JPH0153082B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a filter device for removing combustible particulates contained in gas, particularly combustible particulates such as carbon contained in automobile exhaust gas. More specifically, the present invention relates to a filter device that efficiently burns and removes filtered combustible particulates while maintaining high filterability by applying electricity to the filter itself to generate heat.

[Prior art and its problems] Conventionally, it has been proposed to use a filter in the exhaust system or exhaust recirculation system in order to remove carbon particulates contained in the exhaust gas of an automobile engine as a pollution control measure. The disadvantage of using this was that carbon accumulated and caused clogging, resulting in pressure loss. To overcome this drawback, it is possible to heat the particulate trapping part of the filter by combining it with a nichrome wire heater or a heat-generating metal layer, by injecting fuel into the particulate trapping part and heating it with the combustion heat of the fuel, or by installing a high-voltage electrode. Methods have been used to prevent clogging by heating by spark discharge, or by heating the filter by applying electricity to the carbon fiber to incinerate the carbon particles.

However, when using nichrome wire, the heat generating area is small, resulting in poor energy efficiency, and it is also time-consuming to attach it to the filter.If a heat generating metal layer is provided, it must be thin and small in area so as not to interfere with filtration. However, it is energy inefficient and requires a lot of effort to install.If the temperature cannot be raised properly due to exhaust gas, the engine must be stopped and the carbon particles that have accumulated in the filter must be burned. Something unexpected happened. Additionally, fuel injection and high-pressure discharge methods require particularly complex equipment, consume large amounts of energy, and
Fire problems caused by the fuel and damage to the filter due to discharge occur, and those using carbon fibers have the disadvantage that the fibers themselves are destroyed by combustion.

On the other hand, ceramic honeycomb structure filters are known for similar applications, and these filters generally require less pressure loss than other filters even when the mesh is made finer, and are compact, so they can be used to remove carbon from automobile exhaust gas. Although the filter is suitable for various applications, if it becomes clogged, the filter surface covers a wide area, so the filter must be removed from the area where it is used and the entire filter must be heated to burn off the carbon particles. Furthermore, as a method for preventing clogging, the fineness of filters such as stainless wool and alumina pellets is gradually changed to disperse and capture carbon particles (Japanese Patent Application Laid-Open No. 1983-1999).
190626), and a method of heating and burning carbon particulates by fuel injection has also been proposed, but the capture of carbon particulates is insufficient, and the exhaust gas is in a low oxygen state, so there is a limit to temperature rise, making it difficult to incinerate quickly. However, it has the drawbacks that it is not possible to do so, and that the device becomes complicated.

As a solution to the above problems, it has been considered to use the honeycomb-structured ceramic filter itself as a self-energizing heating element, and its efficient heat generation and carbon particulate trapping properties make it particularly suitable for use in automobile exhaust gas. This is considered to be a promising filter.

However, in that case, since the entire filter is conductive, attaching it to the exhaust pipe or exhaust gas recirculation pipe as it is will cause electrical leakage, since the material of the attached part is generally a conductor such as steel. Some kind of insulation treatment or insulator must be used for attachment, which requires fabrication, assembly steps, or a number of parts that are essentially unrelated to filtration.

In addition, when a solid columnar filter is heated, it generates heat almost uniformly throughout the filter, but since the heat in the center has no way to escape, the rate of temperature rise is different between the center and the periphery. The difference in expansion became large, and there was a risk that the filter would crack.

[Structure of the Invention] As a result of intensive research, the inventors of the present invention found that by using a cylindrical porous body made of conductive ceramic as a filter, the outer circumferential surface of which is a ground potential electrode and the inner circumferential surface of which is the other electrode. We discovered that it is possible to prevent current leakage when electricity is applied, even without insulating the filter itself or combining it with an insulator, and that the temperature gradient is reduced, resulting in less thermal expansion difference and less likely to cause cracks. He completed his invention.

That is, the gist of the present invention is to form a conductive ceramic porous body having an exhaust gas filtration action into a cylindrical shape having a center hole inside, and to attach one electrode for electrical heating to the outer peripheral surface of the conductive ceramic porous body, which has a center hole inside. By providing the other electrode on the surface, the outer peripheral surface of the cylindrical porous body is supported by the case, and exhaust gas can be filtered with the outer peripheral surface electrode on the ground potential side. This exhaust gas filter device is characterized in that it is capable of incinerating combustible particles trapped in a conductive ceramic porous body by generating heat in the body.

[Example] Next, explanation will be given with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention applied to a filter device for automobile exhaust gas.

Here, 1 represents a hollow cylindrical porous conductive ceramic filter, and a filter having a pore diameter of 0.1 to 1 mm is used.

A metallic electrode is formed as a metallized layer 3 on the entire or partial outer peripheral surface of the filter 1, and a metallic electrode is formed as a metallized layer 4 on the entire or partial inner peripheral surface. That is, the cylindrical metallized layers 3 and 4 are coaxially arranged with the filter 1 in between.

The metallized layers 3 and 4 have conductive wires 13 and 1, respectively.
4 are connected by welding or other methods, and each insulator 1
6, 17 in an insulated manner, the conductor 13 is connected to the power supply E via a switch 15, and the other conductor 14 is connected directly to the other pole of the power supply E. Here, the conducting wire 13 side is grounded, and the electrode side of the metallized layer 3 is at ground potential.

With the above configuration, the filter 1, the metallized layers 3 and 4, the conductive wires 13 and 14, the switch 15, and the power source E collectively form an energization heating circuit.

A non-porous insulating ceramic circular plate 5 having the same diameter is tightly coupled to one of the circular end faces of the filter 1. On the other hand, a non-porous insulating ceramic circular plate 7 of the same diameter is tightly coupled to the other end surface of the filter 1, and the circular plate 7 has a circular hole in its center and a cylindrical tube fitted into the hole. 7a is provided to form an outlet 7b having substantially the same shape as the center hole 6 of the filter.

Reference numeral 9 denotes a case for an exhaust pipe, an exhaust gas recirculation pipe, etc. for storing a filter, and has an end wall 19 on the upstream side of the exhaust gas, and an inlet 9a is formed on the periphery of the end wall 19. The number of holes is drilled, and the end wall 1
9 also has a hole 9c concentrically with the end wall 19.
is drilled. However, the hole 9c is provided for weight reduction and does not need to be drilled.

End wall 19 between the inlet 9a and the hole 9c
An annular protrusion 12b whose inner periphery fits the upstream end of the filter 1 is provided at right angles to the filter.
The circular plate 5 connected to the upstream end of the filter 1 is closely supported by the annular protrusion 12b and the end wall 19 inside thereof, thereby maintaining the airtight condition.

The entire upstream end surface of the case 9 is hermetically covered by a short cylindrical connecting lid 8 with peripheral flanges 20 and 21 connected to each other. A pipe body 8c having an exhaust gas inlet 8a is attached to a part of the lid body 8, and the pipe body 8c is connected to an exhaust manifold.

On the other hand, the entire downstream end surface of the case 9 is airtightly covered by the funnel-shaped connecting lid 10, with the flanges 22 and 23 on the respective peripheries connected to each other. The funnel-shaped lid body 10 has a locking protrusion 11a protruding from the inner circumferential surface of the exhaust gas inlet, and the inner circumferential surface thereof is adapted to fit the downstream end surface and the outer circumferential edge of the filter 1. An annular protrusion 11b is provided, and when the lid 10 is attached to the case 9, the locking protrusion 11a and the annular protrusion 11b tightly support the downstream end of the filter 1 to maintain an airtight state. Hold. A small diameter outlet 10d is provided on the downstream side of the lid 10.
and is connected to an exhaust pipe (not shown).

In the above configuration, exhaust gas containing carbon particles from the engine passes through the exhaust manifold as it is and flows into the inlet 8a of the connection lid 8 from the upstream direction F as shown by the dotted line. Further, the flow is divided in the lid body 8 and flows from the inlet 9a opening in the end wall 19 of the case 9 to the case 9.
flows into the interior of. Next, the exhaust gas passes through the metallized layer 3 from the outer peripheral surface of the cylindrical filter 1 exposed inside the case 9 and enters the porous interior thereof. Here, the carbon particles are captured and the exhaust gas passes through the other metallized layer 4 and flows out into the central hole 6. At this point, the carbon particles are dispersed and captured throughout the filter 1, and are hardly recognized in the exhaust gas.

Next, the exhaust gas flows from the center hole 6 to the funnel-shaped lid 10 from inside the case 9 through the outlet 7b of the non-porous insulating ceramic circular plate 7, and is then discharged to the exhaust pipe through the outlet 10d of the lid 10. .

At this time, if the heating circuit switch 15 is turned on and electricity is applied between the metallized layers 3 and 4, which are metal electrodes, the carbon particles dispersed and captured in the filter 1 will be transferred to the filter 1. It quickly burns and disappears due to its own heat generation.

The electrode (metallized layer) 3 on the outer peripheral surface is the case 9
is in a energized state, but since the electrode 3 is on the ground potential side, there is no leakage or short circuit. On the other hand, since the electrode (metalized layer) 4 on the inner peripheral surface is located at the farthest position from the case 9, leakage and shorting can be sufficiently prevented. Furthermore, the center portion of the filter 1 has a center hole 6 and is hollow. Therefore, there is no accumulation of heat and there is no fear of cracks due to differences in thermal expansion.

Next, FIG. 2 shows a second embodiment of the present invention.

Here, 31 indicates a hollow cylindrical porous conductive ceramic filter, and the diameter of the pores is the first
The same filter as in the embodiment is used, and both end faces of the filter 31 have hollow circular plane shapes.

Metalized layers 33 and 34 as metallic electrodes are provided on the outer peripheral surface and the inner peripheral surface of the filter 31, respectively, and are in close contact with the metalized layer 34 on the inner peripheral surface to close the upstream side of the center hole 35 of the filter 31. A non-porous heat resistant closed tube 47 is inserted into the central hole 35.

The filter 31 is arranged so that its outer circumferential surface is in close contact with the inner circumferential surface of the case 38 of the exhaust pipe, exhaust gas recirculation pipe, etc.
It is housed in a case 38 and is locked on the upstream side of the exhaust gas by a locking protrusion 38a protruding inside the outer cylinder 38, and the case 38 and the funnel-shaped connecting pipe 39 are connected at respective flanges 38b and 39a. The filter device is locked at the other flange 39d of the funnel-shaped connecting pipe 39 on the downstream side of the exhaust gas, and is held in that position.

Moreover, the metallized layer 34 on the inner circumferential surface of the filter device
A conducting wire 41 is connected to one end 45 by welding or the like,
On the other hand, the metallized layer 33 on the outer peripheral surface of the filter 31
A conducting wire 40 is connected by welding or the like to a portion 44 of the case 38 that is in direct contact with and is energized.

The conducting wire 41 is led out to the outside through an insulator 43 provided in the funnel-shaped connecting pipe 39, and is connected to the power source E via a switch 42. On the other hand, the conducting wire 40 is connected to the power source E.
The conductor 40 is connected to the opposite pole and grounded on the conducting wire 40 side.

The above filter 31, case 38, conducting wire 40,
41, the switch 42, and the power source E together form an energization heating circuit.

In the above configuration, the exhaust gas containing carbon particles from the engine passes through the exhaust manifold as it is, reaches the case 38, and passes through the filter 3 from the exhaust gas upstream direction F as shown by the dotted line.
Infiltrate into 1. At this time, since the central hole 35 of the filter 31 is blocked by the closed pipe 47, the exhaust gas does not directly pass through to the exhaust pipe side B.

When the exhaust gas enters the holes of the filter 31, the carbon particles in the exhaust gas are dispersed and captured throughout the filter 31, and then the exhaust gas that does not contain carbon particles leaks out from the downstream side of the filter 31 and passes through the funnel-shaped connecting pipe 39. It passes through and is discharged from an exhaust pipe (not shown) in the downstream direction B.

At this time, if the heating circuit switch 42 is turned on and electricity is applied between the metallized layers 33 and 34, which are metal electrodes, the carbon fine particles dispersed and captured in the filter 31 will be transferred to the filter 31.
Due to the heat generated by 1 itself, it quickly burns and disappears.

In addition to the same effects as the first embodiment, this embodiment has
The electrode (metallized layer) 33 on the outer peripheral surface is connected to the case 38
Since it is in contact with the case 38, it can be used as an electrode on the ground potential side without making a special hole in the case 38.

In the above first and second embodiments, the porous conductive ceramic filter is a spongy structure having communicating pores distributed in a distributed manner, a felt-like structure, a felt-like structure,
A conductive ceramic filter, etc., such as an aggregate structure of a large number of cotton-like bodies such as a woven fabric-like molded body, etc., can be employed.

The above-mentioned method for manufacturing the porous conductive ceramic filter is performed, for example, in the following manner, in addition to firing raw ceramic whose composition is blended so that it becomes porous upon firing. In addition to the main ingredients such as silicon carbide or molybdenum disilicide, fine raw material powders such as alumina and silica, organic binders such as sodium alginate, ammonium alginate, and polyvinyl alcohol, and solvents such as water and ethyl alcohol are added and kneaded. By making a slurry-like compound, immersing a polyurethane or other plastiform in the desired shape with a predetermined fineness in the slurry, and after drying, baking it at around 1600℃ in an air atmosphere or nitrogen atmosphere. can get.

The metallic electrode means are formed by baking a metal powder paste such as platinum or a powder paste mixture of nickel, cobalt, etc. and silicon on both end faces of the conductive ceramic filter.
In this case, even if it is not formed on the entire end face, it can be shaped like a lattice,
It may be formed in a striped shape or the like.

[Effects of the Invention] As described above, in the exhaust gas filter device of the present invention, a ground potential electrode is provided on the outer peripheral surface of the cylindrical porous filter made of conductive ceramic, and the other electrode is provided on the inner peripheral surface. It is being Therefore, as can be seen from the fact that the case housing the filter itself replaces the conductor wire for the outer electrode, there is no problem with leakage or shorts from the outer electrode. Since the components are located farthest from the case, the possibility of electrical leakage or shorts occurring is extremely reduced. By using the exhaust gas filter device of the present invention having the above characteristics, electrical energy can be used effectively without having to consider insulating the filter itself.

Furthermore, the conductive ceramic porous body that generates heat has a central hole on its inner surface, so there is no accumulation of heat.
Temperature gradients are suppressed and cracks are prevented from occurring.

[Brief explanation of drawings]

Figure 1 shows the first part of the exhaust gas filter device of the present invention.
FIG. 2 is a cross-sectional view of a second embodiment of the present invention. 1, 13... Cylindrical conductive ceramic porous body, 3, 33... Outer peripheral surface electrode (ground side electrode), 4,
34... Inner peripheral surface electrode, 6, 35... Center hole, 9,
38...Filter case.

Claims (1)

[Scope of Claims] 1. A conductive ceramic porous body having an exhaust gas filtration action is formed into a cylindrical shape with a center hole inside, and one electrode for electrical heating is provided on the outer circumferential surface of the body, and the other electrode is provided on the inner circumferential surface. By providing an electrode, the outer peripheral surface of the cylindrical porous body is supported by the case, and exhaust gas can be filtered with the outer peripheral surface electrode on the ground potential side, and the conductive ceramic porous body generates heat by passing electricity between both electrodes. An exhaust gas filter device characterized in that combustible particles trapped in the conductive ceramic porous body can be incinerated. 2. The exhaust gas filter device according to claim 1, wherein the exhaust gas to be filtered enters from the outer peripheral surface of the cylindrical porous body made of conductive ceramic and is discharged to the inner peripheral surface. 3. The exhaust gas filter device according to claim 1 or 2, wherein the conductive ceramic is molybdenum disilicide. 4. The exhaust gas filter device according to claim 1 or 2, wherein the conductive ceramic is silicon carbide.