JP4254621B2 - Exhaust gas purification device - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus that processes exhaust gas from an internal combustion engine by applying a high voltage.

In recent years, as a technology for purifying exhaust gas from internal combustion engines such as vehicles, it has a cylindrical outer peripheral electrode and a rod-shaped inner electrode extending along the axis of the outer peripheral electrode, and a high voltage is applied between both electrodes. In other words, a so-called transmission type or straight flow type exhaust gas purifying apparatus that purifies the exhaust gas passing therethrough using the generated plasma has been proposed (see, for example, Patent Document 1). In such a device, substances such as NOx in the exhaust gas passing through are converted to N ₂ etc., and PM (particulate matter) in the supplied exhaust gas is charged by the discharge from the internal electrode, The PM is adsorbed on the outer peripheral electrode side by the interaction between this and the electric field between the inner and outer electrodes, and is incinerated by the heat generated when a high voltage is applied.

JP-A-8-323147

  By the way, in this kind of apparatus, purification performance may deteriorate by long-term use. As a result of diligent research, the inventors have found that the reduction in purification performance is caused by the fact that PM, which is mainly composed of carbon, causes leakage between electrodes due to deposition during use, and limits the voltage between the electrodes. I found out that this is the cause.

  The present invention has been made on the basis of such new knowledge, and an object thereof is to suppress leakage between electrodes caused by PM accumulation in an exhaust gas purification apparatus that purifies exhaust gas by the action of a high voltage.

  1st this invention is equipped with the outer periphery electrode and the internal electrode arrange | positioned inside the said outer periphery electrode, and is extended in the flow direction of waste gas, The exhaust gas purification which purifies waste gas by applying a high voltage between both said electrodes In the apparatus, a support arm coupled to a longitudinal end portion of the internal electrode, and a cylindrical spacer made of an insulator and provided on the same axis as the outer peripheral electrode so as to protrude from the end portion of the outer peripheral electrode , The support arm is brought into contact with the spacer, and the support point of the internal electrode by the support arm is disposed outside the outer peripheral electrode.

  In the first aspect of the present invention, a cylindrical spacer is provided so as to protrude from the end of the outer peripheral electrode, the support arm is brought into contact with the spacer, and the support point of the internal electrode by the support arm is disposed outside the outer peripheral electrode. Therefore, the distance between the outer peripheral electrode and the support point of the internal electrode can be increased by the axial length of the spacer, thereby suppressing leakage between the electrodes due to PM deposition.

  A second aspect of the present invention is the exhaust gas purifying apparatus according to claim 1, comprising a plurality of outer peripheral electrodes arranged in parallel to each other, wherein the spacer is a part of the outer peripheral electrodes. An exhaust gas purifying apparatus characterized by being provided.

  Even in the case of the spacer according to the present invention, there is no risk of electric leakage due to creeping discharge or the like passing through the surface of the spacer. In this regard, in the second aspect of the present invention, since the spacer is provided only for some of the plurality of outer peripheral electrodes, it is possible to suppress the possibility of electric leakage via the surface of the spacer in the other outer peripheral electrodes.

  A third aspect of the present invention is the exhaust gas purifying apparatus according to claim 2, wherein the part of the outer peripheral electrodes is an outer peripheral electrode other than the outer peripheral electrode at the center of the exhaust gas flow path among the plurality of outer peripheral electrodes. This is an exhaust gas purification apparatus characterized by the above.

  PM deposition tends to concentrate in the center of the exhaust gas flow path. Therefore, as in the third aspect of the present invention, by setting the spacer installation location as an outer peripheral electrode other than the outer peripheral electrode at the center of the exhaust gas flow path among the plurality of outer peripheral electrodes, the exhaust gas that has a particularly strong risk of leakage due to PM accumulation In the vicinity of the center of the flow path, deposition can be suppressed, which is preferable.

  A fourth aspect of the present invention is the exhaust gas purification apparatus according to any one of claims 1 to 3, wherein the spacer has irregularities on the surface thereof.

  In the fourth aspect of the present invention, since the unevenness is provided on the surface of the spacer, the risk of leakage can be suppressed by increasing the path distance related to creeping discharge.

  A fifth aspect of the present invention is the exhaust gas purifying apparatus according to any one of claims 1 to 4, wherein the support arm is covered with an insulating layer at least in a region near the spacer. An exhaust gas purification device.

  In the fifth aspect of the present invention, since the support arm is covered with the insulating layer, the risk of electric leakage from the support arm can be suppressed.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
1 is a schematic configuration diagram showing a longitudinal sectional view of an exhaust gas purifying apparatus according to the present invention, FIG. 2 is a sectional view taken along line II-II in FIG. 1, and FIG. 3 is III-III in FIG. It is sectional drawing about a line. The exhaust gas purification apparatus 1 shown in these drawings is suitable when applied to a vehicle, and is configured as a plasma reactor or a corona reactor. The exhaust gas purification apparatus 1 is incorporated in an exhaust pipe constituting an exhaust system of the internal combustion engine in order to purify exhaust gas discharged from a combustion chamber of the internal combustion engine (not shown).

  The exhaust gas purifying apparatus 1 includes an upstream case 2a, a downstream case 2b, and a processing unit assembly 3. The exhaust gas discharged from the combustion chamber of the internal combustion engine is introduced into the upstream case 2a in the direction indicated by the white arrow in FIG. Then, the exhaust gas purified inside the processing unit assembly 3 is discharged from the downstream case 2b to the outside through an exhaust pipe (not shown).

  The cases 2a and 2b are made of a heat-resistant material such as metal, particularly SUS, and end portions 21a and 21b constituting an inlet or outlet to be connected to the exhaust pipe, and a generally hexagonal cross section having a larger diameter than the exhaust pipe. The enlarged diameter portions 22a and 22b having a shape, and cone portions 24a and 24b formed between the end portion 21a and the enlarged diameter portion 22a and between the end portion 22b and the enlarged diameter portion 22b are included.

  The processing unit assembly 3 is coupled between the cases 2a and 2b via the fixed frames 7 and 7. The processing unit assembly 3 includes a plurality (19 in the present embodiment) of processing units 6 arranged in parallel to each other. Each processing unit 6 includes a cylindrical outer peripheral electrode 4 and a thin outer electrode 4. It consists of a linear rod-shaped electrode 5 having a diameter. The outer peripheral electrode 4 of each processing unit 6 has its upstream end and downstream end fixed to the fixed frame 7 by welding or copper brazing.

  As shown in FIG. 3, one processing unit 6 is arranged at the center of the fixed frame 7, and twelve processing units 6 are arranged at equal intervals on the inner peripheral surface of the fixed frame 7. Six processing units 6 are arranged between the processing unit 6 at the center of 7 (that is, the center of the case 2) and the 12 processing units 6 described above.

  As shown in FIG. 2, spacers 9 are fixed at three locations on the integral fixing frame 7. The fixed frame 7 has an opening 7a (see FIG. 1) to which the spacer 9 is fixed and the other opening 7b. The outer peripheral electrodes 4 of the processing units 6 are both upstream and downstream. At the end, it is fixed to the opening 7a or the opening 7b. The cross-sectional shape of the opening edge to which the spacer 9 is fixed in the opening 7a is circular.

  On the other hand, the opening 7b to which the spacer 9 is not fixed has a circular cross section at the opening edge in contact with the outer peripheral electrode 4 and the opposite side (that is, the processing unit assembly 3 constituted by the processing unit 6 and the fixed frame 7). The upstream edges and downstream edges of the opening edges (hereinafter referred to as outer opening edges as appropriate) have a regular hexagonal cross section, and these opening edges are connected to each other by smooth curved surfaces. The outer opening edge of the opening 7b is smoothly connected to the outer opening edge of the other adjacent opening 7b on the boundary line BL indicated by a broken line in FIGS. 2 and 4, and the openings 7b, 7b The discharge from the boundary line BL is suppressed by not generating a clear ridge line therebetween.

It is preferable to use stainless steel (thermal expansion coefficient 7.2 × 10 ⁻⁷ × [10 ⁻⁶ / K]) for the outer peripheral electrode 4. The rod-shaped electrode 5 is disposed on the central axis of the outer peripheral electrode 4 and extends in the exhaust gas flow direction. For each rod-shaped electrode 5, it is preferable to use a press-fired tungsten product (thermal expansion coefficient 5.5 × 10 ⁻⁷ × [10 ⁻⁶ / K]) having good discharge characteristics.

  Both end portions of each rod-like electrode 5 are fixed to lattice points and tip portions of a metallic lattice member 8 as shown in FIGS. 1 and 2. The lattice member 8 includes a large number of support arms 8a. As shown in FIGS. 4 to 6, the main body 8b made of a heat-resistant conductive material such as SUS is used as an insulating layer made of a heat-resistant insulating material such as ceramic. It is coated with 8c. The main body 8b is electrically connected to the rod-shaped electrode 5 at the connection point with the rod-shaped electrode 5, and the insulating layer 8c covers the entire surface of the surface of the main body 8b excluding the contact surface related to this conduction. As shown in FIG. 5, each support arm 8a of the lattice member 8 has a cross-sectional shape extending in the axial direction of the apparatus, thereby suppressing the front projection area and ensuring the strength.

  Each lattice member 8 is fixed on the extension of the outer peripheral electrode 4 at three locations on one side via a cylindrical spacer 9 and a fixed frame 7. As shown in FIG. 7, the lattice member 8 includes an engagement shoulder portion 8 d at a portion corresponding to the edge portion of the spacer 9, and the engagement shoulder portion is coupled with the lattice member 8 and the rod-shaped electrode 5. The lattice member 8 is supported by the spacer 9 by the engagement between the portion 8 d and the spacer 9.

  The spacer 9 is a support member for supporting the lattice member 8 and is made of a heat-resistant insulating material such as ceramic. The spacer 9 is a cylindrical shape having substantially the same diameter and substantially the same cross-sectional shape as the outer peripheral electrode 4, and annular unevenness is formed on the outer peripheral surface and inner peripheral surface of the spacer 9. The unevenness has a shape in which the expansion and contraction of the radius are smoothly repeated along the axial direction, that is, so-called corrugation. The unevenness suppresses creeping discharge by increasing the path distance related to the creeping discharge.

  Each rod-like electrode 5 is connected to a power supply unit (not shown) via a lattice member 8 and a power plug 10. The outer peripheral electrode 4 of each processing unit 6 is electrically grounded via a terminal (not shown). As the power supply unit, any one of a DC high voltage power supply, an AC high voltage power supply, a DC pulse power supply, and a DC / pulse superimposed power supply can be used.

  As shown in FIG. 8, the power plug 10 includes a plug electrode 11, an insulator 12, and a metal shell 13. The lower end portion 11a of the plug electrode 11 is supported inside the insulator 12 so as to protrude and retract. A disc spring 11c is set between the main body 11b and the lower end portion 11a of the plug electrode 11, and the lower end portion 11a is always urged in the protruding direction by the elasticity of the disc spring 11c. A conductive friction-resistant material layer 11d is formed at the tip of the lower end portion 11a. As shown in FIG. 1, the lower end portion 11 a of the plug electrode 11 is in sliding contact with an inclined surface 5 a formed at the distal end portion of the rod-shaped electrode 5, and thereby the plug electrode 11 extends before and after the rod-shaped electrode 5 expands and contracts. And the rod-shaped electrode 5 are secured. The power plug 10 is fixed to the upstream case 2 a by a screw portion 13 a formed in the shell 13.

In the exhaust gas purification apparatus 1 configured as described above, in order to generate plasma in each processing unit 6 in accordance with the start of the internal combustion engine, the power supply unit causes the outer electrode 4 and the rod-shaped electrode 5 of each processing unit 6 to be connected. In the meantime, a high voltage is applied using the rod-shaped electrode 5 as an anode. When exhaust gas from the combustion chamber of the started internal combustion engine is introduced into the case 2, a plasma state is generated by discharge between the rod-like electrode 5 and the outer peripheral electrode 4 of each processing unit 6. A predetermined substance such as NOx is activated, and the reaction is promoted to be converted into a substance such as N ₂ . Further, PM in the supplied exhaust gas is charged by the discharge from the rod-shaped electrode 5 and is adsorbed by the outer electrode 4 due to the interaction with the electric field between the rod-shaped electrode 5 and the outer electrode 4, and with the application of a high voltage. The generated heat promotes the combustion or oxidation.

  Here, in the present embodiment, a cylindrical spacer 9 is provided so as to protrude upstream and downstream from the end of the outer peripheral electrode 4, and an intermediate portion of the support arm 8 a is brought into contact with an edge portion of the spacer 9. In addition, since the support point of the internal electrode 5 by the support arm 8a is disposed outside the outer peripheral electrode 4, the distance between the outer peripheral electrode 4 and the support point of the internal electrode 5 is increased by the axial length of the spacer 9. As a result, leakage between the electrodes 4 and 5 due to PM deposition can be suppressed.

  Further, even in the case of the spacer 9 in the present embodiment, there is no risk of electric leakage due to creeping discharge or the like passing through the surface of the spacer 9. However, in this embodiment, the spacers 9 are provided only for some of the plurality of outer peripheral electrodes 4, and sufficient spaces are provided between the other outer peripheral electrodes 4 and the internal electrodes 5. The risk of electric leakage in the other outer peripheral electrode 4 can be suppressed.

  In the present embodiment, the spacers 9 are provided only for some of the plurality of outer peripheral electrodes 4, while the spacers 9 are not provided for the other outer peripheral electrodes 4. Since they are arranged offset in the front-rear direction, it can be expected that the PM adhered to and peeled off from the outer peripheral surface of the spacer 9 is sucked into the outer peripheral electrode 4 where the spacer 9 is not provided and processed.

  Further, because of the fluid dynamic reason, the PM deposition tends to concentrate on the center of the exhaust gas flow path, so that the installation location of the spacer 9 in the exhaust gas flow path among the plurality of outer peripheral electrodes 4 as in the present embodiment. By using the outer peripheral electrode 4 other than the outer peripheral electrode 4 at the center, deposition can be suppressed in the vicinity of the central portion of the exhaust gas flow path where the risk of leakage due to the accumulated PM is particularly strong.

  Moreover, in this embodiment, since the unevenness | corrugation was provided in the surface of the spacer 9, the possibility of an electric leakage can be suppressed by the expansion of the path | route distance concerning creeping discharge.

  Moreover, in this embodiment, since the whole surface of the electroconductive main body 8b of the support arm 8a was coat | covered with the insulating layer 8c, the possibility of the electric leakage from the support arm 8a can be suppressed.

  In addition, this invention is not limited to the aspect as described in each above-mentioned embodiment, A various deformation | transformation is possible. For example, although the spacer 9 and the outer peripheral electrode 4 are cylindrical in the above embodiment, other shapes such as a rectangular tube may be used. In the above embodiment, the support shoulder 8a of the lattice member 8 is provided with the engaging shoulder 8d and is brought into contact with the edge of the spacer 9, but the structure for fixing the lattice member 8 and the spacer 9 is as follows. Other structures may be used. Moreover, in the said embodiment, although the support structure of the internal electrode 5 was made substantially symmetrical by the upstream and downstream of the processing unit 6, both need not be substantially object. Moreover, in the said embodiment, although the substantially whole surface of the electroconductive main body 8b of the support arm 8a was coat | covered with the insulating layer 8c, the area | region covered with an insulating layer is a part of support arm (for example, the edge part of the spacer 9). Or the vicinity of the boundary portion BL of the opening 7b of the fixed frame 7).

  In the present invention, a plurality of outer peripheral electrodes may be provided for a single rod-like electrode or internal electrode, and a plasma structure such as a honeycomb structure such as ceramics is installed in a space surrounded by the outer peripheral electrode 4. Regardless of the presence or absence of PM and the filtration of PM, various configurations that can reform exhaust gas by the action of electric power can be used, and all belong to the category of the present invention. Needless to say, the present invention can be applied to internal combustion engines other than vehicles.

It is a schematic structure figure showing an exhaust gas purification device concerning an embodiment of the present invention. It is sectional drawing about the II-II line | wire in FIG. It is sectional drawing about the III-III line in FIG. It is a front view which shows a fixed frame and a lattice member. It is the sectional view on the AA line of FIG. 4 which shows a fixed frame and a lattice member. FIG. 5 is a cross-sectional view taken along line B-B in FIG. 4 showing the fixed frame and the lattice member. It is a perspective view which shows the attachment structure of a lattice member. It is sectional drawing which shows a power supply stopper.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification apparatus 2a Upstream side case 2b Downstream side case 3 Processing unit assembly 4 Peripheral electrode 5 Rod-shaped electrode 6 Processing unit 8 Lattice member 9 Spacer 10 Feed plug

Claims (5)

In the exhaust gas purifying apparatus comprising an outer peripheral electrode and an inner electrode disposed inside the outer peripheral electrode and extending in the flow direction of the exhaust gas, and purifying the exhaust gas by applying a high voltage between the two electrodes,
A support arm coupled to the longitudinal end of the internal electrode;
A cylindrical spacer made of an insulator and provided on the same axis as the outer peripheral electrode so as to protrude from the end of the outer peripheral electrode;
The exhaust gas purifying apparatus is characterized in that the support arm is brought into contact with the spacer, and the support point of the internal electrode by the support arm is disposed outside the outer peripheral electrode. The exhaust gas purification device according to claim 1,
An exhaust gas purification apparatus comprising a plurality of outer peripheral electrodes arranged in parallel to each other, wherein the spacer is provided for some of the outer peripheral electrodes. An exhaust gas purification device according to claim 2,
The exhaust gas purification apparatus according to claim 1, wherein the part of the outer peripheral electrodes are outer peripheral electrodes other than the outer peripheral electrode at the center of the exhaust gas flow path among the plurality of outer peripheral electrodes. An exhaust gas purification apparatus according to any one of claims 1 to 3,
The exhaust gas purifying apparatus, wherein the spacer has irregularities on a surface thereof. An exhaust gas purification device according to any one of claims 1 to 4,
The exhaust gas purifying apparatus, wherein the support arm is covered with an insulating layer at least in a region near the spacer.

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