JP2007056757A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for suppressing worsening of emission caused by NOx reduction treatment in an exhaust emission control system constituted by combining a plurality of branched passages branched from an exhaust passage with NOx catalyst provided in each branched passage. <P>SOLUTION: In this exhaust emission control system provided with NOx catalyst, a reducing agent adding means, and a flow rate control valve in each branched passage, NOx and/or reducing agent are introduced into another NOx catalyst 111b when NOx and/or reducing agent are discharged from the NOx catalyst 110a, 111a in accordance with NOx reduction treatment for the NOx catalyst 110a, 111a in the branched passage in a part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

The exhaust gas of internal combustion engines contains harmful substances such as NOx. In order to reduce the emission of these harmful substances, it is known to provide a NOx catalyst for purifying NOx in the exhaust gas in the exhaust system of the internal combustion engine. In this technique, for example, when an occlusion reduction type NOx catalyst is provided, the purification capacity decreases as the amount of occluded NOx increases, so a reducing agent is supplied to the occlusion reduction type NOx catalyst and occluded in the catalyst. NOx is reduced and released (hereinafter referred to as “NOx reduction process”).

  When the NOx reduction treatment is performed by supplying a reducing agent to the above-described NOx storage reduction catalyst, it is introduced into the NOx storage reduction catalyst in order to ensure a sufficient NOx reaction time in the NOx storage reduction catalyst. It is desirable to reduce the flow rate of exhaust air.

In contrast, in the exhaust purification system (hereinafter referred to as an “exhaust purification system” including an exhaust purification device including an NOx storage reduction catalyst and its control system), a plurality of branch passages and each branch passage are arranged. An apparatus having an exhaust purification device is known (for example, see Patent Document 1 or Patent Document 2). And the exhaust gas purification device in which the flow rate of exhaust gas introduced into one of those exhaust gas purification devices is suppressed to a predetermined amount by a flow rate control valve capable of changing the cross-sectional area of the flow path, and the flow rate of exhaust gas to be introduced is suppressed It has been proposed to perform a NOx reduction treatment by supplying a fuel as a reducing agent. By doing so, the reduction reaction can be sufficiently caused in the NOx storage reduction catalyst, and the influence of the NOx reduction treatment on the operating performance of the internal combustion engine can be suppressed.

However, even in the above technique, when the supplied fuel does not diffuse sufficiently uniformly in the NOx storage reduction catalyst, NOx in the NOx storage reduction catalyst is discharged without being fully reduced or supplied fuel. HC may be discharged from the NOx storage reduction catalyst by passing through the NOx storage reduction catalyst. As a result, when the NOx reduction process is completed and the flow rate control valve is opened, NOx and HC are diffused outside the vehicle, and the emission may deteriorate.
JP 2003-106142 A JP 2003-74328 A JP-A-5-321636 JP-A-4-194309 JP-A-5-71331

  An object of the present invention is to reduce emissions caused by NOx reduction treatment in an exhaust purification system that combines a plurality of branch passages branched from an exhaust passage and a NOx catalyst provided in each branch passage. It is to provide technology that can be suppressed.

To achieve the above object, the present invention provides an exhaust purification system comprising a NOx catalyst, a reducing agent addition means and a flow control valve in each branch passage.
When NOx and / or a reducing agent is discharged from the NOx catalyst as a result of the NOx reduction treatment for the NOx catalyst in a part of the branch passages, these NOx and / or reducing agent are removed from the NOx in another branch passage. The greatest feature is that it is further introduced into the catalyst.

More specifically, an exhaust passage that is connected at one end to the internal combustion engine and through which exhaust from the internal combustion engine passes and branches into a plurality of branch passages in the middle,
A NOx catalyst provided in each of the plurality of branch passages to purify NOx in the exhaust gas passing through each branch passage;
Reducing agent addition means for adding a reducing agent to the exhaust gas that is provided upstream of the NOx catalyst in each of the plurality of branch passages and passes through each branch passage;
A flow rate control valve that is provided downstream of the NOx catalyst in each of the plurality of branch passages and controls the flow rate of the exhaust gas that passes through each branch passage;
A reducing agent is supplied to the NOx catalyst provided in a part of the plurality of branch passages from the reducing agent addition means upstream of the NOx catalyst, and the flow control valve downstream of the NOx catalyst is closed. NOx reduction means for performing NOx reduction treatment by
Along with the NOx reduction treatment, NOx and / or reducing agent discharged from the NOx catalyst related to the NOx reduction treatment is separated from the branch passage provided with the NOx catalyst related to the NOx reduction treatment. Reintroduction means for introducing into the NOx catalyst;
It is characterized by providing.

  Here, when supplying the reducing agent to the NOx catalyst in order to perform the NOx reduction treatment of the NOx catalyst provided in each of the branch passages, the reducing agent is added from the reducing agent addition means on the upstream side of the NOx catalyst. Is added. And in order to ensure sufficient reduction reaction of NOx in the NOx catalyst, the flow rate of the exhaust gas passing through the branch passage provided with the NOx catalyst to be subjected to NOx reduction treatment is closed by closing the flow rate control valve. Decrease.

However, even in that case, since the reducing agent added from the reducing agent addition means does not necessarily diffuse uniformly throughout the NOx catalyst, a part of the NOx stored in the NOx catalyst is not completely reduced. In some cases, it was released. In some cases, the reducing agent added from the reducing agent addition means passes through the NOx catalyst and is discharged as HC from the NOx catalyst. In this case, NOx and HC are diffused outside the vehicle due to the NOx reduction treatment, and the emission may be deteriorated.

  Therefore, in the present invention, for the reasons described above, NOx and HC exhausted from the NOx catalyst during the NOx reduction treatment are further introduced into the NOx catalyst in another branch passage, and NOx in the other branch passage. It was decided to purify in the catalyst.

  If it does so, NOx and HC dissipated outside the vehicle due to the NOx reduction process can be reduced, and deterioration of the emission during the NOx reduction process can be suppressed.

Further, in the present invention, the reintroduction means includes an introduction source portion that is a downstream portion of the NOx catalyst and an upstream portion of the flow control valve of the branch passage provided with the NOx catalyst related to the NOx reduction treatment, You may make it have a communicating path which connects the introducing | transducing destination part which is a part upstream of this NOx catalyst of the branch passage provided with the NOx catalyst in which said NOx and / or a reducing agent should be introduce | transduced.

That is, NOx and HC exhausted from the NOx catalyst related to the NOx reduction process may be introduced upstream of the NOx catalyst in another branch passage by the communication passage. Then, with a simple configuration, the NOx and HC can be introduced into the NOx catalyst provided in the branch passage together with the exhaust gas flowing through the other branch passage, and these can be purified well.

In the present invention, the exhaust pressure at the introduction destination may be lower than the exhaust pressure at the introduction source. In other words, the communication path is downstream of the NOx catalyst related to the NOx reduction treatment, and the exhaust pressure is increased by closing the flow control valve, and the NOx and / or reducing agent is introduced. A portion of the branch passage provided with the NOx catalyst to be upstream of the NOx catalyst and having a lower exhaust pressure may be communicated.

Then, NOx and HC exhausted from the NOx catalyst due to the NOx reduction treatment,
The NOx and / or the reducing agent can be automatically introduced upstream of the NOx catalyst to be introduced by utilizing the pressure difference between both ends of the communication path.

  Specifically, for example, when the exhaust purification element is further provided upstream of the NOx purification catalyst into which the NOx and / or the reducing agent is to be introduced, the introduction destination portion includes the exhaust purification element and the NOx. And / or a portion between the NOx catalyst into which the reducing agent is to be introduced.

Here, the exhaust pressure at the branch point to the branch passage in the exhaust passage is downstream of the NOx catalyst related to the NOx reduction treatment, and the back pressure is increased by closing the flow control valve. It is almost the same as the exhaust pressure of the original part. On the other hand, the exhaust pressure in the portion between the exhaust purification element and the NOx catalyst into which the NOx and / or reducing agent is to be introduced is after the exhaust has passed through the exhaust purification element, so that the branch in the exhaust passage It becomes lower than the exhaust pressure at the branch point to the passage.

That is, by setting the introduction destination portion as a portion between the exhaust purification element and the NOx catalyst to which the NOx and / or reducing agent is to be introduced, the pressure of the exhaust at the introduction destination portion is reduced to the exhaust gas at the introduction source portion The pressure can be surely lower than the pressure. As a result, N related to the NOx reduction treatment
NOx and HC discharged from the Ox catalyst can be automatically introduced upstream of the NOx catalyst into which the NOx and / or the reducing agent is to be introduced, using the pressure difference between both ends of the communication path.

When this configuration is selected, the other branch passage is preferably a branch passage provided with a NOx catalyst that has not been subjected to NOx reduction treatment. Then, when NOx reduction processing is not performed, the flow control valve in the other branch passage is open, and the exhaust flow rate in the branch passage is large. The pressure difference between the exhaust pressure at the branch point to the exhaust gas and the exhaust pressure in the portion between the exhaust purification element and the NOx catalyst into which the NOx and / or reducing agent is to be introduced can be increased. Further, the NOx and HC can be immediately purified in the downstream NOx catalyst.

Further, in the present invention, the reintroduction means includes a check valve that is provided in the middle of the communication path and restricts the flow of the NOx and / or the reducing agent from the introduction destination side to the introduction source side. You may make it have further. If it does so, it can suppress that the said NOx and HC flow backward in a communicating path, and this NOx and HC can be reliably delivered by the NOx catalyst which these should be introduce | transduced. As a result, NOx and HC released to the outside of the vehicle along with the NOx reduction process can be more reliably reduced, and the emission deterioration during the NOx reduction process can be more reliably suppressed.

In the present invention, the reintroducing means may further include a pump that pumps the NOx and / or the reducing agent from the introduction source side to the introduction destination side in the communication path. Then, even if the difference in the pressure of the exhaust gas at the introduction source part and the introduction destination part is small or the same pressure, the NOx and HC can be prevented from flowing back through the communication path, NOx and HC can be reliably delivered by the NOx catalyst into which they are to be introduced.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  In the present invention, in an exhaust purification system that combines a plurality of branch passages branched from an exhaust passage and a NOx catalyst provided in each branch passage, the deterioration of emissions resulting from NOx reduction treatment is suppressed. be able to.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to the present embodiment and its exhaust system and control system. An internal combustion engine 1 shown in FIG. 1 is a diesel engine. In FIG. 1, the inside of the internal combustion engine 1 and its intake system are omitted.

In FIG. 1, an exhaust pipe 5 through which exhaust gas from the internal combustion engine 1 flows is connected to the internal combustion engine 1, and this exhaust pipe 5 is connected downstream to a muffler (not shown). Further, an exhaust gas purification unit 10 that purifies particulate matter (for example, soot) and NOx in the exhaust gas is disposed in the middle of the exhaust pipe 5. Hereinafter, in the exhaust pipe 5, the upstream side of the exhaust purification unit 10 is referred to as an upstream exhaust pipe 5a, and the downstream side is referred to as a downstream exhaust pipe 5b. Further, in the exhaust purification section 10, the upstream exhaust pipe 5a is branched into a first branch passage 10a and a second branch passage 10b, and the first branch passage 10a and the second branch passage 10b merge downstream. A downstream exhaust pipe 5b is formed. The first branch passage 10a is provided with a first exhaust purification device 11a that collects particulate matter (for example, soot) in the exhaust gas and further occludes and reduces NOx in the exhaust gas. 10b is similarly provided with a second exhaust purification device 11b. Here, the upstream exhaust pipe 5a and the downstream exhaust pipe 5b constitute an exhaust passage in the present embodiment. The first branch passage 10a and the second branch passage 10b constitute a branch passage in the present embodiment.

  In the present embodiment, the first NSR 110a, the first DPNR 111a, and the first oxidation catalyst 112a are arranged in series from the upstream side within the first exhaust purification device 11a. Similarly, the second NSR 110b, the second DPNR 111b, and the second oxidation catalyst 112b are arranged in series from the upstream side in the second exhaust purification device 11b. Here, the first NSR 110a and the second NSR 110b correspond to the exhaust purification element in the present embodiment.

  Further, a first valve 12a for controlling the flow rate of the exhaust gas passing through the first branch passage 10a is provided in the first branch passage 10a at the downstream portion of the first exhaust purification device 11a. Similarly, a second valve 12b is provided in the second branch passage 10b at a downstream portion of the second exhaust purification device 11b. In addition, said 1st valve 12a and said 2nd valve 12b are flow control valves in a present Example.

Further, in FIG. 1, in the first branch passage 10a, upstream of the first exhaust purification device 11a, a fuel as a reducing agent is added to the exhaust during NOx reduction processing of the first exhaust purification device 11a. A fuel addition valve 14a is provided. Similarly, a second fuel addition valve 14b is provided upstream of the second exhaust purification device 11b in the second branch passage 10b. In addition, said 1st fuel addition valve 14a and said 2nd fuel addition valve 14b comprise the reducing agent addition means in a present Example.

The internal combustion engine 1 configured as described above and its exhaust system are provided with an electronic control unit (ECU) 35 for controlling the internal combustion engine 1 and the exhaust system. The ECU 35 is a unit that controls the exhaust gas purification unit 10 of the internal combustion engine 1 in addition to controlling the operation state of the internal combustion engine 1 according to the operation conditions of the internal combustion engine 1 and the request of the driver.

  Sensors related to control of the operating state of the internal combustion engine 1 such as a crank position sensor and an accelerator position sensor (not shown) are connected to the ECU 35 via electric wiring, and their output signals are input to the ECU 35. ing. On the other hand, a fuel injection valve (not shown) in the internal combustion engine 1 is connected to the ECU 35 via an electrical wiring, and the first valve 12a, the second valve 12b, the first fuel addition valve 14a, The second fuel addition valve 14b is connected via electric wiring and is controlled by the ECU 35.

The ECU 35 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data. A NOx reduction processing routine (not shown) for reducing and releasing NOx stored in the first exhaust purification device 11a and the second exhaust purification device 11b is also one of the programs stored in the ROM of the ECU 35. It is executed by the ECU 35. The ECU 35 corresponds to NOx reduction means in this embodiment.

  Further, in this embodiment, the portion between the first exhaust purification device 11a and the first valve 12a in the first branch passage 10a, the second NSR 110b in the second exhaust purification device 11a in the second branch passage 10b, and the second The first communication passage 15a communicating with the portion between the 2DPNRs 111b, the portion between the second exhaust purification device 11b and the second valve 12b in the second branch passage 10b, and the first exhaust purification in the first branch passage 10a A second communication path 15b is provided that communicates between the first NSR 110a and the first DPNR 111a in the device 11a.

  Further, the first communication passage 15a is provided with a first check valve 16a for preventing the exhaust gas passing through the first communication passage 15a from flowing backward, and the second communication passage 15b is provided with a second communication passage 15b. A second check valve 16b is provided to prevent the exhaust passing therethrough from flowing backward.

Next, in the exhaust purification system of the present embodiment, for example, control when performing NOx reduction processing for the first NSR 110a and the first DPNR 111a of the first exhaust purification device 11a will be described.

  In this case, the reducing agent is added from the first fuel addition valve 14a to the exhaust gas passing through the first branch passage 10a, and the first valve 12a is closed. As a result, the exhaust flow rate of the exhaust gas passing through the first branch passage 10a decreases, so that the fuel added from the first fuel addition valve 14a diffuses slowly and reliably into the first NSR 110a and the first DPNR 111a. Further, among the fuel added from the first fuel addition valve 14a, the fuel that is oxidized by contacting with the exhaust gas is reduced, and the NOx reduction treatment can be performed efficiently.

  However, the fuel added from the first fuel addition valve 14a may still not diffuse sufficiently uniformly into the first NSR 110a and the first DPNR 111a. Then, the NOx stored in the first NSR 110a or the first DPNR 111a may be released as NOx.

Of the fuel added from the first fuel addition valve 14a, the first NSR 110a and the first NSR 110a
In some cases, the material passing through the DPNR 111a is discharged as HC from the first exhaust purification device 11a. Then, as shown in FIG. 2, the NOx in the exhaust from the first exhaust purification device 11a is synchronized with the closing of the first valve 12a and the fuel addition from the first fuel addition valve 14a accompanying the NOx reduction process. HC sometimes increased.

As a result, when the first valve 12a is opened after the NOx reduction process is completed, NOx and HC discharged from the first exhaust purification device 11a are diffused outside the vehicle, and the emission may be deteriorated. Here, as shown in FIG. 2, the changes in the concentrations of NOx and HC are steep, but at this time, the exhaust flow rate of the first branch passage 10a is reduced by closing the first valve 12a. Considering this, it cannot be said that the emissions have deteriorated significantly. However, in order to improve the purification performance of the entire exhaust purification system, the above changes in the concentrations of NOx and HC should also be improved.

In contrast, in the present embodiment, during the NOx reduction process of the first NSR 110a and the first DPNR 111a, the portion between the first exhaust purification device 11a and the first valve 12a in the first branch passage 10a and the second branch Since the first communication passage 15a that connects the second NSR 110b and the second DPNR 111b in the second exhaust purification device 11a in the passage 10b is provided, NOx and HC discharged from the first exhaust purification device 11a are Then, it passes through the first communication passage 15a and is introduced between the second NSR 110b and the second DPNR 111b in the second exhaust purification device 11b.

Then, these NOx and HC are then introduced into the second DPNR 111b and purified. As a result, it is possible to suppress NOx and HC discharged from the first exhaust purification device 11a from being diffused outside the vehicle as they are.

Here, since the first valve 12a is closed during the NOx reduction process, the pressure of the exhaust gas at the point A between the first exhaust purification device 11a and the first valve 12a is the upstream exhaust passage 5a. Is substantially equal to the pressure of the exhaust gas at the point C of the branch point from the first branch passage 10a to the second branch passage 10b. On the other hand, since the second valve 12b is open, the exhaust pressure at the point B between the second NSR 110b and the second DPNR 111b is lower than the exhaust pressure at the point C by the back pressure by the second NSR 110b. Yes.

  That is, the exhaust pressure at point C is lower than the exhaust pressure at point A. Therefore, the exhaust gas that has passed through the first exhaust purification device 11a automatically passes through the first communication passage 15a, and enters the portion between the second NSR 110b and the second DPNR 111b in the second exhaust purification device 11a in the second branch passage 10b. Flows in.

  Therefore, in this embodiment, the NOx or HC discharged during the NOx reduction process of the first NSR 110a and the first DPNR 111a can be purified by the second DPNR 111b only by providing the first communication path 15a.

  Here, since the first check valve 16a is provided in the first communication passage 15a, even when the pressure difference between the point A and the point C in the figure becomes small depending on the operation state of the internal combustion engine 1, It is possible to suppress NOx and HC once flowing into the portion between the second NSR 110b and the second DPNR 111b in the second exhaust purification device 11a from flowing back through the first communication passage 15a.

  In this embodiment, the combination of the first communication passage 15a and the first check valve 16a and the combination of the second communication passage 15b and the second check valve 16b correspond to a reintroduction means.

Further, the first exhaust purification device 11a in the present embodiment includes the first NSR 110a and the first DPN.
R111a and the first oxidation catalyst 112a are included, and the second exhaust purification device 11b is configured by the second NSR 110b, the second DPNR 111b, and the second oxidation catalyst 112b. However, the configuration of the first exhaust purification device 11a and the second exhaust purification device 11b to which the present invention is applied is not limited to this. At least the NOx storage reduction catalyst and a filter or a catalyst are arranged on the upstream side of the NOx storage reduction NOx catalyst in the first exhaust purification device 11a.
The NOx or HC discharged due to the Ox reduction process may be introduced between the NOx storage reduction catalyst in the second exhaust purification device 11b and the upstream filter or catalyst.

  Further, in the present embodiment, a pressure difference is generated at both ends of the first communication passage 15a by utilizing the fact that the pressure of the exhaust gas is lower on the downstream side than the upstream side of the second NSR 110b. However, the method of generating a pressure difference at both ends of the first communication path 15a is not limited to this. For example, in addition to the second NSR 110b in the second branch passage 10b, an exhaust throttle valve for reducing the pressure is provided, and the exhaust throttle valve is activated to actively reduce the pressure of the exhaust downstream of the exhaust throttle valve, A pressure difference may be generated at both ends of the first communication path 15a.

Next, a second embodiment of the present invention will be described. In the second embodiment, an example will be described in which NOx and HC exhausted from the exhaust purification device at the time of performing the NOx reduction process are introduced to the branch points from the exhaust passage to each branch passage.

  FIG. 3 shows a schematic configuration of the internal combustion engine according to the present embodiment and its exhaust system and control system. In the present embodiment, the first communication passage 25a includes a portion between the first exhaust purification device 11a and the first valve 12a in the first branch passage 10a, and the first branch passage 10a and the second branch in the upstream exhaust passage 5a. The branch point to the branch passage 10b is communicated. Further, the second communication passage 25b is connected to a portion between the second exhaust purification device 11b and the second valve 12b in the second branch passage 10b, and to the first branch passage 10a and the second branch passage 10b in the upstream exhaust passage 5a. It communicates with the bifurcation point.

According to this configuration, for example, during NOx reduction processing of the first NSR 110a and the first DPNR 111a, NOx and HC discharged from the first first exhaust purification device 11a are converted into the second NSR1.
It can be introduced upstream of both 10b and the second DPNR 111b. Therefore, NOx and HC can be purified more reliably by more NOx catalysts.

However, in this case, since the exhaust pressures at the points A and C in the figure are substantially equal, it is difficult to automatically introduce the exhaust at the point A to the point C. Therefore, in this embodiment, the first communication passage 25a is provided with the first pump 26a, and the second communication passage 25b is provided with the second pump 26b, and the exhaust at the point A is forcibly introduced into the point C. To do. Accordingly, the NOx and HC discharged from the first exhaust purification device 11a can be more reliably removed from the first exhaust passage 5a.
It can be introduced at the branch point to the branch passage 10a and the second branch passage 10b.

  In the above description, the internal combustion engine 1 is a diesel engine. However, the above embodiment may be applied to a gasoline engine.

In the above embodiment, the case where the NOx reduction process is performed on the first NSR 110a and the first DPNR 111a in the first exhaust purification device 11a has been described. However, the NOx is applied to the second NSR 110b and the second DPNR 111b in the second exhaust purification device 11b.
The same applies to the case where the reduction process is performed. In this case, in FIG. 1 and FIG. 3, the control opposite to the left and right may be performed as described in the above embodiment.

In the above embodiment, the case where the NOx reduction treatment is performed by adding fuel as a reducing agent to the NOx storage reduction catalyst has been described. However, urea water is supplied into the exhaust passage as a reducing agent, and the exhaust gas is exhausted. The present invention can also be applied to a selective reduction type NOx catalyst system that reduces NOx in gas.

  In the above embodiment, the case where the NOx reduction treatment is performed on the NOx catalyst provided in one of the branch passages in the exhaust purification system that branches the exhaust passage into two branch passages has been described. In the exhaust gas purification system that branches into the above branch passages, the present invention may be applied when NOx reduction treatment is performed on the NOx catalyst provided in some branch passages.

  Moreover, in the said Example, the valve closing or valve opening operation | movement of the 1st valve 12a or the 2nd valve 12b does not necessarily mean fully closing or fully opening operation | movement. The valve closing operation includes reducing the exhaust flow rate of the first branch passage 10a or the second branch passage 10b by operating the first valve 12a or the second valve 12b to the valve closing side. Further, the valve opening operation includes increasing the exhaust flow rate of the first branch passage 10a or the second branch passage 10b by operating the first valve 12a or the second valve 12b to the valve opening side.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an exhaust system and a control system thereof in Embodiment 1 of the present invention. FIG. It is a graph which shows the change of the density | concentration of NOx and HC discharged | emitted from a 1st exhaust gas purification apparatus at the time of performing NOx reduction process with respect to the 1st exhaust gas purification apparatus in the Example of this invention. It is a figure which shows schematic structure of the internal combustion engine in Example 2 of this invention, its exhaust system, and a control system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust pipe 5a ... Upstream exhaust pipe 5b ... Downstream exhaust pipe 10 ... Exhaust purification part 10a ... 1st branch path 10b ... 2nd branch path 11a ... 1st exhaust purification device 11b ... 2nd exhaust purification device 12a ... 1st valve 12b ... 2nd valve 14a ... 1st fuel addition valve 14b ... 2nd fuel addition valve 15a 25a ... 1st communication path 15b, 25b ... 2nd communication path 16a ... 1st check valve 16b ... 2nd check valve 26a ... 1st pump 26b ... 2nd Pump 35 ... ECU
110a ... 1st NSR
110b 2nd NSR
111a ... 1st DPNR
111b ... 2nd DPNR
112a ... 1st oxidation catalyst 112b ... 2nd oxidation catalyst

Claims (6)

One end is connected to the internal combustion engine and exhaust from the internal combustion engine passes therethrough, and an exhaust passage that branches into a plurality of branch passages along the way,
A NOx catalyst provided in each of the plurality of branch passages to purify NOx in the exhaust gas passing through each branch passage;
Reducing agent addition means for adding a reducing agent to the exhaust gas that is provided upstream of the NOx catalyst in each of the plurality of branch passages and passes through each branch passage;
A flow rate control valve that is provided downstream of the NOx catalyst in each of the plurality of branch passages and controls the flow rate of the exhaust gas that passes through each branch passage;
A reducing agent is supplied to the NOx catalyst provided in a part of the plurality of branch passages from the reducing agent addition means upstream of the NOx catalyst, and the flow control valve downstream of the NOx catalyst is closed. NOx reduction means for performing NOx reduction treatment by
Along with the NOx reduction treatment, NOx and / or reducing agent discharged from the NOx catalyst related to the NOx reduction treatment is separated from the branch passage provided with the NOx catalyst related to the NOx reduction treatment. Reintroduction means for introducing into the NOx catalyst;
An exhaust gas purification system for an internal combustion engine, comprising: The reintroduction means includes
An introduction source portion that is a downstream portion of the NOx catalyst and an upstream portion of the flow rate control valve in the branch passage provided with the NOx catalyst related to the NOx reduction treatment, and the NOx and / or reducing agent should be introduced. 2. The exhaust gas purification system for an internal combustion engine according to claim 1, further comprising a communication passage that communicates a branch passage provided with the NOx catalyst with an introduction destination portion that is an upstream portion of the NOx catalyst.   The exhaust gas purification system for an internal combustion engine according to claim 2, wherein the pressure of the exhaust gas at the introduction destination portion is lower than the pressure of the exhaust gas at the introduction source portion. An exhaust purification element for purifying exhaust gas passing through the branch passage upstream of the NOx catalyst in the branch passage provided with the NOx catalyst into which the NOx and / or reducing agent is to be introduced;
The exhaust purification system of an internal combustion engine according to claim 2, wherein the introduction destination portion is a portion between the exhaust purification element and the NOx catalyst into which the NOx and / or reducing agent is to be introduced. The reintroducing means further includes a check valve that is provided in the middle of the communication path and restricts the flow of the NOx and / or the reducing agent from the introduction destination side to the introduction source side. An exhaust purification system for an internal combustion engine according to any one of claims 2 to 4. 6. The reintroducing means further comprises a pump that pumps the NOx and / or the reducing agent from the introduction source part side to the introduction destination part side in the communication path. 2. An exhaust gas purification system for an internal combustion engine according to 1.

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