JP2000018022A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) Abstract: SO _X released from SO _X absorbent NO _X
Prevents absorption by absorbent. NO that A fuel ratio of the exhaust gas flowing absorbs NO _X in the inflowing exhaust gas when the lean, the oxygen concentration in the inflowing exhaust gas emits NO _X that is absorbed to be lower
The _X absorbent 12 is disposed in the exhaust passage, the air-fuel ratio of the exhaust flowing absorbs SO _X in the exhaust gas flowing at the time of lean, the oxygen concentration in the inflowing exhaust gas is absorbed with lower SO _X the SO _X absorbent 9 release arranging the NO _X absorbent upstream of the exhaust passage. SO _X absorbent first from 9 when it should emit SO _X, if the air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent 12 to the stoichiometric air-fuel ratio _the NO _X absorbent 12
The residual oxygen in the inner removed, then SO _X fuel ratio of the exhaust gas flowing into the absorbent 9 in the rich SO _X from the absorbent 9 SO
Release _X.

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 air amount to the total fuel amount supplied into an exhaust passage, a combustion chamber, and an intake passage upstream of a certain position in an exhaust passage is determined by the air-fuel ratio of exhaust flowing through that position. when referred to, conventionally, 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 absorbed to be lower N to release are NO _X
O _X absorbent disposed engine exhaust passage, N in the exhaust and the air-fuel ratio of the mixture burned in the combustion chamber in the lean
O _X was allowed absorption in the NO _X absorbent, NO _X flowing into the absorbent inside Temporarily rich air-fuel ratio of the exhaust _the NO _X absorbent released NO _X with the release of NO _X that it is absorbed from the There is known an internal combustion engine configured to reduce the pressure.

However, fuel and engine lubricating oil contain
The exhaust contains SO, so SO_XIncludes
And this SO_XAlso for example SO_Four ^2-NO in the form of_XWith
NO _XAbsorbed by absorbent. However, this SO_XIs
NO_XSimply rich air-fuel ratio of exhaust gas flowing into the absorbent
But NO_XNot released from the absorbent and therefore NO
_XSO in absorbent_XWill gradually increase.
But NO_XSO in absorbent_XNO when the amount of
_XNO that can be absorbed by the absorbent_XAmount gradually decreases,
NO_XAbsorbent is NO_XCan hardly absorb
You.

Therefore, the air-fuel ratio of the inflowing exhaust gas is
SO in the exhaust that sometimes flows in_XAbsorbs and inflows exhaust
SO that is absorbed when the oxygen concentration in the inside decreases_XEmit
SO_XNO absorbent_XLocated in the exhaust passage upstream of the absorbent
A known exhaust gas purification device is known (JP-A-6-17365).
No. 2). In this exhaust gas purification apparatus, the SO _X
Is SO_XNO absorbed by the absorbent_XNO in the absorbent_Xof
Only will be absorbed.

[0005]

The object of the invention is to be Solved by the SO _X absorbent of SO _X
Since there is a limit in the absorption capacity, this exhaust gas purification device
O _X fuel ratio of the exhaust gas flowing into the absorbent temporarily made rich so that to release SO _X being absorbed from the SO _X absorbent. Considered In this case, since the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent becomes rich at this time SO _X released from the SO _X absorbent passes through _the NO _X absorbent without being absorbed in _the NO _X absorbent Can be However, for example, NO _X immediately after the air-fuel ratio of the exhaust gas flowing is rich in absorbent has still residual oxygen to the surface of the NO _X absorbent, since the oxygen concentration in _the NO _X absorbent surface does not decrease In addition, there is a problem that SO _X is absorbed in the NO _X absorbent.

[0006]

Means for Solving the Problems] According to the first invention to solve the above problems, the exhaust gas air-fuel ratio of the exhaust flowing absorbs NO _X in the inflowing exhaust gas when the lean, flows SO in the exhaust gas oxygen concentration is arranged _the NO _X absorbent in the engine exhaust passage that releases NO _X that is absorbed decreases, the air-fuel ratio of the exhaust gas flowing flows when the lean
Absorbs _X, place the SO _X absorbent oxygen concentration in the inflowing exhaust gas emits SO _X that is absorbed to be lower in the NO _X absorbent in or _the NO _X absorbent in the engine exhaust passage upstream of the combustion the sO _X in the exhaust air-fuel ratio of the mixture burned in chamber in the lean air-fuel ratio brought absorbed sO _X absorbent, temporarily rich air-fuel ratio of the exhaust gas flowing into the sO _X absorbent S absorbed from SO _X absorbent
In the exhaust purification system of an internal combustion engine in which the O _X to be released, the first removing the oxygen remaining in _the NO _X absorbent when it should emit SO _X from SO _X absorbent, then S
The air-fuel ratio of the exhaust gas flowing into the O _X absorbent to a rich SO
And so as to release the SO _X from _X absorbent. That is, in the first invention, since the SO _X is released from the SO _X absorbent after residual oxygen in _the NO _X absorbent is removed that SO _X is absorbed in the NO _X absorbent is prevented.

Further, in the first aspect according to the second aspect, by making the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent to intermediate air-fuel ratio between the rich air-fuel ratio and the lean air-fuel ratio followed by removal of residual oxygen in _the NO _X absorbent. That is, in the second invention, the SO _X absorbent removes the sulfur from the SO _X absorbent until the residual oxygen in the NO _X absorbent is removed.
With the O _X is released is prevented, the residual oxygen in _the NO _X absorbent can be reliably removed.

According to a third aspect, in the second aspect, the intermediate air-fuel ratio is substantially set to a stoichiometric air-fuel ratio. That is, in the third aspect, the residual oxygen in the NO _X absorbent is reliably and promptly removed. Further, in the fourth invention in the first invention according the air-fuel ratio sensor arranged in _the NO _X absorbent in the exhaust passage downstream of, residual oxygen in _the NO _X absorbent based on the output signal of the air-fuel ratio sensor It determines whether been removed, releasing the SO _X from the SO _X absorbent and the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent rich when the oxygen remaining in _the NO _X absorbent is judged to have been removed I try to make it. That is, in the fourth invention, N
Since O whether removal of _X absorbent in the residual oxygen has been completed can be reliably judged that the SO _X is absorbed in the NO _X absorbent it is reliably prevented.

In order to solve the above-mentioned problem, the fifth method
According to the invention, NOx is generated in an oxidizing atmosphere containing a reducing agent._X
Reduction type catalyst that selectively reacts with a reducing agent to reduce
In the engine exhaust passage to reduce the air-fuel ratio of the inflowing exhaust.
In the exhaust gas flowing in during_XAbsorbs and flows in
SO that is absorbed when the oxygen concentration in the exhaust gas becomes low_XTo
SO released_XAbsorbent in selective reduction catalyst or selective reduction
Placed in the engine exhaust passage upstream of the original catalyst,
Set the air-fuel ratio of the burnt mixture to a lean air-fuel ratio
SO in the air_XTo SO_XAbsorb in absorbent, SO_Xabsorption
The air-fuel ratio of the exhaust gas flowing into the agent is temporarily set to the rich air-fuel ratio.
SO_XSO absorbed from the absorbent _XRelease
In the exhaust gas purifying apparatus for an internal combustion engine, the SO_XSucking
SO from collector_XWhen it should be released, first selective reduction
To remove residual oxygen in the catalyst_XFlow into the absorbent
When the air-fuel ratio of the_XS from absorbent
O _XIs to be released. That is, the fifth departure
In the light, after the residual oxygen in the selective reduction catalyst is removed,
SO_XAbsorbent to SO_XIs released, so SO_XIs selected
Absorption by the reduced catalyst is prevented.

According to a sixth aspect, in the fifth aspect, the air-fuel ratio of the exhaust gas flowing into the selective reduction catalyst is set to an intermediate air-fuel ratio between the lean air-fuel ratio and the rich air-fuel ratio. The remaining oxygen in the selective reduction catalyst is removed. That is, in the sixth invention, the SO _X absorbent is prevented from releasing SO _X until the residual oxygen in the selective reduction catalyst is removed, and the residual oxygen in the selective reduction catalyst is reliably reduced. Removed.

According to a seventh aspect, in the sixth aspect, the intermediate air-fuel ratio is substantially set to a stoichiometric air-fuel ratio. That is, in the seventh invention, the oxygen remaining in the selective reduction catalyst is reliably and promptly removed. According to the eighth invention, in the fifth invention, the air-fuel ratio sensor is disposed in the exhaust passage downstream of the selective reduction catalyst, and the residual oxygen in the selective reduction catalyst is determined based on the output signal of the air-fuel ratio sensor. It is determined whether or not the oxygen has been removed, and when it is determined that the residual oxygen in the selective reduction catalyst has been removed, the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent is enriched to reduce SO 2 from the SO _X absorbent.
_X is released. That is, in the eighth invention, it is reliably determined whether or not the removal of the residual oxygen in the selective reduction catalyst has been completed, so that absorption of SO _X by the selective reduction catalyst is reliably prevented.

[0012]

FIG. 1 shows a case where the present invention is applied to a spark ignition engine. However, the present invention can be applied to a diesel engine. Referring to FIG. 1, the engine body 1 includes, for example, four cylinders 1a.
Each cylinder 1a is connected to a surge tank 3 via a corresponding intake branch pipe 2, and the surge tank 3 is connected to an intake duct 4
Through the air cleaner 5. A throttle valve 6 is arranged in the intake duct 4. Each cylinder 1a is provided with a fuel injection valve 7 for directly injecting fuel into the cylinder. Each cylinder 1a is connected to the casing 10 with a built-SO _X absorbent 9 through an exhaust manifold 8, the casing 10 is connected to the casing 13 with a built-in _the NO _X absorbent 12 via an exhaust pipe 11, the casing 13 is the exhaust pipe 1
4 is connected. The exhaust stroke order of the internal combustion engine of FIG. 1 is # 1- # 3- # 4- # 2.

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
An air-fuel ratio sensor 29 that generates an output voltage proportional to the air-fuel ratio of exhaust flowing through the exhaust pipe 14 is mounted on the exhaust pipe 14. These sensors 28, 29
Are input to the input port 26 via the corresponding AD converters 30, respectively. A vehicle speed sensor 31 for generating an output pulse representing the vehicle speed is provided at the input port 26.
And a rotation speed sensor 32 that generates an output pulse representing the engine rotation speed. In the CPU 24, a pressure sensor 28
The intake air amount is calculated based on the output voltage. on the other hand,
The output ports 27 are connected to the fuel injection valves 7 via corresponding drive circuits 33, respectively.

In the internal combustion engine shown in FIG. 1, for example, the fuel injection time T of the i-th cylinder (i = 1, 2, 3, 4) is calculated based on the following equation.
AU (i) is calculated. TAU (i) = TP · (A / F) S / (A / F) T
(I) where TP is the basic fuel injection time, (A / F) T (i)
Represents the target air-fuel ratio of the i-th cylinder, and (A / F) S represents the stoichiometric air-fuel ratio (= 14.6). The basic fuel injection time TP indicates the fuel injection time required to make the air-fuel ratio of the air-fuel mixture burned in the cylinder 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 target air-fuel ratio (A / F) T (i) is i
This is a target value of the air-fuel mixture burned in the combustion chamber of the cylinder No. The target air-fuel ratio (A / F) T (i) is normally set to a lean air-fuel ratio (A / F) L that is leaner than the stoichiometric air-fuel ratio (A / F) S in all cylinders, for example, 22.0. That is, the air-fuel ratio of the air-fuel mixture burned in the combustion chambers of all the cylinders is made lean.

FIG. 3 schematically shows the concentration of typical components in the exhaust gas discharged from the engine combustion chamber. As can be seen from FIG. 3, unburned HC and C in the exhaust gas discharged from the combustion chamber.
The amount of O increases as the air-fuel ratio of the mixture burned in the combustion chamber becomes richer, and the amount of oxygen O _{2 in} the exhaust gas discharged from the combustion chamber increases as the air-fuel ratio of the mixture burned in the combustion chamber becomes lean. It increases as it becomes.

NO _X contained in casing 13
The absorbent 12 is made of, for example, alumina as a carrier. On this carrier, for example, alkali metals such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La, and yttrium Y are used. At least one selected from such rare earths and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir are supported. This NO
_X absorbent 12 absorbs NO _X when the air-fuel ratio of the exhaust gas flowing is lean, perform absorption and release action of the NO _X that releases NO _X to the oxygen concentration in the exhaust gas absorbed and reduced flowing. The air to the sum of the air-fuel ratio is the amount of fuel supplied to the combustion chamber of each cylinder of the exhaust gas flowing to the NO _X absorbent 12 when the fuel or air is not supplied to _the NO _X absorbent 12 upstream of the exhaust passage match ratio of the total amount, in particular the target air-fuel ratio (a / F) T (i ) the air-fuel ratio the target air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 12 when the same for each cylinder (a / F) coincides with T (i).

If the above-described NO _X absorbent 12 is arranged in the exhaust passage of the engine, the NO _X absorbent 12 actually performs the absorption and release of NO _X , but the detailed mechanism of the absorption and release is not clear. There is also. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIGS. 4 (A) and 4 (B). Next, regarding this mechanism, platinum Pt and barium Ba are deposited on the carrier.
Will be described as an example in the case of carrying other precious metals,
The same mechanism is obtained by using an alkali metal, an alkaline earth, or a rare earth.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases.
As shown in (A), these oxygens O ₂ adhere to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ . On the other hand, NO in the exhaust gas that flows in reacts with O ₂ ⁻ or O ²⁻ on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ). Then part of the produced NO ₂ while bonding with the barium oxide BaO is absorbed into the absorbent while being further oxidized on the platinum Pt, 4 nitrate as shown in (A) ions NO ₃ ^- in It diffuses into the absorbent in form. Thus N
O _X is absorbed in the NO _X absorbent 12.

The NO ₂ is produced on the surface of the oxygen concentration is as high as platinum Pt in the inflowing exhaust gas, as long as NO ₂ to NO _X absorbing capacity of the absorbent is not saturated is absorbed in the absorbent and nitrate ions NO ₃ ^- Is generated. On the other hand, when the oxygen concentration in the exhaust gas that flows in decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ions NO ₃ ⁻ There are released from the absorbent in the form of NO _2. That is, the oxygen concentration in the inflowing exhaust gas are released NO _X from _the NO _X absorbent 12 when lowered. As shown in FIG. 3, if the degree of lean of the inflowing exhaust gas decreases, the oxygen concentration in the inflowing exhaust gas decreases,
Therefore, if the degree of lean of the inflowing exhaust gas is reduced, N
NO _X will be released from the O _X absorbent 12.

On the other hand, if the air-fuel ratio of the inflowing exhaust gas is made rich at this time, a large amount of unburned HC and CO is discharged from the engine as shown in FIG. O ₂ ^- or are oxidized by reacting with O ^2-. Further, when the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas extremely decreases, so that NO ₂ is released from the absorbent, and this NO ₂ is unreacted as shown in FIG. It is reduced by reacting with the fuel HC and CO. In this way, when NO ₂ is no longer present on the surface of platinum Pt, NO ₂ is released from the absorbent one after another. Therefore NO _X from _the NO _X absorbent 12 in a short time when the air-fuel ratio of the exhaust gas flowing into the rich is to be released.

As described above, the target air-fuel ratio (A /
F) T (i) is an air-fuel ratio of the normal because it is a lean air-fuel ratio (A / F) L flowing to the NO _X absorbent 12 exhaust is usually a lean air-fuel ratio (A / F) L, therefore at this time NO _X in the exhaust gas is absorbed by the NO _X absorbent 12. However, the the NO _X absorbing capacity of the NO _X absorbent 12 is necessary to release the NO _X from _the NO _X absorbent 12 before the NO _X absorbing capacity of the NO _X absorbent 12 is saturated because there is a limit.
Therefore, in the internal combustion engine shown in FIG. 1, of the NO _X absorbent 12 N
O _X absorption is the target air-fuel ratio of all the cylinders when it is more than the set predetermined amount of (A / F) T (i ) temporarily rich air-fuel ratio (A / F) RN, for example, 10. 0 and N
The air-fuel ratio of the exhaust gas flowing into the O _X absorbent 12 rich,
Thereby, NO _X is released from the NO _X absorbent 12 and reduced.

However, the inflowing exhaust gas contains sulfur, and the NO _x absorbent 12 absorbs not only NO _x but also sulfur such as SO _x . It is considered that the mechanism of sulfur absorption into the NO _X absorbent 12 is the same as the mechanism of NO _X absorption. That is, as described in the description of the NO _x absorption mechanism, platinum P
Taking the case where t and barium Ba are carried as an example, as described above, when the air-fuel ratio of the inflowing exhaust gas is lean, oxygen P ₂ is converted to platinum P ^{2 in} the form of O ₂ ⁻ or O ^2−.
At the surface of platinum Pt, SO _X, for example, SO ₂ attached to the surface of platinum Pt reacts with O ₂ ⁻ or O ²⁻ to form SO ₃ . Next, the generated SO ₃ is further oxidized on the platinum Pt, is absorbed in the absorbent, and is bonded to barium oxide BaO, and diffuses into the absorbent in the form of sulfate ions SO ₄ ^2- . Next, this sulfate ion SO ₄ ^2- is combined with barium ion Ba ²⁺ to form sulfate BaSO ₄ .

However, this sulfate BaSO_FourDecomposes
It is difficult to simply enrich the air-fuel ratio of the inflowing exhaust
Sulfate BaSO_FourRemains undisassembled. But
NO_XAs time passes, sulfuric acid is contained in the absorbent 12.
Acid salt BaSO_FourIncrease, and thus the time
NO as time goes by_XNO that can be absorbed by the absorbent 12 _X
The amount will be reduced.

[0025] In this embodiment, NO _X absorbent 12
The so SO _X does not flow, the air-fuel ratio of the exhaust flowing absorbs SO _X when the lean, the oxygen concentration in the inflowing exhaust gas to release SO _X are absorbed to decrease SO _X
The absorbent 9 are arranged in _the NO _X absorbent 12 upstream of the exhaust passage. As described above, when SO _X is absorbed by the NO _X absorbent 12, stable sulfate BaSO ₄ is formed. As a result, even if the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 12 is simply made rich, the SO _X Are not released from the NO _x absorbent 12. Therefore, when the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 is made rich, the SO _X absorbent 9
_In order to facilitate the release of _X , the absorbed SO
Either _X is present in the absorbent in the form of sulfate ion SO ₄ ²⁻ or, even if sulfate BaSO ₄ is produced, sulfate BaSO ₄ is present in the absorbent in an unstable state. It is necessary to do. S that makes this possible
O _X absorbent iron Fe is on a support made of, for example, alumina as 9, manganese Mn, nickel Ni, at least one selected from transition metals and lithium Li, such as tin Sn
An absorbent carrying one can be used.

In the SO _X absorbent 9, when the air-fuel ratio of the inflowing exhaust gas is lean, the SO ₂ contained in the exhaust gas is oxidized on the surface of the absorbent while entering into the absorbent in the form of sulfate ions SO ₄ ^2-. Absorbed and then diffused into the absorbent. In this case, if platinum Pt is supported on the carrier of the SO _X absorbent 9, SO ₂ easily adheres to the platinum Pt in the form of SO ₃ ^2- ,
Thus to SO ₂ is likely to be absorbed into the absorbent in the sulfate ions SO ₄ ^2-form. Therefore, in order to promote the absorption of SO ₂ , it is preferable to carry platinum Pt on the carrier of the SO _X absorbent 9.

As described above, SO_XFlows into absorbent 9
The exhaust air-fuel ratio is usually lean and
SO_XIs SO_XAbsorbed by absorbent 9, NO_XAbsorbent 1
NO for 2_XOnly will be absorbed. However, S
O_XSO of absorbent 9_XThere is a limit in absorption capacity, and SO_X
SO of absorbent 9_XSO before the absorption capacity is saturated_XAbsorbent
9 to SO_XMust be released. So this embodiment
In SO_XSO absorbed in absorbent 9_XQuantity
SO when the amount exceeds the set amount_Xabsorption
The air-fuel ratio of the exhaust gas flowing into the agent 9 is temporarily changed to the rich air-fuel ratio.
(A / F) RS, e.g. 13.0, so that SO
_XAbsorbent 9 to SO_XIs to be released.

[0028] However, SO _X from SO _X absorbent 9 even if the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 rich when the temperature is low SO _X absorbent 9 is not released, i.e. SO _X absorbed When SO _X is to be released from the agent 9, the temperature of the SO _X absorbent 9 needs to be raised. On the other hand, S
O _X absorbent large amount in the exhaust gas flowing into the 9 unburned HC, CO
And a large amount of oxygen O ₂ is contained at the same time these unburned HC, the temperature of CO and oxygen O ₂ react in SO _X absorbent 9 SO _X absorbent 9 is raised. Further, FIG.
As can be understood from FIG. 2, if the target air-fuel ratio of the cylinder is set to the rich air-fuel ratio, a large amount of unburned H
C and CO are included, and a large amount of oxygen O
₂ is included.

Therefore, in the internal combustion engine of FIG. 1, the target air-fuel ratios (A / F) T (1), (A / F) of the first and fourth cylinders.
F) T (4) is set to lean air-fuel ratio (A / F) LL, for example, 1
6.0, the target air-fuel ratio of the second cylinder and the third cylinder (A /
F) T (2) and (A / F) T (3) are converted to the rich air-fuel ratio (A
/ F) R, for example, 10.0, whereby the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 is set to the above-described rich air-fuel ratio (A
/ F) In addition to RS, a large amount of unburned HC, CO and oxygen O ₂ are supplied to the SO _X absorbent 9.

[0030] That is, generally speaking, the cylinder of the internal combustion engine first cylinder group, divided into the second cylinder group and the exhaust stroke first cylinder group do not overlap, the SO _X absorbent 9 SO
When it should emit _X is the air-fuel ratio of the mixture burned in the cylinders of the first cylinder group lean, the air-fuel ratio of the mixture burned in the cylinders of the second cylinder group rich, whereby SO _X This means that the air-fuel ratio of the entire exhaust gas flowing into the absorbent 9 is made rich.

[0031] SO Since _X fuel ratio of the exhaust gas air-fuel ratio of the exhaust gas flowing into the absorbent 9 flows into _the NO _X absorbent 12 becomes rich becomes rich, SO _X at this time is released from the SO _X absorbent 9 is believed to pass through _the NO _X absorbent 12 without being absorbed in the NO _X absorbent 12. However, for example, immediately after the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 is switched from lean to rich, oxygen still remains on the surface of the NO _X absorbent 12 and the NO _X absorbent 1
The second surface SO _X released from the SO _X absorbent 9 for the oxygen concentration does not drop is absorbed in the NO _X absorbent 12.

Therefore, in the internal combustion engine shown in FIG. 1, when SO _X is to be released from the SO _X absorbent 9, first, the residual oxygen in the NO _X absorbent 12 is removed, and then the SO _X absorbent 9 is removed.
The air-fuel ratio of the exhaust gas flowing into in the rich SO _X absorbent 9
And so as to release the SO _X from. The target air-fuel ratio (A / F) T (i) of each cylinder is set to the lean air-fuel ratio (A / F) L
Can be reduced smaller to residual oxygen in _the NO _X absorbent 12 by reducing the degree of leanness of the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 12 than, too much too small i.e. the rich NO _X absorbent SO _X from SO _X absorbent 9 before residual oxygen removal agent 12 is completed from being released. Therefore, in the internal combustion engine of FIG. 1, NO _X absorbent 1
2 to remove the residual oxygen in the cylinder 2, the target air-fuel ratio (A / F) T (i) of all the cylinders is changed to the normal lean air-fuel ratio (A / F).
F) An intermediate air-fuel ratio between L and the rich air-fuel ratio (A / F) RS when SO _X is to be released.

In particular, in the internal combustion engine shown in FIG. 1, the intermediate air-fuel ratio is set to the stoichiometric air-fuel ratio (A / F) S. In this way, S
While preventing SO _{X from} being released from the O _X absorbent 9, N
The residual oxygen O _X absorbent 12 can be quickly removed. The intermediate air-fuel ratio may be slightly leaner than the stoichiometric air-fuel ratio (A / F) S, or may be slightly richer than the stoichiometric air-fuel ratio (A / F) S.

The air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 12 is lean air-fuel ratio (A / F) the stoichiometric air-fuel ratio from L (A / F)
Air-fuel ratio of the exhaust gas flowing out is switched to the S from _the NO _X absorbent 12, namely air-fuel ratio detected air-fuel ratio sensor 29 is gradually decreased, NO _X when the removal of residual oxygen absorber 12 is completed air-fuel ratio sensor 29 Is the stoichiometric air-fuel ratio (A / F) S. Therefore, in the internal combustion engine of FIG.
The air-fuel ratio detected by the air-fuel ratio sensor 29 is the stoichiometric air-fuel ratio (A / F)
So that starting the SO _X release action from SO _X absorbent 9 and the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 rich when they become S.

[0035] That is, as shown in FIG. 5, SO _X
When SO _X is to be released from the absorbent 9 (time a), first, the target air-fuel ratio (A / F) TN of the exhaust gas flowing into the NO _X absorbent 12 is set to the stoichiometric air-fuel ratio (A / F) S. You. Then, when the detected air-fuel ratio (A / F) D of the air-fuel ratio sensor 29 becomes the stoichiometric air-fuel ratio (A / F) S (time b) NO _X absorbent 1
The target air-fuel ratio (A / F) TN of the exhaust flowing into the second air-fuel ratio 2 is defined as a rich air-fuel ratio (A / F) RS. Next, for example, after a lapse of a predetermined time (time c), the target air-fuel ratio (A / F) TN of the exhaust gas flowing into the NO _X absorbent 12 becomes the lean air-fuel ratio (A
/ F) is returned to L.

The target air-fuel ratio of each cylinder (A / F) T
(I) is a lean air-fuel ratio (A / F) temperature of the exhaust gas temporarily stoichiometric from L (A / F) is switched to the S flowing into the SO _X absorbent 9 becomes high SO _X absorbent 9 Temperature rises. As a result, when the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 is enriched, SO _X is immediately released.

FIG. 6 shows a routine for executing the above-mentioned SO _X release control. This routine is executed by interruption every predetermined set time. Referring to FIG. 6, first, at step 40, it is determined whether or not the SO _X flag is set. This SO _X flag is set when should the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 in order to release the SO _X from the SO _X absorbent 9 to rich, and the other is reset. When the SO _X flag has been reset, the routine proceeds to step 41, where it is determined whether or not the O ₂ flag has been set. This O ₂ flag is set when the residual oxygen in the NO _X absorbent 12 is to be removed, and reset otherwise. When the O ₂ flag has been reset, the routine proceeds to step 42, where it is determined whether the SO _X release condition has been satisfied. SO _X for example when higher than the set temperature the temperature predetermined for SO _X absorbent 9 absorbed and more than SO _X amount set amount is SO _X absorbent 9
It is determined that the release condition is satisfied, otherwise SO
It is determined that the _X release condition is not satisfied. As described above in the internal combustion engine of FIG. 1, SO _X absorbent 9 in a large amount of unburned HC, increasing the temperature of the SO _X absorbent 9 by supplying CO and oxygen, whereby SO from SO _X absorbent 9 _X Is to be released. Therefore, SO _X when so as to release the SO _X from the SO _X absorbent 9 when the temperature of the absorbent 9 is rather low, a large amount of unburned H for a long time
C and CO must be supplied to the SO _X absorbent 9, and the fuel consumption rate is reduced. Therefore, in the internal combustion engine of FIG.
_{When the} SO _X amount absorbed in the _X absorbent 9 is larger than the set amount and the temperature of the SO _X absorbent 9 is higher than the set temperature, it is determined that the SO _X release condition is satisfied. I have. Incidentally, SO _X absorbed in the SO _X absorbent 9
The amount and the temperature of the SO _X absorbent 9 can be estimated, for example, based on the operating state of the engine.

The SO _X release condition is the processing cycle is ended when it is determined not to be satisfied, SO _X when the release condition is determined to be satisfied then step 43
O ₂ flag is set the routine proceeds to. When O ₂ flag is set, the process proceeds from step 41 to step 44, the detected air-fuel ratio (A / F) D of the air-fuel ratio sensor 29 whether the stoichiometric air-fuel ratio (A / F) S less is determined. (A /
F) When D> (A / F) S, the processing cycle ends. When (A / F) D ≦ (A / F) S, it is determined that the removal of the residual oxygen in the NO _X absorbent 12 has been completed, and then the routine proceeds to step 45, where the O ₂ flag is reset. In the following step 46, the SO _X flag is set.

When the SO _X flag is set, the process proceeds from step 40 to step 47, and it is determined whether a predetermined time has elapsed since the SO _X flag was set.
If the fixed time has not elapsed, the processing cycle ends. If a certain time has elapsed, then step 48
Then, the SO _X flag 48 is reset, and in the following step 49, the NO _X flag is reset or maintained in a reset state. The NO _X flag is set when should the air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent 12 so as to release the NO _X from _the NO _X absorbent 12 rich, the other is reset.

That is, when the SO _X flag is set and S
When the air-fuel ratio of the exhaust gas flowing into the O _X absorbent 9 is made rich, NO air-fuel ratio of the exhaust gas flowing into the _X absorbent 12 becomes rich, NO _X which is absorbed from the time _the NO _X absorbent 12 Is released and reduced. SO of SO _X absorbent 9
_{Since the X} releasing action is generally performed for a longer time than the NO _X releasing action of the NO _X absorbent 12, the SO _X absorbent 9
When the SO _X releasing action of the NO _X absorbent 12 is completed,
NO _X release action also has been completed. Therefore, when the SO _X flag is reset, the NO _X flag is reset or maintained in a reset state.

FIG. 7 shows the above-mentioned NO._XPerform release control
FIG. This routine is predefined
This is executed by an interrupt at each set time. Figure 7
For reference, first, in step 60, the above-described NO_XHula
It is determined whether the tag is set. NO_XHula
If the flag is reset, then go to step 61
Proceed, NO_XIt is determined whether the release condition is satisfied or not.
You. For example, NO_XNO absorbed in the absorbent 12_X
NO when the amount is larger than the set amount _XThe release condition is satisfied
Is determined to be present, otherwise NO_XThe release condition is satisfied
It is determined that they have not. Note that NO_XAbsorbed by absorbent 12
NO_XThe quantity is estimated, for example, based on the engine operating conditions.
Can be specified. NO_XRelease condition not satisfied
When it is determined that the processing cycle is completed,_XRelease
When it is determined that the exit condition is satisfied,
Go to step 62 and NO_XThe flag is set.

When the NO _X flag is set, the process proceeds from step 60 to step 63, and it is determined whether a predetermined time has elapsed since the NO _X flag was set.
If the fixed time has not elapsed, the processing cycle ends. If a certain time has elapsed, then step 64
And the NO _X flag is reset. FIG. 8 shows a routine for calculating the fuel injection time TAU (i) of each cylinder. This routine is executed by interruption every predetermined set crank angle.

Referring to FIG. 8, first, at step 70, the basic fuel injection time TP is calculated from the map of FIG.
In a succeeding step 71, it is determined whether or not the above-mentioned SO _X flag is set. When the SO _X flag is set, the routine proceeds to step 72, where the target air-fuel ratios (A / F) T (1), (A) of the first cylinder and the fourth cylinder are set.
/ F) T (4) is the lean air-fuel ratio (A / F) LL,
Target air-fuel ratio (A / F) T of the second and third cylinders
(2), (A / F) T (3) is the rich air-fuel ratio (A / F)
R. Next, the routine proceeds to step 78.

When the SO _X flag has been reset, the routine proceeds from step 71 to step 73, where it is determined whether or not the O ₂ flag has been set. When the O ₂ flag is set, the routine proceeds to step 74, where the target air-fuel ratio (A / F) T (i) of all cylinders is set to the stoichiometric air-fuel ratio (A
/ F) S. Next, the routine proceeds to step 78. When O ₂ flag is reset, the process proceeds from step 73 to step 75, whether the NO _X flag has been set or not. Routine goes to step 76 when the NO _X flag is set, the target air-fuel ratio of all cylinders (A / F) T (i ) is a rich air-fuel ratio (A / F) RN. Next, the routine proceeds to step 78.

When the NO _X flag is reset, the routine proceeds from step 75 to step 77, where the target air-fuel ratio (A / F) T (i) of all cylinders is set to the lean air-fuel ratio (A / F) L.
It is said. Next, the routine proceeds to step 78. In step 78, the fuel injection time TAU (i) of the i-th cylinder is calculated based on the following equation.
Is calculated.

TAU (i) = TP · (A / F) S / (A
/ F) T (i) By the way, NO as described above _X absorbent 12 is capable of absorbing SO _X, absorbs the oxygen concentration in the inflowing exhaust gas when the temperature of the NO _X absorbent 12 is high to decrease SO
Release _X. Therefore, NO _X absorbent 12 is SO _X
It is also a function of the absorbent, i.e. the same as the provision of the SO _X absorbent in _the NO _X absorbent. Therefore, even when placing the _the NO _X absorbent without arranging the SO _X absorbent in the engine exhaust passage can be applied to the present invention.

Further, a so-called selective reduction type catalyst may be used instead of the NO _x absorbent 12. This selective reduction catalyst is prepared by depositing a noble metal such as platinum Pt, palladium Pd, rhodium Rh, iridium Ir, or copper C on a porous support such as zeolite, mordenite, alumina Al ₂ O _3.
The transition metal such as u, iron Fe, cobalt Co, and nickel Ni is supported and formed. As the zeolite, for example, a zeolite containing high silica such as ZSM-5 type, ferrierite, and mordenite can be used. This selective reduction catalyst selectively reacts NO _X with unburned HC and CO in an oxygen atmosphere containing a reducing agent such as unburned HC and CO, thereby reducing NO _X to nitrogen N _2. Can be. In this case, it is considered that NO _X is temporarily attached to the surface of the catalyst metal, for example, platinum Pt, and is reduced.

When the air-fuel ratio of the inflowing exhaust gas is lean, the selective reduction catalyst adsorbs SO _X in the inflowing exhaust gas. Although the mechanism of this SO _X adsorption action is not clear, it is considered that the mechanism is performed by the following mechanism. That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and oxygen O ₂ adheres to the surface of the catalytic metal, for example, platinum Pt in the form of O ₂ ⁻ or O ²⁻ . On the other hand, SO ₂ in the flowing exhaust gas reacts with O ₂ ⁻ or O ^{2− on} the surface of platinum Pt and is adsorbed on the surface of platinum Pt in the form of SO ₃ ²⁻ or SO ₄ ²⁻ . Thus, SO _X is adsorbed on the selective reduction catalyst.

However, SO _{X in} the form of SO ₃ ²⁻ or SO ₄ ²⁻ can reduce platinum concentration even if the oxygen concentration in the inflowing exhaust gas is simply reduced or the concentration of the reducing agent is increased.
As the time elapses, the amount of SO _X covering the platinum Pt surface increases, and thus the amount of NO _X that can be reduced by the selective reduction catalyst decreases as time elapses. Will be.

Therefore, if an SO _X absorbent is disposed in the exhaust passage upstream of the selective reduction catalyst, it is possible to prevent SO _X from flowing into the selective reduction catalyst, and to reduce the SO _X absorbent from the SO _X absorbent.
The O _X fuel ratio of the exhaust gas flowing into the SO _X absorbent after removal of the remaining oxygen of the selective reduction in catalyst when it should be released to the selective reduction catalyst when the rich SO _X is prevented from being adsorbed Can be.

When the air-fuel ratio of the exhaust gas flowing into the selective reduction catalyst is made rich when the temperature of the selective reduction catalyst is high, the adsorbed SO _X is desorbed from the selective reduction catalyst. Therefore, the selective reduction catalyst also has the function of an SO _X absorbent, that is, it is the same as providing the SO _X absorbent in the selective reduction catalyst.

[0052]

SO _X released from the SO _X absorbent according to the present invention is N
It can be prevented from being absorbed by the _OX absorbent.

[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 schematically showing concentrations of unburned HC, CO, and oxygen in exhaust gas discharged from an engine.

FIG. 4 is a diagram for explaining the effect of absorbing and releasing NO _X.

FIG. 5 is a time chart for explaining SO _X release control.

FIG. 6 is a flowchart for executing SO _X release control.

FIG. 7 is a flowchart for executing NO _X release control.

FIG. 8 is a flowchart for calculating a fuel injection time.

[Explanation of symbols]

1 ... engine body 8 ... exhaust manifold 9 ... SO _X absorbent 12 ... NO _X absorbent 29 ... air-fuel ratio sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 305 F02D 41/04 305A 43/00 301 43/00 301H 301T (72) Inventor Toshiaki Tanaka Aichi 1 Toyota Town, Toyota City F-term in Toyota Motor Corporation (reference) 3G084 AA03 AA04 BA13 BA24 DA10 DA27 EB12 FA05 FA11 FA29 FA33 3G091 AA02 AA12 AA17 AA24 AA28 AB06 AB08 BA01 BA11 BA14 BA20 BA32 BA33 CA18 CB02 DB10 DC03 EA EA34 EA39 FB10 FB11 FB12 GB01W GB01X GB05W GB06W GB07W GB09X GB10X HA08 HA20 HA37 HA47 3G301 HA01 HA06 HA15 JA21 JA25 JA33 JB09 LB04 MA13 NC02 NE01 NE06 NE13 NE14 NE15 PA07A PD02A PE01A PE03A PE05APF01

Claims (8)

[Claims] 1. When the air-fuel ratio of the inflowing exhaust gas is lean
NO in inflowing exhaust_XAbsorb and absorb acid in the exhaust
NO absorbed as element concentration decreases_XReleases NO
_XThe absorbent is placed in the engine exhaust passage, and the exhaust
SO in the exhaust flowing in when the fuel ratio is lean_XAbsorb
And absorbs when the oxygen concentration in the
SO_XReleases SO_XNO absorbent_XIn the absorbent
Is NO_XLocated in the engine exhaust passage upstream of the absorbent, the combustion chamber
The air-fuel ratio of the air-fuel mixture burned inside the engine to a lean air-fuel ratio
SO in exhaust_XTo SO_XAbsorb in absorbent, SO
_XThe air-fuel ratio of the exhaust flowing into the absorbent is temporarily set to rich air-fuel.
SO as a ratio_XSO absorbed from the absorbent_XRelease
In the exhaust gas purifying apparatus for an internal combustion engine,
O_XAbsorbent to SO_XShould be released first
O_XThe residual oxygen in the absorbent is removed and then the SO 2_XAbsorbent
The air-fuel ratio of the exhaust gas flowing into the _XAbsorbent or
SO_XExhaust emission control device for internal combustion engine that emits gas
Place. Wherein to remove residual oxygen in _the NO _X absorbent by making the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent to intermediate air-fuel ratio between the rich air-fuel ratio and the lean air-fuel ratio The exhaust gas purification device for an internal combustion engine according to claim 1. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein said intermediate air-fuel ratio is substantially set to a stoichiometric air-fuel ratio. The air-fuel ratio sensor arranged wherein _the NO _X absorbent in the exhaust passage downstream of the residual oxygen in _the NO _X absorbent is determined whether or not removed on the basis of the output signal of the air-fuel ratio sensor, claim 1 to the air-fuel ratio of the exhaust gas flowing into the sO _X absorbent rich from sO _X absorbent so as to release the sO _X when the oxygen remaining in _the NO _X absorbent is judged to have been removed Exhaust purification device for internal combustion engine. 5. An atmosphere containing NO _{x in} an oxidizing atmosphere containing a reducing agent
A selective reduction catalyst that selectively reacts with the reducing agent to reduce the oxygen is disposed in the engine exhaust passage, absorbs the SO _X in the inflowing exhaust when the air-fuel ratio of the inflowing exhaust is lean, and exhausts the inflowing exhaust. oxygen concentration of arranged absorbed by the SO _X absorbent releases the SO _X are selected in reduction catalyst or a selective reduction catalyst in the engine exhaust passage upstream of low in, the mixture burned in the combustion chamber and the air-fuel ratio to the lean air-fuel ratio allowed absorb sO _X in the exhaust gas sO _X absorbent is absorbed from the sO _X absorbent to temporarily rich air-fuel ratio of the exhaust gas flowing into the sO _X absorbent in the exhaust purification system of an internal combustion engine which is adapted to release sO _X who is, the first removing the residual oxygen of the selective reduction the catalyst when it should emit sO _X from sO _X absorbent, and then flows into the sO _X absorbent Exhaust air-fuel ratio From SO _X absorbent to S
An exhaust purification system of an internal combustion engine which is adapted to release O _X. 6. A method for removing residual oxygen in a selective reduction catalyst by setting an air-fuel ratio of exhaust gas flowing into a selective reduction catalyst to an intermediate air-fuel ratio between the lean air-fuel ratio and the rich air-fuel ratio. An exhaust gas purifying apparatus for an internal combustion engine according to claim 5. 7. The exhaust gas purifying apparatus for an internal combustion engine according to claim 6, wherein said intermediate air-fuel ratio is substantially set to a stoichiometric air-fuel ratio. 8. An air-fuel ratio sensor is disposed in an exhaust passage downstream of the selective reduction catalyst, and it is determined whether or not residual oxygen in the selective reduction catalyst has been removed based on an output signal of the air-fuel ratio sensor. claim 5 which is adapted to release sO _X from sO _X absorbent and the air-fuel ratio of the exhaust gas flowing into the sO _X absorbent rich when the oxygen remaining selective reduction in the catalyst is judged to have been removed Exhaust purification device for internal combustion engine.