JP2003166410A - Exhaust emission controlling particulate filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain pressure losses caused by a particulate filter constantly at a low value. <P>SOLUTION: The particulate filter has a plurality of exhaust emission flow passages 50 and 51 demarcated by bulkheads 54 and 54a formed of a porous material to trap particulate in the gas. Downstream end openings of a part of the exhaust emission flow passages are closed, and the exhaust emission flow passages from an exhaust gas inflow passage to allow the exhaust gas to flow in from an upstream end opening. The upstream end openings of the remaining exhaust emission flow passages are closed, and the exhaust emission flow passages from an exhaust gas outflow passage to allow the exhaust gas to flow out the exhaust gas from the downstream end openings. Each exhaust gas inflow passage is adjacent to the exhaust gas outflow passage via the bulkhead 54 in a downstream side area thereof while it is adjacent to only the exhaust gas inflow passage via a bulkhead 54a in an upstream side area thereof. Oxide matters capable of oxidizing particulate are carried by the bulkhead to demarcate the upstream side area of the exhaust gas inflow passage. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purification particulate filter.

[0002]

2. Description of the Related Art Particulate filters for collecting fine particles in exhaust gas discharged from an internal combustion engine are known. As such a particulate filter, a honeycomb structure is formed from a porous material, and some filter passages out of a plurality of passages (hereinafter referred to as filter passages) extending in parallel to the honeycomb structure are provided at their upstream ends. After blocking with a plug and the remaining filter passage at its downstream end with a stopper, exhaust gas flowing into the particulate filter must pass through the wall defining the filter passage (hereinafter referred to as the filter passage wall). It is known that the particulate filter is allowed to flow out.

According to this type of particulate filter, the exhaust gas always passes through the filter passage wall and then flows out from the particulate filter, so that the particulate filter has a relatively high particulate collection rate. However, the average pore diameter of the filter passage wall is made very small in order to collect the fine particles, and the exhaust gas must pass through this filter passage wall, so the pressure loss due to the particulate filter is high.

Therefore, a particulate filter intended to suppress an increase in pressure loss while increasing the collection rate of fine particles is disclosed in JP-A-8-508199. In this particulate filter, the filter passage is not closed by a plug, but is closed by gathering the ends of the filter passage wall and connecting these ends together. That is, the filter passage is closed with the same porous material as the material forming the filter passage wall. For this reason, in this particulate filter, the exhaust gas can also pass through the wall that closes the filter passage, and the increase in pressure loss is suppressed accordingly.

By the way, in such a particulate filter, the collected fine particles gradually accumulate on the filter passage wall, and eventually the fine particles block the pores of the filter passage wall. In this case, the pressure loss due to the particulate filter becomes very high. Japanese Patent Laid-Open No. 9-94433 discloses a filter carrying a catalyst for burning fine particles in the pores of the filter passage wall in order to burn and remove the fine particles collected by the particulate filter. According to this, since the fine particles collected by the particulate filter are burned and removed by the catalyst, a large amount of fine particles are not deposited on the filter passage wall.

[0006]

By the way, in the above-mentioned type of particulate filter, a large amount of particles tend to be collected on the wall surface of the upstream region of the filter passage having the upstream opening. In this case, the pores of the filter passage wall in the upstream region are blocked by the fine particles, and the pressure loss due to the particulate filter becomes large.

In order to avoid this, it is considered that a large amount of catalyst for burning and removing fine particles is carried on the filter passage wall in the upstream region. However,
Increasing the amount of the catalyst to be carried suppresses the increase in pressure loss due to the accumulation of fine particles, but conversely increases the potential pressure loss due to the particulate filter. In the particulate filter, there is a demand for suppressing the pressure loss to a certain value or less, so that there is an upper limit to the amount of catalyst that can be supported on the filter passage wall. That is, with the conventional technique, it is difficult to always maintain the pressure loss due to the particulate filter at a low value even during its use. Therefore, an object of the present invention is to always maintain the pressure loss due to the particulate filter at a low value.

[0008]

In the first invention for solving the above-mentioned problems, a plurality of exhaust flow passages defined by partition walls made of a porous material are provided to collect fine particles in exhaust gas. The exhaust flow passage has a downstream end opening of a part of the exhaust flow passages closed, whereby the exhaust flow passage serves as an exhaust gas inflow passage through which the exhaust gas flows in from the upstream end opening. In the exhaust gas purification particulate filter, the upstream end opening of the remaining exhaust gas flow passage is blocked, whereby the exhaust gas flow passage serves as an exhaust gas outflow passage through which exhaust gas flows out from the downstream end opening,
Each exhaust gas inflow passage is adjacent to the exhaust gas outflow passage through the partition wall in the downstream side region, and is adjacent only to the exhaust gas inflow passage via the partition wall in the upstream side region, and is upstream of the exhaust gas inflow passageway. An oxidizing substance capable of oxidizing the fine particles is carried on the partition walls that define the region. That is, the partition wall that separates the exhaust gas inflow passage carries the oxidant.

In the second invention, in the first invention,
One of the two adjacent exhaust flow passages serves as the exhaust gas inflow passage, and the other exhaust flow passage serves as the exhaust gas outflow passage, and the upstream side portion of the partition wall that defines the exhaust gas outflow passage is They are gathered together and joined to each other over a predetermined length from their upstream ends, whereby the upstream end opening of the exhaust gas outflow passage is closed.

In the third invention, in the first invention,
The downstream side portions of the partition wall defining the exhaust gas inflow passage are gathered together and joined to each other, thereby closing the downstream end opening of the exhaust gas inflow passage.

According to a fourth aspect of the invention, in the second or third aspect of the invention, the partition walls are gathered so that the passage cross section of the passage becomes narrower toward the end face side of the exhaust gas purification particulate filter.

In the fifth invention, in the first invention,
The partition wall carries an oxidant capable of oxidizing fine particles, and the amount of the oxidant carried on the partition wall defining the upstream region of the exhaust gas inflow passage is the oxidant carried on the remaining partition walls. Than the amount of.

According to a sixth aspect of the present invention, in the method for producing an exhaust purification particulate filter of the fifth aspect, a step of supporting an oxidizing substance on the entire exhaust purification particulate filter, and a predetermined step from the upstream end of the exhaust gas inflow passage are determined. And a step of supporting the oxidizing substance only on the barrier ribs that are joined to each other over a certain length.

In the seventh invention, a plurality of exhaust flow passages defined by partition walls made of a porous material are provided for collecting fine particles in the exhaust gas, and a part of these exhaust flow passages is provided. Of the partition wall defining the exhaust flow passage are gathered together and joined to each other, whereby the downstream end opening of the exhaust flow passage is closed and the exhaust flow passage is exhausted from its upstream end opening. And the upstream side portions of the partition walls defining the exhaust flow passage are gathered together and joined to each other in the remaining exhaust flow passage, whereby the upstream end opening of the exhaust flow passage is formed. In the exhaust gas purification particulate filter base material, which is blocked so that the exhaust flow passage serves as an exhaust gas outflow passage through which the exhaust gas flows out from the downstream end opening, a partition wall defining the exhaust gas outflow passage. And the upstream portion brought together over a predetermined length from its upstream end joined to one another,
As a result, each exhaust gas inflow passage is adjacent to the exhaust gas outflow passage in the downstream region via the partition wall and only adjacent to the other exhaust gas inflow passage in the upstream region via the partition wall.

In the eighth invention, in the seventh invention,
The partition walls are gathered together such that the cross section of the passage becomes narrower toward the end face side of the exhaust gas purification particulate filter.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1A is an end view of the particulate filter, and FIG. 1B is a vertical cross-sectional view of the particulate filter. As shown in FIGS. 1A and 1B, the particulate filter 22 has a honeycomb structure and includes a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages have an exhaust gas inflow passage 50 whose downstream end opening is completely closed by a taper wall 52 and an upstream end opening which is a taper wall 53.
And the exhaust gas outflow passage 51 that is completely closed. That is, a part of the exhaust flow passages 50, one of the two adjacent exhaust flow passages in the present embodiment, is closed by the taper wall 52 at the downstream end thereof,
The remaining exhaust passage 51, the other of the two adjacent exhaust flow passages in this embodiment, is closed by a tapered wall 53 at its upstream end.

By the way, in the particulate filter 22 of this embodiment, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 are alternately arranged through the thin partition wall 54 in the region downstream of the upstream taper wall 53. Is located in. In other words, in the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51, each exhaust gas inflow passage 50 is surrounded by four exhaust gas outflow passages 51, and each exhaust gas outflow passage 51 is surrounded by four exhaust gas inflow passages 50. It is arranged as described.

On the other hand, in the region upstream of the upstream taper wall 53, the exhaust gas inflow passage 50 has the partition wall 54a.
Is adjacent to another exhaust gas inflow passage 50 only. In other words, the exhaust gas inflow passage 50 is surrounded by the four exhaust gas inflow passages 50.

The particulate filter 22 is made of a porous material such as cordierite. Therefore, the exhaust gas that has flowed into the exhaust gas inflow passage 50 passes through the surrounding partition wall 54 and is adjacent to the exhaust gas in the downstream region of the particulate filter 22, as indicated by the arrow in FIG. Outflow passage 51
Flows in.

Of course, the tapered walls 52 and 53 are also the partition walls 54.
These tapered walls 52 and 53 are also part of the partition wall 54.
2B, the exhaust gas flows into the exhaust gas outflow passage 51 through the tapered wall 53 as shown by the arrow in FIG. 2B, and also in FIG. 2A. As shown by the arrow in FIG. 5, the gas flows out of the exhaust gas inflow passage 50 through the tapered wall 52.

In this way, the particulate filter 22
Since the exhaust gas can be passed through the portions 52 and 53 that close the exhaust flow passages 50 and 51, the pressure loss due to the particulate filter 22 is correspondingly reduced.

On the other hand, the partition wall 54a in the region upstream of the upstream taper wall 53 is also made of a porous material like the partition wall 54 in the downstream region. Therefore, even in the region upstream of the upstream tapered wall 53, theoretically, the exhaust gas flowing into the exhaust gas inflow passage 50 flows into the adjacent exhaust gas inflow passage 50 through the surrounding partition wall 54a. It should be possible. However, since the pressures in the adjacent exhaust gas inflow passages 50 are substantially equal to each other, actually, in the region on the upstream side of the upstream taper wall 53, the exhaust gas flows between the exhaust gas inflow passages 50 via the partition wall 54a. It is extremely rare to go back and forth.

By the way, the taper wall 52 that closes the exhaust gas inflow passage 50 at its downstream end has a shape that narrows in a quadrangular pyramid shape so that the flow passage cross-sectional area gradually decreases toward the downstream side. . Therefore, the outlet of the exhaust gas outflow passage 51 formed by being surrounded by the four tapered walls 52 is
It is shaped like a quadrangular pyramid so that the cross-sectional area of the flow path gradually increases toward the downstream side. According to this, FIG.
Exhaust gas is more likely to flow out of the particulate filter than in the case where the outlet of the exhaust gas outflow passage is configured as shown in (A).

That is, in the particulate filter shown in FIG. 3A, the downstream end opening of the exhaust gas inflow passage is closed by the plug 70, and the exhaust gas outflow passage extends straight to the outlet. In this case, a part of the exhaust gas flowing out from the outlet of the exhaust gas outflow passage flows along the downstream end face of the plug 70, so that a turbulent flow 71 is formed near the outlet of the exhaust gas outflow passage. When the turbulent flow is formed in this way, it becomes difficult for the exhaust gas to flow out from the exhaust gas outflow passage.

On the other hand, in the particulate filter of the present invention, the exhaust gas can flow out from the exhaust gas outflow passage 51 without becoming a turbulent flow as shown in FIG. 2 (A).

For this reason, according to the present invention, the exhaust gas is relatively likely to flow out from the particulate filter. Therefore, also by this, the pressure loss due to the particulate filter 22 is set to a low value.

On the other hand, the tapered wall 53 that closes the exhaust gas outflow passage 51 at its upstream end has a shape that narrows in a quadrangular pyramid shape so that the flow passage cross-sectional area gradually decreases toward the upstream side. . Therefore, the region of the exhaust gas inflow passage 50 formed by being surrounded by the four tapered walls 53 is shaped like a quadrangular pyramid so that the flow passage cross-sectional area gradually increases toward the upstream side. According to this, FIG. 3 (B)
Exhaust gas is more likely to smoothly flow into the exhaust gas inflow passage 50 on the downstream side than when the inlet of the exhaust gas inflow passage is configured as shown in FIG.

That is, in the particulate filter shown in FIG. 3B, the upstream end opening of the exhaust gas outflow passage is closed by the plug 72. In this case, since a part of the exhaust gas collides with the plug 72 as indicated by 73, the pressure loss due to the particulate filter becomes large. Also, the stopper 72
Exhaust gas flowing into the exhaust gas inflow passage from the vicinity becomes a turbulent flow near the inlet as shown by 74, so that it becomes difficult for the exhaust gas to flow into the exhaust gas inflow passage.

On the other hand, in the particulate filter 22 of the present invention, as shown in FIG. 2B, the exhaust gas does not become a turbulent flow and the exhaust gas inflow passage 50 on the upstream side to the exhaust gas inflow passage 50 on the downstream side is formed. Can flow into.

For this reason, according to the present invention, the exhaust gas easily flows smoothly into the exhaust gas inflow passage 50 on the downstream side. Therefore, also by this, the pressure loss due to the particulate filter 22 is set to a low value.

Furthermore, in the particulate filter shown in FIG. 3, a large amount of fine particles in the exhaust gas are likely to be deposited on the upstream end surface of the plug 72 and the surface of the partition wall in the vicinity thereof. This is because the exhaust gas collides with the plug 72, and the exhaust gas becomes a turbulent flow near the plug 72. However, in the particulate filter 22 of the present invention, since the tapered wall 53 is in the shape of a quadrangular pyramid, there is no upstream end face with which exhaust gas collides strongly, and exhaust gas does not become turbulent near the upstream end face. Therefore, according to the present invention, a large amount of fine particles are not deposited in the upstream region of the particulate filter 22.

Of course, in the inlet region of the exhaust gas inflow passage 50, the end portion of the partition wall 54a on the upstream side becomes the upstream end face against which the exhaust gas strongly collides. However, the area of this upstream end face is much smaller than the area of the upstream end face in the particulate filter shown in FIG. Therefore, in the present embodiment, the exhaust gas rarely becomes turbulent near the upstream end face. Therefore, according to the present invention, a large amount of fine particles are not deposited in the upstream region of the particulate filter 22.

The tapered walls 52 and 53 may have a shape other than a quadrangular pyramid, for example, a conical shape or a hexagonal pyramid, as long as the tapered walls 52 and 53 gradually narrow toward the outside of the particulate filter 22.

Next, the operation and effect of the particulate filter of the present invention will be described. In terms of performance, it is necessary to configure the particulate filter 22 so that the pressure loss is potentially low, and that the pressure loss is not largely deviated from the potentially achievable value during the use of the particulate filter 22. is important.

That is, for example, when the internal combustion engine has a particulate filter, the operation control of the internal combustion engine is set in consideration of the potential pressure loss of the particulate filter. Therefore, even if the particulate filter is configured to have a low pressure loss, if the pressure loss deviates from a potentially attainable value during use, the performance of the internal combustion engine as a whole will deteriorate.

Therefore, in order to achieve the above object, the wall defining the end of the exhaust gas flow passage of the particulate filter 22 is made into a tapered wall to prevent the exhaust gas from becoming a turbulent flow. Thus, the pressure loss due to the particulate filter 22 is potentially reduced.

As described above, according to the present invention, in order to potentially reduce the pressure loss of the particulate filter 22, the exhaust flow passages 50, 51 are closed by the tapered walls 52, 53 made of a porous material. The deviation from the achievable value of the pressure drop during use of the special particulate filter is well avoided.

Further, in this embodiment, the upstream partition wall 54
The amount a of the oxidizing substance is larger than that of the oxidizing substance carried on the partition wall 54 and the tapered walls 52 and 53 on the downstream side. As described above, the particulate filter 22
In the region on the upstream side of the exhaust gas inflow passages 50, the exhaust gas inflow passages 50 are adjacent to each other through the partition wall 54a, and the pressures in the adjacent exhaust gas inflow passages 50 are substantially equal, so that the exhaust gas cannot pass through the partition wall 54a. Very few.

Therefore, even if the partition wall 54a on the upstream side is loaded with a large amount of an oxidizing substance, and the average pore diameter of the partition wall 54a becomes very small, the pressure loss due to the particulate filter 22 hardly increases.
In other words, when the particulate filter is configured as in the present invention, the ability to remove and oxidize fine particles can be increased without increasing the pressure loss due to the particulate filter.

According to this, in particular, the soluble organic substance (SOF) contained in the exhaust gas is discharged into the exhaust gas inflow passage 5
It is rapidly oxidized and removed in the upstream region of 0. The soluble organic substance has a property of adhering fine particles to each other. Therefore, if the soluble organic substance attached to the upstream side region of the partition wall of the particulate filter 22 is not removed, the fine particles are attached to each other by the soluble organic substance,
Thus, the attached particulates may block the exhaust gas inflow passage 50 of the particulate filter 22 in the upstream region thereof. However, according to the present embodiment, since the soluble organic substance is rapidly oxidized and removed in the upstream region of the exhaust gas inflow passage 50, it is possible to prevent the exhaust gas inflow passage 50 from being blocked by the particles in the upstream region. It

Incidentally, in the above-mentioned embodiment, the opening at the upstream end and the opening at the downstream end of the particulate filter are completely closed, but the idea of the present invention is that either the opening at the upstream end or the opening at the downstream end. It is also applicable to a particulate filter in which only one of them is completely blocked.

Next, a method for manufacturing the particulate filter of this embodiment will be briefly described. First, a cylindrical honeycomb structure 80 as shown in FIG. 4 is extruded from a porous material such as cordierite as a preform. The honeycomb structure 80 has a plurality of exhaust flow passages each having a square cross section, a part of the exhaust flow passages serves as the exhaust gas inflow passage 50 of the particulate filter 22, and the remaining exhaust flow passages include the exhaust gas of the particulate filter 22. It becomes the gas outflow passage 51.

Next, tapered walls 52 and 53 are formed on the honeycomb structure 80 by using the mold 90 shown in FIG. 5 (A). As shown in FIG. 5, the mold 90 has a plurality of quadrangular pyramid-shaped projections 91 and a rectangular parallelepiped portion 94 integrated with each projection 91. Grooves 93 are formed between the rectangular parallelepiped portions 94. FIG. 5 (B) shows one projection 91 and a rectangular parallelepiped portion 94 integral with it.

First, the mold 90 is pressed against the upstream end surface of the honeycomb structure 80 as shown in FIG. At this time, the mold 90 is pressed against the upstream end surface of the honeycomb structure 80 so that the projection 91 is inserted into a predetermined exhaust flow passage, here the exhaust gas inflow passage 50.

When the mold 90 is pressed against the upstream end face of the honeycomb structure 80, the partition walls 54 defining the exhaust gas outflow passage 51 are gathered together to form an upstream taper wall 53. The taper wall 53 causes the exhaust gas to flow. The upstream end of the outflow passage 51 is completely closed.

Further, when the mold 90 is pressed against the upstream end face of the honeycomb structure 80, the partition wall 54 defining the exhaust gas outflow passage 51 enters into the groove 93 of the mold 90 to form an integral upstream partition wall 54a. Become. Here, when the length of the partition wall 54a reaches a predetermined length, the pressing of the mold 90 is finished. As described above, according to the present embodiment, the exhaust gas outflow passage 51 is closed by the partition wall 54a having a relatively long predetermined length, so that the partition walls 54 in the upstream region are partially integrated. Even if not, the exhaust gas outflow passage 51 is surely closed.

Next, the mold 90 is pressed against the downstream end surface of the honeycomb structure 80. At this time, the mold 90 has a protrusion 9 in a predetermined exhaust flow passage, here, the exhaust gas outflow passage 51.
1 is pressed against the downstream end surface of the honeycomb structure 80.

When the mold 90 is pressed against the downstream end face of the honeycomb structure 80, the partition walls 54 defining the exhaust gas inflow passage 50 are gathered together to form a downstream tapered wall 52. The tapered wall 52 causes the exhaust gas to flow. The downstream end of the inflow passage 50 is completely closed. Here, the pressing of the mold 90 is completed.

Next, the honeycomb structure 8 thus formed
0 is dried. Further, the dried honeycomb structure 80 is fired.

Next, the honeycomb structure 8 is fired.
0 is used as a particulate filter base material, and an oxide substance is supported on the entire surface. Next, the oxidizing substance is carried only on the partition walls 54a on the upstream side of the honeycomb structure 80. That is, the oxidizing material is carried twice on the partition walls 54a on the upstream side of the honeycomb structure 80.

Thus, the end opening of the particulate filter 22 is closed by the tapered walls 52 and 53 made of the same porous material as the partition wall 54. Therefore, as described above, the exhaust flow passages 50 and 51 of the particulate filter 22 can be closed with the same material as the partition wall 54 by a very simple method of pressing the mold 90 against the end surface of the honeycomb structure 80.

Two molds 90 are prepared and these molds 90 are used.
Alternatively, the particulate filter 22 may be manufactured by simultaneously pressing against the end faces of the honeycomb structure 80.

Finally, the oxidizing substance carried on the particulate filter 22 will be described in detail. In this embodiment, each exhaust gas inflow passage 50 and each exhaust gas outflow passage 5
One wall surface, that is, inside the pores formed on both side surfaces of each partition wall 54 and inside thereof, and on both side surfaces of the tapered walls 52 and 53 and inside the pores formed inside thereof, is made of, for example, alumina. A layer of a carrier is formed, and on this carrier, the precious metal catalyst absorbs oxygen when excess oxygen exists in the surroundings and retains oxygen, and when the oxygen concentration in the surroundings decreases, the retained oxygen is converted into active oxygen. And an active oxygen releasing agent which is released at. The oxidizing substance in this example is this active oxygen releasing agent.

In this embodiment, platinum Pt is used as the noble metal catalyst, and as the active oxygen releasing agent, potassium K, sodium Na, lithium Li, cesium Cs, alkali metals such as rubidium Rb, barium Ba, calcium Ca, strontium. Alkaline earth metals such as Sr, lanthanum La, yttrium Y, rare earths such as cerium Ce, transition metals such as iron Fe, and tin Sn.
At least one selected from the following carbon group elements is used.

Calcium C is used as the active oxygen releasing agent.
It is preferable to use an alkali metal or alkaline earth metal having a higher ionization tendency than a, that is, potassium K, lithium Li, cesium Cs, rubidium Rb, barium Ba, or strontium Sr.

Next, regarding the action of removing particulates in the exhaust gas by the particulate filter 22, platinum Pt is deposited on the carrier.
A case of supporting potassium and potassium K will be described as an example, but the same fine particle removing action can be performed by using other noble metal, alkali metal, alkaline earth metal, rare earth, or transition metal.

Explaining, for example, that the exhaust gas flowing into the particulate filter 22 is the gas discharged from the compression ignition type internal combustion engine in which combustion is performed under excess air, the exhaust gas flowing into the particulate filter 22 is Contains a large amount of excess air. That is, when the ratio of the air supplied to the intake passage and the combustion chamber 5 to the fuel is called the air-fuel ratio of the exhaust gas, the air-fuel ratio of the exhaust gas is lean in the compression ignition internal combustion engine. Further, NO is generated in the combustion chamber of the compression ignition type internal combustion engine, so N is contained in the exhaust gas.
O is included. Further, the fuel contains a sulfur component S, and this sulfur component S reacts with oxygen in the combustion chamber to form S.
It becomes O ₂ . Therefore, the exhaust gas contains SO ₂ . Therefore, the exhaust gas containing excess oxygen, NO and SO ₂ flows into the exhaust gas inflow passage 50 of the particulate filter 22.

FIGS. 6A and 6B schematically show enlarged views of the surface of the carrier layer formed on the inner peripheral surface of the exhaust gas inflow passage 50. In FIGS. 6A and 6B, 60 indicates particles of platinum Pt, and 61 indicates an active oxygen release agent containing potassium K.

As described above, since the exhaust gas contains a large amount of excess oxygen, when the exhaust gas flows into the exhaust gas inflow passage 50 of the particulate filter 22, FIG.
As shown in (A), these oxygen O ₂ are O ₂ ⁻ or O ^2−.
It adheres to the surface of platinum Pt in the form of. On the other hand, NO in the exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt, and N
It becomes O ₂ (2NO + O ₂ → 2NO ₂ ). Next, a part of the generated NO ₂ is absorbed in the active oxygen release agent 61 while being oxidized on the platinum Pt, and is bonded to the potassium K, as shown in FIG.
As shown in (A), it diffuses into the active oxygen release agent 61 in the form of nitrate ion NO ₃ ⁻ to produce potassium nitrate KNO ₃ .

On the other hand, as described above, the exhaust gas contains SO.
_{2 is} also contained, and this SO ₂ is also absorbed in the active oxygen release agent 61 by the same mechanism as NO. That is, as described above, the oxygen O ₂ is platinum Pt in the form of O ₂ ⁻ or O ^2−.
SO ₂ in the exhaust gas is platinum Pt.
Reacts with O ₂ ⁻ or O ^{2 −} to form SO ₃ . Then, a part of the generated SO ₃ is absorbed on the active oxygen releasing agent 61 while being further oxidized on the platinum Pt, and is bound to the potassium K to form the sulfate ion SO ₄ ²⁻ inside the active oxygen releasing agent 61. Diffuses to produce potassium sulfate K ₂ SO ₄ . In this way, potassium nitrate K is contained in the active oxygen release agent 61.
NO ₃ and potassium sulfate K ₂ SO ₄ are produced.

On the other hand, fine particles mainly composed of carbon C are generated in the combustion chamber 5, and therefore, the exhaust gas contains these fine particles. These fine particles contained in the exhaust gas are shown in FIG. 6 when the exhaust gas flows in the exhaust gas inflow passage 50 of the particulate filter 22 or when it goes from the exhaust gas inflow passage 50 to the exhaust gas outflow passage 51. As indicated by 62 in B), it contacts and adheres to the surface of the carrier layer, for example, the surface of the active oxygen releasing agent 61.

Thus, the fine particles 62 are the active oxygen releasing agent 6
When it adheres to the surface of No. 1, the fine particles 62 and the active oxygen releasing agent 6
The oxygen concentration decreases at the contact surface with 1. When the oxygen concentration decreases, a difference in concentration occurs between the active oxygen release agent 61 and the active oxygen release agent 61 having a high oxygen concentration. Therefore, the oxygen in the active oxygen release agent 61 is directed toward the contact surface between the fine particles 62 and the active oxygen release agent 61. Try to move. As a result, potassium nitrate KNO ₃ formed in the active oxygen release agent 61 is converted into potassium K and oxygen O.
Is decomposed into NO and NO, and oxygen O is directed to the contact surface between the fine particles 62 and the active oxygen release agent 61, while NO is released from the active oxygen release agent 61 to the outside. The NO released to the outside is oxidized on the platinum Pt on the downstream side and is again absorbed in the active oxygen release agent 61.

At this time, potassium sulfate K ₂ SO ₄ formed in the active oxygen releasing agent 61 is also potassium K and oxygen O.
Are decomposed into SO ₂ and SO _2, and oxygen O is directed to the contact surface between the fine particles 62 and the active oxygen release agent 61, while SO ₂ is released from the active oxygen release agent 61 to the outside. The SO ₂ released to the outside is oxidized on the platinum Pt on the downstream side and is again absorbed in the active oxygen release agent 61. However, potassium sulfate K ₂ SO ₄ is stable and difficult to decompose, so potassium sulfate K ₂ SO _4
2 SO ₄ is less likely to release active oxygen than potassium nitrate KNO ₃ .

The active oxygen releasing agent 61 also generates and releases active oxygen in the reaction process with oxygen when absorbing NO _x in the form of nitrate ion NO ₃ ⁻ as described above. Similarly, the active oxygen release agent 61 to the SO ₂ as described above to produce an active oxygen in the reaction process with oxygen even when absorbed by sulfate ions SO ₄ ^2-form release.

By the way, the fine particles 62 and the active oxygen releasing agent 61
Oxygen O toward the contact surface with is oxygen decomposed from a compound such as potassium nitrate KNO ₃ or potassium sulfate K ₂ SO ₄ . Oxygen O decomposed from the compound has high energy and has extremely high activity. Therefore, oxygen toward the contact surface between the fine particles 62 and the active oxygen release agent 61 is active oxygen O. Similarly, oxygen produced in the reaction process of NO _x and oxygen or the reaction process of SO ₂ and oxygen in the active oxygen release agent 61 is also active oxygen. When the active oxygen O comes into contact with the fine particles 62, the fine particles 62 are oxidized in a short time (several seconds to tens of minutes) without emitting a bright flame, and the fine particles 62 are completely extinguished.
Therefore, the fine particles 62 are collected in the particulate filter 22.
It rarely deposits on top.

As in the prior art, the particulate filter 2
When the particulates accumulated in a layered manner on 2 are burned, the particulate filter 22 becomes red hot and burns with a flame. The combustion with such a flame does not last unless it is at a high temperature, and therefore the temperature of the particulate filter 22 must be maintained at a high temperature in order to continue the combustion with such a flame.

On the other hand, in the present invention, the fine particles 62 are oxidized without emitting a luminous flame as described above, and at this time, the surface of the particulate filter 22 does not become red hot. In other words, in other words, in the present invention, the fine particles 62 are oxidized and removed at a temperature much lower than the conventional temperature. Therefore, the particulate removing action by the oxidation of the particulate 62 which does not emit the bright flame according to the present invention is completely different from the particulate removing action by the conventional combustion accompanied by a flame.

By the way, platinum Pt and active oxygen releasing agent 6
No. 1 is activated as the temperature of the particulate filter 22 becomes higher, so the amount of oxidizable / removable fine particles that can be oxidatively removed on the particulate filter 22 per unit time without emitting a luminous flame.
It increases as the temperature of 2 increases.

The solid line in FIG. 8 shows the amount G of oxidatively removable fine particles that can be oxidatively removed without emitting a luminous flame per unit time. In FIG. 8, the horizontal axis indicates the temperature TF of the particulate filter 22. The amount of fine particles that flow into the particulate filter 22 per unit time is referred to as the inflow fine particle amount M. When the inflow fine particle amount M is smaller than the oxidatively removable fine particles G, that is, in the region I of FIG. When all the fine particles that have flowed into the particulate filter 22 come into contact with the particulate filter 22, the particulate filter 22 is oxidatively removed on the particulate filter 22 without emitting a bright flame in a short time (from several seconds to several tens of minutes).

On the other hand, when the amount M of inflowing fine particles is larger than the amount G of fine particles that can be removed by oxidation, that is, in the region II of FIG. 8, the amount of active oxygen is insufficient to oxidize all the fine particles. 7A to 7C show the state of oxidation of the fine particles in such a case. That is, when the amount of active oxygen is insufficient to oxidize all the fine particles, the fine particles 62 are converted into the active oxygen releasing agent 6 as shown in FIG.
When it adheres on the surface 1, only a part of the fine particles 62 is oxidized, and the part of the fine particles not sufficiently oxidized remains on the carrier layer. Next, when the state in which the amount of active oxygen is insufficient continues, the fine particle portions that are not oxidized one after another remain on the carrier layer, and as a result, the surface of the carrier layer is changed as shown in FIG. 7 (B). The residual fine particle portion 63 is covered.

If the surface of the carrier layer is covered with the residual fine particle portion 63, NO and SO ₂ oxidizing action of platinum Pt and active oxygen releasing action of the active oxygen releasing agent 61 become difficult to perform, and moreover, Even if these oxidizing action and releasing action are performed, the residual fine particle portion 63
Is separated from platinum Pt, so that it is hard to receive the oxidation effect of platinum Pt. Therefore, the residual fine particle portion 63 remains as it is without being oxidized,
Next, the fine particles 64 deposited on the residual fine particles 63 remain as they are without being oxidized for the same reason. Thus, as shown in FIG. 7C, the residual fine particle portion 63
Another fine particle 64 is deposited on the surface one after another. That is, the fine particles are deposited in a laminated form.

When the fine particles are stacked in this manner, the fine particles 64 are no longer oxidized by the active oxygen O, so that further fine particles are successively deposited on the fine particles 64. That is, if the state in which the amount M of inflowing fine particles is larger than the amount G of fine particles that can be removed by oxidation continues, the fine particles are accumulated in layers on the particulate filter 22, thus raising the exhaust gas temperature to a high temperature, or Unless the temperature of 22 is raised to a high temperature, the deposited particles cannot be ignited and burned.

As described above, in the region I of FIG. 8, the fine particles are oxidized on the particulate filter 22 in a short time without emitting a bright flame. In the region II of FIG. 8, the fine particles are stacked on the particulate filter 22. Deposits in the shape of. Therefore, in order to prevent the particulates from accumulating in a layered manner on the particulate filter 22, the inflowing particulate amount M must be always smaller than the oxidatively removable particulate amount G.

As can be seen from FIG. 8, in the particulate filter 22 used in the embodiment of the present invention, it is possible to oxidize the particulates even when the temperature TF of the particulate filter 22 is considerably low, and therefore the amount of the incoming particulates. M and temperature TF of the particulate filter 22
Is maintained so that the inflowing particulate amount M is always smaller than the oxidatively removable particulate amount G.

As described above, when the amount M of inflowing fine particles is always smaller than the amount G of fine particles that can be removed by oxidation, almost no fine particles are deposited on the particulate filter 22 and thus the back pressure hardly rises.

On the other hand, as described above, once the fine particles are accumulated in a laminated form on the particulate filter 22, even if the inflowing fine particle amount M becomes smaller than the oxidatively removable fine particle amount G, the fine particles are oxidized by the active oxygen O. Is difficult. However, when the fine particles that have not been oxidized are starting to remain, that is, when the fine particles are deposited below a certain limit, if the inflowing fine particle amount M becomes smaller than the oxidatively removable fine particle amount G, the residual fine particle portions become active oxygen O. Is removed by oxidation without emitting a bright flame.

Considering the case where the particulate filter 22 is disposed in the exhaust passage of the internal combustion engine and used, the fuel and the lubricating oil contain calcium Ca, and therefore the exhaust gas contains calcium Ca. This calcium Ca produces calcium sulfate CaSO ₄ when SO ₃ is present. This calcium sulfate CaSO ₄ is a solid and does not thermally decompose even at high temperatures. Therefore, when calcium sulfate CaSO ₄ is produced, the particulate filter 2 is caused by this calcium sulfate CaSO ₄ .
The second pore is blocked, and as a result, the exhaust gas is hard to flow in the particulate filter 22.

In this case, if an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, such as potassium K, is used as the active oxygen release agent 61, SO ₃ diffused in the active oxygen release agent 61 is bound to potassium K. To form potassium sulfate K ₂ SO ₄ , and calcium Ca does not bind to SO ₃ and the particulate filter 2
It passes through the second partition 54 and flows out into the exhaust gas outflow passage 51. Therefore, the pores of the particulate filter 22 will not be clogged. Therefore, as described above, the active oxygen releasing agent 61 is an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, that is, potassium K, lithium Li, and cesium C.
s, rubidium Rb, barium Ba, strontium S
It will be preferred to use r.

The present invention also relates to the particulate filter 2
The platinum Pt is formed on both sides of the partition wall and the tapered wall of No. 2 and the carrier layer formed in the pores formed inside them.
It can also be applied to the case of carrying only a noble metal such as. However, in this case, the solid line indicating the amount G of particles that can be removed by oxidation moves to the right side slightly as compared with the solid line shown in FIG. In this case, NO ₂ retained on the surface of platinum Pt
Alternatively, active oxygen is released from SO ₃ .

Further, NO ₂ or S is used as an active oxygen releasing agent.
O ₃ is adsorbed and held, and these adsorbed NO ₂ or SO ₃
It is also possible to use a catalyst capable of releasing active oxygen from

[0081]

According to the present invention, since the pressures in the adjacent exhaust gas inflow passages are substantially equal to each other during use of the particulate filter, the exhaust gas rarely passes through the partition wall separating the exhaust gas inflow passages. Therefore, as in the present invention, even if the average pore diameter of the partition wall is reduced by making the partition wall that separates the exhaust gas inflow passage carry an oxidizing substance for oxidizing and removing fine particles, this causes a pressure loss due to the particulate filter. Does not increase. That is, according to the present invention, although the partition wall is made to carry the oxidizing substance, the pressure loss due to the particulate filter is always maintained at a low value.

[Brief description of drawings]

FIG. 1 is a diagram showing a particulate filter according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a part of the particulate filter of the first embodiment.

FIG. 3 is a diagram showing a conventional particulate filter.

FIG. 4 is a diagram showing a honeycomb structure.

FIG. 5 is a view showing a mold.

FIG. 6 is a diagram for explaining an oxidizing effect of fine particles.

FIG. 7 is a diagram for explaining a deposition action of fine particles.

FIG. 8 is a diagram showing a relationship between the amount of fine particles that can be removed by oxidation and the temperature of a particulate filter.

[Explanation of symbols]

22 ... Particulate filter 50 ... Exhaust gas inflow passage (exhaust flow passage) 51 ... Exhaust gas outflow passage (exhaust flow passage) 52, 53 ... Tapered wall 54, 54a ... Partition wall

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 35/04 301 B01J 35/04 301L 4G069 F01N 3/28 301Q B01D 46/42 B F01N 3/28 301 53/36 104B // B01D 46/42 ZAB (72) Inventor Kazuhiro Ito 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Takamitsu Asanuma 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation ( 72) Inventor Shunsuke Toshioka 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Koichi Kimura 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Akira Mikami 1 Toyota Town, Toyota-shi, Aichi F-term in Toyota Motor Corporation (reference) 3G090 AA02 AA03 BA01 CA00 3G091 AB02 AB13 BA00 BA07 BA39 GA06 GB02W GB03W GB06W HA14 4D019 AA01 BA05 BA06 BC05 BC07 CA01 CB04 CB09 4D048 AA18 BA01 BA01 BA01 BA01 BA01 BA01 BA01 BA18Y BA19Y BA21Y BA30X BA36Y BB01 BB12 BB14 CD05 EA04 4D058 JA32 JB06 MA44 NA04 SA08 4G069 AA03 AA08 AA11 BA13 BC13CA BC02 CABC18A BC18BC18ABC18ABC18ABC18ABC18ABC18ABC18ABC18ABC18ABC25ABC25ABC25ABC25ABC25ABC18ABC25ABC25ABC25ABC25ABC25ABC18ABC25ABC18ABC25ABC25ABC25ABC18ABC25ABC25ABC18ABC25ABC18ABC18ABC18ABC25ABC18ABC18ABC07A EA27 EC29 FA03 FB15 FB19

Claims (8)

[Claims] 1. A plurality of exhaust flow passages defined by partition walls made of a porous material for collecting fine particles in exhaust gas, and a part of these exhaust flow passages is downstream of the exhaust flow passages. The end opening is closed so that the exhaust flow passage becomes an exhaust gas inflow passage for allowing exhaust gas to flow in from the upstream end opening, while the remaining exhaust flow passage is closed at the upstream end opening, whereby the exhaust flow passage is closed. In an exhaust purification particulate filter in which the exhaust flow passage is an exhaust gas outflow passage through which the exhaust gas flows out from its downstream end opening, each exhaust gas inflow passage is adjacent to the exhaust gas outflow passage through a partition wall in its downstream region. In the upstream region, only the exhaust gas inflow passage is adjacent to the exhaust gas inflow passage through the partition wall, and the fine particles can be oxidized to the partition wall that defines the upstream side region of the exhaust gas inflow passage. An exhaust gas purification particulate filter characterized in that it carries an oxidant. 2. The exhaust purification particulate filter according to claim 1, wherein one of two adjacent exhaust flow passages is the exhaust gas inflow passage and the other exhaust flow passage is the exhaust gas outflow passage. In, the upstream side portions of the partition walls defining the exhaust gas outflow passage are gathered together and joined to each other over a predetermined length from the upstream end thereof, thereby closing the upstream end opening of the exhaust gas outflow passage. Exhaust gas purification particulate filter characterized by being characterized. 3. A downstream side portion of a partition wall defining the exhaust gas inflow passage is gathered together and joined to each other, whereby a downstream end opening of the exhaust gas inflow passage is closed. Item 1. The exhaust gas purification particulate filter according to Item 1. 4. The exhaust gas purification patty according to claim 2 or 3, wherein the partition walls are gathered together such that the flow passage cross section of the passage becomes narrower toward the end face side of the exhaust gas purification particulate filter. Curate filter. 5. The exhaust purification particulate filter according to claim 1, wherein the partition wall carries an oxidizing substance capable of oxidizing fine particles, and the partition wall defining an upstream side region of the exhaust gas inflow passage is supported. The exhaust gas purification particulate filter is characterized in that the amount of the oxidant is larger than the amount of the oxidant carried on the remaining partition walls. 6. The method for manufacturing an exhaust purification particulate filter according to claim 5, wherein a step of supporting an oxidant on the entire exhaust purification particulate filter, and a predetermined length from the upstream end of the exhaust gas inflow passage. And a step of supporting the oxidizing substance only on the partition walls that are joined to each other over the entire length. 7. A plurality of exhaust flow passages defined by partition walls made of a porous material for collecting fine particles in the exhaust gas, and the exhaust flow passage is provided in a part of these exhaust flow passages. Exhaust gas into which exhaust gas is introduced from the upstream end opening of the exhaust flow passage by closing up the downstream end portions of the partition walls that define the passage and joining them to each other, thereby closing the downstream end opening of the exhaust flow passage. In the remaining exhaust flow passage, the upstream side portions of the partition walls that define the exhaust flow passage are gathered and joined to each other in the remaining exhaust flow passage, whereby the upstream end opening of the exhaust flow passage is closed. In the exhaust gas purification particulate filter base material in which the exhaust flow passage is an exhaust gas outflow passage through which the exhaust gas flows out from the downstream end opening, the upstream side portion of the partition wall defining the exhaust gas outflow passage is brought close. The exhaust gas inflow passages are collected and joined to each other over a predetermined length from the upstream end thereof, whereby each exhaust gas inflow passage is adjacent to the exhaust gas outflow passage via a partition wall in the downstream side region, and the upstream side region thereof. In the above, the exhaust gas purification particulate filter base material is characterized in that it is adjacent only to another exhaust gas inflow passage via a partition wall. 8. The exhaust gas purification particulate filter according to claim 7, wherein the partition wall portions are gathered together such that the flow passage cross section of the passage becomes narrower toward the end face side of the exhaust gas purification particulate filter. Base material.