JP2008190359A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, provided with a plurality of NOx absorption members having NOx absorption functions on an exhaust passage in the internal combustion engine, realizing such layout of the absorption members as to favorably achieve performance of the NOx absorption members. <P>SOLUTION: Exhaust gas discharged from the internal combustion engine 10 is provided with a main exhaust passage 14. A bypass passage 20 to bypass the main exhaust passage 14 is provided. On the bypass passage, a first NOx absorption member 24 comprising zeolite carrying iron Fe, and a second NOx absorption member 26 comprising cerium oxide CeO<SB>2</SB>carrying palladium Pd are provided. The second NOx absorption member 26 is disposed over the first NOx absorption member 24 on the side to be open to the atmospheric air. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus provided with an adsorbent for adsorbing unpurified components that could not be purified by a catalyst downstream of a catalyst in an exhaust passage.

  Conventionally, for example, in Patent Document 1, in an exhaust passage of an internal combustion engine, an HC adsorbent that adsorbs hydrocarbons (HC) contained in exhaust gas and an oxygen storage / release material in order from the upstream side of the flow of exhaust gas. An exhaust emission control device is disclosed that includes an oxidation-reduction catalyst that carries at least one of Rh and Pd. According to the conventional exhaust purification device, the purification performance of the oxidation-reduction catalyst can be improved by supplying the exhaust gas from which HC has been removed by the HC adsorbent to the oxidation-reduction catalyst.

JP 2001-286732 A JP 2001-289035 A

  By the way, when arranging a plurality of NOx adsorbents having a function of adsorbing NOx contained in the exhaust gas on the exhaust passage of the internal combustion engine, in order to bring out the performance of each NOx adsorbent satisfactorily, each NOx It is desirable that the arrangement be in consideration of the properties of the adsorbent.

  The present invention has been made to solve the above-described problems, and in an internal combustion engine having a plurality of NOx adsorbents having a function of adsorbing NOx on an exhaust passage of the internal combustion engine, the performance of the NOx adsorbent is good. It is an object of the present invention to provide an exhaust purification device for an internal combustion engine that realizes the arrangement of an adsorbent that can be drawn out.

The first invention comprises at least two NOx adsorbents having a function of adsorbing NOx in the exhaust passage of the internal combustion engine,
At least one of the NOx adsorbents is a first NOx adsorbent having no oxygen storage capacity,
At least one of the NOx adsorbents is a second NOx adsorbent having oxygen storage capacity,
At least one of the second NOx adsorbents is disposed on the side of the exhaust passage that is open to the atmosphere.

Further, the second invention comprises two NOx adsorbents having a function of adsorbing NOx in the exhaust passage of the internal combustion engine,
One of the two NOx adsorbents is a first NOx adsorbent carrying a metal,
The other of the two NOx adsorbents is a second NOx adsorbent having oxygen storage capacity,
The second NOx adsorbent is disposed on the side of the exhaust passage that is open to the atmosphere with respect to the first NOx adsorbent.

  According to a third aspect, in the second aspect, the metal supported on the first NOx adsorbent is iron.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the exhaust passage includes a main exhaust passage through which exhaust gas discharged from an internal combustion engine flows, and an upstream connection portion between the main exhaust passage. A bypass passage that branches off from the main exhaust passage and joins the main exhaust passage again at the downstream connection portion downstream from the upstream connection portion,
The NOx adsorbent is disposed in the bypass passage.

In a fifth aspect based on the fourth aspect, the exhaust gas purification apparatus for an internal combustion engine comprises:
A catalyst that is disposed in the main exhaust passage upstream of the upstream connection portion and that can purify exhaust gas;
A return passage branched from the bypass passage and connected upstream of the catalyst;
A flow path switching means capable of switching an inflow destination of exhaust gas between the main exhaust passage and the bypass passage;
A portion of the exhaust gas discharged from the internal combustion engine is introduced into the bypass passage from the main exhaust passage through either the upstream connection portion or the downstream connection portion; and the bypass passage The NOx from the first NOx adsorbent and the second NOx adsorbent is controlled in a state where the flow path switching unit is controlled so that the exhaust gas introduced into the exhaust gas is recirculated to the upstream of the catalyst via the return passage. Purge execution means for executing purge,
The NOx adsorbent is disposed in the bypass passage in the order of the second NOx adsorbent and the first NOx adsorbent from the upstream side of the flow of exhaust gas when the purge is executed by the purge execution means. It is characterized by.

In a sixth aspect based on the fourth aspect, the exhaust gas purification apparatus for an internal combustion engine comprises:
A catalyst that is disposed in the main exhaust passage downstream from the downstream connection portion and that can purify exhaust gas;
A flow path switching means capable of switching an inflow destination of exhaust gas between the main exhaust passage and the bypass passage;
The exhaust gas discharged from the internal combustion engine is introduced into the bypass passage from the main exhaust passage through the upstream connection portion, and the exhaust gas introduced into the bypass passage is introduced through the downstream connection portion. And purging NOx from the first NOx adsorbent and the second NOx adsorbent in a state where the flow path switching unit is controlled so as to pass through the catalyst after being returned to the main exhaust passage. And further comprising means
The NOx adsorbent is arranged in the bypass passage in the order of the first NOx adsorbent and the second NOx adsorbent from the side close to the upstream connection portion.

  When the second NOx adsorbent having oxygen storage capacity does not store oxygen in the adsorbent, the NOx adsorption capacity decreases. On the other hand, there is almost no oxygen in the exhaust gas except during fuel cut. According to the first invention, it is possible to store oxygen in the atmosphere in the second NOx adsorbent by convection of the atmosphere while the internal combustion engine is stopped. As a result, the NOx adsorption capacity of the second NOx adsorbent can be ensured satisfactorily at the next start of the internal combustion engine.

  According to the second aspect of the invention, the second NOx adsorbent is disposed on the side of the exhaust passage that is open to the atmosphere, so that oxygen in the atmosphere is occluded in the second NOx adsorbent by the convection of the atmosphere while the internal combustion engine is stopped. It becomes possible to do. As a result, the NOx adsorption capacity of the second NOx adsorbent can be ensured satisfactorily at the next start of the internal combustion engine. In addition, when the first NOx adsorbent carrying the metal is exposed to oxygen under a high temperature condition, the metal is oxidized and the NOx adsorption capacity is lowered. According to the present invention, the second NOx adsorbent having oxygen storage capacity is arranged between the first NOx adsorbent using metal and the atmosphere open end of the exhaust passage. For this reason, it is possible to suppress the atmospheric air from directly touching the first NOx adsorbent while the internal combustion engine is stopped, and the NOx adsorbing capacity of the first NOx adsorbent can be maintained high.

  According to the third invention, it is possible to suppress the first NOx adsorbent carrying iron from being oxidized by being exposed to oxygen under a high temperature condition and reducing the NOx adsorption ability.

  According to the fourth invention, the effects of the first to third inventions can be achieved in the configuration in which the NOx adsorbent is disposed on the bypass passage.

  According to the fifth aspect of the invention, during the purging operation in which high-temperature exhaust gas is introduced into the bypass passage, the high-temperature exhaust gas is added to the second NOx adsorbent 26 having oxygen storage capacity prior to the first NOx adsorbent. Will be introduced. For this reason, since oxygen storage of the second NOx adsorbent 26 is promoted by the high-temperature exhaust gas, the NOx adsorption capacity of the second NOx adsorbent can be maintained high. Further, according to the above arrangement, the amount of oxygen flowing downstream of the second NOx adsorbent 26 is reduced. For this reason, when the first NOx adsorbent carries a metal such as iron, the oxidation of the metal carried on the first NOx adsorbent is suppressed, and the decrease in the NOx adsorption capacity of the first NOx adsorbent is suppressed. be able to.

  According to the sixth aspect of the invention, the second NOx adsorbent 26 having an oxygen storage capacity is disposed upstream of the flow of exhaust gas during the purge operation in which high-temperature exhaust gas is introduced into the bypass passage. A first NOx adsorbent is disposed downstream. For this reason, the oxygen storage of the second NOx adsorbent 26 is promoted by the high-temperature exhaust gas, so that the NOx adsorption capability of the second NOx adsorbent can be kept high. Further, according to the above arrangement, the amount of oxygen flowing downstream of the second NOx adsorbent 26 is reduced. For this reason, when the first NOx adsorbent carries a metal such as iron, the oxidation of the metal carried on the first NOx adsorbent is suppressed, and the decrease in the NOx adsorption capacity of the first NOx adsorbent is suppressed. be able to.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a configuration of an internal combustion engine system including an exhaust purification device according to Embodiment 1 of the present invention. An internal combustion engine 10 shown in FIG. 1 includes an intake passage 12 for taking air into the cylinder and an exhaust passage through which exhaust gas discharged from the cylinder flows.

  The exhaust passage of the present embodiment includes a main exhaust passage 14 for discharging exhaust gas from the cylinder, and a bypass passage 20 described later. In the main exhaust passage 14, a front catalyst (SC) 16 and a rear catalyst (UF) 18 capable of purifying exhaust gas are arranged in series in order from the upstream side.

  The system of this embodiment includes a bypass passage 20 as a passage that bypasses the main exhaust passage 14. The bypass passage 20 branches from the main exhaust passage 14 at the upstream connection portion 20a located downstream of the rear catalyst 18, and again enters the main exhaust passage 14 at the downstream connection portion 20b located downstream of the upstream connection portion 20a. It is configured to merge.

  A switching valve 22 for switching the inflow destination of the exhaust gas between the main exhaust passage 14 and the bypass passage 20 is disposed in the upstream connection portion 20a. The switching valve 22 is driven to open and close when the engine intake negative pressure acting on the negative pressure diaphragm 22a is controlled by a solenoid valve (not shown).

  Further, two NOx adsorbents are disposed in the middle of the bypass passage 20. More specifically, a first NOx adsorbent 24 having a function of adsorbing NOx is first arranged on the upstream side of the main exhaust passage 14, that is, on the side close to the upstream connection portion 20 a provided with the switching valve 22. Has been. As such a first NOx adsorbent 24, for example, a zeolite-based material carrying a metal can be used. In the present embodiment, as a preferred example, it is assumed that a ZSM-5, which is one of zeolites, supports iron Fe by ion exchange and is used as the first NOx adsorbent 24.

The bypass passage 20 further has a function of adsorbing NOx on the downstream side of the first NOx adsorbent 24, that is, on the side close to the downstream side connection portion 20b, and has an oxygen storage capacity. An adsorbent 26 is disposed. Such as the first 2NOx adsorbent 26, for example, it can be used carrying palladium Pd cerium oxide CeO _2.

  As described above, in the present embodiment, the second NOx adsorbent 26 having an oxygen storage capacity is arranged on the side opened to the atmosphere with respect to the first NOx adsorbent 24 having no oxygen storage capacity. . In addition, a first NOx adsorbent 24 using iron Fe (metal) and a downstream connecting portion 20b opened to the atmosphere via the main exhaust passage 14 have a first oxygen storage capacity. A 2NOx adsorbent 26 is arranged.

  The system of this embodiment includes an ECU (Electronic Control Unit) 30. Various sensors for controlling the internal combustion engine 10 are connected to the ECU 30, and the switching valve 22 described above is connected in addition to various actuators for controlling the internal combustion engine 10.

[Switching the flow path]
According to the configuration shown in FIG. 1 described above, the switching valve 22 is controlled by the ECU 30 so as to close the upstream connection portion 20a of the bypass passage 20, whereby the exhaust gas discharged from the cylinder is passed through the bypass passage 20. It can be discharged through the main exhaust passage 14 as it is without being interposed.

  Further, after the ECU 30 controls the switching valve 22 so that the main exhaust passage 14 is closed, the exhaust gas discharged from the cylinder is introduced into the bypass passage 20 and passed through the NOx adsorbent 24 and the like. It can be returned to the main exhaust passage 14 again and released into the atmosphere. If such a flow path configuration of the exhaust gas is selected at the time of cold start, NOx that could not be purified by the catalyst 16 or the like in a situation where the catalyst 16 or the like has not yet been activated is used. It is possible to prevent the product from being released into the atmosphere.

[Effects of Arrangement of NOx Adsorbent of Embodiment 1]
When the second NOx adsorbent 26 having oxygen storage capacity does not store oxygen in the adsorbent, the NOx adsorption capacity decreases. On the other hand, there is almost no oxygen in the exhaust gas except during fuel cut. In the present embodiment, as described above, the exhaust passage (bypass passage 20) has an oxygen storage capacity, not the first NOx adsorbent 24 that does not have an oxygen storage capacity, on the side close to the end portion opened to the atmosphere. The second NOx adsorbent 26 is arranged. For this reason, while the internal combustion engine 10 is stopped, oxygen in the atmosphere can be stored in the second NOx adsorbent 26 by the convection of the atmosphere. As a result, when the internal combustion engine 10 is started next time, the NOx adsorption capability of the second NOx adsorbent 26 can be ensured satisfactorily.

  In addition, when the first NOx adsorbent 24 configured by supporting iron Fe on ZSM-5 (zeolite) is exposed to oxygen under a high temperature condition, the iron Fe is oxidized and the NOx adsorption capacity is reduced. In the present embodiment, as described above, between the first NOx adsorbent 24 using iron Fe (metal) and the downstream connection portion 20b opened to the atmosphere via the main exhaust passage 14. The second NOx adsorbent 26 having oxygen storage capacity is arranged. For this reason, it is possible to suppress the atmospheric air from directly touching the first NOx adsorbent 24 while the internal combustion engine 10 is stopped, and the NOx adsorbing capacity of the first NOx adsorbent 24 can be maintained high.

  By the way, in Embodiment 1 mentioned above, what carried iron Fe on ZSM-5 (zeolite) is used as the 1st NOx adsorption material 24 of the side which does not have oxygen storage capacity. However, the first NOx adsorbent in the present invention is not limited to those using such a material. That is, the first NOx adsorbent may be, for example, a material on which a metal other than iron Fe is supported, and further, if it has a function of adsorbing NOx, it does not support a metal warehouse. May be.

Embodiment 2. FIG.
Next, Embodiment 2 of the present invention will be described with reference to FIG.
FIG. 2 is a diagram for explaining a configuration of an internal combustion engine system including an exhaust purification device according to Embodiment 2 of the present invention. In FIG. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the first embodiment described above, the switching valve 22 for switching the inflow destination of the exhaust gas between the main exhaust passage 14 and the bypass passage 20 to the upstream side connection portion 20 a between the main exhaust passage 14 and the bypass passage 20. Is arranged. On the other hand, in the structure shown in FIG. 2, the same switching valve 40 is arrange | positioned at the downstream connection part 20b.

In the present embodiment, a second NOx adsorbent (Pd / CeO ₂ ) 26 having an oxygen storage capacity is disposed on the upstream side of the main exhaust passage 14, that is, on the side close to the upstream connection portion 20 a. And the 1st NOx adsorption material (Fe / ZSM-5) 24 is arrange | positioned in the downstream of the 2nd NOx adsorption material 26, ie, the near side to the downstream connection part 20b in which the switching valve 40 was provided.

  According to the arrangement of the NOx adsorbent described above, by controlling the switching valve 40 so that the downstream side connection portion 20b of the bypass passage 20 is closed as shown in FIG. The second NOx adsorbent 26 having an oxygen storage capacity can be communicated with the atmosphere via the upstream connection portion 20a. Therefore, as in the first embodiment described above, oxygen in the atmosphere can be stored in the second NOx adsorbent 26 by the convection of the atmosphere while the internal combustion engine 10 is stopped. As a result, when the internal combustion engine 10 is started next time, the NOx adsorption capability of the second NOx adsorbent 26 can be ensured satisfactorily.

  Further, in the arrangement of the NOx adsorbent described above, an oxygen storage capacity is provided between the first NOx adsorbent 24 using iron Fe and the downstream connection portion 20b opened to the atmosphere via the main exhaust passage 14. A second NOx adsorbent 26 having the following is disposed. For this reason, the atmospheric air can be prevented from directly touching the first NOx adsorbent 24 while the internal combustion engine 10 is stopped, and the NOx adsorption capacity of the first NOx adsorbent 24 can be maintained high. .

Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described with reference to FIG.
FIG. 3 is a diagram for explaining a configuration of an internal combustion engine system including an exhaust purification device according to Embodiment 3 of the present invention. In FIG. 3, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  The configuration shown in FIG. 3 is the same as that of the first embodiment described above except that a return passage 50 and a purge control valve 52 are added. More specifically, the return passage 50 communicates with the bypass passage 20 at a portion between the upstream connection portion 20a and the first NOx adsorbent 24. The return passage 50 includes a purge control valve 52 in the middle thereof, and communicates with the intake passage 12 at an end portion thereof. Note that the connection destination of the return passage 50 may not be the intake passage 12 as long as it is an upstream passage of the rear catalyst 18, and may be, for example, the upstream portion of the front catalyst 16 in the main exhaust passage 14.

  According to the configuration described above, by controlling the switching valve 22 and the purge control valve 52 as described below, the NOx adsorbed by the NOx adsorbent 24 and the like when the internal combustion engine 10 is cold-started is returned to the return passage 50. The intake passage 12 can be purged via In the configuration shown in FIG. 3 described above, the two NOx adsorbents are adsorbed such that the second NOx adsorbent 26 having oxygen storage capacity is located upstream of the exhaust gas flowing through the bypass passage 20 when the purge operation is performed. Consideration has been given to the arrangement of the materials.

  Further, the purge operation as described above is performed at a predetermined purge start timing such as when the upstream catalyst 16 is activated in a state where the switching valve 22 is controlled so as to close the upstream connection portion 20a of the bypass passage 20. When it arrives, it starts by opening the purge control valve 52.

  When the purge operation is started, a part of the exhaust gas discharged from the cylinder uses the negative pressure generated in the intake passage 12 of the internal combustion engine 10 to connect the downstream connection portion 20b from the main exhaust passage 14. It passes through and is introduced into the bypass passage 20. The exhaust gas introduced into the bypass passage 20 first passes through the first NOx adsorbent 24 after passing through the second NOx adsorbent 26 having oxygen storage capacity. As a result, the exhaust gas that has become relatively warm after startup is supplied to the NOx adsorbent 26 and the like, so that NOx is desorbed from the NOx adsorbent 26 and the like and is purged to the intake passage 12 via the return passage 50. The NOx returned to the intake passage 12 is purified by the catalyst 16 and the like in an active state after being subjected to combustion again.

As described above, at high temperatures, oxidation of iron Fe supported on the first NOx adsorbent 24 is easily promoted, while oxygen storage in the second NOx adsorbent 26 made of Pd / CeO ₂ is easily promoted. . According to the configuration shown in FIG. 3 described above, the second NOx adsorbent 26 having an oxygen storage capacity is disposed on the upstream side when the high-temperature exhaust gas flows through the bypass passage 20 during the purge operation, and iron is disposed on the downstream side thereof. A first NOx adsorbent 24 carrying Fe is disposed. For this reason, the oxygen storage of the second NOx adsorbent 26 is promoted, and the NOx adsorbing capacity of the second NOx adsorbent 26 can be maintained high. Further, since the amount of oxygen flowing downstream of the second NOx adsorbent 26 is reduced, oxidation of iron Fe supported on the first NOx adsorbent 24 is suppressed, and a decrease in the NOx adsorbing capacity of the first NOx adsorbent 24 is suppressed. be able to.

  In the third embodiment described above, the front catalyst 16 and the rear catalyst 18 are the “catalyst” in the fifth invention, and the switching valve 22 and the purge control valve 52 are the “flow path switching means in the fifth invention. Respectively. Further, in the state where the ECU 30 controls the switching valve 22 so as to close the upstream side connection portion 20a of the bypass passage 20, the purge control valve 52 is given a valve opening command, whereby the “purge execution means” according to the fifth aspect of the present invention. Is realized.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIG.
FIG. 4 is a diagram for explaining a configuration of an internal combustion engine system including an exhaust purification device according to Embodiment 4 of the present invention. In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  The configuration shown in FIG. 4 is the same as that of the second embodiment described above except that a return passage 60 and a purge control valve 62 are added. More specifically, the return passage 60 communicates with the bypass passage 20 at a portion between the downstream side connection portion 20b and the first NOx adsorbent 24. The return passage 60 includes a purge control valve 62 in the middle thereof, and communicates with the intake passage 12 at an end portion thereof.

  Also in the present embodiment, as in the third embodiment described above, the second NOx adsorbent 26 having an oxygen storage capacity is positioned upstream of the exhaust gas flowing through the bypass passage 20 when the purge operation is performed. Consideration is given to the arrangement of the two NOx adsorbents.

  In the purge operation of the present embodiment, a predetermined purge start timing has arrived such that the front catalyst 16 is activated in a state where the switching valve 40 is controlled so as to close the downstream side connection portion 20b of the bypass passage 20. At that point, it begins by opening the purge control valve 62. When the purge operation is started, a part of the exhaust gas discharged from the cylinder passes through the upstream connection portion 20a from the main exhaust passage 14 and bypasses using the negative pressure generated in the intake passage 12. It is introduced into the passage 20. As a result, the exhaust gas introduced into the bypass passage 20 first passes through the first NOx adsorbent 24 after passing through the second NOx adsorbent 26 having oxygen storage capacity. For this reason, there exists an effect similar to Embodiment 3 mentioned above.

Embodiment 5. FIG.
Next, a fifth embodiment of the present invention will be described with reference to FIG.
FIG. 5 is a diagram for explaining a configuration of an internal combustion engine system including an exhaust purification device according to Embodiment 5 of the present invention. In FIG. 5, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

In the configuration shown in FIG. 5, the second NOx adsorbent (Pd / CeO ₂ ) having an oxygen storage capacity on the upstream side of the main exhaust passage 14, that is, on the side close to the upstream side connection portion 20 a provided with the switching valve 22. 26 is arranged. And the 1st NOx adsorption material (Fe / ZSM-5) 24 is arrange | positioned in the downstream of the 2nd NOx adsorption material 26, ie, the near side to the downstream connection part 20b.

  Further, as shown in FIG. 5, a downstream catalyst 70 capable of purifying exhaust gas is disposed in the main exhaust passage 14 further downstream of the downstream side connection portion 20b.

  The purge operation of the present embodiment is performed using the downstream catalyst 70 described above. More specifically, the purge operation is started by controlling the switching valve 22 so as to close the main exhaust passage 14 when a predetermined purge start timing arrives. When the purge operation is started, all of the exhaust gas discharged from the cylinder is introduced into the bypass passage 20 via the upstream connection portion 20a. The exhaust gas introduced into the bypass passage 20 first passes through the first NOx adsorbent 24 after passing through the second NOx adsorbent 26 having oxygen storage capacity. As a result, the exhaust gas that has become relatively warm after startup is supplied to the NOx adsorbent 26 and the like, so that NOx is desorbed from the NOx adsorbent 26 and is purified by the downstream catalyst 70 downstream of the bypass passage 20.

  Even with the configuration of the present embodiment described above, the second NOx adsorbent 26 having oxygen storage capacity is disposed on the upstream side when high-temperature exhaust gas flows through the bypass passage 20 during the purge operation, and iron Fe is disposed on the downstream side thereof. Is disposed. For this reason, the oxygen storage of the second NOx adsorbent 26 is promoted, and the NOx adsorbing capacity of the second NOx adsorbent 26 can be maintained high. Further, since the amount of oxygen flowing downstream of the second NOx adsorbent 26 is reduced, oxidation of iron Fe supported on the first NOx adsorbent 24 is suppressed, and a decrease in the NOx adsorption capacity of the first NOx adsorbent 24 is suppressed. be able to.

  By the way, in Embodiment 5 mentioned above, although the switching valve 22 is arrange | positioned in the upstream connection part 20a, also in the structure provided with the downstream catalyst 70 in the downstream of the bypass channel 20, implementation of the above-mentioned. Similarly to the second embodiment, a switching valve such as the switching valve 40 may be provided in the downstream connection portion 20b.

  In the fifth embodiment described above, the downstream catalyst 70 corresponds to the “catalyst” in the sixth invention, and the switching valve 22 corresponds to the “flow path switching means” in the sixth invention. Further, the “purge execution means” in the sixth aspect of the present invention is realized by controlling the switching valve 22 so that the ECU 30 closes the main exhaust passage 14.

  In the first to fifth embodiments described above, the two NOx adsorbents 24 and the like are provided on the bypass passage 20 that bypasses the main exhaust passage 14, but the arrangement method of the NOx adsorbent in the present invention is as follows. In addition, the present invention is not limited to the case where the NOx adsorbent is disposed on the bypass passage 20. That is, the NOx adsorbent arrangement method according to the present invention is such that the second NOx adsorbent having oxygen storage capacity is arranged on the side of the exhaust passage that is open to the atmosphere in the exhaust passage of the internal combustion engine that does not include the bypass passage. It may be. Further, the first NOx adsorbent having no oxygen storage capacity is a NOx adsorbent carrying a metal such as iron Fe, and in the exhaust passage not provided with the bypass passage, the first NOx adsorbent and the air release side of the exhaust passage A second NOx adsorbent having an oxygen storage capacity may be disposed between the end portions.

It is a figure for demonstrating the structure of an internal combustion engine system provided with the exhaust gas purification apparatus in Embodiment 1 of this invention. It is a figure for demonstrating the structure of an internal combustion engine system provided with the exhaust gas purification apparatus in Embodiment 2 of this invention. It is a figure for demonstrating the structure of an internal combustion engine system provided with the exhaust gas purification apparatus in Embodiment 3 of this invention. It is a figure for demonstrating the structure of an internal combustion engine system provided with the exhaust gas purification apparatus in Embodiment 4 of this invention. It is a figure for demonstrating the structure of an internal combustion engine system provided with the exhaust gas purification apparatus in Embodiment 5 of this invention.

Explanation of symbols

Reference Signs List 10 internal combustion engine 12 intake passage 14 main exhaust passage 16 front catalyst 18 rear catalyst 20 bypass passage 20a upstream connection portion 20b downstream connection portion 22, 40 switching valve 24 first NOx adsorbent 26 second NOx adsorbent 30 ECU (Electronic Control Unit) )
50, 60 Return passages 52, 62 Purge control valve 70 Downstream catalyst

Claims (6)

The exhaust passage of the internal combustion engine includes at least two NOx adsorbents having a function of adsorbing NOx,
At least one of the NOx adsorbents is a first NOx adsorbent having no oxygen storage capacity,
At least one of the NOx adsorbents is a second NOx adsorbent having oxygen storage capacity,
An exhaust emission control device for an internal combustion engine, wherein at least one of the second NOx adsorbents is disposed on a side that is open to the atmosphere in the exhaust passage. Two NOx adsorbents having a function of adsorbing NOx are provided in the exhaust passage of the internal combustion engine,
One of the two NOx adsorbents is a first NOx adsorbent carrying a metal,
The other of the two NOx adsorbents is a second NOx adsorbent having oxygen storage capacity,
The exhaust gas purification apparatus for an internal combustion engine, wherein the second NOx adsorbent is disposed on the side of the exhaust passage that is open to the atmosphere with respect to the first NOx adsorbent.   The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the metal supported on the first NOx adsorbent is iron. The exhaust passage branches from the main exhaust passage at an upstream connection portion between the main exhaust passage through which exhaust gas discharged from the internal combustion engine flows and the main exhaust passage, and is connected downstream from the upstream connection portion. A bypass passage that merges with the main exhaust passage again in the section,
The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the NOx adsorbent is disposed in the bypass passage. The exhaust gas purification device for the internal combustion engine includes:
A catalyst that is disposed in the main exhaust passage upstream of the upstream connection portion and that can purify exhaust gas;
A return passage branched from the bypass passage and connected upstream of the catalyst;
A flow path switching means capable of switching an inflow destination of exhaust gas between the main exhaust passage and the bypass passage;
A portion of the exhaust gas discharged from the internal combustion engine is introduced into the bypass passage from the main exhaust passage through either the upstream connection portion or the downstream connection portion; and the bypass passage The NOx from the first NOx adsorbent and the second NOx adsorbent is controlled in a state where the flow path switching unit is controlled so that the exhaust gas introduced into the exhaust gas is recirculated to the upstream of the catalyst via the return passage. Purge execution means for executing purge,
The NOx adsorbent is disposed in the bypass passage in the order of the second NOx adsorbent and the first NOx adsorbent from the upstream side of the flow of exhaust gas when the purge is executed by the purge execution means. The exhaust emission control device for an internal combustion engine according to claim 4. The exhaust gas purification device for the internal combustion engine includes:
A catalyst that is disposed in the main exhaust passage downstream from the downstream connection portion and that can purify exhaust gas;
A flow path switching means capable of switching an inflow destination of exhaust gas between the main exhaust passage and the bypass passage;
The exhaust gas discharged from the internal combustion engine is introduced into the bypass passage from the main exhaust passage through the upstream connection portion, and the exhaust gas introduced into the bypass passage is introduced through the downstream connection portion. The purge execution is performed to purge NOx from the first NOx adsorbent and the second NOx adsorbent in a state where the flow path switching unit is controlled so as to pass through the catalyst after being returned to the main exhaust passage. And further comprising means
5. The internal combustion engine according to claim 4, wherein the NOx adsorbent is disposed in the bypass passage in an order of the first NOx adsorbent and the second NOx adsorbent from a side close to the upstream connection portion. Engine exhaust purification system.

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