1. Field of the Invention
The invention relates to an electrically heated catalyst apparatus and a method for manufacturing the same.
2. Description of Related Art
Recently, an electrically heated catalyst (EHC) has received a attention as an exhaust gas purifying device for purifying an exhaust gas discharged from an engine of an automobile and the like. In the EHC, even under condition when a temperature of an exhaust gas is low like immediately after an engine start and a catalyst has difficulty in activation, the catalyst can be forcibly activated by electrical heating, and a purifying efficiency of the exhaust gas can be improved.
According to the EHC disclosed in WO 2012/063353 A, on an outer peripheral surface of a cylindrical carrier having a honey-comb structure on which a catalyst such as platinum, palladium or the like is carried, a surface electrode that is extended in an axial direction of the carrier is formed. A pectinate wiring is connected to the surface electrode to supply an electric current. When the electric current spreads in a carrier axis direction in the surface electrode, an entire carrier is electrically heated. Thus, the catalyst carried by the carrier is activated, and unburned HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide) and the like in the exhaust gas which goes through the carrier are purified by a catalytic reaction.
Since the EHC is disposed on an exhaust path in an automobile and the like, for materials of the surface electrode and wiring, a metal material that is excellent not only in the electric conductivity but also in heat resistance, oxidation resistance under high temperatures, corrosion resistance in an exhaust gas atmosphere and the like is used. On the other hand, as a material for the carrier, ceramic materials such as SiC (silicon carbide) and the like are used. Therefore, during electrical heating, thermal strain, due to a difference between a linear expansion coefficient of the metal material that forms the surface electrode and the wiring and a linear expansion coefficient of the ceramic material that forms the carrier, is generated. According to WO 2012/063353 A, in order to reduce the thermal strain, each of pectinately branched wirings is fixed to the surface electrode by a plurality of fixed layers disposed by distancing from each other.
On the other hand, since the wiring is a cold-rolled thin plate, that is, a processed material, the elongation is such small as about 1%. Therefore, the wiring may result in breakdown (thermal cycle fatigue breakdown) due to the thermal strain that is repeatedly loaded by thermal cycle.
The invention was performed in view of the above situation and provides an electrically heated catalyst apparatus in which thermal cycle fatigue property of the wiring is improved.
An electrically heated catalyst apparatus according to an aspect of the invention includes: a carrier formed of ceramics on which a catalyst is carried; a pair of surface electrodes that face each other and are extended in an axial direction of the carrier on an outer peripheral surface of the carrier; a wiring is formed into a pectinate shape and is configured to supply electric power from an outside of the electrically heated catalyst apparatus to the surface electrode; and a plurality of fixed layers configured to fix the wiring to the surface electrode. The electrically heated catalyst apparatus is formed so that the carrier is electrically heated through the surface electrode. Elongation of the wiring is 15% or more. The wiring may be formed of an annealed material. According to such a structure, the thermal cycle fatigue property of the wiring can be improved.
Between the plurality of fixed layers, the wiring may have a bending part. In the structure like this, in particular, the thermal cycle fatigue property of the wiring can be improved. The wiring may have a throughhole at a position where the fixed layer is formed. According to the structure described above, a fixing force due to the fixed layer can be improved. Further, the wiring may be constituted by a first wiring and a second wiring. The first wiring is formed into a pectinate shape, extended in a circumferential direction of the carrier, and connected to a center portion of the surface electrode in the axial direction. The second wiring is formed into a pectinate shape and extended in the axial direction from the first wiring toward an end of the surface electrode in the axial direction.
A method for manufacturing an electrically heated catalyst apparatus according to a second aspect of the invention includes: forming a pair of the surface electrodes that face each other and are extended in an axial direction of a carrier on an outer peripheral surface of the carrier formed of ceramic on which a catalyst is carried; and fixing a wiring on the surface electrode by a plurality of fixed layers, the wiring being configured to supply electric power from an outside of the electrically heated catalyst apparatus, being formed into a pectinate shape and having elongation of 15% or more. The electrically heated catalyst apparatus is formed so that the carrier is electrically heated through the surface electrode. The method for manufacturing according to the second aspect of the invention may include forming the wiring of an annealed material. According to such a structure, the thermal cycle fatigue property of the wiring can be improved.
The method for manufacturing according to the second aspect of the invention may include annealing the wiring by subjecting the wiring to heat treatment. Furthermore, the wiring may be annealed by electrically heating the electrically heated catalyst device after fixing the wiring made of a processed material on the surface electrode. Thus, the productivity can be improved. The method for manufacturing according to the second aspect of the invention may include forming a bending part between positions where the plurality of fixed layers is formed in the wiring. According to such a structure, in particular, the thermal cycle fatigue property of the wiring can be improved. The method for manufacturing according to the second aspect of the invention may include forming a throughhole at a position where the plurality of fixed layers is formed in the wiring. A fixing force due to the fixed layer can be improved. The method for manufacturing according to the second aspect of the invention may include constituting the wiring by a first wiring and a second wiring. The first wiring is formed into a pectinate shape, extended in a circumferential direction of the carrier, and connected to a center part of the surface electrode in the axial direction. The second wiring is formed into a pectinate shape and extended in the axial direction from the first wiring toward an end of the surface electrode.
According to the first and second aspects of the invention, an electrically heated catalyst apparatus of which thermal cycle fatigue property of the wiring was improved can be provided.
Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:
Hereinafter, specific embodiments to which the invention was applied will be described in detail with reference to the drawings. However, the invention is not restricted to embodiments described below. Further, for the purpose of clarification of the description, description and the drawings below are appropriately simplified.
First, with reference to
The electrically heated catalyst apparatus 100 is disposed on a discharge path of an automobile and the like, for example, and purifies an exhaust gas discharged from an engine. As shown in
The carrier 20 is a porous member that carries a catalyst such as platinum, palladium and the like. Further, since the carrier 20 itself is electrically heated, it is formed of ceramics having conductivity, specifically SiC (silicon carbide), for example. As shown in
As shown in
As shown in
As shown in
The second wiring 32b is continuously extended from two first wirings 32a located on the outermost side up to an edge of the surface electrode 31 in a carrier axis direction. In an example of
In the electrically heated catalyst apparatus 100 according to the embodiment, from the first wiring 32a disposed only in a center part in a carrier axis direction of the surface electrode 31, the second wiring 32b is extended toward an end in a carrier axis direction of the surface electrode 31. Therefore, even when the surface electrode 31 is cracked in a carrier circumferential direction due to deterioration, spreading of the electric current in a carrier axis direction can be maintained due to the second wiring 32b. Therefore, the vicinity of the center part in an axis direction of the carrier 20 is not intensively heated, and the thermal stress crack due to the intensive heating can be avoided.
As shown in
Further, according to an example of
Herein,
The fixed layer 33 is a button-shaped sprayed coating that is formed so as to cover the first wiring 32a and has a thickness of about 300 to 500 μm. The fixed layer 33 can be formed in such a manner that the first wiring 32a, is disposed on the surface electrode 31, thereon a masking jig is disposed, and the plasma spraying is carried out. As shown in
Further, each of the first wirings 32a is provided with a bending part 34 in a center part in a carrier circumferential direction. That is, each of the four first wirings 32a located inside is provided with the bending part 34 between two fixed layers 33. On the other hand, each of the second wirings 32b is provided with two bending parts 34. Specifically, one bending part 34 is disposed between two fixed layers 33 in each of the second wirings 32b. The other bending part 34 is disposed at a connection part of each of the second wirings 32b with the first wiring 32a (between the first wiring 32a and one fixed layer 33). According to such a structure, thermal strain (thermal stress) based on the difference of, linear expansion coefficients between the wiring 32 made of metal and the carrier 20 made of ceramics can be reduced.
The sprayed coating that forms the surface electrode 31 and the fixed layer 33 is necessary to be a metal based material for energizing in the same manner as the wiring 32. A metal that forms a matrix of the sprayed coating is necessary to endure high temperatures of 800° C. or more. Therefore, Ni—Cr alloys (Cr content: 20 to 60% by mass) and MCrAlY alloys (M is at least one kind of Fe, Co and Ni), which have excellent oxidation resistance under high temperatures are preferable. Herein, the NiCr alloys and MCrAlY alloys may contain other alloying elements. The sprayed coating that forms the surface electrode 31 and the fixed layer 33 may be porous. When the sprayed coating is porous, a function of reducing the stress can be improved.
The carrier 20 is fixed and held on a discharge path by a mat 50 made of a heat resistant material in the vicinity of both ends in the carrier axis direction. Further, the mat 50 has a function of protecting the carrier 20, sealing an exhaust gas, and not allowing it to leak outside. In order to secure the sealability, the mat 50 preferably has a width w of 30 mm or more.
According to the above structure, in the electrically heated catalyst apparatus 100, the carrier 20 is electrically heated between a pair of surface electrodes 31, and a catalyst carried on the carrier 20 is activated. Thus, unburned HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide) and the like in the exhaust gas, which go through the carrier 20 are purified according to a catalytic reaction.
Herein,
Incidentally, as shown in
In the related art, as the wiring 32, a cold-rolled thin plate, that is, a processed material (elongation: about 1%) has been used. Therefore, in the tip 34a and the root part 34b of the restrained bending part 34, it was likely that the wiring 32 is broken due to thermal cycle load. On the other hand, in the electrically heated catalyst apparatus 100 according to the embodiment, since, as the wiring 32, an annealed material (elongation: 15 to 25%) obtained by annealing a cold rolled thin plate is used, the wiring 32 can be prevented from breaking due to thermal cycle load. That is, the number of thermal cycles during which the wiring 32 reaches breakdown can be increased, and, the wiring 32 can have a longer life thereby. That is, the thermal cycle fatigue property of the wiring 32 can be improved. Herein, the elongation of the wiring 32 is preferably at least 15% or more. There is no particular upper limit in the elongation.
Incidentally, after the electrically heated catalyst apparatus 100 was manufactured using the wiring 32 made of a processed material, an annealed material may be formed by electrically heating the wiring 32 in an energization inspection step. That is, by making use of electrical heating of the electrically heated catalyst apparatus 100, the wiring 32 is subjected to heat treatment, and an annealed material may be formed thereby. Therefore, an annealing treatment step of the wiring 32 can be omitted, and the productivity can be improved thereby.
Herein, with reference to
As shown in a stress-strain curve of
Next, with reference to
On the other hand,
Although, hereinafter, specific examples according to embodiment 1 will be described, the invention is not restricted to these examples. In Example 1, a cold-rolled material of stainless-based alloy (Fe-20% by mass of Cr-5% by mass of Al) having a thickness of 0.1 mm was cooled in a furnace after heat treatment at 900° C. for 5 minutes under an inert gas atmosphere, and the wiring 32 made of an annealed material was prepared thereby. The wiring 32 made of the annealed material had linear expansion coefficient=11.5×10−6/° C., elongation=20%, tensile strength=715 N/mm2, and bickers hardness=236 Hv.
Next, on a surface of the carrier 20 made of SiC, by plasma spraying, the surface electrode 31 having a thickness of 0.15 mm was formed. Herein, a linear expansion coefficient of SiC is 4.6×10−6/° C. Next, on the surface electrode 31, the wiring 32 made of the annealed material was disposed, thereon, by plasma spraying using a masking jig, the fixed layer 33 having a thickness of 0.4 mm was formed. As shown in
A composition of the sprayed coating (surface electrode 31 and fixed layer 33) was Ni-50% by mass of Cr-32.5% by mass of bentonite, that is, a composite material made of a metal phase and a bentonite phase. After loading thermal cycle (150 to 900° C., 10 minutes×1000 cycles) to the prepared electrically heated catalyst apparatus, whether the wiring 32 was disconnected or not was confirmed. None of disconnection of the wiring 32 was found.
According to comparative example 1, the wiring 32 made of a cold-rolled material of stainless-based alloy (Fe-20% by mass of Cr-5% by mass of Al) having a thickness of 0.1 mm was prepared. The wiring 32 made of the processed material had linear expansion coefficient=11.5×10−6/° C., elongation=1%, tensile strength=1330 N/mm2, and bickers hardness=390 Hv. Other conditions than the above were the same as example 1. Twenty one disconnections of the wiring 32 were found. All of the disconnections were found at the bending parts 34 shown in
From results of example 1 and comparative example 1, it was found that when the wiring 32 was changed from the processed material to the annealed material, the disconnection due to the thermal cycle load can be effectively prevented.
The invention is not restricted to the embodiments described above and can be appropriately modified in the range that does not deviate from gist.
Number | Date | Country | Kind |
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2012-261952 | Nov 2012 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2013/002602 | 11/22/2013 | WO | 00 |