JP4505802B2 - 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.

As a technique for purifying exhaust gas from an internal combustion engine such as a vehicle, in recent years, it has a cylindrical outer peripheral electrode and a rod-shaped inner electrode extending in the exhaust gas flow direction along the axis of the outer peripheral electrode. In other words, a so-called transmission type or straight flow type exhaust gas purifying apparatus has been proposed in which a high voltage is applied to the gas to generate a plasma state and purify exhaust gas passing therethrough (see, for example, Patent Document 1). In such an apparatus, substances such as NOx in the exhaust gas passing through are converted to N ₂ etc., and PM (particulate matter) in the exhaust gas is charged by discharge from the internal electrode, The PM is adsorbed on the outer peripheral electrode side by the interaction with the electric field between the inner and outer electrodes, or is captured by the collecting device provided at the rear, and is generated by the active gas (NO ₂ , O ₃ , OH, etc.) generated by the discharge. Incinerated at low temperature.

JP-A-8-323147

  By the way, in this type of apparatus, purification performance may be deteriorated by long-term use. As a result of intensive studies, the inventors have found that one of the major causes of the reduction in purification performance is abnormal discharge during operation.

  The present invention has been made on the basis of such new knowledge, and an object thereof is to suppress abnormal discharge during operation 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, The exhaust gas purification apparatus which purifies waste gas by applying a high voltage between both said electrodes, The said internal electrode The vicinity of one end of the inner electrode is fixed to the first support that constitutes the power feeding path to the internal electrode, and the vicinity of the other end of the internal electrode slides on the second support The exhaust gas purifying apparatus is characterized in that it is supported so that only a free end of the internal electrode is covered with an insulating layer .

In the first aspect of the present invention, part of the internal electrode is fixed to the first support, while the other part of the internal electrode is slidably supported by the second support. The internal electrode is allowed to expand and contract when it is placed at a high temperature by the supply of water, and deformation due to thermal expansion is suppressed, so that the purification performance is improved by suppressing abnormal discharge that may be caused by deformation of the internal electrode. Can do. Moreover, since the free end of the internal electrode is covered with the insulating layer, the purification performance can be improved by suppressing abnormal discharge from the free end of the internal electrode.

  According to a second aspect of the present invention, there is provided an exhaust gas purification apparatus according to claim 1, wherein a plurality of the internal electrodes are fixed to a single first support. .

  In the second aspect of the present invention, the effect of the first aspect of the present invention can be suitably realized in an apparatus having a plurality of internal electrodes.

The third aspect of the present invention is the exhaust gas purifying apparatus according to claim 1 or 2 , wherein the radius of curvature of the contour in the cross section of the first support is greater than the radius of curvature of the contour in the cross section of the internal electrode. It is an exhaust gas purification device characterized in that it is also large.

In the third aspect of the present invention, since the discharge from the first support is suppressed, the purification performance can be improved by suppressing the abnormal discharge.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  In FIG. 1, an exhaust gas purification apparatus 1 according to an embodiment of the present invention 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 purification apparatus 1 includes an upstream case 2a, a downstream case 2b, and an intermediate case 3. The upstream case 2a, the downstream case 2b, and the intermediate case 3 are formed of a metal, particularly a heat resistant material such as SUS. 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. The exhaust gas purified inside the intermediate case 3 is discharged to the outside from the downstream case 2b through an exhaust pipe (not shown).

  The upstream case 2a and the downstream case 2b are generally the same diameter and substantially cylindrical end portions 21a and 21b as the exhaust pipe constituting the inlet or outlet for connection to the exhaust pipe, and are generally larger in diameter than the exhaust pipe. A large-diameter portion having a racetrack-shaped cross-section, and cone portions 24a and 24b formed between the end portion 21a and the large-diameter portion and between the end portion 21b and the large-diameter portion are included.

  Between the upstream case 2a and the downstream case 2b, a cylindrical intermediate case 3 having a substantially racetrack cross-sectional shape is coupled. Insulating blocks 7a and 7b are fixed to the upstream and downstream openings of the intermediate case 3 via alumina mats. The insulating blocks 7a and 7b are made of an insulator such as alumina.

  A plurality (24 in this embodiment) of processing units 6 are fixed in parallel between the insulating blocks 7a and 7b. Each processing unit 6 includes a cylindrical discharge tube 4a, a cylindrical outer peripheral electrode 4b formed on the outer peripheral surface of the discharge tube 4a, and an inner electrode 5 in the shape of a small-diameter right circular cylinder. Each discharge tube 4a has its upstream end and downstream end fixed to the insulating blocks 7a and 7b, respectively, and the axial center of the discharge tube 4a is formed by a circular through hole 7c formed in the insulating blocks 7a and 7b. It is matched with the axis.

  The arrangement of the through holes 7c in the insulating blocks 7a and 7b is as shown in FIG. That is, a set of four through-holes 7c in a vertical row is arranged in parallel with each other in three rows, and a set of three through-holes 7c in a vertical row is arranged between these columns and on both sides, a total of four rows. Arranged in columns. The through-holes 7c in each column are arranged so that the vertical position is shifted by the approximate radius of the outer peripheral electrode 4b with respect to the adjacent through-holes 7c, thereby reducing the distance between the columns and thus the width of the entire apparatus. Reduction is being attempted. The processing unit 6 is fixed to each of the through holes 7c arranged in this way. Between the outer peripheral electrodes 4b of the plurality of processing units 6, an electrically connecting mesh 9 made of mesh-like SUS or the like is inserted in a meandering manner and held by its own elasticity. Due to the contact of the electrical connection mesh 9, the outer peripheral electrodes 4 b are electrically connected to each other. It is preferable to use SUS for the outer peripheral electrode 4b.

  The internal electrode 5 is substantially rigid and is disposed on the central axis of the outer peripheral electrode 4b and extends in the exhaust gas flow direction. For each internal electrode 5, it is preferable to use a tungsten press-fired product or SUS having good discharge characteristics.

  The upstream end of each internal electrode 5 in the longitudinal direction is fixed to the electrode support frame 8 as shown in FIGS. 1 and 2 outside the discharge tube 4a and the outer peripheral electrode 4b. Has been. The electrode support frame 8 is made of a heat-resistant conductive material such as metal, particularly SUS, and as shown in FIG. 2, seven support arms 8 a having a longitudinal direction as a longitudinal direction and the seven support arms 8 a are crossed. In this manner, the two support arms 8a provided obliquely are combined. In the present embodiment, the two support arms 8a provided in a skewed manner generally have a front surface at the boundary between the through holes 7c so as to avoid as much as possible the shielding of the front surface of the through hole 7c of the insulating block 7a. Is arranged. In addition, since PM deposition tends to concentrate in the center of the exhaust gas flow path for hydrodynamic reasons, the two support arms 8a that run obliquely insulate that the amount of PM passing is relatively large. Shifting up and down is arranged so as to avoid the central portion of the block 7a, thereby suppressing leakage due to PM accumulation.

  Each support arm 8a of the electrode support frame 8 is rounded at each corner as shown in FIG. 3, and the contour in the cross section of each support arm 8a, particularly the radius of curvature of the surface of each corner, is The radius of curvature is larger than the radius of curvature of the peripheral surface of the internal electrode 5 having a circular cross section, thereby suppressing air discharge from the support arm 8a to the internal electrode 5.

  As shown in FIGS. 3 and 4, for example, as shown in FIGS. 3 and 4, each internal electrode 5 and the electrode support frame 8 are fixed to each other by forming a lateral groove 81, a vertical hole 82, and a notch 83. The internal electrode 5 is configured to be fitted into the vertical hole 82 by inserting the large-diameter head 51 formed in the portion into the lateral groove 81 through the guide slope 84 (see FIG. 4) of the notch 83. Is preferred. In this case, the small-diameter shaft portion 52 (see FIG. 3) of the internal electrode 5 is locked by the narrowed portion 85 provided at the boundary portion between the guide inclined surface 84 and the vertical hole 82.

  Also, as shown in FIG. 3, the vicinity of the downstream end of each internal electrode 5 is supported by the support arm 18a of the downstream electrode support frame 18 outside the discharge tube 4a and the outer peripheral electrode 4b. However, as shown in FIG. 3, the downstream support arm 18 a includes a through hole 181 having a slightly larger diameter than the shaft portion 52 of the internal electrode 5, and the internal electrode 5 is inserted into the through hole 181. By being fitted into the gap, the support arm 18a is slidably supported. A free end 53 which is an end portion on the downstream side of the internal electrode 5 is covered with an insulating layer 54 made of insulator or the like.

  In FIG. 1 again, a power supply line 10 is connected to the electrode support frame 8, and the power supply line 10 is connected to a power supply unit (not shown). Further, a sleeve 11 covering the power supply line 10 and a holding material 12 are fixed to the electrode support frame 8, and the electrode support frame 8 is fixed to the insulating block 7 a via the sleeve 11 and the holding material 12. . The sleeve 11 and the holding material 12 are made of an insulating material such as an insulator.

  Of the 24 processing units 6, the conductive wire 13 is connected to the outer peripheral electrode 4b of the processing unit 6 at the top of the widthwise central row, and the conductive wire 13 is connected to an appropriate body ground point of a vehicle body (not shown). It is electrically grounded by being connected. The conductive wire 13 is covered with a sleeve 14 made of an insulator such as an insulator, and the sleeve 14 is fixed to the intermediate case 3. As described above, since the outer peripheral electrodes 4b of the plurality of processing units 6 are electrically connected to each other by the electrical connection mesh 9, the outer peripheral electrodes 4b of all the processing units 6 are grounded. 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.

In the exhaust gas purification apparatus 1 configured as described above, a high voltage is applied between the outer peripheral electrode 4b and the internal electrode 5 of each processing unit 6 by using the internal electrode 5 as an anode in accordance with the start of the internal combustion engine. Applied. When the exhaust gas from the combustion chamber of the started internal combustion engine is introduced from the upstream case 2a into the discharge tube 4a, air discharge between the internal electrode 5 and the outer peripheral electrode 4b of each processing unit 6 occurs. plasma state occurs, the predetermined substance such as NOx in the exhaust gas is activated and is the reaction is promoted is converted into substances such as N _2. Further, PM in the supplied exhaust gas is charged by the discharge from the internal electrode 5 and is adsorbed by the outer peripheral electrode 4b due to the interaction with the electric field between the inner electrode 5 and the outer peripheral electrode 4b. The combustion or oxidation is promoted by the active gas generated.

  Here, in this embodiment, a part of the internal electrode 5 is fixed to the support arm 8a of the electrode support frame 8, while the other part of the internal electrode 5 is slidable on the support arm 18a of the electrode support frame 18. Therefore, the expansion and contraction of the internal electrode 5 is allowed when the exhaust gas is supplied at a high temperature, and the bending due to the thermal expansion is suppressed. Therefore, in this embodiment, the purification performance can be improved by suppressing abnormal discharge that may be caused by bending.

  In the present embodiment, since the plurality of internal electrodes 5 are fixed to the single electrode support frame 8, the effect of the present invention can be suitably realized in an apparatus having a plurality of internal electrodes.

  Moreover, in this embodiment, since the free end 53 of the internal electrode 5 is covered with the insulating layer 54, the discharge from the free end 53 is suppressed, and the purification performance can be improved by suppressing abnormal discharge.

  In this embodiment, the radius of curvature of the contour in the cross section of the support arm 8a is larger than the radius of curvature of the contour in the cross section of the internal electrode 5, so that air discharge from the support arm 8a to the internal electrode 5 occurs. And the purification performance can be improved by suppressing abnormal discharge.

  In addition, this invention is not limited to the aspect as described in the said embodiment, A various deformation | transformation is possible. For example, in the above-described embodiment, the electrode support frame 8 includes a large number of support arms 8a arranged with the vertical vertical direction as a longitudinal direction as shown in FIG. 2, and two support arms 8a that run obliquely across the support arms 8a. However, the structure of the electrode support frame provided with the support arm 8a in the present invention is not limited to such a structure. For example, the electrode support frame 108 shown in FIG. It may be configured by a combination of a large number of support arms 108a arranged as a single support arm 108a intersecting these support arms 108a in a substantially orthogonal direction. In the above embodiment, the electrode support frames 8 and 18 including a large number of support arms 8a and 18a are used as the first and second supports. However, in the present invention, it is essential to combine a large number of support arms. Alternatively, only one support arm 8a, 18a may be used, and the first and second supports may not be arm-shaped. Further, the fixing of the support arm 4a and the internal electrode 5 is not limited to the coupling by fitting as shown in FIGS. 3 and 4, and may be performed by other methods such as welding or integral molding.

  Moreover, in the said embodiment, although the discharge tube 4a and the outer periphery electrode 4b were made into the cylindrical shape, it is good also as other shapes, such as a rectangular tube shape. In the above embodiment, the electrode support frame 8 is fixed to the insulating blocks 7a and 7b via the sleeve 11 or the holding member 12. However, the electrode support frame 8 may be fixed to other structures. In the above-described embodiment, the electrode support frames 8 and 18 that are the support structure of the internal electrode 5 are substantially symmetric between the upstream side and the downstream side of the processing unit 6, but it is not necessary that both are substantially symmetric. Further, a part of the support arms 8a and 18a (for example, the vicinity of the edge of the through hole 7c) or the entire surface thereof may be covered with an insulating layer. Moreover, you may carry | support a catalyst substance on an outer peripheral electrode or an internal electrode.

  Furthermore, although the electrode support frames 8 and 18 are separated from each other in the present invention, the first and second supports in the present invention may be integral with each other. In the present invention, a plurality of outer peripheral electrodes divided from each other in the circumferential direction and the longitudinal direction may be provided for a single inner electrode, and a honeycomb structure such as ceramics is formed in a space surrounded by the outer peripheral electrode 4b. Regardless of whether plasma is used or whether PM is filtered, various configurations that can modify 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 a front view which shows an intermediate | middle case, an insulation block, and an electrode support frame. It is sectional drawing which shows the support structure of an internal electrode. It is a front view which shows an insulation block and an electrode support frame. It is a front view which shows the other structural example of an electrode support frame.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification apparatus 2a Upstream side case 2b Downstream side case 3 Intermediate case 4a Discharge tube 4b Outer electrode 5 Internal electrode 6 Processing unit 8 Electrode support frame (first support)
8a Support arm 9 Electrical connection mesh 10 Feed line 18 Electrode support frame (second support)

Claims (3)

In an exhaust gas purifying apparatus comprising an outer peripheral electrode and an internal electrode disposed inside the outer peripheral electrode, and purifying exhaust gas by applying a high voltage between the two electrodes,
The vicinity of one end of the internal electrode is fixed to a first support that constitutes a power feeding path to the internal electrode,
The vicinity of the other end of the internal electrode is slidably supported on the second support ,
Only the free end of the internal electrode is covered with an insulating layer . The exhaust gas purification device according to claim 1,
An exhaust gas purification apparatus, wherein a plurality of the internal electrodes are fixed to a single first support. The exhaust gas purifying device according to claim 1 or 2 ,
An exhaust gas purifying apparatus, wherein a radius of curvature of a contour in a cross section of the first support is larger than a radius of curvature of a contour in a cross section of the internal electrode.

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