Patent Application
20090235652
1. Field of the Invention
The present invention relates to an exhaust gas purification apparatus.
2. Discussion of the Background
Conventionally, exhaust gas discharged from an internal combustion engine such as a diesel engine contains particulate matter (also referred to as PM hereafter), and in recent years, the harm that the PM causes to the environment and the human body has become a problem. The exhaust gas also contains harmful gas components such as CO, HC and NOx, and the harm that these harmful gas components cause to the environment and the human body has become a further problem.
Therefore, various exhaust gas purification apparatuses for capturing PM contained in exhaust gas and converting harmful gas components such as CO, HC and NOx contained in exhaust gas have been proposed. The exhaust gas purification apparatus of this kind includes a honeycomb structure formed from a porous ceramic such as cordierite and silicon carbide; a casing in which the honeycomb structure is disposed and which is connected to an introduction pipe connected to an internal combustion engine, through which exhaust gas is introduced, and an exhaust pipe connected to the outside, through which the exhaust gas is discharged; and a holding sealing material, which is disposed between the honeycomb structure and the casing to prevent a gap from being formed between the honeycomb structure and the casing, and which holds the honeycomb structure.
However, in the exhaust gas purification apparatus of this kind, pressure (also referred to as exhaust gas pressure hereafter) is applied to the honeycomb structure as the exhaust gas flows from the introduction pipe side to the exhaust pipe side, and as a result, the entire honeycomb structure may move to the exhaust pipe side from its initial disposal position. In such a case, the honeycomb structure collides with the casing such that the honeycomb structure is damaged, leading to a reduction in PM capture efficiency, a reduction in harmful gas component purification efficiency, an increase in pressure loss, and so on. As a result, the purification performance of the honeycomb structure decreases dramatically.
In response to this problem, an exhaust gas purification apparatus that prevents collisions between the honeycomb structure and the casing has been proposed (JP 08-281034 A, JP 2000-45759 A).
JP 08-281034 A discloses an exhaust gas purification apparatus in which a peripheral portion of an end face of a honeycomb structure is fixed by a fixing member disposed in a casing such that the honeycomb structure is held fixedly in the casing.
JP 2000-45759 A discloses an exhaust gas purification apparatus in which an end portion of the casing is formed in a cone shape and the cone-shaped end portion of the casing is brought into contact with the peripheral portion of the end face of the honeycomb structure such that the honeycomb structure is held fixedly in the casing.
The contents of JP 08-281034 A and JP 2000-45759 A are incorporated herein by reference in their entirety.
According to one aspect of the present invention, an exhaust gas purification apparatus includes at least one honeycomb structure, a casing housing, a holding sealing material, and a stopping member. The at least one honeycomb structure includes a plurality of honeycomb fired bodies which are bound together via an adhesive layer and each of which includes cell walls extending along a longitudinal direction of the at least one honeycomb structure to define cells. The at least one honeycomb structure includes an introduction end face and an exhaust end face opposite to the introduction end face in the longitudinal direction. The casing houses the at least one honeycomb structure and includes an introduction casing end face and an exhaust casing end face. The introduction casing end face is connected to an introduction pipe to introduce an exhaust gas, and the exhaust casing end face is connected to an exhaust pipe to discharge the exhaust gas. The introduction end face of the at least one honeycomb structure faces the introduction casing end face, and the exhaust end face of the at least one honeycomb structure faces the exhaust casing end face. The holding sealing material is disposed between the at least one honeycomb structure and the casing to hold the at least one honeycomb structure. The stopping member has a plurality of openings and disposed in the casing. The stopping member covers the exhaust end face of the at least one honeycomb structure.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.
Embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.
An exhaust gas purification apparatus described according to the embodiment of the present invention includes a honeycomb structure formed by binding together a plurality of honeycomb fired bodies, in which a large number of cells separated by cell walls are disposed in parallel in a longitudinal direction, by interposing an adhesive layer; a casing to which an introduction pipe for introducing an exhaust gas and an exhaust pipe for discharging the exhaust gas are connected, the honeycomb structure being disposed in the interior of the casing; a holding sealing material disposed between the honeycomb structure and the casing for holding the honeycomb structure; and a stopping member having a plurality of openings and disposed in the casing, wherein of end faces of the honeycomb structure, at least an end face positioned on the exhaust pipe side is covered by the stopping member.
In the exhaust gas purification apparatus according to the embodiment of the present invention, of the end faces of the honeycomb structure, at least the end face positioned on the exhaust pipe side is covered by the stopping member.
Therefore, even when exhaust gas pressure is applied to the honeycomb structure, it is easy to prevent movement of a honeycomb fired body from the honeycomb structure to the exhaust pipe side. Moreover, even when a honeycomb fired body moves, the moving honeycomb fired body is stopped upon contact with the stopping member.
Hence, displacement and drop of the honeycomb fired bodies are more likely to be prevented.
Note that in this description, the phrase “the exhaust pipe side end face of the aggregated honeycomb structure is covered by the stopping member” means that when seen from the exhaust pipe side, the entire exhaust pipe side end face of the aggregated honeycomb structure overlaps the end face of the stopping member. In this case, the distance (shown by a double-headed arrow C in
Furthermore, in this description, displacement of the honeycomb fired body indicates a case in which a distance from the end face of the aggregated honeycomb structure to the end face of the projecting honeycomb fired body is 5 mm or more.
In comparison with such an exhaust gas purification apparatus of the present embodiment, in the conventional exhaust gas purification apparatus described in JP 08-281034 A, the honeycomb structure seems to be held fixedly in the casing by a holding sealing material and the fixing member, and therefore collisions between the honeycomb structure and the casing seems to be prevented.
In the conventional exhaust gas purification apparatus described in JP 2000-45759 A, the honeycomb structure seems to be held by a holding sealing material and fixed by the contact between the cone-shaped end portion of the casing and the peripheral portion of the end face of the honeycomb structure, and therefore collisions between the honeycomb structure and the casing seems to be prevented.
However, in the conventional exhaust gas purification apparatuses described in JP 08-281034 A and JP 2000-45759 A, the following problem occurs when a honeycomb structure (also referred to as an aggregated honeycomb structure hereafter) formed by binding together a plurality of pillar-shaped honeycomb fired bodies, each of which includes a large number of cells disposed in parallel in a longitudinal direction and separated by cell walls, by interposing an adhesive layer is used as the honeycomb structure.
An aggregated honeycomb structure is manufactured by adhering a plurality of honeycomb fired bodies, each of which is formed by molding a wet mixture into a predetermined shape and then firing the wet mixture, to each other using an adhesive, and then carrying out drying, solidifying, and so on. The strength of the dried and solidified adhesive layer is lower than that of the honeycomb fired body. Therefore, when exhaust gas pressure is applied to the aggregated honeycomb structure, cracks may form in the adhesive layer.
When a regenerating process or the like for removing PM is carried out while the adhesive layer is cracked, the crack may develop due to thermal shock, causing the adhesive layer to break, and as a result, a part of the honeycomb fired bodies bound together by the cracked adhesive layer may be pushed and moved toward the exhaust pipe side from the aggregated honeycomb structure. When the honeycomb fired body moves dramatically (also referred to hereafter as displacement of the honeycomb fired body), a reduction in the purification performance of the aggregated honeycomb structure is more likely to occur. Furthermore, when the moved honeycomb fired body is pushed out of the aggregated honeycomb structure, the honeycomb fired bodies may come off.
As above described, displacement and coming off of the honeycomb fired bodies may occur in the conventional exhaust gas purification apparatuses described in JP 08-281034 A and JP 2000-45759 A.
In the exhaust gas purification apparatus according to the embodiment of the present invention, a fixing member used for fixing the stopping member is desirably disposed in the casing.
In such an exhaust gas purification apparatus, the stopping member is less likely to shift from its initial disposal position.
Hence, even when exhaust gas pressure is applied to the honeycomb structure, movement of a honeycomb fired body from the honeycomb structure to the exhaust pipe side is more likely to be prevented reliably. Moreover, even when a honeycomb fired body moves, the moving honeycomb fired body is stopped reliably upon contact with the stopping member. As a result, displacement and drop of the honeycomb fired bodies is more likely to be prevented efficiently.
In the exhaust gas purification apparatus according to the embodiment of the present invention, the stopping member is desirably joined to the fixing member.
In such an exhaust gas purification apparatus, the stopping member is less likely to shift from its initial position. Accordingly, contact is unlikely to occur between the stopping member and the end face (exhaust pipe side end face) of the honeycomb structure.
Hence, damage such as chips and cracks is more likely to be prevented from occurring on the end face (exhaust pipe side end face) of the honeycomb structure on which damage is particularly likely to occur.
As a result, a reduction in the purification performance of the honeycomb structure is more likely to be prevented.
In the exhaust gas purification apparatus according to the embodiment of the present invention, the stopping member is desirably joined to the casing.
In such an exhaust gas purification apparatus, the stopping member is less likely to shift from its initial disposal position.
Hence, even when exhaust gas pressure is applied to the honeycomb structure, movement of a honeycomb fired body from the honeycomb structure to the exhaust pipe side is more likely to be prevented. Moreover, even when a honeycomb fired body moves, the moving honeycomb fired body is stopped upon contact with the stopping member. As a result, displacement and drop of the honeycomb fired bodies is more likely to be prevented efficiently.
In the exhaust gas purification apparatus according to the embodiment of the present invention, a buffer member is desirably disposed between the honeycomb structure and the stopping member.
In such an exhaust gas purification apparatus, the exhaust pipe side end face of the honeycomb structure contacts the buffer member having a buffering function, and therefore, even when exhaust gas pressure is applied such that the entire honeycomb structure moves from its initial disposal position to the exhaust pipe side, shock such as vibration is unlikely to be applied to the exhaust pipe side end face of the honeycomb structure.
Hence, in the exhaust gas purification apparatus according to the embodiment of the present invention, damage is more likely to be prevented from occurring on the end face (exhaust pipe side end face) of the honeycomb structure on which damage is particularly likely to occur.
As a result, a reduction in the purification performance of the honeycomb structure is more likely to be prevented efficiently.
In the exhaust gas purification apparatus according to the embodiment of the present invention, the honeycomb structure is desirably a honeycomb filter in which one of end portions of each of the cells is sealed.
With such an exhaust gas purification apparatus, it is possible to remove PM contained in the exhaust gas.
In the exhaust gas purification apparatus according to the embodiment of the present invention, a catalyst is desirably supported on the honeycomb filter (honeycomb structure).
In such an exhaust gas purification apparatus, during a regenerating process, it is possible to reduce the activation energy required to burn the PM captured in the honeycomb filter through contact between the PM and the catalyst. As a result, the captured PM is more likely to be burned at a lower temperature. Moreover, by bringing the catalyst into contact with harmful gas components such as CO, HC and NOx contained in the exhaust gas, these harmful gas components contained in the exhaust gas are more likely to be converted.
In the exhaust gas purification apparatus according to the embodiment of the present invention, the honeycomb structure may be a catalyst supporting carrier in which the one of end portions of each of the cells is not sealed, and a catalyst may be supported on the catalyst supporting carrier.
With such an exhaust gas purification apparatus, harmful gas components such as CO, HC and NOx contained in the exhaust gas are more likely to be converted by bringing the catalyst into contact with these harmful gas components contained in the exhaust gas.
In the exhaust gas purification apparatus according to the embodiment of the present invention, it is desirable that a plurality of honeycomb structures are disposed in the casing, and of end faces of each of the honeycomb structures, at least an end face positioned on the exhaust pipe side is desirably covered by the stopping member.
In such an exhaust gas purification apparatus, movement of a part of the honeycomb fired bodies of one honeycomb structure to the exhaust pipe side is more likely to be prevented even when exhaust gas pressure is applied. Moreover, even when a honeycomb fired body moves, the moving honeycomb fired body is stopped upon contact with the stopping member. Hence, a part of the honeycomb fired bodies of the one honeycomb structure is never pushed out to the exhaust pipe side. Accordingly, the honeycomb fired body is unlikely to collide with another honeycomb structure disposed downstream of the one honeycomb structure, and therefore damage to the another honeycomb structure is more likely to be prevented. As a result, a reduction in the purification performance of the another honeycomb structure is more likely to be prevented.
In the exhaust gas purification apparatus according to the embodiment of the present invention, it is desirable that the plurality of honeycomb structures include at least one honeycomb filter and at least one catalyst supporting carrier and the catalyst supporting carrier is disposed further toward the introduction pipe side than the honeycomb filter.
In such an exhaust gas purification apparatus, heat generated when the catalyst supporting carrier converts harmful gas components contained in the exhaust gas is likely to be used easily during PM combustion in the honeycomb filter positioned downstream of the catalyst supporting carrier. Hence, with the exhaust gas purification apparatus according to the embodiment of the present invention, PM contained in the exhaust gas is more likely to be removed extremely efficiently.
In the exhaust gas purification apparatus according to the embodiment of the present invention, a distance between an end face of the honeycomb structure and an end face of the stopping member is desirably less than about 1 mm.
In such an exhaust gas purification apparatus, when exhaust gas pressure is applied such that a part of the honeycomb fired bodies of the honeycomb structure is pushed out to the exhaust pipe side, the pushed-out honeycomb fired body does not project from the end face of the honeycomb structure to the exhaust pipe side by about 1 mm or more.
Hence, with the exhaust gas purification apparatus according to the embodiment of the present invention, a reduction in purification performance due to displacement of the honeycomb fired body is likely to be prevented more efficiently.
A first embodiment serving as an embodiment of the present invention will be described below using the drawings.
Note that in the first embodiment, a honeycomb filter is used as an aggregated honeycomb structure.
As shown in
Further, a distance C (see
A joint portion 60b mainly including metal is provided near the periphery of the stopping member 60, and by welding the joint portion 60b to the casing 30, the stopping member 60 and the casing 30 are joined to each other (in
A case in which exhaust gas passes through the exhaust gas purification apparatus 10 having the configuration described above will be described below using
As shown in
In the exhaust gas purification apparatus 10 of the first embodiment of the present invention, PM contained in the exhaust gas is purified in the manner described above. At the same time, however, pressure generated by the exhaust gas G1 is applied to the honeycomb filter 40.
The honeycomb filter and each member forming the exhaust gas purification apparatus 10 will be described below using the drawings.
First, the honeycomb filter 40 will be described using
As shown in
Further, as shown in
Next, the stopping member, holding sealing material, casing, introduction pipe, and exhaust pipe will be described using
First, the stopping member 60 will be described. As shown in
The size of the opening 60a is sufficiently larger than that of the cells on a perpendicular cross-section to the longitudinal direction of the honeycomb fired body of the honeycomb filter 40.
Further, the joint portion 60b mainly including metal is provided near the periphery of the stopping member 60.
An aperture ratio of the stopping member 60 is preferably at least about 65% and at most about 95%, and more preferably in the range of about 70% to about 90%.
When the aperture ratio is about 65% or more, the exhaust gas tends to pass easily and pressure loss is less likely to be increased.
When the aperture ratio is about 95% or less, on the other hand, strength is more likely to be ensured. As a result, when a honeycomb fired body or the entire honeycomb filter is moved to the exhaust pipe side by the exhaust gas pressure, it may become easier to stop the honeycomb fired body or the entire honeycomb filter reliably.
When the aperture ratio is in the range of about 70% to about 90%, the exhaust gas passes more easily, and therefore pressure loss is more likely to be reduced. Moreover, sufficient strength is more likely to be ensured, and therefore the honeycomb fired body or the entire honeycomb filter is more likely to be stopped more reliably.
Next, the holding sealing material 50 will be described. The holding sealing material 50 shown in
Of the end faces of the holding sealing material 50 that are parallel to the width direction, a projected portion 50a is provided on one end face and a recessed portion 50b is provided on the other end face. The projected portion 50a and the recessed portion 50b are formed to fit together when the holding sealing material 50 is wrapped around the periphery of the honeycomb filter 40, as shown in
Next, the casing 30 will be described. The casing 30 shown in
Finally, the introduction pipe 20a and exhaust pipe 20b will be described.
The introduction pipe 20a mainly includes a metal such as stainless steel, and takes a cylindrical shape. As shown in
If necessary, the other end face of the introduction pipe 20a is connected to the internal combustion engine via an exhaust gas pipe further connected to the introduction pipe 20a.
The exhaust pipe 20b is configured similarly to the introduction pipe 20a, except that the other end face is connected to the outside.
A method for manufacturing the exhaust gas purification apparatus according to the first embodiment of the present invention will now be described.
First, a method for manufacturing the honeycomb filter will be described.
First, silicon carbide powders each having a different average particle diameter are mixed, and an organic binder such as carboxymethyl cellulose and a dispersion medium such as water are added thereto and then kneaded, whereupon a plasticizer such as glycerin, a lubricant such as polyoxyethylene monobutyl ether, a forming auxiliary such as ethylene glycol, and so on are added and kneaded to form a wet mixture. Extrusion molding is then carried out using the wet mixture to manufacture a raw molded body.
Next, the raw molded body is dried and then a paste having a similar composition to the raw molded body described above is filled into a predetermined cell of a ceramic dried body, whereupon drying and degreasing are carried out. Firing is then carried out, and thus a honeycomb fired body of a predetermined size, in which one of end portions of each cell is sealed, is manufactured.
Next, using a heat-resistant adhesive paste containing inorganic fibers such as alumina fibers, inorganic particles such as silicon carbide powder, an inorganic binder such as silica sol, an organic binder such as carboxymethyl cellulose, water, and so on, a large number of the honeycomb fired bodies described above are bound together and then dried, hardened, and cut to manufacture a ceramic block.
Next, inorganic fibers including alumina silicate or the like, inorganic particles such as silicon carbide powder, an inorganic binder such as silica sol, an organic binder such as carboxymethyl cellulose, water, and so on are kneaded to prepare a sealing material paste (a coat layer paste).
Using the sealing material paste (coat layer paste) described above, a sealing material layer (coat layer) is formed on the periphery of the ceramic block, whereupon the sealing material layer (coat layer) is dried, resulting in manufacturing of a honeycomb filter taking the form of a round pillar-shaped aggregated honeycomb structure, in which one of end portions of each cell is sealed.
Next, a mat material mainly including inorganic fibers such as alumina fibers is cut to manufacture a holding sealing material having a substantially rectangular shape of a predetermined size, in which, of the end faces thereof that are parallel to the width direction, a projected portion is formed on one end face and a recessed portion having a shape that fits the projected portion is formed on the other end face.
Further, wire mesh is manufactured by cutting wire mesh having a predetermined mesh, wire diameter, and aperture ratio into a disc shape such that the diameter of an end face thereof is substantially identical to the inner diameter of the casing. Next, a joint member having an outer diameter that is substantially identical to the inner diameter of the casing and an inner diameter that is substantially identical to the diameter of the end face of the honeycomb filter is manufactured by carrying out a punching process on a disc-shaped metal plate mainly including a metal such as stainless steel. This joint member is placed over the disc-shaped wire mesh and then welded to the wire mesh, whereby a stopping member formed with a joint portion is manufactured.
A method for manufacturing an exhaust gas purification apparatus using the honeycomb filter and the various members described above will now be described.
First, the holding sealing material is wrapped around the periphery of the honeycomb filter such that the recessed portion and projected portion of the holding sealing material are fitted together. Next, a first casing divided body is disposed such that the inner face thereof is oriented upward, and the honeycomb filter wrapped in the holding sealing material is disposed on the inner face of the first casing divided body. Further, the stopping member is disposed adjacent to one end face of the honeycomb filter. At this time, the stopping member is disposed such that, of the end faces thereof, the end face not formed with the joint portion is disposed on the honeycomb filter side.
Thus, the respective lower halves of the honeycomb filter and the stopping member are disposed on the first casing divided body.
Next, a second casing divided body is placed on the respective upper halves of the honeycomb filter and the stopping member disposed on the first casing divided body, whereupon the casing divided bodies are compressed from a vertical direction. Once the casing divided bodies come into contact, the casing divided bodies are joined by welding to form the casing. Note that a joining device such as a screw or a predetermined fitting may be used instead of welding.
Next, the casing is joined to the joint portion of the stopping member by welding. Note that a joining device such as a screw or a predetermined fitting may be used instead of welding.
Next, the exhaust pipe is connected to the end portion of the casing that is positioned on the stopping member disposal side by welding. Similarly, the introduction pipe is connected to the end portion of the casing on the opposite side to the exhaust pipe connection side.
Through the processes described above, the exhaust gas purification apparatus according to the first embodiment of the present invention is manufactured.
Effects of the exhaust gas purification apparatus according to the first embodiment of the present invention will be cited below.
(1) In the exhaust gas purification apparatus according to the first embodiment of the present invention, the exhaust pipe side end face of the honeycomb filter is covered by the stopping member.
Therefore, in a case where the exhaust pipe side end face of the honeycomb filter and the end face of the stopping member come into contact, it is easier to prevent a honeycomb fired body from moving to the exhaust pipe side from the honeycomb filter even when exhaust gas pressure is applied to the honeycomb filter.
Further, in a case where the exhaust pipe side end face of the honeycomb filter and the end face of the stopping member are disposed at a remove, the honeycomb fired body is stopped upon contact with the stopping member even when a honeycomb fired body moves.
Hence, in the exhaust gas purification apparatus according to the first embodiment of the present invention, the honeycomb fired body is not displaced from the honeycomb filter to the exhaust pipe side. Moreover, the honeycomb fired body is not pushed out from the honeycomb filter, and therefore drop of the honeycomb fired body is more likely to be prevented.
Note that when exhaust gas pressure is applied to the honeycomb filter, the entire honeycomb filter may move from its initial disposal position to the exhaust pipe side. As described above, however, the exhaust pipe side end face of the honeycomb filter is covered by the stopping member. Therefore, in a case where the exhaust pipe side end face of the honeycomb filter and the end face of the stopping member are disposed in contact with each other, the honeycomb filter is more likely to be reliably prevented from moving to the exhaust pipe side.
Furthermore, in a case where the exhaust pipe side end face of the honeycomb filter and the end face of the stopping member are disposed at a remove, the exhaust pipe side end face of the moving honeycomb filter comes into contact with the stopping member such that the entire honeycomb filter is stopped even when the entire honeycomb filter moves to the exhaust pipe side. Thus, collisions between the honeycomb filter and the casing are more likely to be prevented, and as a result, damage to the entire honeycomb filter is more likely to be prevented.
(2) In the exhaust gas purification apparatus according to the first embodiment of the present invention, the stopping member is joined to a predetermined position in the casing such that the stopping member is unlikely to shift from its initial disposal position. Therefore, even when exhaust gas pressure is applied to the honeycomb filter, a honeycomb fired body is more likely to be prevented from moving from the honeycomb filter to the exhaust pipe side. Moreover, even when a honeycomb fired body moves, the moving honeycomb fired body is stopped upon contact with the stopping member. Hence, displacement and drop of the honeycomb fired bodies are more likely to be prevented efficiently.
(3) In the exhaust gas purification apparatus according to the first embodiment of the present invention, the distance between the end face of the honeycomb filter and the end face of the stopping member is less than about 1 mm, and therefore a pushed-out honeycomb fired body does not project from the end face of the honeycomb filter toward the exhaust pipe side by about 1 mm or more.
Hence, a reduction in the purification performance caused by displacement of the honeycomb fired body is more likely to be prevented even more efficiently.
Specific examples of the first embodiment of the present invention are illustrated below. However, the first embodiment is not limited to these examples alone.
An amount of 60% by weight of α-type silicon carbide powder having an average particle diameter of 11 μm and 40% by weight of α-type silicon carbide powder having an average particle diameter of 0.5 μm were mixed. To 100 parts by weight of the obtained mixture were added 5 parts by weight of an organic binder (carboxymethyl cellulose) and 10 parts by weight of water serving as a dispersion medium and then kneaded. Small amounts of a plasticizer (glycerin) and a lubricant (UNILUB, manufactured by NOF Corp.) were then added and kneaded to form a wet mixture, whereupon extrusion molding was carried out to manufacture a raw molded body.
Next, the raw molded body was dried using a microwave drying apparatus or the like to form a ceramic dried body, whereupon a paste having a similar composition to the raw molded body was filled into a predetermined cell. Drying was then carried out again using the drying apparatus, whereupon degreasing was carried out at 400° C. and firing was carried out for three hours at 2200° C. in a normal-pressure argon atmosphere. As a result, a honeycomb fired body having a porosity of 42%, an average pore diameter of 9 μm, a size of 34.3 mm×34.3 mm×150 mm, a cell density of 23.3 pcs/cm2, and a cell wall thickness of 0.4 mm was manufactured.
A large number of the honeycomb fired bodies were bound using a heat-resistant adhesive paste containing 30% by weight of alumina fibers having an average fiber length of 20 μm, 21% by weight of silicon carbide powder having an average particle diameter of 0.6 μm, 15% by weight of silica sol (SiO2 solids content: 30% by weight), 5.6% by weight of carboxymethyl cellulose, and 28.4% by weight of water. The bound honeycomb fired bodies were dried at 120° C. and then cut using a diamond cutter to manufacture a round pillar-shaped ceramic block.
Next, 23.3% by weight of ceramic fibers (average fiber length: 50 μm) including alumina silicate, 30.2% by weight of silicon carbide powder having an average particle diameter of 0.3 μm, 7% by weight of silica sol (SiO2 solids content: 30% by weight), 0.5% by weight of carboxymethyl cellulose, and 39% by weight of water were kneaded together to prepare a sealing material paste.
Next, a sealing material layer having a thickness of 0.2 mm was formed on the periphery of the ceramic block using the sealing material paste. The sealing material layer was then dried at 12° C. to manufacture a honeycomb filter taking the form of a round pillar-shaped aggregated honeycomb structure of diameter 143.8 mm×length 150 mm, in which one of end portions of each cell was sealed.
A non-expansive alumina fiber mat (MAFTEC, manufactured by Mitsubishi Chemical Corp.) was cut to manufacture a holding sealing material at a size of length 452 mm×width 150 mm×thickness 8 mm, in which a projected portion was formed on one of the end faces parallel to the width direction and a recessed portion shaped to fit into the projected portion was formed in a part of the other end portion.
Disc-shaped wire mesh having a diameter of 152 mm was manufactured by cutting 16-mesh (the “mesh” represents the number of openings in 1 inch (25.4 mm)) plain weave wire mesh having a wire diameter of 0.2 mm and an aperture ratio of 76.6%. Further, a joint member of outer diameter 152 mm (inner diameter 143.8 mm)×thickness 4 mm was manufactured by carrying out a punching process on a disc-shaped metal plate mainly including a metal such as stainless steel. The joint member was then placed over the disc-shaped wire mesh and welded to the wire mesh, whereby a stopping member formed with a joint portion was manufactured.
The holding sealing material manufactured in Process (2) was wrapped around the periphery of the honeycomb filter manufactured in Process (1) such that the recessed portion and projected portion fitted together. Next, a first stainless steel casing divided body having a U-shaped cross-section and including an inner face and an outer face was prepared by dividing a cylindrical body mainly including stainless steel or the like parallel to the longitudinal direction, and the first casing divided body was disposed such that the inner face of the first casing divided body was oriented upward. In this state, the honeycomb filter wrapped in the holding sealing material was disposed on the inner face of the first casing divided body.
Next, the stopping member manufactured in Process (3) was disposed adjacent to one end face of the honeycomb filter. At this time, the stopping member was disposed such that, of the end faces of the stopping member, the end face not formed with the joint portion was provided on the honeycomb filter side.
Next, a second casing divided body was placed on the first casing divided body provided with the honeycomb filter and the stopping member, whereupon the casing divided bodies were compressed from a vertical direction. When the casing divided bodies came into contact, the casing divided bodies were joined by welding to form a casing. Further, the casing was joined to the joint portion of the stopping member by welding.
Next, an exhaust pipe including stainless steel and formed in a tapered shape was disposed on the end portion of the casing on the stopping member disposal side and connected to the end portion of the casing by welding. Similarly, an introduction pipe shaped identically to the exhaust pipe was connected to the end portion of the casing on the opposite side to the exhaust pipe connection side.
Through the processes described above, the exhaust gas purification apparatus according to Example 1 was manufactured.
Note that in the exhaust gas purification apparatus manufactured in this manner, the distance between the exhaust pipe side end face of the honeycomb filter and the end face of the stopping member was 0.5 mm.
In the exhaust gas purification apparatus of Example 1, the exhaust pipe side end face of the honeycomb filter is covered by the stopping member and the stopping member is joined to a predetermined position in the casing, and therefore the stopping member is unlikely to shift from its initial disposal position. It may therefore be assumed that even when exhaust gas pressure is applied, displacement and drop of the honeycomb fired bodies can be prevented efficiently.
Furthermore, the distance between the end face of the honeycomb filter and the end face of the stopping member is less than about 1 mm. It may therefore be assumed that a reduction in the purification performance of the honeycomb filter can be prevented efficiently.
A second embodiment serving as an embodiment of the present invention will be described below with reference to
In
Note that in the second embodiment of the present invention, a honeycomb filter is used as an aggregated honeycomb structure.
As shown in
Note that the honeycomb filter 140, holding sealing material 150, buffer member 170, stopping member 160, and fixing member 180 disposed in the casing will occasionally be referred to together as a purification portion 190.
Next, the interior configuration of the exhaust gas purification apparatus 100 according to the second embodiment of the present invention will be described.
In the exhaust gas purification apparatus 100, a distance (indicated by a double-headed arrow E in
Further, the stopping member 160 and the fixing member 180 are joined to each other by welding a joint portion 160b of the stopping member 160 to the fixing member 180 (in
Further, the exhaust pipe 120b is formed to taper toward an end face on a side connected to the outside, and a part of a peripheral portion of the fixing member 180 contacts the exhaust pipe 120b. Thus, the fixing member 180 does not move from its initial disposal position to the exhaust pipe 120b side.
Furthermore, in the purification portion 190 disposed in the casing 130, the buffer member 170 is disposed to contact the entire exhaust pipe side end face 140a of the honeycomb filter 140 (honeycomb fired body 141), as shown in
A case in which exhaust gas is passed through the exhaust gas purification apparatus 100 of the second embodiment of the present invention, configured as described above, will now be described.
Exhaust gas G2 introduced through the introduction pipe 120a flows into one cell 145 that opens onto an end face 140b of the honeycomb filter 140 positioned on the introduction pipe side, and then passes through a cell wall 146 separating the cell 145. At this time, PM contained in the exhaust gas is captured in the interior of the cell wall 146 such that the exhaust gas is purified. The purified exhaust gas then flows out from another cell 145 that opens onto the exhaust pipe side end face 140a. The effluent exhaust gas then passes through the buffer member 170 and an opening 160a in the stopping member 160 to be discharged to the outside through the exhaust pipe 120b.
During this exhaust gas purification process, pressure is applied to the honeycomb filter 140 by the exhaust gas G2.
Each member of the exhaust gas purification apparatus 100 described above will now be described in detail with reference to
The respective configurations of the honeycomb filter 140, casing 130, holding sealing material 150, stopping member 160, introduction pipe 120a, and exhaust pipe 120b shown in
First, the buffer member 170 will be described. As shown in
Next, the fixing member 180 will be described. As shown in
A method for manufacturing the exhaust gas purification apparatus according to the second embodiment of the present invention will now be described.
First, the honeycomb filter, casing, holding sealing material, stopping member, introduction pipe, and exhaust pipe are manufactured in a similar manner to the method for manufacturing the exhaust gas purification apparatus according to the first embodiment of the present invention.
Next, a mat material produced by a sheet-forming process of inorganic fibers mainly including alumina or the like is processed such that the diameter of an end face of the mat material is substantially identical to the inner diameter of the casing and the thickness is less than about 1 mm, whereby a buffer member including a sheet-form fiber body is manufactured.
Next, a ring-shaped fixing member in which the outer diameter of an end face thereof is substantially identical to the inner diameter of the casing and the inner diameter of the end face is slightly larger than the diameter of the end face of the honeycomb filter is manufactured by carrying out a punching process on a disc-shaped metal plate mainly including a metal such as stainless steel.
A method for manufacturing an exhaust gas purification apparatus using the honeycomb filter and the various members described above will now be described.
First, the holding sealing material is wrapped around the periphery of the honeycomb filter such that the recessed portion and projected portion of the holding sealing material are fitted together. Next, the first casing divided body is disposed such that the inner face thereof is oriented upward, and the honeycomb filter wrapped in the holding sealing material is disposed on the inner face of the first casing divided body. Further, the buffer member is disposed adjacent to one end face of the honeycomb filter. Next, the fixing member, which is joined to the stopping member by carrying out welding at the joint portion, is disposed such that the stopping member is adjacent to the buffer member.
Next, the second casing divided body is placed on the first casing divided body in which the honeycomb filter and the respective members described above are disposed, whereupon the casing divided bodies are compressed from a vertical direction. Once the casing divided bodies have come into contact, the casing divided bodies are joined by welding to form the casing. Note that a joining device such as a screw or a predetermined fitting may be used instead of welding.
Next, the exhaust pipe is connected to the end portion of the casing that is positioned on the stopping member disposal side by welding. Similarly, the introduction pipe is connected to the end portion of the casing on the opposite side to the exhaust pipe connection side.
Through the processes described above, the exhaust gas purification apparatus according to the second embodiment of the present invention is manufactured.
The effects (1) and (3) described in the first embodiment of the present invention are exhibited similarly in the second embodiment of the present invention.
The second embodiment also exhibits the following effects.
(4) In the exhaust gas purification apparatus according to the second embodiment of the present invention, the fixing member for fixing the stopping member is disposed in a predetermined position in the casing. Therefore, the stopping member is unlikely to shift from its initial disposal position.
Hence, even when exhaust gas pressure is applied to the honeycomb filter, movement of a honeycomb fired body from the honeycomb filter to the exhaust pipe side is more likely to be prevented reliably. Furthermore, even if a honeycomb fired body moves, the moving honeycomb fired body is stopped reliably upon contact with the stopping member. Therefore, displacement and drop of the honeycomb fired bodies are more likely to be prevented efficiently.
(5) In the exhaust gas purification apparatus according to the second embodiment of the present invention, the stopping member is joined to the fixing member.
Therefore, the stopping member is unlikely to be displaced from its initial disposal position, and contact between the stopping member and the honeycomb fired body is unlikely to occur.
Hence, damage such as chips and cracks is more likely to be prevented from occurring on the end face (exhaust pipe side end face) of the honeycomb filter on which damage is particularly likely to occur.
As a result, a reduction in the purification performance of the honeycomb filter is more likely to be prevented.
(6) In the exhaust gas purification apparatus according to the second embodiment of the present invention, the exhaust pipe side end face of the honeycomb filter contacts the buffer member having a buffering function, and therefore, even when the entire honeycomb filter moves from its initial disposal position to the exhaust pipe side due to exhaust gas pressure, shock such as vibration is unlikely to be applied to the exhaust pipe side end face of the honeycomb filter. Hence, damage is more likely to be prevented from occurring on the end face (exhaust pipe side end face) of the honeycomb filter on which damage is particularly likely to occur.
As a result, a reduction in the purification performance of the honeycomb filter is more likely to be prevented efficiently.
The honeycomb filter was manufactured in a similar manner to (1) of Example 1.
The holding sealing material was manufactured in a similar manner to (2) of Example 1.
The stopping member was manufactured in a similar manner to (3) of Example 1.
A mat material produced by a sheet-forming process of non-expansive alumina fibers was processed to a size of diameter 152 mm×thickness 0.5 mm to manufacture a buffer member including a sheet-form fiber body.
A ring-shaped fixing member was manufactured to a size of outer diameter 152 mm (inner diameter 142 mm)×thickness 4 mm by carrying out a punching process on a disc-shaped stainless steel metal plate having a size of diameter 152 mm×thickness 4 mm.
The honeycomb filter wrapped in the holding sealing material was disposed on the inner face of the first casing divided body in a similar manner to Process (4) of Example 1.
Next, the buffer member manufactured in Process (4) was disposed on the inner face of the first casing divided body adjacent to one end face of the honeycomb filter. Next, the fixing member was joined to the joint portion of the stopping member, whereupon the fixing member was disposed on the inner face of the first casing divided body such that the stopping member was adjacent to the buffer member.
The second casing divided body was then placed on the first casing divided body provided with the honeycomb filter and stopping member, whereupon the casing divided bodies were compressed from a vertical direction. When the casing divided bodies came into contact, the casing divided bodies were joined by welding to form a casing.
Next, an exhaust pipe including stainless steel and formed in a tapered shape was disposed on the end portion of the casing on the stopping member disposal side, and connected to the end portion of the casing by welding. Similarly, an introduction pipe shaped identically to the exhaust pipe was connected to the end portion of the casing on the opposite side to the exhaust pipe connection side.
Through the processes described above, the exhaust gas purification apparatus according to the second embodiment was manufactured.
Note that in the exhaust gas purification apparatus manufactured in this manner, the distance between the exhaust pipe side end face of the honeycomb filter and the end face of the stopping member was 0.5 mm.
Further, the exhaust pipe was formed in a tapered form, and the fixing member joined to the stopping member contacted a part of the exhaust pipe.
In the exhaust gas purification apparatus according to Example 2, the exhaust pipe side end face of the honeycomb filter is covered by the stopping member. It may therefore be assumed that even when exhaust gas pressure is applied, displacement and drop of the honeycomb fired bodies can be prevented.
Further, the fixing member for fixing the stopping member is disposed in a predetermined position within the casing, and in addition, the stopping member is joined to the fixing member. It may therefore be assumed that the stopping member is unlikely to shift from its initial disposal position, and that contact between the stopping member and the honeycomb structure due to movement of the stopping member is unlikely to occur.
Moreover, the distance between the end face of the honeycomb filter and the end face of the stopping member is less than about 1 mm. It may therefore be assumed that a reduction in the purification performance of the honeycomb filter can be prevented efficiently.
Next, a third embodiment serving as an embodiment of the present invention will be described.
In the third embodiment of the present invention, the stopping member according to the exhaust gas purification apparatus of the second embodiment of the present invention is not joined to the fixing member.
The effects (1) and (3) described in the first embodiment of the present invention and the effects (4) and (6) described in the second embodiment of the present invention are exhibited similarly in the third embodiment.
Next, a fourth embodiment serving as an embodiment of the present invention will be described using the drawings.
In the fourth embodiment of the present invention, the fixing member according to the exhaust gas purification apparatus of the second embodiment of the present invention is formed from a plurality of fittings formed mainly by a metal such as stainless steel. More specifically, as shown in
Further, the fittings are joined to a stopping member (not shown) by welding.
The effects (1) and (3) described in the first embodiment of the present invention and the effects (4) to (6) described in the second embodiment of the present invention are exhibited similarly in the fourth embodiment of the present invention.
Next, a fifth embodiment serving as an embodiment of the present invention will be described.
In the fifth embodiment of the present invention, a catalyst made of platinum or the like is supported on the honeycomb filter according to the exhaust gas purification apparatus of the first embodiment of the present invention. Note that methods for supporting a catalyst on the honeycomb filter include a method for immersing the honeycomb filter in a diamine dinitro platinum nitric acid ([Pt(NH3)2(NO2)2]HNO3) solution or the like and then heating the honeycomb filter, for example.
The effects (1), (2) and (3) described in the first embodiment of the present invention are exhibited similarly in the fifth embodiment of the present invention.
The fifth embodiment also exhibits the following effect.
(7) In the exhaust gas purification apparatus according to the fifth embodiment of the present invention, a honeycomb filter with a catalyst supported thereon is disposed in the casing.
Hence, by causing the PM captured in the honeycomb filter to contact the catalyst, the captured PM is more likely to be burned at lower temperatures. Therefore, in the exhaust gas purification apparatus according to the fifth embodiment of the present invention, PM contained in the exhaust gas is more likely to be removed efficiently.
Moreover, by causing the harmful gas components contained in the exhaust gas to contact the catalyst, the harmful gas components contained in the exhaust gas are more likely to be converted.
A sixth embodiment serving as an embodiment of the present invention will now be described.
In the sixth embodiment of the present invention, a casing is provided with a purification portion formed by a catalyst supporting carrier in which the honeycomb filter according to the exhaust gas purification apparatus of the second embodiment of the present invention is formed such that one of the end portions of each of the cells is not sealed, a holding sealing member disposed between the catalyst supporting carrier and the casing, a buffer member disposed on the exhaust pipe side end face of the catalyst supporting carrier, a stopping member disposed adjacent to the buffer member, and a fixing member disposed adjacent to the stopping member and joined to the casing. Further, a catalyst is supported on the catalyst supporting carrier.
A method for manufacturing the catalyst supporting carrier according to the exhaust gas purification apparatus of the sixth embodiment of the present invention will now be described.
First, inorganic particles such as alumina or silica particles, inorganic fibers such as alumina or silica fibers, and an inorganic binder such as silica sol are mixed to prepare a wet mixture. As necessary and in accordance with formability, an organic binder such as carboxymethyl cellulose, a dispersion medium such as water, a lubricant such as polyoxyethylene monobutyl ether, and a forming auxiliary such as ethylene glycol are appropriately added thereto. Extrusion molding is then carried out using the prepared wet mixture to manufacture a raw molded body. The raw molded body is then dried to manufacture a ceramic dried body.
An aggregated honeycomb structure is then manufactured using a similar method to the method for manufacturing the honeycomb filter according to the exhaust gas purification apparatus of the first embodiment of the present invention, except that predetermined cells of the ceramic dried body are not sealed and the firing temperature is between at least about 500° C. and at most about 1200° C.
The obtained aggregated honeycomb structure forms a catalyst supporting carrier in which one of the end portions of each of the cells is not sealed.
Next, the catalyst supporting carrier is caused to support a catalyst using an identical method to the method for causing the honeycomb filter according to the exhaust gas purification apparatus of the fifth embodiment of the present invention to support a catalyst. Through the processes described above, the catalyst supporting carrier with a catalyst supported thereon is manufactured.
Note that an identical catalyst to the catalyst described in the fifth embodiment of the present invention may be used as the catalyst of the sixth embodiment of the present invention.
Effects of the exhaust gas purification apparatus according to the sixth embodiment of the present invention will be listed below.
(8) In the exhaust gas purification apparatus according to the sixth embodiment of the present invention, the catalyst supporting carrier is disposed in the casing, with one of the end portions of each of the cells in the aggregated honeycomb structure not being sealed, and a catalyst is supported on the catalyst supporting carrier.
Hence, the exhaust gas purification apparatus according to the sixth embodiment of the present invention is more likely to be capable of converting harmful gas components contained in the exhaust gas.
(9) Furthermore, for similar reasons to those described in the effects (1) to (3) of the first embodiment of the present invention, the exhaust gas purification apparatus according to the sixth embodiment of the present invention is more likely to maintain high levels of PM capture efficiency and harmful gas component conversion efficiency over a long time period.
Next, the interior configuration of an exhaust gas purification apparatus according to a seventh embodiment serving as an embodiment of the present invention will be described with reference to
As shown in
The interior configuration of the exhaust gas purification apparatus 300 according to the seventh embodiment of the present invention will now be described using the drawings.
As shown in
Further, the fixing member 380 is joined to the casing 330 by a screw, a predetermined fitting, or the like.
Meanwhile, the second purification portion 190, which has an identical configuration to the purification portion according to the exhaust gas purification apparatus of the second embodiment except that a buffer member is not provided and the stopping member is not joined to the fixing member, is disposed on the exhaust pipe 320b side of the casing 330. More specifically, a honeycomb filter 140, a holding sealing material 150 disposed between the honeycomb filter 140 and the casing 330, a stopping member 160 disposed on an exhaust pipe side end face 140a of the honeycomb filter 140, and a fixing member 180 disposed adjacent to the stopping member 160 are provided in the second purification portion 190.
Further, the fixing member 180 is joined to the casing 330 by a screw, a predetermined fitting, or the like.
In the exhaust gas purification apparatus 300 of the seventh embodiment, having the configuration described above, exhaust gas (in
During this exhaust gas purification process, pressure is applied to the catalyst supporting carrier 340 and the honeycomb filter 140 by the exhaust gas G3.
A method for manufacturing the exhaust gas purification apparatus according to the seventh embodiment of the present invention will now be described.
First, a catalyst supporting carrier manufactured using a similar method to the method for manufacturing the catalyst supporting carrier according to the exhaust gas purification apparatus of the sixth embodiment of the present invention and a honeycomb filter manufactured using a similar method to the method for manufacturing the honeycomb filter according to the exhaust gas purification apparatus of the first embodiment of the present invention are prepared.
Next, the first purification portion is disposed on the inner face of a first casing divided body in a similar manner to the second embodiment, except that the buffer member is not used and the fixing member and stopping member are not fixed.
Next, the second purification portion is disposed adjacent to the first purification portion in a similar manner to the second embodiment, except that the buffer member is not used and the fixing member and stopping member are not fixed. In this case, the second purification portion is disposed such that an end face of the catalyst supporting carrier of the first purification portion on the side where the various members are disposed and an end face of the honeycomb filter of the second purification portion on the side where the various members are disposed are oriented in an identical direction.
Next, a second casing divided body is placed on the casing divided body provided with the catalyst supporting carrier, the honeycomb filter, and the various members, whereupon the casing divided bodies are compressed from a vertical direction. Once the casing divided bodies have come into contact, the casing divided bodies are joined by welding to form the casing.
Note that a joining device such as a screw or a predetermined fitting may be used instead of welding.
Next, the fixing member of the first purification portion and the fixing member of the second purification portion are joined respectively to the casing using a screw, a predetermined fitting, or the like.
Finally, the exhaust gas purification apparatus according to the seventh embodiment of the present invention is manufactured by carrying out a similar connection process to that of the method for manufacturing the exhaust gas purification apparatus according to the second embodiment of the present invention.
In the exhaust gas purification apparatus according to the seventh embodiment manufactured in this manner, the first purification portion (catalyst supporting carrier) is positioned on the introduction pipe side. Further, the second purification portion (honeycomb filter) is positioned on the exhaust pipe side, or in other words downstream of the catalyst supporting carrier.
Effects of the exhaust gas purification apparatus according to the seventh embodiment of the present invention will be listed below.
In the exhaust gas purification apparatus according to the seventh embodiment of the present invention, a purification portion having an identical configuration to the purification portion of the sixth embodiment, except that the buffer member is not provided and the stopping member and fixing member are not joined, is used as the first purification portion, and therefore the effects (8) and (9) described in the sixth embodiment are exhibited.
Further, a purification portion having an identical configuration to the purification portion of the second embodiment of the present invention, except that the buffer member is not provided and the stopping member and fixing member are not joined, is used as the second purification portion, and therefore the effect (4) described in the second embodiment of the present invention are exhibited.
Moreover, the following effects can be exhibited.
(10) In the exhaust gas purification apparatus according to the seventh embodiment of the present invention, from among the end faces of the catalyst supporting carrier of the first purification portion and the honeycomb filter of the second purification portion, the end faces positioned on the respective exhaust pipe sides are covered by the stopping members.
Hence, a part of the honeycomb fired bodies of the catalyst supporting carrier is not pushed out to the exhaust pipe side when exhaust gas pressure is applied. As a result, the honeycomb fired bodies are unlikely to collide with the honeycomb filter disposed downstream of the catalyst supporting carrier, and damage to the entire honeycomb filter is more likely to be prevented.
Thus, a reduction in the purification performance of the honeycomb filter is more likely to be prevented.
(11) In the exhaust gas purification apparatus according to the seventh embodiment of the present invention, the catalyst supporting carrier is disposed further toward the introduction pipe side than the honeycomb filter.
Therefore, heat generated when the catalyst supporting carrier converts harmful gas components contained in the exhaust gas can be used easily during PM combustion in the honeycomb filter positioned downstream of the catalyst supporting carrier. As a result, PM contained in the exhaust gas is more likely to be removed extremely efficiently.
The stopping member of the exhaust gas purification apparatus according to the embodiment of the present invention is preferably formed by a material that is unlikely to be eroded by a flow of exhaust gas.
Specifically, this material is not limited to the above-described stainless steel, and includes carbon steel, titanium, iron, aluminum, and so on. When the stopping member includes carbon steel, nickel plating is preferably carried out on the surface of the stopping member.
When a stopping member including wire mesh is used as the stopping member, the type of the wire mesh is not limited to the above-described plain weave wire mesh, and instead, twill weave wire mesh, crimped wire mesh, lock-crimped wire mesh, ton-cap weave wire mesh, ty-rod weave wire mesh, and so on, for example, may be used.
The stopping member is not limited to the above-described wire mesh, and may be a punching metal or the like formed by carrying out a punching process on a metal plate, for example, to form openings (round holes) of a predetermined size over substantially the entire end face.
Further, the openings formed in the punching metal are not limited to the above-described round holes, and may be square holes, hexagonal holes, rectangular holes, elongated round holes, rhombic holes, cross holes, combination of round holes and cross holes, and so on. Moreover, the openings are not limited to the above-described straight arrangement, and may be formed in an about 60° staggered arrangement, an about 45° staggered arrangement, and so on.
There are no particular limitations on the shape of the fixing member of the exhaust gas purification apparatus according to the embodiment of the present invention, and instead of the above-described ring shape, an L shape or the like may be used. In this case, a plurality of fixing members are preferably disposed in the casing so that the stopping member is more likely to be fixed more rigidly.
There are no particular limitations on the materials of the casing, fixing member and introduction pipe of the exhaust gas purification apparatus according to the embodiment of the present invention, and instead of the above-described stainless steel, metals such as aluminum and iron, for example, may be used.
The casing of the exhaust gas purification apparatus according to the embodiment of the present invention is not limited to a cylindrical shape, and may take any tubular shape, such as an elliptical shape, a triangular shape, a hexagonal shape, an octagonal shape, or a dodecagonal shape, when seen from above.
Further, the cylindrical casing may be a cylindrical casing that is divided into a plurality of pieces along the longitudinal direction (i.e. a clam shell-type casing) or a cylindrical casing having a C-shaped or U-shaped cross-section in which a slit (opening portion) extending in the longitudinal direction is formed in only one location.
The shape of the stopping member, and the shape of the buffer member and fixing member provided as necessary, may be modified appropriately in accordance with the shape of the casing.
The main component of the material of the honeycomb filter is not limited to silicon carbide, and may be another ceramic raw material, for example a nitride ceramic such as aluminum nitride, silicon nitride, boron nitride, or titanium nitride, a carbide ceramic such as zirconium carbide, titanium carbide, tantalum carbide, or tungsten carbide, a complex of a metal and nitride ceramic, a complex of a metal and carbide ceramic, and the like.
Further, a ceramic raw material such as a silicon-containing ceramic, in which metal silicon is mixed with the above-described ceramics, and a ceramic joined by silicon or a silicate compound may also be used as the material of the honeycomb filter.
The inorganic particles included in the material of the catalyst supporting carrier are not limited to the above-described inorganic particles including alumina or silica, and may be inorganic particles including zirconia, titania, ceria, mullite, zeolite, and so on. These inorganic particles may be used singly or in combinations of two or more kinds. Of these kinds, inorganic particles including alumina and ceria are particularly preferable.
The inorganic fibers included in the material of the catalyst supporting carrier is not limited to the above-described inorganic fibers including alumina or silica, and may be inorganic fibers or whiskers including silicon carbide, silica-alumina, glass, potassium titanate, aluminum borate, and so on. These may be used singly or in combinations of two or more kinds. Of the above-described inorganic fibers, inorganic fibers including aluminum borate whiskers are preferable.
Note that in this description, the inorganic fibers and whiskers are assumed to have an aspect ratio (length/diameter) of more than 5. The aspect ratio of the inorganic fibers and whiskers is preferably at least about 10 and at most about 1000.
There are no particular limitations on firing conditions when manufacturing the catalyst supporting carrier, but preferably at least about 500° C. and at most about 1200° C., and more preferably in the range of about 600° C. to about 1000° C.
The reason for this is that when the firing temperature is about 500° C. or more, the adhesive function of the inorganic binder is more likely to appear and sintering of the inorganic particles and the like is more likely to advance, so that a reduction in the strength of the honeycomb fired body is less likely to occur. When the firing temperature is about 1200° C. or less, sintering of the inorganic particles and the like is less likely to advance excessively, so that a reduction in specific surface area per unit volume is less likely to occur. As a result, the catalyst component supported on the catalyst supporting carrier when a honeycomb structure including honeycomb fired bodies is used as the catalyst supporting carrier for converting the exhaust gas is more likely to be dispersed to a sufficiently high degree.
The catalyst supporting carrier may have a catalytic function.
In addition to the above described catalyst supporting carrier to which a catalytic function is provided by supporting a catalyst on a catalyst supporting carrier (honeycomb structure) not having a catalytic function, examples of the catalyst supporting carrier having a catalytic function may include a catalyst supporting carrier produced by using a material having a catalytic function such as ceria and aluminum so that the catalyst supporting carrier (honeycomb structure) has a catalytic function in itself.
The aggregated honeycomb structure (unless otherwise indicated, it is assumed in the following description that the aggregated honeycomb structure includes a honeycomb filter and a catalyst supporting carrier) of the exhaust gas purification apparatus according to the embodiment of the present invention is not limited to a round pillar shape, and may take any pillar shape such as a cylindroid shape or a polygonal pillar shape.
The catalyst supported on the aggregated honeycomb structure of the exhaust gas purification apparatus according to the embodiment of the present invention is not limited to the above-described platinum catalyst, and a noble metal such as palladium or rhodium, an alkali metal such as potassium or sodium, an alkaline-earth metal such as barium, or a metal oxide, for example, may be used instead. These catalysts may be used singly or in combinations of two or more kinds.
Further, there are no particular limitations on the above-described metal oxide as long as it is capable of reducing the combustion temperature of the PM, and a composite oxide represented by CeO2, ZrO2, FeO2, Fe2O3, CuO, CuO2, Mn2O3, MnO, the composition formula AnB1-nCO3 (in the formula, A is La, Nd, Sm, Eu, Gd or Y, B is an alkali metal or alkaline-earth metal, and C is Mn, Co, Fe or Ni) or the like, for example, may be used instead.
These metal oxides may be used singly or in combinations of two or more kinds, and a metal oxide containing at least CeO2 is preferable.
When this kind of metal oxide is supported, the combustion temperature of the PM is more likely to be reduced.
As a method for supporting a catalyst on the aggregated honeycomb structure, a method for forming a catalyst supporting layer including an alumina film on the surface of the aggregated honeycomb structure and supporting a catalyst on the alumina film or the like may be employed instead of the above-described method for immersing the aggregated honeycomb structure in a solution containing a catalyst and then heating the aggregated honeycomb structure.
Examples of methods for forming an alumina film include a method for immersing the aggregated honeycomb structure in a metallic compound solution containing aluminum, such as Al(NO3)3, and then heating the aggregated honeycomb structure, and a method for immersing the aggregated honeycomb structure in a solution containing alumina powder and then heating the aggregated honeycomb structure.
Further, examples of methods for supporting a catalyst on the alumina film include a method for immersing the aggregated honeycomb structure formed with the alumina film in a solution containing a noble metal, an alkali metal, an alkaline-earth metal, or a metal oxide, or the like, and then heating the aggregated honeycomb structure.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2008/054405 | Mar 2008 | JP | national |
The present application claims priority under 35 U.S.C. §119 to PCT Application No. PCT/JP2008/054405 filed Mar. 11, 2008, the contents of which are incorporated herein by reference in their entirety.
