WO2006133999A1

WO2006133999A1 - Exhaust gas aftertreatment arrangement and method for producing the same

Info

Publication number: WO2006133999A1
Application number: PCT/EP2006/062058
Authority: WO
Inventors: Bernd Reinsch; Joerg Jockel; Teruo Komori; Lars Thuener; Matthias Kruse
Original assignee: Robert Bosch Gmbh
Priority date: 2005-06-15
Filing date: 2006-05-04
Publication date: 2006-12-21
Also published as: DE102005027649A1

Abstract

The invention relates to an exhaust gas aftertreatment arrangement for treating the exhaust gas of an internal combustion engine, especially a self-igniting internal combustion engine of a motor vehicle, and to a method for producing a corresponding arrangement. Said arrangement comprises a supporting structure, the exhaust gas interacting with said supporting structure for the treatment thereof. A layer of fibres (S) is arranged on the surface of the supporting structure (F; 26; 35), limiting the porosity thereof. This ensures long-term stability and a high filtration efficiency.

Description

Exhaust after-treatment arrangement and method for producing an exhaust aftertreatment arrangement

State of the art

The invention is based on an exhaust aftertreatment arrangement or a method for producing the exhaust aftertreatment arrangement according to the preamble of the independent claims. It is known to de-excite exhaust of motor vehicles by means of NOx storage catalysts or to decrypt by means of a Partikelfϊlters. From WO 01/19493 Al is known to provide tubes made of pressed steel fibers as filter elements, wherein the filter elements have regions of different porosity. Partial exhaust gas aftertreatment arrangements use catalyst layers to control the oxidation of CO and hydrocarbons in diesel oxidation catalysts and the

Soil regeneration in Dieselpartikelfϊltern to improve. It is known, for example, from WO 01/36097 A1 to apply catalyst layers (layers containing active material, namely catalyst material), often together with a surface-enlarging, because uneven, coating, a so-called washcoat, to a base structure.

Advantages of the invention

The exhaust aftertreatment arrangement according to the invention or the inventive method for producing the exhaust aftertreatment arrangement with the characterizing features of the independent claims have the advantage that an arrangement with a fiber layer, in particular high porosity, applied to an open-porous support structure with limited porosity, for example, ensures a structure which is also stable against thermal stresses. the one easily adjustable proportion especially highly porous areas for safe effective filtering of exhaust gases. The high-fiber surface layer provides a high surface area porous structure which improves the pressure drop performance of particulate filters loaded with soot, such as sintered metal filters, by reducing exhaust gas backpressure increase with soot loading. With the aid of the particularly highly porous or irregular fiber structure, a deep filtration remains active for a long period of time (more than 50 percent of a regeneration interval), which results in a significantly lower backpressure increase as compared to a filtering mechanism based mainly on the surface filtration effect. In a deep filtration, soot particles can advantageously penetrate partially deeply into the fiber structure before they are bound to the fibers. Due to the high porosity, there is no closure of individual pores or openings or even the formation of a continuous, the entire surface covering the filter cake. As a result, the counterpressure increase during soot loading is significantly lower than with conventional wall flow filters, in which a filter cake is formed even in the early stage of soot loading. Furthermore, a good gas-solid contact is created, a better contact for the oxidation of the exhaust gas and the soot allows and a larger area for catalytic

Coatings in particular provided on sintered metal filter integrated diesel oxidation catalysts or NO _x storage catalysts. For best performance, good contact between the exhaust gas and the deposited soot and the exhaust aftertreatment device or the filter or catalyst is of great importance; This contact is advantageously required by the fact that their effective area compared to a base of the

Support structure is enlarged by three-dimensional design of the effective area. All this is ensured with an easy-to-manufacture arrangement, which ensures a stable construction despite a particularly highly porous fiber layer. Possible provided catalytically active elements can be introduced into the fiber layer and need not be arranged in the support structure, so that the stability of the support structure advantageously via an inventive

Limiting the porosity to less than 60 percent, can be guaranteed because larger pore portions for a provision of catalytically active material in the support structure are no longer required. The targeted adaptation of fiber structure and carrier material according to the invention makes it possible to already provide a two-stage filter. Here, the first stage, the fiber structure, takes over the filtration of most of the particles (more than 80 percent). The second filter stage is by the

Support structure formed. For example, the high porosity of the first stage has a filter efficiency of less than 95 percent. By the inventive setting the porosity of the Sützstuktur leaves the filter efficiency or the filtration efficiency of the combination of first and second stage or of deep-filtering fiber layer and the support structure acting as Oberflächenfϊlter set so that values greater than 95 percent can be achieved. The percentage indicates the filtered proportionate volume flow. In this case, the deposition rates or porosities of the first and second stages are designed so that the amount of particles that pass through the first stage and therefore must be deposited in the second stage is so low that it advantageously does not lead to the formation of a closed filter cake immediately on the surface of the support structure, ie the second stage, to come. Although the formation of a closed filter cake of deposited soot in the current filter operation would increase the filtration efficiency beyond the Ausgangsflltrationseffizienz of the pure material addition, but allow the exhaust back pressure excessively increase.

The measures listed in the dependent claims advantageous refinements and improvements of the independent claims exhaust gas treatment arrangement or the specified method for producing the exhaust aftertreatment arrangement are possible.

The use of sintered metal in the construction of the aftertreatment arrangement ensures a robust and durable arrangement even under extreme thermal conditions, in particular a flexible choice of the structure of such an arrangement compared to ceramic arrangements, in which the choice of design by the commonly used manufacturing method, namely Continuous casting of the ceramic body is limited. Information relating to the porosity of the support structure here relate in the case of the use of expanded metal mesh to the filled with sintered sintered metal powder, in particular open-pore expanded metal mesh interstices.

If the exhaust aftertreatment device is designed as a particle filter using sintered metal, this has a longer life than comparable ceramic filters. Due to the freedom of design, the filter design can be chosen so that with an always required regeneration of the filter to burn off accumulated soot, the onset of soot burns occurs in several places simultaneously and not just on one side of the filter, as is usually the case

Ceramic filters is the case. This results in a more balanced and thus life-increasing thermal stress. The exhaust gas back pressure of a sintered metal filter is advantageously reduced due to a synergy effect in the combination of a fiber layer with depth filter effect and the Oberflächenfϊlters sintered metal. The fiber layer acting as a depth filter does not form any filter cake which closes the continuous pores of the fiber layer, as a result of which only a low exhaust backpressure is ensured even if the particle filter or the flow-through arrangement is already advanced. This is advantageously combined with the surface filter acting as a boundary layer between the fiber layer and the sintered metal volume, which has a high filtration efficiency. Furthermore, given a small layer thickness, a highly active surface is also present without the use of catalytic material, integrated into a mechanically robust and stable arrangement or support structure.

For example, in the case of a sintered metal particle filter with pockets made of sintered metal, the filter pockets can be arranged closer together without a certain minimum distance between the walls of adjacent filter bags, in particular at the downstream end of a filter according to DE 102 23 452 Al is exceeded, which can increase the exhaust back pressure slightly can. To ensure optimal functioning of the fiber layer, regardless of whether sintered metal particle filters or honeycomb filters, the distance of opposite filter walls, more precisely, the distance of opposite surfaces or walls of support structures (without inclusion of the fiber layers), only greater than 0, 5 mm, ideally greater than 1.2 mm.

If a very high fibrous layer porosity is selected, then such a large-volume layer designed in the case of a particle filter leads to a particularly loose, more reactive precipitate of the carbon black. Such an embodiment is therefore particularly advantageous for the collection and loose storage of soot.

Particularly advantageous is the use of long fibers, because with long fibers health hazards avoided and beyond very easily a high fiber layer porosity can be adjusted.

The washcoat advantageously enhances the adhesion between catalytically active material and the fiber structure and, in the case of washcoated fibers, further increases the active fiber surface area. Furthermore, it is advantageous that when using a washcoat to connect the

Fibers a special binder is not necessary and the production is easy and inexpensive. Fibers with a diameter of 1 to 10 micrometers, especially 3 to 8 micrometers, ensure a high active fiber surface area while maintaining health safety by avoiding cancer risk, which would be if even finer fibers were used.

It is also advantageous to provide a basis weight of the fiber layer in a range between 15 and 200 grams per square meter.

It proves particularly advantageous to adjust the porosity of the support structure between 30 and 60 percent, preferably between 45 and 60 percent. An upper limit of the porosity values below 60 percent advantageously ensures a sufficient filtering effect of the

Support material, in particular in the case of support structures, in which no catalytically active elements are applied or introduced or in the case of support structures in which fiber layers are applied without catalytically active elements. A lower limit of the porosity of the support structure to a minimum of 30 percent has the advantage of a low flow resistance of the filter material, in particular with a lower limit to a minimum of 45 percent. It also proves particularly advantageous to adjust the porosity of the fiber structure in a range between 70 and 90 percent, in particular greater than 80 percent. The latter can be realized particularly advantageously by the use of fibers having a length in a range between 40 and 500 microns, preferably greater than 150 microns. To ensure a very high filtration efficiency in combination with a stable support structure, it is advantageous to set the thickness of the fibrous layer in a range between 50 and 700 microns, ideally in a range between 150 and 500 microns.

Furthermore, it is advantageous to produce the support structure from a cordierite material, which benefits in a special way from a fiber coating. The existing of heat-insulating and heat-resistant material fibers serve as a heat storage, whereby the underlying substrate is protected from too thermally not so strong cordierite against excessive temperatures, which increases the thermal capacity of the overall structure. drawing

Exemplary embodiments of the exhaust aftertreatment arrangement according to the invention are shown in the drawing and explained in more detail in the following description. Here Washcoat refers partly to the ready-to-use layer, partly to the material from which the actual layer is made. An embodiment of a part of a Abgasfϊlters invention is shown in Figure 1. It shows schematically in a longitudinal section and a perspective view combining representation of a section of a catalyst or catalytically coated Abgasfϊlter with a three-dimensional support structure which is supported on a support structure and held by this. Figure 2 a-c shows the structure of various support structures, Figure 3 shows an alternative structure of a support structure. Figure 4 shows a section of an exhaust aftertreatment device with a honeycomb structure, Figure 5 is a temperature diagram.

Description of the embodiments

FIG. 1 shows a detail of an exhaust aftertreatment arrangement for mainly catalytically-but also non-catalytically-supported soot loading on sintered metal base (but also for other sootblower systems). An improvement is the use of a high proportion of fibers, especially long fibers. When applied or stacked on filter materials or on a support structure, these fibers allow highly porous, three-dimensional support structures for catalyst material of 0.05 mm to 0.7 mm thickness and a porosity of at least 70% to form. The support structure F itself thus serves as a support for a thin layer

(or multiple layers) of fibers, particularly low washcoat coated fibers, which serve as a supporting structure for the catalytic active material and can stabilize this material (in its spatial position). 1 shows a support structure F, which is part of a catalyst for diesel engines. The support structure F has metallic wall sections 2, between which a rigid layer 3 formed in the example of sintered sintered metal powder is arranged, on which a three-dimensional support structure S is supported and connected to the support structure sufficiently firmly as required for reliable operation of the catalyst. The support structure S has fibers 5, which are made of ceramic in the example. The fibers 5 in the example are straight sections of limited length. Each individual fiber 5 is shown in longitudinal section. The individual fibers 5 are arranged in a three-dimensional, random state. The fibers 5 are almost all coated, inter alia, to increase the surface with a coating, a so-called washcoat 6, which has an irregular outer contour and surrounds the fibers on the entire circumference. Although not shown in the drawing, the washcoat may also cover the ends of the fibers 5. Some fibers 5 are shown in the figure without washcoat; This may happen by chance, but may also be intended during manufacture. The washcoat 6 carries on its outside active material 8, namely catalyst material. This is symbolized in the figure by individual very small globules. This is intended to indicate that the active material 8 does not necessarily have to cover all fibers over a large area or completely, but that it may be sufficient if the active material is applied to the washcoat as a more or less interrupted layer. As FIG. 1 shows, the individual fibers 5 are in a direction at right angles to the plane of the drawing partly at the bottom, partially at the top, partially extending from the very bottom to the top, thus filling the space formed by them three-dimensionally and forming it a structure similar to that of a nonwoven fabric ("nonwoven fabric") Thus, there is a support structure S for catalytically active material for an internal combustion engine exhaust gas filter, the effective area compared to a base of the support structure by three-dimensional The supporting structure S has open-pore cavities with the spatial regions between the fibers, the fibers 5 being connected to one another in the region of mutually adjacent regions by a binder, or alternatively the catalytically active material may be omitted on the fibers become.

The cohesion of the fibers 5 in the present embodiment by the washcoat 6, which is fixed after the preparation, with a preferably a low washcoat coating of up to 80 grams per liter filter volume is selected, or by inorganic binder materials (binder, see above) in Area of contact points of the fibers 5 accomplished. It is not essential that all points of contact or adjacent areas of the fibers are firmly joined together. In the example, the layer 3 of the support layer or support structure F is made

Sintered metal powder is formed, which has been solidified by sintering and having open-pore gas-permeable spaces, so as to give a total of a sintered metal filter (SMF). The Flow direction of the exhaust gas to be cleaned is in the illustration of the figure from top to bottom. The support layer or support structure S (fibrous layer) with the catalytically active material located thereon in the example captures soot from the diesel exhaust gases, and converts this soot in cooperation with the active material 8 in the presence of oxygen (and / or NO ₂ ) in CO ₂ , Depending on the application, ie type of washcoat, the active material 8 also causes a conversion of nitrogen oxides (NO _x ) into nitrogen and oxygen.

In other embodiments of the invention, the layer 3 is gas-impermeable, and the flow of the exhaust gas in the illustration of Figure 1 in the horizontal direction. In this case, the support structure is formed as a flow-through substrate, that is, the support structure is not porous, so has no passing through walls for gas-permeable pores, but at best on the surface to increase the gas contact surface is porous. Such a device, referred to in English as a "flow-through" arrangement such as an oxidation catalyst, in particular a diesel oxidation catalyst, may be made of silicon carbide or cordierite in addition to metal or sintered metal.

The porosity of the base layer S in the example is at least 70%, preferably 80 to about 90%. In this case, the porosity of the base layer or fiber layer is the proportion of the voids of the base layer in relation to the volume formed by the outer boundary of the base layer. The fibers 5 have a diameter in the range of 1 to 10 micrometers, in the above

Embodiment, a thickness of about 5 micrometers. It is advantageous to use fibers having a thickness in a range between 3 and 8 microns, as these have sufficient thermo-mechanical strength and provide a sufficiently large active surface area. The fibers have a length in the example of about 40 to 500 microns, ideally they are longer than 150 microns. Longer fibers are particularly suitable for forming a three-dimensional

Structure of a support structure in a wound, woven, curled or braided arrangement, thus in an irregular or even regular arrangement. A woven fabric may preferably be fabricated in linen weave, having a first layer of parallel fibers over which is disposed a second parallel layer of 90 ° longitudinal fibers whose fibers are interwoven with those of the first layer as in a linen fabric

(Support structure with arranged according to an order principle fibers). The fibers contained in the support structure S have an active fiber surface area of at least 0.5 square meters per gram Fiber weight. When using rough fibers, an active fiber surface can be advantageously achieved which exceeds the value of 20 square meters per gram fiber weight. As active material, any material suitable for soot catalysts and / or NOx storage catalysts is contemplated. In the example, a material based on precious metals, for example based on platinum, is provided as the active material. Alternatively, palladium, rhodium and mixtures of said materials may be provided, but also other metals or metal mixtures containing, for example, cerium, lanthanum, silver and their oxides. In addition to the above effect in the reaction of soot and NOx, the active material 8 also supports the conversion of CO into CO ₂ and of hydrocarbons in the exhaust gas into water and CO ₂ . In this case, the noble metal content, ie the content of catalytically active material, is preferably in a range between 0.6 and 10 grams per liter of filter volume. The

Material of the fibers, ceramic, is in the exemplary embodiment Al ₂ O ₃ . Instead, or in mixture, for the ceramic in embodiments of the invention TiO ₂ , SiO ₂ , zirconium oxide, cerium oxide, lanthanum oxide or molybdenum oxide may be provided. The washcoat may be formed from the same just-mentioned oxides, either one of the oxides, or a mixture. In the example, Al ₂ O _{3 is also} provided here.

The support structure F used in the case of the configuration of the exhaust aftertreatment arrangement as a wall-flow filter, in particular as sintered metal particle filter having filter pockets similar to that described in DE 10301037, preferably has an average pore diameter which is greater than 6 microns is the percentage of pores with one

Pore diameters above 10 microns in the total number of pores in the support structure greater than 10 percent, and the porosity of the support structure has a value between 30 and 60 percent. In a sintered metal particulate filter bag having filter pockets in which the walls of the filter bags consist at least partially of an expanded metal grid and sintered metal disposed in the openings of the expanded metal grid (see below), the above information relates to mean pore diameter, pore fraction with pores greater than 10 micrometers, and porosity to the areas of the filter pocket walls formed by the open porous sintered metal between the expanded metal mesh webs. Alternatively, the support structure may also be formed as a wall flow filter, for example as a silicon carbide filter or as a filter, which is made of cordierite, with appropriate pore dimensions and pore proportions on

Total volume, with the advantage of low exhaust backpressure coupled with high filtration efficiency. The production of the large volume occupying fiber layer S can be carried out, for example, in a single-step or two-step process. For the single-step coating process, a coating mixture comprising a high proportion of material fibers, a small proportion of material grains (US Pat. as binder, among other functions), washcoat additives (especially TiO ₂ , SiO ₂ and / or Al ₂ O ₃ ) and optionally active compounds (catalytically active material). Washcoat material may obviate the use of the material grains, which are mainly composed of alumina, for example. If necessary or desired, the fiber structure may be coated as a first layer to form the three-dimensional support structure on which the material grains plus additives plus active

Compounds are piled up in a second step. A simple manufacturing method for the three-dimensional support layer of the figure results from providing a slurry of fibers 5 in a suspension of particles of the above-mentioned oxides or binder in water (or other suitable liquid) such that the fibers and the binder can be applied in a flowable state. The support structure is immersed in the suspension and then pulled out again. Another possibility is the application by sucking a slurry through the filter material. The content of the slurry of solids is adjusted so that a washcoat of suitable thickness is formed on the fibers 5, and that on the support structure a support layer of desired thickness, advantageously in the range of 0.05 mm to 0.7 mm, in particular Range is between 0.15 and 0.5 mm thickness forms. After drying (with or without the action of heat), this layer has interconnected interspaces between the individual fibers, which allow a flow of the base layer through diesel engine exhaust gas. The dried washcoat material also causes the backing layer to adhere firmly to the support structure. In an alternative manufacturing method, the fibers are first applied to the support structure F for the production of the support structure S and provided in a further step with binder and interconnected.

FIG. 2 shows, in part a, a per se known expanded metal grid in plan view, as it can be used for the production of an expanded metal sintered metal filter. It is a flat, flat metal grid 20 with braces that surround Öflhungen 21. Such an expanded metal is a flat material or semi-finished product with openings in the surface, which caused by staggered cuts without material loss, under simultaneous stretching deformation. The meshes of the material thus produced are, as shown in part a, usually diamond-shaped, but can also be round or square and are neither braided nor welded. The material can be cut to any size without losing its firm internal cohesion or dissolving. Such an expanded metal having openings with a cross-sectional area of about 0.5 to about 5 square millimeters and braces having a width of about 0.1 to about 1 millimeter can be used to form a support structure F according to partial image b or an alternative support structure 26 according to partial image c manufacture.

Partial image b here shows a periodically continuing section of a support structure F already known from FIG. 1 in a longitudinal section side view, in which the metallic wall sections 2 are formed by the expanded metal grid and the rigid layer 3 made of metal powder sintered with the expanded metal and inserted into the openings 21 of FIG Expanded metal grid has been previously introduced; In Figure 2b and Figure 1, this sintered metal powder is shown in the form of metal balls. The rigid layer 3 of sintered metal in the case of a wall flow filter has an open-porous structure and a thickness 24 of 0.1 to 0.8 millimeters, in particular approximately 0.5 millimeters, corresponding to the thickness of the expanded metal grid.

In an alternative embodiment, a metal mesh may be used instead of the expanded metal mesh. In a further alternative embodiment, the rigid layer 3 may also be thicker than the expanded metal mesh and / or the expanded metal mesh cover, wherein the side of the support structure on which the rigid layer projects beyond the expanded metal mesh is subsequently arranged downstream of an application as a filter material.

The alternative support structure 26 according to FIG. 2c, which likewise shows a section of such

Support structure in longitudinal sectional side view is prepared in a similar manner as the structure of Figure 2b, but with the difference that the openings 21 of the expanded metal grid 2 are not completely filled with sintered metal, so that the openings 21 of the expanded metal mesh (except for the open-pore structure the sintered metal regions 3) are sealed, but in the region of these former openings depressions with a height 25 free of sintered metal can still be found.

This free height 25 is at a thickness 24 of the expanded metal grid of 0.5 millimeters in a range between 0.2 and 0.4 millimeters. The only partial filling can be achieved by that the expanded metal mesh is guided when infested with sintered metal powder via a soft, elastic roller or a soft stamp, so that the depth of the expanded metal is filled to a certain extent. During filling, the sintered metal can thus penetrate to an adjustable degree in the expanded metal spaces.

FIG. 3 shows a periodically continuing section of a further alternative support structure 35 in which the openings of the expanded metal lattice 20 have not been filled with metal powder which has subsequently been sintered, but in which a sintered metal foil 30 is applied, in particular pressed, on one side of the expanded metal lattice , has been. This sintered metal foil is still a "green", ie not yet sintered, metal foil consisting of a mixture of a sintered metal powder with a binder at the time of application, this metal foil can be produced by extension or casting and has a thickness which is smaller than that Thickness of the expanded metal lattice After the foil has been struck onto the metal mesh grid under mechanical pressure and heat, in particular by lamination or rolling, a sintering takes place in which the sintered metal also forms an inseparable bond with the metal mesh grid The sintered metal foil 30 likewise has an open-pore structure , and the support control 35 has recesses between the Versteebungen the Steeckmetallgitters similar to the illustrated in Figure 2c embodiment of a support structure.

Here, too, a fiber layer applied thereto and not shown in detail in FIG. 3 can be dimensioned in its porosity in such a way that it acts as a depth filter as described above. This means that the "meshes" of the three-dimensional mesh formed by the interlinked fibers are very wide, especially at a porosity above 70% by volume, preferably above 80%. docks ", due to the large mesh size next to it still sufficient space that more (soot) particles can pass through the pore in question in the fiber layer. However, a sufficient thickness of the fiber layer ensures that particles are trapped with sufficient probability when flying through the fiber layer on a path to the rigid region 3. On the other hand, the support structure 35 is also open-pored, but due to the smaller-diameter pores it acts as a surface filter because a pore becomes clogged as soon as a particle settles in this single pore. The inventive dimensioning of the porosity of the support structure can also develop their advantageous effect here. As a fibrous layer, a fleece or a fiber mat made of ceramic fibers can also be applied on the upstream side to a support structure, which serves for soot filtration and storage. The basic material of fiber webs known per se is a ceramic material, for example aluminum oxide.

The invention using a fiber layer for depth filtration can be applied in particular to all filter substrates or support structures whose filtration principle is based on surface filtration, that is, in particular in sintered metal filters, as known for example from DE 101 28 936, but also in filters with honeycomb structure, i. in filters with adjacent, mutually closed channels symmetric or asymmetric geometry, in which the support structure is constructed for example of silicon carbide, cordierite, mullite and / or aluminum titanate. Even with metal foam filters, the invention can be used. Except for particulate filters, the invention can also be used in other exhaust aftertreatment arrangements, in particular in oxidation catalysts.

The above information on the length and thickness of the fibers refer to a majority of the fibers. If a value of x is given for the diameter, the proportion of these fibers with a value x +/- 1 micrometer is more than 90 percent. Accordingly, for specifying a fiber length y, more than 90 percent of the fibers have a length y +/- 30 percent. Indicated aspect ratios are to be regarded as mean values.

FIG. 4 shows a section 40 of a cordierite honeycomb support structure. The section is limited to the representation of an inflow channel 42 and an adjacent outflow channel 44. The perspective illustration illustrates the flow direction 52 of FIG

Exhaust gas entering the inflow channel penetrates a wall separating the inflow channel from the outflow channel and finally relieving the particle filter arrangement via the outflow channel 44. In this case, the outflow channel 44 is closed on the inflow side by means of a closure or a wall 46, so that the exhaust gas can only penetrate into the arrangement via the inflow channel. A plurality of such mutually closed on one side and arranged side by side channels (the inflow channels are entprechend downstream sealed) forms a honeycomb filter. In the inflow channels 42, an inflow-side fiber layer 48 is applied to the inner wall thereof, while a respective outflow-side fiber layer 50 is applied to the inner wall of the outflow channels 44. The fibers consist essentially, in particular to more than 95 percent, of η - alumina and of a three to fivefrozen portion of silicon dioxide. The fibers have a diameter between 3 to 5 microns and a length greater than 150 microns, which can give a fiber layer porosity in excess of 90 percent. The porosity of the support structure can be selected in particular less than 60 percent.

The fibrous sheet material demands the thermal resistance of the entire assembly. In addition, the high porosity of the fibrous layers 48 and 50 also adds to the protection against high temperatures because the air trapped in the voids serves as a thermal buffer and reduces spatial temperature gradients.

In an alternative embodiment, the large surface area of the fibers of 150 to 200 square meters per gram can be used in the exemplary embodiment according to FIG. 4 for a catalytic coating. It is possible to introduce upstream fibers that are coated with catalysts to reduce Rußabbrandtemperatur. On the downstream side, however, catalysts can be installed which have a de-nitrogening, ie nitrogen oxides reducing effect to realize an integrated DeNOx catalyst or an oxidizing effect to realize an integrated oxidation catalyst, so that, for example, hydrocarbons and / or carbon monoxide can be oxidized to carbon dioxide. The fibers are in this case impregnated in the case of a desired oxidative catalytic activity with platinum, palladium or rhodium, impregnated in the case of a desired abgasentstickenden catalytic activity, for example with barium carbonate. Alternatively, the fiber coating 50 can be omitted and only the inflow channels 42 can be provided with a fiber coating (inflow-side fiber layer 48). This opens up the possibility of reducing the area of the flow cross section of the inflow channels at the expense of the area of the

To increase flow cross-section of the outflow, so the filter in its honeycomb geometry asymmetric design.

FIG. 5 shows a representation of the equilibrium temperatures T in ceramic bodies in a test setup for the detection of the heat-insulating function of a body

Fiber layer when these ceramic body with a heating power P (shown in the diagram 60 in arbitrary units) intrinsically, ie with a tentatively laid by the ceramic body electrical heating wire, are heated. Shown are temperature curves that describe equilibrium temperatures within the intrinsically heated substrates and temperature profiles that were measured on the surface of the uncoated or the fiber-coated ceramic. Here, the set of curves with curves 70, 71 and 72 show the internal temperature within the uncoated or fiber-coated ceramic substrates. Curve 70 shows the internal temperature as a function of heating power for an uncoated ceramic, curve 71 for a fiber-coated ceramic having a fiber layer thickness of about 80 microns and Curve 72 in a fiber-coated ceramic, in which the fiber layer has a thickness which is three to four times as large as in the ceramic whose internal temperature profile is shown in curve 71 (fiber layer thickness about 250 to 300 microns). The family of curves with the curves 80, 81 and 82 shows the respective outside temperatures in said experimental setup on the surface of the uncoated ceramic or on the fiber layer surface, curve 80 in the uncoated ceramic, curve 81 in the fiber-coated ceramic (layer thickness about 80 micrometers ) and curve 82 in the ceramic whose internal temperature is shown in curve 72.

Both temperatures ("inside" and "outside") increase with increasing heating power. No significant difference can be seen between the internal temperature of the ceramic body without fiber coating and the internal temperatures of the fiber-coated ceramics. In the

Outside temperature, however, are noticeable deviations. The outside temperature of the ceramic body with fiber coating with a single thickness (curve 81) is about 100 degrees Celsius below the value of an uncoated ceramic body. This temperature difference can be increased to over 200 degrees Celsisus in a ceramic with a fiber coating of three to four times the thickness (curve 82). When transferred to a real filter through which hot exhaust gas flows, this means that significant amounts of heat are absorbed by the fiber layer applied to the filter substrate. Thus, the temperature influence of the hot exhaust gas, which first comes into contact with the fiber coating on the substrate, so for example, consisting of cordierite support structure can be significantly minimized. The fiber coating protects the substrate from excessive temperatures and increases its service life.

Claims

claims

1. Aftertreatment arrangement for treating the exhaust gas of an internal combustion engine, in particular a self-igniting internal combustion engine of a motor vehicle, with a support structure, wherein the exhaust gas can interact with the support structure for the treatment of the exhaust gas, characterized in that on the surface of the support structure (F; 26, 35) a particularly highly porous layer of fibers (S) is arranged and that the porosity of the support structure is less than 60 percent.

2. exhaust aftertreatment device according to claim 1, characterized in that the porosity of the support structure is greater than 30 percent, in particular greater than 45 percent.

3. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that the layer of fibers (S) has a porosity of at least 70%, in particular a porosity in a range between 80 and 90% or greater.

4. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that the fibers have a length between 40 and 500 microns, in particular a length greater than 150 microns.

5. Aftertreatment device according to one of the preceding claims, characterized in that the fibers are 40 to 200 times longer than thick, in particular, that the fibers are more than 60 to 200 times longer than thick.

6. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that the layer (S) of fibers has a thickness in the range of about 0.05 millimeters to about 0.7 millimeters, in particular from about 0.15 millimeters to about 0.5 millimeters , having.

7. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that the fibers contain ceramic material or consist of ceramic material.

8. Exhaust after-treatment arrangement according to one of the preceding claims, characterized in that the support structure is gas-permeable, in particular that the support structure is open-porous.

9. exhaust aftertreatment device according to claim 7, characterized in that the ceramic material in particular contains alumina, titania or silica or a mixture of two or more oxides.

10. Exhaust after-treatment arrangement according to one of the preceding claims, characterized in that the support structure itself is free of fibers.

11. exhaust aftertreatment arrangement according to one of the preceding claims, characterized in that the support structure itself does not contain fibers of the type which on the

Surface of the support structure are arranged.

12. exhaust gas after treatment arrangement according to one of the preceding claims, characterized in that the layer (S) of fibers as a support structure for a catalytically active material, in particular for a gas-solid reactions and / or for a solid-solid reactions catalytically active Material, serves.

13. exhaust aftertreatment device according to claim 12, characterized in that the catalytically active material supports an oxidative degradation of exhaust gas components.

14. exhaust aftertreatment device according to claim 12 or 13, characterized in that the support structure contains no catalytically active material or contains no catalytically active material of the kind which is arranged on the fibers.

15. Exhaust after-treatment arrangement according to one of the preceding claims, characterized in that the fibers have an active fiber surface which is greater than 0.5 square meters per gram of fiber weight, in particular greater than 20 square meters per gram of fiber weight.

16. Aftertreatment arrangement according to one of the preceding claims, characterized in that the basis weight of the fiber layer between 15 and 200 grams per

Square meters.

17. Exhaust after-treatment arrangement according to one of the preceding claims, characterized in that the support structure is at least partially formed of sintered metal.

18. exhaust aftertreatment arrangement according to one of claims 1 to 16, characterized in that the material of the support structure consists essentially of silicon carbide.

19. exhaust aftertreatment arrangement according to one of claims 1 to 16, characterized in that the material of the support structure consists essentially of cordierite.

20. Exhaust after-treatment arrangement according to one of the preceding claims, characterized in that the support structure is designed as Wanddurchflussfllter.

21. A method for producing an exhaust gas aftertreatment arrangement for treating the exhaust gas of an internal combustion engine, in particular a self-igniting internal combustion engine of a motor vehicle, in which a support structure (F; 26; 35) is provided, wherein the support structure is used to interact with the exhaust gas for the treatment of the exhaust gas , characterized in that a support structure (F, 26; 35) with a porosity smaller than 60 percent is used and that on the surface of the support structure is a particularly highly porous

Layer of fibers (S) is arranged.