EP0325111B1 - Filter and afterburning device for exhaust gases, especially for internal combustion engines - Google Patents

Abstract

In the filter and afterburning device for exhaust gases, especially for internal combustion engines, a plurality of layers of cylindrical filter elements of essentially circular-ring-shaped or oval-ring-shaped cross-section, through which the gas can flow radially, are arranged with equidistant radial spacing one inside the other in a housing between an inlet funnel and an outlet funnel, forming similarly shaped inlet and outlet spaces. Each filter element comprises a gas-permeable filter body made of wire mesh, ceramic fibres or a combination of the two and surrounded on both sides by a gas-permeable metallic jacket, the filter bodies being wound into a spiral using spacing elements, with a spiral inlet channel and outlet channel, each of which is closed on the opposite side, and the surrounding jackets, designed as perforated metal bands or metal mesh bands, being provided with a catalytic coating for the purpose of converting gaseous pollutants. <IMAGE>

Description

The invention relates to a filter and afterburning device for exhaust gases, in particular internal combustion engines, in which between an inlet funnel and an outlet funnel within a housing several layers of radially flowable cylindrical filter elements of essentially circular or oval ring-shaped cross section with radial spacing equidistantly from one another with formation of entry and exit spaces of a similar shape are arranged, each filter element comprising a gas-permeable filter body made of wire mesh or ceramic fibers, which is bordered on both sides by a gas-permeable metallic jacket.

Such a filter and afterburning device, as described in DE-A-32 28 325, uses concentric nested filter elements, the intermediate channels being divided by sheet metal rings into outlet channels for the inner filter ring and a gas inlet channel for the outer filter ring body. This requires a very high manufacturing outlay, so that such filters are extremely expensive. In addition, the catalytic coating described in this laid-open publication does not only apply to the filter material but, if necessary, also the inner casing or additional coated material introduced into the gas inlet channels, a fully satisfactory afterburning and filtering cannot be achieved.

The invention is therefore based on the object of designing a filter and afterburning device of the type mentioned at the outset in such a way that it can be produced very simply and, in addition to optimal filtering and afterburning, also avoids the formation of nitrogen oxides.

To achieve this object, it is provided according to the invention that the filter bodies are wound up using a spacer elements to form a spiral winding body with a spiral inlet channel and outlet channel, which are each closed on the opposite side, and that the casing sheaths, which are designed as perforated metal strips or metal knitted strips, have a catalytic coating for converting gaseous pollutants are provided.

Due to the winding design of the filter according to the invention, this can be produced with considerably less effort than the previously known filter, with the fact that the winding design according to the invention is equally suitable for all sizes and cross-sectional shapes of the filter. The decisive factor here is the coating of both surround sleeves of the actual filter body with a catalytic coating for converting gaseous pollutants in the exhaust gas. This means that the metal strips are heated much more strongly than the exhaust gas stream itself. The filter material with the soot or other solid particles deposited thereon then lies between two hot metal strips, which promote the burning of the soot or the solid particles. It goes without saying that, in addition, a separate catalyst for promoting the soot burn-off can also be provided on the filter material. With this special selective heating of the casing of the filter body, the invention goes a completely different way than the aforementioned publication, in which only one of the coats is optionally catalytically coated and, moreover, is also provided as an advantageous solution that the entire inlet space is additionally filled with a porous mixture which is catalytically coated. In this way, however, it is just not achieved that selectively only the binding bands are heated to a great extent, namely by up to several hundred degrees above the temperature of the exhaust gas itself, in order in this way to selectively burn off the solid particles on the filter bodies and thus to receive continuous self-cleaning. By promoting the soot burn-off according to the invention through the selectively more heated jacket of the filter body compared to the exhaust gas stream, the temperature of the exhaust gas can be kept low, so that practically no nitrogen oxides are formed, which only arise at high exhaust gas temperatures, but then inevitably. Nevertheless, extremely effective oxidation of carbon monoxide or hydrocarbons, for example, which are still present in the exhaust gas, is achieved, ie effective post-combustion of gaseous pollutants.

The heat of reaction from this afterburning of the gaseous pollutants then serves for the selective heating of the binding bands and thus for the promotion the burn-up of the solid pollutants accumulating in the filter, preferably soot.

To simplify the winding production of the filter and afterburning device according to the invention, a winding mandrel can be provided, which can preferably be made hollow. The cross-sectional shape of the winding mandrel immediately determines the shape of the resulting filter arrangement, that is to say, for example, whether it should be a circular or oval-cylindrical body. Due to the hollow design of the central winding mandrel, there is the possibility of arranging an optionally provided injection device for introducing fuel and / or oxygen for afterburning in such a way that it is connected to the outlet end of the winding mandrel and thus the fuel or, contrary to the inflow direction of the exhaust gases Introduces oxygen into it and mixes and swirls it particularly effectively. In addition, the winding mandrel can serve on the input side as a carrier for a diffuser for uniform filter application. Such a diffuser can be designed very simply as a perforated cone or the like.

The sealing strips, which alternately close the spiral channels between the filter elements in order to form a spiral inlet channel and a spiral outlet channel separated by the filter elements, can be formed in a further development of the invention by the folded edges of the filter mats themselves. In this production, a multilayer layer consisting of two filter material tapes with their metallic casing shells is then to be provided as the starting material, so that the filter structure according to the invention can be created by simple spiral winding.

However, the sealing strips can also be formed by angled edges or flanges of the metal strips enclosing the filter.

The spacer elements, which keep the filter webs bordered by the casing coats at a distance from each other during winding, so that the gas inlet and outlet channels already mentioned can form, can either be corrugated strips, which are also wound up as intermediate layers. In addition, it has also proven to be advantageous to design the spacer elements as windings or passages of the metal strips enclosing the filters themselves, so that separate components, such as the corrugated strips already mentioned, are no longer required at all. By appropriate design of the lifts or passages, for example in the form of longitudinal ribs which interrupt the intermediate channels, it can also be achieved that the exhaust gas flow is not directed from an inlet annular space through the passage of a filter layer into the adjacent ring as an outlet channel, but is deflected several times in a meandering manner a variety of filter layers interspersed. As a result, the filter can be used more evenly and its effectiveness can be increased.

When designing the casing sheaths as metal strips, it has proven to be expedient to form them in a thickness between approximately 0.03 and 1 mm.

In addition to the catalytic coating of the casing sleeves of the filter elements with an oxidation or 3-way coating, and the catalytic coating, if necessary, of the filter material itself, with another filter material that promotes solid-state burnup, the diffuser and the in and Outlet funnel of the metal housing receiving the winding body may be coated with special catalysts. The filter elements themselves made of knitted wire or ceramic fibers can not only be made entirely of one or the other material, but possibly also of a mixed knitted fabric and possibly in the form of a fleece, fabric, blankets or felt. If a mixed knitted fabric is used, the perforated films may be omitted.

Finally, it is also within the scope of the invention that the gas inlet and outlet channels have different thicknesses between the filter layers provided with casing sleeves, which can be achieved very easily by using spacers of different thicknesses. It may even be provided that the distance from the exhaust gas inlet end surface to the outlet end surface of the winding body changes in order to achieve a more uniform penetration of the filter material in this way.

Fig. 1

einen Schnitt durch eine erfindungsgemäße Filter- und Nachverbrennungseinrichtung, bei der im unteren Teil verschiedene Varianten der Abdichtstreifen gegenüber der oben dargestellten Umbördelung der Filtermatten angedeutet sind,

Fig. 2

einen Querschnitt durch den Wickelkörper der Filter- und Nachverbrennungseinrichtung nach Fig. 1,

Fig. 3

einen schematischen Teilschnit durch einen abgewandelten Filterkörper mit anderer Ausbildung der Abdichtstreifen und der Abstandselemente, und

Fig. 4

einen vergrößerten Schnitt durch die Schichtfolge zur Wickelfertigung des in Fig. 1 und 2 gezeigten Filterkörpers.

Further advantages, features and details of the invention result from the following description of some exemplary embodiments and from the drawing. Show:

Fig. 1

3 shows a section through a filter and afterburning device according to the invention, in which different variants of the sealing strips compared to the flanging of the filter mats shown above are indicated in the lower part,

Fig. 2

a cross section through the winding body of the filter and afterburning device Fig. 1,

Fig. 3

a schematic partial section through a modified filter body with a different design of the sealing strip and the spacer elements, and

Fig. 4

an enlarged section through the layer sequence for winding production of the filter body shown in FIGS. 1 and 2.

The filter and afterburning device shown in Figures 1 and 2 comprises a metallic outer housing 1, which in the illustrated embodiment (indicated in Fig. 1 above) comprises an outer jacket 2 and an inner jacket 3, which by ceramic fiber mats 4, preferably in the form of so-called swelling mats , are isolated from each other. The cross-sectional shape of the cylindrical central section between the inlet funnel 5 and the outlet funnel 6 can be circular, oval or possibly polygonal. The shape can be given very cheaply by appropriate selection of the cross-sectional shape of the hollow mandrel 7, which carries on its inlet side a diffuser 8 in the form of a perforated cone made of metal or, if necessary, also ceramic, while on the output side it is connected to a line 9 to an injection device for fuel and / or oxygen is connected, which is introduced opposite to the exhaust gas flow 10 in the input space of the filter device, in order to possibly influence the afterburning favorably.

The actual filter consists of a spirally wound bobbin 11, in which filter mats 12, which are bordered on both sides by perforated metal strips 13 and 14, with the aid of spacer elements are wound up, which in the case of FIGS. 1 and 2 are designed as corrugated strips 15. The channels receiving the corrugated strips 15 are alternately closed on the inlet and outlet sides, so that there is a gas inlet channel 16 which is spiral in cross-section and results in a separate spiral outlet channel 17 through the filter layers 12 with their metal strip surround 13, 14. In the case of FIG. 1, the upper half is formed in that the edges 18 and 19 of the filter mats 12 are folded over and fastened on the outside of the respective metal sheet 13, 14. In the lower half of FIG. 1, two other variants are indicated, namely an angling of the non-perforated edges 20 and 21 of the metal strips 13, 14, which can possibly be held together by a part 22. In addition, a further possibility of simply folded edges 20 ′ and 21 ′ lying one on top of the other to form the seal of the gas inlet and outlet channels is also indicated.

Instead of the sealing of the gas inlet ducts 16 and gas outlet ducts 17 described above, spacer webs 23 can also be provided, which can either be placed on the metal strips 13, 14 in the longitudinal direction or can be formed directly into them by deformation. These webs 23 not only keep the filter layers at a distance - for the sake of clarity, the metal strips 13, 14 are not shown in detail in FIG. 3 - and the sealing strips are also formed, but in this way a forced meandering penetration of the filter mats is achieved , with the help of which a more even utilization and thus a better utilization of the effectiveness of the filter can be achieved.

Instead of the corrugated strips or the webs 23, the metal strips in the form of knobs or domes can also be drawn up or pulled through to serve as spacers. In this case, however, either separate sealing strips or flanging the edges of the filter mats again are required to seal the gas inlet channels 16 and the gas outlet channels 17.

FIG. 4 shows an 8-fold layer sequence of tapes, with the aid of which the filter body shown in FIG. 1 above or FIG. 2 can be wound.

Claims (12)

1. A filter and afterburning device for exhaust gases, more particularly of internal combustion engines, in which between an inlet funnel (5) and an outlet funnel (6) within a housing (1) a plurality of layers of cylindrical filter elements, through which the exhaust gas can flow radially and which has a substantially circular ring-shaped or oval ring-shaped cross section are arranged within one another spaced apart equidistantly in the radial direction, forming inlet and outlet chambers of similar shape, each filter element comprising a gas-permeable filter body (12) made of knitted wire, ceramic fibres or a combination of both, which is enclosed on both sides by a gas-permeable metallic casing (13, 14), characterised in that the filter bodies are wound with the use of spacing elements to form a helical winding element (11) with a helical inlet duct (16) and outlet duct (17), said ducts being closed on the opposite side in each case, and the enclosing casings designed as perforated metal strips (13, 14) or knitted metal strips are provided with a catalytic coating for converting harmful gaseous substances.
2. An exhaust gas cleaning device according to claim 1, characterised by a preferably hollow winding mandrel (7).
3. An exhaust gas cleaning device according to claim 1 or 2, characterised by an injection device for introducing fuel and/or oxygen for afterburning.
4. An exhaust gas cleaning device according to one of claims 1 to 3, characterised in that the spacing elements are formed by the folded-back edges (18, 19) of the filter mats (12).
5. An exhaust gas cleaning device according to claim 1 or 2, characterised in that the spacing elements are formed by angled or flanged edge sections (20, 21; 20', 21') of the metal strips (13, 14).
6. An exhaust gas cleaning device according to one of claims 1 to 5, characterised in that the spacing elements are raised or drawn sections of the metal strips (13, 14).
7. An exhaust gas cleaning device according to claim 6, characterised in that the arrangement, size and shape of the raised or drawn section of the metal strips (13, 14) is selected so that they conduct the exhaust gas flow radially and axially in such a manner that uniform filter loading is ensured.
8. An exhaust gas cleaning device according to one of claims 1 to 5, characterised in that the spacing elements are corrugated strips (15).
9. An exhaust gas cleaning device according to one of claims 1 to 8, characterised in that the filter body is wound from an eight-layer sequence of two filter mats (12) and four metal strips (13, 14) and the associated spacing elements and sealing strips.
10. An exhaust gas cleaning device according to one of claims 1 to 9, characterised in that the thickness of the metal strips (13, 14) is between 0.03 and 1.0 mm.
11. An exhaust gas cleaning device according to one of claims 1 to 10, characterised in that the catalytic coatings of the converter annular inlet duct (16) and/or of the converter annular outlet duct (17) are oxidation coatings.
12. An exhaust gas cleaning device according to one of claims 1 to 10, characterised in that the catalytic coatings of the converter annular outlet duct (17) are three-way coatings.

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