JP2006266144A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress sulfur poisoning of a NOx catalyst when fuel of high sulfur concentration is used while deterioration of fuel economy being avoided in a device having a SOx catalyst in an upstream of the NOx catalyst. <P>SOLUTION: This device is provided with a first catalyst 31 capable of collecting SOx composition in exhaust gas in an exhaust pipe 20. a second catalyst 32 provided in the exhaust pipe in a down stream side of the first catalyst and collecting particulate matters and eliminating NOx, the SOx concentration sensor 23 provided in an upstream of the first catalyst and detecting SOx concentration in exhaust gas, and a reducing agent injection valve 15 supplying reducing agent at a predetermined interval in the exhaust pipe at a middle of the first catalyst and the second catalyst. A bypass pipe 21 connects the upstream part of the first catalyst and the downstream part of the second catalyst of the exhaust pipe with bypassing the first catalyst and the second catalyst. An exhaust gas control valve 22 changes over a flow passage of exhaust gas between the exhaust pipe and the bypass pipe. If Sox concentration is higher than a predetermined value, the exhaust gas control valve is controlled to make exhaust gas pass through the bypass pipe. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for a diesel engine.

As an exhaust purification device that purifies NOx in exhaust gas discharged from an internal combustion engine, there is a NOx absorbent represented by a NOx storage reduction catalyst. The NOx absorbent absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean (that is, in an oxygen-excess atmosphere), and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas decreases, The NOx storage reduction catalyst, which is a kind of NOx absorbent, absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean (ie, in an oxygen-excess atmosphere) and absorbs when the oxygen concentration of the inflowing exhaust gas decreases. This catalyst releases released NOx and reduces it to N ₂ .

When this NOx storage reduction catalyst (hereinafter also referred to simply as a catalyst or NOx catalyst) is disposed in the exhaust pipe of an internal combustion engine, when exhaust gas having a lean air-fuel ratio flows, NOx in the exhaust gas is absorbed by the catalyst, When exhaust gas with stoichiometric (theoretical air / fuel ratio) or rich air / fuel ratio flows, NOx absorbed in the catalyst is released as NO ₂ and further reduced to N ₂ by reducing components such as HC and CO in the exhaust gas. That is, NOx is purified.

By the way, in general, the fuel of the internal combustion engine contains a sulfur content. When the fuel is burned in the internal combustion engine, the sulfur content in the fuel is combusted to generate sulfur oxides (SOx) such as SO ₂ and SO _3. appear. The NOx storage reduction catalyst absorbs SOx in the exhaust gas by the same mechanism that absorbs NOx. Therefore, when this NOx catalyst is arranged in the exhaust pipe of an internal combustion engine, only NOx is present in the NOx catalyst. SOx is also absorbed.

  However, since SOx absorbed by the NOx catalyst forms a stable sulfate with time, it is difficult to decompose and release under the same conditions as NOx release / reduction from the NOx catalyst and accumulate in the catalyst. There is a tendency to be easily done. Therefore, if the amount of SOx accumulated in the NOx catalyst increases, the NOx absorption capacity of the catalyst decreases, and NOx in the exhaust gas cannot be sufficiently removed, resulting in a reduction in NOx purification efficiency. This is so-called SOx poisoning.

Therefore, in order to maintain the NOx purification capacity of the NOx storage reduction catalyst high over a long period of time, an SOx absorbent that mainly absorbs SOx in the exhaust gas is disposed upstream of the NOx catalyst, and the SOx is disposed in the NOx catalyst. Exhaust gas purification devices have been developed that prevent SOx poisoning of the NOx storage reduction catalyst so as not to flow in.
As an exhaust purification device in which the SOx absorbent that mainly absorbs SOx in the exhaust gas is arranged upstream of the NOx catalyst as described above, for example, there are devices described in Patent Literature 1 and Patent Literature 2.

Said SOx absorbent, the air-fuel ratio of the inflow gas absorbs SOx when the lean, but the SOx absorbed when the oxygen concentration in the inlet gas is low it is to release as SO _2, SOx in the SOx absorbent Since the absorption capacity is also limited, it is necessary to perform a process for releasing SOx from the SOx absorbent, that is, a regeneration process, before the SOx absorbent is saturated with SOx.

  For this purpose, for example, as disclosed in Patent Document 3, fuel is injected upstream of the SOx absorbent, and the air-fuel ratio of the inflowing exhaust gas is stoichiometric or rich to reduce the oxygen concentration and release SOx. There is.

  However, in this case, SOx is released little by little from the SOx absorbent. Therefore, in order to release all absorbed SOx from the SOx absorbent, the air-fuel ratio must be rich for a long time, and a large amount of fuel is required, resulting in a deterioration in fuel consumption.

JP 2000-230419 A JP 2004-92524 A JP-A-6-346768

  In view of the above problems, an object of the present invention is to suppress sulfur poisoning of a NOx catalyst without inducing deterioration of S fuel consumption.

According to the first aspect of the present invention, the first catalyst provided in the exhaust pipe captures SOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and the air-fuel ratio of the inflowing exhaust gas A first catalyst having the property that when the temperature rises under lean, the trapped SOx gradually diffuses into the interior and the SOx trapping function on the surface side recovers;
A second catalyst that is provided in an exhaust pipe on the downstream side of the first catalyst and collects particulate matter and purifies NOx. NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean A second catalyst that releases the stored NOx when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich,
SOx concentration detecting means provided upstream of the first catalyst for detecting the SOx concentration in the exhaust gas;
When the reducing agent supply means for supplying the reducing agent to the exhaust pipe between the first catalyst and the second catalyst at a predetermined interval is provided, and the SOx concentration detecting means detects SOx having a concentration higher than the predetermined value, An exhaust gas purifying device for an internal combustion engine is provided that restricts the exhaust gas from flowing into the first catalyst and the second catalyst.

According to the invention of claim 2, in the invention of claim 1, a bypass pipe that bypasses the first catalyst and the second catalyst and connects the upstream part of the first catalyst and the downstream part of the second catalyst in the exhaust pipe; An exhaust gas control valve that switches an exhaust gas flow path between an exhaust pipe and a bypass pipe;
An exhaust gas purification device is provided that controls the exhaust gas control valve so that the exhaust gas passes through the bypass passage when the SOx concentration detection means detects SOx having a concentration higher than a predetermined value.

  According to a third aspect of the present invention, there is provided the exhaust gas purifying apparatus according to the second aspect of the present invention, wherein the oxidation catalyst is disposed in the exhaust pipe downstream of the attachment position of the downstream end of the bypass passage.

  According to the invention of claim 4, in the invention of claim 1, when the SOx concentration detection means detects SOx having a concentration higher than a predetermined value, the supply of the reducing agent by the reducing agent supply means is stopped. Thus, an exhaust gas purification device is provided.

  According to the invention of claim 5, in the invention of claim 1, when the SOx concentration detecting means detects SOx having a concentration higher than a predetermined value, the reducing agent supply means extends the interval for supplying the reducing agent. An exhaust gas purification apparatus configured as described above is provided.

  According to the invention of claim 6, in the invention of claim 1, when the SOx concentration detecting means detects SOx having a concentration higher than a predetermined value, the supply amount when the reducing agent supply means supplies the reducing agent. There is provided an exhaust gas purification device that reduces the amount of exhaust gas.

  According to the invention of claim 7, in the invention of claim 1, it comprises SOx poisoning detection means for detecting the poisoning amount of the second catalyst by SOx, and when the poisoning amount exceeds a predetermined amount, Provided is an exhaust gas purifying apparatus that performs a first catalyst function recovery process for recovering the SOx capturing function of a first catalyst.

  According to the invention of claim 8, in the invention of claim 7, the first catalytic function recovery processing is performed by delaying the fuel injection timing to the combustion chamber after the compression top dead center with the air-fuel ratio being lean. There is provided an exhaust gas purifying apparatus having an increased temperature.

  According to the ninth aspect of the invention, in the seventh aspect of the invention, the SOx poisoning detection means is provided with NOx detection means for detecting the NOx concentration downstream of the second catalyst, and the NOx concentration detected by the NOx detection means is adjusted. Based on the above, an exhaust gas purifying device for detecting the poisoning amount of a catalyst by SOx is provided.

  The exhaust gas purification apparatus of the present invention is a first catalyst provided in an exhaust pipe, captures SOx contained in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and air-fuel ratio of the inflowing exhaust gas However, when the temperature rises under lean, the trapped SOx gradually diffuses into the interior and the SOx trapping function on the surface side recovers, and the exhaust pipe on the downstream side of the first catalyst is provided. A second catalyst that collects particulate matter and purifies NOx, and stores the NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and the air-fuel ratio of the inflowing exhaust gas is theoretically A second catalyst that releases the stored NOx when it becomes air-fuel ratio or rich, SOx concentration detection means that is provided upstream of the first catalyst and detects the SOx concentration in the exhaust gas, and intermediate between the first catalyst and the second catalyst In the exhaust pipe When the SOx concentration detecting means detects SOx having a concentration higher than a predetermined value, the exhaust gas flows into the first catalyst and the second catalyst. This limits the poisoning of the catalyst when a fuel having a high sulfur concentration is used.

Hereinafter, embodiments of the exhaust emission control device of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a hardware configuration of a first embodiment of an exhaust emission control device according to the present invention, and shows a case where the present invention is applied to an in-cylinder injection type compression ignition type diesel internal combustion engine. The exhaust purification device used in the present invention can also be mounted on a spark ignition internal combustion engine.

Referring to FIG. 1, 1 is an engine body, 2 is an intake manifold, 3 is an exhaust manifold, 4 is an intake pipe, and 20 is an exhaust pipe. The intake manifold 2 is connected to a compressor 6 a of an exhaust turbocharger 6 through an intake pipe 4. The intake pipe 4 is provided with a throttle valve 30 driven by a motor 31 and an intercooler 7 for cooling air pressurized by the compressor 6 a of the exhaust turbocharger 6.
Each fuel injection valve 10 is connected to a common rail 11. Fuel is supplied into the common rail 11 by an electrically controlled fuel pump 12 having a variable discharge amount. A fuel pump 14 provided in a fuel tank 13 is connected to the fuel pump 12. Then fuel is delivered.

  On the other hand, the exhaust manifold 3 is connected to the turbine 6 b of the exhaust turbocharger 6, and the outlet of the turbine 6 b is connected to the exhaust pipe 20. A first catalyst 31 and a second catalyst 32 are provided in the exhaust pipe 20, and the bypass passage 21 bypasses the first catalyst 31 and the second catalyst 32, and the upstream portion of the first catalyst 31 in the exhaust pipe 20 The downstream portion of the second catalyst 32 is in communication. An exhaust control valve 22 for switching the exhaust gas passage is provided at the upstream attachment portion of the bypass passage 21. Reference numeral 15 denotes a reducing agent injection valve for adding a reducing agent to the second catalyst 32. The reducing agent injection valve 15 injects the fuel supplied from the fuel pump 12 into the exhaust pipe 20 between the first catalyst 31 and the second catalyst 32 from the nozzle 15a.

  An SOx sensor 23 detects the concentration of SOx in the exhaust gas. The SOx sensor 23 has a structure as disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-239706. That is, a solid electrolyte having oxide ion conductivity, and a sulfate layer formed on a part of the surface of the solid electrolyte, comprising an alkali metal element and / or an alkaline earth metal element and a rare earth element A sulfate layer mainly composed of a bisulfate, an electrode in electrical contact with the sulfate layer, and an electrode in electrical contact with the solid electrolyte at a position away from the sulfate layer. A signal corresponding to the concentration of SOx is generated.

  Reference numeral 50 denotes an electronic control unit (ECU). The electronic control unit 50 includes a digital computer, and is connected to a ROM (read only memory) 52, a RAM (random access memory) 53, a CPU ( A microprocessor) 54, an input port 55, and an output port 56.

  The first catalyst 31 is a catalyst for collecting SOx. For example, a coat layer is formed on the surface of a honeycomb monolithic carrier, and a noble metal such as platinum (Pt) is dispersed and supported on the coat layer. The carrier is formed of alumina and has a large number of exhaust gas flow holes extending straight in the axial direction. The coating layer is an alkali metal such as potassium (K), sodium (Na), cesium (Cs), alkaline earth such as barium (Ba), calcium (Ca), lanthanum (La), yttrium (Y), etc. The coating layer contains at least one rare earth element and has a strong basicity.

SOx contained in the exhaust gas, that is, SO ₂ is oxidized by platinum (Pt) and then trapped in the coat layer. That is, SO ₂ diffuses into the coat layer in the form of SO ₄ ^2- to form a sulfate. The SOx concentration in the coat layer is highest near the surface, and gradually decreases toward the back. When the SOx concentration in the vicinity of the surface of the coat layer increases, the basicity of the surface of the coat layer weakens and the SOx collecting ability decreases.
The first catalyst 31 has a coating layer so that the SOx concentration existing in the vicinity of the surface of the coating layer becomes uniform in the coating layer when the temperature is raised while the air-fuel ratio of the exhaust gas is lean. It spreads toward the back of the. When SOx concentrated in the vicinity of the surface of the coat layer diffuses toward the inner part of the coat layer, the SOx concentration in the vicinity of the surface of the coat layer decreases and the SOx trapping function is restored.

  The second catalyst 32 is a NOx storage catalyst, and an exhaust gas inflow passage comprising an elongated passage with the downstream end closed and an exhaust gas outflow passage comprising an elongated passage with the upstream end closed via a thin partition wall. Alternatingly arranged, a large number of filter structures are arranged adjacent to each other. This partition is made of a porous material such as cordierite as a catalyst carrier.

  A noble metal such as platinum (Pt) and an alkali metal such as potassium (K), sodium (Na), lithium (Li), and cesium (Cs) on both side surfaces of the partition walls and the surfaces of both end walls; A NOx occlusion agent containing at least one of alkaline earth metals such as barium (Ba) and calcium (Ca), and rare earths such as lanthanum (La) and yttrium (Y) is supported.

When the exhaust gas is lean, NO contained in the exhaust gas is oxidized on platinum (Pt) to become NO ₂ and then absorbed by the NOx storage agent. For example, when the NOx storage agent contains barium (Ba), it is oxidized. It diffuses into the inside of the NOx storage agent in the form of nitrate ions NO ₃ ⁻ while being combined with barium (BaO). In this way, NOx is absorbed by the NOx storage agent. As long as the oxygen concentration in the exhaust gas is high, NO ₂ is generated on the surface of platinum (Pt). As long as the NOx storage capacity of the NOx storage agent is not saturated, NO ₂ is absorbed in the NOx storage agent and nitrate ions NO ₃ ⁻ are generated. Generated.

On the other hand, when the fuel as the reducing agent is supplied from the reducing agent injection valve 15 into the exhaust gas, if the air-fuel ratio of the going gas is made rich or stoichiometric, the oxygen concentration in the exhaust gas decreases, so the reaction is reversed. In the direction (NO ₃ ⁻ → NO ₂ ), nitrate ions NO ₃ ⁻ in the NOx storage agent are released from the NOx storage agent in the form of NO ₂ , and the released NO ₂ is unburned contained in the exhaust gas. Reduced by HC and CO. Therefore, in this embodiment, before the NOx absorption capacity of the NOx storage agent is saturated, the fuel as the reducing agent is supplied from the reducing agent injection valve 15 into the exhaust gas to temporarily enrich the air-fuel ratio of the exhaust gas, and thus the NOx storage agent. NOx is released from the air.

  FIG. 5 shows a flowchart of the control according to the first embodiment. In step S11, the SOx concentration SOX detected by the SOx sensor 23 is read. In step S12, it is determined whether the SOX read in step S11 is larger than a predetermined determination value SOXA. If an affirmative determination is made in step S12, that is, if SOX is larger than a predetermined determination value SOXA, the process proceeds to step S13, the exhaust control valve 22 is controlled so that the exhaust gas flows through the bypass pipe 21, and then the process returns. . On the other hand, if a negative determination is made in step S12, that is, if SOX is smaller than a predetermined determination value SOXA, the process proceeds to step S14 and the exhaust control valve 22 is controlled so that the exhaust gas flows through the exhaust pipe 20, That is, control is performed so that normal operation is possible, and then the process returns.

  Next, a modification of the first embodiment will be described. FIG. 2 shows a hardware configuration of a modified example of the first embodiment. In the modified example of the first embodiment, the exhaust gas is the first catalyst 31 in the first embodiment. Since the second catalyst 32 is discharged without being purified without passing through the second catalyst 32, a third catalyst 33 made of an oxidation catalyst is disposed in the exhaust pipe 20 downstream of the downstream attachment portion of the bypass pipe 21, and this third catalyst is arranged. 33 is for purifying at least HC and CO.

Next, a second embodiment will be described. FIG. 3 is a diagram illustrating a hardware configuration of the second embodiment. As shown in FIG. 3, the second embodiment does not include the bypass pipe 21 unlike the first embodiment. Therefore, in the second embodiment, when the SOx concentration is high, the reducing agent injection valve 15 is closed to prevent the second catalyst 32 from being contaminated with fuel having a high sulfur content.
FIG. 6 is a flowchart of the control of the second embodiment. Step S13 of the flowchart of the first embodiment is set to step S13a, and the supply of the reducing agent is stopped in step S13a. The other steps are the same except for the difference.

  FIG. 7 is a flowchart of the control of the first modification of the second embodiment. Step S13a of the second embodiment is changed to step S13b to reduce the reducing agent supply amount. However, the other steps are the same as in the second embodiment. By doing so, the poisoning of the second catalyst 32 by SOx is suppressed, but the reduction of NOx is not completely stopped.

  FIG. 8 is a flowchart of the control of the second modification of the second embodiment. Step S13a of the second embodiment is changed to step S13c, and the interval for supplying the reducing agent is expanded. However, the other steps are the same as in the second embodiment. By doing so, the poisoning of the second catalyst 32 by SOx is suppressed, but the reduction of NOx is not completely stopped. FIG. 10 shows the relationship between the SOx concentration and the interval, and the interval increases as the detected SOx concentration increases.

Next, a third embodiment will be described.
In the first embodiment and the second embodiment (including the first and second modifications), the function recovery process of the first catalyst is not performed. In the embodiment, when the S poisoning of the second catalyst 32 becomes large, a process for recovering the SOx capturing function of the first catalyst 31 is performed.

  FIG. 4 shows the hardware configuration of the third embodiment. Compared with the second embodiment, a NOx sensor 24 for detecting the concentration of NOx is provided at the outlet of the second catalyst 32. When the concentration of NOx detected by the NOx sensor 24 is higher than a predetermined value, it is assumed that the amount of S poisoning has increased, and the processing for recovering the SOx capturing function is performed as described above.

  The recovery of the SOx trapping function of the first catalyst 31 is performed by increasing the exhaust gas temperature while the air-fuel ratio of the exhaust gas is lean as described above. Therefore, in the third embodiment, the fuel injection timing is retarded until after the compression top dead center. Thus, if the fuel injection timing is retarded, the afterburning period becomes longer, and as a result, the exhaust gas temperature rises.

  FIG. 9 is a flowchart of the control of the third embodiment. Step S15 for reading the NOx concentration in the flowchart of the second embodiment shown in FIG. 6, and the read NOx concentration NOX is obtained from the determination value NOXA. Step S16 for determining whether the catalyst is larger or not, and Step S17 for regenerating the SOx capturing function of the first catalyst 31 when an affirmative determination is made in Step S16, are added.

  Various types of NOx sensors have already been proposed, and any type may be used. For example, Japanese Patent Laid-Open No. 7-325059 discloses a NOx sensor in which the NOx gas sensitive body is made of strontium, titanium, and oxygen.

  The present invention is applied to an exhaust gas purification device for an internal combustion engine, but is particularly suitable for a diesel engine.

It is a figure which shows the hardware constitutions of 1st Embodiment. It is a figure which shows the hardware constitutions of the modification of 1st Embodiment. It is a figure which shows the hardware constitutions of 2nd Embodiment. It is a flowchart of control of a 3rd embodiment. It is a flowchart of control of a 1st embodiment. It is a flowchart of control of a 2nd embodiment. It is a flowchart of control of the 1st modification of 2nd Embodiment. It is a flowchart of control of the 2nd modification of 2nd Embodiment. It is a flowchart of control of a 3rd embodiment. It is a graph which shows the relationship between SOx density | concentration and the interval in the 2nd modification of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake manifold 3 Exhaust manifold 4 Intake pipe 6 Exhaust turbocharger 10 Fuel injection valve 11 Common rail 12 Fuel pump 15 Reducing agent injection valve 16 Reducing agent injection valve 20 Exhaust pipe 21 Bypass pipe 22 Exhaust control valve 23 SOx sensor 24 NOx Sensor 31 First catalyst 32 Second catalyst 33 Third catalyst 50 ECU

Claims (9)

A first catalyst provided in the exhaust pipe that captures SOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and the temperature rises when the air-fuel ratio of the inflowing exhaust gas is lean Then, the trapped SOx gradually diffuses into the inside, and the first catalyst having the property of recovering the surface-side SOx trapping function;
A second catalyst that is provided in an exhaust pipe on the downstream side of the first catalyst and collects particulate matter and purifies NOx. NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean A second catalyst that releases the stored NOx when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich,
SOx concentration detecting means provided upstream of the first catalyst for detecting the SOx concentration in the exhaust gas;
A reducing agent supply means for supplying a reducing agent to the exhaust pipe between the first catalyst and the second catalyst at a predetermined interval;
An exhaust gas purifying device for an internal combustion engine, wherein when the SOx concentration detecting means detects SOx having a concentration higher than a predetermined value, the exhaust gas is restricted from flowing into the first catalyst and the second catalyst. A bypass pipe that bypasses the first catalyst and the second catalyst and connects the upstream part of the first catalyst and the downstream part of the second catalyst in the exhaust pipe, and exhaust gas that switches the flow path of the exhaust gas between the exhaust pipe and the bypass pipe A gas control valve,
2. The internal combustion engine according to claim 1, wherein when the SOx concentration detecting means detects SOx having a concentration higher than a predetermined value, the exhaust gas control valve is controlled so that the exhaust gas passes through the bypass passage. Exhaust gas purification device.   The exhaust gas purifying device for an internal combustion engine according to claim 2, wherein an oxidation catalyst is disposed in the exhaust pipe downstream of the attachment position of the downstream end of the bypass passage.   2. The exhaust gas purification of an internal combustion engine according to claim 1, wherein when the SOx concentration detecting means detects SOx having a concentration higher than a predetermined value, supply of the reducing agent by the reducing agent supply means is stopped. apparatus.   2. The exhaust of an internal combustion engine according to claim 1, wherein when the SOx concentration detecting means detects SOx having a concentration higher than a predetermined value, the reducing agent supplying means lengthens the interval for supplying the reducing agent. Gas purification device.   2. The internal combustion engine according to claim 1, wherein when the SOx concentration detecting means detects SOx having a concentration higher than a predetermined value, the supply amount when the reducing agent supply means supplies the reducing agent is reduced. Engine exhaust gas purification device.   SOx poisoning detection means for detecting the poisoning amount of the second catalyst by SOx, and when the poisoning amount exceeds a predetermined amount, a first catalyst function recovery process for recovering the SOx capturing function of the first catalyst The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein   8. The first catalytic function recovery process is characterized in that the temperature of exhaust gas is increased by delaying the fuel injection timing into the combustion chamber after the compression top dead center with the air-fuel ratio being lean. Exhaust gas purification device for internal combustion engine.   The SOx poisoning detection means is provided with NOx detection means for detecting the NOx concentration downstream of the second catalyst, and detects the poisoning amount of the catalyst due to SOx based on the NOx concentration detected by the NOx detection means. The exhaust gas purification device according to claim 7.

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