JP2005299486A - Exhaust emission control device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of effectively processing PM contained in exhaust of a diesel engine even in the case of miniaturizing and reducing weight, and possible to be manufactured at low cost. <P>SOLUTION: A first metal net coated with catalyst oxide such as Pt in a surface thereof and a second metal net separately prepared from the first metal net and not coated with in a surface thereof are compressed at the same time in the condition wherein they are combined with each other. The second metal net and the first metal net are integrally connected to each other to form a porous structure 9a provided with a clearance, in which exhaust can flow freely, between the adjacent metal wires. In this porous structure 9a, catalyst oxide coating exists in an outside diameter side half part 22 positioned on an upstream side of an exhaust flow, but such a coating does not exist in an inside diameter side half part 23 positioned on a downstream side thereof. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device for removing particulate matter (hereinafter simply referred to as “PM”) contained in the exhaust of a diesel engine and an improvement of the manufacturing method thereof, and relates to a small and lightweight exhaust. A purification device is realized.

While diesel engines have better thermal efficiency than gasoline engines, it is widely known that nitrogen oxides (NO _x ) and PM, which are abundant in the exhaust of gasoline engines, can cause serious air pollution. Yes. For this reason, in order to popularize diesel engines for resource saving and the like, it is necessary to realize an exhaust purification device that can effectively remove the nitrogen oxides and PM. As such an exhaust purification device, those described in many publications such as Patent Documents 1 to 3 and Non-Patent Document 1 are known, and some of them have been implemented.

FIG. 4 shows the structure described in Patent Document 1 among them. In the case of this conventional structure, exhaust gas discharged from the diesel engine 1 to the exhaust manifold 2 and added with light oil from the nozzle 3 is sent to the exhaust purification device 6 via the supercharger 4 and the carburetor 5. . In the exhaust purification device 6, the nitrogen oxide and PM are rendered harmless by the action of the catalyst. Specifically, NO in nitrogen oxides is changed to NO ₂ having a high function as an oxidizing agent by an (oxidation) catalyst such as Pt (or a simple substance or a mixture of Co and Pd), and then this NO ₂ And PM are reacted {PM (C) is burned with NO ₂ O ₂ } to detoxify nitrogen oxides and PM (change them to N ₂ and CO ₂ ). Patent Documents 2 and 3 describe such detoxification treatment of nitrogen oxides and PM in the exhaust gas purification apparatus.

As can be seen from the descriptions in Patent Documents 2 and 3, etc., in order to detoxify the nitrogen oxides and PM contained in the exhaust discharged from the diesel engine, the above NO is provided upstream in the exhaust flow direction. It is necessary to provide an oxidation catalyst for changing NO to NO ₂ and a trapping portion for trapping PM on the downstream side. Conventionally, as described in Non-Patent Document 1, a ceramic-made exhaust purification device having such a catalyst and a trapping portion has been used.

That is, a catalyst such as Pt is attached to the surface of a ceramic carrier disposed on the upstream side, and a ceramic porous filter is disposed on the downstream side to capture unburned PM. The unburned PM trapped by the filter in this way becomes CO ₂ by reacting (burning) with NO ₂ sent from the upstream catalyst, and is diffused into the atmosphere. The exhaust gas from the diesel engine contains hydrocarbon (HC) and carbon monoxide (CO) in addition to the nitrogen oxides and PM. These HC and CO are also contained in the exhaust of the gasoline engine, and can be rendered harmless by the same technology as the exhaust gas purification device for the gasoline engine. Further, an exhaust gas purification device having a structure in which an electric heater is provided in a filter portion for burning the PM and the PM is heated and burned is conventionally known.

  In the case of a structure in which a ceramic filter for burning PM and a catalyst carrier are provided independently in series in the exhaust flow direction, the exhaust purification device is reduced in size, weight and cost. Hateful. The reason why it is difficult to reduce the size and weight is to provide a filter and a catalyst carrier that are independent of each other. The reason why it is difficult to reduce the cost is that the manufacturing cost of the ceramic filter itself is increased, and a buffer structure is required to prevent the thin and brittle ceramic from being damaged by vibration during vehicle running. This is because it becomes.

  On the other hand, Patent Documents 4 and 5 describe an exhaust emission control device for a diesel engine that uses a nonwoven fabric or the like and integrates a filter and a catalyst carrier. Of these, Patent Document 4 describes an exhaust emission control device in which a heater, a ceramic nonwoven fabric, a catalyst layer, and a wire mesh are laminated to form an overall waveform. Of these, the catalyst layer is made to disperse a metal powder serving as a catalyst, such as Pt, on the surface of a metal mesh based on Ni. Further, as shown in FIG. 5, Patent Document 5 discloses an exhaust purification device in which flat plates 7 and corrugated plates 8 made of metal fiber nonwoven fabric are alternately overlapped and wound, and a catalyst is supported on the metal fibers. Has been described.

  According to the structures described in Patent Documents 4 and 5 as described above, the exhaust purification device is smaller and lighter than the structure in which the filter and the catalyst carrier are provided independently of each other as conventionally performed. Although it is considered that the cost and cost can be reduced, there is still room for improvement. For example, in the case of the structure described in Patent Document 4, the thickness dimension in the exhaust flow direction is small. In the case of the structure described in Patent Document 5, there is a linearly continuous passage with respect to the flow direction of the exhaust. For this reason, in any structure, when trying to reduce the size and weight, PM contained in the exhaust gas is not trapped by the filter and diffused into the atmosphere without being detoxified. It is thought that the ratio will increase.

JP 2004-27881 A JP 2003-269204 A JP 2003-245552 A JP 2002-97928 A JP 2002-113798 A Takakura Takashi et al., “High Performance Exhaust Gas Purifier (DPR)”, Eco Industry, CMC Publishing Co., Ltd., November 2003, Vol. 8 No. 11, p. 21-31

  In view of the circumstances as described above, the present invention realizes an exhaust purification device that can effectively process PM contained in the exhaust of a diesel engine and can be manufactured at low cost even when it is reduced in size and weight. Invented as much as possible.

Of the exhaust purification device and the manufacturing method thereof according to the present invention, the invention of the exhaust purification device according to claim 1 is a metal mesh formed by braiding metal wires, and a gap through which exhaust gas can freely flow between adjacent metal wires. It is provided with a porous structure formed by compressing to the extent that exists. Of the metal wires constituting the porous structure, at least the surface of the metal wire constituting the upstream portion in the exhaust flow direction is coated with a catalyst such as Pt. The porous structure is housed in a casing having an exhaust introduction port and an exhaust discharge port to form an exhaust purification device.
In addition, examples of the braid as referred to in the claims and the specification of the present case include mesh weave, twill weave, knitted weave, and plain weave. Among these, it is preferable to use a knitted wire mesh because it has excellent moldability and can easily control the density.
The coating of the catalyst such as Pt is not particularly limited as long as Pt on the surface of the metal wire adheres firmly, but is generally performed by plating.

  According to a third aspect of the present invention, there is provided an exhaust purification device manufacturing method comprising: a first wire mesh braided with a metal wire and coated with a catalyst such as Pt on the surface; and the first wire mesh separately. The second wire mesh and the first wire mesh that are prepared by braiding the metal wire and compressing at the same time in combination with a second wire mesh that is not coated with a catalyst such as Pt on the surface. And are integrally coupled. A porous structure in which there is a gap through which exhaust can flow between adjacent metal wires, and the surface of the metal wire constituting the upstream portion in the exhaust flow direction is coated with a catalyst such as Pt. Let it be the body.

According to the present invention configured as described above, it is possible to realize an exhaust purification device that is small and light and can effectively perform the detoxification process of PM contained in the exhaust of a diesel engine at low cost.
These effects can be achieved by compressing a wire mesh formed of braided metal wires to form a porous structure and coating the surface of the metal wires existing in the upstream portion with a catalyst such as Pt. That is, since the porous structure has a large number of fine passages bent inside, the PM can be captured effectively and detoxified without being detoxified even if the dimensions in the exhaust flow direction are reduced. The amount of PM released into the can be kept to a minimum.
That is, the exhaust gas that has flowed into the porous structure flows without being linearly bent and flows (becomes turbulent flow). Therefore, the contact area between the catalyst and the exhaust gas can be increased as compared with an exhaust gas purification device using a honeycomb-shaped catalyst carrier in which the exhaust gas advances linearly. For this reason, even if it reduces in size, sufficient exhaust gas purification performance is securable. In addition, since the porous structure itself has a buffering action, there is no need to install a separate buffer as in the case of using a ceramic honeycomb catalyst carrier. From this aspect as well, the exhaust purification device is compact and lightweight. Can be realized.
Moreover, since the porous structure portion is coated with a catalyst such as Pt, the volume efficiency is improved as compared with the structure in which the filter and the catalyst carrier are provided independently of each other as in the conventional structure described above. From the aspect, it is possible to reduce the size and weight.
In addition, the porous structure formed by compressing the wire mesh can be manufactured at a low cost when the mass production effect is the same as that of the ceramic porous structure, and has a very excellent impact resistance. Therefore, there is no need to use a separate cushioning material. Since the buffer material is omitted, the cost can be reduced and the size can be reduced by reducing the space between the porous structure and the inner surface of the case housing the exhaust purification device.
The porosity of the porous structure formed by compressing the wire mesh can be arbitrarily adjusted by changing the wire diameter of the metal wire and the degree to which the wire mesh is compressed (compression rate). By changing the porosity, it is possible to adjust the PM trapping rate by the porous structure and the resistance to the flow of exhaust gas. Therefore, the porosity is determined in terms of design in order to ensure the necessary performance while taking into account the installation space of the exhaust purification device.

Of the present invention, when the invention relating to the exhaust emission control device according to claim 1 is carried out, preferably, as described in claim 2, the porous structure is formed into a cylindrical shape, and the exhaust gas is discharged from one peripheral surface. It is set as the structure which flows to radial direction toward the other surrounding surface.
If comprised in this way, the structure which is small and can be easily installed under the floor of the vehicle, has good performance regarding the detoxification process of PM, and can suppress the exhaust passage resistance to a low level.
That is, when the exhaust emission control device is installed under the floor of the vehicle, the longitudinal dimension can be sufficiently secured because the longitudinal dimension of the vehicle is sufficient. Therefore, by ensuring the length of the cylindrical porous structure, the passage area of the exhaust can be widened and the passage resistance can be kept low. In order to widen this passage area, it is possible to increase the cross-sectional area related to the virtual plane orthogonal to the longitudinal direction of the vehicle, but when this cross-sectional area is widened, the lowest position becomes lower, Installation under the floor may be difficult, for example, it may be easy to collide with obstacles on the road surface. If the structure described in claim 2 is adopted, such a problem is hardly caused.

Further, when carrying out the invention relating to the method for manufacturing an exhaust emission control device described in claim 3, preferably, as described in claim 4, the first metal mesh is coated with a catalyst such as Pt on the surface in advance. It is made by braiding metal wires.
The coating of the catalyst such as Pt can be performed after the metal wire is braided to form the first wire mesh. However, in this case, an object to be coated (first wire mesh) becomes large, and a plating tank or the like is formed. The equipment for coating is increased. Further, there is a possibility that a catalyst such as Pt does not sufficiently adhere to the contact portion between the metal wires.
On the other hand, as described in claim 4 above, if the metal wire previously coated with a catalyst such as Pt is braided to form the first wire mesh, the object to be coated (metal wire) Because of the small size, the equipment for coating such as a plating tank can be reduced. Further, since the catalyst such as Pt is sufficiently adhered to the contact portion between the metal wires, the performance of the exhaust gas purification device can be improved accordingly.

  Preferably, when carrying out the invention relating to the method for manufacturing an exhaust emission control device according to claim 3 or 4, the metal constituting the first and second wire meshes as described in claim 5. The wire is made of stainless steel. And after performing Ni plating on the surface of the metal wire made of stainless steel constituting the first wire mesh of these, or after further applying Cr plating to the surface of Ni plating, the surface of this Ni plating or Cr plating Then, a coating of Pt as a catalyst is applied.

  Since the stainless steel metal wire has excellent heat resistance (oxidation resistance), excellent durability can be obtained regardless of the temperature rise associated with the treatment of nitrogen oxides and PM. That is, when practicing the present invention, in order to increase the porosity of the porous structure in order to keep the resistance to the flow of exhaust gas low, and to increase the chance of contact between the exhaust gas and the catalyst Pt, the porous structure In order to complicate the internal fine flow path (increase the number of times of bending), it is necessary to make the diameter of the metal wire small (thin). And when this wire diameter is made small, it is necessary to use what has the outstanding heat resistance as this metal wire. If it is sufficient to satisfy only heat resistance, the metal wire may be made of W or Ti. However, in consideration of cost and plastic deformability (when compressed into a porous structure) It cannot be adopted. On the other hand, if the metal wire is made of stainless steel, all of heat resistance, low cost, and workability can be obtained at a sufficiently practical level.

  However, when a stainless steel metal wire is used, the bond strength of Pt coated (plated) on the surface of the metal wire cannot be obtained as it is. On the other hand, if the surface of the metal wire made of stainless steel is plated with Ni as described above and then the surface of this Ni plating is coated with Pt, the bond strength of Pt to the metal wire can be sufficiently secured. . That is, the bond strength of Ni plating to stainless steel can be made sufficiently high, and the bond strength of the Pt coating (plating) layer to this Ni plating can also be made sufficiently high. Thus, the Ni plating functions as a binder, so that the bonding strength of the Pt coating layer to the stainless steel metal wire is increased. As a result, the exhaust purification action by Pt existing on the surface of the first wire mesh can be sufficiently exhibited over a long period of time.

  1 and 2 show a first embodiment of the present invention corresponding to claims 1 and 2. In the case of the present embodiment, a metal mesh formed by braiding stainless steel metal wires such as SUS316L, for example, by knitting, etc., to the extent that there is a gap through which exhaust can freely flow between adjacent metal wires. The porous structure 9 is lightly compressed and entirely cylindrical. In the case of the present embodiment, the entire stainless steel metal wire constituting the porous structure 9 is subjected to Pt plating via Ni plating. These Ni plating and Pt plating are performed in the state of a metal wire before braiding the wire mesh.

  The porous structure 9 as described above is housed in a casing 15 having an exhaust introduction port 13 and an exhaust discharge port 14 as shown in FIG. In this case, the porous structure 9 is installed in the casing 15 in a state where the porous structure 9 separates the exhaust introduction port 13 and the exhaust discharge port 14. Specifically, the space leading to the exhaust inlet 13 is made to face only the outer peripheral surface 10 of the porous structure 9, and the inner peripheral surface 11 and the axial end surfaces 12, 12 of the porous structure 9 are Do not face each other. Further, the space leading to the exhaust discharge port 14 is opposed only to the inner peripheral surface 11 of the porous structure 9 and is not opposed to the outer peripheral surface 10 and the axial end surfaces 12 and 12 of the porous structure 9.

  For this purpose, both axial end surfaces 12 and 12 of the porous structure 9 abut against stepped portions 17 a and 17 b provided in the casing 15. Further, in the case of the present embodiment, the inner peripheral surface of the casing 15 is corrugated in the cross-sectional shape in the circumferential direction, so that the outer peripheral surface 10 of the porous structure 9 is suppressed and the porous structure Exhaust gas can be introduced to the outer peripheral surface 10 side of the body 9. That is, in the case of the present embodiment, a plurality of concave grooves 18 and 18 that are long in the axial direction (left-right direction in FIG. 2) of the porous structure 9 are formed on the inner peripheral surface of the casing 15 in the circumferential direction. It is formed intermittently. The outer peripheral surface 10 of the porous structure 9 is suppressed by a bank-like portion that exists between the concave grooves 18, 18, thereby preventing rattling in the casing 15. Further, one end of each of the concave grooves 18 and 18 communicates with the exhaust inlet 13. Further, in order to prevent the exhaust from being short-circuited from the exhaust flow passages 19 and 19 where the one end of each of the concave grooves 18 and 18 and the exhaust introduction port 13 are continuous, the porous structure 9 includes The end surface 12 facing the exhaust inlet 13 is closed by a disk-like closing plate 20.

In the case of the exhaust emission control device 16 of the present embodiment configured as described above, the exhaust gas introduced into the casing 15 from the exhaust gas inlet 13 passes through the concave grooves 18 and 18 and surrounds the porous structure 9. Led to. Next, the exhaust gas flows from the radially outer side to the inner side in the porous structure 9 as indicated by arrows in FIG. During this time, harmful components contained in the exhaust gas are detoxified by the action of Pt coated on the surface of the metal wire. Specifically, Pt is By acting as a catalyst, the NO of nitrogen oxides in the exhaust is changed to NO _2, it is reacted with the NO ₂ and PM, nitrogen oxides, and detoxification of PM (Change to N ₂ and CO ₂ ).

  In the case of the present invention, since there are a large number of bent and complicated fine flow paths inside the porous structure 9, the time during which the exhaust remains in the porous structure 9 is long. Contact with Pt is effected effectively. In addition, PM is effectively captured. For this reason, the efficiency of the exhaust gas detoxification process is improved. The exhaust gas detoxified as described above is discharged from the central hole 21 of the porous structure 9 through the exhaust discharge port 14. The feature of the present invention resides in the porous structure 9 part, and the structure of the casing 15 is not particularly limited.

FIG. 3 shows Embodiment 2 of the present invention corresponding to claims 1 to 5. In the case of the present embodiment, Pt coating is applied only to the surface of the metal wire constituting the outer diameter side half 22 of the porous structure 9a, and Pt coating is applied to the surface of the metal wire constituting the inner diameter side half 23. Is not given. Thus, when the porous structure 9a having different properties between the outer diameter side half portion 22 and the inner diameter side half portion 23 is manufactured, first, a Pt coating is formed on the surface by braiding metal wires. A first wire mesh that is provided and a second wire mesh that is prepared separately from the first wire mesh and is formed by braiding metal wires and having no surface coated with Pt coating, Combine with the second wire mesh inserted on the side. Next, both the wire meshes are compressed at the same time, and the both wire meshes are joined together.
In the case of this embodiment, the amount of expensive Pt used can be suppressed and the cost can be reduced by omitting the Pt plating of the inner diameter side half portion 23 which does not need to be subjected to Pt plating in terms of function. Other configurations and operations are the same as those in the first embodiment described above, and thus redundant description is omitted.

1 is a schematic perspective view of a porous structure showing Example 1 of the present invention. FIG. 3 is a schematic cross-sectional view showing a state in which the porous structure is stored in a casing. The schematic perspective view of the porous structure which shows Example 2 of this invention. The schematic diagram which shows the 1st example of the exhaust gas purification apparatus conventionally known. The schematic perspective view which shows the 2nd example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Exhaust manifold 3 Nozzle 4 Supercharger 5 Vaporizer 6 Exhaust purification device 7 Flat plate 8 Corrugated plate 9, 9a Porous structure 10 Outer peripheral surface 11 Inner peripheral surface 12 End surface 13 Exhaust inlet 14 Exhaust outlet 15 Casing 16 Exhaust purification devices 17a, 17b Stepped portion 18 Concave groove 19 Exhaust flow path 20 Closing plate 21 Center hole 22 Outer diameter side half portion 23 Inner diameter side half portion

Claims (5)

  A metal mesh formed by braiding metal wires is compressed to such an extent that there is a gap through which exhaust can flow between adjacent metal wires, and at least the metal wire constituting the upstream portion in the exhaust flow direction. An exhaust purification device comprising a porous structure having a catalyst coating on the surface.   2. The exhaust emission control device according to claim 1, wherein the porous structure has a cylindrical shape and exhaust gas flows in a radial direction from one peripheral surface toward the other peripheral surface.   A first wire mesh braided with metal wire and coated with catalyst on the surface, and prepared separately from the first wire mesh, braided with metal wire and not coated with catalyst on the surface The second wire mesh is compressed simultaneously with the second wire mesh combined, and the second wire mesh and the first wire mesh are joined together, and there is a gap between the adjacent metal wires that allows exhaust to flow freely. And a method of manufacturing an exhaust emission control device having a porous structure in which the surface of the metal wire constituting the upstream portion in the exhaust flow direction is coated with a catalyst.   The manufacturing method of the exhaust gas purification device according to claim 3, wherein the first wire net is formed by braiding a metal wire having a surface coated with a catalyst beforehand.   After the catalyst is Pt, the metal wires constituting the first and second wire mesh are made of stainless steel, and the surface of the stainless steel metal wire constituting the first wire mesh is subjected to Ni plating. The method of manufacturing an exhaust emission control device according to any one of claims 3 to 4, wherein the surface of Ni plating is further subjected to Cr plating and then the surface of Ni plating or Cr plating is subjected to Pt coating.

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