JP2008215304A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more suitably supply reducer to a particulate filter when a front stage catalyst having oxidation function, a storage reduction type NOx catalyst, and the particulate filter carrying the catalyst having oxidation function, are arranged in order from an upstream side. <P>SOLUTION: This system is provided with: a bypass passage formed to pass through the front stage catalyst 4 and the NOx catalyst 5 and making exhaust gas flow with bypassing the catalysts; an open close valve 9 shutting off and opening the bypass passage 8; and a reducer adding valve 7 adding reducer into exhaust gas in a direct upstream of an upstream side opening part of the bypass passage 8 in the exhaust passage 2. When reducer is supplied to the filter 6, reducer is added from the reducer adding valve 9 in the state where the bypass passage 8 is opened by the open close valve 9. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust purification system for an internal combustion engine provided with a catalyst having an oxidation function and a NOx storage reduction catalyst arranged in series in an exhaust passage of the internal combustion engine, and a particulate filter carrying the catalyst having an oxidation function. .

As an exhaust gas purification system for an internal combustion engine, a catalyst that has an oxidation function, a NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst), and a particulate matter (hereinafter referred to as PM) in exhaust gas are collected. A curate filter (hereinafter simply referred to as a filter) or the like may be arranged in series in the exhaust passage of the internal combustion engine.

In Patent Document 1, a CCC (Close Catalytic Converter) in which an HC adsorption catalyst and a NOx adsorption catalyst are installed in series is provided on an exhaust path near the exhaust manifold, and a vehicle body floor located downstream of the CCC is provided. A technique for providing a UCC (Underfloor Catalytic Converter) in the lower exhaust pipe is described. Furthermore, this patent document 1 discloses a bypass passage formed through the HC adsorption catalyst and the NOx adsorption catalyst and through which exhaust flows.

  Further, a catalyst having an oxidation function and a NOx catalyst in the exhaust passage of the internal combustion engine, a filter carrying the catalyst having an oxidation function are arranged in order from the upstream side, and a catalyst having an oxidation function provided in the uppermost stream (hereinafter referred to as a pre-stage catalyst) In some cases, a reducing agent addition valve for adding a reducing agent into the exhaust gas is provided on the upstream side. In such a case, a bypass passage that further communicates a portion of the exhaust passage downstream of the reducing agent addition valve and upstream of the preceding catalyst with a portion of downstream of the NOx catalyst and upstream of the filter, and In some cases, an on-off valve is provided to block or open the bypass passage.

  In such a configuration, by adding the reducing agent into the exhaust gas from the reducing agent addition valve while opening the bypass passage by the opening / closing valve, a part of the reducing agent added from the reducing agent addition valve is reduced to the front catalyst and the NOx. The filter can be supplied without using a catalyst.

  However, in this case, since the reducing agent added from the reducing agent addition valve tends to flow more downstream in the exhaust passage than the bypass passage, most of the reducing agent is supplied to the pre-stage catalyst and the NOx catalyst. The reducing agent supplied to the pre-stage catalyst and the NOx catalyst is oxidized in these catalysts. Further, the longer the bypass passage is, the more reducing agent adheres to the inner wall surface of the bypass passage.

Therefore, for example, when it is attempted to supply a reducing agent to the filter through the bypass passage in order to remove PM collected by the filter, it may be difficult to supply a sufficient amount of the reducing agent to the filter. In addition, when a reducing agent is unnecessarily supplied to the pre-stage catalyst and the NOx catalyst and the reducing agent is oxidized, there is a risk of promoting the deterioration of the NOx catalyst due to oxidation heat generated at that time.
JP-A-2005-299631 JP-A-2005-76539 Japanese Utility Model Publication No. 5-61418 JP 2006-22738 A

  In the present invention, when a pre-stage catalyst having an oxidation function, a NOx catalyst, and a filter carrying the catalyst having an oxidation function are sequentially arranged in the exhaust passage of the internal combustion engine from the upstream side, the reducing agent is suitably supplied to the filter. The purpose is to provide a technology that can do this.

  The present invention includes a bypass passage that is formed so as to pass through the pre-stage catalyst and the NOx catalyst and through which the exhaust flows, an on-off valve that blocks or opens the bypass passage, and an upstream side of the bypass passage in the exhaust passage A reducing agent addition valve for adding a reducing agent into the exhaust gas immediately upstream of the opening. And in this invention, when supplying a reducing agent to a filter, a reducing agent is added from a reducing agent addition valve in the state which opened the bypass channel by the on-off valve.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
A pre-stage catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine;
An NOx storage reduction catalyst provided in the exhaust passage downstream of the front catalyst;
A particulate filter provided in the exhaust passage downstream of the NOx storage reduction catalyst and carrying a catalyst having an oxidation function;
A bypass passage formed so as to penetrate the front stage catalyst and the NOx storage reduction catalyst, and through which the exhaust gas bypasses the front stage catalyst and the NOx storage reduction catalyst,
An on-off valve for blocking or opening the bypass passage;
A reducing agent addition valve for adding a reducing agent into the exhaust gas immediately upstream of the upstream side opening of the bypass passage in the exhaust passage,
When supplying the reducing agent to the particulate filter, the reducing agent is added from the reducing agent addition valve in a state where the bypass passage is opened by the on-off valve.

  In the present invention, the bypass passage is formed so as to penetrate the front stage catalyst and the NOx catalyst. Therefore, it is possible to suppress the heat dissipation of the exhaust gas flowing through the bypass passage. When the reducing agent is supplied to the filter, since the bypass passage is opened, the reducing agent is supplied to the filter together with the exhaust gas flowing through the bypass passage.

  Therefore, according to the present invention, it is possible to suppress a decrease in the temperature of the filter when the reducing agent is supplied to the filter. In addition, the reducing agent can be supplied to the filter in a state in which it is more likely to chemically react with the catalyst supported on the filter.

  In the present invention, the reducing agent addition valve adds the reducing agent into the exhaust immediately upstream of the upstream opening of the bypass passage. Thereby, the reducing agent added from the reducing agent addition valve easily flows into the bypass passage. Therefore, it becomes easy to supply the reducing agent to the filter via the bypass passage.

  In the present invention, the bypass passage is provided in the exhaust passage. Thereby, it is not necessary to consider the handling of the bypass passage as in the case where the bypass passage is provided outside the exhaust passage, and the bypass passage can be provided more easily. Further, since the length of the bypass passage can be made shorter than when the bypass passage is provided outside the exhaust passage, the amount of reducing agent adhering to the inner wall surface of the bypass passage can be reduced.

In the present invention, the reducing agent addition valve may be capable of changing the addition direction of the reducing agent when the reducing agent is added to the exhaust gas. In this case, when supplying the reducing agent to the filter, the reducing agent addition valve adds the reducing agent toward the upstream opening of the bypass passage, and when supplying the reducing agent to the NOx catalyst, the upstream end of the front catalyst. Add the reducing agent toward the part.

  As a result, when the reducing agent is supplied to the filter, the reducing agent can easily flow into the bypass passage, so that it is possible to suppress unnecessary supply of the reducing agent to the pre-stage catalyst and the NOx catalyst. As a result, deterioration of the pre-stage catalyst and the NOx catalyst can be suppressed. Further, when the reducing agent is supplied to the NOx catalyst, the inflow of the reducing agent into the bypass passage can be suppressed.

  In the present invention, the reducing agent addition valve may be added toward the upstream opening of the bypass passage. The on-off valve may be configured to block or open the upstream opening of the bypass passage. In this case, when supplying the reducing agent to the NOx catalyst, the reducing agent is added from the reducing agent addition valve in a state where the upstream side opening of the bypass passage is blocked by the on-off valve.

  Assuming that the reducing agent is added toward the upstream opening of the bypass passage, the reducing agent is added from the reducing agent addition valve while the bypass passage is opened by the on-off valve when supplying the reducing agent to the filter. By adding the agent, it is possible to suppress unnecessary supply of the reducing agent to the upstream catalyst and the NOx catalyst.

  On the other hand, when the reducing agent is added from the reducing agent addition valve in a state where the upstream side opening portion of the bypass passage is blocked by the opening / closing valve, the reducing agent strikes the opening / closing valve and scatters and flows into the upstream catalyst. As a result, the reducing agent can be supplied to the NOx catalyst while suppressing the inflow of the reducing agent into the bypass passage. That is, it is possible to suppress supply of unnecessary reducing agent to the filter.

  In the present invention, when the reducing agent is added to the reducing agent addition valve toward the upstream opening of the bypass passage, a through hole may be provided in the wall surface between the preceding catalyst and the NOx catalyst in the bypass passage. .

  According to this, when supplying the reducing agent to the NOx catalyst, if the reducing agent is added from the reducing agent addition valve, a part of the reducing agent that has flowed into the bypass passage is supplied to the NOx catalyst through the through hole. That is, it is possible to supply the reducing agent to the NOx catalyst without passing through the front stage catalyst. Therefore, unnecessary oxidation of the reducing agent in the front catalyst can be suppressed, and deterioration of the front catalyst and the NOx catalyst can be suppressed.

  Further, when the reducing agent is added to the reducing agent addition valve toward the upstream opening portion of the bypass passage, the on-off valve may be blocked or opened on the downstream side of the through hole of the bypass passage. In this case, when supplying the reducing agent to the NOx catalyst, the reducing agent may be added from the reducing agent addition valve in a state where the bypass passage is blocked by the on-off valve.

  According to this, it is possible to supply more reducing agent to the NOx catalyst through the through hole while suppressing supply of unnecessary reducing agent to the filter.

  According to the present invention, even when a pre-stage catalyst having an oxidation function, a NOx catalyst, and a filter carrying a catalyst having an oxidation function are arranged in order from the upstream side in the exhaust passage of the internal combustion engine, the filter is more suitable. A reducing agent can be supplied.

  Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Example 1>
<Schematic configuration of exhaust system of internal combustion engine>
Here, a case where the present invention is applied to a diesel engine for driving a vehicle will be described as an example. FIG. 1 is a diagram showing a schematic configuration of an exhaust system of an internal combustion engine according to the present embodiment.

  The internal combustion engine 1 is a diesel engine for driving a vehicle. An exhaust passage 2 is connected to the internal combustion engine 1. The exhaust passage 2 is provided with a turbine housing 17b of a turbocharger 17 having a compressor housing 17a and a turbine housing 17b.

  An oxidation catalyst 4 is provided downstream of the turbine housing 17 b in the exhaust passage 2, and a NOx catalyst 5 is provided immediately downstream of the oxidation catalyst 4. A filter 6 is provided in the exhaust passage 2 on the downstream side of the NOx catalyst 5. An oxidation catalyst 11 is supported on the filter 6. In this embodiment, the oxidation catalyst 4 corresponds to the former catalyst according to the present invention. The oxidation catalyst 4 and the oxidation catalyst 11 are not limited to the oxidation catalyst, and may be any catalyst having an oxidation function.

  In the present embodiment, a bypass passage 8 is provided in the exhaust passage 2 so as to penetrate the oxidation catalyst 4 and the NOx catalyst 5. Exhaust gas flowing in from the upstream opening of the bypass passage 8 bypasses the oxidation catalyst 4 and the NOx catalyst 5 and flows out of the downstream opening of the bypass passage 8. An opening / closing valve 9 is provided in the vicinity of the downstream opening of the bypass passage 8. When the on-off valve 9 is closed, the bypass passage 8 is shut off, and when the on-off valve 9 is opened, the bypass passage 8 is opened.

  Further, a fuel addition valve 7 is provided upstream of the oxidation catalyst 4 in the exhaust passage 2. The fuel addition valve 7 adds fuel into the exhaust gas immediately upstream of the upstream opening of the bypass passage 8 in the exhaust passage 2. The hatched portion in FIG. 1 represents the spray of fuel added from the fuel addition valve 7. As represented by the hatched portion, fuel is injected in a conical shape from the fuel addition valve 7 according to the present embodiment, and the fuel is injected into the upstream opening of the bypass passage 8 and the upstream end of the oxidation catalyst 4. It flows into both.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. A fuel addition valve 7 and an on-off valve 9 are electrically connected to the ECU 10. These are controlled by the ECU 10.

<Filter regeneration control>
In this embodiment, filter regeneration control is performed to remove the PM collected by the filter 6. In order to remove PM collected by the filter 6, it is necessary to supply fuel to the filter 6. The fuel supplied to the filter 6 is oxidized in the oxidation catalyst 11, and the temperature of the filter 6 is raised by the oxidation heat generated at that time. As a result, PM is oxidized and removed from the filter 6.

  Here, the routine of the filter regeneration control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, the ECU 10 first determines in S101 whether or not an execution condition for the filter regeneration control is satisfied. The execution condition of the filter regeneration control is determined in advance based on the integrated value of the fuel injection amount in the internal combustion engine 1, the travel distance of the vehicle on which the internal combustion engine 1 is mounted, and the like. If an affirmative determination is made in S101, the ECU 10 proceeds to S102, and if a negative determination is made, the ECU 10 once ends the execution of this routine.

  In S102, the ECU 10 opens the on-off valve 9.

  Next, the ECU 10 proceeds to S103 and executes fuel addition from the fuel addition valve 7. Thereafter, the ECU 10 once terminates execution of this routine.

  In this embodiment, the bypass passage 8 is formed so as to penetrate the oxidation catalyst 4 and the NOx catalyst 5. Thereby, the heat dissipation of the exhaust gas flowing through the bypass passage is suppressed. When the filter regeneration control is executed, the bypass passage 8 is opened, so that fuel is supplied to the filter 6 together with the exhaust gas flowing through the bypass passage 8.

  Therefore, according to this embodiment, it is possible to suppress a decrease in the temperature of the filter 6 when the filter regeneration control is executed. In addition, since the fuel is supplied to the filter 6 together with the exhaust gas having a higher temperature, the fuel is supplied to the filter 6 in a state where it is more easily oxidized in the oxidation catalyst 11 carried on the filter 6.

  In this embodiment, the fuel addition valve 7 adds fuel into the exhaust just upstream of the upstream opening of the bypass passage 8. Thereby, the fuel added from the fuel addition valve 7 easily flows into the bypass passage 8. Therefore, it becomes easy to supply fuel to the filter 6 via the bypass passage 8.

  In this embodiment, since the bypass passage 8 is provided in the exhaust passage 2, it is not necessary to consider the handling of the bypass passage 8 as in the case where the bypass passage 8 is provided outside the exhaust passage 2. The bypass passage 8 can be provided more easily. Further, since the length of the bypass passage 8 can be made shorter than when the bypass passage 8 is provided outside the exhaust passage 2, the amount of fuel adhering to the inner wall surface of the bypass passage 8 can be reduced.

<Modification>
Next, a modification of the present embodiment will be described with reference to FIG. FIG. 3 is a diagram showing a schematic configuration in the vicinity of the fuel addition valve 7 according to this modification. The fuel addition valve 7 according to this modification injects the fuel radially. The fuel addition valve 7 can change the fuel addition direction.

  In the present modification, when the filter regeneration control is executed, fuel is added from the fuel addition valve 7 toward the upstream opening of the bypass passage 8 as shown by a solid line in FIG.

  As a result, the fuel becomes easier to flow into the bypass passage 8 when the filter regeneration control is executed, so that unnecessary fuel supply to the oxidation catalyst 4 and the NOx catalyst 5 can be suppressed. As a result, deterioration of the oxidation catalyst 4 and the NOx catalyst 5 can be suppressed.

  Further, in this modification, NOx reduction control for reducing NOx stored in the NOx catalyst 5 is performed. When performing the NOx reduction control, it is necessary to supply fuel to the NOx catalyst 5 so that the ambient atmosphere of the NOx catalyst 5 is a reducing atmosphere.

  Therefore, when the NOx reduction control is executed, fuel is added from the fuel addition valve 7 toward the upstream end of the oxidation catalyst 4 as indicated by a broken line in FIG. Part of the fuel supplied to the oxidation catalyst 4 passes through the oxidation catalyst 4 and is supplied to the NOx catalyst 5.

  When the NOx reduction control is executed, the fuel can be prevented from flowing into the bypass passage 8 by adding the fuel from the fuel addition valve 7 in the above-described direction.

<Example 2>
FIG. 4 is a diagram showing a schematic configuration of an exhaust system of the internal combustion engine according to the present embodiment. In the present embodiment, the configurations of the on-off valve 9 and the fuel addition valve 7 are different from those of the first embodiment, and other components are the same as those of the first embodiment. Therefore, only the on-off valve 9 and the fuel addition valve 7 will be described, and description of other components will be omitted.

  The on-off valve 9 according to this embodiment is a valve that blocks or opens the upstream opening of the bypass passage 8. In FIG. 4, the solid line represents a state in which the opening / closing valve 9 opens the upstream opening of the bypass passage 8, and the broken line represents a state in which the opening / closing valve 9 blocks the upstream opening of the bypass passage 8. Yes.

  Further, the fuel addition valve 7 according to the present embodiment is configured to add fuel toward the upstream opening of the bypass passage 8 as shown in FIG. Also in FIG. 4, the hatched portion indicates the spray of fuel added from the fuel addition valve 7.

<Filter regeneration control and NOx reduction control>
Also in this embodiment, filter regeneration control for removing PM trapped in the filter 6 and NOx reduction control for reducing NOx occluded in the NOx catalyst 5 are performed. Here, the routine of the filter regeneration control and the NOx reduction control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is obtained by adding S201 and 202 to the filter regeneration control routine according to the first embodiment. Therefore, description of S101 to S103 is omitted, and only S201 and S202 are described. This routine is stored in advance in the ECU 10 and is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, if a negative determination is made in S101, the ECU 10 proceeds to S201. In step S201, the ECU 10 determines whether or not an execution condition for NOx reduction control for reducing the NOx stored in the NOx catalyst 5 is satisfied. Similar to the execution condition of the filter regeneration control, the execution condition of the NOx reduction control is determined in advance based on the integrated value of the fuel injection amount in the internal combustion engine 1, the travel distance of the vehicle on which the internal combustion engine 1 is mounted, and the like. If an affirmative determination is made in S201, the ECU 10 proceeds to S202, and if a negative determination is made, the ECU 10 once ends this routine.

  In step S202, the ECU 10 closes the on-off valve 9. Thereafter, the ECU 10 proceeds to S103.

  In this embodiment, the fuel addition valve 7 is configured to add fuel toward the upstream opening of the bypass passage 8. When filter regeneration control is executed, fuel is added from the fuel addition valve 7 with the on-off valve 9 opened. Thereby, the fuel added from the fuel addition valve 7 flows into the bypass passage 8. Therefore, according to the present embodiment, it is possible to suppress unnecessary fuel supply to the oxidation catalyst 4 and the NOx catalyst 5 when the filter regeneration control is executed.

  On the other hand, when the NOx reduction control is executed, fuel is added from the fuel addition valve 7 with the on-off valve 9 closed. As a result, the fuel added from the fuel addition valve 7 strikes the on-off valve 9 and scatters and flows into the oxidation catalyst 4. Therefore, according to the present embodiment, the fuel can be supplied to the NOx catalyst 5 while suppressing the inflow of the fuel into the bypass passage 8 during the execution of the NOx reduction control. That is, unnecessary fuel supply to the filter 6 can be suppressed.

<Example 3>
FIG. 6 is a diagram showing a schematic configuration of an exhaust system of the internal combustion engine according to the present embodiment. This embodiment is different from the first embodiment in that the configuration of the fuel addition valve 7 and the through-hole 12 are provided in the bypass passage 8, and other components are the same as those in the first embodiment. Therefore, only the fuel addition valve 7 and the through hole 12 will be described, and description of other components will be omitted.

  As shown in FIG. 6, the fuel addition valve 7 according to the present embodiment is configured to add fuel toward the upstream opening of the bypass passage 8. In FIG. 6, the hatched portion indicates the spray of fuel added from the fuel addition valve 7.

  In the present embodiment, a through hole 12 is provided in the wall surface between the oxidation catalyst 4 and the NOx catalyst 5 in the bypass passage 8. Part of the exhaust gas flowing through the bypass passage 8 flows out from the bypass passage 8 to the exhaust passage 2 through the through hole 12. Then, the exhaust gas flows into the NOx catalyst 5. The on-off valve 9 is located on the downstream side of the through hole 12 in the bypass passage 8.

  According to this embodiment, the fuel added from the fuel addition valve 7 flows into the bypass passage 8. A part of the fuel flowing into the bypass passage 8 is supplied to the NOx catalyst 5 through the through hole 12 together with the exhaust gas. That is, by adding fuel from the fuel addition valve 7 during execution of NOx reduction control, it becomes possible to supply fuel to the NOx catalyst 5 without passing through the oxidation catalyst 4. Therefore, since unnecessary oxidation of the fuel in the oxidation catalyst 4 can be suppressed, deterioration of the oxidation catalyst 4 can be suppressed. Moreover, since the temperature increase of the NOx catalyst 5 is suppressed by suppressing the unnecessary temperature increase of the oxidation catalyst 4, the deterioration of the NOx catalyst 5 can also be suppressed.

  In the present embodiment, the fuel may be added from the fuel addition valve 7 in a state where the bypass passage 8 is blocked by the on-off valve 9 when the NOx reduction control is executed. According to this, it becomes possible to supply more fuel to the NOx catalyst 5 through the through hole 12 while suppressing supply of unnecessary fuel to the filter 6.

  In the present embodiment, an exhaust introduction plate for guiding exhaust to the through hole 12 may be provided on the inner wall surface of the bypass passage 8. Thereby, more of the exhaust gas flowing through the bypass passage 8 can be introduced into the NOx catalyst 5. Therefore, more fuel can be supplied to the NOx catalyst 5 when the NOx reduction control is executed.

  In the first to third embodiments, the case where the filter regeneration control is executed has been described as an example when the fuel is supplied to the filter 6. However, when the catalyst supported on the filter 6 is a NOx catalyst, the filter according to the first to third embodiments is also used when fuel is supplied to the filter 6 to reduce NOx or SOx stored in the NOx catalyst. The fuel addition valve 7 and the on-off valve 9 may be controlled in the same manner as when the regeneration control is executed.

  In the first to third embodiments, the time when the NOx reduction control is executed is described as an example when the fuel is supplied to the NOx catalyst 5. However, when the fuel is supplied to the NOx catalyst 5 to reduce the SOx stored in the NOx catalyst 5, the fuel addition valve 7 and the on-off valve are opened in the same manner as in the execution of the NOx reduction control according to the first to third embodiments. 9 may be controlled.

  Examples 1 to 3 can be combined as much as possible.

1 is a diagram illustrating a schematic configuration of an exhaust system of an internal combustion engine according to a first embodiment. 5 is a flowchart illustrating a routine for filter regeneration control according to the first embodiment. FIG. 5 is a diagram illustrating a schematic configuration in the vicinity of a fuel addition valve according to a modification of the first embodiment. FIG. 3 is a diagram illustrating a schematic configuration of an exhaust system of an internal combustion engine according to a second embodiment. 9 is a flowchart illustrating a routine for filter regeneration control and NOx reduction control according to the second embodiment. FIG. 5 is a diagram illustrating a schematic configuration of an exhaust system of an internal combustion engine according to a third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 4 ... Oxidation catalyst 5 ... Occlusion reduction type NOx catalyst 6 ... Particulate filter 7 ... Fuel addition valve 8 ... Bypass passage 9 ...・ Open / close valve 10 ・ ・ ECU
11. Oxidation catalyst 12. Through hole

Claims (5)

A pre-stage catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine;
An NOx storage reduction catalyst provided in the exhaust passage downstream of the front catalyst;
A particulate filter provided in the exhaust passage downstream of the NOx storage reduction catalyst and carrying a catalyst having an oxidation function;
A bypass passage formed so as to penetrate the front stage catalyst and the NOx storage reduction catalyst, and through which the exhaust gas bypasses the front stage catalyst and the NOx storage reduction catalyst,
An on-off valve for blocking or opening the bypass passage;
A reducing agent addition valve for adding a reducing agent into the exhaust gas immediately upstream of the upstream side opening of the bypass passage in the exhaust passage,
An exhaust gas purification system for an internal combustion engine, wherein when supplying the reducing agent to the particulate filter, the reducing agent is added from the reducing agent addition valve in a state where the bypass passage is opened by the on-off valve.   The reducing agent addition valve can change the addition direction of the reducing agent when adding the reducing agent into the exhaust, and when the reducing agent is supplied to the particulate filter, the upstream side of the bypass passage The reducing agent is added toward the upstream end portion of the preceding catalyst when the reducing agent is added toward the opening and the reducing agent is supplied to the NOx storage reduction catalyst. Exhaust gas purification system for internal combustion engines. The reducing agent addition valve is for adding a reducing agent toward the upstream opening of the bypass passage;
The on-off valve blocks or opens the upstream opening of the bypass passage;
When supplying the reducing agent to the NOx storage reduction catalyst, the reducing agent is added from the reducing agent addition valve in a state where the upstream opening of the bypass passage is blocked by the on-off valve. Item 6. An exhaust purification system for an internal combustion engine according to Item 1. The reducing agent addition valve is for adding a reducing agent toward the upstream opening of the bypass passage;
The exhaust purification system for an internal combustion engine according to claim 1, wherein a through hole is provided in a wall surface between the upstream catalyst and the NOx storage reduction catalyst in the bypass passage. The on-off valve blocks or opens the downstream side of the through-hole of the bypass passage;
5. The internal combustion engine according to claim 4, wherein when supplying the reducing agent to the NOx storage reduction catalyst, the reducing agent is added from the reducing agent addition valve in a state where the bypass passage is blocked by the on-off valve. Engine exhaust purification system.

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