Patent ID: 12247510

DETAILED DESCRIPTION OF THE INVENTION

The present invention is not limited to each embodiment, and components can be modified and embodied without departing from the spirit of the present invention. Further, various inventions can be formed by appropriately combining a plurality of components disclosed in each embodiment. For example, some components may be removed from all of the components shown in the embodiments. Furthermore, the components of different embodiments may be optionally combined.

Embodiment 1

FIG.1is a perspective view showing an exhaust gas purification device1according to Embodiment 1 of the present invention, andFIG.2is a cross-sectional view of the exhaust gas purification device1taken along the line II-II inFIG.1. The exhaust gas purification device1as shown inFIGS.1and2is provided, for example, on an exhaust path of a motor vehicle or the like, and is a device for purifying an exhaust gas discharged from an engine.

As shown inFIGS.1and2, the exhaust gas purification device1has an electrically heating support2and a can body3.

The electrically heating support includes: a honeycomb structure4and a pair of metal electrodes5. The honeycomb structure4is a pillar shaped member made of ceramics, and includes: an outer peripheral wall40; and a partition wall41which is arranged on an inner side of the outer peripheral wall10and defines a plurality of cells41aeach extending from one end face to other end face to form a flow path. The pillar shape is understandable as a three-dimensional shape having a thickness in a flow path direction of the cells41a(an axial direction of the honeycomb structure4). A ratio of an axial length of the honeycomb structure4to a diameter or width of the end face of the honeycomb structure4(aspect ratio) is arbitrary. The pillar shape may also include a shape in which the axial length of the honeycomb structure4is shorter than the diameter or width of the end face (flat shape).

An outer shape of the honeycomb structure4is not particularly limited as long as it has a pillar shape. For example, it can be other shapes such as a pillar shape having circular end faces (cylindrical shape), a pillar shape having oval end faces, and a pillar shape having polygonal (rectangular, pentagonal, hexagonal, heptagonal, octagonal, etc.) end faces. As for the size of the honeycomb structure4, an area of the end faces is preferably from 2,000 to 20,000 mm2, and even more preferably from 5,000 to 15,000 mm2, in order to increase heat resistance (to suppress cracks generated in the circumferential direction of the outer peripheral wall).

A shape of each cell in the cross section perpendicular to the flow path direction of the cells41amay preferably be a quadrangle, hexagon, octagon, or a combination thereof, although not limited thereto. Among these, the quadrangle and the hexagon are preferred. Such a cell shape can lead to a decreased pressure loss when an exhaust gas flows through the honeycomb structure4, which can provide improved purification performance.

The partition wall41that defines the cells41apreferably has a thickness of from 0.1 to 0.3 mm, and more preferably from 0.1 to 0.2 mm. The thickness of 0.1 mm or more of the partition wall41can suppress a decrease in the strength of the honeycomb structure4. The thickness of the partition wall41of 0.3 mm or less can suppress a larger pressure loss when an exhaust gas flows through the honeycomb structure4if the honeycomb structure4is used as a catalyst support to support a catalyst. In the present invention, the thickness of the partition wall41is defined as a length of a portion passing through the partition wall41, among line segments connecting the centers of gravity of adjacent cells41a, in the cross section perpendicular to the flow path direction of the cells41a.

The honeycomb structure4preferably has a cell density of from 40 to 150 cells/cm2, and more preferably from 70 to 100 cells/cm2, in the cross section perpendicular to the flow path direction of the cells41a. The cell density in such a range can allow the purification performance of the catalyst to be increased while reducing the pressure loss when the exhaust gas flows. The cell density of 40 cells/cm2or more can allow a catalyst supported area to be sufficiently ensured. The cell density of 150 cells/cm2or less can prevent the pressure loss when the exhaust gas flows through the honeycomb structure4from being increased if the honeycomb structure4is used as a catalyst support to support the catalyst. The cell density is a value obtained by dividing the number of cells by the area of one end face portion of the honeycomb structure4excluding the outer peripheral wall40portion.

The provision of the outer peripheral wall40of the honeycomb structure4is useful from the viewpoints of ensuring the structural strength of the honeycomb structure4and suppressing the leakage of a fluid flowing through the cells41afrom the outer peripheral wall40. Specifically, the thickness of the outer peripheral wall40is preferably 0.05 mm or more, and more preferably 0.10 mm or more, and even more preferably 0.15 mm or more. However, if the outer peripheral wall40is too thick, the strength will be too high, and a strength balance between the outer peripheral wall40and the partition wall41will be lost, resulting in a decrease in thermal shock resistance. Therefore, the thickness of the outer peripheral wall40is preferably 1.0 mm or less, and more preferably 0.7 mm or less, and even more preferably 0.5 mm or less. The thickness of the outer peripheral wall40is defined as a thickness of the outer peripheral wall40in the normal line direction relative to the tangent line at a measured point when the point of the outer peripheral wall40where the thickness is to be measured is observed in the cross section perpendicular to the flow path direction of the cells41a.

The honeycomb structure4is made of ceramics and is preferably electrically conductive. Volume resistivity is not particularly limited as long as the honeycomb structure4is capable of heat generation by Joule heat when a current is applied. Preferably, the volume resistivity is from 0.1 to 200 Ωcm, and more preferably from 1 to 200 Ωcm. As used herein, the volume resistivity of the honeycomb structure4refers to a value measured at 25° C. by the four-terminal method.

The honeycomb structure4can be made of a material selected from the group consisting of oxide ceramics such as alumina, mullite, zirconia and cordierite, and non-oxide ceramics such as silicon carbide, silicon nitride and aluminum nitride, although not limited thereto. Further, silicon carbide-metal silicon composite materials and silicon carbide/graphite composite materials can also be used. Among these, it is preferable that the material of the honeycomb structure4contains ceramics mainly based on a silicon-silicon carbide composite material or silicon carbide, in terms of balancing heat resistance and electrical conductivity. The phrase “the material of the honeycomb structure4is mainly based on silicon-silicon carbide composite material” means that the honeycomb structure4contains 90% by mass of more of silicon-silicon carbide composite material (total mass) based on the total material. Here, the silicon-silicon carbide composite material contains silicon carbide particles as an aggregate and silicon as a binding material to bind the silicon carbide particles, preferably in which a plurality of silicon carbide particles are bound by silicon such that pores are formed between the silicon carbide particles. The phrase “the material of the honeycomb structure4is mainly based on silicon carbide” means that the honeycomb structure4contains 90% or more of silicon carbide (total mass) based on the total material.

When the honeycomb structure4contains the silicon-silicon carbide composite material, a ratio of the “mass of silicon as a binding material” contained in the honeycomb structure4to the total of the “mass of silicon carbide particles as an aggregate” contained in the honeycomb structure4and the “mass of silicon as a binding material” contained in the honeycomb structure4is preferably from 10 to 40% by mass, and more preferably from 15 to 35% by mass.

The partition wall41may be porous. When the partition wall41is porous, the porosity of the partition wall41is preferably from 35 to 60%, and even more preferably from 35 to 45%. The porosity is a value measured by a mercury porosimeter. Further, the partition wall41may be dense, and when the partition wall41is dense, the porosity of the partition wall41may be 10% or less, or 5% or less.

The partition wall41of the honeycomb structure4preferably has an average pore diameter of from 2 to 15 μm, and even more preferably from 4 to 8 μm. The average pore diameter is a value measured by a mercury porosimeter.

Although not shown, the honeycomb structure4is provided with electrode layers on the outer surface of the outer peripheral wall40. The electrode layers are provided as a pair of electrode layers, for example, on the outer surface of the outer peripheral wall40so as to extend in the direction of the flow path of the cells41ain a form of a band across the central axis of the honeycomb structure4. The providing method is not limited thereto as long as it can be connected to a pair of metal electrodes5, which will be described below. The pair of metal electrodes5are provided on those electrode layers, and the electrode layers and the metal electrodes5are connected to each other. Although not shown, the metal electrodes5can be connected to an external power source such as a battery via a power cable. By applying a voltage to the honeycomb structure4through the metal electrodes5and the electrode layers, the honeycomb structure4can generate heat.

The volume resistivity of the electrode layers is preferably 1/200 or more and 1/10 or less of that of the honeycomb structure4, in terms of facilitating the flow of electricity to the electrode layers.

Each electrode layer may be made of conductive ceramics, a metal, or a composite material (cermet) of a metal and a conductive ceramic. Examples of the metal include a single metal of Cr, Fe, Co, Ni, Si or Ti, or an alloy containing at least one metal selected from the group consisting of those metals. Non-limiting examples of the conductive ceramics include silicon carbide (SiC), and metal compounds such as metal silicides such as tantalum silicide (TaSi2) and chromium silicide (CrSi2).

As a method for producing the honeycomb structure4having the electrode layers, first, an electrode layer forming raw material containing ceramic raw materials is applied onto a side surface of a honeycomb dried body and dried to form a pair of unfired electrode layers on the outer surface of the outer peripheral wall so as to extend in the form of band in the flow path direction of the cells, across the central axis of the honeycomb dried body, thereby providing a honeycomb dried body with unfired electrode layers. Then, the honeycomb dried body with unfired electrode layers is fired to produce a honeycomb fired body having a pair of electrode layers. The honeycomb structure4having the electrode layers is thus obtained.

The pair of metal electrodes5is for applying a voltage to the honeycomb structure4. The pair of metal electrodes5are attached onto the outer peripheral surface of the honeycomb structure4, more specifically, onto the electrode layers as described above. The pair of metal electrodes5are spaced apart from each other in the circumferential direction of the honeycomb structure4. The pair of metal electrodes5may be arranged at the center of the honeycomb structure4in the axial direction, or may be arranged at positions displaced from the center in the axial direction. One of the pair of metal electrodes5is handled as a positive electrode and the other is handled as a negative electrode. That is, current flows from one metal electrode5through the honeycomb structure4to the other metal electrode5.

Each of the pair of metal electrodes5has a connection portion50fixed to the outer peripheral surface of the honeycomb structure4and a drawer portion51extending from the connection portion50. The connection portion50is in contact with and connected to the outer peripheral surface of the honeycomb structure4. An external power source can be connected to the drawer portion51via a power cable (not shown). Details of the connection portion50and the drawer portion51will be described later with reference to the drawings.

By supporting a catalyst on the electrically heating support2, the electrically heating support2can be used as a catalyst body. Examples of the catalyst include noble metal-based catalysts and catalysts other than those. Illustrative examples of the noble metal catalysts include three-way catalysts and oxidation catalysts having a noble metal such as platinum (Pt), palladium (Pd), and rhodium (Rh) supported on surfaces of alumina pores, and containing a co-catalyst such as ceria and zirconia; or lean NOx trap catalysts (LNT catalysts) containing an alkaline earth metal and platinum as storage components for nitrogen oxides (NOx). Examples of catalysts that do not use noble metals include NOx catalytic reduction catalysts (SCR catalysts) containing copper-substituted or iron-substituted zeolites, and the like. Further, two or more types of catalysts selected from those catalysts may be used. A method of supporting the catalyst is also not particularly limited, and it can be carried out according to the conventional method of supporting the catalyst on the honeycomb structure.

The can body3is a cylindrical metal member for housing the electrically heating support2. The can body3has an opening30for drawing the drawer portion51to the outside. Examples of the metal include various stainless steels including chromium-based stainless steels. The inner peripheral surface of the can body3may also be provided with an insulating layer made of glass. The providing of the insulating layer can further enhance the effect of preventing electric leakage when the electrically heating support2is energized. Although not shown, a mat may be inserted between the outer peripheral surface of the honeycomb structure4and the inner peripheral surface of the can body3.

Next,FIG.3is a perspective view showing the metal electrode5ofFIG.2. The metal electrode5according to the present embodiment is composed of a single metal plate as a whole, and the connection portion50and the drawer portion51are integrally formed with each other.

The connection portion50has a comb-like shape as a whole. More particularly, the connection portion50includes: a longitudinal base portion500; and a plurality of tooth portions501extending parallel to each other from one side edge of the base portion500while being spaced apart from each other in the longitudinal direction of the base portion500. Each tooth portion501extends in a direction perpendicular to the longitudinal direction of the base portion500.

The drawer portion51is formed by bending a metal piece extending from the connection portion50. More specifically, the drawer portion51is formed by bending the metal piece extending from the side edge of the base portion500opposite to the side edge from which the tooth portions501extend. The metal piece forming the drawer portion51can extend in a direction orthogonal to the longitudinal direction of the base portion500from the central portion of the base portion500in the longitudinal direction of the base portion500. The metal piece forming the drawer portion51may extend from a position shifted in the longitudinal direction of the base portion500from the central portion of the base portion500in the longitudinal direction of the base portion500.

The drawer portion51is provided with at least two bent portions510. The drawer portion51according to the present invention is provided with the two bent portions510. However, the number of the bent portions510may be three or more. The at least two bent portions510are formed such that the extending directions of the respective ridgelines R are different from each other. The ridgeline R is a line along which the top of the bent portion510that appears on an outer side of a bent part of the bent portion510extends, and is also understandable as a bending line when forming the bent portion510.

Each portion of the drawer portion51can rotate about an axis which is the extending direction of the ridgeline R of the bent portion510. The drawer portion51can be expanded and contracted by rotating each portion. Since the extending directions of the at least two bent portions510are different from each other as described above, the rotation directions of the portions connected by the bent portions510are also different from each other. This can allow each portion to be rotated in a larger number of directions than a case where all the bending portions510extend in the same direction, so that the resistance of the metal electrodes5to vibration can be improved.

More particularly, the drawer portion51according to the present embodiment is provided with a first bent portion511and a second bent portion512(two bent portions510) and a first plate portion513and a second plate portion514. The first bent portion511is provided between the base portion500of the connection portion50and the first plate portion513. A ridgeline R of the first bent portion511extends in the longitudinal direction of the base portion500of the connection portion50. The second bent portion512is provided between the first plate portion513and the second plate portion514. The second bent portion512is arranged on the tip side of the first plate portion513. A ridgeline R of the second bent portion512extends in a direction orthogonal to the ridgeline R of the first bent portion511. An angle at which the ridgeline R of the first bent portion511and the ridgeline R of the second bent portion512intersect with each other may be less than 90° or more than 90°. However, from the viewpoint of stress buffering (vibration absorption), the angle at which the ridgeline R of the first bent portion511intersects with the ridgeline R of the second bent portion512is preferably close to 90° (perpendicular), and the angle is more preferably 90±45°, and even more preferably 90±30°, and still more preferably 90±15°. When the ridgeline R of the first bent portion511and the ridgeline R of the second bent portion512are in a twisted relationship, the angle at which these ridgelines R intersect with each other may be understandable as an intersection angle when one of the ridgelines R intersects with the other.

For convenience of explanation, X, Y and Z axes orthogonal to one another are defined as shown inFIG.3. It is understandable that the X axis is the axis extending in the direction in which the teeth portions501extend from the base portion500of the connection portion50, the Y axis is the axis extending in the longitudinal direction of the base portion500of the connection portion50, and the Z axis is the axis extending in the thickness direction of the base portion500.

When the connection portion50is fixed to the outer peripheral surface of the honeycomb structure4, the first plate portion513can rotate about the Y axis. That is, the first plate portion513can be displaced in the X and Z axis directions. This means that the first bent portion511can absorb vibrations in the X and Z axis directions. Also, the second plate portion514can rotate about an axis located on a plane defined by the X and Z axes. That is, the second plate portion514can be displaced at least in the Y axis direction. This means that the second bent portion512can absorb at least the vibration in the Y axis direction. That is, it is found that the drawer portion51according to the present embodiment can absorb vibrations in the directions of all three axes.

The extending directions of the ridgelines R of the at least two bent portions510can include a first direction parallel to the axial direction of the honeycomb structure4and a second direction orthogonal to the first direction. As shown inFIGS.1and2, the metal electrode5is arranged so that the longitudinal direction of the base portion500of the connection portion50is parallel to the axial direction of the honeycomb structure4, whereby the ridgeline R of the first bent portion511can extend in the first direction. However, another arrangement may be used, such as inclining the extending direction of the ridgeline R of the bent portion510by an angle of less than 90° with respect to the axial direction of the honeycomb structure4.

The thickness of the drawer portion51is preferably 0.03 mm or more and 1 mm or less. The thickness of the drawer portion51of 0.03 mm or more can sufficiently ensure the strength of the drawer portion51. The thickness of the drawer portion51of 1 mm or less can avoid the rigidity of the drawer portion51from being too high, lead to easy expansion and contraction of the drawer portion51, and result in more easy absorption of vibration. The thickness of the drawer portion51is more preferably 0.03 mm or more and 0.8 mm or less, and further preferably 0.05 mm or more and 0.7 mm or less. The thickness of the drawer portion51in the above range can lead to smooth expansion and contraction of the drawer portion51while ensuring sufficient strength for the drawer portion51. The thickness of the connection portion50may be the same as or different from the thickness of the drawer portion51.

The metal electrode5may preferably be made of an alloy containing at least one selected from the group consisting of Cr, Fe, Co, Ni and Ti, and more preferably stainless steel and an Fe—Ni alloy.

In the electrically heating support2and the exhaust gas purification device1according to the present embodiment, the at least two bent portions510are provided in the drawer portion51, and the extension directions of the ridgelines R of the at least two bent portions510are different from each other, so that the resistance of the metal electrodes5to vibration can be improved.

Moreover, since the thickness of the drawer portion51is 0.03 mm or more and 1 mm or less, the expansion and contraction of the drawer portion51can be smoothly performed while ensuring sufficient strength for the drawer portion51.

Further, since the extending directions of the ridgelines R of the at least two bent portions510include the first direction parallel to the axial direction of the honeycomb structure4and the second direction perpendicular to the first direction, the electrically heating support2and the exhaust gas purification device1can more reliably improve the resistance of the metal electrodes5to the vibration that would be applied when they are mounted on a vehicle.

Embodiment 2

FIG.4is a perspective view showing an exhaust gas purification device1according to Embodiment 2 of the present invention,FIG.5is a cross-sectional view of the exhaust gas purification device1taken along the line V-V inFIG.4, andFIG.5is a perspective view showing a metal electrode5ofFIG.5.

As shown inFIGS.4to6, the drawer portion51of the metal electrode5according to Embodiment 2 is formed by bending a metal piece extending in the longitudinal direction from one end of the base portion500in the longitudinal direction. A ridgeline R of the first bent portion511of the drawer portion51extends in a direction orthogonal to the longitudinal direction of the base portion500. A ridgeline R of the second bent portion512of the drawer portion51extends in the longitudinal direction of the base portion500. That is, in Embodiment 2, the bending order of the first and second bending portions511,512is reversed from that in Embodiment 1. Other structures are the same as those of Embodiment 1.

Thus, the bending order of the bent portion510of the drawer portion51may be arbitrarily changed.

Embodiment 3

FIG.7is a perspective view showing a metal electrode5of an exhaust gas purification device1according to Embodiment 3 of the present invention. As shown inFIG.7, the metal electrode5may be composed of a plurality of metal plates. The metal electrode5according to this embodiment has a first metal plate6and a second metal plate7. Each of the first and second metal plates6,7has a connection portion50and a drawer portion51. That is, the metal electrode5according to this embodiment has a plurality of connection portions50and a plurality of drawer portions51.

The electrically heating support2according to Embodiment 3 has a pair of metal electrodes5, as with the electrically heating support2according to Embodiment 1. The pair of metal electrodes5can be the metal electrodes5shown inFIG.7. That is, the pair of metal electrodes5in the electrically heating support2according to Embodiment 3 has a plurality of connection portions50and a plurality of drawer portions51, respectively.

The first and second metal plates6,7are arranged such that the base portion500and the drawer portion51of each connection portion50overlap with each other. The tooth portions501of the connection portions50of the first and second metal plates6,7extend from their respective base portions500in opposite directions. The structure of each of the drawer portions51of the first and second metal plates6,7is the same as that of Embodiment 2. However, the bending angles of the bent portions510are appropriately adjusted so that the drawer portions51of the first and second metal plates6,7are entirely in surface contact with each other. Other structures are the same as those of Embodiments 1 and 2.

Embodiment 4

FIG.8is a perspective view showing a metal electrode5of an exhaust gas purification device1according to Embodiment 4 of the present invention. Although Embodiment 4 (FIG.7) discloses that the drawer portions51of the first and second metal plates6,7are entirely in surface contact with each other.51may not be in contact with each other, the drawer portions51of the first and second metal plates6,7may not be in contact with each other. Vibration can be absorbed even if these drawer portions51are not in surface contact. In the embodiment shown inFIG.8, curvature radii of the bent portions510are different from each other so that the bent portion510positioned on the outer side of the bent part and the bent portion510positioned on the inner side of the bent part are not in contact with each other. Other structures are the same as those of Embodiments 1 to 3.

Examples

The present inventors prepared a plurality of stainless steel metal electrodes5each having a plurality of teeth portions501as shown inFIG.3, and conducted a vibration test. As shown in the table below, the plurality of metal electrodes5are made different from each other in the form of the bent portion510in the drawer portion51and the thickness of the drawer portion51. In the table below, a metal electrode5having two bent portions510in which the extending directions of the ridgelines R of the two bent portions510are the same as each other is shown as a comparative example, and a metal electrode5having two different bend portions510in which the extending directions of the ridgelines R are different from each other is shown as an example. The comparative example is a metal electrode5having a bellows-shaped drawer portion51(the extending directions of the ridgelines R of the two bent portions510are the same) obtained by simply folding a long metal piece twice.

In the vibration test, the tip portion of each tooth portion501(the portion spaced apart from the base portion500) was joined to a ceramic test piece sample, and a terminal for external connection was fastened to the tip of the drawer portion51with a nut. Also, the single vibration in the X axis direction and the single vibration in the Y axis direction shown inFIG.3were individually applied to a work piece (the test piece sample and the metal electrode5). The vibration frequency was 150 Hz, the vibration acceleration was 40 G, and the time applied for the simple vibration was 2 hours. Also, ten metal electrodes5were used for simple vibration in each axial direction. Then, it was investigated whether or not the joint portion between the tip portion of each tooth portion501and the test piece sample, and the bent portion510were broken. The breakage of the joint portion includes peeling of the tip portion of each tooth portion501and the test piece sample. The results are shown in the table below.

TABLE 1ExtendingVibration in X Axis DirectionVibration in Y Axis DirectionNumber of BentDirection ofThickness ofNumber ofNumber ofNumber ofNumber ofTotal NumberPortions inRidgeline ofDrawer PortionBent PortionsJoint PortionsBent PortionsJoint Portionsof BrokenDrawer PortionBent Portion(mm)BrokenBrokenBrokenBrokenSamplesCompar-12Same0.039/100/100/108/1017ative20.052/100/100/1010/1012Examples30.10/100/100/1010/101040.50/100/100/1010/101050.70/101/100/1010/101160.80/108/100/1010/1018Examples12Different0.035/100/105/100/101020.051/100/102/100/10330.10/100/100/100/10040.50/100/100/100/10050.70/101/100/100/10160.80/106/100/105/1011

For example, as can be seen from the comparison of the total numbers of broken samples in Comparative Examples and Examples having the same thickness of the drawer portions51such as Comparative Example 1 and Example 1, the metal electrodes5in which the extending directions of the ridgelines R are different from each other are difficult to be broken as compared to the metal electrodes5in which the extending directions of the ridgelines R are the same. Particularly, in Examples, it is found that the breakage of the joint portion is suppressed when the vibration is applied in the Y axis direction. This would be because the metal electrodes5according to Examples can absorb the vibration in the Y axis direction by providing the second bent portion512. It is, therefore, understandable that the superiority of providing the drawer portion51with the at least two bent portions510in which the extension directions of the ridgelines R of the bent portions are different from each other.

It is found from the comparison of Comparative Examples 1-6 with Examples 1-6 that the number of breakages is suppressed when at least the thickness of the drawer portion51is 0.03 mm or more and 0.8 mm or less.

DESCRIPTION OF REFERENCE NUMERALS

1: exhaust gas purification device2: electrically heating support3: can body30: opening4: honeycomb structure40: outer peripheral wall41: partition wall41a: cell5: metal electrode50: connection portion51: drawer portion510: bent portionR: ridgeline