JP2006022739A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique for allowing a plurality of modes including a single mode, a dual mode, a tandem mode and a bypass mode in an exhaust emission control system combining two exhaust emission control devices. <P>SOLUTION: The system comprises an exhaust pipe 5 connected at one end to an internal combustion engine 1 and branched at a branch point into a first branch passage 10a and a second branch passage 10b, a first connection passage 10c and a second connection passage 10d formed to bridge the first branch passage 10a and the second branch passage 10d, a first filter 11a disposed in the first connection passage 10c and a second filter 11b disposed in the second connection passage 10d. The first branch passage 10a and the second branch passage 10b are further provided with a first valve 12a to a sixth valve 12f. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  The exhaust gas of the internal combustion engine contains particulate matter mainly composed of carbon. A technique for providing a particulate filter (hereinafter referred to as “filter”) for collecting particulate matter in an exhaust system of an internal combustion engine is known in order to prevent such particulate matter from being released into the atmosphere.

  In such a filter, when the amount of collected particulate matter increases, the back pressure in the exhaust increases due to clogging of the filter and the engine performance decreases, so by increasing the exhaust temperature upstream of the filter, The collected particulate matter is oxidized and removed to regenerate the exhaust purification performance of the filter (hereinafter referred to as “filter regeneration process”).

  Here, as a method for raising the exhaust temperature upstream of the filter in the regeneration process, an oxidation catalyst having an oxidizing ability is disposed upstream of the filter, and fuel as a reducing agent is supplied to the oxidation catalyst during the regeneration process. Thus, there is known a method of causing an oxidation reaction of fuel in the oxidation catalyst and increasing the exhaust temperature upstream of the filter.

  It is also known to provide a NOx catalyst in the exhaust system of an internal combustion engine in order to purify NOx in the exhaust. Here again, for example, in the case of an NOx storage reduction catalyst, the purification performance deteriorates as the amount of NOx stored increases. Therefore, fuel as a reducing agent is supplied to the NOx storage reduction catalyst, and NOx stored in the catalyst is reduced and released (hereinafter referred to as “Ox reduction treatment”). Furthermore, it is known that SOx poisoning in which the purification performance deteriorates due to the SOx in the exhaust gas being stored in the NOx catalyst, and in order to eliminate this SOx poisoning, a reducing agent is added to the NOx catalyst. May be supplied (hereinafter referred to as “SOx poisoning recovery process”).

  Here, when supplying the fuel as the reducing agent to the exhaust purification device such as the filter or the NOx catalyst, if the exhaust flow rate introduced into the filter or the NOx catalyst is large, a part of the supplied fuel is used. Oxidation in contact with high-temperature exhaust gas may not be used for the oxidation reaction in the oxidation catalyst or NOx catalyst. In this case, fuel efficiency may deteriorate in filter regeneration processing, NOx reduction processing, and SOx poisoning recovery processing (hereinafter collectively referred to as “regeneration processing”).

  On the other hand, the exhaust gas purification system (hereinafter referred to as the “exhaust gas purification system” including the exhaust gas purification device and its control system) includes two exhaust gas purification devices. The exhaust gas is introduced only into one side, the amount of exhaust introduced into the other exhaust purification device is suppressed, and the fuel as the reducing agent is supplied to the exhaust purification device with the reduced amount of exhaust introduced. Increasing the proportion of fuel used for regeneration processing among the remaining fuel is being carried out. As a result, the fuel efficiency in the regeneration process can be improved, and the filter regeneration process can be performed without affecting the operation state or emission of the internal combustion engine (hereinafter, this mode is referred to as “ Single mode ").

In addition, there are various advantages if two exhaust purification devices are provided in the exhaust purification system. For example, by providing two exhaust purification devices in parallel, the back pressure in the exhaust can be reduced, and the purification and durability of the exhaust purification device can be improved (hereinafter, this mode is referred to as “dual mode”). In addition, by providing two exhaust purification devices in series, the exhaust purification device can be passed through the exhaust twice to improve exhaust purification (hereinafter, this mode is referred to as a “tandem mode”). ). Furthermore, when the temperature of the exhaust purification device becomes excessively high, by bypassing both exhaust purification devices to the hot exhaust gas, and when the temperature of the exhaust purification device becomes excessively low By allowing both exhaust purification devices to bypass the low-temperature exhaust, the temperature of the exhaust purification device can be properly maintained (hereinafter, this mode is referred to as “bypass mode”).

As described above, the performance of the exhaust purification system can be improved by switching various modes in which two exhaust purification devices are combined (see, for example, Patent Document 1). However, even though the above-described individual modes can be realized in the exhaust purification system, it is difficult to realize all the modes with one system.
JP 07-189655 A Japanese Patent No. 2727906 JP 2002-13409 A

  An object of the present invention is to provide a technology capable of realizing a plurality of modes including a single mode, a dual mode, a tandem mode, and a bypass mode in an exhaust purification system in which a plurality of exhaust purification devices are combined. is there.

  In order to achieve the above object, according to the present invention, an exhaust passage is connected to an internal combustion engine at one end and branches into a first branch passage and a second branch passage at a branch point, and the first branch passage and the second branch passage are bridged. And first and second exhaust purification devices disposed in the first and second connection passages, and further, the first and second branch passages are provided in the first and second branch passages. The most characteristic feature is that a plurality of modes including a single mode, a dual mode, a tandem mode, and a bypass mode are realized by providing first to sixth valves and opening and closing the first to sixth valves as appropriate.

More specifically, one end is connected to the internal combustion engine, branches into a first branch passage and a second branch passage at a branch point, and an exhaust passage through which exhaust from the internal combustion engine passes,
One end is connected to the first branch passage at the first connection portion, the other end is connected to the second branch passage at the second connection portion, and a first exhaust purification device for purifying exhaust gas is provided. A connecting passage,
One end of the third connection portion downstream of the first connection portion in the first branch passage is connected to the first branch passage, and the fourth connection portion downstream of the second connection portion in the second branch passage. The other end is connected to the second branch passage, and a second connection passage provided with a second exhaust purification device for purifying exhaust,
A first valve provided between the branch point in the first branch passage and the first connection portion;
A second valve provided between the branch point in the second branch passage and the second connection portion; and provided between the first connection portion and the third connection portion in the first branch passage. A third valve;
A fourth valve provided between the second connection portion and the fourth connection portion in the second branch passage;
A fifth valve provided downstream of the third connection portion in the first branch passage;
A sixth valve provided downstream of the fourth connecting portion in the second branch passage;
Control means for controlling the opening and closing of the first to sixth valves,
By controlling the opening and closing of the first to sixth valves, the control means,
A first mode in which only one of the first exhaust purification device or the second exhaust purification device is included in a path through which the exhaust passes;
A second mode in which the first exhaust purification device and the second exhaust purification device are connected in parallel to the path through which the exhaust passes; and
A third mode in which the first exhaust purification device and the second exhaust purification device are connected in series in a path through which the exhaust passes; and
A fourth mode in which neither the first exhaust purification device nor the second exhaust purification device is included in the path through which the exhaust passes;
Can be selected.

  That is, in the above configuration, the first, fourth, and sixth valves are opened, and the second, third, and fifth valves are closed, so that only the first exhaust purification device is included in the exhaust path. One mode can be realized. Further, by opening the second, fourth, and fifth valves and closing the first, third, and sixth valves, the first mode in which only the second exhaust purification device is included in the exhaust path is achieved. It is feasible.

  Next, in the above configuration, the second mode can be realized in the exhaust path by opening the second, third, fourth, and fifth valves and closing the first and sixth valves. . Further, the third mode can be realized in the exhaust path by opening the first, fourth, and fifth valves and closing the second, third, and sixth valves. Furthermore, the fourth mode can be realized by opening all of the first to sixth valves.

  Thus, in the present invention, the first to fourth modes corresponding to the single mode, the dual mode, the tandem mode, and the bypass mode are realized by controlling the first to sixth valves to be appropriately opened and closed. It is possible to improve the purification performance and durability performance of the exhaust purification system.

  In the present invention, the control means controls the opening and closing of the first to sixth valves in each of the first to fourth modes, whereby the first exhaust purification device and the second exhaust purification. The exhaust passage direction with respect to the exhaust purification device included in the path through which the exhaust passes may be reversed.

  That is, in the first mode in which only the first exhaust purification device is included in the exhaust path, the second, third, and fifth valves are opened, and the first, fourth, and sixth valves are closed. Thereby, the passage direction of the exhaust gas in the first exhaust gas purification device can be reversed. Similarly, in the first mode in which only the second exhaust purification device is included in the exhaust path, the first, third, and sixth valves are opened, and the second, fourth, and fifth valves are closed. Thus, the exhaust passage direction in the second exhaust purification device can be reversed.

  In the second mode of the exhaust path, the first, second, fifth valves are opened, and the first and second exhausts are closed by closing the second and fifth valves. The exhaust passage direction in the purification device can be reversed. Further, in the third mode of the exhaust path, the second, third, and sixth valves are opened, and the first, fourth, and fifth valves are closed, so that the first and second valves are closed. The exhaust passage direction in the exhaust purification device can be reversed.

In this case, for example, when the ash after the particulate matter is oxidized by the regeneration process is still accumulated in the first and / or second exhaust purification device, the passage direction of the exhaust gas is reversed to reverse the above. The particulate matter ash can be released, and the exhaust purification performance of the first and / or second exhaust purification device can be more reliably regenerated. Further, by periodically reversing the exhaust passage direction, the distribution of particulate matter collected in the first and / or second exhaust purification devices and the first and / or second exhaust purification devices occluded. The distribution of NOx and SOx can be made uniform. Accordingly, the first and / or second exhaust purification device can be used more efficiently. Furthermore, when the temperature difference in the first and / or second exhaust purification device is large, such as when the internal combustion engine is started, the temperature distribution in the first and / or second exhaust purification device can be made uniform. .

  In addition, if the passage direction of the exhaust gas is reversed when the third mode is selected, the particulate matter released from one of the first and second exhaust gas purification devices is removed from the first and second exhaust gases. It can also be collected on the other side of the purification device so that they are not released outside the vehicle. Furthermore, the amount of the reducing agent used in the regeneration process can be suppressed by collecting the particulate matter in one of the first and second exhaust purification apparatuses and then performing the regeneration process by adding the reducing agent. . As a result, the consumption efficiency of the reducing agent in the regeneration process can be improved.

  Further, the present invention further includes intake air amount detection means for detecting an intake air amount sucked into the internal combustion engine, and the control means is configured to detect the first air when the intake air amount is less than a predetermined value. Mode or the third mode may be selected, and the second mode may be selected when the intake air amount is equal to or greater than the predetermined value.

  Here, it is possible to estimate the exhaust flow rate discharged from the internal combustion engine by detecting the amount of intake air taken into the internal combustion engine. When the second mode is compared with the first and third modes, the total pressure loss of the first and second exhaust purification devices in the second mode is the first and third modes. Has been found to be less than that.

  On the other hand, as described above, since the first mode corresponds to the single mode, after the first mode is selected, the reducing agent is supplied to the exhaust purification device that is not included in the exhaust path and regenerated. By performing the treatment, the consumption efficiency of the reducing agent in the regeneration treatment or the like can be improved. Further, in the third mode, by reversing the exhaust passage direction, the reducing agent is supplied after collecting the particulate matter in one of the first and second exhaust purification apparatuses, and the reducing agent consumption efficiency in the regeneration process Can be improved. In addition, the distribution of particulate matter, NOx, and SOx in the first and second exhaust purification apparatuses can be made uniform, and the temperature distribution can be made uniform.

  Therefore, in the present invention, the advantages of each mode are effectively utilized by switching between the second mode and the first and / or third mode according to the amount of intake air of the internal combustion engine. . That is, when the amount of intake air is less than a predetermined value, the exhaust flow rate discharged from the internal combustion engine is also small, so the possibility that the pressure loss of the exhaust purification device will affect the engine performance is low. Therefore, in such a case, the first or third mode is selected.

  When the intake air amount exceeds a predetermined value, the exhaust flow rate exhausted from the internal combustion engine increases, so the pressure loss of the exhaust purification device may affect the engine performance. The corresponding second mode is selected. In this way, the optimum mode can be selected according to the operating state of the internal combustion engine, and the exhaust gas purification system can be selected without affecting the engine performance of the internal combustion engine by the pressure loss in the first and / or second exhaust gas purification devices. Can be operated efficiently.

  Here, the predetermined value means that the engine performance of the internal combustion engine is the first and / or the second when the intake air amount is more than that and the first or third mode is selected in the exhaust purification system. 2 An intake air amount as a threshold value that is determined to be affected by pressure loss in the exhaust purification device.

The present invention further includes exhaust temperature detection means for detecting the temperature of the exhaust,
The control means selects the third mode when the temperature of the exhaust gas is equal to or lower than a predetermined first temperature, and when the temperature of the exhaust gas is equal to or higher than a predetermined second temperature higher than the first temperature. Alternatively, the first mode or the second mode may be selected.

  Here, when the first and / or second exhaust purification device has a catalyst such as a NOx catalyst, especially immediately after the start of the internal combustion engine, the temperature of the exhaust gas is low, so that the catalyst is activated. It may take time. If it does so, there exists a possibility that the emission of the period until the said NOx catalyst may be activated will deteriorate.

  On the other hand, in the case where the first and / or second exhaust purification device includes a filter that collects particulate matter in the exhaust, and when such regeneration processing is performed, depending on the operating state of the internal combustion engine, May increase the temperature of the exhaust gas, and the temperature of the first and / or second exhaust gas purification device may become excessively high.

  Here, when the third mode in the exhaust purification system of the present invention is compared with the first and second modes, the first and second exhaust purification devices are connected in series in the third mode. Therefore, the exhaust gas whose temperature is increased by passing through the upstream side exhaust purification device is introduced into the downstream side exhaust purification device. As a result, in the third mode, there is less heat escape than in the first and second modes, and the temperature of the exhaust emission control device can be increased efficiently.

  Therefore, in the present invention, the third mode may be selected when the temperature of the exhaust gas from the internal combustion engine detected by the exhaust gas temperature detecting means is equal to or lower than a predetermined first temperature. Then, when the temperature of the first or second exhaust purification device is low, such as when the internal combustion engine is started, the temperature can be increased efficiently. Here, the predetermined first temperature means that if the exhaust temperature is lower than that, the catalyst in the first or second exhaust purification device is not activated, and it is difficult to obtain sufficient exhaust purification performance. It is temperature as a threshold value considered.

  Further, when the temperature of the exhaust gas from the internal combustion engine detected by the exhaust gas temperature detection means is equal to or higher than a predetermined second temperature higher than the first temperature, the first or second mode may be selected. Good. Thereby, since it becomes difficult for the temperature of the 1st and 2nd exhaust gas purification device to rise, it can control that those temperature becomes high temperature too much. The predetermined second temperature is a threshold at which the temperature of the first or second exhaust purification device is determined to be excessively high if the temperature of the exhaust gas from the internal combustion engine is higher than that. Temperature.

In the present invention, the first exhaust gas purification device and the second exhaust gas purification device have a NOx catalyst that purifies NOx in the exhaust gas,
A reducing agent supply means for supplying a reducing agent to the first exhaust purification device or the second exhaust purification device;
When the first mode is selected, a reducing agent is supplied by a reducing agent supply means to one of the first exhaust purification device and the second exhaust purification device that is not included in the exhaust path. Thus, NOx in the first exhaust purification device and the second exhaust purification device that are not included in the exhaust path may be reduced.

  As described above, when the first and second exhaust purification devices have NOx catalysts, the supply is performed by supplying the reducing agent to the one of the first and second exhaust purification devices in which the introduction amount of exhaust gas is suppressed. Among the reduced agents, the proportion of the reducing agent used for reducing NOx without being consumed by oxidation in contact with exhaust gas can be increased.

Therefore, in the exhaust purification system of the present invention, when the first mode is selected, the one of the first exhaust purification device and the second exhaust purification device that is not included in the exhaust path, You may make it reduce | restore NOx in the said exhaust gas purification apparatus by supplying a reducing agent with a reducing agent supply means. If it does so, the consumption efficiency of the reducing agent in NOx reduction processing etc. can be improved. This can be applied not only to NOx reduction processing of the first or second exhaust purification device, but also to SOx poisoning recovery processing and regeneration processing when the first and second exhaust purification devices have filters. it can.

In the present invention, the first exhaust gas purification device and the second exhaust gas purification device have a NOx catalyst that purifies NOx in the exhaust gas,
A reducing agent supply means for supplying a reducing agent to the first exhaust purification device and / or the second exhaust purification device;
When the second mode is selected, a reducing agent is supplied to the first exhaust purification device and / or the second exhaust purification device by a reducing agent supply means, whereby the first exhaust purification device and / or Alternatively, NOx in the second exhaust purification device may be reduced.

  Here, as described above, in the present exhaust purification system, when the second mode is selected, assuming that the exhaust flow rate from the internal combustion engine is the same, the first and third modes are selected. However, the amount of exhaust gas introduced into the first and second exhaust gas purification devices is small as much as the exhaust gas from the internal combustion engine is divided. Accordingly, if the reducing agent is supplied to the first exhaust purification device and / or the second exhaust purification device by the reducing agent supply means after the second mode is selected, the first and third modes are simply set. The ratio of the reducing agent used for the NOx reduction treatment among the supplied reducing agents can be increased as compared with the case where it is selected, and the consumption efficiency of the reducing agent in the NOx reduction treatment can be improved. This can be applied not only to NOx reduction processing of the first or second exhaust purification device, but also to SOx poisoning recovery processing and regeneration processing when the first and second exhaust purification devices have filters. it can.

  In the present invention, the reducing agent supply means is disposed on both sides of the first exhaust purification device in the first connection passage and on both sides of the second exhaust purification device in the second connection passage. May be.

  Then, regardless of which mode is selected in the exhaust purification system of the present invention, and even if the passage direction of the exhaust gas in the first and / or second exhaust purification device is reversed, the first and / or second is ensured. A reducing agent can be supplied to the exhaust emission control device.

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

  In the present invention, a plurality of modes including a single mode, a dual mode, a reverse mode, and a bypass mode can be realized in an exhaust purification system in which two exhaust purification devices are combined.

  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 a first exhaust pipe 5a, and the downstream side is referred to as a second exhaust pipe 5b. Further, in the exhaust purification section 10, the first 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 join downstream. The second exhaust pipe 5b is formed. In the exhaust purification unit 10, a first connection passage 10c is provided so as to bridge the first branch passage 10a and the second branch passage 10b. Further, a second connection passage 10d is provided on the downstream side of the first connection passage 10c so as to bridge the first branch passage 10a and the second branch passage 10b. The first connection passage 10c is provided with a first filter 11a that collects particulate matter (for example, soot) in the exhaust gas and further occludes and reduces NOx in the exhaust gas. Similarly, a second filter 11b is provided.

  In the present embodiment, the first filter 11a and the second filter 11b are obtained by supporting a NOx storage reduction catalyst on a wall flow type particulate filter made of a porous base material. However, the first filter 11a and the second filter 11b do not necessarily have a configuration in which the NOx storage reduction catalyst is supported on the particulate filter. For example, a particulate filter in which the NOx storage reduction catalyst is not supported You may make it the structure which consists of a NOx storage reduction catalyst provided in series with it. Further, a NOx catalyst other than the NOx storage reduction catalyst may be used.

  Further, in the first branch passage 10a, the exhaust gas passing through the first branch passage 10a can be passed or blocked between the connection portion with the first exhaust pipe 5a and the connection portion with the first connection passage 10c. A first valve 12a is provided. Similarly, a third valve 12c is provided between the connection portion of the first branch passage 10a with the first connection passage 10c and the connection portion of the second connection passage 10d with the second connection passage in the first branch passage 10a. A fifth valve 12e is provided between the connection portion with 10d and the connection portion with the second exhaust pipe 5b.

  On the other hand, between the connecting portion with the first exhaust pipe 5a and the connecting portion with the first connecting passage 10c in the second branch passage 10b, the exhaust gas passing through the second branch passage 10b can be passed or blocked. A second valve 12b is provided. Similarly, a fourth valve 12d is provided between the connection portion of the second branch passage 10b with the first connection passage 10c and the connection portion of the second connection passage 10d with the second connection passage in the second branch passage 10b. A sixth valve 12f is provided between the connecting portion with 10d and the connecting portion with the second exhaust pipe 5b.

  Here, the connection part with the 1st exhaust pipe 5a in the 1st branch passage 10a and the 2nd branch passage 10b is equivalent to the branch point in a present Example. In the first branch passage 10a, the connection portion of the first connection passage 10c corresponds to the first connection portion, and in the second branch passage 10b, the connection portion to the first connection passage 10c corresponds to the second connection portion. In the first branch passage 10b, the connection portion of the second connection passage 10d corresponds to a third connection portion, and the connection portion of the second branch passage 10b to the second connection passage 10d corresponds to a fourth connection portion. Further, the first exhaust pipe 5a, the first branch passage 10a, the second branch passage 10b, and the second exhaust pipe 5b constitute an exhaust passage in the present embodiment.

Further, in FIG. 1, a first fuel addition valve 14 a that injects fuel as a reducing agent and a second fuel on the left and right sides of the first filter 11 a in the first connection passage 10 c during the regeneration process of the first filter 11 a and the like. Two fuel addition valves 14b are provided. Similarly, a third fuel addition valve 14c and a fourth fuel addition valve 14d are provided on both the left and right sides of the second filter 11b in the second connection passage 10d. The first fuel addition valve 14a to the fourth fuel addition valve 14d constitute the reducing agent supply means in this embodiment.

  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 to the sixth valve 12f and the first fuel addition valve 14a to the present embodiment are used. The fourth fuel addition valve 14d is connected via electric wiring and is controlled by the ECU 35. Therefore, ECU35 comprises the control means in a present Example.

  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. In addition to the regeneration processing routine for regenerating the particulate matter capturing ability of the first filter 11a and the second filter 11b, the NOx reduction processing routine, the SOx poisoning recovery processing routine (both are not described), etc. This is one of the programs stored in the ROM.

  Next, modes that the exhaust purification system according to the present embodiment can take and their functions will be described.

  [Dual Mode] First, the most basic dual mode realized by controlling the exhaust purification unit 10 of the internal combustion engine 1 will be described with reference to FIG. This dual mode corresponds to the second mode in this embodiment. In this case, for example, as shown in FIG. 2A, the second valve 12b, the third valve 12c, the fourth valve 12d, and the fifth valve 12e are opened, and the first valve 12a and the sixth valve 12f are closed. To do. Then, as shown in FIG. 2A, the exhaust discharged from the internal combustion engine 1 passes through the second branch passage 10b from the first exhaust pipe 5a, and passes through the first connection passage 10c and the second connection passage 10d in parallel. And then passes through the first branch passage 10a and the second exhaust pipe 5b and is discharged out of the vehicle.

  When this mode is selected, the exhaust from the internal combustion engine 1 passes through both the first filter 11a and the second filter 11b in parallel, so that the total filter sectional area as the exhaust purification unit 10 is increased. Can be made. As a result, pressure loss in the exhaust purification unit 10 can be suppressed. In addition, since the amount of exhaust gas that passes per unit cross-sectional area of the first filter 11a and the second filter 11b can be relatively reduced, the exhaust gas purification performance of the first filter 11a and the second filter 11b can be improved. Furthermore, since the burden on the first filter 11a and the second filter 11b is reduced, the durability can be improved.

In the present embodiment, the regeneration process of the first filter 11a and / or the second filter 11b may be performed in a state where this mode is selected. That is, in the dual mode, the exhaust gas from the internal combustion engine 1 is introduced into the first filter 11a and the second filter 11b after being divided into the first connection passage 10c and the second connection passage 10d. Therefore, the flow rate of the exhaust gas introduced into the first filter 11a and the second filter 11b can be reduced to half of the amount discharged from the internal combustion engine 1. As a result, it is possible to prevent the fuel added from the fuel addition valve from being oxidized and consumed during contact with the high-temperature exhaust during the regeneration process, and to improve the fuel efficiency during the regeneration process. .

  In this dual mode, as shown in FIG. 2B, the first valve 12a, the third valve 12c, the fourth valve 12d, and the sixth valve 12e are opened, and the second valve 12b, the fifth valve are opened. By closing the valve 12e, the exhaust passage direction with respect to the first filter 11a and the second filter 11b can be reversed. As described above, in the dual mode, the passage direction of the exhaust gas with respect to the first filter 11a and the second filter 11b is appropriately reversed to store the NOx storage reduction catalyst carried by the first filter 11a and the second filter 11b. The distribution of NOx can be made uniform inside the first filter 11a and the second filter 11b, and the capacity of the filter can be used effectively. In addition, the temperature distribution in the first filter 11a and the second filter 11b can be made uniform, and it is possible to suppress only a part of the first filter 11a and the second filter 11b from becoming excessively high or low in temperature.

  Note that the timing for reversing the exhaust passage direction with respect to the first filter 11a and the second filter 11b in the dual mode may be determined by the accumulated travel distance, the accumulated travel time, or the like of the vehicle on which the internal combustion engine 1 is mounted. However, it is desirable that the timing be after the regeneration processing of the first filter 11a and the second filter 11b. This is because when the exhaust passage direction with respect to the first filter 11a and the second filter 11b is reversed, the particulate matter deposited on the first filter 11a and the second filter 11b may be released and directly diffused outside the vehicle. is there. The ash after the particulate matter is oxidized in the regeneration process is released from the first filter 11a and the second filter 11b by reversing the exhaust passage direction after the regeneration process of the first filter 11a and the second filter 11b. Thus, the purification performance can be more reliably regenerated.

  [Tandem Mode] Next, a tandem mode in which exhaust from the internal combustion engine 1 passes through each of the first filter 11a and the second filter 11b in series will be described with reference to FIG. FIG. 3 is a diagram for explaining the operation when the tandem mode is realized in the exhaust purification system of the present embodiment.

  In this mode, for example, as shown in FIG. 3A, the first valve 12a, the fourth valve 12d, and the fifth valve 12e are opened, and the second valve 12b, the third valve 12c, and the sixth valve 12f are opened. By closing the valve, the exhaust gas from the internal combustion engine 1 is introduced from the first exhaust pipe 5a into the first branch passage 10a, and the first connection passage 10c, the second branch passage 10b, the second connection passage 10d, the first branch passage. After passing in the order of the passage 10a, it is introduced into the second exhaust pipe 5b.

  In this mode, the exhaust from the internal combustion engine 1 passes through the first filter 11a and the second filter 11b in series, so that the exhaust purification capacity per unit volume of exhaust can be increased.

  In this mode, as shown in FIG. 3B, the second valve 12b, the third valve 12c, and the sixth valve 12f are opened, and the first valve 12a, the fourth valve 12d, and the fifth valve 12e are closed. By performing the valve operation, the exhaust passage direction with respect to the first filter 11a and the second filter 11b can be reversed. In this mode, by reversing the exhaust passage direction with respect to the first filter 11a and the second filter 11b, as described above, the NOx stored in the NOx storage reduction catalyst of the first filter 11a and the second filter 11b is stored. The distribution can be made uniform inside the first filter 11a and the second filter 11b, and the temperature distribution in the first filter 11a and the second filter 11b can also be made uniform.

In the tandem mode, it is considered that the particulate matter in the exhaust gas is accumulated most in the vicinity of the end face on the exhaust gas introduction side in the first filter 11a into which the exhaust gas is introduced first. Then, if the exhaust passage direction with respect to the first filter 11a and the second filter 11b is reversed as described above, the particulate matter collected by the first filter 11a can be released, and the released particulate matter is further removed. Two filters 11b can collect. Thus, in the tandem mode, by reversing the exhaust passage direction with respect to the first filter 11a and the second filter 11b, the particulate matter before being oxidized by the regeneration process can be released as it is from the first filter 11a. The released particulate matter can be prevented from being released outside the company.

  Further, in the above state, the second filter 11b that has collected the particulate matter released from the first filter 11a is reduced from the upstream fuel addition valve, that is, the third fuel addition valve 14c in FIG. 3B. The second filter 11b may be regenerated by supplying fuel as an agent. Then, the particulate matter collected by the first filter 11a can be collected in the second filter 11b and the regeneration process can be performed, and the amount of fuel used for the regeneration process can be reduced. As a result, the fuel consumption in the regeneration process can be improved.

  In addition, in the above, when the ash after the particulate matter is oxidized by the regeneration process is concentrated and distributed in the exhaust introduction portion of the filter, the ash is also clogged in the portion, and the particulate matter In some cases, it was difficult for the ash to pass through the filter and be emitted outside the vehicle. In addition, even when the particle size of the ash of the particulate matter is large, it may be difficult to pass through the filter and dissipate outside the vehicle. As a result, the filter purification performance may not be sufficiently regenerated after the regeneration process.

  Even in such a case, by reversing the exhaust passage direction in the first filter 11a and the second filter 11b in the tandem mode, the ash of the particulate matter is concentrated and distributed in a part of the filter, thereby clogging. It can be suppressed. Furthermore, when the particulate ash moves between the filters, the ash is finely divided, and easily passes through the second filter 11b and is diffused outside the vehicle. As a result, the particulate matter purification ability of the first filter 11a and the second filter 11b can be more reliably regenerated.

  [Single Mode] Next, a single mode in which the exhaust gas is allowed to pass through only one of the first filter 11a and the second filter 11b in the exhaust gas purification unit 10 of the internal combustion engine 1 will be described with reference to FIG. This single mode works suitably by being selected when performing the regeneration process of the first filter 11a or the second filter 11b.

  That is, for example, when the regeneration processing of both the first filter 11a and the second filter 11b is performed at a time during operation in the dual mode, the temperature of the first filter 11a and the second filter 11b is set to the operation of the internal combustion engine 1. Affected by the condition. For example, if the operating state of the internal combustion engine 1 becomes a high engine load and a high engine speed during the regeneration process of the first filter 11a and the second filter 11b, the first filter 11a and the second filter 11b Since the temperature of exhaust gas to be introduced becomes high, the temperatures of the first filter 11a and the second filter 11b may become excessively high. Further, when a fuel as a reducing agent is supplied for a regeneration process of the first filter 11a and / or the second filter 11b in a state where the exhaust gas flow rate is large, the supplied fuel is oxidized and consumed in the exhaust gas. The amount of fuel that ends up increases. As a result, the proportion of fuel used for regeneration processing or the like may decrease, and fuel consumption may deteriorate.

Therefore, when performing regeneration processing of the first filter 11a and the second filter 11b, as shown in FIG. 4A, for example, the first valve 12a, the fourth valve 12d, and the sixth valve 12f are opened. Then, the second valve 12b, the third valve 12c, and the fifth valve 12e are closed. If it does so, the exhaust_gas | exhaustion from the internal combustion engine 1 will pass only the 1st filter 11a. Then, fuel is injected only from the fourth fuel addition valve 14d on the right side in FIG. 4 in the second filter 11b in which the passage of exhaust gas has substantially stopped. That is, only the first filter 11a is allowed to pass through the exhaust gas from the internal combustion engine 1, and the regeneration process of the second filter 11b is performed. By doing so, the fuel can be supplied to the second filter 11b in a state where the exhaust flow rate introduced into the second filter 11b is reduced, so that the fuel efficiency in the regeneration process or the like can be improved. Moreover, it can suppress that the driving | running state of the internal combustion engine 1 influences the regeneration process etc. of the 2nd filter 11b.

  Here, the introduction of the exhaust gas into the second filter 11b is substantially stopped because the fifth valve 12e is closed. However, since the amount of exhaust gas passing through the fifth valve 12e is not zero, it is not zero exhaust gas introduced into the second filter 11b from the second branch passage 10b. Therefore, in the above, fuel is added from the fourth fuel addition valve 14d on the second branch passage 10b side of the second filter 11b.

  As shown in FIG. 4B, the second valve 12b, the third valve 12c, and the fifth valve 12e are opened, and the first valve 12a, the fourth valve 12d, and the sixth valve 12f are closed. Thus, the exhaust passage direction with respect to the first filter 11a can be reversed in the single mode. In this case, in the regeneration process of the second filter 11b, fuel as a reducing agent may be supplied from the third fuel addition valve 14c.

  Similarly, FIG. 5 shows a single mode in which exhaust gas is allowed to pass only through the second filter 11b. FIG. 5A shows a single mode by opening the second valve 12b, the fourth valve 12d, and the fifth valve 12e, and closing the first valve 12a, the third valve 12c, and the sixth valve 12f. An example of realizing is shown. In FIG. 5 (b), the first valve 12a, the third valve 12c, and the sixth valve 12f are opened, and the second valve 12b, the fourth valve 12d, and the fifth valve 12e are closed. An example in which the exhaust passage direction with respect to the filter 11a is reversed will be described.

  [Bypass Mode] Next, the bypass mode will be described with reference to FIG. As described above, when the regeneration processing of both the first filter 11a and the second filter 11b is performed at one time during the operation in the dual mode, the temperatures of the first filter 11a and the second filter 11b are set to the internal combustion engine 1. May be affected by the driving conditions. For example, when the operation state of the internal combustion engine 1 becomes a high engine load and a high engine speed during the regeneration process of the first filter 11a and the second filter 11b, the first filter 11a and the second filter 11b are introduced. Since the temperature of the exhaust gas to be heated becomes high, the temperatures of the first filter 11a and the second filter 11b may become excessively high.

  In such a case, all of the first valve 12a to the sixth valve 12f are opened. If it does so, the exhaust_gas | exhaustion from the internal combustion engine 1 will pass only the 1st branch passage 10a and the 2nd branch passage 10b with a low back pressure, and will be introduce | transduced into the 2nd exhaust pipe 5b as it is. As a result, when the first filter 11a or the second filter 11b is at a high temperature during the regeneration process, the supply of the high-temperature exhaust gas to the first filter 11a or the second filter 11b can be suppressed. An excessive temperature rise of the filter 11a or the second filter 11b can be suppressed.

  Conversely, when the internal combustion engine 1 is in a fuel cut state, if the exhaust from the internal combustion engine 1 is introduced into the first filter 11a and the second filter 11b, the first filter 11a and the second filter 11b The temperature is lowered, and excessive oxygen is supplied to the NOx catalyst supported on the first filter 11a and the second filter 11b. Therefore, in the subsequent first filter 11a and second filter 11b, The NOx purification performance may be deteriorated. In such a case, the bypass mode may be applied.

  Needless to say, the bypass mode may be applied when one of the first filter 11a and the second filter 11b is in the high temperature state, the low temperature state, or the high oxygen supply state.

  As described above, in the present embodiment, the dual mode, the tandem mode, and the single mode in the exhaust purification unit 10 are appropriately opened and closed according to the operating state of the internal combustion engine 1 to open and close the first valve 12a to the sixth valve 12f. The mode and the bypass mode can be selectively used, the performance of the exhaust purification system can be improved, and the regeneration process can be effectively performed with low fuel consumption.

  It should be noted that when the modes are switched in the above, the first valve 12a to the sixth valve are arranged in such an order that the exhaust gas from the internal combustion engine 1 passes through at least one of the first filter 11a and the second filter 11b during the switching. 12f should be opened and closed. For example, when switching from the dual mode shown in FIG. 2A to the single mode shown in FIG. 4A, the third valve 12c is closed → the first valve 12a is opened → the second valve 12b. By closing the valve → opening the sixth valve 12f → closing the fifth valve 12e, the exhaust gas that does not pass through either the first filter 11a or the second filter 11b is diffused outside the vehicle during mode switching. Can be suppressed.

  Next, a second embodiment of the present invention will be described. In the present embodiment, an example will be described in which the amount of intake air taken into the internal combustion engine 1 is detected by an air flow meter, and the mode selected in the exhaust purification system is changed according to the detected amount of intake air.

  The internal combustion engine 1 in this embodiment is provided with an air flow meter (not shown), and the amount of intake air to the internal combustion engine 1 is detected by inputting an output signal of the air flow meter to the ECU 35. Other configurations are the same as those shown in FIG. In this embodiment, when the detected intake air amount is less than Ga0, the tandem mode is selected. Here, Ga0 has a large exhaust flow rate from the internal combustion engine 1 when the intake air amount is larger than this, and therefore when the single mode or the tandem mode is selected, the pressure loss in the exhaust purification unit 10 increases, and the internal combustion engine 1 is a value as a threshold value that is determined to cause a risk of affecting the engine performance. This value is obtained experimentally in advance.

  In the present embodiment, when the detected intake air amount is less than Ga0, the tandem mode is selected as described above. When the regeneration process is performed in the first filter 11a and the second filter 11b from that state, the exhaust passage direction in the first filter 11a and the second filter 11b is first reversed in the tandem mode. As a result, the particulate matter deposited so far is released to the first filter 11a and collected by the second filter 11b. Thereafter, the single mode in which the exhaust gas is introduced only into the first filter 11a is selected. Then, with the exhaust introduced into the second filter 11b substantially stopped, fuel as a reducing agent is supplied from the third fuel addition valve 14c or the fourth fuel addition valve 14d to the second filter 11b.

  Then, the temperature of the second filter 11b is raised by an oxidation reaction in the NOx catalyst supported on the second filter 11b, and the particulate matter deposited on the second filter 11b is oxidized and removed. By doing so, the particulate matter deposited on the first filter 11a is collected in the second filter 11b and then the reducing agent is supplied, so that the regeneration process can be performed by adding fuel from one fuel addition valve. Further, when the reducing agent is actually supplied, the introduction of the exhaust gas into the second filter 11b is substantially stopped by selecting the single mode, so that the supplied fuel comes into contact with the high temperature exhaust gas and is oxidized and consumed. This can be suppressed, and can be prevented from being used for the regeneration process in the second filter 11b.

  In this embodiment, as a synergistic effect of these two controls, the fuel consumption in the regeneration process can be greatly improved.

  On the other hand, if the detected intake air amount is equal to or greater than Ga0, the dual mode is selected. If it carries out like this, the exhaust_gas | exhaustion from the internal combustion engine 1 will be divided into 2 and each will be introduce | transduced into the 1st filter 11a and the 2nd filter 11b. Therefore, even when the exhaust gas flow rate from the internal combustion engine 1 is large, the pressure loss in the exhaust gas purification unit 10 does not increase, and it is possible to suppress the engine performance of the internal combustion engine 1 from being affected.

  As described above, in the present embodiment, the mode selected in the exhaust purification system is switched depending on the amount of intake air to the internal combustion engine 1, so that even when the amount of intake air is large, the pressure loss in the exhaust purification unit 10 causes engine loss. It is possible to suppress the influence on the performance, and when the intake air amount is small, the fuel efficiency in the regeneration process or the like can be improved. The above air flow meter constitutes an intake air amount detection means in the present embodiment.

  Next, a third embodiment of the present invention will be described. In the present embodiment, an example will be described in which the temperature of exhaust gas from the internal combustion engine 1 is detected by an exhaust gas temperature sensor, and the mode selected in the exhaust gas purification system is changed according to the detected exhaust gas temperature.

  The first exhaust pipe 5a in the present embodiment is provided with a temperature sensor (not shown), and the temperature of the exhaust from the internal combustion engine 1 is detected by inputting an output signal of this temperature sensor to the ECU 35. Other configurations are the same as those shown in FIG. In this embodiment, the tandem mode is selected when the detected exhaust temperature is equal to or lower than T1. Here, T1 indicates that the temperature of the first filter 11a and the second filter 11b in the exhaust purification unit 10 does not rise sufficiently when the exhaust temperature is lower than this or when the single mode or dual mode is selected. The temperature is a threshold value at which it is determined that it is difficult to obtain sufficient exhaust purification performance. This value is obtained experimentally in advance.

  In this embodiment, when the detected temperature of the exhaust gas is equal to or lower than T1, the first filter 11a and the second filter 11b are passed through the exhaust gas in series in the tandem mode. Then, if the temperature of the first filter 11a is sufficiently high at this time, the temperature of the exhaust gas discharged from the first filter 11a is increased. Then, the raised exhaust gas can be introduced into the second filter 11b.

  In this way, in the tandem mode, exhaust heat escape in the exhaust purification unit 10 can be reduced, so that even if the exhaust temperature is equal to or lower than T1, deterioration of the purification performance in the exhaust purification unit 10 can be suppressed. . In the above, when the temperature of the first filter 11a is not sufficiently high, fuel may be added to the first filter 11a from the first fuel addition valve 14a or the second fuel addition valve 14b. By doing so, the temperature of the exhaust gas discharged from the first filter 11a can be more reliably increased, and the purification performance of the exhaust gas purification unit 10 can be suppressed more reliably.

  On the other hand, when the exhaust temperature detected by an exhaust temperature sensor (not shown) is equal to or higher than T2, the single mode or the dual mode is selected. Here, T2 is determined that when the temperature of the exhaust is higher than this, the temperature of the exhaust purification device in the exhaust purification unit 10 may become abnormally high when the tandem mode is selected. Temperature. This value is obtained experimentally in advance.

In such a case, by selecting the single mode and the dual mode, the amount of exhaust heat escape in the exhaust purification unit 10 can be increased as compared with the case where the tandem mode is selected. As a result, it can suppress that the 1st filter 11a or the 2nd filter 11b becomes high temperature too much.

  As described above, in the present embodiment, since the mode selected in the exhaust purification system is switched depending on the temperature of the exhaust gas from the internal combustion engine 1, the first filter 11a is used regardless of the temperature of the exhaust gas from the internal combustion engine 1. And the temperature of the 2nd filter 11b can be maintained appropriately. The exhaust temperature sensor in the above constitutes the exhaust temperature detecting means in the present embodiment.

  In addition, in the above, it demonstrated on the assumption that the valve which can select only two types of states of opening and closing is used as the 1st valve 12a-6th valve 12f. However, for example, at the connection portion between the first exhaust pipe 5a and the first branch path 10a and the second branch path 10b, either the first exhaust pipe 5a, the first branch path 10a, or the second branch path 10b is connected. A valve having a function of communicating may be used. If it does so, the function of the 1st valve 12a and the 2nd valve 12b can be substituted by one valve.

  Further, instead of using the third valve 12c to the sixth valve 12f, the connection portion of the first branch passage 10a with the first connection passage 10c and / or the second connection passage 10d and the first connection in the second branch passage 10b. In the connection portion with the passage 10c and / or the second connection passage 10d, a valve having a function capable of determining a combination of passages to be communicated among the passages may be used.

  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, an exhaust purification system that performs NOx reduction treatment by adding fuel as a reducing agent to the NOx storage reduction catalyst has been described. However, the present invention provides exhaust gas using urea water as a reducing agent. The present invention can also be applied to an exhaust purification system that includes a selective reduction type NOx catalyst that is supplied into a passage and reduces NOx in exhaust gas.

It is a figure which shows schematic structure of the internal combustion engine in the Example of this invention, its exhaust system, and a control system. It is a figure for demonstrating the dual mode of the exhaust gas purification part in the Example of this invention. It is a figure for demonstrating the tandem mode of the exhaust gas purification part in the Example of this invention. It is a figure for demonstrating the single mode of the exhaust gas purification part in the Example of this invention. It is a figure for demonstrating the case where the passage direction of exhaust gas is reversed about the single mode of the exhaust gas purification part in the Example of this invention. It is a figure for demonstrating the bypass mode of the exhaust gas purification part in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust pipe 5a ... 1st exhaust pipe 5b ... 2nd exhaust pipe 10 ... Exhaust gas purification part 10a ... 1st branch passage 10b ... 2nd branch Passage 10c ... 1st connection passage 10d ... 2nd connection passage 11a ... 1st filter 11b ... 2nd filter 12a ... 1st valve 12b ... 2nd valve 12c ... 2nd 3 valve 12d ... 4th valve 12e ... 5th valve 12f ... 6th valve 14a ... 1st fuel addition valve 14b ... 2nd fuel addition valve 14c ... 3rd fuel addition valve 14d ... Fourth fuel addition valve 35 ... ECU

Claims (7)

One end of which is connected to the internal combustion engine, branches into a first branch passage and a second branch passage at a branch point, and an exhaust passage through which exhaust from the internal combustion engine passes;
One end is connected to the first branch passage at the first connection portion, the other end is connected to the second branch passage at the second connection portion, and a first exhaust purification device for purifying exhaust gas is provided. A connecting passage,
One end of the third connection portion downstream of the first connection portion in the first branch passage is connected to the first branch passage, and the fourth connection portion downstream of the second connection portion in the second branch passage. The other end is connected to the second branch passage, and a second connection passage provided with a second exhaust purification device for purifying exhaust,
A first valve provided between the branch point in the first branch passage and the first connection portion;
A second valve provided between the branch point in the second branch passage and the second connection portion; and provided between the first connection portion and the third connection portion in the first branch passage. A third valve;
A fourth valve provided between the second connection portion and the fourth connection portion in the second branch passage;
A fifth valve provided downstream of the third connecting portion in the first branch passage;
A sixth valve provided downstream of the fourth connecting portion in the second branch passage;
Control means for controlling the opening and closing of the first to sixth valves,
By controlling the opening and closing of the first to sixth valves, the control means,
A first mode in which only one of the first exhaust purification device or the second exhaust purification device is included in a path through which the exhaust passes;
A second mode in which the first exhaust purification device and the second exhaust purification device are connected in parallel to the path through which the exhaust passes; and
A third mode in which the first exhaust purification device and the second exhaust purification device are connected in series in a path through which the exhaust passes; and
A fourth mode in which neither the first exhaust purification device nor the second exhaust purification device is included in the path through which the exhaust passes;
An exhaust gas purification system for an internal combustion engine characterized by being selectable.   The control means controls the opening and closing of the first to sixth valves in the first to fourth modes, so that the exhaust of the first exhaust purification device and the second exhaust purification device is 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein a direction of passage of the exhaust gas with respect to an exhaust gas purification device included in a passage route can be reversed. An intake air amount detecting means for detecting an intake air amount sucked into the internal combustion engine;
When the intake air amount is less than a predetermined value, the first mode or the third mode is selected, and when the intake air amount is not less than the predetermined value, the second mode is selected. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2. Exhaust temperature detecting means for detecting the temperature of the exhaust,
The control means selects the third mode when the temperature of the exhaust gas is equal to or lower than a predetermined first temperature, and when the temperature of the exhaust gas is equal to or higher than a predetermined second temperature higher than the first temperature. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein the first mode or the second mode is selected. The first exhaust purification device and the second exhaust purification device have a NOx catalyst that purifies NOx in the exhaust,
A reducing agent supply means for supplying a reducing agent to the first exhaust purification device or the second exhaust purification device;
When the first mode is selected, a reducing agent is supplied by a reducing agent supply means to one of the first exhaust purification device and the second exhaust purification device that is not included in the exhaust path. 5. The internal combustion engine according to claim 1, wherein NOx in the first exhaust purification device and the second exhaust purification device that is not included in the exhaust path is reduced. Exhaust purification system. The first exhaust purification device and the second exhaust purification device have a NOx catalyst that purifies NOx in the exhaust,
A reducing agent supply means for supplying a reducing agent to the first exhaust purification device and / or the second exhaust purification device;
When the second mode is selected, by supplying a reducing agent to the first exhaust purification device and / or the second exhaust purification device by a reducing agent supply means, the first exhaust purification device and / or The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 4, wherein NOx in the second exhaust gas purification device is reduced.   6. The reducing agent supply means is disposed on both sides of the first exhaust purification device in the first connection passage and on both sides of the second exhaust purification device in the second connection passage. 6. An exhaust gas purification system for an internal combustion engine according to 6.

Images