JP2000274279A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent unwanted regeneration operation of an NOX storing and reducing catalyst. SOLUTION: In this exhaust emission control device, an NOX storing and reducing catalyst 7 is disposed in an exhaust passage 2 of an engine 1, while an O2 sensor 31 and an NOX sensor 33 disposed in the exhaust passage 2 on the downstream side of the catalyst 7, respectively detect an air-fuel ratio and NOX density of exhaust emission passing through the catalyst 7. An electronic control unit(ECU) 30 of the engine 1 allows execution of regeneration operation to discharge stored NOX from the catalyst 7 by operating the engine 1 in a rich air-fuel ratio for a short time when the NOX density detected by the NOX sensor 33 becomes a prescribed value or above. The ECU 30 prohibits the execution of the regeneration operation, while the exhaust air-fuel ratio detected by the sensor 31 is the rich air-fuel ratio after starting of the regeneration operation. Thereby, unpurified NOX discharged from the catalyst 7 at an early stage of the regeneration operation is not detected by the NOX sensor 33 after the regeneration operation to prevent the execution of the unnecessary regeneration operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to a method for absorbing NO _X in exhaust gas when the air-fuel ratio of the flowing exhaust gas is lean, thereby reducing the concentration of oxygen in the flowing exhaust gas. NO that releases absorbed NO _X when lowered
_{The present} invention relates to an exhaust gas purification device for an internal combustion engine using an _X storage reduction catalyst.

[0002]

Examples of the exhaust purification apparatus using the Related Art _the NO _X storage reduction catalyst of this type, for example, JP-A-7-16685
There is one described in Japanese Patent Publication No. The apparatus of the publication, the placing _the NO _X storage reduction catalyst in an exhaust passage of an internal combustion engine, _the NO _X storage reduction catalyst with NO _X sensor for detecting the concentration of NO _X in the exhaust gas of the NO _X occluding and reducing catalyst downstream it is obtained so as to monitor the concentration of NO _X in the exhaust gas that has passed through the. NO _X when the concentration of NO _X in the exhaust gas of the NO _X occluding and reducing catalyst downstream exceeds a predetermined value in the apparatus of the publication
When the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is made rich, N
NO _X absorbed from the O _X storage reduction catalyst is released for reduction purification.

[0003] NO_XThe occlusion reduction catalyst, the absorbed NO_Xamount
Increases as NO increases_XStorage capacity decreases.
That is, NO_XNO when no water is absorbed_X
NO of storage reduction catalyst_XThe storage capacity is the highest,
NO in inflowing exhaust_XIs mostly NO_XStorage reduction catalyst
NO in the inflow exhaust gas_XConcentration is relatively high
NO even if it's gone_XN in exhaust gas after passing through the storage reduction catalyst
O_XThe concentration will be lower. But NO_XIn the storage reduction catalyst
NO absorbed_XAmount (NO_XStorage capacity)
NO_XNO of storage reduction catalyst_XStorage capacity decreases and inflow
NO in exhaust gas_XNO_XAbsorbed by storage reduction catalyst
The amount of material that passes through the catalyst without being increased increases. For this reason,
NO_XNO of storage reduction catalyst_XAs the amount of storage increases
NO in exhaust gas after passing through the catalyst_XConcentration increases, during inflow exhaust
NO_XIt approaches the concentration. And NO_XOcclusion
NO absorbed by the reduction catalyst_XWhen it becomes saturated at
O _XNO in the exhaust gas_XCan not absorb at all
NO in the exhaust after passing_XThe concentration is
NO_XIt will be at the same level as the concentration.

[0004] As described above, NO _X NO of storage reduction catalyst
_{The X} storage capacity decreases as the NO _X storage amount increases,
When the storage amount reaches the saturation amount, the NO _X storage reduction catalyst does not absorb NO _X in the exhaust at all. Therefore, NO _X in order to prevent occlusion saturation reduction catalyst constantly monitors _the NO _X storage amount of the NO _X occluding and reducing catalyst, NO from _the NO _X storage reduction catalyst before the storage amount reaches the saturation amount _It is necessary to perform _X release and reduction purification. However, in practice, it is sometimes difficult to accurately determine the amount of NO _X stored in the NO _X storage reduction catalyst. The maximum amount of NO _X occluding possible of the NO _X occluding and reducing catalyst (saturation amount) decreases with the deterioration of the NO _X occluding and reducing catalyst. Therefore, since when degraded to _the NO _X storage capability in a small amount of occlusion in the catalyst is reduced occurs, even if it is possible to determine if exactly the _the NO _X storage amount of the NO _X occluding and reducing catalyst, _the NO _X storage There is a case where the saturation of the NO _X storage reduction catalyst cannot be prevented only by the determination based on the amount alone.

[0005] In the apparatus of the above publication, N each time the concentration of NO _X in the exhaust gas after _the NO _X storage reduction catalyst passage reaches a predetermined value
O _X occluding and reducing catalyst of the exhaust air-fuel ratio flowing in the rich air-fuel ratio to release NO _X absorbed from _the NO _X storage reduction catalyst, thereby preventing a decrease in storage capacity of the NO _X occluding and reducing catalyst by reduction purification I have. In the following description, N
O _X occluding and reducing catalyst of the exhaust air-fuel ratio flowing in the rich air-fuel ratio to release NO _X absorbed from _the NO _X storage reduction catalyst, and that the operation of reduction purification is referred to as "regeneration operation" of the NO _X occluding and reducing catalyst I do.

When the NO _X storage reduction catalyst is deteriorated, the storage capacity is greatly reduced as compared with the case where there is no deterioration even with the same NO _X storage amount, and the NO _X concentration in the passing exhaust gas is increased. Therefore, as in the device of the Japanese Patent 7-166851 discloses was detected using the NO _X sensor NO
By performing a regeneration operation every time the NO _X concentration in the exhaust gas passing through the _X storage reduction catalyst reaches a predetermined value, the saturation of the NO _X storage reduction catalyst is reliably prevented, and the storage capacity of the NO _X storage reduction catalyst is reduced. It can be prevented from being used continuously in the state where it was done.

[0007]

[0008] However, as the concentration of NO _X in _the NO _X storage reduction catalyst passing exhaust as device of the Japanese Patent 7-166851 discloses to perform a reproduction operation for each to reach a predetermined value May cause problems. In the NO _X storage reduction catalyst, a relatively large amount of unpurified NO _X may be discharged to the downstream side at the beginning of the regeneration operation, that is, immediately after the air-fuel ratio of the inflowing exhaust gas changes from the lean air-fuel ratio to the rich air-fuel ratio. As described later, in this specification, the release of unpurified NO _X from the NO _X storage reduction catalyst occurring at the initial stage of the regeneration operation is referred to as “NO _X discharge” for convenience. This discharge of NO _X is completed in a short time, and thereafter, unpurified NO _X is not released.
O _X immediately after the start of the regenerating operation of the storage-reduction catalyst in the exhaust gas passing through the _the NO _X storage reduction catalyst by discharging the NO _X NO _X
The density may temporarily increase from before the start of the reproduction operation.

On the other hand, since during the regenerating operation of the NO _X occluding and reducing catalyst is terminated in a very short time and reduction purification and release of the NO _X from _the NO _X storage reduction catalyst, the air-fuel ratio of the exhaust gas flowing to the NO _X occluding and reducing catalyst After returning to the rich air-fuel ratio for a short time, the air-fuel ratio returns to the lean air-fuel ratio. For this reason, the above-mentioned Japanese Patent Application Laid-Open No.
When it detects the concentration of NO _X in the catalyst passing exhaust by NO _X sensor disposed on the downstream side of the catalyst as 166,851 discloses a device, a high concentration due to discharging of the NO _X NO _X
Exhaust reproducing operation after the end containing (air-fuel ratio of the exhaust gas flowing into the catalyst is restored after a lean air-fuel ratio) case to reach the NO _X sensor occurs. In the device disclosed in the above publication, when exhaust containing high-concentration NO _X due to discharge reaches the NO _X sensor after the end of the regeneration operation, the regeneration operation of the NO _X storage reduction catalyst is actually completed, and the NO _X storage reduction catalyst _X
In some cases, the regeneration operation is restarted even though the storage capacity has been recovered. As described later, N
O _X catalyst regeneration operation of the reduction catalyst is generally switches the engine operating air-fuel ratio to a rich air-fuel ratio to the exhaust air-fuel ratio to a rich air-fuel ratio or, in an exhaust passage of the NO _X occluding and reducing catalyst upstream of a hydrocarbon such as This is performed by supplying a reducing agent and setting the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst to a rich air-fuel ratio. For this reason, if the regeneration operation that is originally unnecessary as described above is repeated, the fuel efficiency of the engine deteriorates, the consumption of the reducing agent increases, and the exhaust properties deteriorate due to the discharge of the unpurified reducing agent, HC, CO, and the like. There's a problem.

SUMMARY OF THE INVENTION In view of the above problems, the present invention can prevent an excessive regeneration operation by discharging NO _X during a regeneration operation from a NO _X storage reduction catalyst, and prevent deterioration of engine fuel efficiency and exhaust characteristics. It is an object of the present invention to provide an exhaust purification device for an internal combustion engine.

[0010]

According to the invention described in claim 1 SUMMARY OF THE INVENTION, and disposed in an exhaust passage of an internal combustion engine, air-fuel ratio of the exhaust gas flowing into absorbs NO _X in the exhaust gas when the lean, flows NO absorbed when oxygen concentration in exhaust gas decreased
And _the NO _X storage reduction catalyst that emits _X, the _the NO _X storage and NO _X concentration detecting means for detecting the concentration of NO _X in the exhaust gas after the reduction catalyst passes, NO _X in the exhaust gas the NO _X concentration detecting means detects When the concentration exceeds a predetermined value, the N
Regenerating means for releasing the NO _X absorbed from the NO _X storage reduction catalyst by setting the exhaust air-fuel ratio flowing into the O _X storage reduction catalyst to a rich air-fuel ratio, thereby reducing and purifying the NO _X ;
The NO _X from storage reduction catalyst unpurified N when the air-fuel ratio of the exhaust gas flowing into the _X occluding and reducing catalyst becomes a rich air-fuel ratio
And NO _X emission determining means for determining that the O _X is discharged to the downstream side, the when the release of unpurified of the NO _X is determined to have occurred, said reproducing means rich air the exhaust air-fuel ratio An exhaust purification device for an internal combustion engine, comprising: prohibition means for prohibiting the fuel ratio.

That is, in the first aspect of the present invention, NO
_When the NO _X concentration in the exhaust gas after passing through the _X storage reduction catalyst becomes equal to or higher than a predetermined value, the regeneration operation of the NO _X storage reduction catalyst is performed. However, in the early stage of the regeneration of the NO _X storage reduction catalyst, since unpurified NO _X is released by discharge,
If the regeneration operation is performed based on only the NO _X concentration, NO
Because of the NO _X concentration increases due to the discharging of the _X occluding and reducing catalyst, in some cases it has been reproduced operation starts again after regeneration operation completes. In the present invention, the NO _X release determination means determines the discharge of NO _X at the time of the regeneration of the NO _X storage reduction catalyst, and if the discharge occurs, starts the regeneration operation. This prevents the regenerating operation of the NO _X storage reduction catalyst from being repeated even when an increase in the NO _X concentration in the exhaust gas due to the discharge is detected after the end of the regenerating operation.

According to the invention described in claim 2, the N
O _X release determining means, the atmosphere air-fuel ratio of the _the NO _X storage reduction the catalyst comprises a catalyst air-fuel ratio determining means for determining whether or not rich air-fuel ratio, the atmosphere air in the _the NO _X storage reduction catalyst it is determined that rich air-fuel ratio, and the NO _X concentration NO _X concentration detected by the detection means unpurified from the _the NO _X storage reduction catalyst when the predetermined determination value or more NO _X
The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein it is determined that the exhaust gas is discharged.

That is, according to the second aspect of the present invention, N
O _X release judging means _the NO _X storage atmosphere air-fuel ratio of the reduction in the catalyst has become rich air-fuel ratio, and NO _X concentration NO _X concentration detected by the detection means occurs discharged when the predetermined determination value or more It is determined that there is. NO unpurified NO _X from _X occluding and reducing catalyst discharged is, NO _X storage at the start of the regenerating operation of the reduction catalyst, that is, the results when the ambient air in the NO _X occluding and reducing catalyst becomes a rich air-fuel ratio, NO _If the NO _X concentration detected by the _X concentration detecting means is higher than the determination value and the atmospheric air-fuel ratio in the NO _X storage reduction catalyst is a rich air-fuel ratio, the unpurified NO _X from the NO _X storage reduction catalyst It can be determined that spitting has occurred.

According to the third aspect of the present invention, the catalyst air-fuel ratio determination means is arranged in at least one of the upstream exhaust passage and the downstream exhaust passage of the NO _X storage reduction catalyst, and detects the exhaust air-fuel ratio. An air-fuel ratio sensor is provided, and NO is determined based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor.
An exhaust gas purification device for an internal combustion engine according to claim 2, wherein it is determined whether or not the atmospheric air-fuel ratio in the _X storage reduction catalyst is a rich air-fuel ratio.

That is, according to the third aspect of the present invention, NO
Atmosphere air-fuel ratio of the _X occluding and reducing catalyst upstream exhaust manifold or an _the NO _X storage reduction catalyst based on the air-fuel ratio sensor output that is disposed on at least one of the downstream side exhaust passage is determined whether or not it is the rich air-fuel ratio . When the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst is rich, and when the air-fuel ratio of the exhaust gas after passing through the NO _X storage reduction catalyst is rich, the atmosphere in the NO _X storage reduction catalyst The air-fuel ratio is rich. For this reason, in the present invention, the atmospheric air-fuel ratio in the NO _X storage reduction catalyst is easily determined using the air-fuel ratio sensor.

According to the invention described in claim 4, the N
O _X release determining means, said reproducing means of said unpurified until a predetermined time has elapsed from the time of changing the air-fuel ratio of the exhaust gas flowing into the _the NO _X storage reduction catalyst to a rich air-fuel ratio NO _X An exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein it is determined that the emission is occurring. That is,
In the invention according to claim 4, NO _X emission determining means, N
O _X catalyst regeneration operation after start within a predetermined time of the reduction catalyst is NO
It is determined that unpurified NO _X has been discharged from the _X storage reduction catalyst. That is, in the present invention, the execution of the next regeneration operation is prohibited until the predetermined time has elapsed since the start of the regeneration operation of the NO _X storage reduction catalyst.

The release of unpurified NO _X during the regeneration operation of the NO _X storage reduction catalyst ends shortly after the start of the regeneration operation, and thereafter, the unpurified NO _X is not released downstream.
Therefore, the start of the regenerating operation after a predetermined time in the present invention is assumed to have occurred is discharged unpurified of the NO _X, this time in the reproducing operation even if increased detected concentration of NO _X NO _X concentration detecting means Do not do. Thus, it is possible to easily determine the discharge of the unpurified NO _X from the NO _X storage reduction catalyst. Incidentally, unpurified from the time actually _the NO _X storage reduction catalyst is determined that discharging of the NO _X occurs NO _X
Is set to be larger than the sum of the time during which the NOx is released and the time until the released unpurified NO _X reaches the NO _X concentration detecting means.

According to the invention described in claim 5, further,
NO_XDeterioration judgment to determine whether the storage reduction catalyst has deteriorated
Setting means, and the deterioration determining means_XRelease judgment
The said unpurified NO by means_XThat the release of
The above NO at the time of determination _XDetected by concentration detection means
NO_XWhen the density is equal to or higher than a predetermined deterioration determination value,
NO_XClaiming that the storage reduction catalyst is determined to have deteriorated.
An exhaust gas purification device for an internal combustion engine according to claim 1 is provided.

That is, in the invention according to claim 5, N
O_XDeterioration determination means for determining whether or not the storage reduction catalyst has deteriorated
Is provided. NO_XThe regeneration operation of the storage reduction catalyst is completed.
Immediately after (ie, absorbed NO_XImmediately after releasing the entire amount of
NO most in the state of_XThe storage capacity increases. For this reason,
NO for unconverted catalyst_XNO from storage reduction catalyst _X
NO after the end of spitting_XIn the exhaust after passing through the storage reduction catalyst
NO_XThe concentration will be very low. But NO_XOcclusion return
With the original catalyst, the storage capacity decreases as the deterioration progresses,
After the completion of the playback operation with the progress of_XLow storage capacity
Become. Therefore, NO_XAs the deterioration of the storage reduction catalyst progresses,
NO during raw operation_XNO after the end of spitting_XOcclusion reduction
NO in exhaust gas after passing through the medium_XSo that the concentration gradually increases
Become. That is, NO at the time of the reproduction operation_XImmediately after the end of spitting
NO_XNO of exhaust gas passing through the storage reduction catalyst_XMonitor concentration
NO_XKnow the degree of deterioration of the storage reduction catalyst
Can be. In the present invention, NO_XUnpurified from storage reduction catalyst
NO_XNO at the end of spitting_XPassing the storage reduction catalyst
Exhaust NO_XDensity is equal to or higher than the predetermined deterioration judgment value
Sometimes NO_XTo determine that the storage reduction catalyst has deteriorated
are doing. This allows accurate NO_XPoor storage reduction catalyst
Can be determined.

According to the sixth aspect of the present invention, when the deterioration determining means determines that the NO _X storage reduction catalyst has deteriorated, the NO _X storage reduction catalyst has a NO.
An exhaust gas purification apparatus for an internal combustion engine according to claim 5, further comprising a recovery control means for performing a recovery operation for recovering the _X storage capacity. That is, in the invention described in claim 6, claim 5
Of if _the NO _X storage reduction catalyst is determined to have deteriorated in the invention performs a recovery operation to recover _the NO _X storage ability of the NO _X occluding and reducing catalyst. For example, as the deterioration of the NO _X storage reduction catalyst, SO _X poisoning by absorbing SO _X (sulfur oxide) in exhaust gas is most common. Also,
SO _X poisoning of the NO _X occluding and reducing catalyst can be eliminated by holding _the NO _X storage reduction catalyst for a predetermined time high temperature and rich air-fuel ratio atmosphere. Therefore, in the present invention, when it is determined that the NO _X storage reduction catalyst has deteriorated, for example, N 2
The exhaust gas flowing into the O _X occluding and reducing catalyst performs recovery operation such as the exhaust gas temperature is raised while the rich air-fuel ratio. Thus, it is possible to always maintain a high _the NO _X storage ability of the NO _X occluding and reducing catalyst in the present invention.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an internal combustion engine for a vehicle. In FIG. 1, reference numeral 1 denotes an automobile internal combustion engine.
In the present embodiment, the engine 1 is a four-cylinder gasoline engine having four cylinders # 1 to # 4, and fuel injection valves 111 to 1 for directly injecting fuel into the cylinders # 1 to # 4.
14 are provided. As will be described later, the internal combustion engine 1 of the present embodiment is a lean burn engine that can operate at a higher (lean) air-fuel ratio than the stoichiometric air-fuel ratio.

In this embodiment, the cylinders # 1 to # 4 are grouped into two cylinder groups each including two cylinders whose ignition timings are not continuous with each other. (For example, in the embodiment of FIG. 1, the cylinder ignition order is 1-3-4-2, and #
The cylinders # 1 and # 4 and the cylinders # 2 and # 3 each constitute a cylinder group. The exhaust port of each cylinder is connected to an exhaust manifold for each cylinder group, and is connected to an exhaust passage for each cylinder group. In FIG. 1, reference numeral 21a denotes an exhaust manifold for connecting the exhaust ports of the cylinder group consisting of # 1 and # 4 cylinders to the individual exhaust passage 2a, and reference numeral 21b denotes the exhaust ports of the cylinder group consisting of # 2 and # 4 cylinders for the individual exhaust passage 2b. Exhaust manifold connected to the In this embodiment, the individual exhaust passages 2a, 2a
On b, there is a start catalyst 5a composed of a three-way catalyst.
And 5b are respectively arranged. The individual exhaust passages 2a and 2b join the common exhaust passage 2 downstream of the start catalysts 5a and 5b. Start catalysts 5a, 5b of this embodiment is a three-way catalyst of known configuration, HC in the exhaust gas when the air-fuel ratio of the exhaust gas flowing is in the narrow range of stoichiometric air-fuel ratio near, CO, of the NO _X three It has the function of purifying components simultaneously.

On the common exhaust passage 2, a NO _X storage reduction catalyst 7 described later is arranged. In FIG. 1, reference numeral 29 denotes an upstream air-fuel ratio sensor disposed on the upstream side of the NO _X storage reduction catalyst 7 in the common exhaust passage 2, and reference numeral 31 denotes NO _X
This is a downstream air-fuel ratio sensor disposed in the exhaust passage 2 downstream of the storage reduction catalyst 7. In the present embodiment, the air-fuel ratio sensor 2
Reference numerals 9 and 31 denote so-called O ₂ sensors that generate output signals of different levels depending on whether the exhaust air-fuel ratio is lean or rich based on the oxygen concentration in the exhaust gas.

[0024] The arrangement is NO _X sensor 33 for outputting a signal corresponding to the NO _X concentration in the exhaust gas in the vicinity of the downstream O ₂ sensor 31 in the exhaust passage 2 of the NO _X occluding and reducing catalyst 7 downstream in this embodiment Have been. It will be described later NO _X sensor 33. Further, reference numeral 30 in FIG. 1 denotes an electronic control unit (ECU) of the engine 1. In the present embodiment, the ECU 30 is a microcomputer having a known configuration including a RAM, a ROM, and a CPU, and performs basic control such as ignition timing control and fuel injection control of the engine 1. Further, in the present embodiment, ECU 30 in addition to performing basic control of the, NO _X absorbed from _the NO _X storage reduction catalyst 7 as described below
Means for performing a regeneration operation for releasing, reducing and purifying NOx, NO _x
Discharging has a function as each means such inhibiting means for inhibiting the execution of the regeneration operation based on the output NO _x sensor 33 when occurring.

The input port of the ECU 30_TwoSensor
NO from 29 and 31 respectively_XUpstream of the storage reduction catalyst 7
A signal representing the exhaust air-fuel ratio on the side and the downstream side also
NO _XNO from sensor 33_XExhaust after passing through the storage reduction catalyst 7
NO in the air_XA signal representing the density is A (not shown).
It is input via a D converter. Also, the ECU 30
The output port is the fuel injection amount and fuel injection timing for each cylinder
In order to control the
It is connected to the fuel injection valves 111 to 114 of the cylinder.

Next, the NO _X storage reduction catalyst 7 of this embodiment
Will be described. _The NO _X storage reduction catalyst 7 in this embodiment
Uses, for example, alumina as a carrier, on which potassium K, sodium Na, lithium Li, cesium C
alkali metals such as s, barium Ba, calcium C
alkaline earth such as a, lanthanum La, cerium C
e, carrying at least one component selected from rare earths such as yttrium Y and a noble metal such as platinum Pt. When the air-fuel ratio of the inflowing exhaust gas is lean, the NO _X storage-reduction catalyst reduces the NO _X (NO ₂ ,
The NO) nitrate ions NO ₃ ^- is absorbed in the form of inflow exhaust gas is performed to absorbing and releasing action of the NO _X that releases NO _X absorbed and becomes rich.

The mechanism of the absorption and release will be described below by taking platinum Pt and barium Ba as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths. When the oxygen concentration in the inflowing exhaust gas increases (that is, when the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio), these oxygens become
₂ ^- or deposited at O ^2- form, NO _X in the exhaust gas platinum P
O ₂ on t ^- or react with O ^2-, thereby NO ₂ is produced. Further, NO ₂ and NO ₂ produced by the above in the inflowing exhaust gas is further oxidized nitrate ions NO ₃ while being absorbed in the catalyst bonding with the barium oxide BaO while on the platinum Pt ^- diffuses in the catalyst in the form of . Therefore, so NO _X in the exhaust gas is absorbed in the form of nitrates in the catalyst under a lean atmosphere.

Further, the oxygen concentration in the inflow exhaust gas is greatly reduced.
Then (that is, the air-fuel ratio of the exhaust gas becomes
NO on platinum Pt)_TwoGeneration amount
As the reaction decreases, the reaction proceeds in the opposite direction,
Nitrate ion NO_Three ^-Is NO _TwoReleased from the catalyst in the form of
Become so. In this case, reducing components such as CO and
HC, CO_TwoWhen these components are present, these
NO_TwoIs reduced.

In this embodiment, the engine 1 capable of operating at a lean air-fuel ratio is used. When the engine 1 is operated at a lean air-fuel ratio, the NO _X storage reduction catalyst absorbs NO _X in the exhaust gas flowing into the engine. I do. Further, when the engine 1 is operated at a rich air-fuel ratio, NO _X occluding and reducing catalyst 7 absorbs NO
_Releases and purifies _X. In the present embodiment, non of _the amount of NO _X absorbed in the NO _X occluding and reducing catalyst 7 is increased during the lean air-fuel ratio operation, passes without being absorbed in the NO _X occluding and reducing catalyst 7 by exudation described later NO _X When the purification NO _X amount increases, a rich spike operation is performed in which the engine air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio for a short period of time.
Release of NO _X from the _X storage reduction catalyst and reduction purification (NO _X
(Regeneration of the storage reduction catalyst). In addition,
Regarding the actual air-fuel ratio control and the rich spike control of the engine 1, any known control can be used and is not related to the essential part of the present invention, so that the detailed description is omitted.

[0030] Next, N of the NO _X sensor 33 of this embodiment
The principle of _OX detection will be described. FIG. 2 is a diagram schematically illustrating the configuration of the NO _X sensor 33 of the present embodiment. FIG.
In, NO _X sensor 33, zirconia (Zr
O ₂ ) or the like, and a first solid electrolyte 331 that communicates with the exhaust passage through the diffusion controlling section 335 in the solid electrolyte.
The reaction chamber 340 includes a second reaction chamber 350 communicating with the first reaction chamber 340 via the diffusion control section 337, and an atmosphere chamber 360 into which the atmosphere as a standard gas is introduced. The diffusion control sections 335 and 337 are respectively provided in the first reaction chamber 340 and the second reaction chamber 340.
Suppressing the inflow of the oxygen component into the reaction chamber 350 by diffusion,
An oxygen concentration difference between the exhaust gas in the exhaust passage and the first reaction chamber and between the first reaction chamber and the second reaction chamber can be maintained.

In FIG. 2, reference numeral 341 denotes a first reaction chamber 340.
A reference numeral 342 denotes a platinum electrode (cathode) disposed inside the cathode electrode 341 and a similar platinum electrode (anode) provided outside the sensor 33 with the solid electrolyte 331 interposed therebetween. Also, the second
The reaction chamber similar platinum electrode 350 is within 350 and NO _X detecting rhodium (Rh) electrode 353, platinum electrode 361 for reference to the air chamber 360 are disposed respectively. An electric heater 370 for heating the solid electrolyte is shown in the figure.

The electrode 341 and the external electrode 342 in the first reaction chamber 340, and the electrode 351 and the external electrode 342 in the second reaction chamber 340.
Function as oxygen pumps for exhausting oxygen in the exhaust gas in the first reaction chamber 340 and the second reaction chamber 350, respectively. When a voltage is applied between the electrodes 341 and 342 and the electrodes 351 and 342 when the solid electrolyte 331 is at a certain temperature or higher, oxygen molecules in the exhaust gas are ionized on the cathodes 341 and 351 and the ionized oxygen molecules are solidified. It moves inside the electrolyte 331 toward the anode 342 and becomes an oxygen molecule again on the anode 342. Therefore, the first reaction chamber 340,
Oxygen in the exhaust gas in the second reaction chamber 350 is exhausted to the outside. In addition, the electrodes 342 and 3
A current proportional to the amount of oxygen molecules moved per unit time flows between 41 and 351. Therefore, by controlling this current, the amount of oxygen discharged from each reaction chamber can be controlled.

In this embodiment, an oxygen battery is formed between the electrode 361 in the atmosphere chamber 360 and the electrodes 341 and 351 in each reaction chamber. Since the exhaust gas in the first and second reaction chambers has a lower oxygen concentration than the atmosphere, there is a difference in oxygen concentration between the air in the atmosphere chamber 360 and the exhaust gas in each reaction chamber. When the temperature of the solid electrolyte separating the atmosphere chamber 360 and each of the reaction chambers 340 and 350 is equal to or higher than a certain temperature, the solid electrolyte 331 flows from the inside of the atmosphere chamber 360 due to a difference in oxygen concentration when no voltage is applied between the electrodes from the outside. Reaction chamber 34
Oxygen moves to 0,350. That is, oxygen in the atmosphere in the atmosphere chamber 360 is ionized on the electrode 361, moves in the solid electrolyte 331, and becomes oxygen again on the electrodes 341 and 351 of the reaction chambers 340 and 350 having a low oxygen concentration. Therefore, a voltage is generated between the electrode 361 and each of the electrodes 341 and 351 according to the difference between the oxygen concentration in the atmosphere and the oxygen concentration in each reaction chamber. Since the oxygen concentration in the atmosphere is constant, the potential difference V between the electrode 361 and each of the electrodes 341 and 351 is determined.
0 and V1 (FIG. 2) represent the oxygen concentration of the exhaust gas in the first reaction chamber 340 and the second reaction chamber 351 respectively.

In this embodiment, as described above, the oxygen pumps (electrodes 341 and 342 and the electrodes 351 and 342) for discharging oxygen from the respective reaction chambers to the outside are provided. By adjusting the pump currents Ip0, Ip1 (FIG. 2) between the respective electrodes,
The oxygen concentration of the exhaust gas in each reaction chamber (that is, the voltages V0, V
1) is controlled to be a predetermined constant value. In the present embodiment, the oxygen concentration in the first reaction chamber 340 is, for example, 1 ppm.
Pump current Ip0, so that the oxygen concentration in the second reaction chamber 350 is, for example, about 0.01 ppm.
Ip1 is controlled. Therefore, the second reaction chamber 350
The inside is maintained in a reducing atmosphere having an extremely low oxygen concentration. On the other hand, NO _X (NO, NO ₂ ) in the exhaust gas is not discharged to the outside by the oxygen pump, so that the NO _X concentration of the exhaust gas in the first and second reaction chambers is maintained at the same level as the external exhaust gas. However, NO _X detection electrode 353 of the second reaction chamber acts as a reduction catalyst for a rhodium (Rh), reducing NO _X (NO, NO ₂₎ in a reducing atmosphere. Further, since a voltage is applied between the reference electrode 361 and the NO _X detection electrode 353 in the atmosphere chamber 360, the NO _X detection electrode 3
On 53, NO → (1/2) N ₂ + (1/2) O ₂ , or N
A reaction of O ₂ → (1/2) N ₂ + O ₂ occurs and oxygen is generated by reduction of NO _x . This oxygen is supplied to the electrode 353
The ions are ionized above and move in the solid electrolyte 331 toward the reference electrode 361 in the atmosphere chamber 360 to form oxygen molecules on the reference electrode 361. Since the oxygen concentration in the second reaction chamber 350 is very low, oxygen ions through the solid electrolyte toward the reference electrode 361 will be the total amount is caused by the reduction of the NO _X in the exhaust gas. That is, the amount of oxygen ions flowing in the solid electrolyte per unit time will amount corresponding to the NO _X concentration in the second reaction chamber (concentration of NO _X exhaust in the exhaust passage). Therefore, it is possible to detect the concentration of NO _X exhaust in the exhaust passage by measuring the current value generated along with the movement of the oxygen ions (Fig. 2, Ip2). NO _X sensor 33 of the present embodiment, the current value Ip
2 converts the voltage signal, and outputs a voltage signal VNOX in accordance with the concentration of NO _X in the exhaust gas of the NO _X occluding and reducing catalyst 7 after passing through.

Next, the NO _X from the NO _X storage reduction catalyst 7
The phenomenon referred to as “spitting” and “smearing” will be described. In this specification, it is referred to a phenomenon that unpurified of the NO _X is released downstream of the catalyst immediately after the start of the regenerating operation of the NO _X occluding and reducing catalyst as described above as "spitting" of the NO _X.
NO "discharging" of _X is, NO _X is occluded air-fuel ratio of the exhaust gas flowing into the reduction catalyst occurs immediately after the change from a lean air-fuel ratio to a rich air-fuel ratio, apart from the actual NO _X and "spit" in this NO _X "seepage" of the NO _X in the storage-reduction catalyst
This phenomenon occurs.

In an actual NO _X storage-reduction catalyst, while the NO _X storage-reduction catalyst is absorbing NO _X in the exhaust gas (ie, when the inflowing exhaust air-fuel ratio is lean), unpurified NO _X storage-reduction catalyst is downstream of the NO _X storage reduction catalyst. A phenomenon occurs in which NO _x is released. In this specification, in order to distinguish it from the "spit", which refers to the release of the NO _X unpurified under the lean exhaust air-fuel ratio as "oozing" of the NO _X.

NO_X"Spitting" and "smearing"
The reason for this is currently unclear.
Not disclosed, but presumed to be due to the reasons described below
Have been. First, NO_XThe reason for spitting
Will be described. As mentioned above, NO_XThe storage reduction catalyst is
NO collected_XIn the form of nitrates. At this time, nitric acid
Ion is NO_XAbsorbent (eg, Ba) in the storage reduction catalyst
O) moves from the surface to the inside by diffusion to form nitrate
I do. Therefore, NO_XNitric acid on the surface of the absorbent during absorption
Ion concentration is higher than internal nitrate ion concentration
You. NO in this state_XThe regeneration operation of the storage reduction catalyst has started.
If the oxygen concentration in the atmosphere on the absorbent surface drops sharply,
High concentration of nitrate ion near the surface of the absorbent is NO_TwoAll at once
Will be released from the absorbent. Therefore, the playback operation
A relatively large amount of NO in a short time immediately after the start of cropping_XIs NO_XSucking
Is released from the storage reduction catalyst,
Momentary shortage and released NO_XNot part of
NO as purified _XSo that it is released downstream of the storage reduction catalyst.
It is thought to be.

Further, the above are separately NO _X from the upstream portion of the exhaust gas is _the NO _X storage reduction catalyst when it reaches _the NO _X storage reduction catalyst rich air-fuel ratio is discharged, HC in the exhaust gas, CO
Etc., but the heat of this reduction reaction causes NO _x
Storage reduction catalyst surface locally becomes very hot, unpurified of the NO _X occurs a shortage of the temporary reduction components for rapid NO _X is released from the vicinity of the surface of a portion heated to a high temperature is the downstream It is also believed that exhalation occurs.

After the nitrate ions in the vicinity of the absorbent surface are released, the nitrate ions retained inside the absorbent move to the surface and are released in the form of NO _2. Since the release rate of NO ₂ from the agent is determined by the moving speed of nitrate ions inside the absorbent, the release rate is relatively low, and there is no shortage of reducing agent. Therefore, it is of _the NO _X storage reduction NO _X temporarily unpurified immediately after the start of the regenerating operation of the catalyst of the NO _X released downstream "spitting" occurs.

NO released by discharge_XThe amount of
It becomes larger as the concentration of nitrate ions on the surface of the absorbent is higher. This
NO_XNO absorbed by the storage reduction catalyst_XQuantity (N
O_XUncleanness released by exhalation as the amount of occluded) increases
NO_XWill increase. NO_X"Some
NO is NO_XN absorbed by the absorbent of the storage reduction catalyst
O _XAbsorbent NO_XStorage capacity decreases
It is thought to occur because. As described above, NO_XSucking
Nitrate ions generated on platinum Pt of the storage reduction catalyst are absorbed
It moves from the agent surface to the inside by diffusion. Therefore, NO_X
NO of storage reduction catalyst _XThe amount of occlusion increases,
As the acid ion concentration increases, nitrate ions diffuse
And the nitrate ion concentration on the surface of the absorbent increases.
As a result, NO on platinum Pt_Two→ NO_Three ^-Reaction
NO in exhaust_XIs NO _XFor storage reduction catalyst
No longer absorbed. Therefore, NO_XN of the storage reduction catalyst
O_XNO during absorption_XNO as storage capacity increases_X
Unpurified N flowing out downstream without being absorbed by the storage reduction catalyst
O_XThe amount will increase.

Unpurified N released by "smear"
O _X increases as the amount of NO _X absorbed by the NO _X storage reduction catalyst increases, that is, as the amount of absorbent that can absorb and retain NO _X decreases. Further, when _the NO _X storage reduction catalyst is saturated with absorbed NO _X (i.e., it absorbs NO _X, the absorbent can hold quite eliminated) _the NO _X storage reduction catalyst can no longer completely absorb the NO _X in the exhaust gas, flowing The entire amount of NO _{X in} the exhaust gas flows out to the downstream side due to “exudation”.

The amount of NO _X unpurified released from _the NO _X storage reduction catalyst by "exudation" is increased as the absorbed amount of NO _X in _the NO _X storage reduction catalyst is large. Also, when the maximum NO _X amount (saturation amount) that can be absorbed by the NO _X storage reduction catalyst decreases due to deterioration or the like, the amount of unpurified NO _X released by oozing even if the absorbed NO _X amount is the same. Increases.

[0043] In this embodiment, the amount of the NO _X flowing out to the downstream side from _the NO _X storage reduction catalyst by the "oozing" (concentration) detected by the NO _X sensor 33, the detected NO _X
Every time the concentration reaches a predetermined value, the engine 1 is operated at a rich air-fuel ratio for a short time to perform a regeneration operation of the NO _X storage reduction catalyst. FIG. 3 is a diagram showing a change in the NO _X concentration in the exhaust gas after passing through the NO _X storage reduction catalyst 7 due to execution of the regeneration operation.

[0044] In FIG. 3, the vertical axis represents _the NO _X storage and reduction catalyst 7 downstream of the NO _X sensor 33 outputs VNOx, the horizontal axis represents time. Engine 1 is operated in _the NO _X storage and reduction catalyst 7 at a lean air-fuel ratio to absorb NO _X in the exhaust gas but, _the NO _X storage by exudation as the amount of _the NO _X storage absorbed in reduction catalyst 7 was NO _X increases The amount of unpurified NO _X flowing to the downstream side of the reduction catalyst 7 gradually increases. Therefore, NO
_The output VNOX of the _X sensor 33 also gradually increases (FIG. 3, N
S part). In the present embodiment, the outflow NO _X due to seepage
When the concentration reaches a predetermined value (VNOX1 in FIG. 3), the control circuit 30 performs a rich spike operation for operating the engine 1 at a rich air-fuel ratio for a short time to regenerate the NO _X storage reduction catalyst 7 (FIG. 3, time point). RS). When exhaust gas of a rich air-fuel ratio is rich spike operation is performed flows to the NO _X occluding and reducing catalyst 7, occurs discharging the NO _X, unpurified NO _X is NO
It is released from the _X storage reduction catalyst 7. Therefore, the output VNOX of the NO _X sensor 33 increases relatively large immediately after the start rich spike RS (Fig. 3, NH moiety).

The discharge of NO _X immediately after the rich spike is completed in a very short time. However, unpurified of the NO _X released by discharging the, _the NO _X storage by the distance from the size and _the NO _X storage reduction catalyst 7 of the reduction catalyst 7 to NO _X sensor 33, NO _X diffuses in the longitudinal exhaust flow direction When reaching the sensor 33, a layer having a certain thickness is formed. For this reason, the NO sensor 33 detects a high concentration of NO _X for a certain period after the rich spike (FIG. 3, period NT). On the other hand, since the rich spike ends in a relatively short time, if the period NT is longer than the rich spike period, the rich spike ends and the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst 7 becomes the lean air-fuel ratio. the output of the NO _X sensor 33 even after the recovery is sometimes if it is higher than the determination value VNOX1 for rich spike start occurs. In such a case, the rich spike is performed again immediately after the end of the rich spike, and the fuel efficiency and the exhaust properties are deteriorated due to an increase in the frequency of the rich air-fuel ratio operation of the engine.

In the present invention, it is determined that the exhaust is generated from the NO _X storage reduction catalyst, and when it is determined that the increase in the NO _X concentration of the exhaust gas after passing through the NO _X storage reduction catalyst is generated by the exhaust, The above problem is solved by prohibiting the execution of the regeneration operation of the NO _X storage reduction catalyst.
That is, in the present invention, the increase in the NO _X concentration due to the discharge and the increase in the NO _X concentration due to the exudation are discriminated, and the execution of the reproducing operation is permitted only when the increase in the NO _X concentration occurs due to the exudation.

Hereinafter, several embodiments of a method for judging that the discharge from the NO _X storage reduction catalyst has occurred will be described. (1) In the first embodiment the present embodiment, or not _the NO _X storage reduction catalyst exhaust air-fuel ratio after the passage of NO _X concentration increased during the passage evacuated by whether or not it is the rich air-fuel ratio is caused by spitting Determine whether or not.

As described above, the discharge of NO _X is NO
Occurs when the air-fuel ratio of the exhaust gas flowing into the _X storage reduction catalyst 7 becomes a rich air-fuel ratio. Therefore, NO with the exhaust of the NO _X are rich air-fuel ratio emitted by discharging _X
The light reaches the sensor 33. On the other hand, since the release of NO _X due to the exudation occurs at a lean air-fuel ratio, the NO _X released by the exudation reaches the NO _X sensor 33 together with the exhaust at the lean air-fuel ratio. Thus, N in NO _X sensor 33
By the exhaust air-fuel ratio in the vicinity of NO _X sensor 33 when the increase in the O _X concentration is detected to determine whether a lean air-fuel ratio or a rich air-fuel ratio, or by exudation or by discharging an increase of the NO _X concentration Can be determined. When in the present embodiment, which determines the air-fuel ratio of the exhaust gas in the NO _X sensor 33 based on the downstream O ₂ sensor 31 outputs disposed near NO _X sensor 33, the exhaust air-fuel ratio is rich, NO _X sensor By prohibiting the start of the rich spike operation based on the 33 output VNOX, the unnecessary rich spike operation is prevented from being performed.

It should be noted, that prohibits the start of the rich-spike operation when the exhaust air-fuel ratio in the NO _X sensor 33 is in a rich air-fuel ratio may have a meaning other than the determination of the presence or absence of discharging. For example, when the NO _X sensor 33 having the configuration shown in FIG. 2 is used, a stable NO _X concentration can be detected when the exhaust air-fuel ratio is a lean air-fuel ratio, but the exhaust air-fuel ratio becomes a rich air-fuel ratio. Then, the output of the NO _X sensor 33 becomes unstable, and the detection accuracy of the NO _X concentration may vary. As described previously, the NO _X sensor 33 of the present embodiment is provided with the first reaction chamber 34.
0 and oxygen in the exhaust gas in the second reaction chamber 350 is removed, and NO
NO by detecting the amount of oxygen generated by the reduction of _X
X concentration is detected. However, when a large amount of components such as HC and CO exist in the first reaction chamber 340 or the second reaction chamber 350, that is, when the air-fuel ratio of the exhaust gas flowing into the reaction chamber is a rich air-fuel ratio, NO _X reacts with HC and CO in the exhaust gas and is converted into N ₂ . Therefore, when the exhaust air-fuel ratio becomes a rich air-fuel ratio,
If the output of the NO _X sensor 33 when the amount of oxygen ions generated on the electrode 351 of the second reaction chamber is no longer corresponds to the actual concentration of NO _X in the exhaust gas is caused to become unstable it is from occurring. Therefore, if the start of the rich spike is determined based on the output of the NO _X sensor 33 under the rich air-fuel ratio, the rich spike may be started erroneously due to a decrease in the detection accuracy of the NO _X sensor 33. .

In this embodiment, the execution of the rich spike is prohibited when the exhaust air-fuel ratio in the NO _X sensor 33 is the rich air-fuel ratio. Therefore, the above-mentioned problem occurs due to the decrease in the detection accuracy of the NO _X sensor 33 under the rich air-fuel ratio. Can also be prevented at the same time. FIG. 4 shows the NO _{X of} this embodiment.
5 is a flowchart illustrating a regeneration determination operation for determining whether or not a regeneration operation of the storage reduction catalyst 7 needs to be started. This operation is performed by a routine executed by the ECU 30 at regular intervals.

[0051] In the operation of FIG. 4, when the output of the downstream O ₂ sensor 31 is rich air-fuel ratio corresponding output, NO _X sensor 33 outputs a based regeneration operation (rich-spike operation)
Execution is prohibited. That is, in step 401 in the operation of FIG. 4 NO _x sensor 33 output VNOX and downstream O ₂
Sensor 31 outputs VOD is read, necessity of regenerating operation of the step 403 NO _x storage-reduction catalyst is determined based on the NO _x sensor 33 output VNOx. That is, it is determined whether or not output VNOX has reached predetermined value VNOX1 (FIG. 3). VNOX in step 403
≧ a when it is VNOX1, since the amount of NO _x unpurified flowing into _the NO _x storage reduction catalyst downstream side is increased, typical stains or those produced by discharging the increase of the NO _x flow advances to step 405 It is determined whether it is caused by the delivery.

That is, in step 405, the current downstream side
O_TwoWhether the sensor 31 output VOD is rich air-fuel ratio equivalent output
Is determined. Currently VOD is rich air-fuel ratio equivalent output
In some cases, NO_xIncrease due to spitting
And NO _xAnxiety about output of sensor 33
It may be fixed. Therefore, in this case
Terminates the execution of this operation without executing the playback operation
I do. Thereby, NO_xNot purified from storage reduction catalyst 7
NO_xUnnecessary playback operation is started by
Is prevented.

In step 403, VNOX <VNO
Be a X1, the release amount of unpurified NO _x by exuding it is not necessary to run is within the allowable range playback operation immediately terminates the execution of this operation. Step 40
If VOD is not rich air-fuel ratio corresponding output 5 (lean air-fuel ratio or a stoichiometric air-fuel ratio corresponding output) is actually _the amount of NO _x due to exudation is increased, it is necessary to immediately start the reproduction operation Step 4
In step 07, the value of the rich spike flag XRS is set to 1, and the operation ends.

When the value of the rich spike flag XRS is set to 1, the operating air-fuel ratio of the engine 1 is switched to the rich air-fuel ratio for a certain period of time by a routine separately executed by the ECU 30, and thereafter returns to the lean air-fuel ratio. Further, the value of the flag XRS is reset to 0 when the lean air-fuel ratio returns. The NO _X which has been absorbed in the NO _X occluding and reducing catalyst 7 by the rich spike operation is released, HC in the rich air-fuel ratio exhaust gas is reduced and purified by the CO component.

(2) Second Embodiment Next, a second embodiment of the present invention will be described. In the above-described first embodiment, whether or not the discharge from the NO _X storage reduction catalyst 7 has occurred is determined by using the output of the downstream O ₂ sensor 31. In the present embodiment, however, the upstream O ₂ sensor 29 is used. The discharge is determined based on the output.

As described above, NO_XIn the sensor 33
NO while the exhaust air-fuel ratio is the rich air-fuel ratio_XSen
NO 33 output VNOX is NO_XUnpurified from storage reduction catalyst 7
Chemical NO_XAnd the output of the sensor 33 becomes unstable.
May be higher due to In this embodiment
Is the upstream O_TwoThe exhaust air-fuel ratio detected by the sensor 29 is
H from a time when the air-fuel ratio changes to a lean air-fuel ratio
NO until time elapses _XRegeneration based on sensor 33 output
Prohibit operation execution. That is, the upstream O_TwoSensor 29
Detected that the exhaust air-fuel ratio became lean
In some cases, after a certain time, this lean air-fuel ratio exhaust
Is NO_XReaching the sensor 33 and ensuring NO _XSensor 33
The exhaust air-fuel ratio in the vicinity is lean. In this state
Is NO by exhalation_XReleased from the storage reduction catalyst 7
Unpurified NO_XIs already NO_XFinished passing sensor 33
ing. Therefore, the upstream O_TwoSensor 29 output
Change from the air-fuel ratio equivalent output to the lean air-fuel ratio equivalent output.
From the specified time (exhaust gas is _TwoFrom the position of sensor 29
NO_XThe time it takes to reach the position of the sensor 33) has elapsed
NO until_XOf the reproduction operation based on the output of the sensor 33
Unnecessary playback operation due to spitting if execution is prohibited
Is reliably prevented from being executed. this
NO_XOnly at the upstream side of the storage reduction catalyst 7 is the air-fuel ratio
Unnecessary regeneration operation can be executed easily even in an organization with
Can be prevented from being performed.

FIG. 5 is a flowchart similar to FIG. 4 for explaining the reproduction determination operation of the present embodiment. This operation is also EC
This is performed by a routine executed at regular intervals by U30. When the operation of FIG. 5 is started, at step 501 NO _X sensor 33 output VNOX upstream O ₂ sensor 2
9 output VOU are read, and in step 503, the VO
It is determined whether U is an output corresponding to a rich air-fuel ratio. If the VOU is not an output corresponding to a rich air-fuel ratio (a lean or stoichiometric air-fuel ratio), step 507 is executed.
Increases the value of the time counter CT by one. Counter CT
Lean air-fuel ratio (or theoretical output of the upstream O ₂ sensor 29 for VOU is between a rich air-fuel ratio corresponding output is reset to 0 every operation execution (step 505) from a rich air-fuel ratio corresponding output in step 503 The value corresponds to the elapsed time from the time when the output changes to the (air-fuel ratio) equivalent output.

In step 509, step 403 in FIG.
NO as well as_xSensor 33 output VNOX is VNOX1 or more
It is determined whether or not VNOX ≧ VNOX1
In step 511, the above counter C
Based on the value of T, VOU determines the lean air-fuel ratio (or stoichiometric air-fuel ratio).
Whether a predetermined time has elapsed since the output changed to (fuel ratio) equivalent
(That is, CT ≧ CT₀Or not) is determined. here
And CT₀Is upstream O _TwoExhaust passing through the sensor 29 is N
O_xNO on the downstream side of the storage reduction catalyst 7_xReach sensor 33
This is a counter value corresponding to the required time until the start.

If it is determined in step 511 that CT <CT ₀ , the exhaust air-fuel ratio in the NO _x sensor 33 may still be a rich air-fuel ratio, so the NO _x concentration increase in step 509 is caused by the discharge. Could be. Therefore, in this case, the start of the reproduction operation in step 513 is skipped, and the execution of the current operation ends. This prevents unnecessary reproducing operation is started by discharging unpurified NO _x from _the NO _x storage-reduction catalyst 7.

If CT ≧ CT ₀ at step 511, the exhaust air-fuel ratio in the NO _x sensor 33 has already become the lean air-fuel ratio, and NO _x
It is considered that the unpurified NO _x released from the storage reduction catalyst 7 has passed through the NO _x sensor 33. Therefore, increase in the concentration of NO _x in step 509 is caused by the out ordinary spots, it is necessary to immediately start playing operation of the NO _x storage-reduction catalyst, the 1 the value of the flag XRS proceeds to step 513 set. The function of the flag XRS is the same as that of FIG.

As a result, the regeneration operation is started only when the NO _X storage capacity of the NO _X storage reduction catalyst 7 is truly reduced, and execution of an unnecessary regeneration operation is prevented. (3) In a third embodiment the present embodiment, from the O _{2 the} NO _X storage reduction catalyst 7 on the basis of only the reproducing operation after the start time of the NO _X occluding and reducing catalyst 7 without using the output of the sensor 29, 31 It is determined whether or not ejection has occurred.

Unpurified NO from NO _X storage reduction catalyst 7
The discharge of _X ends within a short time after the start of the reproduction operation.
Therefore, it can be considered that the discharge of the unpurified NO _X from the NO _X storage reduction catalyst 7 has been completed when a predetermined time has elapsed since the start of the regeneration operation. Therefore, in this embodiment, so as to prohibit the regenerating operation based in the NO _X sensor 33 outputs only between the time the start of the regenerating operation of the NO _X occluding and reducing catalyst 7 until a predetermined time elapses. In this embodiment, it is possible to easily determine whether or not the discharge from the NO _X storage reduction catalyst 7 has occurred without using the output of the O ₂ sensor.

FIG. 6 is a flowchart similar to FIGS. 4 and 5 for explaining the reproduction determination operation of this embodiment. This operation is also performed by a routine executed by the ECU 30 at regular intervals. When the operation of FIG. 6 is started, step 6
With NO _x sensor 33 output VNOX is read in 01, in step 603 NO _x sensor 33 output V
It is determined whether or not NOX has reached VNOX1.

[0064] When was VNOX ≧ VNOX1 in step 603, i.e. concentration of NO _x is a predetermined value VNOx
If you are increasing the 1 or more, then based on the value of the proceeds counter CTR in Step 607 whether or not caused by discharging an increase in the NO _x is determined. In step 607, if CTR <CTR ₀ , step 60
Increase of the NO _x concentration at 3 is determined to have occurred by the spit. The counter CTR is reset to 0 at the same time that the value of the rich spike flag XRS is set to 1 in step 609, that is, when the reproduction operation is started (step 611), otherwise (step 603).
In the case of VNOX <VNOX1, and in the case of CTR <CTR ₀₎ in step 607 is increased by one for each operation execution (step 605). Therefore, the counter CTR
Is a value corresponding to the elapsed time from when the reproduction operation was started last time. Further, the predetermined value CTR ₀ is a time from the start of the regeneration operation to the end of the discharge of the unpurified NO _x from the NO _x storage reduction catalyst 7 until the released unpurified NO _x passes through the position of the NO _x sensor 33. Is set to a value corresponding to.

In step 607, CTR ≧ CTR₀in the case of
Is NO in step 603 _xIncrease of the normal dyeing
NO immediately because it is caused by protrusion_xStorage reduction catalyst
It is necessary to perform the playback operation. Therefore, in this case,
At step 609, the value of the rich spike flag XRS becomes 1
The value of the counter CTR is set in step 611.
Reset to zero. In step 603, a reproduction operation is performed.
Is determined to be unnecessary (VNOX <VNOX1),
In step 607, the discharge is currently occurring (CTR
<CTR₀), The flag XRS is set.
In this case, the value of the counter CTR is increased by 1
End the operation.

As described above, in this embodiment, the N ₂ O ₃ from the NO _X storage reduction catalyst 7 is used without using the output of the O ₂ sensor.
Since it determines discharging of O _X, it is possible to prevent the execution of simple to unnecessary play operation at engine having no O ₂ sensor in the exhaust system. (4) Fourth Embodiment Next, a fourth embodiment of the present invention will be described. In the present embodiment, whether or not unpurified NO _X is discharged from the NO _X storage reduction catalyst 7 is determined based on the output of the downstream O ₂ sensor 31 in the same manner as in the first embodiment.
_The NO _X storage reduction catalyst 7 on the basis of the NO _X sensor 33 output VNOX when the O _X discharged is determined to have ended
Perform the operation to determine the deterioration of.

NO_XThe storage reduction catalyst 7 may have various causes.
Deteriorated, and NO with deterioration_XThe storage capacity is reduced. An example
For example, sulfur oxides (SO_X) Is included
NO _XThe storage reduction catalyst 7 is the same as the NO_XAbsorption and release mechanism
Sulfur oxide is converted into sulfate by the same mechanism
To absorb. However, the sulfate in the absorbent (eg, BaS
O_Four) Is more stable than nitrate,_XSucking
It is not released by the regeneration operation of the storage reduction catalyst. For this reason,
Usual NO_XWhen the storage reduction catalyst regeneration operation is repeated,
NO_XSulfate is gradually accumulated in the storage reduction catalyst.
No, no_XOf absorbent that can participate in the absorption of NO_X
Storage capacity is reduced. In this specification, this exhaust S
O_XBy absorption of NO_XDeterioration of storage reduction catalyst_XSuffered
Call it poison.

[0068] When the regenerating operation of the NO _X occluding and reducing catalyst 7 is completed, storage ability of the NO _X occluding and reducing the total amount of the absorbed NO _X in the catalyst 7 is released _the NO _X storage reduction catalyst 7 is maximized. However, when the NO _X storage reduction catalyst is deteriorated such as the above-mentioned SO _X poisoning, the NO _X storage capacity after the completion of the regeneration operation gradually decreases. FIG. 7 is a diagram similar to FIG. 3 showing the change in the NO _X concentration in the exhaust gas before and after the regeneration operation after passing through the NO _X storage reduction catalyst, and the solid line in the diagram indicates the normal (non-degraded) NO _X In the case of the storage reduction catalyst, the dotted line indicates S
Where O _X deterioration due poisoning of the catalyst occurs, respectively.

[0069] As shown in FIG. 7 the dotted line, in _the NO _X storage reduction catalyst has degraded, because _the NO _X storage ability after regeneration operation ends is reduced, the time when the discharging of the NO _X from _the NO _X storage reduction catalyst is completed NO _X concentration (Fig. 7 in the downstream exhaust,
(Point A) is higher than that of a normal NO _X storage reduction catalyst.
Also, discharging concentration of NO _X downstream exhaust after completion increases as concentration of NO _X in the exhaust gas flowing progresses deterioration of the NO _X occluding and reducing catalyst may be the same.

In the present embodiment, the point in time when the discharge of the unpurified NO _X from the NO _X storage reduction catalyst 7 is completed (FIG. 7, A
Point) as well as determination based on the downstream O ₂ sensor 31 outputs VOD, determines whether catalyst based the NO _X sensor 33 output at this time is deteriorated to an unacceptable extent. FIG. 8 is a flowchart illustrating a deterioration determination operation according to the present embodiment. This operation is performed by a routine executed by the ECU 30 at regular intervals.

Although not shown, in this embodiment, the same operation as that in the first embodiment is performed separately, and unpurified NO _X is discharged from the NO _X storage reduction catalyst. During the period, execution of the reproduction operation is prohibited. In the operation of FIG. 8, it is determined when the exhaust air-fuel ratio detected by the downstream air-fuel ratio sensor 31 has changed from a rich air-fuel ratio to a lean air-fuel ratio (or a stoichiometric air-fuel ratio) (steps 803, 80).
5, 807). If the NO _X concentration detected by the NO _X sensor 33 at this time (that is, the NO _X concentration at point A in FIG. 7) has increased to a predetermined determination value VNOX2 or more, N
O _X occluding and reducing catalyst 7 is so determined to have deteriorated.

That is, when the operation is started in FIG.
Step 801 In NO _X sensor 33 output VNOX and the downstream O ₂ sensor 31 outputs VOD is read, the O ₂ sensor 31 outputs at step 803 whether or not rich air-fuel ratio corresponding output or not is determined. If the output of the downstream O ₂ sensor 31 is an output equivalent to the rich air-fuel ratio in step 803, the value of the flag R is reset to 0 in step 805, and the execution of the current operation ends. That is, the value of the flag R is always reset to 0 while the output VOD of the downstream O ₂ sensor 31 is an output corresponding to a rich air-fuel ratio. Further, the value of the flag R is set to 1 in step 815 described later when the air-fuel ratio becomes lean.

If the output VOD is not the output corresponding to the rich air-fuel ratio in step 803, that is, if the output VOD is the output corresponding to the lean air-fuel ratio or the stoichiometric air-fuel ratio, then step 807 is executed.
It is determined whether the value of the flag R is 0 or not. Flag R
Is set to 0 in step 805 while the VOD is the output corresponding to the rich air-fuel ratio, and is set to 1 in step 815 when the VOD becomes the output corresponding to the lean air-fuel ratio or the stoichiometric air-fuel ratio. Therefore, in step 803, VOD is an output corresponding to a lean air-fuel ratio or a stoichiometric air-fuel ratio, and
If R = 0 at 07, this operation is executed first after the exhaust air-fuel ratio after passing through the NO _X storage reduction catalyst 7 changes from the rich air-fuel ratio to the lean air-fuel ratio or the stoichiometric air-fuel ratio. That is, the current NO _X storage reduction catalyst 7
A point concentration of NO _X in the exhaust gas after passing shown in FIG. 7 (NO
₍ Value corresponding to maximum NO _X storage capacity of _X storage reduction catalyst 7)
It means that there is.

[0074] Therefore, the current of the NO _X sensor 33 output VNOX in step 809 in this case is a predetermined value VNOX2
It is determined whether or not this is the case. VNOX ≧ VN
If it is OX2, to _the NO _X storage reduction catalyst 7 is degraded unacceptably _the NO _X storage capability deteriorates, that the concentration of NO _X downstream exhaust has become higher after the reproduction operation ends Means Therefore, in this case, after setting the value of the deterioration flag XF to 1 in step 813,
In step 815, the value of the aforementioned flag R is set to 1, and the operation ends. In step 809, VNOX <V
Since _the NO _X storage reduction catalyst 7 in the case of NOX2 is not deteriorated to the extent that unacceptable, step 811
The value of the deterioration flag XF is set to 0 at step 815.
To set the value of the flag R to 1 and end the operation. Thus, the operation ends immediately after step 807 from the next operation execution, and the deterioration determination in step 809 is not executed. In the present embodiment, when the value of the flag XF is set to 1, for example, a warning lamp in the driver's seat is turned on by a routine separately executed by the ECU 30, and the driver is notified that the NO _X storage reduction catalyst 7 has deteriorated. .

By the operation shown in FIG. 8, in this embodiment, NO _X
Whether or not the storage reduction catalyst 7 has deteriorated depends on the downstream O ₂ sensor output V
It is accurately determined based on the OD and NO _X sensor 33 outputs VNOx. (5) Fifth Embodiment In this embodiment, to determine the discharged at the end of the NO _X from _the NO _X storage reduction catalyst 7 on the basis of the upstream O ₂ sensor 29 outputs VOU, NO _X discharged at the end of the NO _X Sensor 3
3 based on the output VNOX determines the presence or absence of deterioration of the NO _X occluding and reducing catalyst 7.

FIG. 9 is a flowchart showing the deterioration determination operation of this embodiment. This operation is also performed by a routine executed by the ECU 30 at regular intervals. In the operation of FIG. 9, the same time counter C as that of the second embodiment (FIG. 5) is used.
A predetermined time from when the output of the upstream O ₂ sensor 29 changes from the output corresponding to the rich air-fuel ratio to the lean air-fuel ratio or the output corresponding to the stoichiometric air-fuel ratio using T and the same flag R as in the fourth embodiment (FIG. 8). The deterioration of the NO _X storage-reduction catalyst 7 is determined based on the output V NOX of the NO _X sensor 33 at the time after (CT ₂ ). That is, the upstream O ₂ sensor 29
Exhaust gas air-fuel ratio at the location of the changes to the lean air-fuel ratio or stoichiometric air-fuel ratio from the rich air-fuel ratio, the exhaust gas air-fuel ratio after the change reaches the predetermined time (CT ₂₎ NO _X sensor 33 after the elapse. For this reason, at the position of the upstream air-fuel ratio sensor 29, N
The output of the _OX sensor 33 corresponds to the point A in FIG. Here, the predetermined time (CT ₂ ) corresponds to a time required for the exhaust gas passing through the upstream O ₂ sensor 29 to pass through the NO _X storage reduction catalyst 7 and reach the NO _X sensor 33.

In the operation shown in FIG._X
Sensor 33 output VNOX and upstream O _TwoSensor 29 output V
OU and the fourth embodiment described above using the flag R.
VNOX is equivalent to rich air-fuel ratio by the same operation as in the embodiment (FIG. 8).
Output to output equivalent to lean air-fuel ratio (or stoichiometric air-fuel ratio)
Detect the time point of change (steps 903, 905, 9)
09, 921). Then, using the time counter CT,
The same operation as in the second embodiment (FIG. 5) (step 90)
7, 911, 913)_TwoOutput of sensor 29
Time CT from change time_TwoNO when has elapsed_X
Deterioration judgment based on sensor 33 output (steps 915 and 91)
7, 919). The operation of each step in FIG.
Since the operation is the same as that of FIG. 5 or FIG.
Description is omitted.

[0078] Although not shown the same operations separately second embodiment in the present embodiment (FIG. 5) is performed while the discharging of the NO _X from _the NO _X storage reduction catalyst 7 has occurred regenerating operation is inhibited based on the output NO _X sensor 33. In the above-described fourth embodiment, NO _X is determined based on the output of the downstream O ₂ sensor 31, and in the present embodiment, based on the output of the upstream O ₂ sensor 29.
Deterioration determination based on the output of the sensor 33 (step 80 in FIG. 8)
9, the execution timing of step 915) is determined, but the O ₂ sensors 29 and 31 are determined in the same manner as in the third embodiment.
Without using the output of, it is also possible to carry out the deterioration determination based on the output NO _X sensor 33 when the start of the regenerating operation after a predetermined time has elapsed.

(6) Sixth Embodiment Next, a sixth embodiment of the present invention will be described. In the present embodiment, the determining the deterioration of the NO _X occluding and reducing catalyst 7 by one of the embodiments of the fourth or fifth, it is determined that _the NO _X storage reduction catalyst 7 is deteriorated unacceptably In this case, an operation for restoring the NO _X storage capacity of the NO _X storage reduction catalyst 7 is performed.

[0080] _the NO _X storage recovery operation of the NO _X storage ability of the reduction catalyst, various methods depending on the type of deterioration is taken, NO _X from deterioration by SO _X poisoning of the NO _X occluding and reducing catalyst here The operation for recovering the storage capacity will be described by way of an example. As described above, degradation due to SO _X poisoning of the NO _X occluding and reducing catalyst is caused by the sulfate is accumulated in _the NO _X storage reduction catalyst. In order to release the sulfate, it has been found effective to maintain the NO _X storage reduction catalyst in a rich air-fuel ratio atmosphere for a certain period of time at a temperature higher than a normal regeneration operation.

Therefore, in the present embodiment, when it is determined that the NO _X storage reduction catalyst 7 has deteriorated, the engine 1
Is operated at a rich air-fuel ratio, and the exhaust temperature of the engine is increased by, for example, retarding the ignition timing of the engine. Thus, NO _X occluding and reducing the catalyst 7 normal exhaust gas of a rich air-fuel ratio of a temperature higher than the reproducing operation is to pass, NO _X occluding and reducing catalyst 7 in a high-temperature rich air-fuel ratio atmosphere
, The SO _X absorbed is released.

FIG. 10 is a flowchart showing the recovery operation of the present embodiment. This operation is executed by the ECU 30 at regular intervals. When the operation starts in FIG. 10, in step 1001, the value of the deterioration flag XF becomes 1
It is determined whether (deterioration) is set. The value of the flag XF is set by the operation of the above-described fourth or fifth embodiment. If the value of the flag XF has been set to 1, the value of the time counter KT is incremented by 1 every time the operation is executed in step 1005, and in step 1007
In the value of the counter KT is to perform the recovery operation of step 1009 until it reaches the predetermined value KT _0. Since the value of the counter KT is reset to 0 when the value of the deterioration flag XF is set to 0 (normal) in step 1001, the value of KT is set to the time from the start of execution of the recovery operation in step 1009. Yes, it is.

In the recovery operation in step 1009 of this embodiment, the engine 1 is operated at a rich air-fuel ratio, the ignition timing of the engine is retarded, and the exhaust temperature is maintained at a higher value than during a normal regeneration operation. Thus, now it absorbed SO _X not NO _X only is released from _the NO _X storage reduction catalyst 7, _the NO _X storage ability of the NO _X occluding and reducing catalyst 7 is recovered.

[0084] recovery operation in step 1009, the value of the counter KT is completed to reach the predetermined value KT ₀ (step 1011), the engine 1 resumes normal lean air-fuel ratio operation. Here, the predetermined value KT ₀ corresponds to the time required for the total amount of SO _X absorbed from the NO _X storage reduction catalyst 7 to be released, and differs depending on the size and type of the NO _X storage reduction catalyst 7. Is preferably determined by an experiment using an actual NO _X storage reduction catalyst. Step 101
After the end of the recovery operation in step 1, the value of the deterioration flag XF is set to 0 (normal) in step 1013. Thus, from the next operation execution, the recovery operation is not executed until the value of XF is set to 1 next time.

Although the above-described first to sixth embodiments have described the case where the present invention is applied to a gasoline engine, the present invention is also applicable to a diesel engine. Add this case, either as a regenerating operation of the NO _X occluding and reducing catalyst for injecting _the NO _X storage reduction catalyst upstream of the exhaust passage to the reducing agent (e.g., fuel oil or the like such as hydrocarbons), or during the exhaust stroke of each cylinder The fuel injection is performed in such a manner that the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst is made rich for a short time.

[0086]

According to the invention described in each claim, NO _X
By preventing the execution of unnecessary regeneration operations by releasing unpurified NO _X from the storage reduction catalyst, a common effect is achieved in that it is possible to prevent deterioration of fuel efficiency and exhaust properties of the engine. In the invention described in claim 5, further an effect that it becomes possible to accurately determine the deterioration of the common in addition to the effect _the NO _X storage reduction catalyst.

According to the sixth aspect of the present invention, in addition to the effect of the fifth aspect, when the deterioration of the NO _X storage reduction catalyst is determined, the operation of restoring the storage capacity of the NO _X storage reduction catalyst is performed. This has the effect that the storage capacity of the NO _X storage reduction catalyst can be constantly maintained at a high level.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration in a case where an exhaust gas purification device of the present invention is applied to an automobile gasoline engine.

FIG. 2 is a schematic diagram showing an example of the structure of the NO _X sensor of FIG.

FIG. 3 is a diagram for explaining “exhalation” and “exudation” of NO _X from a NO _X storage reduction catalyst.

FIG. 4 is a flowchart illustrating a first embodiment of the present invention.

FIG. 5 is a flowchart illustrating a second embodiment of the present invention.

FIG. 6 is a flowchart illustrating a third embodiment of the present invention.

FIG. 7: Downstream exhaust N due to deterioration of the NO _X storage reduction catalyst
FIG. 4 is a diagram for explaining a change in _OX concentration.

FIG. 8 is a flowchart illustrating a fourth embodiment of the present invention.

FIG. 9 is a flowchart illustrating a fifth embodiment of the present invention.

FIG. 10 is a flowchart illustrating a sixth embodiment of the present invention.

[Explanation of symbols]

1 ... internal combustion engine 2 ... exhaust passage 7 ... NO _X occluding and reducing catalyst 30 ... electronic control unit (ECU) 29, 31 ... O ₂ sensor 33 ... NO _X sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/24 R 3/28 301 3/28 301C 3/36 3/36 B F02D 41 / 14 310 F02D 41/14 310K 310J 41/22 305 41/22 305Z 43/00 301 43/00 301E 301B 45/00 314 45/00 314Z F term (reference) 3G084 BA09 BA17 DA02 DA10 DA27 EA11 EB22 FA28 FA30 3G091 AA02 AA12 AA17 AA18 AA24 AA28 AB03 AB06 BA11 BA14 BA15 BA19 CA18 CB01 CB05 DA02 DA03 DA08 DB10 DC01 EA26 EA30 EA33 EA34 FB06 FB07 FB10 FB12 FC01 FC04 GB02W GB03W GB04W GB05W GB06W GB10X HA08 HA13 HA01 HA36 HA01 HA36 PD01Z PD08Z

Claims (6)

[Claims] 1. A were placed in an exhaust passage of an internal combustion engine, air-fuel ratio of the exhaust gas flowing into absorbs NO _X in the exhaust gas when the lean, the NO _X in which the oxygen concentration in the exhaust gas absorbed when drops flowing and _the NO _X storage reduction catalyst to release the NO _X concentration detecting means for detecting the concentration of NO _X in the exhaust gas after the _the NO _X storage reduction catalyst passage, the NO _X concentration detecting means is concentration of NO _X in the detected exhaust When the predetermined value or more is reached, the exhaust air-fuel ratio flowing into the NO _X storage-reduction catalyst is set to a rich air-fuel ratio to release the NO _X absorbed from the NO _X storage-reduction catalyst, thereby reducing and purifying the regeneration. Means for judging that unpurified NO _X is discharged from the NO _X storage reduction catalyst to the downstream side when the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst becomes a rich air-fuel ratio. and _X release determining means, the non Of when the release of the NO _X is determined to have occurred, an exhaust purifying apparatus for an internal combustion engine and a prohibiting means for said reproducing means is prohibited from the exhaust air-fuel ratio to a rich air-fuel ratio. Wherein said NO _X emission determining means, the NO _X
Atmosphere air-fuel ratio of the storage-reduction the catalyst comprises a catalyst air-fuel ratio determining means for determining whether or not rich air-fuel ratio, the NO _X
Atmosphere air-fuel ratio of the storage-reduction the catalyst is determined to rich air-fuel ratio, and the NO _X concentration the when NO _X concentration detected by the detection means is a predetermined judgment value or more NO _X from storage reduction catalyst unpurified NO The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein it is determined that _X is released. Wherein the catalyst air-fuel ratio determining means, the NO _X
Disposed on at least one of the storage-reduction catalyst upstream exhaust passage or the downstream exhaust passage, comprising an air-fuel ratio sensor for detecting an exhaust air-fuel ratio, NO _X occluding and reducing catalyst based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor 3. The exhaust gas purification device for an internal combustion engine according to claim 2, wherein it is determined whether or not the atmosphere air-fuel ratio in the inside is a rich air-fuel ratio. Wherein said NO _X emission determining means, until a predetermined time has elapsed from when said reproducing means changing the air-fuel ratio of the exhaust gas flowing into the _the NO _X storage reduction catalyst to a rich air-fuel ratio an exhaust purification system of an internal combustion engine according to claim 1 determines that the unpurified of the NO _X emission occurs. 5. The fuel cell system according to claim 1, further comprising a deterioration determination unit configured to determine whether the NO _X storage reduction catalyst has deteriorated, wherein the deterioration determination unit terminates the release of the unpurified NO _X by the NO _X release determination unit. when it is determined, if the detected concentration of NO _X the NO _X concentration detecting means is a predetermined deterioration determination value or more, it is determined that the _the NO _X storage reduction catalyst has degraded, in claim 1 An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 6. The method according to claim 1, wherein the deterioration determination unit determines the NO.
_When it is determined that the _X storage reduction catalyst has deteriorated, the N
6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5, further comprising a recovery control means for performing a recovery operation for recovering the NO _X storage capacity of the O _X storage reduction catalyst.