JP6015278B2 - Electric heating type catalytic converter - Google Patents

Description

  The present invention relates to an electrically heated catalytic converter disposed in an exhaust system for exhaust gas.

  Various industries are making various efforts to reduce environmental impact on a global scale. Among them, in the automobile industry, not only gasoline engine cars with excellent fuel efficiency, but also hybrid cars and electric cars. The development of the so-called eco-cars such as the above and the further improvement of its performance is being promoted every day.

  By the way, in the exhaust system of exhaust gas connecting the vehicle engine and the muffler, in addition to purifying exhaust gas at normal temperature, electric heating that activates the catalyst as quickly as possible by electric heating in cold weather and purifies the exhaust gas A catalytic converter may be installed. This electric heating type catalytic converter has a structure in which, for example, a pair of electrodes are attached to a honeycomb structure base material provided with a catalyst coat layer disposed in an exhaust gas exhaust system, and the pair of electrodes are connected by an external circuit having a power source. In addition, the honeycomb catalyst is heated by energizing the electrodes, and the activity of the honeycomb catalyst is increased and the exhaust gas passing through the honeycomb catalyst is rendered harmless (EHC (Electrically Heated Converter)).

  In general, the base material of the honeycomb structure described above has a columnar outer shape. This is because the EHC is mounted in the exhaust pipe of a hollow vehicle with a circular cross section, so it is excellent in terms of mountability, fixing of the exhaust pipe and EHC after mounting, and ensuring a cross section of exhaust gas. That is why.

  In the base material having a circular cross section described above, a pair of electrodes is arranged on the surface of the base material and opposed to each other in the diameter direction, and the paired electrodes are connected by a cable with a power supply interposed between them. is there. Note that, as described above, Patent Document 1 discloses an EHC having a configuration in which a pair of electrodes are formed at opposing positions in the diameter direction on the surface of a cylindrical base material.

  In this general structure EHC having a base material with a circular cross section, the distance between the pair of electrodes is not constant because the cross section of the base material is circular, and varies depending on the location. Specifically, the center position of the electrode has the longest cross-sectional diameter as the distance between the electrodes, and the distance between the electrodes becomes shorter from the center of the electrode toward the outer circumferential direction.

  In this way, the distance between the electrodes is different for each part of the base material, so that the electric resistance is different for each part of the base material, and the electric resistance is the largest at the center part of the electrode having the longest distance between the electrodes. It becomes difficult for current to flow.

  As described above, the easiness of the flow of current differs depending on the part of the base material, so that the temperature rise of the base material becomes non-uniform for each part, resulting in temperature variations in the base material.

  In contrast to this temperature variation, the EHC disclosed in Patent Document 1 tries to cancel the temperature variation by offsetting the electrical resistance of each part of the base material by changing the thickness of the electrode film constituting the electrode for each part. To do.

  However, when a slurry made of ceramic powder, carbon powder, solvent, etc. is applied to the substrate surface and baked to produce an electrode film, it requires a high skill to form by changing the thickness for each part. It is clear that the production efficiency is low.

  Therefore, the present inventors have come up with an idea of an electrically heated catalytic converter having a structure that can accurately eliminate the difference in electric resistance for each part of the base material without lowering the production efficiency.

JP 2012-92821 A

  The present invention has been made in view of the above problems, and is an electrically heated catalyst having a structure capable of accurately eliminating the difference in electrical resistance for each part of the base material without lowering the production efficiency. The purpose is to provide a converter.

  In order to achieve the above object, an electrically heated catalytic converter according to the present invention includes a base material having a honeycomb structure having a cylindrical shape and provided with a catalyst coating layer, and a surface of the base material that is opposed to the base material in the diameter direction. In the electrically heated catalytic converter composed of a pair of electrodes formed on each other, an external circuit composed of a cable connecting the pair of electrodes, and a power source interposed between the cables, In the region corresponding to each of the electrodes, a plurality of lead electrodes extending to the other electrode side and having different lengths are arranged, from the lead electrode located at the center side of the electrode toward the lead electrode located outside. The length of the lead electrode is shortened, and a part or all of the electrical resistance in the substrate is adjusted to be the same or substantially the same by adjusting the length of the lead electrode.

  The electric heating type catalytic converter of the present invention is provided with a plurality of lead electrodes having different lengths in a base material, more specifically, a lead electrode located outside a lead electrode located at the center side of the electrode. By disposing a plurality of lead electrodes whose lead electrodes are shortened toward each other, it is possible to eliminate the difference in distance between a pair of electrodes in a base material having a circular cross section for each part. The EHC can be manufactured much more efficiently than the method of adjusting the thickness of the film, etc., and the electric resistance that differs from site to site can be eliminated with high accuracy.

  Here, the “electrode” includes a form composed of electrode terminals and a form composed of electrode terminals and an electrode film disposed on the surface of the base material around the electrode terminals. Moreover, in the form which consists only of an electrode terminal, the form etc. which provided the base which protruded outside at the base position where an electrode terminal is attached to a base material may be sufficient.

  The “lead electrode” is an electrode having a structure in which a conductive material having a good conductivity is formed in a counterbore groove having different lengths (lengths in a circular cross section of the base material) in the base material. Means.

  For example, in the form in which the electrode includes an electrode film, the conductor can be formed by pouring the paste for forming the electrode film into the counterbored groove and baking it. Moreover, an electrode body can also be arrange | positioned in a counterbore groove | channel by inserting the electrode body manufactured by the shape and dimension previously accommodated in a counterbore groove | channel like an electrode terminal in a counterbore groove | channel.

  In addition, among “a part or all of the electrical resistance in the substrate is adjusted to be the same or substantially the same”, “a part or all of the electrical resistance in the substrate” refers to a substrate having a circular cross section. A form in which the lead electrode is disposed from the center position of the circular cross section to the side of the end of the circular cross section so that all the electric resistances are the same, for example, an electrode film having a constant width Including a configuration in which a plurality of lead electrodes are disposed at intervals within the width of the electrode film when the electrode terminal is disposed at the center of the substrate surface. Yes. Further, “substantially the same electrical resistance” means that the desired resistance of the substrate is not necessary even if the electrical resistance is different by an error of about 10%, for example, even if the electrical resistance is not completely the same in the desired range of the circular cross section. When the temperature rise in the range is substantially uniform, the difference due to this error is made “substantially the same”.

  Moreover, it is preferable that the electrode body has a volume resistivity smaller than the volume resistivity of a base material. According to this form, it can adjust so that a lead electrode may not become a heat generating body.

  As can be understood from the above description, according to the electrically heated catalytic converter of the present invention, a plurality of lead electrodes having different lengths are arranged in a base having a circular cross section, and more specifically, the center of the electrode. Efficient part or all of the electrical resistance in the substrate by arranging multiple lead electrodes with the length of the lead electrode decreasing from the lead electrode located on the side toward the lead electrode located on the outside And can be adjusted to be the same or substantially the same. As a result, the electrical resistance of each part of the substrate can be offset and temperature variations can be eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic diagram explaining Embodiment 1 of the electrically heated catalytic converter (EHC) of this invention. It is an II-II arrow line view of FIG. It is the III-III arrow line view of FIG. 1, Comprising: It is the figure which simulated the electrical resistance formed. (A) is the perspective view explaining the flow of the applied electric current, (b) is sectional drawing explaining the flow of the applied electric current. It is the schematic diagram explaining Embodiment 2 of an electrically heated catalyst converter (EHC). It is the schematic diagram explaining Embodiment 3 of an electrically heated catalyst converter (EHC).

  Hereinafter, an embodiment of an electrically heated catalytic converter of the present invention will be described with reference to the drawings. Although the illustrated example shows a form in which the electrode is composed of the electrode terminal and the electrode film, it is needless to say that the electrode may be composed only of the electrode terminal.

(Embodiment 1 of electric heating type catalytic converter)
FIG. 1 is a schematic diagram illustrating Embodiment 1 of an electrically heated catalytic converter (EHC) of the present invention, FIG. 2 is a view taken along the line II-II in FIG. 1, and FIG. FIG. 3 is a view taken in the direction of arrow -III, simulating the electric resistance to be formed.

  The illustrated electrically heated catalytic converter 10 includes an exhaust gas exhaust system, more specifically, an unillustrated engine, an electrically heated catalytic converter 10 (EHC), an unillustrated three-way catalytic converter, and an unillustrated sub-muffler. And the main muffler are arranged in order, and are incorporated into an exhaust system that is connected to each other by a system pipe. When the engine is started, the precious metal catalyst constituting the electrically heated catalytic converter 10 is heated to a predetermined temperature as quickly as possible, and the exhaust gas flowing from the engine is purified by the precious metal catalyst. Exhaust gas that could not be purified by the heated catalytic converter 10 is purified by a three-way catalyst purification device located downstream thereof.

  The electrically heated catalytic converter 10 is fixed to a hollow of the metal outer tube 6 (metal case) and the outer tube 6 via a mat (holding material) (not shown), and a catalyst coat layer (not shown) is attached to the cell wall 1a. A base material 1 having a honeycomb structure provided on the surface, electrode films 2 and 2 constituting a pair of electrodes disposed on the surface of the base material 1, and electrode terminals 3 and 3 disposed on the inner side thereof, each electrode terminal 3 and 3 is generally composed of an external circuit 4 composed of external electrodes 4 and 4 and a cable 5a connecting the external electrodes 4 and 4 and a power source 5b interposed in the middle of the cable 5a.

  The outer tube 6 has a hollow cylindrical shape in which the exothermic base material 1 can be accommodated, and the accommodated base material 1 has a cylindrical shape and is mutually complementary by a mat (not shown) The base material 1 is firmly fixed to the outer tube 6 having a similar circular shape.

The base material 1 is composed of a sintered body of a composite material of SiC or SiC / Si two-element system, and can be composed of a novel composite material described below. The base material 1 is formed with an exhaust gas flow path having a honeycomb structure composed of a large number of cell walls 1a, and a catalyst coat layer (not shown) is formed on the cell walls 1a. This catalyst coat layer is composed of oxides such as alumina (Al ₂ O ₃ ), platinum group elements such as palladium (Pd), rhodium (Rh), platinum (Pt), platinum group element compounds, or other noble metals and their The compound is supported on alumina or ceria zirconia-based composite oxide (CeO ₂ -ZrO ₂ ), and a slurry obtained by adjusting this with alumina sol or water is impregnated, ion exchange, sol-gel, It is formed by applying a wash coat method or the like.

  The exhaust gas that has flowed down from the upstream side of the exhaust gas exhaust system (X direction) is purified by the activity of the noble metal catalyst in the process of flowing through the exhaust gas flow path composed of a large number of cell walls 1a, and the purified exhaust gas is electrically heated. It flows from the catalytic converter 10 to the downstream side of the exhaust system.

  An electrode film 2 is formed at a pair of upper and lower electrodes formed in the diameter direction on the surface of the base material 1, and the electrode terminal 3 is placed on the surface of the base material 1 through an opening 2 a formed in the electrode film 2. It is fixed. Specifically, the lower surface of the electrode terminal 3 is formed into a curved surface having the curvature of the substrate 1, and a ceramic paste having the same composition as the electrode terminal 3 is applied to the interface between the lower surface and the substrate 1 and fired. Thus, the base material 1 made of a ceramic material and the electrode terminal 3 are joined. In addition, it is desirable that the resistance of the electrode terminal 3 is lower than that of the base material and that the thermal expansion coefficient is about the same as that of the base material 1.

  An external electrode 4 is attached to the electrode terminal 3, and a cable 5 a having a power source 5 b interposed between the upper and lower external electrodes 4, 4 is connected to form an external circuit 5.

  Here, the outline of the current path in the substrate 1 will be described with reference to FIG. 4A is a perspective view illustrating the flow of the applied current, and FIG. 4B is a cross-sectional view illustrating the flow of the applied current. When the power source 5b is ON-controlled at the time of starting the engine, the electrode terminals 3 and 3 located in the center of the base material 1 are energized (Y1 direction), and the diameter in the cross section of the base material 1 as shown in FIG. Flows linearly in the cross section of the substrate 1 (Y6 direction) through the path flowing in the path (Y5 direction) and the electrode film 2 around the electrode terminal 3 (Y2 direction), and passes through the electrode film 2 on the opposite side. Thus, a path (Y4 direction) is formed that circulates through the opposing electrode terminals 3 (Y4 direction).

  As described above, the electrode film 2 has a current diffusion function, and conducts as much current as possible in the entire base material 1 to achieve equal current diffusion and rectification.

  The insulating mat (not shown) interposed between the outer tube 6 and the base material 1 is formed of a ceramic fiber sheet made of alumina or the like having excellent heat resistance and strength in addition to insulating properties. be able to.

  However, as is apparent from FIG. 4B, the current paths formed in the substrate 1 having a circular cross section have different path lengths for each part (the path length at the center position of the substrate 1 is different). This is the longest and the path length becomes shorter as it goes outward in the radial direction), which means that the electrical resistance is different for each part. And the problem that the temperature rising in the base material 1 cannot be controlled uniformly may arise due to the difference in the electric resistance.

  Therefore, in the illustrated electrically heated catalytic converter 10, as shown in FIGS. 2 and 3, the lead electrode 7 </ b> A having a long length (length: t <b> 1) is provided in the vicinity of the electrode terminal 3 in the substrate 1. A lead electrode 7B having a relatively short length is disposed outside the lead electrode 7A at a predetermined interval from the lead electrode 7A, and the plurality of lead electrodes 7A and 7B having different lengths are used to form an electrode. In the region A (see FIG. 3) inside the left and right end portions of the film 2, the distance between the electrodes is unified to t3 in all the parts, and the electric resistance R formed by the distance between the electrodes t3 is the same. It is adjusted to. Note that the adjustment target region is not limited to the region A in the illustrated example, and may be the entire cross-section of the circular cross-section of the substrate 1. Further, the arrangement position and the number of the lead electrodes are not limited to the illustrated example.

  Here, the lead electrodes 7A and 7B are composed of a counterbore groove 7a and an electrode body 7b accommodated therein.

  The forming method is such that a plurality of (four in the illustrated example) counterbore grooves 7a having a length corresponding to each part are formed in advance in the manufacturing stage of the base material 1, and a paste for forming the electrode film 2 is used. The electrode body 7b can be formed by pouring into the spot facing groove 7a and firing. Moreover, the electrode body 7b can also be formed in the counterbore groove 7a by inserting the electrode body 7b manufactured in the shape and dimension previously accommodated in the counterbore groove 7a into the counterbore groove 7a.

  In order to prevent the lead electrode from becoming a heating element, it is desirable that the electrode body 7 b has a volume resistivity smaller than the volume resistivity of the substrate 1.

(Embodiment 2 of electric heating type catalytic converter)
FIG. 5 is a schematic diagram for explaining the second embodiment of the electrically heated catalytic converter (EHC). The electric heating type catalytic converter 10A shown in the figure is formed by forming an electrode film from two types of electrode films 2A and 2B having different resistances, and the electrode film 2A on the center side on the electrode terminal 3 side has a relatively low resistance. Electrode film. Although not apparent from the drawings, the electrode film has a three-band structure in which the electrode films 2B are disposed on both sides of the center-side electrode film 2A.

  By adjusting the electrode film 2A on the electrode terminal 3 side where the current flows in and out to a relatively low resistance compared to the electrode film 2B on the outer side, diffusion of the current over a wide range can be promoted. .

  In the electrically heated catalytic converter 10A, the electric resistance in the desired range of the substrate 1 is made uniform by the configuration of both the lead electrodes (not shown) formed inside the substrate 1 and the electrode films 2A and 2B shown. In addition, the resistance values of the electrode films 2A and 2B and the lengths of the plurality of lead electrodes are adjusted so as to achieve such uniformity.

(Embodiment 3 of electric heating type catalytic converter)
FIG. 6 is a schematic diagram for explaining Embodiment 3 of an electrically heated catalytic converter (EHC). In the electric heating type catalytic converter 10B shown in the figure, two electrode films 2D and 2E are disposed on both sides of the electrode film 2C so as to have a large dimension in a tapered shape in the radial direction from the center electrode film 2C.

  In this electrode film configuration, a current is combined with a current path that flows through the center of the substrate, and a path that flows from the anode to the side of the substrate on the radiation, flows through the inside of the substrate, and flows toward the cathode on the side of the substrate. The electric resistance of each part is determined by the resistance. Also in the illustrated electrically heated catalytic converter 10B, the desired range of the substrate 1 is determined by the configuration of both the unillustrated lead electrodes formed inside the substrate 1 and the illustrated electrode films 2C, 2D and 2E. The electric resistances of the electrode films 2C, 2D, and 2E and the lengths of the plurality of lead electrodes are adjusted so that the electric resistance can be made uniform. It is.

  According to the electrically heated catalytic converter 10B, the substrate 1 can be uniformly heated while gradually transferring heat radially from the center.

  Although not shown, a pedestal (not shown) is disposed around the base of the electrode terminal 3, and the lower surfaces of both the electrode terminal 3 and the pedestal have the curvature of the base material. 1 may be bonded to the interface of the surface of the electrode 1 via the paste of the same material as the electrode film.

  Further, in order to obtain a high bonding strength between the base material 1 and the electrode terminal 3, a counterbore portion (not shown) is provided at the electrode terminal 3 attachment portion of the base material 1, and the lower end of the electrode terminal 3 is provided at the counterbore portion. The form which accommodates and joins both may be sufficient. In this embodiment, regarding the bonding between the electrode terminal 3 and the bottom surface of the spot facing portion, the base material 1 has unevenness reflecting the honeycomb structure, so that the paste is sufficiently filled in the spot facing portion, and By bonding after uniformly dispersing at the interface, the bonding strength at the interface can be effectively improved. Moreover, in the structure by this form, since the side surface of the electrode terminal 3 can be supported by the side surface of a spot facing part, it leads also to the improvement of the bending strength of a junction part. Furthermore, by forming unevenness on the electrode terminal 3 and bonding it to the counterbore part, it is possible to improve the strength against the rotational stress in the axial direction of the electrode terminal 3 and to join the counterbore part to the electrode terminal 3. Further expanding the tensile strength and bending strength at the same time.

  Alternatively, an electrode in a form in which an external lead (not shown) such as a SUS plate, a cylindrical SUS lead, or a prismatic SUS lead is attached to a slit or a counterbore provided on the end face of the electrode terminal 3 may be used. The electrode terminal 3 and the external lead can be joined using a brazing material, but the brazing material is heat resistant in the temperature range in view of the formed joint being exposed to about 700 (° C.) or more. It is preferable to use an Ag—Cu brazing material (for example, Bag8 (Ag—Cu), TKC711 (Ag—Cu—Ti)).

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Honeycomb structure base material, 1a ... Cell wall, 1A ... Divided body, 2, 2A, 2B, 2C, 2D, 2E ... Electrode film, 3 ... Electrode terminal, 4 ... External electrode, 5 ... External circuit, 5a ... Cable, 5b ... Power source, 6 ... Outer tube (metal case), 7A, 7B ... Lead electrode, 7a ... Counterbore groove, 7b ... Electrode body, 10, 10A, 10B ... Electric heating type catalytic converter (EHC)

Claims (3)

A cylindrical substrate with a catalyst coat layer and a honeycomb structure;
A pair of electrodes formed on the surface of the substrate at opposite positions in the diameter direction of the substrate;
In an electrically heated catalytic converter composed of a cable connecting a pair of electrodes and an external circuit consisting of a power source interposed between the cables,
Within the base material, a plurality of lead electrodes extending to the other electrode side and having different lengths are arranged in regions corresponding to the respective electrodes, and the outside from the lead electrode located on the center side of the electrode The length of the lead electrode is shortened toward the lead electrode located at the position, and by adjusting the length of the lead electrode, part or all of the electrical resistance in the substrate is adjusted to be the same or substantially the same,
The electrode consists of an electrode terminal and an electrode film disposed on the surface of the base material around the electrode terminal,
The electrode film is disposed in the radial direction from the central electrode film and the central electrode film, and the planar shape has a tapered portion, and the planar dimension is larger than that of the central electrode film. An electrically heated catalytic converter formed from two electrode films. The electric heating catalytic converter according to claim 1 , wherein the lead electrode includes a counterbored groove formed in the base material and an electrode body accommodated in the counterbored groove. The electric heating catalytic converter according to claim 1 or 2 , wherein the electrode body has a volume resistivity smaller than a volume resistivity of the substrate.

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