JP2004092591A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent thermal degradation of an NOx storage/reducing catalyst, to prevent lowering of engine performance, and to prevent thermal breakage, in an exhaust emission control device equipped with the NOx storage/reducing catalyst and a bypass passage. <P>SOLUTION: In the exhaust emission control device for an internal combustion engine provided with the NOx storage/reducing catalyst in an exhaust passage, the exhaust bypass passage bypassing the NOx storage/reducing catalyst is provided, and an opening/closing valve opening/closing the exhaust bypass passage is provided. In an operation state of the internal combustion engine wherein many NOx components exist in exhaust gas, the opening/closing valve is closed, and in an operation state of the internal combustion engine wherein few NOx components exist in the exhaust gas, the opening/closing valve is opened. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an improvement in an exhaust gas purifying apparatus for an internal combustion engine provided with a NOx storage reduction catalyst for purifying NOx components of exhaust gas.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a three-way catalyst is generally provided in an exhaust passage of an internal combustion engine as an exhaust gas purification device for an internal combustion engine. It is known that this three-way catalyst can efficiently purify HC, CO, and NOx components contained in exhaust gas while the internal combustion engine is operated at a stoichiometric air-fuel ratio.
[0003]
On the other hand, as one of the methods for improving the fuel efficiency of the internal combustion engine, in recent years, the internal combustion engine has been operated at a lean air-fuel ratio in which the amount of air is excessive than the stoichiometric air-fuel ratio. Then, even in the exhaust gas discharged from the internal combustion engine operated at the lean air-fuel ratio, the air amount becomes excessive, and the reduction amount of NOx in the three-way catalyst becomes small.
[0004]
Therefore, in an internal combustion engine operating at a lean air-fuel ratio, NOx in exhaust gas discharged from the internal combustion engine operated at a lean air-fuel ratio is provided by providing a NOx storage reduction catalyst separately from the three-way catalyst in the exhaust passage. Reductions have been made.
[0005]
However, it is known that the NOx storage reduction catalyst has a purification temperature window and is deteriorated by sulfur poisoning. Further, in a high temperature state, the sulfur poisoning component may be crystallized, and the sulfur component may be permanently poisoned.
[0006]
Therefore, a NOx decomposition catalyst is arranged in series downstream of the NOx absorbent, a bypass passage for bypassing the NOx decomposition catalyst is provided, and a bypass valve is provided in the bypass passage so that the temperature of the exhaust gas becomes higher than a predetermined temperature. An exhaust gas purifying device has been proposed in which the bypass valve is opened when the exhaust gas flows through the bypass passage to prevent the high-temperature exhaust gas from poisoning the NOx decomposition catalyst with sulfur (see, for example, Patent Document 1). .
[0007]
[Patent Document 1]
JP-A-5-98954 (Claims, FIG. 1)
[0008]
[Problems to be solved by the invention]
By the way, the pressure loss of the exhaust pipe forming the exhaust passage is determined by adding the throttle amount of each exhaust passage component such as a catalyst, a muffler, and a pipe, and when the exhaust passage component is added on the exhaust passage, The partial pressure loss increases. The effect of the pressure loss increases as the flow rate of the exhaust gas flowing through the exhaust passage increases, and when the pressure loss increases, the intake air amount decreases due to a rise in the pressure when the intake valve and the exhaust valve overlap, and the internal combustion is reduced. There is a problem that the performance of the engine is reduced.
[0009]
In addition, the temperature of the exhaust pipe changes in the order of several hundred degrees, and in the case of an exhaust passage in which exhaust pipes having different lengths are connected in parallel, when exhaust gas flows through only one of the exhaust pipes, two exhaust pipes are used. There is a problem that a strain is generated between the two exhaust pipes due to a difference in elongation of the exhaust pipes and the exhaust pipes are broken. That is, as disclosed in Patent Document 1, when a NOx decomposition catalyst is arranged in series and a bypass passage for bypassing the NOx decomposition catalyst is provided, the flow rate of the exhaust gas is reduced by opening and closing the valve in the bypass passage. The temperature changes greatly on the bypass passage side), the temperature difference between the two passages increases, and distortion occurs between the two exhaust passages, and the exhaust pipe is broken.
[0010]
Further, in a gasoline direct injection engine in which fuel gasoline is directly injected into a cylinder of the internal combustion engine, stratified combustion (lean combustion) is performed in a low rotation and low flow rate region of the internal combustion engine, and the high rotation and high rotation of the internal combustion engine are performed. At the time of flow, the internal combustion engine is operated at the stoichiometric air-fuel ratio.
Therefore, when the internal combustion engine is rotating at a high speed and at a high flow rate, the exhaust gas is sufficiently purified by the three-way catalyst, so that the NOx storage reduction catalyst becomes unnecessary.
[0011]
In view of the above, the present invention provides an internal combustion engine having an NOx storage reduction catalyst in an exhaust passage and a bypass passage that bypasses the NOx storage reduction catalyst. Prevention of deterioration of the internal combustion engine due to an increase in pressure loss at the time of high rotation and high flow rate of the internal combustion engine, and prevention of destruction of the exhaust passage due to thermal expansion of one of the exhaust passages arranged in parallel. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine.
[0012]
[Means for Solving the Problems]
The exhaust gas purifying apparatus for an internal combustion engine of the present invention that achieves the above object can take the following first to eighth modes.
[0013]
According to a first aspect, in an exhaust gas purifying apparatus for an internal combustion engine in which an NOx storage reduction catalyst is provided in an exhaust passage of the internal combustion engine, an exhaust bypass passage that bypasses the NOx storage reduction catalyst is provided, and an opening and closing that opens and closes the exhaust bypass passage is provided. A valve is provided, wherein the on-off valve is closed in an operating state of the internal combustion engine having a high NOx component in the exhaust gas, and the on-off valve is opened in an operating state of the internal combustion engine having a low NOx component in the exhaust gas. Is what you do.
[0014]
The second embodiment is characterized in that, in the first embodiment, a bypass passage is provided so that the axis of the bypass passage is coaxial with the axis of the exhaust passage before and after the NOx storage reduction catalyst.
[0015]
The third embodiment is characterized in that, in the first or second embodiment, the on-off valve is provided in the middle of the bypass passage.
[0016]
The fourth embodiment is characterized in that, in the first or second embodiment, an on-off valve is provided at a branch portion of the bypass passage from the exhaust passage.
[0017]
According to a fifth aspect, in any one of the first to fourth aspects, the on-off valve is controlled by an electronic control circuit that detects an operating state of the internal combustion engine and controls the internal combustion engine. The valve is configured to be opened at the time of high rotation of the engine whose rotation speed exceeds a predetermined rotation speed.
[0018]
The sixth mode is characterized in that, in any one of the first to fifth modes, a flexible pipe capable of absorbing thermal expansion and contraction of an exhaust gas passage portion parallel to the bypass passage is provided in the middle of the bypass passage. Things.
[0019]
The seventh mode is characterized in that in any one of the first to sixth modes, the NOx storage reduction catalyst is constituted by a first NOx storage reduction catalyst and a second NOx storage reduction catalyst. is there.
[0020]
An eighth aspect is characterized in that in any one of the first to seventh aspects, a three-way catalyst is provided on each of an upstream side and a downstream side of a bypass passage connected to the exhaust passage. It is.
[0021]
According to the exhaust gas purifying apparatus for an internal combustion engine of the first embodiment, in an operating state of the internal combustion engine in which the exhaust gas contains a large amount of NOx, the exhaust gas passes through the NOx storage reduction catalyst and the exhaust gas contains a small amount of the NOx component. In the operation state, the exhaust gas bypasses the NOx storage reduction catalyst, so that the performance of the internal combustion engine can be improved without lowering the NOx purification performance.
[0022]
According to the exhaust gas purifying apparatus for an internal combustion engine of the second embodiment, it is possible to suppress the pressure loss when the exhaust gas bypasses the NOx storage reduction catalyst.
[0023]
According to the third and fourth embodiments of the exhaust gas purifying apparatus for an internal combustion engine, the on-off valve does not have exhaust resistance when the exhaust gas flows through the NOx storage reduction catalyst.
[0024]
According to the exhaust gas purifying apparatus for an internal combustion engine according to the fifth aspect, the exhaust gas passes through the bypass passage when the internal combustion engine is rotating at a high speed, so that unnecessary temperature rise is prevented and the sulfur poisoning amount of the NOx storage reduction catalyst is reduced. At the same time, the pressure loss is reduced and the performance of the internal combustion engine is improved.
[0025]
According to the exhaust gas purifying apparatus for an internal combustion engine of the sixth aspect, even if the exhaust passage provided with the NOx storage reduction catalyst expands and contracts due to a temperature difference from the bypass passage, the bypass passage is not damaged.
[0026]
According to the exhaust gas purifying apparatus for an internal combustion engine of the seventh aspect, the capacity of the NOx storage reduction catalyst can be increased.
[0027]
According to the exhaust gas purifying apparatus for an internal combustion engine of the eighth aspect, the purification performance of the exhaust gas is improved.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings based on specific examples.
[0029]
FIG. 1 shows a configuration of an embodiment of an exhaust gas purifying apparatus for an internal combustion engine (hereinafter referred to as an engine) of the present invention, and is a configuration diagram showing an entire exhaust path of the engine.
[0030]
The intake air is introduced into the engine 1 shown in FIG. 1 through an intake passage (not shown).
A throttle valve for adjusting the amount of intake air is provided in the intake path. The intake air passing through the throttle valve passes through the surge tank 2 and enters the engine 1 from the intake port 3.
The engine 1 of this embodiment has six cylinders, and each cylinder is provided with an intake port 3 or a fuel injection valve (not shown) for injecting fuel into the cylinder. Fuel from a fuel tank (not shown) is guided to the fuel injection valve, and the fuel is injected by being opened by a signal from an electronic control unit (hereinafter referred to as ECU) 10 for controlling the engine 1. You.
[0031]
In this embodiment, the exhaust gas discharged from each cylinder of the engine 1 after the combustion is combined into three cylinders by two sets of exhaust manifolds 4, and a three-way catalyst (start catalyst) provided downstream of each exhaust manifold 4 is provided. ) Purified by 5 and 6. Exhaust gas that has passed through the three-way catalysts 5 and 6 is collected into one by a collecting pipe 7. The collecting pipe 7 includes a first branch pipe 7A connected to the three-way catalyst 5, a second branch pipe 7B connected to the three-way catalyst 6, and a main pipe 7C. The main pipe 7C is provided with an A / F sensor (oxygen sensor) 9 for detecting the air-fuel ratio of the air-fuel mixture sucked into the engine 1 from the oxygen concentration in the exhaust gas. Is input to the ECU 10.
[0032]
In this embodiment, a first NOx occlusion / reduction catalyst 11 and a second NOx occlusion / reduction catalyst 12 for purifying NOx components in exhaust gas are provided on the exhaust pipe 8 on the downstream side of the main pipe 7C of the collecting pipe 7. , Arranged in series. The exhaust pipe 8 on the downstream side of the second NOx storage reduction catalyst 12 is provided with another three-way catalyst (sweeper) 13, a sub-muffler 14, and a main muffler 15, and the exhaust gas passes therethrough. Released into the atmosphere. In this embodiment, the first and second two NOx storage reduction catalysts 11 and 12 are provided in the exhaust pipe 8, but the number of NOx storage reduction catalysts may be one.
[0033]
On the other hand, in this embodiment, a bypass passage 20 is provided in parallel with the exhaust pipe 8 in which the first NOx storage reduction catalyst 11 and the second NOx storage reduction catalyst 12 are provided. The bypass passage 20 has a first bypass pipe 21 having one end connected to a connection portion between the main pipe 7C of the collecting pipe 7 and the exhaust pipe 8, a flexible pipe 22 connected to the other end of the first bypass pipe 21, and a flexible pipe. An on-off valve 23 connected to the other end of the valve 22 and a second bypass pipe 23 connecting the downstream side of the on-off valve 23 to the exhaust pipe 8 on the upstream side of the three-way catalyst 13.
[0034]
The on / off valve 23 is controlled by the ECU 10 to open and close. In addition to the air-fuel ratio signal from the A / F sensor 9, the ECU 10 outputs an engine speed signal, a throttle opening signal, an exhaust temperature signal, an intake pressure signal, an intake air amount signal, a vehicle speed signal, and a negative pressure sensor output. A signal such as a signal indicating the operating state of the engine 1 is input, and the ECU 10 controls the opening and closing of the on-off valve 23 according to the operating state of the engine 1. The on / off control of the on-off valve 23 by the ECU 10 will be described later.
[0035]
FIG. 2A shows an exhaust pipe 8 having the first and second NOx storage reduction catalysts 11 and 12 shown in FIG. 1, a first bypass pipe 21, a flexible pipe 22, an on-off valve 23, and a FIG. 3 is an enlarged view of a portion where the bypass passages 20 each including two bypass pipes 23 are arranged in parallel, and shows a state where the on-off valve 23 is closed. In this state, the exhaust gas flows through the exhaust pipe 8 without flowing through the bypass passage 20, and therefore, as shown in FIG. 1, the exhaust gas flows through the three-way catalyst and the first and second NOx storage reduction catalysts 11, 12 as shown in FIG. Purified by.
[0036]
As the flexible pipe 22 constituting the bypass passage 20, a flexible pipe 22 having a variable length in the front-rear direction, such as a bellows pipe, is used. Further, as the on-off valve 23, a dynamic pressure valve that opens and closes by a negative pressure, and an electromagnetic valve that can open and close by an electric signal can be used, and a butterfly valve can be used for the valve body of the on-off valve 23. The type of the on-off valve 23 is not limited as long as the on-off valve can be controlled by the ECU 10.
[0037]
Further, the bypass passage 20 in this embodiment is straight, and the first bypass pipe 21, the flexible pipe 22, the on-off valve 23, and the second bypass pipe 23 are coaxial. Further, the axis BX of the bypass passage 20 is coaxial with the axis AX of the main pipe 7C of the collecting pipe 7 connected to the bypass passage 20 on the upstream side, and also the axis CX of the exhaust pipe 8 connected to the bypass passage 20 on the downstream side. It is coaxial.
[0038]
Therefore, as shown in FIG. 2B, when the on-off valve 23 is open, the exhaust gas flowing through the collecting pipe 7 smoothly flows to the first bypass pipe 21 coaxial with the main pipe 7C. It flows and hardly flows into the exhaust pipe 8 having flow path resistance due to the first and second NOx storage reduction catalysts 11 and 12. Therefore, if the on-off valve 23 is opened in an operating state of the engine 1 in which the engine 1 is operated at a high rotation speed and a stoichiometric air-fuel ratio and the exhaust gas can be purified only by the three-way catalyst, the high- Does not flow to the first and second NOx storage reduction catalysts 11 and 12, unnecessary temperature rises of the first and second NOx storage reduction catalysts 11 and 12 can be avoided, and thermal deterioration can be prevented. . Further, it is possible to prevent a decrease in engine performance due to an increase in pressure loss at a high flow rate of the exhaust gas.
[0039]
In the state of FIG. 2A, the length of the exhaust pipe 8 through which the exhaust gas flows increases due to heat, so that the length of the exhaust pipe 8 is longer than that of the bypass passage 20, and conversely, the state of FIG. In the state of ()), the length of the bypass passage 20 through which the exhaust gas flows increases due to heat, so that the length of the bypass passage 20 is longer than that of the exhaust pipe 8. However, the difference between the length of the exhaust pipe 8 and the length of the bypass passage 20 is absorbed by the expansion and contraction of the flexible pipe 22 provided in the bypass passage 20. No damage due to distortion occurs.
[0040]
In the embodiment described above, the on-off valve 23 for switching the flow of the exhaust gas is provided at the center of the bypass passage 20. However, the position of the on-off valve 23 is not limited to the center of the bypass passage 20. FIGS. 3A and 3B show an embodiment in which the on-off valve 23 is provided at a branch portion between the bypass passage 20 and the exhaust pipe 8, and the same portion as in FIGS. 2A and 2B is shown. 1 shows the configuration. In the embodiment shown in FIGS. 3A and 3B, the configuration of other members other than the installation position of the on-off valve 23 is the same. Therefore, the same components as those in FIGS. 2A and 2B are denoted by the same reference numerals, and description thereof will be omitted.
[0041]
In the embodiment shown in FIG. 3A, the on-off valve 23 is provided at the exhaust gas inlet of the first bypass pipe 21 forming the bypass passage 20. Therefore, when the on-off valve 23 closes the bypass passage 20, the exhaust gas smoothly flows into the exhaust pipe 8 along the valve body of the on-off valve 23, and the first and second NOx storage reduction catalysts 11 , 12. At this time, the exhaust gas flows into the exhaust pipe 8 without entering the bypass passage 20 at all, so that the flow resistance of the exhaust gas is reduced, and the operation of the engine 1 becomes smooth.
[0042]
On the other hand, as shown in FIG. 3B, in a state in which the bypass passage 20 is opened by the on-off valve 20 and the inlet of the exhaust pipe 8 is closed, the exhaust gas flows through the first bypass pipe coaxial with the main pipe 7C. The gas smoothly flows into the exhaust pipe 21 and does not flow at all into the exhaust pipe 8 having the flow path resistance due to the first and second NOx storage reduction catalysts 11 and 12. Also in this embodiment, if the exhaust gas is caused to flow through the bypass passage 20 by the on-off valve 23 in a state where the engine 1 is operated at a high rotation speed and a stoichiometric air-fuel ratio, the first and second NOx storage reduction catalysts 11 and 12 are provided. Can be prevented from deteriorating due to heat, and a decrease in engine performance due to an increase in pressure loss at a high flow rate of exhaust gas can be prevented.
[0043]
Also, in the embodiment shown in FIGS. 3A and 3B, the difference between whether the exhaust gas flows through the exhaust pipe 8 or the bypass passage 20 depends on whether the exhaust gas flows through the exhaust pipe 8 or the bypass passage 20. Since the difference in length is absorbed by the expansion and contraction of the flexible pipe 22 provided in the bypass passage 20, the exhaust pipe 8 and the bypass passage 20 are not damaged by thermal distortion.
[0044]
FIG. 4 is a flowchart illustrating an example of the procedure of the opening / closing control of the on-off valve 23 of the present invention described with reference to FIGS. 2 and 3. This procedure is executed every predetermined time.
[0045]
In step 401, first, the operation state parameters of the engine 1 are read. The operating state parameters of the engine 1 include, for example, an air-fuel ratio from the A / F sensor 9, an engine speed, a throttle opening, an exhaust temperature, an intake pressure, an intake air amount, a vehicle speed, and a negative pressure sensor output. After the operation state parameters of the engine 1 are read in step 401 in this manner, it is determined in step 402 whether the operation state of the engine 1 is at high rotation. If the operation state of the engine 1 is at high rotation, step Proceeding to 403, it is determined whether the engine 1 is operating at the stoichiometric air-fuel ratio.
[0046]
If the engine 1 is not rotating at high speed in step 402, or if the engine 1 is not operating at the stoichiometric air-fuel ratio in step 403, the process proceeds to step 404, in which the on-off valve 23 is rotated to the closing side to bypass. Close the passage. On the other hand, proceeding from step 402 to step 403, if it is determined that the engine 1 is operating at a high speed and at a stoichiometric air-fuel ratio, proceed to step 405 to rotate the on-off valve 23 bypass passage 20 to open the bypass passage. Let it open.
[0047]
As a result, when the engine 1 is operating at a high speed and a stoichiometric air-fuel ratio, the exhaust gas passes through the bypass passage 20 as shown in FIGS. It does not flow to the catalysts 11 and 12.
[0048]
As described above, in the present invention, the exhaust gas flows through the bypass passage 20 when the engine 1 is rotating at a high speed, so that the sulfur poisoning amount of the NOx storage reduction catalyst can be reduced. Further, it is possible to reduce the exhaust noise from the side branch effect due to the length of the bypass passage 20.
[0049]
In the embodiment described above, when the engine 1 is operating at a high speed and a stoichiometric air-fuel ratio, the on-off valve is opened so that the exhaust gas flows through the bypass passage provided in parallel with the exhaust pipe having the NOx storage reduction catalyst. However, a NOx sensor may be provided upstream of the exhaust pipe having the NOx storage reduction catalyst, and when the NOx concentration becomes low, the on-off valve may be opened to allow the exhaust gas to flow through the bypass passage.
[0050]
【The invention's effect】
As described above, according to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, in an internal combustion engine having an NOx storage reduction catalyst and a bypass passage that bypasses the NOx storage catalyst in the exhaust passage, the internal combustion engine has a small NOx component in the exhaust gas. In the operating state of the engine, the exhaust gas is caused to flow through the bypass passage by the on-off valve. Therefore, it is possible to prevent a decrease in the NOx purification rate due to thermal deterioration of the NOx storage reduction catalyst at the time of high rotation and high flow rate of the internal combustion engine, and There is an effect that it is possible to prevent the performance of the internal combustion engine from deteriorating due to an increase in pressure loss at the time of rotation and high flow rate, and to prevent the exhaust pipe from being broken due to thermal expansion of one of the exhaust passages arranged in parallel.
[Brief description of the drawings]
FIG. 1 shows a configuration of an embodiment of an exhaust gas purifying apparatus for an internal combustion engine of the present invention, and is a configuration diagram showing an entire exhaust system of the internal combustion engine.
2 is an enlarged view of a portion of a NOx storage reduction catalyst and a bypass passage thereof in an exhaust system of the internal combustion engine shown in FIG. 1, and FIG. 2 (a) is a view for explaining a flow of exhaust gas when an on-off valve is closed. (B) is a diagram for explaining the flow of exhaust gas when the on-off valve is open.
FIG. 3 is an enlarged view showing the configuration of another embodiment of the configuration of the NOx storage reduction catalyst and its bypass passage shown in FIG. 1, and FIG. 3 (a) is a flow of exhaust gas when the on-off valve is closed. FIG. 4B is a diagram illustrating the flow of exhaust gas when the on-off valve is open.
FIG. 4 is a flowchart illustrating an example of the on-off control of the on-off valve according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine 4 ... Exhaust manifolds 5, 6, 13 ... Three-way catalyst 8 ... Exhaust pipe 9 ... A / F sensor 10 ... ECU (Electronic control unit)
11 First NOx storage reduction catalyst 12 Second NOx storage reduction catalyst 20 Bypass passage 21 First bypass pipe 22 Flexible pipe 23 On-off valve 24 Second bypass pipe

Claims (8)

In an exhaust gas purifying apparatus for an internal combustion engine provided with a NOx storage reduction catalyst in an exhaust passage of the internal combustion engine,
An exhaust bypass passage for bypassing the NOx storage reduction catalyst, and an on-off valve for opening and closing the exhaust bypass passage;
In the operating state of the internal combustion engine having a large amount of NOx component in the exhaust gas, the on-off valve is closed,
An exhaust gas purifying apparatus for an internal combustion engine, wherein the on-off valve is opened when the internal combustion engine has a low NOx component in the exhaust gas. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the bypass passage is provided so that an axis of the bypass passage is coaxial with an axis of an exhaust passage before and after the NOx storage reduction catalyst. . 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the on-off valve is provided in the middle of the bypass passage. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2, wherein the on-off valve is provided at a branch portion of the bypass passage with the exhaust passage. The on-off valve is controlled by an electronic control circuit that detects an operating state of the internal combustion engine and controls the internal combustion engine, and opens when the engine speed of the internal combustion engine exceeds a predetermined rotation speed at a high speed. The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 4, wherein the exhaust gas purifying device is configured to be a valve. The internal combustion engine according to any one of claims 1 to 5, wherein a flexible pipe capable of absorbing thermal expansion and contraction of an exhaust gas passage portion parallel to the bypass passage is provided in the middle of the bypass passage. Exhaust gas purification device. The exhaust gas of an internal combustion engine according to any one of claims 1 to 6, wherein the NOx storage reduction catalyst comprises a first NOx storage reduction catalyst and a second NOx storage reduction catalyst. Purification device. The exhaust gas for an internal combustion engine according to any one of claims 1 to 7, wherein a three-way catalyst is provided on each of an upstream side and a downstream side of the connection portion of the bypass passage with the exhaust passage. Purification device.

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