JP2000073817A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily purify NOX or SOX by NOX absorbent. SOLUTION: NOX absorbent 10 is disposed in an engine exhaust passage. When an air-fuel ratio of inflow exhaust is lean, the NOX absorbent 10 absorbs the NOX. When oxygen concentration in the inflow exhaust is lowered, the NOX absorbent 10 emits the absorbed NOX or SOX. The air-fuel ratio of the exhaust flowed into the absorbent 10 is temporally made to be rich so that the absorbent 10 emits the absorbed NOX or SOX. When the NOX or SOX is desired to be emitted from the absorbent 10, oxygen is made to be remained in the exhaust gas flowed in the absorbent 10 and the oxygen concentration in the exhaust gas is kept to be within a predetermined range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art The ratio of the total amount of air to the total amount of fuel and the total amount of reducing agent supplied into an exhaust passage, a combustion chamber, and an intake passage upstream of a certain position in an exhaust passage flows through the position. when referred to as air-fuel ratio of the exhaust gas, in an internal combustion engine which is adapted allowed to combust a lean air-fuel mixture, air-fuel ratio of the exhaust flowing absorbs NO _X when the lean, the oxygen concentration in the inflowing exhaust gas is lowered and the absorption to the _the NO _X absorbent to release the NO _X disposed engine exhaust passage and, temporarily rich or the stoichiometric air-fuel ratio of the exhaust gas flowing to the NO _X absorbent is absorbed from _the NO _X absorbent NO _X
2. Description of the Related Art There is known an exhaust gas purifying apparatus for an internal combustion engine which releases and reduces (see Japanese Patent No. 2600492).

[0003]

[Problems to be solved by the invention] NO_XFlows into the absorbent
NO if the oxygen concentration in the exhaust_XOr SO_XBut
NO, considering that it is released and purified_XFlow into absorbent
The lower the oxygen concentration in the exhaust gas, the lower the NO_XMa
Or SO_XIs well purified and NO_XFlows into the absorbent
NO if exhaust gas contains almost no oxygen_X
Or SO_XIs believed to be more effectively purified.
However, according to the present inventor, NO _XIn the absorbent
NO if there is a certain amount of oxygen_XFor absorbent
NO _XOr SO_XTo be able to purify
It has been certified. Therefore, NO_XNO in absorbent
_XOr SO_XNO for good purification of NO_XAbsorbent
From NO_XOr SO_XNO when should be released_X
It is necessary to have oxygen present in the absorbent. Up
The above publication does not suggest anything about this point.

[0004]

Means for Solving the Problems] According to the first invention to solve the above problems, the air-fuel ratio of the exhaust flowing absorbs NO _X when the lean, the oxygen concentration in the inflowing exhaust gas decreases then place the _the NO _X absorbent to release the NO _X that is absorbed in the engine exhaust passage, are absorbed from _the NO _X absorbent is temporarily made to decrease the air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent in the exhaust purification system of an internal combustion engine which is adapted to release NO _X or sO _X, with leaving the oxygen in the exhaust gas flowing to the NO _X absorbent when it should emit NO _X or sO _X from _the NO _X absorbent The oxygen concentration in the exhaust gas is maintained within a predetermined range. That is, in the first invention, when NO _X or SO _X is to be released from the NO _X absorbent, NO _X
Since oxygen is contained in exhaust gas flowing into the _X absorbent NO _X
Oxygen is present in the absorbent.

Further, in the first aspect according to the second invention, _the NO _X absorbent sought amount of hydrocarbon attached to, NO from _the NO _X absorbent as when the hydrocarbon amount is large
_{When X} or SO _X is to be released, the concentration of oxygen in the exhaust gas flowing into the NO _X absorbent is increased.
That is, as the NO _X or SO _X is satisfactorily purified in _the NO _X absorbent when the oxygen is present in the _the NO _X absorbent will be described later, a hydrocarbon attached to _the NO _X absorbent by the oxygen It believed to be due reformed into effective reducing agent of the NO _X or SO _X. Therefore, in the second invention, so that to increase the amount of oxygen in _the NO _X absorbent as when the amount of hydrocarbon adhering to _the NO _X absorbent is larger.

Further, in the first aspect according to the third invention, detecting the temperature of the NO _X absorbent, as when the temperature is higher from _the NO _X absorbent when it should emit NO _X or SO _X The oxygen concentration in the exhaust gas flowing into the NO _X absorbent is increased. That is, the reaction between the hydrocarbons adhering to the NO _X absorbent and oxygen as described above becomes more active as the temperature of the NO _X absorbent increases. Therefore, in the third invention, as when the temperature of the NO _X absorbent is high N
It is thus increase the amount of oxygen in the O _X absorbent.

[0007] According to the fourth invention to solve the above problems, the air-fuel ratio of the exhaust flowing absorbs NO _X when the lean, the oxygen concentration in the inflowing exhaust gas is absorbed and reduced the _the NO _X absorbent to release the are NO _X disposed engine exhaust passage, NO _X fuel ratio of the exhaust gas flowing into the absorbent is temporarily made to drop is absorbed from _the NO _X absorbent NO _X or sO _In an exhaust gas purifying apparatus for an internal combustion engine configured to release _X , an oxygen storage agent that stores oxygen when the oxygen concentration in the inflowing exhaust gas increases and releases the stored oxygen when the oxygen concentration in the inflowing exhaust gas decreases. NO _X
Provided in the absorbent. That is, in the fourth invention, N
N 2 to release NO _X or SO _X from the O _X absorbent
O the oxygen concentration in the exhaust gas flowing into the _X absorbent is released oxygen from the is caused to decrease the oxygen storage component, thereby NO
Oxygen is supplied to the _X absorbent.

Further, in the first or fourth invention according to the fifth invention, in _the NO _X absorbent is provided a hydrocarbon adsorbent, the hydrocarbon adsorbent when the temperature of the hydrocarbon adsorbent is low When the hydrocarbon is adsorbed and the temperature of the hydrocarbon adsorbent increases, the adsorbed hydrocarbon is desorbed. That is, in the fourth invention, NO from _the NO _X absorbent _X or S
O _X The temperature of the exhaust gas oxygen concentration in the exhaust gas flowing into the caused to drop flowing into _the NO _X absorbent to be released hydrocarbon from the hydrocarbon adsorbent to be increased desorbed,
This is reformed into an effective reducing agent in hydrocarbon then reacts with oxygen in _the NO _X absorbent NO _X or SO _X. As a result, NO _X or SO _X is satisfactorily purified.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a case where the present invention is applied to a spark ignition type engine. Referring to FIG. 1, the engine body 1 includes, for example, four cylinders. Each cylinder is connected to a surge tank 3 via a corresponding branch pipe 2, and the surge tank 3 is connected to an air cleaner 5 via an intake duct 4. A throttle valve 6 is arranged in the intake duct 4. Each cylinder is provided with a fuel injection valve 7 for directly injecting fuel into the cylinder. Each cylinder is connected to a catalytic converter 11 having a _the NO _X absorbent 10 via an exhaust manifold 8 and an exhaust pipe 9, the catalytic converter 11 is connected to the exhaust pipe 12.

The electronic control unit 20 is composed of a digital computer, and a ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) 24, and a constant power supply are connected to each other by a bidirectional bus 21. It has a supplied B-RAM (backup RAM) 25, an input port 26 and an output port 27. A pressure sensor 2 that generates an output voltage proportional to the pressure in the surge tank 3
The exhaust pipe 12 is provided with a temperature sensor 29 for generating an output voltage proportional to the temperature of exhaust gas flowing through the exhaust pipe 12. These sensors 28 and 29
Are input to the input port 26 via the corresponding AD converters 30, respectively. The CPU 24 calculates the intake air amount Q from the output voltage of the pressure sensor 28. The input port 26 is connected to a rotation speed sensor 31 that generates an output pulse representing the engine rotation speed N. On the other hand, the output ports 27 are connected to the fuel injection valves 7 via the corresponding drive circuits 32, respectively.

In the internal combustion engine shown in FIG. 1, the fuel injection time TAU (i) of the i-th cylinder is calculated based on, for example, the following equation. TAU (i) = TP · K (i) Here, TP represents the basic fuel injection time, and K (i) represents the correction coefficient of the i-th cylinder. Basic fuel injection time T
P indicates the fuel injection time required for setting the air-fuel ratio of the air-fuel mixture burned in the cylinder to the stoichiometric air-fuel ratio. The basic fuel injection time TP is previously obtained by an experiment, and is stored in the ROM 22 in advance in the form of a map as shown in FIG. 2 as a function of the engine load Q / N (intake air amount Q / engine speed N) and the engine speed N. Is stored in

On the other hand, the correction coefficient K (i) is a coefficient for controlling the air-fuel ratio of the air-fuel mixture burned in the combustion chamber of the i-th cylinder. If K (i) = 1.0, the i-th cylinder is used. The air-fuel ratio of the air-fuel mixture burned in the combustion chamber becomes the stoichiometric air-fuel ratio. On the other hand, when K (i) <1.0, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber of the i-th cylinder becomes larger than the stoichiometric air-fuel ratio, that is, lean, and K
When (i)> 1.0, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber of the i-th cylinder becomes smaller than the stoichiometric air-fuel ratio, that is, becomes rich.

In the internal combustion engine of FIG. 1, for example, K (i)
= KL (<1.0), that is, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber in all cylinders is maintained lean. Therefore, in all cylinders of the internal combustion engine shown in FIG. 1, a lean air-fuel mixture is usually burned. _The NO _X absorbent 10, for example alumina as a carrier, the carrier on, for example potassium K, sodium Na, lithium Li, alkaline earth such as alkali metal, barium Ba, calcium Ca, such as cesium Cs, lanthanum La, yttrium At least one selected from rare earths such as Y and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir are supported. This _the NO _X absorbent 10 absorbs NO _X or SO _X when the air-fuel ratio of the exhaust gas flowing is lean, the oxygen concentration in the inflowing exhaust gas to release NO _X or SO _X absorbed and reduced NO _X or SO _X absorbs and releases. If fuel or air is not supplied into the exhaust passage upstream of the NO _X absorbent 10, NO _X
The air-fuel ratio of the exhaust gas flowing into the absorbent 10 matches the ratio of the total amount of air to the total amount of fuel supplied into the combustion chamber of each cylinder.

If the above-mentioned NO _X absorbent 10 is disposed in the engine exhaust passage, the NO _X absorbent 10 actually performs the absorption and release of NO _X or SO _X. The detailed mechanism of this absorption and release is described below. Some parts are not clear. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIGS. 3 (A) and 3 (B). Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, the exhaust gas flowing in is considerably lean.
When this happens, the oxygen concentration in the inflowing exhaust gas greatly increases, and FIG.
As shown in FIG._TwoIs O_Two ^-Or
O^2-On the surface of platinum Pt. Meanwhile, inflow
NO, SO in exhaust_TwoIs O on the surface of platinum Pt_Two ^-Also
Is O^2-And react with NO_Two, SO_Three(2N
O + O_Two→ 2NO_Two, 2SO_Two+ O_Two→ 2SO_Three). Next
NO generated_Two, SO_ThreeSome of them are on platinum Pt
Barium oxide is absorbed into the absorbent while being oxidized further
While binding with BaO, as shown in FIG.
Acid ion NO_Three ^-Or sulfate ion SO_Four ^2-Absorbed in the form of
Diffuses into agent. NO in this way_XOr SO_XBut
NO_XIt is absorbed in the absorbent 10.

As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ and SO ₃ are generated on the surface of platinum Pt, and NO
_As long as the _X- absorbing capacity is not saturated, NO ₂ and SO ₃ are absorbed in the absorbent and nitrate ions NO ₃ ^- or sulfate ions SO
₄ ^2- is generated. On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the production amount of NO ₂ and SO ₃ decreases, the reaction proceeds in the opposite direction (NO ₃ ⁻ → NO ₂ , SO ₄ ²⁻ → SO ₃ ), and comb nitrate ions NO in absorbent ₃ ^- or ion SO ₄ ^2-sulfuric acid is released from the absorbent in the form of NO _2, SO _3. That, NO _X or SO _X is oxygen concentration in the exhaust from _the NO _X absorbent 10 when lowered flowing is to be released. The oxygen concentration in the exhaust gas lean degree of the exhaust gas flowing to flow the lower the lowered, thus from _the NO _X absorbent 10 when lowering the lean degree of the exhaust gas flowing to NO _X or SO _X is released become.

On the other hand, the air-fuel ratio of the exhaust gas flowing in at this time is reset.
A large amount of unburned HC and CO is emitted from the engine.
These unburned HC and CO are oxygen O on platinum Pt._Two ^-Ma
Or O^2-And oxidize. Also inflow
When the air-fuel ratio of the exhaust gas is made rich, the oxygen concentration
NO from the absorbent due to extremely low degree_Two, SO_ThreeBut
Released and this NO_Two, SO_ThreeIs shown in FIG. 3 (B)
Thus, it is reduced by reacting with unburned HC and CO. This
NO on the surface of platinum Pt_Two, SO _Threeexist
When it is no longer used, NO will change from absorbent to next_Two, SO_ThreeBut
Released. Therefore, the air-fuel ratio of the inflowing exhaust gas is rich.
If set to NO in a short time_XNO from absorbent 10_XMa
Or SO_XWill be released.

As described above, in all the cylinders of the internal combustion engine shown in FIG.
Air-fuel ratio of the exhaust gas flowing into the O _X absorbent 10 is usually lean, thus NO _X and SO _X in the exhaust that time
Is absorbed in the NO _X absorbent 10. However, NO _X absorbent 10 NO _X and SO _X since the absorption capacity is limited in _the NO _X absorbent 10 NO _X and SO _X before the absorbent capacity is saturated from _the NO _X absorbent 10 NO _X or SO _X
Must be released. Therefore, in the internal combustion engine shown in FIG. 1, the temporary air-fuel ratio of the mixture burned in the cylinders when the NO _X absorption or SO _X absorption amount of the NO _X absorbent 10 becomes more than the set predetermined amount of so that the reduction with is to be released from _the NO _X absorbent 10 is made rich NO _X or sO _X. That is, N
When NO _X or SO _X is to be released from the O _X absorbent 10, K (i) = KR (> 1.0) in all cylinders.

In this case, NO_XReleased from the absorbent 10
NO_XOr SO_XConsidering the reduction effect of NO_Xabsorption
NO if oxygen is present in agent 10_XIn absorbent 10
NO _XOr SO_XThat you cannot purify the water well
Can also. However, according to the present inventor, NO_X
If a certain amount of oxygen is present in the absorbent 10, N
O_XNO in absorbent 10_XOr SO_XGood clean
It has been confirmed that this can be achieved.

NO_XAir-fuel ratio of exhaust gas flowing into absorbent 10
NO when is rich_XOxygen in the absorbent 10
If so, why NO_XOr SO_XIs well purified?
It was not disclosed. However,
It is thought to be due to reasons. That is, during normal operation
If the air-fuel ratio of the air-fuel mixture burned in the cylinder is lean
Even so, the exhaust gas discharged from each cylinder contains HC
ing. Some of this HC is NO_XAcid in absorbent 10
But the remaining HC is not oxidized.
For example, it adheres on the surface of platinum Pt. NO_XAbsorbent
10 to NO_XOr SO_XWhen should be released above
NO as I did_XThe air-fuel ratio of the exhaust gas flowing into the absorbent 10 is
NO because it is made rich_XA large amount of HC and C in the absorbent 10
O flows in, and part of the HC and CO is deposited on the platinum Pt surface.
Adhere to. However, there is a large amount of HC and CO on the platinum Pt surface.
NO when covering the surface of platinum Pt_XFlow into absorbent 10
When the air-fuel ratio of the incoming exhaust gas is lean,
Oxygen O_TwoIs O_Two ^-Or O ^2-Can no longer adhere in the form of
NO_XIs NO_XBecomes difficult to be absorbed by the absorbent 10,
Thus NO_XLarge amount of NO from absorbent 10_XIs discharged
You. On the other hand, NO_XThe air-fuel ratio of the exhaust gas flowing into the absorbent 10 is
When rich, NO on platinum Pt surface_XAbsorbent 10?
NO released from_XOr SO_XIs HC, CO in exhaust
And it is difficult to react with_Xabsorption
A large amount of NO from agent 10_XOr SO_XIs discharged.

On the other hand, NO_XNO from absorbent 10_XOr
SO_XOf the air-fuel mixture burned in each cylinder to release
When the air-fuel ratio is made rich or stoichiometric, NO
_XWhen oxygen is present in the absorbent 10, local around the platinum Pt
Oxidation reaction takes place. At this time, compared to normal operation
NO_XThe temperature of the exhaust gas flowing into the absorbent 10 is increased.
NO_XThe temperature of the absorbent 10 is increased, so that the platinum
HC and CO on the Pt surface are further oxidized by oxygen
You. Therefore, HC and CO are removed from the platinum Pt surface.
And thus NO_XGood NO for absorbent 10_XOr
SO_XPurification action is ensured. Or combustion in each cylinder
When the air-fuel ratio of the air-fuel mixture is made rich,
NO_XFor example, HC and CO in the exhaust gas flowing into the absorbent 10
For example, it reacts with oxygen on the platinum Pt surface. As a result, platinum P
t is locally heated, so that platinum Pt
Reaction between HC and CO adhering to the surface and oxygen accelerates
And thus HC and CO from the platinum Pt surface
Removed. Furthermore, in each case, the platinum Pt surface
HC is NO when removed from_X, SO_XEffective reduction of
Is modified into an agent. Therefore, NO_XRelease from absorbent 10
NO issued_X, SO _XWith this reducing agent
Can be reduced to

[0022] However, NO _X concentration of oxygen absorber 10 is on excessively high consisting of oxygen and platinum Pt surface HC, CO
Or excessive reaction with HC and CO in the inflow exhaust gas occurs,
As a result, the temperature of the catalytic converter 11 becomes excessively high, and the catalytic converter 11 may be melted. Thus, resulting in a set range determined in advance the amount of oxygen in _the NO _X absorbent 10 in order to satisfactorily purify NO _X or SO _X in _the NO _X absorbent 10, that is the erosion of the NO _X absorbent 10 It is necessary to maintain the Pt surface within a range in which HC and CO can be satisfactorily removed without any problem.

Therefore, in the present embodiment, the NO _x absorbent 10
From NO _X or oxygen concentration in the exhaust gas flowing to the NO _X absorbent 10 when releasing the SO _X is the air-fuel ratio of the mixture burned in the cylinders to be within the set range,
That is, the coefficient KR is controlled. In the spark ignition gasoline engine as in the present embodiment, the set range is, for example, about 0.3% to 1.0%. On the other hand, for diesel engines, the setting range is 1.0%, for example.
From about 2.0%. The reason that the setting range of the diesel engine is higher than that of the gasoline engine is that the exhaust temperature of the diesel engine is lower than that of the gasoline engine, so that the catalytic converter 11 is less likely to be melted. This is because a relatively large amount of oxygen is required due to low activity.

[0024] NO temperature _X absorbent 10 on the platinum Pt surface when a high HC, when the temperature of the NO _X absorbent 10 since the reaction between CO and oxygen becomes more active the higher _the NO _X absorbent 10 in a large amount If oxygen is supplied, HC on the platinum Pt surface
CO can be removed well. On the other hand, can not be effectively utilized to supply a large amount of oxygen the oxygen HC, for CO removal in the NO _X absorbent 10 when the temperature of the NO _X absorbent 10 is low. Rather, to reduce the temperature of the NO _X absorbent 10, or to inhibit the release action or reducing action of the NO _X or SO _X from _the NO _X absorbent 10. on the other hand,
The temperature TEX of the exhaust gas discharged from the NO _X absorbent 10 detected by the temperature sensor 29 indicates the temperature of the NO _X absorbent 10. Therefore, in the present embodiment, as shown in FIG. 4 (A), the coefficient KR is determined so as to become smaller as the exhaust temperature TEX becomes higher, so that the exhaust gas flowing into the NO _X absorbent 10 becomes higher as the exhaust temperature TEX becomes higher. The oxygen concentration inside is made higher.

Further, requiring a large amount of oxygen in order to remove the HC The more amount of HC that has adhered onto the platinum Pt surface of the NO _X absorbent 10. Therefore, in the present embodiment, the HC amount SHC adhering to the NO _X absorbent 10 is obtained, and as shown in FIG. 4B, the coefficient KR is determined so as to decrease as the adhering HC amount SHC increases. Accordingly, the higher the attached HC amount SHC, the higher the oxygen concentration in the exhaust gas flowing into the NO _X absorbent 10. Note that the coefficient KR is set in advance in the form of a map shown in FIG.
It is stored in M22.

FIG. 5 shows NO in this embodiment._XRelease control
Shows a routine. This routine is a predefined
It is executed by interruption every set time. See FIG.
Then, first, in step 40, NO_XAbsorbent 10 to N
O_XOr SO_XIs set when it should be released,
Otherwise, is the flag to be reset set?
It is determined whether or not it is. When the flag is reset
Then goes to step 41, NO_XAbsorbed by absorbent 10
NO_XAmount or SO_XThe amount SN is the engine operating state
Is calculated based on For example, NO_XFlow into absorbent 10
NO to enter_XAmount or SO_XThe quantity is the engine load Q / N (intake
It increases as the air amount Q / engine speed N) increases.
The engine speed N increases as the engine speed N increases.
To the integrated value of the product Q / N · N of the relevant load Q / N and the engine speed
NO absorbed based on_XAmount or SO_XEstimate the quantity SN
Can be specified. In the next step 42
NO_XAmount or SO_XThe quantity SN is greater than the constant value SN1
It is determined whether it is larger. This constant value SN1 is NO_X
Maximum NO that can be absorbed by the absorbent 10 _XAmount or SO_Xamount
About 30% of Processing cycle when SN ≦ SN1
End On the other hand, when SN> SN1,
Then, the process proceeds to a step 43, wherein a flag is set.

When the flag is set, step 4
Proceeds from 0 to step 44, whether the flag has passed a predetermined time or more since the set, i.e. _the NO _X absorbent 1
It is determined whether the NO _X or SO _X releasing action of 0 has been performed for a predetermined time or more. If the predetermined time has not elapsed since the flag was set, the processing cycle ends. On the other hand, when a predetermined time or more has elapsed since the flag was set, the process proceeds to step 45, where the flag is reset. In the following step 46, the absorbed NO _X amount or SO _X amount SN is cleared (SN =
0).

FIG. 6 shows the fuel injection time TAU (i) of each cylinder.
2 shows a routine for calculating. This routine is executed by interruption every predetermined set time. Referring to FIG. 6, first, at step 50, the basic fuel injection time TP is calculated from the map of FIG. HC amount SHC adhering to Step 51 in _the NO _X absorbent 10 continues is calculated. For example, the attached HC amount SHC increases as the amount of fuel supplied to the engine 1 increases, so that the attached HC amount SHC can be estimated based on the integrated value of the fuel injection time TAU (i) of each cylinder. Next step 5
At 2, it is determined whether the flag is set.
When the flag is reset, that is, when it is not time to release NO _X or SO _X from the NO _X absorbent 10, the routine proceeds to step 53, where the correction coefficient K (i) of all cylinders is set to KL, for example, 0.6. You. In the following step 54, the fuel injection time TAU (i) is calculated (T
AU (i) = TP · K (i)).

On the other hand, when the flag is set, the process proceeds from step 52 to step 55, and FIG.
Is calculated from the map. Next step 56
In, the correction coefficients K (i) of all cylinders are set to KR. In the following step 54, the fuel injection time TAU (i) is calculated. Next, another embodiment will be described.

Also in this embodiment, during normal operation, all cylinders
And K (i) = KL (<1.0), and NO_XAbsorbent
The air-fuel ratio of the exhaust flowing into 10 is made lean. Also,
NO _XNO from absorbent 10_XOr SO_XRelease
NO when it should_XAir-fuel ratio of exhaust gas flowing into absorbent 10
Is enriched. However, in this embodiment,
When the air-fuel ratio of exhaust discharged from
The air-fuel ratio of exhaust discharged from the remaining cylinders
And thereby NO_XOf the mixed exhaust gas flowing into the absorbent 10
Enrich air-fuel ratio and NO_XFlows into absorbent 10
Make sure that the exhaust gas contains oxygen within the set range.
ing.

That is, in this embodiment, the first cylinder, the second cylinder,
Air-fuel of air-fuel mixture burned in cylinder and cylinder # 3
Richer the ratio of the mixture to be burned in the fourth cylinder.
Make the air-fuel ratio lean, thereby reducing NO_XFlow into absorbent 10
In addition to enriching the air-fuel ratio of
_XIn the exhaust gas flowing into the absorbent 10, the concentration
Oxygen is included. In this case, the first cylinder,
Correction coefficients K (1), K for the second and third cylinders
(2), K (3) is a constant coefficient KRR (> 1.0)
And the correction coefficient K (4) of the fourth cylinder is a coefficient KLL (<1.
0). This coefficient KLL is NO_XAbsorbent 10 temperature
Degree and NO_XAccording to the amount of HC adhering to the absorbent 10
Controlled. That is, as shown in FIG.
The coefficient KL is set so that it decreases as the exhaust gas temperature TEX increases.
L, whereby the higher the exhaust temperature TEX, the more NO
_XThe oxygen concentration in the exhaust gas flowing into the absorbent 10 increases.
I'm trying. Also, as shown in FIG.
The coefficient KLL is set so as to decrease as the HC amount SHC increases.
And the more the amount of adhering HC SHC is, the more NO
_XThe oxygen concentration in the exhaust gas flowing into the absorbent 10 increases.
I'm trying. Note that the coefficient KLL is the coefficient shown in FIG.
It is stored in the ROM 22 in advance in the form of a tip.

FIG. 8 shows the fuel injection time TAU (i) of each cylinder.
2 shows a routine for calculating. This routine
Is executed by interruption every predetermined time.
It is. In this embodiment, the NO shown in FIG._XRelease control
A routine is running. Referring to FIG.
In step 60, the basic fuel injection time TP is obtained from the map of FIG.
Is calculated. In the following step 61, NO_XAttach to 10
The calculated HC amount SHC is calculated. Subsequent step 62
Then, it is determined whether or not the flag is set. H
When the lag is reset, that is, NO_XAbsorbent
10 to NO _XOr SO_XWhen should you release
If not, the process proceeds to step 63, and the correction section for all cylinders
The number K (i) is set to KL, for example, 0.6. Next steps
At 64, the fuel injection time TAU (i) is calculated (TA
U (i) = TP · K (i)).

On the other hand, when the flag is set, the process proceeds from step 62 to step 65, and FIG.
Is calculated from the map. Next step 6
In 6, the correction coefficients K (1), K (2), and K (3) of the first cylinder, the second cylinder, and the third cylinder are set as coefficients KRR, and 4
The correction coefficient K (4) of the cylinder No. is set as the coefficient KLL. In the following step 64, the fuel injection time TAU (i) is calculated.

By the way, as described above, NO if _X fuel ratio of the exhaust gas flowing into the absorbent 10 contains oxygen in the inflowing exhaust when rich, first H of the inflowing exhaust
C and CO react with oxygen on, for example, the platinum Pt surface, and thereby, for example, local heating around the platinum Pt promotes the reaction between HC and oxygen attached on the platinum Pt surface, Thus, from the platinum Pt surface, H
There is also the idea that C and CO are removed. Based on this idea, the reducing agent in the exhaust gas flowing to the NO _X absorbent 10 (HC, CO) concentration is attached to _the NO _X absorbent 10 when increasing the oxygen concentration in the inflowing exhaust gas as when high HC , C
O can be removed satisfactorily.

On the other hand, the reducing agent in the exhaust gas flowing to the NO _X absorbent 10 (HC, CO) concentration is dependent on the air-fuel ratio of the inflowing exhaust. That is, for example, the embodiment described with reference to FIGS. 7 and 8 depends on the coefficient KRR for the cylinder in which the rich mixture is burned. Therefore, the coefficient KLL for the cylinder in which the lean air-fuel mixture is burned may be determined so that the coefficient KRR decreases as the coefficient KRR increases.

Further, even when the air-fuel ratio of the exhaust gas is the same, the concentration of the reducing agent in the exhaust gas discharged from the cylinder differs for each internal combustion engine because the combustion method and the cylinder volume are different for each internal combustion engine. Therefore, the concentration of the reducing agent in the exhaust gas discharged from the cylinder is determined in advance for each internal combustion engine.
_The concentration of oxygen in the exhaust gas flowing into the _X absorbent 10 may be determined.

FIG. 9 shows a case where the present invention is applied to a diesel engine. Referring to FIG. 9, a depression sensor 33 that generates an output voltage proportional to the depression amount of an accelerator pedal (not shown) is connected to the input port 26 of the electronic control unit 20 via the corresponding AD converter 30.
FIG. 10 is a partially enlarged sectional view of the catalytic converter 11. Referring to FIG. 10, a wall-flow type catalytic converter 11 includes a plurality of cells formed of a porous material such as ceramics and defined by cell walls 14 extending substantially parallel to an exhaust passage axis. 15u
Are formed by alternately and repeatedly arranging an upstream end open cell 16u in which the exhaust gas is opened and the exhaust downstream end 15d is closed, and a downstream end open cell 16d in which the exhaust upstream end 15u is closed and the exhaust downstream end 15d is opened. ing. _The NO _X absorbent 10 is disposed on the inner wall surface of the upstream end open cells 16u,
However, on the inner wall surface of the downstream end open cell 16d, NO
_{The X} absorbent 10 is not arranged. Thus, exhaust gas flowing into the catalytic converter 11 as shown with an arrow EG 10 is first flows into the upstream end open cells within 16u, then successively passed through the downstream end and open _the NO _X absorbent 10 and the cell walls 14 It flows into the cell 16d and thus out of the catalytic converter 11.

The mixture usually at engine is a diesel engine air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 10 since burned in excess air state is maintained normally in a lean, therefore at this time _the NO _X absorbent 10 NO _X or SO _X is absorbed in. When NO _X NO _X amount absorbed in the absorbent 10 or SO _X amount becomes larger than a set amount is the air-fuel ratio rich temporarily for the exhaust gas discharged from the engine 1, whereby NO _X absorption NO _X or SO _X absorbed in the agent 10 is released and reduced.

In the present embodiment, in order to enrich the air-fuel ratio of the exhaust gas discharged from the engine 1, the fuel injection valve 7 separates the fuel from the fuel injection valve 7 during the expansion stroke or the exhaust stroke separately from the fuel injection performed around the compression top dead center. The second fuel injection, that is, the secondary fuel injection is performed. The fuel from the secondary fuel injection hardly contributes to the engine output. NO _X absorbent 10
The secondary fuel injection time TAUS when NO _X or SO _X is to be released from
IT is ADV. The air-fuel ratio of the exhaust This TN is flowing into _the NO _X absorbent 10, from _the NO _X absorbent 10 NO _X
Or a fuel injection time required to the optimum air-fuel ratio to reduce the released NO _X or SO _X with the release of SO _X, depression of the accelerator pedal amount D
It is obtained in advance by an experiment as a function of the EP and the engine speed N. This TN is stored in the ROM 22 in advance in the form of a map shown in FIG. On the other hand, ADV is, for example, 90 ° crank angle after compression top dead center (ATDC) (C
A) is set to about 120 ° CA from A).

[0040] As described above _the NO _X absorbent 1
It is considered that, for example, when oxygen is supplied around platinum Pt when the air-fuel ratio of the exhaust gas flowing into 0 is made rich, NO _X or SO _X can be satisfactorily purified by the NO _X absorbent 10. Although if it contains oxygen in the exhaust gas flowing to the NO _X absorbent 10 is oxygen around platinum Pt is supplied, not necessarily with the oxygen in this case the exhaust gas is always reach around the platinum Pt, thus oxygen It cannot be used effectively for removing HC and CO on the platinum Pt surface.

On the other hand, most of the oxygen be supplied oxygen from _the NO _X absorbent 10 around platinum Pt is possible to reach the platinum Pt. Therefore, in this embodiment, stored oxygen when the oxygen concentration in the inflowing exhaust gas is high, NO _X absorbent oxygen storage agent around platinum Pt to the oxygen concentration in the exhaust gas releases oxygen that accumulated a lower flowing 10 Provided within
O _X fuel ratio of the exhaust gas flowing into the absorbent 10 stored oxygen to an oxygen storage material in the case of lean, NO _X from _the NO _X absorbent
Or so that oxygen is supplied to around the platinum Pt from the oxygen storage component when the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 10 in order to release the SO _X is rich. On the other hand, HC on temperature increases when platinum Pt surface around the platinum Pt as described above, oxidation and removal action of CO is promoted, or is released NO _X or SO _X release action from _the NO _X absorbent 10 NO _X or SO _X reduction reaction is promoted. When oxygen reacts with a reducing agent such as HC on the surface of platinum Pt, the temperature around platinum Pt rises. Therefore, if a reducing agent is supplied around platinum Pt, the temperature around platinum Pt can be increased. On the other hand, as described above, N
O _X fuel ratio of the exhaust gas flowing into the absorbent 10 is oxygen around platinum Pt is supplied from the oxygen storage component becomes rich. Therefore, in this embodiment, the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 10 is adapted to supply HC to the platinum Pt around when the rich.

The exhaust gas flowing into the NO _x absorbent 10 contains HC
Can be effectively utilized HC to those who supplied the HC from _the NO _X absorbent 10 around platinum Pt than to include increases the temperature around the platinum Pt. Therefore, in the present embodiment, the HC adsorbent that adsorbs HC when the temperature is low and desorbs the adsorbed HC when the temperature is high becomes N
Is provided on O _X absorbent 10, the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 10 is low the temperature of the exhaust gas when the lean of the exhaust gas flowing to the NO _X absorbent 10 air-fuel ratio is rich Sometimes the temperature of this exhaust is raised. That is, since the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 10 is the temperature of the HC adsorbent is low when the lean is the HC adsorbed by the HC adsorbent, the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 10 rich In this case, the temperature of the HC adsorbent is raised, so that HC is desorbed from the HC adsorbent, and this HC is supplied around the platinum Pt.

[0043] That is, the oxygen storage component OC, the HC adsorbent as shown in FIG. 12 is expressed respectively AD (A), NO _X absorbent when the air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent 10 is lean In the exhaust gas flowing into the agent 10
_X is absorbed, oxygen O ₂ in the exhaust gas flowing into the oxygen storage material OC is stored, and HC in the exhaust gas flowing into the HC adsorbent AD is adsorbed. In contrast, NO _X fuel ratio of the exhaust gas flowing into the absorbent 10 is NO _X from _the NO _X absorbent 10 as shown in FIG. 12 (B) becomes rich is released, oxygen O ₂ from the oxygen storage material OC Is released, and HC is desorbed from the HC adsorbent. The oxygen O ₂ released from the oxygen storage material OC and the HC desorbed from the HC adsorbent then move to and react on the surface of the platinum Pt, thus increasing the temperature around the platinum Pt. Further, HC desorbed from the HC adsorbent reacts with oxygen O ₂ to be reformed into an effective reducing agent for NO _x and SO _x . As a result, NO _X absorbent 1
At 0, NO _X or SO _X can be purified well.

As the oxygen storage material, for example, ceria CeO ₂
Can be used. As the HC adsorbent, zeolite or mordenite can be used, and zeolite or mordenite can be used as a carrier. Therefore, in this embodiment, the the _the NO _X absorbent 10, for example zeolite or mordenite as a support, such as the carrier on, for example, potassium K, sodium Na, lithium Li, cesium Cs, barium Ba, calcium Ca At least one selected from alkaline earths, rare earths such as lanthanum La and yttrium Y, platinum Pt, palladium Pd, rhodium Rh and iridium I
It is formed by supporting a noble metal such as r and ceria CeO ₂ .

In a diesel engine as shown in FIG. 9, the HC concentration in the exhaust gas discharged during normal operation is relatively low, so that a sufficient amount of HC cannot be adsorbed on the HC adsorbent during normal operation. Therefore, in the present embodiment, secondary fuel is injected during normal operation, and thereby HC is supplied to the HC adsorbent. However during normal operation, i.e. NO _X when the air-fuel ratio of the exhaust gas flowing into the absorbent 10 is the oxygen concentration in the exhaust gas flowing to the NO _X absorbent 10 performs secondary fuel injection at the time of lean decrease _the NO _X absorbent 10 to N
O _X or SO _X from being released. Further, HC by the secondary fuel injection is oxidized within _the NO _X absorbent 10 when the H
The temperature of the C adsorbent increases and HC is desorbed from the HC adsorbent. Therefore, the secondary fuel injection time TAUS of when to supply HC to the HC adsorbent, NO _X absorbent 10 from the NO _X is HC from and HC adsorbent is not released is defined injection time TA is not desorbed . This TA is obtained in advance by an experiment as a function of the accelerator pedal depression amount DEP and the engine speed N, and is stored in the ROM 22 in advance in the form of a map shown in FIG.

On the other hand, the secondary fuel injection timing FIT is set to RTD, and this RTD is retarded from ADV, for example, AT
DC is set to about 150 ° CA to about 180 ° CA.
Thus _the NO _X absorbent the ratio of HC to be burned is reduced in the combustion chamber or the exhaust passage of the HC by the secondary fuel injection Slower secondary fuel injection timing 10
The temperature of the exhaust gas flowing into is kept low. At this time, HC supplied to the HC adsorbent is heavy HC (polymer H).
Since it is C), it is not easily oxidized in the NO _x absorbent 10.
Therefore, the temperature rise of the HC adsorbent during the normal operation can be suppressed, and thus the desorption of HC from the HC adsorbent can be suppressed.

Conversely, if the secondary fuel injection timing is advanced, such as when NO _X or SO _X is to be released from the NO _X absorbent 10, the proportion of HC burned in the combustion chamber or in the exhaust passage increases. NO _X temperature of the exhaust gas flowing into the absorbent 10 is increased, thus HC desorption is promoted from the HC adsorbent. Further, at this time _the NO _X absorbent 1
Since HC supplied to 0 is light HC (low molecular HC), it easily reacts in the NO _x absorbent 10. Therefore, N
NO _X or SO _X released from the O _X absorbent 10 can be easily reduced. Further, when a part of the HC by the secondary fuel injection is burned in the combustion chamber or the exhaust passage, oxygen in the exhaust gas discharged from the engine is consumed.
The oxygen concentration in the exhaust gas flowing into the NO _X absorbent 10 is shown in FIG.
To the setting range in the embodiment described with reference to FIG.

As described above, the present embodiment uses the wall-flow type catalytic converter 11.
In this way, all of the exhaust gas flowing into the catalytic converter 11 flows through the HC adsorbent. Therefore, HC can be efficiently adsorbed by the HC adsorbent during normal operation, and oxygen can be efficiently stored in the oxygen storage material.

FIG. 14 shows a secondary fuel injection control routine in this embodiment. This routine is executed by interruption every predetermined crank angle. Incidentally, NO _X release control routine in the present embodiment shown in FIG. 5 is executed. Referring to FIG. 14, first, at step 70, it is determined whether or not the flag is set. When the flag is reset, that is, when NO _X
If NO _X or SO _X is not to be released from the absorbent 10, the routine proceeds to step 71, where TA is calculated from the map of FIG. In the following step 72, the secondary fuel injection time TAUS is set to TA. Next step 73
In this case, the secondary fuel injection timing FIT is set to RTD. On the other hand, when the flag is set, that is, when NO _X or SO _X is to be released from the NO _X absorbent 10, the process proceeds from step 70 to step 74, and TN is calculated from the map of FIG. In the following step 75, the secondary fuel injection time TAUS is set to TN. In the following step 76, the secondary fuel injection timing FIT is set to ADV.

[0050] Incidentally, NO electrical heater provided in the _X absorbent 10, NO when the air-fuel ratio of the exhaust gas flowing is rich in _X absorbent 10 by the electric heater NO _X with absorbent 10 HC
The adsorbent may be heated. Alternatively, since immediately after or during acceleration operation the engine acceleration operation increases the temperature of the NO _X absorbent 10, NO fuel ratio of the exhaust gas flowing to the NO _X absorbent 10 at this time from _the NO _X absorbent 10 is made rich
_X or SO _X can also be released.

[0051]

Effects of the Invention] NO in _the NO _X absorbent _X or SO
_X can be purified well.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a map of a basic fuel injection time.

FIG. 3 is a diagram for explaining the NO _X absorbing / releasing action of a NO _X absorbent.

FIG. 4 is a diagram showing a map of a coefficient KR.

FIG. 5 is a flowchart showing a NO _X or SO _X release control routine.

FIG. 6 is a flowchart for calculating a fuel injection time.

FIG. 7 is a diagram showing a map of a coefficient KLL.

FIG. 8 is a flowchart for calculating a fuel injection time in another embodiment.

FIG. 9 is an overall view of an internal combustion engine showing another embodiment.

FIG. 10 is a partially enlarged sectional view of a catalytic converter.

FIG. 11 is a diagram showing a map of a secondary fuel injection time TN.

FIG. 12 is a diagram for explaining the NO _X absorbing / releasing action of the NO _X absorbent, the oxygen absorbing / releasing action of the oxygen storage material, and the HC adsorbing / desorbing action of the HC adsorbent.

FIG. 13 is a diagram showing a map of a secondary fuel injection time TA.

FIG. 14 is a flowchart for controlling secondary fuel injection.

[Explanation of symbols]

1 ... engine body 7 ... fuel injector 8 ... exhaust manifold 10 ... NO _X absorbent

Continued on the front page F-term (reference) 3G091 AA13 AA18 AA24 AB05 AB06 AB09 AB11 CA18 CB02 CB03 DB06 DB10 EA01 EA03 EA06 EA07 EA08 EA17 EA33 FA17 FB10 FB12 GB02Y GB03Y GB04Y GB05Y GB06Y GB09 MA11 HA03 MA04 HA04 MA26 NA04 NA08 NB02 NC02 NE12 NE13 NE15 NE23 PA07Z PA17Z PB03Z PD02Z PD11Z PE01Z PF03Z

Claims (5)

[Claims] 1. When the air-fuel ratio of the inflowing exhaust gas is lean
NO_XAbsorbs oxygen and reduces the oxygen concentration in the inflowing exhaust
NO absorbed_XReleases NO_XExhaust absorbent
Placed in air passage, NO_XAir-fuel of exhaust flowing into the absorbent
NO by temporarily lowering the ratio_XAbsorbing from the absorbent
NO_XOr SO_XInternal combustion engine that emits
NO in the exhaust purification system of_XNO from absorbent_XAlso
Is SO _XNO when should be released_XFlows into the absorbent
Oxygen in the exhaust and the oxygen concentration in the exhaust
Internal combustion that maintains the pressure within a predetermined set range
Engine exhaust purification device. Wherein _the NO _X absorbent sought amount of hydrocarbon attached to, as when the hydrocarbon content is often _the NO _X absorbent from N
Exhaust gas purification apparatus for an O _X or internal combustion engine according to claim 1 which is adapted to increase the oxygen concentration in the exhaust gas flowing to the NO _X absorbent when it should emit SO _X. Detecting a temperature of wherein _the NO _X absorbent, the oxygen concentration in the exhaust gas flowing to the NO _X absorbent when higher at high temperature from _the NO _X absorbent to be released the NO _X or SO _X 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is configured to be higher. Wherein the air-fuel ratio of the exhaust gas flowing absorbs NO _X when the lean engine and _the NO _X absorbent to the oxygen concentration in the inflowing exhaust gas to release NO _X which is absorbed to decrease the exhaust passage In the exhaust gas purifying apparatus for an internal combustion engine, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is temporarily reduced to release the NO _X or SO _X absorbed from the NO _X absorbent. An oxygen storage agent that stores oxygen when the oxygen concentration in the inflowing exhaust gas increases and releases the stored oxygen when the oxygen concentration in the inflowing exhaust gas decreases becomes NO _X
An exhaust gas purification device for an internal combustion engine provided in an absorbent. 5. provided _the NO _X absorbent in the hydrocarbon adsorbent, the hydrocarbon adsorbent adsorbs hydrocarbons when the temperature of the hydrocarbon adsorbent is low, high temperature of the hydrocarbon adsorbent The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 4, wherein the adsorbed hydrocarbons are desorbed.