JP2016037867A - Electric heating type catalyst device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of crack in a catalyst support due to a heating cycle.SOLUTION: An electric heating type catalyst device includes a catalyst support 10 for supporting a catalyst, a pair of electric diffusion layers 11 formed opposing each other on the outer peripheral face of the catalyst support 10, wiring members 30 fixed to the respective electric diffusion layers 11, and an outer cylinder 60 covering the outer peripheral face of the catalyst support 10 and having openings 61 in the side face for the wiring members 30 to be drawn out thereof to the outside. The catalyst support 10 is subjected to electric heating via the wiring members 30. Each wiring member 30 has a heat release suppressing structure on a drawn part 32 drawn out of the outer cylinder 60 for suppressing heat release.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an electrically heated catalyst device.

  2. Description of the Related Art In recent years, an electrically heated catalyst (EHC) device has attracted attention as an exhaust purification device that purifies exhaust gas discharged from an engine such as an automobile. In EHC, even if the exhaust gas temperature is low, such as immediately after the engine is started, and the catalyst is difficult to activate, the catalyst is forcibly activated by energization heating to increase the exhaust gas purification efficiency. Can do.

  In the EHC disclosed in Patent Document 1, a surface electrode extending in the axial direction of the carrier is formed on the outer peripheral surface of a columnar carrier having a honeycomb structure carrying a catalyst such as platinum or palladium. Then, comb-like wiring is connected to the surface electrode, and current is supplied. When this current spreads in the direction of the carrier axis in the surface electrode, the whole carrier is heated by energization. As a result, the catalyst supported on the carrier is activated, and unburned HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide), etc. in the exhaust gas passing through the carrier are purified by the catalytic reaction. The

JP 2013-136997 A

The inventors have found the following problems with respect to the electrically heated catalyst device.
In the above-mentioned current heating type catalyst device, cracks occur in the carrier due to repeated heating and cooling (thermal cycle), current becomes difficult to flow in some wirings, and current concentrates in other wirings, There was a problem of fusing.

  The inventors sought the cause of cracking in this carrier. FIG. 7 is a graph showing the temperature change between the carrier and the electric diffusion layer in the conventional electrically heated catalyst device. The horizontal axis indicates time, and the vertical axis indicates temperature. As shown in FIG. 7, the temperature difference between the carrier and the electric diffusion layer formed immediately above the carrier increases when the temperature drops (when the carrier energization is turned off), and the thermal stress generated between the two increases. This is presumed to be caused by the temperature decrease of the electric diffusion layer being promoted by heat radiation from the wiring. The electric diffusion layer is provided between the carrier and the surface electrode in order to spread the electricity supplied from the wiring in the axial direction and the circumferential direction of the carrier, and is omitted in Patent Document 1.

  The present invention has been made in view of the above, and an object of the present invention is to provide an electrically heated catalyst device in which the occurrence of cracks in a carrier due to thermal cycling is suppressed.

The electrically heated catalyst device according to one aspect of the present invention is
A carrier carrying a catalyst;
A pair of electric diffusion layers formed opposite to each other on the outer peripheral surface of the carrier;
A wiring member fixed to each of the electric diffusion layers;
An outer cylinder covering the outer peripheral surface of the carrier and having an opening on the side surface for pulling out the wiring member to the outside; and
An electrically heated catalyst device in which the carrier is energized and heated through the wiring member,
The said wiring member is equipped with the heat dissipation suppression structure for suppressing heat dissipation in the drawer | drawing-out part pulled out from the said outer cylinder.

  In the electrically heated catalyst device according to one aspect of the present invention, since the wiring member has a heat dissipation suppressing structure for suppressing heat dissipation in the lead-out portion that is pulled out from the outer cylinder, the electric diffusion layer is turned off when the carrier is turned off. Can be suppressed. As a result, the temperature difference between the carrier and the electric diffusion layer when energization is turned off is reduced, and the thermal stress generated between them is also reduced, so that the occurrence of cracks in the carrier due to thermal cycling can be suppressed.

  According to the present invention, it is possible to provide an energization heating type catalyst device in which the generation of cracks in the carrier due to thermal cycling is suppressed.

1 is a perspective view of an electrically heated catalyst device according to a first embodiment. It is the perspective view which removed the outer cylinder 60 in FIG. FIG. 3 is a plan view seen from directly above a surface electrode 20 in FIG. 2. FIG. 4 is a transverse sectional view taken along the line IV-IV in FIG. 3. It is a top view of the wiring member 30 which concerns on 2nd Embodiment. It is a top view of wiring member 30 concerning a 3rd embodiment. It is the graph which showed the temperature change of the support | carrier and an electric-diffusion layer in the conventional electrically heated catalyst apparatus.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiment. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

(First embodiment)
First, with reference to FIGS. 1-4, the electroheating type catalyst apparatus which concerns on 1st Embodiment is demonstrated. FIG. 1 is a perspective view of an electrically heated catalyst device according to the first embodiment. FIG. 2 is a perspective view with the outer cylinder 60 removed in FIG. FIG. 3 is a plan view as viewed from directly above the surface electrode 20 in FIG. 2 (plus side in the x-axis direction). 4 is a cross-sectional view taken along the line IV-IV in FIG.

  As a matter of course, the right-handed xyz coordinates shown in the drawings are for convenience in explaining the positional relationship between the components. The xyz coordinates in each drawing are common, and the y-axis direction is the axial direction of the carrier 10. Here, when using the electrically heated catalyst device 100, it is preferable to match the positive z-axis direction with the upward vertical direction as shown in FIG.

  As shown in FIG. 1, the electrically heated catalyst device 100 includes a carrier 10 and an outer cylinder 60. Here, as shown in FIG. 2, the electrically heated catalyst device 100 includes the electric diffusion layer 11, the surface electrode 20, the wiring member 30, and the fixed layer 40 on the outer peripheral surface of the carrier 10. As shown in FIGS. 3 and 4, the electrically heated catalyst device 100 includes a mat 50 between the carrier 10 and the outer cylinder 60. That is, the electrically heated catalyst device 100 includes the carrier 10, the electric diffusion layer 11, the surface electrode 20, the wiring member 30, the fixed layer 40, the mat 50, and the outer cylinder 60.

  In FIG. 1, the mat 50 is omitted. 3 shows the positional relationship between the carrier electrode 10, the electric diffusion layer 11, the wiring member 30, the fixing layer 40, and the mat 50 for one surface electrode 20, but the same applies to the other surface electrode 20. It is. Specifically, as shown in FIGS. 2 and 4, the two surface electrodes 20 are in a mirror-symmetrical positional relationship with respect to a symmetry plane parallel to the yz plane.

  The electrically heated catalyst device 100 is provided on an exhaust path of an automobile or the like, for example, and purifies exhaust gas discharged from the engine. In the electrically heated catalyst device 100, the carrier 10 is electrically heated between the pair of surface electrodes 20, and the catalyst supported on the carrier 10 is activated. Thereby, unburned HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide) and the like in the exhaust gas passing through the carrier 10 are purified by the catalytic reaction.

  The carrier 10 is a porous member that supports a catalyst such as platinum or palladium. Further, since the carrier 10 itself is energized and heated, it is preferable that the carrier 10 is made of conductive ceramics, specifically, for example, SiC (silicon carbide). As shown in FIG. 2, the carrier 10 has a substantially cylindrical shape and has a honeycomb structure inside. As indicated by the white arrow, the exhaust gas passes through the inside of the carrier 10 in the axial direction (y-axis direction) of the carrier 10.

  The electric diffusion layer 11 is a ceramic layer having a thickness of about 50 to 200 μm formed on the outer surface of the carrier 10 in order to spread electricity supplied from the wiring member 30 in the axial direction and the circumferential direction of the carrier 10. Here, the electric diffusion layer 11 is made of ceramics having a resistance lower than that of the carrier 10, and is formed integrally with the carrier 10, for example. Specifically, the resistance can be made lower than that of the carrier 10 by adding metal Si to SiC (silicon carbide) constituting the carrier 10, for example. As a matter of course, the electric diffusion layer 11 has a higher resistance than the surface electrode 20.

  Moreover, the electric diffusion layer 11 is formed in each lower layer of a pair of surface electrode 20, as shown in FIG. Moreover, as shown in FIG. 3, each electric diffusion layer 11 has a rectangular planar shape and extends in the carrier axis direction (y-axis direction). Here, the electric diffusion layer 11 is formed so as to extend in the carrier axis direction and the circumferential direction from the surface electrode 20.

  As shown in FIG. 2, the surface electrode 20 is a pair of electrodes formed on the electric diffusion layer 11 and arranged to face each other via the carrier 10. The surface electrode 20 is in physical contact with and electrically connected to the electric diffusion layer 11. As shown in FIG. 3, each surface electrode 20 has a rectangular planar shape and extends in the carrier axis direction (y-axis direction). Further, as shown in FIG. 4, the surface electrode 20 is electrically connected to the battery 83 via the wiring member 30, the external electrode 81, and the external wiring 82. With such a configuration, a current is supplied to the carrier 10 and is heated by energization. One of the pair of surface electrodes 20 is a positive electrode and the other is a negative electrode. However, any surface electrode 20 may be a positive electrode or a negative electrode. That is, the direction of the current flowing through the carrier 10 is not limited.

  The surface electrode 20 is a sprayed coating having a thickness of about 50 to 200 μm formed by plasma spraying, for example. Since the surface electrode 20 is energized in the same manner as the wiring member 30, this thermal spray coating needs to be a metal base. The metal constituting the matrix of the thermal spray coating is a Ni-Cr alloy having excellent oxidation resistance at high temperatures in order to withstand use at high temperatures of 800 ° C. or higher (however, the Cr content is 20 to 60% by mass) ), MCrAlY alloy (where M is at least one of Fe, Co and Ni). Here, the NiCr alloy and MCrAlY alloy may contain other alloy elements.

  As shown in FIG. 3, the wiring member 30 is disposed on each surface electrode 20. As shown in FIG. 3, the wiring member 30 has a comb-like wiring 31 extending in the carrier circumferential direction on the surface electrode 20 and a lead portion 32 connected to the external electrode 81 (FIG. 4). Yes. The entire wiring member 30 is a thin metal plate having a thickness of about 0.1 mm, for example. The width of the comb-like wiring 31 is, for example, about 1 mm. In addition, the wiring member 30 is preferably made of a heat-resistant (oxidation-resistant) alloy such as a stainless-based alloy, a Ni-based alloy, or a Co-based alloy in order to endure use at a high temperature of 800 ° C. or higher. In consideration of performance and cost such as electrical conductivity, heat resistance, oxidation resistance at high temperature, and corrosion resistance in an exhaust gas atmosphere, stainless steel alloys are preferable.

  As shown in FIG. 3, the plurality of comb-like wirings 31 extend in the carrier circumferential direction over substantially the entire region where the surface electrode 20 is formed, and extend along the carrier axis direction (y-axis direction). Are arranged at approximately equal intervals. Further, all the comb-like wirings 31 are connected to the lead portion 32 on the plus side in the z-axis direction of the formation region of the surface electrode 20. In the example of FIG. 3, twelve comb-like wirings 31 are provided on the surface electrode 20. Each of the comb-like wirings 31 is fixed to the surface electrode 20 by the fixing layer 40 and is electrically connected. As a matter of course, the number of the comb-like wirings 31 is not limited to 12 and is appropriately determined.

  The lead portion 32 is not fixed to the surface electrode 20 and is drawn to the outside of the outer cylinder 60. Here, the drawer | drawing-out part 32 has a some bending part, and is formed so that expansion-contraction is possible. That is, the drawer part 32 is formed in a bellows shape. In the example of the drawing, as shown in FIG. 4, for example, the lead-out portion 32 has three bent portions (two mountain folds and one valley fold when viewed from the positive side in the z-axis direction) and is formed in an M-shaped cross section. Has been. The lead portion 32 may have two bent portions (one mountain fold and one valley fold), and may be formed in an N-shaped cross section. Furthermore, the drawer | drawing-out part 32 may have four or more bending parts. In FIG. 3, a state in which the drawer portion 32 is extended is shown.

  The bellows-like drawer 32 is in a folded state at the manufacturing stage. Therefore, the lead portion 32 of the wiring member 30 and the outer cylinder 60 do not interfere with each other, and the carrier 10 including the wiring member 30 can be press-fitted into the outer cylinder 60. Then, after the carrier 10 is press-fitted into the outer cylinder 60, the drawer portion 32 can be easily pulled out to the outside of the outer cylinder 60. Here, by using an annealed material (elongation of 15% or more) obtained by annealing a cold-rolled thin plate as the wiring member 30, the lead-out portion 32 can be easily folded into a bellows shape.

  The fixed layer 40 is a button-shaped sprayed coating having a thickness of about 300 to 500 μm formed on the comb-like wiring 31. The fixed layer 40 can be formed by disposing the wiring member 30 on the surface electrode 20, disposing the masking jig jig thereon, and performing plasma spraying. The composition of the thermal spray coating may be the same as that of the surface electrode 20 described above.

  As described above, the comb-like wiring 31 is fixed to the surface electrode 20 and electrically connected by the fixing layer 40. In the example of FIG. 3, each comb-like wiring 31 is fixed to the surface electrode 20 by only one fixing layer 40. With such a configuration, thermal strain (thermal stress) based on a difference in linear expansion coefficient between the wiring member 30 made of metal and the carrier 10 made of ceramics can be relaxed. That is, the thermal strain (thermal stress) is alleviated by making the individual fixed layers 40 as small as possible and interspersed. Each comb-like wiring 31 may be fixed by two or more fixing layers 40. In this case, the number and interval of the fixed layers 40 can be determined as appropriate.

  The mat (holding member) 50 is a heat insulating member having flexibility. The mat 50 is wound around the entire outer peripheral surface of the carrier 10 as shown by a broken line in FIG. 3, and is filled between the carrier 10 and the outer cylinder 60 as shown in FIG. By the mat 50, the carrier 10 is fixed and held on the outer cylinder 60, and the exhaust gas is sealed so as not to leak to the outside of the outer cylinder 60.

  As shown in FIGS. 3 and 4, the mat 50 is provided with two openings 51 for leading the lead-out portion 32 of the wiring member 30 to the outside of the outer cylinder 60. As shown in FIG. 3, the opening 51 is formed in a rectangular shape in the central portion in the axial direction of the carrier 10 corresponding to the position where the wiring member 30 is formed. Further, in the cross-sectional view shown in FIG. 4, the two openings 51 are arranged in mirror symmetry with respect to a symmetry plane parallel to the yz plane. In order to ensure sealing performance, the frame width w of the opening 51 in the y-axis direction shown in FIG. 3 is preferably 30 mm or more. In the example of the drawing, the shape of the opening 51 is rectangular, but is not particularly limited. For example, the shape of the opening 51 may be a circular shape or an elliptical shape.

  The outer cylinder 60 is a casing for housing the carrier 10 and is a pipe having a diameter that is slightly larger than that of the columnar carrier 10. As shown in FIG. 1, the outer cylinder 60 covers substantially the entire carrier 10 via a mat 50. Here, the outer cylinder 60 is preferably made of a metal such as a stainless alloy.

  As shown in FIGS. 1 and 4, the side surface of the outer cylinder 60 is provided with an opening 61 for leading the lead-out portion 32 of the wiring member 30 to the outside of the outer cylinder 60. Therefore, as shown in FIG. 1, the opening 61 is provided at two positions in the central portion in the axial direction of the outer cylinder 60 corresponding to the position where the lead-out portion 32 is formed. Further, in the cross-sectional view shown in FIG. 4, the two openings 61 are arranged mirror-symmetrically with respect to a plane parallel to the yz plane on the slightly upper side (z-axis direction plus side) from the center. In the example of the drawing, the shape of the opening 61 is circular, but is not particularly limited. For example, the shape of the opening 61 may be an elliptical shape or a rectangular shape.

  Here, in the electrically heated catalyst device 100 according to the present embodiment, a heat radiation suppressing structure for suppressing heat radiation is provided in the drawing portion 32 of the wiring member 30. The heat radiation suppressing structure is, for example, a heat insulating structure for blocking heat released from the lead portion 32 or a low radiation structure for reducing heat released from the lead portion 32. The heat insulation structure and the low radiation structure are formed on one side or both sides of the lead portion 32. As a matter of course, it is preferable to form the heat radiation suppressing structure on both surfaces of the drawing portion 32 from the viewpoint of heat radiation suppression.

  Examples of the heat insulating structure include a coating layer made of ceramics having heat insulating properties such as zirconia and alumina, that is, a heat insulating layer. The coating layer is preferably porous from the viewpoint of heat insulation. The coating layer can be formed by thermal spraying or sputtering.

  Examples of the low radiation structure include a coating layer made of a metal having a high thermal reflectance (for example, Au, Al, Ni, etc.), that is, a metal reflective film. The coating layer can be formed by plating or sputtering. Moreover, you may mirror-finish the surface of the extraction | drawer part 32 as a low radiationization structure.

  As described above, in the electrically heated catalyst device 100 according to the first embodiment, the drawing portion 32 of the wiring member 30 is provided with a heat dissipation suppressing structure for suppressing heat dissipation. Therefore, the temperature drop of the electric diffusion layer 11 due to heat radiation from the wiring member 30 can be suppressed when the carrier 10 is turned off. As a result, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the energization is turned off becomes smaller than in the conventional case, and the thermal stress generated between the two can be reduced. Therefore, in the electrically heated catalyst device according to the present embodiment, the occurrence of cracks in the carrier due to the thermal cycle can be suppressed.

  As a result of the thermal analysis, in the conventional structure, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the energization was turned off was 150 ° C., and the thermal stress generated in the carrier 10 was 37 MPa. On the other hand, in the electrically heated catalyst device 100 according to the first embodiment, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the electricity is turned off is 30 ° C., and the thermal stress generated in the carrier 10 is 10 MPa. Reduced to.

(Second Embodiment)
Next, with reference to FIG. 5, an electrically heated catalyst device according to a second embodiment will be described. FIG. 5 is a plan view of the wiring member 30 according to the second embodiment.
As shown in FIG. 5, in the electrically heated catalyst device according to the second embodiment, the foil-like lead portion 32 is bent into a U-shaped section (a U-shaped section) as a heat dissipation suppressing structure. . Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  In the electrically heated catalyst device according to the second embodiment, the folded wires face each other on the inner side (upper surface) of the lead-out portion 32 that is folded into a U-shaped cross section. Therefore, it can be considered that heat is not radiated from the inside (upper surface) of the drawing portion 32. That is, the heat radiation area in the lead-out portion 32 is about ½. Therefore, the temperature drop of the electric diffusion layer 11 due to heat radiation from the wiring member 30 can be suppressed when the carrier 10 is turned off. As a result, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the energization is turned off becomes smaller than in the conventional case, and the thermal stress generated between the two can be reduced. Therefore, in the electrically heated catalyst device according to the present embodiment, the occurrence of cracks in the carrier due to the thermal cycle can be suppressed.

  As a result of the thermal analysis, in the conventional structure, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the energization was turned off was 150 ° C., and the thermal stress generated in the carrier 10 was 37 MPa. In contrast, in the electrically heated catalyst device according to the second embodiment, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the current is turned off is 90 ° C., and the thermal stress generated in the carrier 10 is up to 25 MPa. Reduced.

(Third embodiment)
Next, with reference to FIG. 6, an electrically heated catalyst device according to a third embodiment will be described. FIG. 6 is a plan view of the wiring member 30 according to the third embodiment.
As shown in FIG. 6, in the electrically heated catalyst device according to the third embodiment, the cross-sectional shape of the lead-out portion 32 is circular as the heat dissipation suppressing structure. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  In the electrically heated catalyst device according to the third embodiment, since the cross-sectional shape of the extraction portion 32 is circular, the surface area can be reduced to about 1/6 with the same cross-sectional area. That is, the heat radiation area in the lead-out part 32 is about 1/6. Therefore, the temperature drop of the electric diffusion layer 11 due to heat radiation from the wiring member 30 can be suppressed when the carrier 10 is turned off. As a result, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the energization is turned off becomes smaller than in the conventional case, and the thermal stress generated between the two can be reduced. Therefore, in the electrically heated catalyst device according to the present embodiment, the occurrence of cracks in the carrier due to the thermal cycle can be suppressed.

  As a result of the thermal analysis, in the conventional structure, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the energization was turned off was 150 ° C., and the thermal stress generated in the carrier 10 was 37 MPa. In contrast, in the electrically heated catalyst device according to the third embodiment, the temperature difference between the outer surface of the carrier 10 and the electric diffusion layer 11 when the current is turned off is 30 ° C., and the thermal stress generated in the carrier 10 is up to 10 MPa. Reduced.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 Support | carrier 11 Electrical diffusion layer 20 Surface electrode 30 Wiring member 31 Comb-shaped wiring 32 Lead part 40 Fixed layer 50 Mat 51 Opening part 60 Outer cylinder 61 Opening part 81 External electrode 82 External wiring 83 Battery 100 Electric heating type catalytic device

Claims (1)

A carrier carrying a catalyst;
A pair of electric diffusion layers formed opposite to each other on the outer peripheral surface of the carrier;
A wiring member fixed to each of the electric diffusion layers;
An outer cylinder covering the outer peripheral surface of the carrier and having an opening on the side surface for pulling out the wiring member to the outside; and
An electrically heated catalyst device in which the carrier is energized and heated through the wiring member,
The wiring member is provided with a heat dissipation suppressing structure for suppressing heat dissipation in the lead-out portion that is pulled out from the outer cylinder.
Electric heating type catalytic device.

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