIG. 23 as a function of the depression amount L and the engine rotational speed N of the accelerator pedal 40. Next, at step 155, the NO _x amount ΣN
_The NO _x releasing amount D 'is subtracted from OX, then _the amount of NO _x ΣNOX step 156 whether it is smaller than the lower limit value MIN or not. .SIGMA.NOX <when it becomes MIN proceeds to step 157 it is determined that the releasing action of the NO _x has been completed, release completion flag is set. Next, the routine proceeds to step 158. Once the release completion flag is set, the process jumps from step 150 to step 158.

In step 158, post-processing is performed from the completion of the NO _x releasing action to the return to the strong stratification state. The post-processing in the embodiment shown in FIG. 21, NO _x
Processing release effect of reducing the intake stroke injection amount when completed, it switches the process for opening the throttle valve 23, the compression stroke injection from the intake stroke injection after t ₁ hour elapses after the releasing action of the NO _x has been completed When the throttle valve after t ₂ hours elapsed after _the NO _x releasing action is completed 23 and EGR
The process consists of opening the valve 29. In step 159 whether the post-processing is completed it is discriminated, when the post-processing is completed _the NO _x releasing flag and releasing completion flag is reset routine proceeds to step 160.

FIG. 24 shows another embodiment of the rich processing I performed in the strong stratification state. In this embodiment, N
When the _Ox release flag is set, the throttle valve 23 is slightly closed, and the EGR valve 29 is closed by about half. Then _the NO _x releasing flag t from setting
_{After one} hour, the compression stroke injection amount is decreased, and the intake stroke injection is started. That is, at this time, two injections of the intake stroke injection and the compression stroke injection are performed, and therefore, a weak stratification state is obtained. Next, when the time t ₂ elapses after the NO _x release flag is set, the compression stroke injection is stopped, and only the intake stroke injection is performed. At this time, the throttle valve 23 is slightly closed again.

Next, when the time t ₃ elapses after the NO _x release flag is set, the EGR valve 29 is fully closed and the throttle valve 23 is further slightly closed.
Furthermore the average air-fuel ratio A / F intake stroke injection amount this time is made to increase is made rich, NO _x absorbent 26 and thus
_The NO _x releasing action from begins.

On the other hand, when the NO _x releasing action is completed, the state returns to the strong stratified state in the reverse order. That is, when the NO _x releasing operation is completed, the intake stroke injection amount is reduced, and the throttle valve 23 and the EGR valve 29 are opened. Next, when the time t ₁ has elapsed after the completion of the NO _x releasing action, the intake stroke injection amount is reduced, the compression stroke injection is started, and a weak stratification state is set. At this time, the throttle valve 23 is further opened. Next, when the time t ₂ elapses from the completion of the NO _x releasing operation, the intake stroke injection is stopped, and a strong stratification state is established. Then, after the NO _x releasing operation is completed, t _3
The NO _x releasing flag is reset with the elapsed time has throttle valve 23 and EGR valve 29 is caused to further open.

[0081] In this embodiment is a homogeneous mixture state through a weakly stratified state from the strong stratification state when starting the releasing action of the NO _x, a stratified charge state from the homogeneous mixture state when the releasing action of the NO _x has been completed After that, it becomes a strong stratified state.
As described above, the mode of combustion gradually changes by interposing the weak stratification state when switching between the strong stratification state and the homogeneous mixture state, thereby preventing misfiring from occurring at the time of switching. .

FIG. 25 shows a routine of the rich process I for executing the NO _x release control shown in FIG. Referring to FIG. 25, first, at step 170, it is determined whether or not the release completion flag is set.
If the release completion flag is not set, step 17
Proceeding to step 1, jump to step 178 if the release completion flag is set. Pretreatment of step 171 in _the NO _x releasing flag from being set to an average air-fuel ratio A / F is made rich is performed. Then step 17
In step 2, it is determined whether or not the pre-processing has been completed. When the pre-processing has been completed, the routine proceeds to step 173, where the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount.

Next, at step 174, the NO in FIG.
_x release amount D 'is calculated, and then at step 175, N
O _x amount ΣNOX from _the NO _x releasing amount D 'is subtracted. Next, at step 176, the NO _x amount ΣNO _{x is} reduced to the lower limit value MI.
It is determined whether it has become smaller than N. ΣNOX <
Becomes the MIN release completion flag proceeds to step 177 is set, then the post-processing to return to strong stratified state from the discharge completion of step 178 NO _x is carried out. Then whether the post-processing step 179 is completed or not is judged, when the post-processing is completed _the NO _x releasing flag and releasing completion flag proceeds to step 180 is reset.

FIG. 26 and FIG. 27 show still another routine of the rich processing I. As described above, it is preferable to interpose a weakly stratified state between the strongly stratified state and the homogeneous mixture state without causing misfire. However, if the fuel injection amount is small and the stratified state is set, the lean mixture spread in the entire combustion chamber 5 becomes extremely lean, and there is a risk that these lean mixtures cannot be burned. Therefore, in this embodiment, when the fuel injection amount is small, the transition from the strong stratified state to the homogeneous mixture state is made to directly proceed from the strong stratified state to the homogeneous mixture state without passing through the weak stratified state. In FIG. 26, steps 191, 192, and 193 in a frame indicated by X indicate pre-processing, and steps 200, 201, and 202 indicated by Y indicate post-processing.

That is, referring to FIG. 26 and FIG.
First, at step 190, the release completion flag is set.
It is determined whether or not it has been turned on. Release complete flag is set
If not, proceed to step 191 of preprocessing X.
If the release completion flag is set, the post-processing Y
Jump to step 200. In step 191, the fuel
The injection amount Q is a predetermined set value Q₀ Is greater than
Is determined. Q> Q ₀ At step 192
Proceeding to the pretreatment shown in FIG.
Pre-processing to shift to a homogeneous mixture state through a stratified state is performed
It is. On the other hand, Q ≦ Q₀ At step 193
And proceed from the pretreatment shown in FIG.
Direct transition to homogeneous mixture without weak stratification
Preprocessing is performed.

Next, at step 194, it is determined whether or not the pre-processing is completed. When the pre-processing is completed, the routine proceeds to step 195, where the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. . Then step 1
'Is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 197' _the NO _x releasing amount D from 96 in FIG. 23 is subtracted. Next, at step 198, NO _x
It is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. Step 199 when ＜ NOX <MIN
, The release completion flag is set, and then the routine proceeds to step 200.

[0087] whether the step 200, the fuel injection amount Q is larger than the set value Q ₀ which is determined in advance is determined.
When Q> Q _0, the routine proceeds to step 201, where the post-processing shown in FIG. 24, that is, the post-processing for shifting from the homogeneous mixture state to the weak stratification state through the weak stratification state, is performed. On the other hand, when Q ≦ Q _0, the routine proceeds to step 202, where the post-processing shown in FIG. 21, that is, the post-processing for directly shifting from the homogeneous mixture state to the strong stratification state without passing through the weak stratification state, is performed. Next, at step 203, it is determined whether or not the post-processing has been completed.
_The NO _x releasing flag and releasing completion flag is reset proceeds to.

FIG. 28 shows still another embodiment of the rich processing I performed in the strong stratification state. When _the NO _x releasing flag is set in this embodiment the throttle valve 23
Is slightly closed, and the EGR valve 29 is fully closed. Then _the NO _x releasing flag is made to decrease the compression stroke injection amount and the elapsed t ₁ hour after being set, the intake stroke injection is started. That is, at this time, two injections of the intake stroke injection and the compression stroke injection are performed, and therefore, a weak stratification state is obtained. At this time, the throttle valve 23 is slightly closed. Next, when the time t ₂ elapses after the NO _x release flag is set, the compression stroke injection is stopped, and only the intake stroke injection is performed. At this time, the throttle valve 23 is slightly closed again.

Next, when the time t ₃ elapses after the NO _x release flag is set, the throttle valve 23 is further closed a little, and the intake stroke injection amount is increased, so that the average air-fuel ratio A / F is made rich. comb _the NO _x releasing action from _the NO _x absorbent 26 is started.

On the other hand, when the NO _x releasing operation is completed, the intake stroke injection amount is reduced. Next, when the time t ₄ has elapsed after the completion of the NO _x releasing operation, the intake stroke injection is stopped and a strong stratification state is established. At this time, the throttle valve 23 is opened. Next, when the time t ₅ has elapsed since the completion of the NO _x releasing operation, the throttle valve 23 and the EGR valve 2
9 is _the NO _x releasing flag is reset with is caused to open.

In this embodiment, when the release operation of NO _x is started, the state is changed from a strong stratification state to a uniform mixture state through a weak stratification state, and when the release operation of NO _x is completed, the homogeneous mixture state is changed to a weak stratification state. It is directly in a strong stratified state without passing through. Also in this embodiment, in the pre-processing when shifting from the strong stratification state to the homogeneous mixture state, it is determined whether or not the vehicle passes through the weak stratification state according to the fuel injection amount.

FIGS. 29 and 30 show the NO _x shown in FIG.
7 shows a routine of a rich process I for executing release control. Note that the inside of the frame indicated by X represents preprocessing. Referring to FIG. 29 and FIG. 30, first, at step 210, it is determined whether or not the release completion flag is set. If the release completion flag has not been set, the process proceeds to step 211 of preprocessing X, and if the release completion flag has been set, the process jumps to step 220. Whether step 211 the fuel injection amount Q is larger than the set value Q ₀ which is determined in advance is determined. Q> Q ₀
In the case of, the routine proceeds to step 212, where the pre-processing shown in FIG. 24, that is, the pre-processing for shifting from the strong stratification state to the uniform mixture state via the weak stratification state is performed. On the other hand, Q ≦ Q
_{If the value} is _0, the routine proceeds to step 213, where the pre-processing shown in FIG. 21, that is, the pre-processing for directly shifting from the strong stratification state to the homogeneous mixture state without passing through the weak stratification state, is performed.

Next, in step 214, the preprocessing is completed.
Is determined, and when the preprocessing is completed,
To step 215 to increase the intake stroke injection amount.
The average air-fuel ratio A / F is made rich. Then step 2
In FIG. 16, NO from FIG._x The release amount D 'is calculated,
NO in step 217_x From NOx to NO_x release
The quantity D 'is subtracted. Next, at step 218, NO_x 
It is determined whether the amount な っ NOX has become smaller than the lower limit value MIN.
Is determined. Step 219 when に な る NOX <MIN
To set the release complete flag, then step
NO at 220 _x From the completion of release to the state of strong stratification
Is performed. Next, in step 221, post-processing is performed.
Is completed or not, and when the post-processing is completed
Proceeds to step 222 and returns NO_x Emission flag and emission
The completion flag is reset.

FIGS. 31 and 32 show still another embodiment of the rich processing I performed in the strong stratified state.
Are to be injected into the combustion chamber 5 in the expansion stroke or exhaust stroke additional fuel to when releasing the NO _x from the NO _x absorbent 26 in this embodiment. FIG. 31 shows a case where the additional fuel is supplied to the expansion stroke or the compression stroke in this manner.
Is supplied from the fuel injection valve 11 in the section Z. During the expansion stroke and the exhaust stroke, the temperature of the burned gas in the combustion chamber 5 is considerably high, so that when additional fuel is injected into the burned gas, the hydrocarbons are broken down into small molecules and some hydrocarbons are converted into radicals. next, the fuel will have a strong reactivity against activated by NO _x and thus. Thus good NO _x is released from _the NO _x absorbent 26 release the NO _x will be satisfactorily reduced.
Incidentally, it is preferable to inject additional fuel when the temperature of the burned gas is high in enhancing responsiveness to NO _x,
Therefore, the additional fuel injection is preferably performed during the expansion stroke as shown in FIG.

Note that this additional fuel does not contribute to the generation of output even if burned, and therefore the output torque of the engine does not fluctuate by supplying the additional fuel.

In this embodiment, as shown in FIG.
O_x When the release flag is set, the throttle valve 23 closes.
The EGR valve 29 is fully closed. Next
NO_x T after the release flag is set₁ Passing time
Then, the compression stroke injection amount is maintained as it is, and additional fuel
Is injected during the expansion stroke and NO_x NO from absorbent 26 _x 
The release action of is started. At this time, the intake stroke injection
Is not done.

On the other hand, when the NO _x releasing action is completed, the state returns to the strong stratified state in the reverse order. That is, the additional fuel injection in the expansion stroke releasing action of the NO _x is completed is stopped, then with the throttle valve 23 and EGR valve 29 is made to open after a lapse of t ₁ hours after the releasing action of the NO _x is completed NO _x releasing flag is reset.

FIG. 33 shows a routine of the rich process I for executing the NO _x release control shown in FIG. Referring to FIG. 33, first, at step 230, it is determined whether or not the release completion flag is set.
If the release completion flag is not set, step 23
The process jumps to step 238 if the release completion flag is set. In step 231, preprocessing is performed from when the NO _x release flag is set to when additional fuel is supplied. Next, at step 232, it is determined whether or not the pre-processing has been completed. When the pre-processing has been completed, the routine proceeds to step 233, where additional fuel is supplied.

Next, at step 234, NO from FIG.
_x emission amount D 'is calculated, and then at step 236, N
O _x amount ΣNOX from _the NO _x releasing amount D 'is subtracted. Next, at step 236, the NO _x amount ΣNO _{x is} reduced to the lower limit value MI.
It is determined whether it has become smaller than N. ΣNOX <
Becomes the MIN release completion flag proceeds to step 237 is set, then the post-processing to return to strong stratified state from the discharge completion of step 238 NO _x is carried out. Then whether the post-processing step 239 is completed or not is judged, when the post-processing is completed _the NO _x releasing flag and releasing completion is reset routine proceeds to step 240.

FIG. 34 shows a time chart of one embodiment of the rich process II. As shown in FIG. 21 NO _x
During engine middle load operation before the release flag is set, two injections of an intake stroke injection and a compression stroke injection are performed. That is, at this time, the vehicle is in a weakly stratified state, and the average air-fuel ratio A / F in the combustion chamber 5 is lean. _The NO _x releasing flag average air-fuel ratio A in the combustion chamber 5 by intake stroke injection amount remains the stratified charge state when set is increased
/ F is made rich, releasing action of the NO _x from _the NO _x absorbent 26 is performed. When the NO _x releasing operation is completed, the intake stroke injection amount is reduced.

FIG. 35 shows a routine of the rich process II for executing the NO _x release control shown in FIG. Referring to FIG. 35, first, in step 250, the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. Then 'is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 252' _the NO _x releasing amount D from step 251 in FIG. 23 is subtracted. Then _the amount of NO _x ΣNOX step 253 whether it is smaller than the lower limit value MIN or not. ΣN
When OX <MIN, the routine proceeds to step 254, where the intake stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 255, the NO _x release flag is reset.

FIG. 36 shows another embodiment of the rich process II performed in the weakly stratified state. In this embodiment, N
When the _Ox release flag is set, the compression stroke injection is stopped, and the intake stroke injection amount is increased. That is, the average air-fuel ratio A / F in the combustion chamber 5 is switched to the homogeneous mixture state from semi-stratified charge state when _the NO _x releasing flag is set is made rich, NO _x emissions from _the NO _x absorbent 26 The action is started. When the NO _x releasing action is completed, the state is returned from the homogeneous mixture state to the weakly stratified state.

FIG. 37 shows a routine of the rich process II for executing the NO _x release control shown in FIG. Referring to FIG. 37, first, at step 260, the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. Then 'is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 262' _the NO _x releasing amount D from step 261 in FIG. 23 is subtracted. Then _the amount of NO _x ΣNOX step 263 whether it is smaller than the lower limit value MIN or not. ΣN
When OX <MIN, the routine proceeds to step 264, where the intake stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 265, the NO _x release flag is reset.

FIG. 38 shows still another embodiment of the rich process II performed in the weakly stratified state. Or to enrich in the weak stratified state in accordance with the fuel injection amount Q when in this embodiment should be released NO _x from the NO _x absorbent 26, or whether to enrichment is selected in a homogeneous mixture state. In the routine shown in FIG. 38, the frame indicated by Z indicates rich processing.

Referring to FIG. 38, first, step 2
Setpoint injection quantity Q is predetermined in 70 Q _i
It is determined whether or not it is greater than When Q> Qi, the routine proceeds to step 271, where the enrichment is performed by the uniform mixture state. That, NO _x releasing flag when set is the compression stroke injection as shown in Figure 36 is stopped, the intake stroke injection amount is increased. On the other hand, when Q ≦ Qi, the routine proceeds to step 272, where the enrichment is performed in the weakly stratified state. That is, when _the NO _x releasing flag is set the intake stroke injection amount while performing the compression stroke injection as shown in Figure 34 is increased.

Next, at step 273, NO from FIG.
_x discharge amount D 'is calculated, and then at step 274, N
O _x amount ΣNOX from _the NO _x releasing amount D 'is subtracted. Next, at step 275, the NO _x amount ΣNO _{x is} reduced to the lower limit value MI.
It is determined whether it has become smaller than N. ΣNOX <
When MIN is reached, the routine proceeds to step 276, where the intake stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 277, the NO _x release flag is reset.

FIG. 39 shows a time chart of one embodiment of the rich processing III. NO as shown in FIG.
_During high engine load operation before the _x release flag is set, only the intake stroke injection is performed and uniform mixture combustion is performed.When the NO _x release flag is set, the intake stroke injection amount is increased. The average air-fuel ratio A / F is made rich.

FIG. 40 shows a routine of the rich process III for executing the NO _x release control shown in FIG.
Referring to FIG. 40, first, at step 280, the average air-fuel ratio A / F is increased by increasing the intake stroke injection amount.
Is considered rich. Next, at step 281, the NO _x release amount D ′ is calculated from FIG.
In _the NO _x releasing amount D 'is subtracted from _the amount of NO _x .SIGMA.NOX. Then _the amount of NO _x ΣNOX step 283 whether it is smaller than the lower limit value MIN or not. ΣN
When OX <MIN, the routine proceeds to step 284, where the intake stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 285, the NO _x release flag is reset.

FIGS. 41 to 48 show still another embodiment. In this embodiment, as shown in FIG. 41, a fuel injection valve 50 for injecting fuel toward the second intake port 7b downstream of the intake control valve 17, that is, a so-called port injection valve 50 is provided. Fuel to be supplied into the combustion chamber 5 is supplied from the port injection valve 50. That is, in this embodiment, during normal operation, L> L ₁ as shown in FIG.
If engine low load operation is only the compression stroke injection Q ₂ is performed, from the port injection valve 50 in addition to the compression stroke injection Q ₂ if the engine during the time of load operation is L ₁ ≦ L ≦ L ₂ port injection Q ₁ is performed, only the port injection Q ₁ is performed if the engine high load operation is L> L _2.

Accordingly, in this embodiment, similarly to the above-described embodiments, a strong stratification state occurs when the engine is under a low load operation, a weak stratification state occurs when the engine is under a middle load operation, and a uniform mixture state occurs when the engine is under a high load operation. In this embodiment, the fuel injection control uses the injection control routine shown in FIG. 20, and the rich process I, the rich process II, and the rich process III shown in FIG. 20 will be sequentially described below.

FIG. 43 is a view showing the state of the lid performed in the strong stratified state.
H processing I. As shown in FIG.
NO during load operation_x The release flag is set
If not, only the compression stroke injection is being performed. Then
NO_x When the release flag is set, the compression stroke injection stops
Then, the intake stroke injection from the fuel injection valve 11 into the combustion chamber 5 is performed.
Done. Also, at this time, the port injection valve 50
No port injection is performed. Therefore, at this time, the fuel injection
The average in the combustion chamber 5 due to the intake stroke injection from the valve 11
A uniform air-fuel mixture with a rich air-fuel ratio A / F is formed,
NO _x NO from absorbent 26_x Release effect of
Done.

[0112] engine during low load operation not performed is port injection, the injected fuel immediately after the start of injection and start the port injection to perform the action of release of this time NO _x is deposited on the inner wall surface of the second intake port 7b Therefore, the average air-fuel ratio A / F does not immediately become rich. That is, a response delay occurs in the NO _x releasing action. Therefore, when NO _x is to be released from the NO _x absorbent 26 when port injection is not being performed, the average air-fuel ratio A / F is made rich by increasing the amount of fuel injected from the fuel injection valve 11. . Ports when the emit NO _x from the NO _x absorbent 26 when the since no causing the response delay by increasing the amount of port injection port injection is performed when it is this port injection respect is performed The average air-fuel ratio A / F is made rich by increasing the injection amount.

FIG. 44 is a block diagram showing the NO shown in FIG._x Release control
9 shows a routine of a rich process I for performing the process. Figure
Referring to FIG. 44, first, in step 290, the suction
By starting the air stroke injection, the average air-fuel ratio A / F is reset.
It is said that Next, at step 291, N
O_x The release amount D 'is calculated, and then in step 292
NO_x From NOx to NO_x The release amount D 'is subtracted.
Next, at step 293, NO_x The quantity ΣNOX is the lower limit M
It is determined whether it has become smaller than IN. ΣNOX
When <MIN, the routine proceeds to step 294, where the intake stroke injection is performed.
Is stopped, and the average air-fuel ratio A / F changes from rich to lean.
You. Next, at step 295, NO _x Release flag
Reset.

FIG. 45 shows a rich process II performed in a weakly stratified state. Before _the NO _x releasing flag is set in the engine during the time of load operation as shown in FIG. 45 is performed addition port injection in the compression stroke injection. N
O _x compression stroke injection and releasing flag is set is performed a continuation pulled, releasing action of the NO _x from the average air-fuel ratio A / F is made rich _the NO _x absorbent 26 by port injection amount is made to increase Is performed.

FIG. 46 shows the NO shown in FIG._x Release control
9 shows a routine of a rich process II for executing the process. Figure
Referring to FIG. 46, first, at step 300,
The average air-fuel ratio A / F is reduced by increasing the fuel injection amount.
It is said that Next, at step 301, N
O_x The release amount D 'is calculated, and then in step 302
NO_x From NOx to NO_x The release amount D 'is subtracted.
Next, at step 303, NO_x The quantity ΣNOX is the lower limit M
It is determined whether it has become smaller than IN. ΣNOX
If <MIN, the routine proceeds to step 304, where the port injection amount is set.
Is reduced, and the average air-fuel ratio A / F changes from rich to lean.
You. Next, at step 305, NO _x Release flag
Reset.

FIG. 47 shows a rich process III performed in a uniform mixture state. Before _the NO _x releasing flag at the time of engine high load operation as shown in FIG. 47 is set is only the port injection is performed, thus have been made homogeneous mixture fuel at this time. NO _x when releasing flag is set port injection amount is increased by an average air-fuel ratio A
/ F is made rich.

FIG. 48 shows a routine of a rich process III for executing the NO _x release control shown in FIG. 47.
Referring to FIG. 48, first, at step 310, the average air-fuel ratio A / F is made rich by increasing the port injection amount. Next, at step 311, the NO _x release amount D ′ is calculated from FIG. 23, and then at step 312, the NO _x amount ΣNOx is reduced by the NO _x release amount D ′. Then _the amount of NO _x ΣNOX step 313 whether it is smaller than the lower limit value MIN or not. ΣN
When OX <MIN, the routine proceeds to step 314, where the port injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 315, the NO _x release flag is reset.

FIGS. 49 to 56 show still another embodiment in which port injection is performed. Only the compression stroke injection Q ₂ is performed also at the time of normal operation of the time of engine low load in this embodiment, as shown in Figure 49. On the other hand, in this embodiment, if L ₁ <L <L _m during the engine middle load operation, the intake stroke injection Q ₁ and the compression stroke injection Q ₂ by the fuel injection valve 11 are performed, and L _m <L <L ₂ . If so, port injection from the port injection valve 50 is performed in addition to the injections Q ₁ and Q ₂ by the fuel injection valve 11. In addition, fuel is injected from both the fuel injection valve 11 and the port injection valve 50 during the engine high load operation.

FIG. 50 is a view showing a state in which the engine is operated at a low engine load.
H processing I. NO as shown in FIG._x 
When the release flag is set, the strong stratification continues
Additional fuel is injected during the expansion stroke.
NO_x NO from absorbent 26 _x Is released.

FIG. 51 shows a routine of the rich process I for executing the NO _x release control shown in FIG. Referring to FIG. 51, first, in step 320, the average air-fuel ratio A / F is made rich by injecting additional fuel during the expansion stroke. Then 'is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 322' _the NO _x releasing amount D from step 321 in FIG. 23 is subtracted. Next, at step 323 NO _x amount ΣNOX
Is smaller than the lower limit value MIN. If ΣNOX <MIN, the routine proceeds to step 324, where additional fuel injection is stopped, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 325, NO
_{The x} release flag is reset.

FIG. 52 shows an engine middle load operation in which L ₁ <L <L _m in FIG. In this case, NO _x
When the release flag is not set, the fuel injection valve 1
1 is in a weakly stratified state by the fuel injection from
O and _x releasing flag is set the additional fuel from _the NO _x absorbent 26 by injecting the expansion stroke NO _x is released. On the other hand, FIG. 53 shows L _m <L <in FIG.
L ₂ is a institution shows during load operation. in this case,
When the NO _x release flag is not set, the fuel is in a weakly stratified state by the fuel injected from the fuel injection valve 11 and the port injection valve 50. When the NO _x release flag is set, the port injection amount is increased.

FIG. 54 shows the NO _x shown in FIGS. 52 and 53.
7 shows a routine of a rich process II for selectively executing release control. In FIG. 54, a frame indicated by Z indicates a rich process. Whether the amount of depression L of the accelerator pedal 40, first, at step 330 that the reference is greater than the set value L _m (Fig. 49) is determined to FIG. 54. When L> L _m is the enrichment is carried out by increasing the port injection quantity as shown in FIG. 53 proceeds to step 331. On the other hand, L ≦ L _m
In the case of, the routine proceeds to step 332, where the enrichment is performed by injecting additional fuel during the expansion stroke as shown in FIG.

Next, at step 333, NO from FIG.
_x discharge amount D 'is calculated, and then at step 334, N
O _x amount ΣNOX from _the NO _x releasing amount D 'is subtracted. Next, at step 335 NO _x amount ΣNOX lower limit MI
It is determined whether it has become smaller than N. ΣNOX <
When MIN is reached, the routine proceeds to step 336, where the air-fuel ratio enrichment is stopped, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 337, the NO _x release flag is reset.

FIG. 55 shows the rich process III at the time of engine high load operation. As shown in FIG. 55 NO _x
Increase both fuel is injected and homogeneous mixture is burned from the NO _x releasing flag is set port injection amount of the fuel injection valve 11 and the port injection valve 50 before releasing flag is set By doing so, the average air-fuel ratio A / F is made rich.

FIG. 56 shows a routine of the rich process III for executing the NO _x release control shown in FIG.
Referring to FIG. 56, first, at step 340, the average air-fuel ratio A / F is made rich by increasing the port injection amount. Then 'is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 342' _the NO _x releasing amount D from step 341 in FIG. 23 is subtracted. Then _the amount of NO _x ΣNOX step 343 whether it is smaller than the lower limit value MIN or not. ΣN
When OX <MIN, the routine proceeds to step 344, where the port injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 345, the NO _x release flag is reset.

FIGS. 57 to 63 show another embodiment. In this embodiment, an automatic transmission 60 is mounted on the engine body 1, and the automatic transmission 60 detects a vehicle speed sensor 61 for detecting a vehicle speed and detects that the automatic transmission 60 is in a neutral position. Neutral position sensor 6
2 is attached. FIG. 58 shows a torque converter 63 of the automatic transmission 60.
A lock-up mechanism 64 is provided therein. That is, the torque converter 63 is connected to the engine crankshaft and the pump cover 65 that rotates with the crankshaft.
, A pump impeller 66 supported by a pump cover 65, a turbine runner 68 attached to an input shaft 67 of the automatic transmission 60, and a stator 69. Input shaft 67 via a turbine runner 68
Is transmitted to

On the other hand, the lock-up mechanism 64 is
And a lock-up clutch plate 69 movably mounted in the axial direction with respect to the input shaft 67 and rotated together with the input shaft 67. Normally, that is, at the time of lock-up off, the input shaft 6
Lock-up clutch plate 69 through an oil passage in
The pressurized oil is supplied to a room 70 between the pump cover 65 and the pressurized oil. Then, the pressurized oil flowing out of the room 70 is sent into a room 71 around the pump impeller 66 and the turbine runner 68 and then the input shaft 67. It is discharged through an oil passage inside. At this time, since the pressure difference between the chambers 70 and 71 on both sides of the lock-up clutch plate 69 hardly occurs, the lock-up clutch 64 is separated from the pump cover 65 as shown in FIG. The rotational force of the shaft is transmitted to the input shaft 67 via the pump cover 65, the pump impeller 66, and the turbine runner 68.

On the other hand, when the lock-up is to be turned on, pressurized oil is supplied into the room 71 through the oil passage in the input shaft 67, and the oil in the room 70 is discharged through the oil passage in the input shaft 67. Is done. At this time, the pressure in the room 71 becomes higher than the pressure in the room 70.
As shown in FIG. 8 (A), the lock-up clutch 69 is pressed against the pump cover 65, and the crankshaft and the input shaft 67 are directly connected to rotate at the same speed. Room 7
The oil supply control to the inside 0, 71, that is, the ON / OFF control of the lock-up mechanism 64, is controlled by a control valve provided in the automatic transmission 60, and this control valve is based on an output signal of the electronic control unit 30. Controlled.

Also in this embodiment, the fuel injection control is performed as shown in FIG.
The routine is performed according to the routine shown in FIG. 0, so that the engine is in a strong stratified state at the time of engine low load operation. By the way, when the output torque of the engine fluctuates, the lower the engine load, the larger the rate of fluctuation of the output torque. Therefore, when the output torque of the engine fluctuates, a shock is particularly likely to occur during low engine load operation. Become. Thus variation in the engine output torque when the output torque of the engine is varied when the average air-fuel ratio A / F in order to release the NO _x from the NO _x absorbent 26 to rich the most shock at the time of engine low load operation It will be easy to appear.

As shown in FIG. 58 (A), if the engine output torque fluctuates when the lock-up clutch 69 is turned on and is in the direct connection state, this fluctuation is transmitted directly to the automatic transmission 60, which is significant. Shock occurs. On the other hand, if the engine output torque fluctuates while the lock-up clutch 69 is off as shown in FIG. 58 (B), almost no shock No longer occurs. Therefore, from the viewpoint of occurrence of a shock, when the lock-up clutch 69 is off, the engine output torque may fluctuate. However, when the lock-up clutch 69 is on, it is preferable that the engine output torque does not fluctuate.

[0131] Therefore the average air-fuel ratio A so as to release the NO _x from the NO _x absorbent 26 at the time of engine low load operation in this embodiment
When the lock-up clutch 69 is turned off when the / F is made rich, as shown in FIG. 59, the state is shifted from the strong stratified state to the homogeneous mixture state, and the average air-fuel ratio A / F is made rich, and the lock-up is performed. If the clutch 69 is on, the average air-fuel ratio A / F is made rich by injecting additional fuel during the expansion stroke as shown in FIG. The control method shown in FIG. 59 is the same as the control method shown in FIG. 24 already described, and the control method shown in FIG. 60 is the same as the control method shown in FIG. 32 already described. A description of the control method shown in FIG. 60 will be omitted.

FIG. 61 shows a routine for controlling the NO _x release flag. This routine is executed by interruption every predetermined time.

Referring to FIG. 61, first, in step 3
NO at 50_x Presumed to be absorbed by absorbent 26
NO_x The amount ΣNOX is larger than the allowable value MAX
Is determined.と き に は When NOX> MAX
Proceed to step 351 and NO _x Release flag is set
You. Next, at step 352, the accelerator pedal 40 is depressed.
L is L₁ Smaller than the engine load,
It is determined whether or not the vehicle is turning. L <L₁ When step
Proceeding to 353, lock-up clutch 69 is on
Is determined. Lock-up clutch 69 is on
In the case of, the routine proceeds to step 354, where the flag X is set.
When the lock-up clutch 69 is off.
Proceeding to step 355, the flag X is reset.

FIGS. 62 and 63 show the rich processing I. FIG. In FIGS. 62 and 63, a frame indicated by X indicates pre-processing, and a frame indicated by Y indicates post-processing.

Referring to FIGS. 62 and 63, first, at step 360, it is determined whether or not the release completion flag is set. If the release completion flag has not been set, the process proceeds to step 361 of preprocessing X, and if the release completion flag has been set, step 3 of postprocessing Y
Jump to 70. In step 361, it is determined whether the flag X is set. When the flag X is set, the routine proceeds to step 362, where the pre-processing shown in FIG. 60, that is, the pre-processing for shifting to the expansion stroke injection, is performed. On the other hand, when the flag X is not set, the routine proceeds to step 363, where the pre-processing shown in FIG. 59, that is, the pre-processing for shifting from the strong stratified state to the weakly stratified state to the homogeneous mixture state is performed.

Next, at step 364, it is determined whether or not the pre-processing has been completed. When the pre-processing has been completed, the routine proceeds to step 365, where the average air-fuel ratio A is obtained by performing the expansion stroke injection or performing the intake stroke injection. / F is made rich. Next, at step 366, N
O _x release amount D 'is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 367' is subtracted.
Lower limit M Next, in step 368 NO _x amount ΣNOX has
It is determined whether it has become smaller than IN. ΣNOX
When <MIN, the routine proceeds to step 369, where the release completion flag is set, and then proceeds to step 370.

At step 370, it is determined whether or not the flag X is set. When the flag X is set, the routine proceeds to step 371, where the post-processing shown in FIG. 60, that is, the post-processing for shifting to the strong stratification state after the completion of the expansion stroke injection, is performed. On the other hand, when the flag X is not set, the routine proceeds to step 372, where the post-processing shown in FIG. 59, that is, the post-processing of shifting from the homogeneous mixture state to the weak stratification state via the weak stratification state is performed. Then whether the post-processing step 373 is completed or not is judged, when the post-processing is completed _the NO _x releasing flag and releasing completion flag proceeds to step 374 is reset.

FIGS. 64 to 66 show still another embodiment. In this embodiment as well, the fuel injection control is performed according to the routine shown in FIG. As described above, when the output torque of the engine fluctuates, the lower the engine load, the greater the output torque fluctuation rate. Thus variation in the engine output torque when the output torque of the engine is varied when the average air-fuel ratio A / F in order to release the NO _x from the NO _x absorbent 26 rich are the most shock when the engine is idling It will be easy to show.

When the engine is idling,
Automatic transmission 60 (FIG. 57)
Almost shock when in the neutral position
do not do. Therefore, in this embodiment, during engine idling operation
NO_x NO from absorbent 26 _x To release the average air-fuel ratio
When making the A / F rich, the starting transmission 60
If it is in the ral position, it is in a strong stratified state as shown in FIG.
The air-fuel ratio A / F to
If the automatic transmission 60 is not in the neutral position
Additional fuel is injected during the expansion stroke as shown in FIG.
To make the average air-fuel ratio A / F rich.
I have to.

FIG. 64 shows a control routine of the NO _x release flag, and this routine is executed by interruption every predetermined time.

Referring to FIG. 64, first, in step 3
NO at 80_x Presumed to be absorbed by absorbent 26
NO_x The amount ΣNOX is larger than the allowable value MAX
Is determined.と き に は When NOX> MAX
Proceed to step 381 and NO _x Release flag is set
You. Next, at step 382, the accelerator pedal 40 is depressed.
L is L₁ Smaller than the engine load,
It is determined whether or not the vehicle is turning. L <L₁ When step
Proceeding to 383, it is determined whether or not the engine is idling.
Is determined. When the engine is not idling,
Proceeding to step 586, the flag X is reset. this
When the engine is idling, the operation proceeds to step 384.
move on.

At step 384, it is determined whether or not the automatic transmission 60 is at the neutral position based on the output signal of the neutral position sensor 62 (FIG. 57). When the automatic transmission 60 is not in the neutral position,
The program proceeds to step 5 where the flag X is set. When the flag X is at the neutral position, the program proceeds to step 386 where the flag X is reset.

FIGS. 65 and 66 show the rich processing I. The routine shown in FIGS. 65 and 66 is the same as the routine shown in FIGS. 62 and 63.

That is, referring to FIGS. 65 and 66, first, at step 390, it is determined whether or not the release completion flag is set. If the release completion flag is not set, the process proceeds to step 391 of the pre-processing X, and if the release completion flag is set, the process jumps to step 400 of the post-processing Y. In step 391, it is determined whether or not the flag X is set. Flag X
If is set, the routine proceeds to step 392, where the pre-processing shown in FIG. 60, that is, the pre-processing for shifting to the expansion stroke injection, is performed. On the other hand, when the flag X is not set, the routine proceeds to step 393, where the pre-processing shown in FIG. 59, that is, the pre-processing for shifting from the strong stratification state to the homogeneous mixture state via the weak stratification state is performed.

Next, at step 394, it is determined whether or not the pre-processing has been completed. When the pre-processing has been completed, the routine proceeds to step 395, where the average air-fuel ratio A is obtained by performing the expansion stroke injection or by performing the intake stroke injection. / F is made rich. Next, at step 396, N
O _x release amount D 'is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 397' is subtracted.
Next, at step 398, the NO _x amount ΣNO _{x is} reduced to the lower limit M.
It is determined whether it has become smaller than IN. ΣNOX
When <MIN, the routine proceeds to step 399, where the release completion flag is set, and then proceeds to step 400.

At step 400, it is determined whether or not the flag X is set. When the flag X is set, the routine proceeds to step 401, where the post-processing shown in FIG. 60, that is, the post-processing for shifting to the strong stratification state after the completion of the expansion stroke injection, is performed. On the other hand, when the flag X is not set, the routine proceeds to step 402, where the post-processing shown in FIG. 59, that is, the post-processing for shifting from the homogeneous mixture state to the strong stratification state via the weak stratification state is performed. Then whether the post-processing step 403 is completed or not is judged, when the post-processing is completed _the NO _x releasing flag and releasing completion flag proceeds to step 404 is reset.

FIG. 67 is a time chart of the NO _x release control similar to FIG. ΣNO _x> MA in the embodiment described so far, as shown by Y ₁ in FIG. 67
And the average air-fuel ratio A / F in order to release the NO _x from the NO _x absorbent 26 to be rich when it is X.
In this case, in any engine operating state, ΣNO _x >
It is not known whether it will be MAX and, therefore, it is not known in what engine operating state the average air-fuel ratio A / F is made rich.

When the engine is operating under a high load, the fuel injection amount is large. Therefore, in order to make the average air-fuel ratio A / F rich at this time, a large amount of fuel to be increased is required. On the other hand, during low engine load operation, the fuel injection amount is small, so that the average air-fuel ratio A / F can be made rich only by increasing the small amount of fuel. Thus the fuel quantity to be increased, which is needed for _the NO _x releasing from _the NO _x absorbent 26 becomes small amounts smaller the lower the engine load, thus to to improve the fuel consumption at the time of engine low load operation NO from NO _x absorbent 26
It would be preferable to have an _x release action.

[0149] Therefore the allowable value MAX with respect to _the amount of NO _x ΣNOX as The rest described embodiment shown in FIG. 67
And setting the intermediate decision value MID is an intermediate value between the lower limit value MIN, NO _x amount ΣNOX has not yet reached the allowable value MAX engine low load operation when exceeds the intermediate decision value MID is performed so that to perform _the NO _x releasing action from _the NO _x absorbent 26 as sometimes shown in FIG. 67 in Y _2. Thus _the NO _x releasing action from _the NO _x absorbent 26 in which the engine low load operation the chance increases that take place, will be able to thus to reduce the fuel consumption.

FIG. 68 shows an embodiment in which the intermediate judgment value MID is used. In this embodiment, a routine shown in FIG. 20 is used for controlling the fuel injection.

Referring to FIG. 68, first, in step 4
Whether _the amount of NO _x ΣNOX has exceeded the allowable value MAX is determined at 10. .SIGMA.NOX> becomes MAX When _the NO _x releasing flag proceeds to step 413 is set. Thus the average air-fuel ratio A / F by the routine shown in FIG. 20 in this case is made rich, N from _the NO _x absorbent 26
_Ox releasing action is performed. On the other hand, when it is determined in step 410 that ΣNOX ≦ MAX, the routine proceeds to step 411, where the NO _x amount ΣNOX is set to the intermediate determination value MID.
It is determined whether or not it is greater than At this time ΣNOX>
If it is MID, the process proceeds to step 412.

At step 412, the vehicle speed sensor 61 (FIG. 5)
It is determined whether or not the vehicle is stopped based on the output signal of 7). At this time, if the vehicle is stopped, step 41
_The NO _x releasing flag proceeds to 3 is set, the average air-fuel ratio A / F by the routine shown in FIG. 20 is made rich by thus. Normal and idling is performed, is _the NO _x releasing action from _the NO _x absorbent 26 at this time is so that it is possible to reduce the fuel consumption takes place when the vehicle is stopped.

FIG. 69 shows another embodiment using the intermediate judgment value MID. In this embodiment, the routine shown in FIG. 20 is used for controlling the fuel injection.

Referring to FIG. 69, first, in step 4
_The amount of NO _x ΣNOX at 20 whether exceeds the allowable value MAX or not. .SIGMA.NOX> becomes MAX When _the NO _x releasing flag proceeds to step 424 is set. Thus the average air-fuel ratio A / F by the routine shown in FIG. 20 in this case is made rich, N from _the NO _x absorbent 26
_Ox releasing action is performed. On the other hand, NO _x amount .SIGMA.NOX intermediate decision value MID proceeds to step 421 when it is judged that .SIGMA.NOX ≦ MAX in step 420
It is determined whether or not it is greater than At this time ΣNOX>
If it is MID, the process proceeds to step 422.

In Step 422, the vehicle speed sensor 61 (FIG. 5)
It is determined whether or not the vehicle is stopped based on the output signal of 7). At this time, if the vehicle is stopped, step 42
Proceeding to 3, it is determined whether or not the automatic transmission 60 is at the neutral position based on the output signal of the neutral position sensor 62 (FIG. 57). Automatic transmission 60 at this time is _the NO _x releasing flag proceeds to step 423, if the neutral position is set, the average air-fuel ratio A / F by the routine shown in FIG. 20 is made rich by thus. Vehicle is normally idling is performed when it is stopped, since _the NO _x releasing action from _the NO _x absorbent 26 is performed at this time it is possible to reduce fuel consumption. Further, in this embodiment, when the automatic transmission 60 is in the neutral position, the average air-fuel ratio A / F is made rich, so that it is possible to prevent the occurrence of a shock.

FIG. 70 shows still another embodiment using the intermediate judgment value MID. In this embodiment, the routine shown in FIG. 20 is used for controlling the fuel injection.

Referring to FIG. 70, first, in step 4
Whether _the amount of NO _x ΣNOX has exceeded the allowable value MAX is determined at 30. .SIGMA.NOX> becomes MAX When _the NO _x releasing flag proceeds to step 434 is set. Thus the average air-fuel ratio A / F by the routine shown in FIG. 20 in this case is made rich, N from _the NO _x absorbent 26
_Ox releasing action is performed. On the other hand, if it is determined in step 430 that ΣNOX ≦ MAX, the routine proceeds to step 431, where the NO _x amount ΣNOX is set to the intermediate determination value MID.
It is determined whether or not it is greater than At this time ΣNOX>
If it is MID, the process proceeds to step 432.

In step 432, it is determined from the output signal of the load sensor 41 and the engine speed whether or not the vehicle is in a deceleration operation. At this time, if deceleration operation is being performed, step 433
Then, it is determined whether or not the lock-up clutch 69 (FIG. 58) is off. Lockup clutch 69 is in the off _the NO _x releasing flag proceeds to step 434 is set, the average air-fuel ratio A / F by the routine shown in FIG. 20 is made rich by thus. During vehicle deceleration small amount of fuel injection, since _the NO _x releasing action from _the NO _x absorbent 26 at this time is carried out it is possible to reduce fuel consumption. In this embodiment, when the lock-up clutch 69 is off, the average air-fuel ratio A / F is made rich, so that it is possible to prevent the occurrence of a shock.

FIG. 71 shows still another embodiment using the intermediate judgment value MID. In this embodiment, the routine shown in FIG. 20 is used for controlling the fuel injection.

Referring to FIG. 71, first, in step 4
Whether _the amount of NO _x ΣNOX has exceeded the allowable value MAX is determined at 40. .SIGMA.NOX> becomes MAX When _the NO _x releasing flag proceeds to step 445 is set. Thus the average air-fuel ratio A / F by the routine shown in FIG. 20 in this case is made rich, N from _the NO _x absorbent 26
_Ox releasing action is performed. On the other hand, if it is determined in step 440 that ΣNOX ≦ MAX, the routine proceeds to step 441, where the NO _x amount ΣNOX is set to the intermediate determination value MID.
It is determined whether or not it is greater than At this time ΣNOX>
If it is MID, the process proceeds to step 442.

In step 442, it is determined from the output signal of the load sensor 41 and the engine speed whether or not the vehicle is in a deceleration operation. At this time, if a deceleration operation is being performed, step 443
Then, it is determined whether or not the lock-up clutch 69 (FIG. 58) is off. When the lockup clutch 69 is off, the routine proceeds to step 444, where the engine speed NE
Is lower than a predetermined set rotational speed NE ₀ . At this time, if NE <NE ₀ , step 4
Is willing _the NO _x releasing flag 45 is set, the average air-fuel ratio A / F by the routine shown in FIG. 20 is made rich by thus. Less fuel injection amount at the time of vehicle deceleration, moreover the fuel injection amount is further reduced when the NE <NE _0. Since _the NO _x releasing action from _the NO _x absorbent 26 is carried out when this way is extremely small amount of fuel injection in this embodiment it is possible to reduce the fuel consumption. In this embodiment, when the lock-up clutch 69 is off, the average air-fuel ratio A / F is made rich, so that it is possible to prevent the occurrence of a shock.

FIG. 72 shows still another embodiment using the intermediate judgment value MID. In this embodiment, the routine shown in FIG. 20 is used for controlling the fuel injection.

Referring to FIG. 72, first, in step 4
Whether _the amount of NO _x ΣNOX has exceeded the allowable value MAX is determined at 50. .SIGMA.NOX> becomes MAX When _the NO _x releasing flag proceeds to step 453 is set. Thus the average air-fuel ratio A / F by the routine shown in FIG. 20 in this case is made rich, N from _the NO _x absorbent 26
_Ox releasing action is performed. On the other hand, NO _x amount .SIGMA.NOX intermediate decision value MID proceeds to step 451 when it is judged that .SIGMA.NOX ≦ MAX in step 450
It is determined whether or not it is greater than At this time ΣNOX>
If it is MID, the process proceeds to step 452.

At step 452, based on the output signal of the load sensor 41 and the engine speed, it is determined whether or not the fuel injection has been stopped and the lockup clutch 69 has been turned on so that the engine braking operation is performed. Is determined. A deceleration operation by the fuel injection has been stopped and the lock-up clutch 69 is in the on set is _the NO _x releasing flag proceeds to step 453, the average air-fuel ratio A / F by the routine shown in FIG. 20 and thus Is considered rich. When the vehicle is decelerated, the amount of intake air is small. Therefore, at this time, the average air-fuel ratio A / F can be made rich only by injecting a small amount of fuel. Thus, in this embodiment, only a small amount of fuel is injected and N
Since the NO _x releasing action from the O _x absorbent 26 is performed, the fuel consumption can be reduced.

FIGS. 73 to 77 show still another embodiment using the intermediate judgment value MID. In this embodiment, ΣNOX>
When the MID is reached, the MID flag is set, and as shown in FIG. 73, when the MID flag is set, the operating state of the engine changes from the medium-load operation in the weak stratification state to the low-load operation to be in the strong stratification state. Sometimes, the weak stratification state is continued for a while, and during this time, the intake stroke injection amount is increased to make the average air-fuel ratio A / F rich. Then NO _x
The average air-fuel ratio A / F after the release effect is completed of the NO _x from the absorbent 26 is made to shift to strong stratified state from semi-stratified charge state with switched from rich to lean.

That is, in this embodiment, when the operation state in which the weak stratification state is set and the operation state in which the strong stratification state is to be changed when the MID flag is set, the transition from the weak stratification state to the strong stratification state is performed. delayed, and so as to meantime perform releasing action of the NO _x from _the NO _x absorbent 26. Thus, also in this embodiment, when the engine load is reduced, the average air-fuel ratio A / F is made rich, so that the fuel consumption can be reduced. When the average air-fuel ratio A / F is made to be rich after the engine load becomes low and the engine shifts from the weak stratification state to the strong stratification state, the engine is returned from the strong stratification state to the weak stratification state again. The average air-fuel ratio A / F is made rich. Therefore, since the stratification state is frequently changed, combustion becomes unstable, and there is a risk that torque fluctuations may occur. Therefore, in this embodiment, when the engine load is reduced, the N
Performs action of releasing O _x, so that to change the stratified state after releasing action of the NO _x has been completed.

On the other hand, in this embodiment, as shown in FIG. 74, even if the MID flag is set during low engine load operation, the average air-fuel ratio A / F is not enriched at this time, and
The average air-fuel ratio A / F is made rich immediately in the weak stratification state when the engine load shifts from low load operation to medium load operation after the ID flag is set.
In this case also stratified state is prevented from be frequently switched, and releasing action of the NO _x is performed when a relatively low engine load.

FIG. 75 shows a routine for controlling the flag. This routine is executed by interruption every predetermined time.

Referring to FIG. 75, first, in step 4
_The amount of NO _x ΣNOX at 60 whether becomes larger than the allowable value MAX or not. If ΣNOX ≦ MAX, the routine jumps to step 462, where ΣNOX> MAX
To become the _the NO _x releasing flag proceeds to step 461 proceeds to step 462 after being set. Step 462
In _the amount of NO _x .SIGMA.NOX whether becomes greater than the intermediate setting value MID is determined, when it becomes .SIGMA.NOX> MID MID flag is set the routine proceeds to step 463.

FIGS. 76 and 77 show a fuel injection control routine, which is executed, for example, by interruption every predetermined time.

[0171] _the NO _x releasing flag, first, at step 470 and referring to FIGS. 76 and 77 whether has been set or not. _The NO _x releasing flag whether when not set is set execution flag proceeds to step 471 is determined. This execution flag is set when the MID flag is set and the engine load changes from a medium-high load to a low load, or when the engine load changes from a low load to a medium-high load. If the execution flag has not been set, the routine proceeds to step 472, where it is determined whether the MID flag has been set. If the MID flag has not been set, the process proceeds to step 475.

In step 475, the ROM 33 is previously determined based on the depression amount L of the accelerator pedal 40 and the engine speed N.
Intake stroke injection amount Q ₁ and compression stroke injection amount Q ₂ is calculated from the relationship shown in FIG. 6 stored within. Next, at step 476, the injection timing is calculated from the relationship shown in FIG. 6 previously stored in the ROM 33 based on the depression amount L of the accelerator pedal 40 and the engine speed N, and then at step 477, the depression amount L of the accelerator pedal 40 is calculated. The opening of the throttle valve 23 is calculated from the relationship shown in FIG. 7 stored in the ROM 33 in advance based on the engine speed N and the engine speed N. Next, at step 478, the opening degree of the accelerator pedal 40 and the engine speed N are calculated. And ROM33 in advance
The opening degree of the EGR valve 29 is calculated from the relationship stored in the ECU 33. Next, in step 479, based on the depression amount L of the accelerator pedal 40, the intake control valve 17 is stored in the ROM 33 from the relationship shown in FIG. Is calculated.

Next, at step 480, it is determined whether or not the depression amount L of the accelerator pedal 40 is lower than L ₀ (FIG. 7). L <NO _x emissions A from the map shown in FIG. 14 (A) proceeds to step 481 when the L ₀ is calculated. Next, at step 482 NO _x emissions D is made zero, then the routine proceeds to step 485. Step 4
If it is determined in step 80 that L ≧ L ₀ , the process proceeds to step 483 to determine NO from the map shown in FIG.
_{The x} release amount D is calculated. Next, at step 484, N
The O _x absorption amount A is set to zero, and the process proceeds to step 485. _The amount of NO _x .SIGMA.NOX which is estimated to be absorbed in the step 485 in _the NO _x absorbent 26 (= ΣNOX + A-
D) is calculated. Next, at step 486, ΣNOX
Is determined to be negative, and if ΣNOX <0, the routine proceeds to step 487, where ΣNOX is made zero.

On the other hand, if it is determined in step 472 that the MID flag has been set, step 4
Proceed to 73 whether the amount of depression L of the accelerator pedal 40 becomes L ₁ or less, that the engine load is whether changes to the low load from the medium and high load is determined. If L <L ₁ has not been changed, the routine proceeds to step 474, where the accelerator pedal 4
0 of whether the amount of depression L becomes L ₁ or more, i.e., the engine load is whether changes in medium and high load from a low load is determined. Unless when changed to L> L ₁ step 475
Proceed to.

On the other hand, after the MID flag is set, at step 473, the depression amount L of the accelerator pedal 40 is
There becomes L ₁ or less, that the engine load is set execution flag proceeds to step 488 when it is determined to have changed to the low load from the medium and high load, then the routine proceeds to step 489. Note that once the execution flag is set, the process jumps from 471 to step 489. In step 489, a weak stratification state in which the intake stroke injection and the compression stroke injection are performed is performed. As shown in FIG. 73, in this weak stratification state, the average air-fuel ratio A /
F is made rich.

Next, at step 490, NO from FIG.
_x release amount D 'is calculated, and then at step 491, N
O _x amount ΣNOX from _the NO _x releasing amount D 'is subtracted. Next, at step 492, the NO _x amount ΣNO _{x is} reduced to the lower limit value MI.
It is determined whether it has become smaller than N. ΣNOX <
When MIN is reached, the routine proceeds to step 493, where the MID flag and the execution flag are reset. When these flags are reset, the state is shifted to the normal strong stratification state.

On the other hand, after the MID flag is set, in step 474, the depression amount L of the accelerator pedal 40 is set.
There has become L ₁ or more, i.e., the engine load is when it is determined to have changed to the medium and high load from low load is set execution flag proceeds to step 488, then the routine proceeds to step 489. In step 489, if the engine is in the middle-load operation, as shown in FIG. 74, a weak stratification state in which the intake stroke injection and the compression stroke injection are performed is performed. In this weak stratification state, the intake stroke injection amount is increased. Average air-fuel ratio A
/ F is made rich. On the other hand, at this time, in the case of high load operation, the average air-fuel ratio A / F is made rich in the uniform mixture state.

Then, the flow advances to step 492 via steps 489, 490 and 491, and if ΣNOX <MIN, the flow advances to step 493 to reset the MID flag and the execution flag. When these flags are reset, the state is returned to the normal weak stratified state or the homogeneous mixture state.

On the other hand, if it is determined in step 470 that the NO _x release flag has been set, then step 4
The amount of depression L of the accelerator pedal 40 proceeds to 94 whether smaller is determined than L _1. When L <the L ₁ is rich processing I for the average air-fuel ratio A / F rich proceeds to step 496 is performed. In contrast when the L ≧ L ₁ the amount of depression L of the accelerator pedal 40 proceeds to step 495 is determined whether or not smaller than L _2. L <L
_{In the case of 2,} the routine proceeds to step 497, where the average air-fuel ratio A / F
Is performed, and when L ≧ L ₂ , the routine proceeds to step 498, where a rich process III for enriching the average air-fuel ratio A / F is performed.

FIGS. 78 to 81 show still another embodiment. In this embodiment, as shown in FIGS. 78 and 79, an air injection valve 80 is disposed at the center of the inner wall surface of the cylinder head 4 on the side of the ignition plug 10. The average air-fuel ratio A / F in order to release the NO _x from the NO _x absorbent 26 is the air in the combustion chamber 5 around the spark plug 10 as indicated by J from this air injection valve 80 when it is rich It is injected. FIG.
In the embodiment shown in FIGS. 8 and 79, the air injection from the air injection valve 80 is performed at the end of the compression stroke.

When the air is injected around the ignition plug 10 in this manner, the oxygen concentration in the air-fuel mixture around the ignition plug 10 increases, and thus, even if an over-enriched air-fuel mixture is formed around the ignition plug 10 Even if it is performed, good ignition can be ensured without misfiring.

[0182] Figure 80 shows an example of _the NO _x releasing control at the time of engine low load operation in the case of using such an air injection valve 80. Before _the NO _x releasing flag in this example as shown in FIG. 80 is set are performed only the compression stroke injection, also _the NO _x releasing flag is set only compression stroke injection is performed. However, when the NO _x release flag is set, the compression injection amount is increased and the air injection from the air injection valve 80 is performed. At this time, the average air-fuel ratio A / F becomes rich due to the increase in the compression injection amount, but an air-fuel mixture having an optimum air-fuel ratio is formed around the ignition plug 10 by the air injected from the air injection valve 80.

FIG. 81 shows a rich process I for executing the NO _x release control shown in FIG. In this embodiment, the fuel injection control routine shown in FIG.
The routine shown at 0 is used. Referring to FIG. 81, first, at step 500, a process of opening the air injection valve 80 at the end of the compression stroke is performed. Next, at step 501, the average air-fuel ratio A / F is made rich by increasing the compression stroke injection amount. Next, step 502
In _the NO _x releasing amount D 'is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 503' from Figure 23 is subtracted. Then _the amount of NO _x ΣNOX step 504 whether it is smaller than the lower limit value MIN or not. If ΣNOX <MIN, the routine proceeds to step 505, where the compression stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 506, the air injection valve 80 is kept closed. Next, at step 507, the NO _x release flag is reset.

FIGS. 82 and 83 show the rich processing in the case where the intake control valve 17 (FIG. 3) is controlled. In the embodiment shown in FIGS. 1 to 5, the intake control valve 17 is closed at the time of engine low load operation, and at this time, a swirling flow S (FIG. 3) is generated in the combustion chamber 5. The fuel injected during the compression stroke is collected in a predetermined limited area by the swirling flow, and the fuel collected in the limited area is ignited by the spark plug 10.

As described above, it may be necessary to generate a swirl flow in order to create a strong stratified state in which good ignition can be obtained at the time of low engine load operation. The swirling flow does not need to be particularly generated. Therefore, in the embodiment shown in FIG. 82, the average air-fuel ratio A /
When F is made rich, the intake control valve 17 is opened. That is, as shown in FIG. 82 showing the rich process at the time of engine low load operation, NO _x
Before the release flag is set, only the compression stroke injection is performed, and at this time, the intake control valve 17 is closed. On the other hand, when the NO _x release flag is set, the compression stroke injection is stopped, and the intake stroke injection is started. At this time, the intake control valve 17 is opened. This _the NO _x releasing action from the average air-fuel ratio A / F is formed a uniform mixture is richer _the NO _x absorbent 26 is performed when.

FIG. 83 shows a rich process I for executing the NO _x release control shown in FIG. In this embodiment, the fuel injection control routine shown in FIG.
The routine shown at 0 is used. Referring to FIG. 83, first, at step 510, the intake control valve 17 is fully opened. Next, at step 511, the compression stroke injection is stopped, and the intake stroke injection is started, whereby the average air-fuel ratio A / F is made rich. Then 'is calculated, and then _the NO _x releasing amount D from _the amount of NO _x ΣNOX step 513' _the NO _x releasing amount D from step 512 in FIG. 23 is subtracted. Next, at step 514 NO _x amount ΣNOX
Is smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 515, where the intake stroke injection is stopped and the compression stroke injection is started, so that the average air-fuel ratio A / F changes from rich to lean. Next, at step 516, the intake control valve 17 is fully closed. Next, at step 517, the NO _x release flag is reset.

FIG. 84 shows an internal combustion engine having no fuel injection valve in the combustion chamber 5 and having the fuel injection valve 11 mounted on the intake branch pipe 15, and the present invention relates to such an internal combustion engine. It can also be applied to institutions. In such a so-called port injection type internal combustion engine, the air-fuel mixture is conventionally stratified by various methods, and the present invention is applied to all internal combustion engines in which the air-fuel mixture is stratified during low engine load operation. can do. For example, in internal combustion engines, which stratified at the time of engine low load operation is an average air fuel ratio or the degree of stratification is weakened when switched from lean to rich, or homogeneous mixture for _the NO _x releasing.

[0188] In addition or weaken the swirl flow when switched to rich average air-fuel ratio from lean to for _the NO _x releasing the internal combustion engine so as to stratify by generating a swirling flow in the combustion chamber 5, or turning By stopping the generation of the flow, the degree of stratification is reduced, or a uniform mixture is obtained.

[0189]

Effect of the Invention can be prevented from misfiring in an internal combustion engine of stratified charge combustion from _the NO _x absorbent when increasing the fuel supply in order to release the NO _x occurs.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine showing a cross section of an engine body.

FIG. 2 is a plan view schematically showing the entire internal combustion engine shown in FIG.

FIG. 3 is a plan sectional view of a cylinder head.

FIG. 4 is a plan view of a piston top surface.

FIG. 5 is a side sectional view of FIG. 3;

FIG. 6 is a diagram showing a fuel injection amount and a fuel injection timing.

FIG. 7 is a diagram showing a fuel injection amount, a throttle opening, an EGR valve opening, and an average air-fuel ratio in a combustion chamber.

FIG. 8 is a diagram showing an opening degree of an intake control valve.

FIG. 9 is a diagram for explaining a combustion method during low-load operation.

FIG. 10 is a diagram for explaining a combustion method during a medium load operation.

FIG. 11 is a diagram showing the concentrations of CO, HC, and O ₂ in exhaust gas.

FIG. 12 is a view for explaining the NO _x absorbing / releasing action of the NO _x absorbent.

FIG. 13 is a time chart of NO _x release control.

FIG. 14 is a diagram showing a map of an NO _x absorption amount and a NO _x release amount.

FIG. 15 is a diagram showing a fuel injection amount, a throttle valve opening, and an average air-fuel ratio in a combustion chamber.

FIG. 16 is a time chart showing NO _x release control.

FIG. 17 is a flowchart for performing injection control.

FIG. 18 is a flowchart for performing injection control.

FIG. 19 is a flowchart for controlling a NO _x release flag.

FIG. 20 is a flowchart for performing injection control.

FIG. 21 is a time chart showing NO _x release control for performing a rich process I.

FIG. 22 is a flowchart for performing a rich process I.

FIG. 23 is a view showing a map of an NO _x release amount.

FIG. 24 is a time chart of _the NO _x releasing control showing another embodiment for carrying out the rich processing I.

FIG. 25 is a flowchart showing another embodiment for performing the rich process I.

FIG. 26 is a flowchart showing still another embodiment for performing the rich process I.

FIG. 27 is a flowchart showing still another embodiment for performing the rich process I.

Figure 28 is a further timing chart of _the NO _x releasing control showing another embodiment for carrying out the rich processing I.

FIG. 29 is a flowchart showing yet another embodiment for performing the rich process I.

FIG. 30 is a flowchart showing still another embodiment for performing a rich process.

FIG. 31 is a diagram showing additional fuel injection.

32 is a further timing chart of _the NO _x releasing control showing another embodiment for carrying out the rich processing I.

FIG. 33 is a flowchart showing still another embodiment for performing the rich process I.

FIG. 34 is a time chart showing NO _x release control for performing rich processing II.

FIG. 35 is a flowchart for performing a rich process II.

FIG. 36 is a time chart of NO _x release control showing another embodiment for performing the rich process II.

FIG. 37 is a flowchart showing another embodiment for performing the rich process II.

FIG. 38 is a flowchart showing still another embodiment for performing the rich process II.

39 is a further timing chart of _the NO _x releasing control showing another embodiment for carrying out the rich processing III.

FIG. 40 is a flowchart showing still another embodiment for performing the rich process III.

FIG. 41 is a sectional plan view of a cylinder head showing another embodiment.

FIG. 42 is a diagram showing a fuel injection amount.

FIG. 43 is a time chart showing NO _x release control for performing rich processing I.

FIG. 44 is a flowchart for performing a rich process I.

FIG. 45 is a time chart showing NO _x release control for performing rich processing II.

FIG. 46 is a flowchart for performing a rich process II.

FIG. 47 is a time chart showing NO _x release control for performing a rich process III.

FIG. 48 is a flowchart for performing a rich process III.

FIG. 49 is a diagram showing a fuel injection amount.

FIG. 50 is a time chart showing NO _x release control for performing rich processing I.

FIG. 51 is a flowchart for performing a rich process I;

FIG. 52 is a time chart showing NO _x release control for performing rich processing II.

FIG. 53 is a time chart showing NO _x release control for performing a rich process II.

FIG. 54 is a flowchart for performing a rich process II.

FIG. 55 is a time chart showing NO _x release control for performing a rich process III.

FIG. 56 is a flowchart for performing a rich process III.

FIG. 57 is an overall view of an internal combustion engine showing another embodiment.

FIG. 58 is a side view schematically showing a torque converter.

FIG. 59 is a time chart showing NO _x release control for performing rich processing I.

FIG. 60 is a time chart showing NO _x release control for performing rich processing I.

FIG. 61 is a flowchart for controlling a NO _x release flag.

FIG. 62 is a flowchart for performing a rich process I;

FIG. 63 is a flowchart for performing a rich process I;

FIG. 64 is a flowchart for controlling a NO _x release flag.

FIG. 65 is a flowchart showing still another embodiment for performing the rich process I.

FIG. 66 is a flowchart showing still another embodiment for performing the rich process I.

FIG. 67 is a time chart of NO _x release control.

FIG. 68 is a flowchart for controlling a NO _x release flag.

FIG. 69 is a flowchart showing another embodiment for controlling the NO _x release flag.

FIG. 70 is a flowchart showing yet another embodiment for controlling the NO _x release flag.

FIG. 71 is a flowchart showing yet another embodiment for controlling the NO _x release flag.

FIG. 72 is a flowchart showing yet another embodiment for controlling the NO _x release flag.

FIG. 73 is a time chart of NO _x release control showing still another embodiment for performing rich processing.

Figure 74 is a further timing chart of _the NO _x releasing control showing another embodiment for performing the rich operation.

FIG. 75 is a flowchart for controlling a flag.

FIG. 76 is a flowchart for performing injection control.

FIG. 77 is a flowchart for performing injection control.

FIG. 78 is a side sectional view showing another embodiment of the internal combustion engine.

FIG. 79 is a plan sectional view of the cylinder head shown in FIG. 78;

FIG. 80 is a time chart showing NO _x release control for performing rich processing I.

FIG. 81 is a flowchart for performing a rich process I;

Figure 82 is a further timing chart of _the NO _x releasing control showing another embodiment for carrying out the rich processing I.

FIG. 83 is a flowchart showing still another embodiment for performing the rich process I.

FIG. 84 is an overall view showing another embodiment of the internal combustion engine.

[Explanation of symbols]

10 ... ignition plug 11 ... Fuel injection valve 16 ... surge tank 24 ... exhaust manifold 26 ... NO _x absorbent 28 ... EGR gas passage

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/20 F01N 3/20 B 3/24 3/24 RS 3/28 301 3/28 301C F02B 17 / 00 F02B 17/00 Z F02D 41/02 301 F02D 41/02 301F 41/04 305 41/04 305A 330 330A 335 335A 41/34 41/34 F F term (reference) 3G023 AA01 AA05 AA17 AB01 AC02 AC04 AD07 AF01 AG01 AG02 AG03 3G084 AA03 AA04 BA09 BA13 BA19 BA20 BA21 BA24 BA32 CA00 CA03 CA04 DA10 DA11 EB12 EC02 EC07 FA10 FA13 FA17 FA31 FA33 FA37 FA38 3G091 AA02 AA11 AA12 AA23 AA24 AA28 AB06 BA00 BA14 CB00 CB03 CB00 CB02 CB00 FA11 FA12 FA13 FA14 GB02W GB02Y GB03W GB03Y GB04W GB04Y GB05W GB06W GB17X 3G301 HA01 HA04 HA06 HA13 HA16 HA17 JA23 JA25 KA04 KA06 KA 08 KA09 LA01 LA05 LB02 LB04 LC04 MA01 MA11 MA18 MA19 MA26 NA08 NC02 ND02 NE13 NE14 NE15 PA00Z PA11Z PB03A PB03Z PB05Z PD15Z PE01Z PE03Z PF03Z PF08Z PF10Z

Claims (8)

[Claims] Air-fuel ratio of 1. A inflowing exhaust gas is absorbed NO _x when the lean air-fuel ratio of the inflowing exhaust gas to release NO _x absorbed and becomes the stoichiometric air-fuel ratio or rich N
In the exhaust purification method of O _x absorbent was placed in the engine exhaust passage has an internal combustion engine, a lean mixture combustion operating region where the average air-fuel ratio in the combustion chamber mixture is burned in a lean state is predetermined, When the operating state of the engine is in the lean air-fuel mixture combustion operation region, the air-fuel mixture formed in the combustion chamber is stratified to form an ignitable air-fuel mixture in a limited area in a part of the combustion chamber. N which occurs
The O _x was absorbed in the NO _x absorbent from _the NO _x absorbent when the operating state of the engine is in lean mixture combustion operating region N
When O _x is to be released, the average air-fuel ratio in the combustion chamber is temporarily reduced from lean to the stoichiometric air-fuel ratio or rich, and the degree of stratification of the air-fuel mixture formed in the combustion chamber is reduced. An exhaust purification method for an internal combustion engine, wherein an average air-fuel ratio is switched from a stoichiometric air-fuel ratio or rich to lean, and the degree of stratification of an air-fuel mixture formed in a combustion chamber is increased. To 2. A method according to claim 1, the average air-fuel ratio in the combustion chamber so as to release the NO _x from the NO _x absorbent is the mixture when it is switched from lean to the stoichiometric air-fuel ratio or rich is substantially homogeneous mixture An exhaust purification method for an internal combustion engine according to the above. To 3. A process according to claim 1 in which the fuel supply timing into the combustion chamber is advanced when the average air-fuel ratio in the combustion chamber so as to release the NO _x from the NO _x absorbent is switched from lean to the stoichiometric air-fuel ratio or rich An exhaust purification method for an internal combustion engine according to the above. 4. A wherein the average air-fuel ratio in the combustion chamber so as to release the NO _x from the NO _x absorbent is to be changed to the intake stroke to supply timing of the fuel from the compression stroke when it is switched from lean to the stoichiometric air-fuel ratio or rich Item 4. The method for purifying exhaust gas of an internal combustion engine according to Item 3. 5. to allow the selective fuel injection into the combustion chamber into the intake port, NO _x absorbent from the NO _x
4. The exhaust gas purification method for an internal combustion engine according to claim 3, wherein when the fuel is to be discharged, the average air-fuel ratio in the combustion chamber is switched from lean to the stoichiometric air-fuel ratio or rich by increasing the fuel injection amount into the intake port. 6. Selective into combustion chamber and into intake port
So that fuel can be injected into the combustion chamber only.
NO when supplied_x NO from absorbent _x Released
When it is determined that fuel should be
Advance the injection timing and increase the amount of fuel injected into the combustion chamber
The average air-fuel ratio in the combustion chamber from lean to the stoichiometric air-fuel ratio or
Switched to rich, fuel is being supplied into the intake port
Sometimes NO_x NO from absorbent_x Should be released
The fuel injection amount into the intake port is increased.
The average air-fuel ratio in the combustion chamber from lean to the stoichiometric air-fuel ratio or
4. The internal combustion engine according to claim 3, wherein the switch is made rich.
Seki's exhaust purification method. 7. An air-fuel mixture in the combustion chamber is switched between a strong stratified state, a weak stratified state in which the degree of stratification is lower than that in a forced stratified state, and a substantially uniform state in accordance with an operation state of the engine, and NO _x
Exhaust gas purifying method for an internal combustion engine according to claim 1 which is switched in a substantially uniform state after being subjected to a stratified charge state when it is switched to a substantially uniform state from the strong stratification condition when releasing the NO _x from the absorbent. 8. An air-fuel mixture in the combustion chamber is switched between a strongly stratified state, a weakly stratified state in which the degree of stratification is lower than that in a forced stratified state, and a substantially uniform state in accordance with an operation state of the engine, and NO _x
Or when it is switched to a substantially uniform state from the strong stratification condition when releasing the NO _x from the absorbent is switched to a substantially uniform state after passing through the semi-stratified charge state in accordance with the engine operating state, or from the strong stratified state 2. The method for purifying exhaust gas of an internal combustion engine according to claim 1, wherein one of the switching methods is used for directly switching to a substantially uniform state.