JP2005146975A - Particulate filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To purify HC in a particulate filter. <P>SOLUTION: The filter traps particulates in exhaust gas exhausted from an internal combustion engine and comprises a plurality of cells 21, 22 divided by partition walls 3m made of porous material, with passage cross-sectional areas approximately equal to each other. Predetermined cells 21 are sealed on one end part side while the other cells 22 are sealed on the other end part side. A catalyst having oxidation capability is supported on the partition walls. Partition walls 3s for dividing cells 22 are added into the cell 22 which the exhaust gas passed through the partition walls flows into. The catalyst having the oxidation capability is also supported on the additional partition wall. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a particulate filter.

  Particulates may be contained in the exhaust gas discharged from the internal combustion engine. In this case, it is required to remove the particulates from the exhaust gas before the exhaust gas is discharged to the atmosphere. Patent Document 1 discloses a so-called wall flow type exhaust gas purifying filter for collecting particulates in such exhaust gas. This filter includes a large number of cells (passages for passing exhaust gas) defined by porous partition walls, and openings at both ends of these cells are partition walls in which exhaust gas flowing into the filter defines the cells. After passing through, the plugs are alternately plugged so as to flow out of the filter (see FIG. 1 of Patent Document 1).

  In addition, since the amount of particulates that can be collected by the filter is limited, the collected particulates must be collected before the amount of particulates collected by the filter exceeds the collection limit value of the filter. Need to be removed from the filter. For this purpose, in the filter described in Patent Document 1, a catalyst having oxidizing ability is supported on the partition walls defining the cell, and the particulates are burned in the filter using this catalyst and removed from the filter. (See paragraph 0012).

Japanese Patent No. 3387290 JP-A-9-168723 JP-A-11-210440 Japanese Patent No. 3147372 Japanese National Patent Publication No. 8-508199

  By the way, hydrocarbon (HC) may be contained in exhaust gas for various reasons. Since this HC should not be discharged to the atmosphere, it is preferable if the particulate filter as described above can purify HC.

  Accordingly, an object of the present invention is to purify HC in a particulate filter.

  In order to solve the above problems, according to a first aspect of the present invention, there is provided a particulate filter for collecting particulates in exhaust gas discharged from an internal combustion engine, the particulate filter being defined by a partition made of a porous material and having a passage cut. A plurality of cells having substantially the same area are provided, a predetermined cell is closed on one end side, and the remaining cells are closed on the other end side, and a catalyst having oxidizing ability is supported on the partition wall. In the particulate filter, a partition that divides the cell was added to the cell into which the exhaust gas that passed through the partition flowed, and a catalyst having oxidation ability was supported on the added partition.

  In the second invention, in the first invention, the thickness of the added partition is thinner than the thickness of the partition defining the cell.

  According to a third aspect, in the first aspect, the catalyst carried on the added partition holds NOx in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the particulate filter is lean, and This is a NOx catalyst that reduces and purifies the stored NOx when the air-fuel ratio of the exhaust gas flowing into the particulate filter is the stoichiometric air-fuel ratio or rich.

  According to a fourth aspect, in the first aspect, the catalyst supported on the partition walls defining the cell is a catalyst having a high active oxygen generation capacity, and the catalyst supported on the additional partition walls has a NOx reduction capacity. High catalyst.

  In the first invention, when the exhaust gas passes through the partition walls defining the cells, the HC in the exhaust gas is reformed so as to be easily purified by the catalyst supported on the partition walls. In the first invention, a partition that divides the cell is added to the cell into which the exhaust gas that has passed through the partition flows, and a catalyst having an oxidizing ability is also carried on the added partition. Therefore, the HC reformed into a form that can be easily purified is surely purified by the catalyst supported on the added partition wall.

  In the second invention, since the thickness of the added partition is thinner than the thickness of the partition defining the cell, an increase in the flow resistance in the cell due to the addition of the partition is suppressed.

  In the third aspect of the invention, NOx in the exhaust gas is reliably reduced and purified by the HC reformed through the partition walls defining the cell and the NOx catalyst supported on the added partition walls.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is an end view of a particulate filter (hereinafter simply referred to as “filter”) according to a first embodiment of the present invention, and FIG. 1B is a BB line in FIG. It is sectional drawing of the filter in alignment with. For example, the filter is disposed in an exhaust passage connected to a combustion chamber of an internal combustion engine, and collects particulates (fine particles) in exhaust gas discharged from the combustion chamber.

  In the present embodiment, the filter 1 has a substantially cylindrical shape and includes a plurality of cells 21 and 22 extending in parallel with each other along the central axis C of the filter 1. The cell is defined by a partition wall 3m made of a porous material, and a cross section of the cells 21 and 22 perpendicular to the central axis C of the filter 1 (hereinafter simply referred to as “cell cross section” or “cell cross section”). , Approximately square. The cross sections of the cells 21 and 22 are substantially equal to each other.

  In the following, the present invention will be described by taking a filter having a substantially square cell cross section as an example. However, the present invention is a filter having a cell whose cross section is a quadrangle including a square, or a triangle whose cell cross section includes a regular triangle. The present invention can also be applied to a certain filter, a filter whose cell cross section is a hexagon including a regular hexagon, or a filter whose cell cross section is another shape.

  In FIG. 1B, exhaust gas flows into the filter 1 from the left side, and in FIG. 1B, exhaust gas flows out from the right side. In FIG. 1B, the left side is referred to as “upstream side”, and FIG. ), The right side is referred to as the “downstream side”, and about half of the cells 21 have their downstream end openings closed by plugs 41, and the remaining almost half of the cells 22 have upstream end openings. Is closed by a plug 42. The cell 21 whose downstream end opening is blocked by the plug 41 is referred to as a “first cell”, and the cell 22 whose upstream end opening is blocked by the plug 42 is referred to as a “second cell”. When referred to, the first cells 21 and the second cells 22 are alternately positioned as can be seen with reference to FIG.

  Therefore, the exhaust gas arriving at the filter 1 first flows into the first cell 21 as indicated by an arrow in FIG. Next, the exhaust gas flows through the pores inside the partition wall 3 m defining the first cell 21 and flows into the adjacent second cell 22. Then, the exhaust gas flows out from the second cell 22. Thus, while the exhaust gas flows through the filter 1, the particulates (fine particles) in the exhaust gas define the pores on the wall surface of the partition wall 3 m that defines the first cell 21 and inside the partition wall 3 m. It is collected on the wall surface. Of course, the particulates are also collected on the wall surface of the partition wall 3m defining the second cell 22, although the amount is smaller than this.

  By the way, as shown in FIG. 2 and FIG. 3, on the wall surface of the partition wall 3m and on the wall surface defining the pores 5 inside the partition wall 3m, a catalyst having oxidation ability (for example, platinum or the like) Noble metal) is supported in a form held on a coat layer 6 made of alumina or the like. Further, a NOx holding agent capable of absorbing or adsorbing nitrogen oxide (NOx) in the exhaust gas may be carried on the coat layer 6. Examples of the NOx retention agent include alkali metals (for example, potassium (K), sodium (Na), lithium (Li), cesium (Cs)), alkaline earths (for example, barium (Ba), calcium (Ca)). And at least one selected from rare earths (for example, lanthanum (La) and yttrium (Y)) and a noble metal such as platinum (Pt). The NOx retention agent retains NOx in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the filter is leaner than the stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust gas flowing into the filter is the stoichiometric air-fuel ratio or higher If it becomes rich, the retained NOx is reduced and purified by a reducing agent (for example, hydrocarbon or carbon monoxide) in the exhaust gas.

  Note that the air-fuel ratio of the exhaust gas is the air sucked into the combustion chamber with respect to the amount of fuel supplied to the combustion chamber when a filter is disposed in the exhaust passage connected to the combustion chamber of the internal combustion engine. Means the ratio of the amount of

  By the way, as shown in FIG. 1B, a partition 3s is added in the second cell 22, and the second cell 22 is formed by the added partition (hereinafter referred to as “sub-partition”). It is divided. As shown in FIG. 4 showing the end face on the downstream side of the filter 1, the sub partition 3 s extends along the diagonal line in the second cell 22 having a substantially square cross section. Of course, such a configuration of the sub-partition wall 3s is merely an example. For example, as illustrated in FIG. 5, two sub-partition walls 3s extending along a diagonal line and perpendicular to each other are included in the second cell 22. It may be added. Further, as shown in FIG. 6, two sub-partitions 3m extending between the opposing partition walls (hereinafter referred to as “main partition walls”) 3m of the second cell 22 and perpendicularly intersecting each other are added in the second cell. May be. 5 is combined with the configuration of the sub-partition shown in FIG. 6, and the configuration of the sub-partition 3s disposed in the second cell 22 is shown in FIG. It is good also as composition which has.

  The sub partition 3s is thinner than the main partition 3m. By adopting the sub-partition wall 3s having such a small thickness, an increase in the flow resistance against the exhaust gas in the second cell 22 due to the addition of the sub-partition wall 3s in the second cell 22 can be suppressed.

  Next, the operation of the filter will be described. As described above, particulates in the exhaust gas are collected by the filter 1 while the exhaust gas flows through the filter 1. The particulates thus collected are oxidized and removed by the catalyst supported on the partition walls 3m and 3s.

  When the NOx holding agent is supported on the partition walls 3m and 3s, the NOx holding agent continues to hold NOx in the exhaust gas while the air-fuel ratio of the exhaust gas flowing into the filter is lean. When the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or rich, or when the air-fuel ratio of the exhaust gas is forcibly made the stoichiometric air-fuel ratio or rich, the NOx held in the NOx holding agent is It is reduced and purified by a reducing agent (for example, hydrocarbon or carbon monoxide).

  By the way, the hydrocarbon (HC) in the exhaust gas is generally oxidized and removed by the catalyst supported on the main partition 3m, but flows into the second cell 22 through the main partition 3m without being removed by oxidation. There are also things. Here, when the sub-partition 3s is not added in the second cell 22, since there is little chance of HC contacting the catalyst, the HC that has flowed into the second cell 22 flows out of the second cell 22 without being oxidized and removed. There is a high possibility that However, in this embodiment, since the sub partition 3s is added in the second cell 22, the chance that the HC flowing into the second cell 22 comes into contact with the catalyst is increased, so that the HC is reliably oxidized in the filter 1. Will be removed.

  Also, HC is reformed to highly reactive HC by at least the catalyst while passing through the main partition 3m. Therefore, even if the amount of HC flowing into the second cell 22 through the main partition 3m without being oxidized and removed increases, the HC flowing into the second cell 22 is highly reactive HC. It is sufficiently oxidized and removed by the catalyst supported on the partition 3s.

  Further, when the NOx holding agent is supported on the sub partition 3s, the NOx flowing into the second cell 22 through the main partition 3m is not held by the NOx holding agent supported on the main partition 3m. Is held by the NOx holding agent carried on the sub partition 3s. The NOx held in the NOx holding agent in the sub partition 3s is reduced and removed by the HC flowing through the main partition 3m and flowing into the second cell 22. Since HC passing through the main partition 3m and flowing into the second cell 22 is reformed to have high reactivity, NOx held in the NOx holding agent of the sub partition 3s is surely absorbed by HC. Reduced and removed.

  Of course, even if the particulates pass through the main partition 3m without being oxidized and removed by the catalyst supported on the main partition 3m, these particulates are oxidized and removed by the catalyst supported on the sub partition 3s. .

  In the above-described embodiment, it is assumed that the catalyst or NOx holding agent supported on the main partition 3m is the same as the catalyst or NOx holding agent supported on the sub partition 3s. A catalyst having a high oxidizing ability (particularly a catalyst having a high ability to generate active oxygen) is supported on the wall surface of the main partition wall 3m defining the cell 21 and on the wall surface defining the pore 5 on the side close to the wall surface. On the wall surface of the main partition wall 3m on the side defining the second cell 22 and on the wall surface defining the pores 5 on the side close to the wall surface, and on the wall surface of the sub partition wall 3s, a highly reducing catalyst May be supported. That is, the catalyst and other substances supported on the main partition 3m and the sub partition 3s may be changed for each predetermined region of the partition 3m, 3s. In this case, various substances in the exhaust gas can be purified or removed by supporting the partition walls 3m and 3s with catalysts and substances corresponding to the various substances contained in the exhaust gas.

  The present invention can also be applied to filters as shown in FIGS. 8A and 8B. In this filter 1, the downstream end portions 3 md of the four main partition walls 3 m that define the first cell 21 are connected to each other, thereby closing the downstream end opening of the first cell 21. . On the other hand, with respect to the second cell 22, the upstream end portions 3 mu of the four main partition walls 3 m that define the second cell 22 are connected to each other, thereby closing the upstream end opening of the second cell 22. It is peeling off. Thus, the partition portions 3 md and 3 me blocking the end openings of the cells 21 and 22 are inclined with respect to the central axis C of the filter 1. And the part of the quadrangular pyramid which protruded toward the outer side of the filter 1 by the partition part 3md and 3me which block | close the edge part opening of each cell 21 and 22 is formed.

  Further, similarly to the first embodiment, a sub partition 3s is added in the second cell 22. Of course, as in the first embodiment, the main partition 3m and the sub partition 3s carry a catalyst having an oxidizing ability and a NOx holding agent.

  Moreover, it is applicable also to a filter as shown in FIG. 9 (A) and FIG. 9 (B). In the filter 1, a sub partition 3 s is also added in the first cell 21.

  Further, the amount of the catalyst supported on the sub partition 3s may be larger than the amount of the catalyst supported on the main partition 3m. According to this, the oxidation removal of HC passing through the main partition wall 3m and the reduction purification of NOx are more reliably performed. The main partition 3m must be able to pass exhaust gas, but the sub partition 3s may not necessarily be able to pass exhaust gas, so the amount of catalyst supported on the sub partition 3s is increased. As a result, even if the average diameter of the pores inside the sub-partition wall 3s is reduced, the flow resistance of the second cell to the exhaust gas does not increase so much.

  Of course, the amount of the catalyst supported in the region on the second cell 22 side of the main partition 3m may be larger than the amount of the catalyst supported on the region on the first cell 21 side of the main partition 3m. Thus, by varying the amount of catalyst supported on the main partition 3m for each region, or by varying the amount of catalyst supported on the main partition 3m and the amount of catalyst supported on the sub partition 3s, The average diameter of the pores 5 inside the partition wall is different for each region. According to this, particulates having various particle sizes can be reliably collected in any region, and the particulate collection ability and particulate oxidation removal ability of the filter are improved as a whole.

  Further, since the amount of NOx that can be held by the NOx holding agent is limited, before the amount of NOx held by the NOx holding agent exceeds the limit value, the stoichiometric air-fuel ratio or rich exhaust gas is supplied to the filter. It is necessary to reduce and purify NOx retained by the NOx retention agent. Therefore, as described above, when the NOx holding agent is carried on the partition walls 3m and 3s, the stoichiometric air-fuel ratio or rich exhaust gas is supplied to the filter at every predetermined timing. At this time, a larger amount of HC than usual is supplied to the filter. When the amount of HC supplied to the filter increases in this way, the amount of HC that passes through the main partition wall 3m without being used for NOx reduction purification also increases. Here, according to the above-described embodiment, since the sub partition 3s is added in the second cell 22, HC that has passed through the main partition 3m is also used for NOx reduction purification. Therefore, the HC supplied to the filter is fully utilized without being wasted.

  Further, when the exhaust gas contains sulfur oxide (SOx), the NOx retention agent also retains this SOx. In this case, the amount of NOx that can be held by the NOx holding agent is reduced. Here, when the temperature of the filter becomes relatively high and the air-fuel ratio of the exhaust gas flowing into the filter becomes the stoichiometric air-fuel ratio or rich, SOx is excluded from the NOx holding agent. Therefore, when the NOx holding agent is supported on the partition walls 3m and 3s as described above, the filter temperature is periodically made relatively high and the stoichiometric air-fuel ratio or rich exhaust gas is supplied to the filter. In this case as well, a larger amount of HC than usual is supplied to the filter. However, since the sub partition 3s is additionally provided in the second cell 22, the filter passes through the main partition 3m. Stuck HC is also used to eliminate SOx. Therefore, the HC supplied to the filter is fully utilized without being wasted.

  Furthermore, according to the above-described embodiment, the particulate oxidation removal capability, the HC oxidation removal capability, and the NOx reduction purification capability of the filter are increased, and therefore the filter itself can be downsized. In addition, conventionally, a so-called sweeper for capturing particulates, HC, or NOx flowing out from the filter may be disposed in the exhaust passage downstream of the filter. According to the above-described embodiment, such a sweeper is filtered. It is not necessary to arrange in the downstream exhaust passage, and the cost is reduced accordingly.

  Further, since the sub partition 3s disposed in the second cell 22 also functions as a reinforcing material, the rigidity of the entire filter is increased.

(A) is the end elevation which showed the upstream end face of the filter of 1st Embodiment of this invention, (B) is sectional drawing of the filter along the BB line of (A). It is a partial expanded sectional view of the filter of a 1st embodiment. It is a partial expanded sectional view of the partition of the filter of 1st Embodiment. It is the end view which showed the downstream end surface of the filter of 1st Embodiment. It is the end elevation which showed the downstream end face of the filter of another embodiment of the present invention. It is the end view which showed the downstream end surface of the filter of another embodiment of this invention. It is the end view which showed the downstream end surface of the filter of another embodiment of this invention. (A) is the end elevation which showed the upstream end face of the filter of another embodiment of this invention, (B) is sectional drawing of the filter along the BB line of (A). (A) is the end elevation which showed the upstream end face of the filter of another embodiment of this invention, (B) is sectional drawing of the filter along the BB line of (A).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Filter 21, 22 ... Cell 3m, 3s ... Partition 41, 42 ... Plug 5 ... Fine pore 6 ... Coat layer

Claims (4)

  A particulate filter for collecting particulates in exhaust gas discharged from an internal combustion engine, comprising a plurality of cells defined by partition walls made of a porous material and having substantially equal passage cross-sectional areas. In the particulate filter in which the cell is closed on one end side and the remaining cells are closed on the other end side, and the partition wall carries a catalyst having oxidizing ability, exhaust gas that has passed through the partition wall flows in. A particulate filter, characterized in that a partition wall for dividing the cell is added to the cell, and a catalyst having oxidizing ability is supported on the added partition wall.   2. The particulate filter according to claim 1, wherein a thickness of the added partition is thinner than a thickness of the partition defining the cell.   When the catalyst carried on the added partition wall has a lean air-fuel ratio of the exhaust gas flowing into the particulate filter, the air-fuel ratio of the exhaust gas holding NOx in the exhaust gas and flowing into the particulate filter is retained. 2. The particulate filter according to claim 1, wherein the particulate filter is a NOx catalyst that reduces and purifies the retained NOx when the stoichiometric air-fuel ratio is rich.   2. The catalyst supported on the partition walls defining the cell is a catalyst having a high active oxygen generation ability, and the catalyst supported on the added partition walls is a catalyst having a high NOx reduction ability. The particulate filter described in 1.

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