Title of Invention	PARTICULATE TRAP WITH COATED FIBER LAYER
Abstract	A high-temperature-resistant fiber layer (1) comprising metal fibers for an open particulate trap (2) for purifying exhaust gases from mobile internal combustion engines (13), characterized in that the fiber layer (1), at least in a section (3), has a catalytically active and/or adsorbent coating (4), in particular such as that of an oxidation catalyst and/or a three-way catalyst and/or an SCR catalyst.

Title of Invention

PARTICULATE TRAP WITH COATED FIBER LAYER

Abstract

A high-temperature-resistant fiber layer (1) comprising metal fibers for an open particulate trap (2) for purifying exhaust gases from mobile internal combustion engines (13), characterized in that the fiber layer (1), at least in a section (3), has a catalytically active and/or adsorbent coating (4), in particular such as that of an oxidation catalyst and/or a three-way catalyst and/or an SCR catalyst.

Full Text	Particulate trap with coated fiber layer The invention relates to a high-temperature-resistant fiber layer for a particulate trap for purifying exhaust gases from mobile internal combustion engines, and to a particulate trap of this type itself. If we consider the purification of exhaust gases, in particular from diesel engines, it is known that hydrocarbons (HC) and carbon monoxides (CO) in the exhaust gas can be oxidized, for example by bringing them into contact with components which may have a catalytically active surface. However, the reduction of nitrogen oxides (NOx) is more difficult under oxygen-rich conditions. A three-way catalytic converter, as is used, for example, in spark-ignition engines, does not on its own achieve the desired effects for diesel engines. For this reason, by way of example, the selected catalytic reduction (SCR) process has been developed. Furthermore, storage catalytic converters have been tested for use for the reduction of nitrogen oxides. The coating of a storage catalytic converter contains, in addition to the standard precious metal components, barium carbonate or barium oxide. This makes it possible to store NOx when there is an excess of oxygen. On the precious metal components, nitrogen monoxide (NO) from the exhaust gas is oxidized to form nitrogen dioxide (NO2) . This is then stored on the catalytic converter by forming barium nitrate. During this storage process, a nitrate layer, which slows storage, since NO2 for further storage has to penetrate through this layer, is formed on the barium nucleus. Since the storage capacity is therefore limited, the catalytic converter has to be regenerated at regular intervals. This is effected, for example, by briefly producing a rich exhaust gas, i.e. by operating under substoichiometric conditions for a short period of time. In a reduced atmosphere, the nitrate is converted back into (for example) carbonate and nitrogen monoxide is released. This is immediately reduced to form nitrogen. Since the regeneration takes place more quickly than the storage, the regeneration periods can be significantly shorter than the storage periods. To reduce particulate emissions, it is known to use particulate traps which are constructed from a ceramic substrate. They have passages, so that the exhaust gas which is to be purified can flow into the particulate trap. Adjacent passages are alternately closed up, so that the exhaust gas enters the passage on the inlet side, passes through a ceramic wall and escapes again on the outlet side through an adjacent passage. Filters of this type achieve an effectiveness of approx. 95% over the entire range of particulate sizes which occur. In addition to chemical interactions with additives and special coatings, the reliable regeneration of the filter in the exhaust system of an automobile still presents problems. It is necessary to regenerate the particulate trap, since the increasing accumulation of particulates in the passage walls through which the exhaust gas is to flow leads to a constantly rising pressure Toss, which has adverse effects on the engine performance. The regeneration step substantially comprises brief heating of the particulate trap and the particulates which have accumulated therein, so that the carbon particulates are converted into gaseous constituents. This can also be achieved, for example, by using an upstream exothermic reaction (e.g. oxidation of fuel which has additionally been injected into the exhaust pipe in an oxidation catalytic converter ("after burning")) to ensure that the exhaust gas briefly reaches the temperatures which are sufficient to convert the particulates which are stuck in the particulate trap. However, this high thermal load on the particulate trap has adverse effects on the service life. To avoid this discontinuous regeneration, which in thermal terms leads to a high likelihood of wear, a system for the continuous regeneration of filters has been developed (CRT: "continuous regeneration trap"). In a system of this type, the particulates are burnt at temperatures of over 200°C by means of oxidation with NO2. The NO2 required for this purpose is often generated by an oxidation catalytic converter which is arranged upstream of the particulate trap. In this case, however, the problem has arisen, in particular with a view to use in motor vehicles which use diesel fuel, that there is only an insufficient level of nitrogen monoxide (NO) which can be converted into the desired nitrogen dioxide (NO2) in the exhaust gas. Consequently, it has not hitherto been possible to ensure that the particulate trap will be continuously regenerated in the exhaust system. It should also be taken into account that in addition to particulates which cannot be converted, oil or additional residues of additives also accumulate in a particulate trap and cannot readily be regenerated. For this reason, known filters have to be replaced and/or washed at regular intervals. In addition to a minimum reaction temperature and a specific residence time, it is also necessary for sufficient nitrogen oxide to be provided for the continuous regeneration of particulates using NO2. Tests relating to the dynamic emission of nitrogen monoxide (NO) and particulates have clearly demonstrated that the particulates are emitted in particular if there is no nitrogen monoxide or only a very small amount of nitrogen monoxide in the exhaust gas, and vice versa. This means that a filter with real continuous regeneration substantially has the function as a compensator or store, so that it is ensured that the two reaction partners are simultaneously present in the required quantities in the filter at a given time. Furthermore, the filter is to be arranged as close as possible to the internal combustion engine, in order to allow it to reach temperatures which are as high as possible immediately after a cold start. To provide the required nitrogen dioxide, an oxidation catalytic converter, which reacts carbon monoxide (CO) and hydrocarbons (HC) , and in particular also converts nitrogen monoxide (NO) into nitrogen dioxide (NO2) , is to be connected upstream of the filter. If this system comprising oxidation catalytic converter and filter is arranged close to the engine, a position upstream of a turbocharger, which is often used in diesel motor vehicles to increase the boost pressure in the combustion chamber, is especially suitable. On looking at these fundamental considerations, the question arises, for actual use in automobile construction, as to how a filter of this type, which in such a position and in the presence of extremely high thermal and dynamic loads has a satisfactory filter efficiency, is constructed. In this context, it is necessary to take into account in particular the spatial conditions, which require a new design of filter. Whereas with conventional filters, which were arranged in the underbody of a motor vehicle, the primary factor was to achieve as large a volume as possible, in order to ensure a long residence time of the as yet unconverted particulates in the filter and therefore a high efficiency, with a filter arranged close to the engine insufficient space or room is available. In view of this, a new concept has been developed, substantially known by the name "open filter system". These open filter systems are distinguished by the fact that it is possible to dispense with an inbuilt, alternating closure of the filter passages. In this case, the passage walls are constructed at least partially from porous or highly porous material and the flow passages of the open filter have diversion or guide structures. These internal fittings cause the flow or the particulates contained therein to be deflected toward the regions made from porous or more highly porous material. In this context, surprisingly, it has emerged that the particulates continue to adhere on and/or in the porous passage wall as a result of interception and/or impaction. The pressure differences in the flow profile of the flowing exhaust gas are of importance in connection with the combination of these effects. The diversion may additionally give rise to local subatmospheric or superatmospheric pressure conditions, which lead to a filtration effect through the porous wall, since it is necessary to compensate for the abovementioned pressure differences. The particulate trap is in this case, unlike with the known closed screen or filter system, open, since no flow blind alleys are provided. Therefore, this property can also be used to characterize particulate filters of this type, so that, for example, the parameter "freedom of flow" is suitable for describing such a particulate trap. Therefore, a "freedom of flow" of 20% means that when viewed in cross section it is possible to see all the way through approx. 20% of the surface area. In the case of a particulate filter with a passage density of approx. 600 cpsi (cells per square inch) with a hydraulic diameter of 0.8 mm, this freedom of flow would correspond to a surface area of over 0.1 mm2. In other words, this means that a particulate trap can be referred to as open if particulates can in principle pass all the way through it, specifically including particulates which are considerably larger than the particulates which are actually to be filtered out (in particular the particulate size range which is characteristic of diesel fuel and/or gasoline). As a result, a filter of this type cannot become blocked even in the event of an agglomeration of particulates during operation. A suitable method for measuring the openness of particulate traps is, for example, to test the diameter up to which spherical particulates can still pass through a filter of this type. In current applications, a particulate trap is "open" in particular if spheres with a diameter of greater than or equal to 0.1 mm can still pass through it, preferably spheres with a diameter of over 0.2 mm. "Open" filter elements of this type are known, for example, from documents DE 201 17 873 U1, DE 201 17 659 Ul, WO 02/00326, WO 01/92692, WO 01/80978, the content of disclosure of which is hereby incorporated in its entirety in the subject matter of the present description. By way of example, German Utility Model DE 89 08 738 Ul gives indications as to the general configuration of honeycomb bodies with internal flow-guiding surfaces. This document describes honeycomb bodies, in particular catalyst support bodies for motor vehicles, made from metal sheets which are arranged in layers, are structured at least in partial regions and form the walls of a multiplicity of passages through which a fluid can flow. This document describes that in most applications and given the standard dimensions of honeycomb bodies of this type, the flow in the passages is substantially laminar, i.e. very small passage cross sections are used. Under these conditions, relatively thick boundary layers, which reduce contact between the core flow in the passages and the walls, are built up on the passage walls. To swirl up the exhaust-gas stream inside the passages and thereby to ensure intensive contact between the entire exhaust-gas stream and a catalytically active surface of the passages, it is proposed in this document to use protuberances which form surfaces which face the flow in the interior of the passage, so that the exhaust gas is deflected transversely with respect to the main direction of flow. In particular with a view to realizing an open particulate trap of this nature, therefore, it is an object of the present invention to improve the effectiveness with regard to the conversion of pollutants contained in the exhaust gas. In particular, it is intended to open up the possibility of providing exhaust-gas systems of particularly small design in particular for automobiles with a diesel engine. Moreover, the production, assembly and maintenance of exhaust-gas systems of this type is to be significantly simplified and thereby made less expensive. These objects are achieved by a high-temperature-resistant fiber layer for a particulate trap for purifying exhaust gases from an internal combustion engine having the features of patent claim 1 and by a corresponding particulate trap having the features of patent claim 8. Further advantageous configurations are described in the dependent patent claims, and the features disclosed therein can be employed individually or in any desired and suitable combination with one another. The high-temperature-resistant fiber layer according to the invention made from metal for a particulate trap for purifying exhaust gases from mobile internal combustion engines is distinguished by the fact that, at least in a section, there is a coating which at least in part corresponds to that of an oxidation catalyst and/or a three-way catalyst and/or an SCR catalyst. The provision of a catalytically active coating of this type has numerous advantages, which will be briefly outlined below. For example, it is possible to ensure that the components for oxidation and/or reduction and/or storage of pollutants contained in the exhaust gas which were originally provided in the exhaust system can be constructed with a smaller volume or can even be dispensed with altogether. This means that the exhaust system per se can be of significantly more streamlined or smaller design, so that a simple structure, simple maintenance and inexpensive production of the exhaust system become possible. Moreover, surprisingly, synergistic effects are also achieved. For example, exhaust-gas constituents which are helpful to the conversion or elimination of the accumulated particulates are generated directly in the interior of a particulate trap equipped with a fiber layer of this type. These exhaust-gas constituents are therefore produced and provided in the immediate vicinity of the surface of the fiber layer to which the particulates adhere. Therefore, by way of example, it is also possible to considerably reduce the regeneration temperature of the particulate trap, for example from over 900°C to temperatures below 600°C. With regard to the arrangement of the at least one section of the fiber layer, it should be noted that this section may also extend over the entire surface of the fiber layer. However, it is also possible to provide a plurality of sections, which may be coated and/or in some cases also uncoated, in which case if appropriate it is also possible to select different types of coating, different shapes of section or section areas. It is also possible for the at least one section to be located only on one outer surface or outer side of the high-temperature- resistant fiber layer. With regard to the properties of the coating of an oxidation catalyst, it should be noted that catalysts of this type are used to increase the rate of certain reactions without themselves being consumed. Suitable catalyst substances allow the oxidation reactions for CO (carbon monoxide) and HC (hydrocarbons) in the exhaust gas to take place at lower temperatures. Coatings of this type, which generally contain catalyst substances belonging to the platinum group, allow gaseous hydrocarbons and carbon monoxide to be oxidized at exhaust-gas temperatures in the diesel engine exhaust gas of only 250°C and above. One particular feature of oxidation coatings of this type is that under certain circumstances the hydrocarbons which still adhere to carbon particulates undergo afterburning, with the result that the particulate emissions can be reduced further. Hitherto, a combination of oxidation- promoting coatings and filter elements of this type has not been provided in a unit since it was feared that the catalytically active substances would be adversely affected by an increasing coverage with particulates. The present invention ignored this commonly held prejudice in the specialist field and developed a high-temperature-resistant fiber layer which makes it possible to produce particularly effective particulate traps. If the levels of the three pollutant components CO, HC and NOX (nitrogen oxide) are to be lowered by further reaction, this can be achieved by coating the fiber layer with the coating of a three-way catalyst. The active catalyst substance in this case comprises platinum metal (Pt), palladium metal (Pd) and/or rhodium metal (Rh) distributed finely over a large surface area. At a lambda value of 1, CO is oxidized to form carbon dioxide (CO2) , CH is oxidized to form CO2 and water (H2O) , and NOx is reduced to form nitrogen (N2) . In this context, the following coating is recommended for the oxidation catalyst: Pt/Pd = 2/1 0.93 - 1.2 gram Pt/litercatalyst support volume 0.46 - 0.6 gram Pt/litercatalyst support volume With regard to the multifunctional catalyst (reduction) , it is proposed for the following relationships to apply: Pt/Rh = 5/1 1.16 - 1.5 gram Pt/litercatalyst support volume 1.23 - 0.3 gram Rh/litercatalyst support volume The catalyst support body volume is to be understood as meaning the volume of the material of the support (honeycomb structure, etc.) and the cavities, passages, etc. formed by the support. The coating of an SCR catalyst may if appropriate also be of multilayer and/or multistage form. One possible urean SCR catalyst system comprises a plurality of partial regions of the coating which are arranged in succession and are applied to the fiber layer. The partial regions may in this case be arranged as follows, as seen in the direction of the flow of the exhaust gas: a coating of an oxidation catalyst (optional), the coating of a hydrolysis catalyst, the coating of an SCR catalyst, and if appropriate a downstream oxidation catalyst. The oxidation catalyst which is optionally provided upstream is used to increase the SCR activity at low exhaust-gas temperatures (in particular in the case of a diesel automobile) . By increasing the NO2 content (optimum: 50% by vol.) in the exhaust gas by means of partial oxidation of NO, it is possible to significantly increase the reaction rate of the SCR reaction in a temperature range below approximately 573 K. In addition, carbon monoxide is oxidized to form carbon dioxide and incompletely burnt hydrocarbons are reacted to form carbon dioxide and water at the catalyst surface. If an upstream region with an oxidation coating of this type were not used, the oxidation of the hydrocarbons would take place in part at the SCR catalyst and would therefore reduce the nitrogen oxide conversion rate. The coating of a hydrolysis catalyst allows an aqueous urea solution to be completely broken down even at low temperatures, for example around 470 K. Decomposition of the urea has proven difficult below approx. 470 K, since undesirable by-products may form on account of incomplete decomposition. The coating of the SCR catalyst serves for the selective reduction of the nitrogen oxides NOX with ammonia to form the harmless products nitrogen and water. According to a further configuration of the high-temperature- resistant fiber layer, the coating comprises washcoat. Coating the relatively smooth surfaces of the fibers with washcoat causes the catalytically active surface area to be increased. This fissured surface on the one hand ensures that sufficient space is available for fixing a catalyst (e.g. platinum, rhodium, etc.) and on the other hand serves to swirl up the exhaust gas flowing through, effecting particularly intensive contact with the catalyst. The washcoat layer with a large surface area promoting catalysis is applied in a known way by the fiber layer (or subsequently the entire particulate trap comprising fiber layers and metal foils) being immersed in a liquid washcoat dispersion or sprayed with such a dispersion. Then, the excess washcoat dispersion is removed, the washcoat in the fiber layer is dried and finally the entire assembly is calcined at temperatures of generally over 450°C. During calcining, the volatile constituents of the washcoat dispersion are expelled, so that a temperature-resistant, catalysis-promoting layer with a high specific surface area is produced. If appropriate, this operation is repeated a number of times in order to achieve a desired layer thickness. The mean layer thickness is preferably in a range from 0.001 to 0.02 mm, in particular between 0.005 and 0.012 mm. The washcoat usually consists of a mixture of an aluminum oxide and at least one promoter oxide, such as for example rare-earth oxides, zirconium oxide, nickel oxide, iron oxide, germanium oxide and barium oxide. The washcoat dispersion must have optimum flow properties during its application during its application to the honeycomb body, in order to achieve a desired uniform layer thickness over the entire passage length. To achieve flow properties of this nature, known washcoat dispersions have a specified pH, and only a limited solids content is permitted. However, tests have shown that a washcoat dispersion of this nature has a time-dependent viscosity. This means that the washcoat dispersion very quickly forms a gel, preventing a uniform layer thickness frorr. being generated. This gelation can be delayed by keeping the washcoat dispersion in motion, i.e. moving, in particular vibrating, the dispersion or the filter layer which it wets. According to yet a further configuration of the fiber layer, the latter consists of a porous sintered and/or fiber material (e.g. steel). In this context, in particular high-temperature- resistant, corrosion-resistant steels with relatively high chromium, nickel, aluminum and/or molybdenum contents are recommended. In this context, it is particularly advantageous for the fiber layer to include fibers with a mean diameter of less than 0.082 mm, in particular in a range from 0.01 to 0.05 mm. To prevent a filter layer of this type from generating a high dynamic pressure in the exhaust-gas stream, it is proposed for the fiber layer to have a porosity of at least 50%, in particular at least 75%, preferably at least 85% and for preference even at least 95%. In this context, it should be noted that fiber layers of this type can be produced relatively successfully using fibers with a mean length of 0.4 mm to 0.05 mm, in which case it is preferable to select shorter fiber lengths for thicker fibers. Furthermore, it is proposed for the fiber layer, in a longitudinal section substantially parallel to the largest outer surface, to have openings which on average have a size of 0.01 mm to 0.5 mm, in particular 0.05 mm to 0.25 mm. At this point, it should be pointed out that the fiber layer may fundamentally include fibers in virtually any desired arrangement, and is to be understood as encompassing in particular random layers, woven fabrics or other similar structures. In this case, regular structures may also be present only in regions, whereas a more chaotic arrangement of the fibers is present in the remaining regions. To ensure that sufficiently large cavities for particulates and/or their agglomerates are provided, it is proposed here, in particular for use in exhaust systems of diesel engines, for a certain pore size to be provided. A longitudinal section through the material which shows small cross sections of the pores or cavities, referred to here as openings, is used to determine the pore size. On average, all these openings have an extent in the range mentioned above. What is meant in this context is a mean of all the maximum extents of the openings which can be seen in longitudinal section. Since the dimension of the opening relates to the fiber layer which has already been coated, it is also possible to use a corresponding mean fiber spacing which is preferably to be selected as less than 0.6 mm, in particular between 0.05 mm and 0.35 mm. Furthermore, it is proposed for the fiber layer to have a thickness of less than 3 mm, in particular less than 1.5 mm, preferably less than 0.5 mm and for preference less than 0.1 mm. The thicknesses mentioned here are selected in particular with a view to the use of the fiber layer for particulate traps for the purification of exhaust gases from mobile internal combustion engines. A further aspect of the invention proposes a particulate trap for purifying exhaust gases from mobile internal combustion engines which has at least one partially structured metal foil and at least one high-temperature-resistant fiber layer of the type described above, in which, preferably, a plurality of structured metal foils and a plurality of fiber layers are arranged alternately and in particular wound together in a housing. This forms in particular an "open" particulate trap, as described in the introduction. Accordingly, it is especially advantageous to form an "open" filter element as described in documents DE 201 17 873 U1, DE 201 17 659 U1, WO 02/00326, WO 01/92692, WO 01/80978. Furthermore, it is proposed for the particulate trap to form passages running substantially parallel to the axis, with guide surfaces, preferably guide surfaces of the metal foil, projecting into at least some of the passages and diverting gas streams flowing through the passages toward the fiber layer. Guide surfaces of this type may be formed by projections, bosses, micro-undulations, vanes or similar structures. It is also possible for these guide surfaces to be formed by edges of holes in metal foils of this type. The guide surfaces themselves may likewise have holes. According to a further configuration, the particulate trap has a volume, and the quantity of coating of the particulate trap based on this volume is in the range from 20 to 300 g/1 (grams per liter), preferably even between 50 and 120 g/1. In this context, the term volume is to be understood as meaning the volume which is composed of the metal foils, the fiber layers and the passages formed. A volume of this type is usually in the range from 0.01 1 to 1.5 1, preferably between 0.3 1 and 0.8 1. Furthermore, it is proposed for the at least one, at least partially structured metal foil to have apertures which extend over at least one structure width, preferably even over 2, in particular 3 structure widths. This means that, for example, an aperture of this type connects a plurality of adjacent passages formed by the structure to one another. This ensures particularly effective mixing between the partial exhaust-gas streams without an undesirably high dynamic pressure being generated upstream of the particulate trap. In this context, it should also be noted that the apertures extend substantially in the plane of the metal foil. The invention will now be explained in more detail with reference to the figures. In this context, it should be noted that the figures show particularly preferred exemplary embodiments of the invention, but the invention is not restricted to these embodiments. In the accompanying figures. Fig. 1 shows a diagrammatic, exploded view of a detail of a particulate trap according to the invention, Fig. 2 shows a further detail of a configuration of the particulate trap according to the invention, Fig. 3 diagrammatically depicts a configuration of an exhaust system of a mobile internal combustion engine, Fig. 4 shows a diagrammatic and perspective illustration of a further configuration of the particulate trap according to the invention, Fig. 5 diagrammatically depicts a longitudinal section through a configuration of the fiber layer in accordance with the invention, and Fig. 6 shows a further longitudinal section through a fiber layer in the coated state. Fig. 1 shows a diagrammatic, exploded view of a detail of a particulate trap as is used, for example, to treat the exhaust gas from mobile internal combustion engines. The figure illustrates two fiber layers 1 according to the invention, between which a metal foil 14 is arranged. The fiber layers 1 each have a section 3 in which a coating 4 is arranged. This coating 4 may be the coating of an oxidation catalyst, of a three-way catalyst and/or of an SCR catalyst. It is preferable for the metal foils 14 (at least in partial regions) to have a catalytically active and/or storing coating. It is usual for the adjacent layers to bear against one another, and they are preferably connected to one another by a joining technique, in particular by soldering. For this purpose it is necessary, for example, for a partial region, in particular the edge of the fiber layer 1, not to be coated, in order to ensure that the possibility of forming connections by a joining technique is preserved in this partial region. The structuring of the metal foil 14 allows an exhaust gas to flow through this "sandwich" of smooth layers (fiber layer 1) and corrugated layer (metal foil 14) in a direction of flow 21. Guide surfaces 18 are arranged in the passages 17, causing the partial gas stream to be swirled up, so that they are guided in particular onto the coated fiber layer 1. The structure of the metal foil 14 is in this case a corrugated structure with a predetermined structure width 36. It is preferable for the guide surfaces 18 and/or apertures 19 below to be designed to be larger than the structure width 36, so that a plurality of adjacent passages 17 can be connected to one another through the apertures 19. Fig. 2 shows an arrangement of metal foils 14 and a fiber layer 1 in detail. Once again, the metal foils 14 and the fiber layer 1 are arranged alternately, the structure of the metal foils 14 in combination with the fiber layer 1 forming passages 17 through which the exhaust gas can flow in a direction of flow 21. Guide surfaces 18, which are produced from the metal foil 14 itself by stamping, pressing or in some other way, project into the passages 17. This simultaneously creates apertures 19, so that a partial edge flow "peels off" from the gas flowing through a passage 17 and can be diverted toward the fiber layer 1. In this way, the particulates 22 are also entrained and guided toward the fiber layer 1, where they remain on the outer surface 9, for example sticking to it or accumulating in cavities, pores or similar openings in the fiber layer 1. The fiber layer 12 illustrated here has a plurality of chaotically arranged fibers 6 which are provided with a coating 4. Overall, the fiber layer 1 has a thickness 12 of less than 3 mm. Fig. 3 diagrammatically depicts the structure of an exhaust system of an automobile internal combustion engine 13. The exhaust gas which is generated in the internal combustion engine 13 is fed via an exhaust pipe 23 to the numerous components for exhaust-gas treatment before ultimately being released to the environment. The exhaust system illustrated in Fig. 3 includes the following components in succession in the direction of flow 21: a starting catalytic converter 24, a turbo charger 25, an oxidation catalytic converter 26, a reducing-agent feed 27, a mixer 28, a particulate trap 2 according to the invention and a main catalytic converter 29. The starting catalytic converter 24 is distinguished by its particularly small volume (for example less than 0.1 liter) and, on account of its low heat capacity and its immediate proximity to the engine, has been heated up sufficiently for it to be possible to catalytically convert pollutants contained in the exhaust gas just a short time after the engine has started (e.g. to temperatures of over 230°C after a few seconds). The function of the oxidation catalytic converter 26 upstream of a particulate trap 2 for regeneration has already been explained extensively above. The reducing- agent feed 27 and the mixer 28 are used, for example, to supply solid or liquid urea, so that it is also possible to convert pollutants using the SCR method. The mixer 28 may be designed as a guide surface, a grate, a honeycomb body or in some similar form. However, it is also possible to omit the mixer 28 upstream of the particulate trap 2, since the particulate filter 2 itself is also responsible for swirling up the exhaust-gas stream and/or finely distributing the reducing agent which has been introduced. The downstream main catalytic converter 29 usually has a relatively large volume, in particular of greater than 1.5 liters. Fig. 4 shows a perspective and diagrammatic view of the structure of a particulate trap 2. The particulate trap 2 for the purification of exhaust gases from mobile internal combustion engines comprises a structured metal foil 14 and a high-temperature-resistant fiber layer 1, which are arranged helically around an axis 16 of the particulate trap 2 (simple stacked arrangements, S-shaped loops or other wound arrangements of the metal foils and/or fiber layers are also possible as alternatives). The metal foil 14 and the fiber layer 1 form passages 17 which extend through the particulate trap 2 substantially parallel to the axis 16. The assembly comprising metal foil 14 and fiber layer 1 is accommodated in a housing 15 and is advantageously also connected to this housing by a joining technique. In the embodiment of the particulate trap 2 which is illustrated, the housing 15 projects beyond the end face 34 of the particulate trap 2 or the metal foil 14 and the fiber layer 1. The material thickness 30 of the corrugated metal foil 14 is preferably in a range below 0.05 mm, preferably even below 0.02 mm. In this context, it is recommended in particular for the material thickness 30 or the coating 4 (not shown) or other parameters of the particulate trap 2 not to be constant over the entire length 31 of the particulate trap 2, which means, for example, that in a first length section 32, the particulate trap 2 has a lower heat capacity, a higher porosity, a higher loading with regard to the catalytically active coating, a greater number/size of apertures 19, guide surfaces 18 or fibers than in a second length section 33. In principle, it is also possible for the particulate trap 2 to be divided into more than two length sections. The particulate trap 2 illustrated has a volume 20 which is characterized by the volume in the interior of the housing 20 which is filled by the fiber layer 1 and the metal foil 14, also encompassing the volume of the passages 17. With regard to the coating 4, the particulate trap according to the invention is provided with a quantity in the range from 20 to 300 g/1. In this context, it is possible for this quantity to be arranged over the entire length 31 uniformly on the outer surfaces 9 of the fiber layer 1 and/or the metal foil 14, but it is also possible for only the fiber layer 1 or only partial regions of the metal foil 14 to be provided with a catalytically active coating 4. It is also possible for different types or quantities of the coating 4 to be provided in different length sections. Fig. 5 diagrammatically depicts the longitudinal section 8 through the fiber layer 1. In this context, it can be seen that the fiber layer 1 is formed by a multiplicity of fibers 6, which are in this case connected to one another in partially ordered and partially random fashion. The fibers 6 preferably have a diameter 7 in the range from 0.012 to 0.03 5 mm. Openings 10 are formed by the arrangement of the fibers 6 in the longitudinal section 8. These openings in practice constitute a cross section through the cavities which are formed in the interior of the fiber layer 1. Fig. 6 likewise diagrammatically depicts a longitudinal section 8 through the fiber layer 1, the fibers 6 now being designed with a coating 4. The coating 4 comprises washcoat 5, which on account of its fissured surface offers sufficient options for the accumulation of the catalytically active substances 35. Despite the coating 4, the longitudinal section 8 still has openings 10 with an extent 11. This extent 11 of all the openings 10 on average is between 0.05 and 0.4 mm. At the same time, it is preferable to maintain a porosity of approx. 87%. The present invention is the result of a large number of technically complex attempts to improve the efficiency of particulate traps in the exhaust systems of automobile internal combustion engines. WE CLAIM: 1. A high-temperature-resistant fiber layer (1) comprising metal fibers for an open particulate trap (2) for purifying exhaust gases from mobile internal combustion engines (13), wherein the fiber layer (1), at least in a section (3) has a catalytically active coating (4), in particular such as that of an oxidation catalyst and/or a three-way catalyst and/or an SCR catalyst, characterized in that the fiber layer (1) has a porosity of at least 50% and in a longitudinal section (8) taken substantially parallel to the largest outer surface (9), has openings (10) which on average have a size (11) of 0.01 mm to 0.5 mm, in particular 0.05 mm to 0.25 mm. 2. The high-temperature-resistant fiber layer (1) as claimed in claim 1, wherein the coating (4) comprises washcoat (5). 3. The high-temperature-resistant fiber layer (1) as claimed in claim 1 or 2, wherein the fiber layer (1) comprises a porous sintered and/or fiber material. 4. The high-temperature-resistant fiber layer (1) as claimed in one of the preceding claims, wherein the fiber layer (1) comprises fibers (6) with a mean diameter (7) which is less than 0.082 mm, in particular in a range from 0.01 to 0.05 mm. 5. The high-temperature-resistant-fiber layer (1) as claimed in one of the preceding claims, wherein the fiber layer (1) has a porosity of at least 75%, preferably at least 85% and for preference even at least 95%. 6. The high-temperature-resistant fiber layer (1) as claimed in one of the preceding claims, wherein the fiber layer (1) has a thickness (12) of less than 3 mm, in particular less than 1.5 mm, preferably less than 0.5 mm and for preference less than 0.1 mm. 7. A particulate trap (2) for purifying exhaust gases from mobile least, one CM partially structured metal foil (14) and at least one high- temperature-resistant fiber layer (1) as claimed in one of claims 1 to 6, preferably with a plurality of structured metal foils (14) and a plurality of fiber layers (1) arranged alternately, in particular wound together, in a housing (15). 8. The particulate trap (2) as claimed in claim 7, wherein passages (17) running substantially parallel to an axis (16) of the particulate trap (2) are formed, with guide surfaces (18), preferably guide surfaces (18) of the metal foils (14), projecting into at least some of the passages (17) and diverting gas streams flowing through the passages (17) toward the fiber layer (1). 9. The particulate trap (2) as claimed in claim 7 or 8, wherein the particulate trap (2) has a volume (20), and the quantity of coating with respect to this volume is in the range from 20 to 300 g/1 (grams per liter), preferably even between 50 and 120g/1. 10. The particulate trap (2) as claimed in one of claims 7 to 9,wherein at least one, at least partially structured metal foil (14) has apertures (19) which extend over at least one structure width (36), preferably even over two or in particular even three structure widths (36). A high-temperature-resistant fiber layer (1) comprising metal fibers for an open particulate trap (2) for purifying exhaust gases from mobile internal combustion engines (13), characterized in that the fiber layer (1), at least in a section (3), has a catalytically active and/or adsorbent coating (4), in particular such as that of an oxidation catalyst and/or a three-way catalyst and/or an SCR catalyst.

Full Text

Particulate trap with coated fiber layer
The invention relates to a high-temperature-resistant fiber
layer for a particulate trap for purifying exhaust gases from
mobile internal combustion engines, and to a particulate trap
of this type itself.
If we consider the purification of exhaust gases, in
particular from diesel engines, it is known that hydrocarbons
(HC) and carbon monoxides (CO) in the exhaust gas can be
oxidized, for example by bringing them into contact with
components which may have a catalytically active surface.
However, the reduction of nitrogen oxides (NOx) is more
difficult under oxygen-rich conditions. A three-way catalytic
converter, as is used, for example, in spark-ignition engines,
does not on its own achieve the desired effects for diesel
engines. For this reason, by way of example, the selected
catalytic reduction (SCR) process has been developed.
Furthermore, storage catalytic converters have been tested for
use for the reduction of nitrogen oxides. The coating of a
storage catalytic converter contains, in addition to the
standard precious metal components, barium carbonate or barium
oxide. This makes it possible to store NOx when there is an
excess of oxygen. On the precious metal components, nitrogen
monoxide (NO) from the exhaust gas is oxidized to form
nitrogen dioxide (NO2) . This is then stored on the catalytic
converter by forming barium nitrate. During this storage
process, a nitrate layer, which slows storage, since NO2 for
further storage has to penetrate through this layer, is formed
on the barium nucleus. Since the storage capacity is therefore
limited, the catalytic converter has to be regenerated at
regular intervals. This is effected, for example, by briefly
producing a rich exhaust gas, i.e. by operating under
substoichiometric conditions for a short period of time. In a
reduced atmosphere, the nitrate is converted back into (for
example) carbonate and nitrogen monoxide is released. This is
immediately reduced to form nitrogen. Since the regeneration
takes place more quickly than the storage, the regeneration
periods can be significantly shorter than the storage periods.
To reduce particulate emissions, it is known to use
particulate traps which are constructed from a ceramic
substrate. They have passages, so that the exhaust gas which
is to be purified can flow into the particulate trap. Adjacent
passages are alternately closed up, so that the exhaust gas
enters the passage on the inlet side, passes through a ceramic
wall and escapes again on the outlet side through an adjacent
passage. Filters of this type achieve an effectiveness of
approx. 95% over the entire range of particulate sizes which
occur.
In addition to chemical interactions with additives and
special coatings, the reliable regeneration of the filter in
the exhaust system of an automobile still presents problems.
It is necessary to regenerate the particulate trap, since the
increasing accumulation of particulates in the passage walls
through which the exhaust gas is to flow leads to a constantly
rising pressure Toss, which has adverse effects on the engine
performance. The regeneration step substantially comprises
brief heating of the particulate trap and the particulates
which have accumulated therein, so that the carbon
particulates are converted into gaseous constituents. This can
also be achieved, for example, by using an upstream exothermic
reaction (e.g. oxidation of fuel which has additionally been
injected into the exhaust pipe in an oxidation catalytic
converter ("after burning")) to ensure that the exhaust gas
briefly reaches the temperatures which are sufficient to
convert the particulates which are stuck in the particulate
trap. However, this high thermal load on the particulate trap
has adverse effects on the service life.
To avoid this discontinuous regeneration, which in thermal
terms leads to a high likelihood of wear, a system for the
continuous regeneration of filters has been developed (CRT:
"continuous regeneration trap"). In a system of this type, the
particulates are burnt at temperatures of over 200°C by means
of oxidation with NO2. The NO2 required for this purpose is
often generated by an oxidation catalytic converter which is
arranged upstream of the particulate trap. In this case,
however, the problem has arisen, in particular with a view to
use in motor vehicles which use diesel fuel, that there is
only an insufficient level of nitrogen monoxide (NO) which can
be converted into the desired nitrogen dioxide (NO2) in the
exhaust gas. Consequently, it has not hitherto been possible
to ensure that the particulate trap will be continuously
regenerated in the exhaust system.
It should also be taken into account that in addition to
particulates which cannot be converted, oil or additional
residues of additives also accumulate in a particulate trap
and cannot readily be regenerated. For this reason, known
filters have to be replaced and/or washed at regular
intervals.
In addition to a minimum reaction temperature and a specific
residence time, it is also necessary for sufficient nitrogen
oxide to be provided for the continuous regeneration of
particulates using NO2. Tests relating to the dynamic emission
of nitrogen monoxide (NO) and particulates have clearly
demonstrated that the particulates are emitted in particular
if there is no nitrogen monoxide or only a very small amount
of nitrogen monoxide in the exhaust gas, and vice versa. This
means that a filter with real continuous regeneration
substantially has the function as a compensator or store, so
that it is ensured that the two reaction partners are
simultaneously present in the required quantities in the
filter at a given time. Furthermore, the filter is to be
arranged as close as possible to the internal combustion
engine, in order to allow it to reach temperatures which are
as high as possible immediately after a cold start. To provide
the required nitrogen dioxide, an oxidation catalytic
converter, which reacts carbon monoxide (CO) and hydrocarbons
(HC) , and in particular also converts nitrogen monoxide (NO)
into nitrogen dioxide (NO2) , is to be connected upstream of
the filter. If this system comprising oxidation catalytic
converter and filter is arranged close to the engine, a
position upstream of a turbocharger, which is often used in
diesel motor vehicles to increase the boost pressure in the
combustion chamber, is especially suitable.
On looking at these fundamental considerations, the question
arises, for actual use in automobile construction, as to how a
filter of this type, which in such a position and in the
presence of extremely high thermal and dynamic loads has a
satisfactory filter efficiency, is constructed. In this
context, it is necessary to take into account in particular
the spatial conditions, which require a new design of filter.
Whereas with conventional filters, which were arranged in the
underbody of a motor vehicle, the primary factor was to
achieve as large a volume as possible, in order to ensure a
long residence time of the as yet unconverted particulates in
the filter and therefore a high efficiency, with a filter
arranged close to the engine insufficient space or room is
available.
In view of this, a new concept has been developed,
substantially known by the name "open filter system". These
open filter systems are distinguished by the fact that it is
possible to dispense with an inbuilt, alternating closure of
the filter passages. In this case, the passage walls are
constructed at least partially from porous or highly porous
material and the flow passages of the open filter have
diversion or guide structures. These internal fittings cause
the flow or the particulates contained therein to be deflected
toward the regions made from porous or more highly porous
material. In this context, surprisingly, it has emerged that
the particulates continue to adhere on and/or in the porous
passage wall as a result of interception and/or impaction. The
pressure differences in the flow profile of the flowing
exhaust gas are of importance in connection with the
combination of these effects. The diversion may additionally
give rise to local subatmospheric or superatmospheric pressure
conditions, which lead to a filtration effect through the
porous wall, since it is necessary to compensate for the
abovementioned pressure differences.
The particulate trap is in this case, unlike with the known
closed screen or filter system, open, since no flow blind
alleys are provided. Therefore, this property can also be used
to characterize particulate filters of this type, so that, for
example, the parameter "freedom of flow" is suitable for
describing such a particulate trap. Therefore, a "freedom of
flow" of 20% means that when viewed in cross section it is
possible to see all the way through approx. 20% of the surface
area. In the case of a particulate filter with a passage
density of approx. 600 cpsi (cells per square inch) with a
hydraulic diameter of 0.8 mm, this freedom of flow would
correspond to a surface area of over 0.1 mm2. In other words,
this means that a particulate trap can be referred to as open
if particulates can in principle pass all the way through it,
specifically including particulates which are considerably
larger than the particulates which are actually to be filtered
out (in particular the particulate size range which is
characteristic of diesel fuel and/or gasoline). As a result, a
filter of this type cannot become blocked even in the event of
an agglomeration of particulates during operation. A suitable
method for measuring the openness of particulate traps is, for
example, to test the diameter up to which spherical
particulates can still pass through a filter of this type. In
current applications, a particulate trap is "open" in
particular if spheres with a diameter of greater than or equal
to 0.1 mm can still pass through it, preferably spheres with a
diameter of over 0.2 mm. "Open" filter elements of this type
are known, for example, from documents DE 201 17 873 U1, DE
201 17 659 Ul, WO 02/00326, WO 01/92692, WO 01/80978, the
content of disclosure of which is hereby incorporated in its
entirety in the subject matter of the present description.
By way of example, German Utility Model DE 89 08 738 Ul gives
indications as to the general configuration of honeycomb
bodies with internal flow-guiding surfaces. This document
describes honeycomb bodies, in particular catalyst support
bodies for motor vehicles, made from metal sheets which are
arranged in layers, are structured at least in partial regions
and form the walls of a multiplicity of passages through which
a fluid can flow. This document describes that in most
applications and given the standard dimensions of honeycomb
bodies of this type, the flow in the passages is substantially
laminar, i.e. very small passage cross sections are used.
Under these conditions, relatively thick boundary layers,
which reduce contact between the core flow in the passages and
the walls, are built up on the passage walls. To swirl up the
exhaust-gas stream inside the passages and thereby to ensure
intensive contact between the entire exhaust-gas stream and a
catalytically active surface of the passages, it is proposed
in this document to use protuberances which form surfaces
which face the flow in the interior of the passage, so that
the exhaust gas is deflected transversely with respect to the
main direction of flow.
In particular with a view to realizing an open particulate
trap of this nature, therefore, it is an object of the present
invention to improve the effectiveness with regard to the
conversion of pollutants contained in the exhaust gas. In
particular, it is intended to open up the possibility of
providing exhaust-gas systems of particularly small design in
particular for automobiles with a diesel engine. Moreover, the
production, assembly and maintenance of exhaust-gas systems of
this type is to be significantly simplified and thereby made
less expensive.
These objects are achieved by a high-temperature-resistant
fiber layer for a particulate trap for purifying exhaust gases
from an internal combustion engine having the features of
patent claim 1 and by a corresponding particulate trap having
the features of patent claim 8. Further advantageous
configurations are described in the dependent patent claims,
and the features disclosed therein can be employed
individually or in any desired and suitable combination with
one another.
The high-temperature-resistant fiber layer according to the
invention made from metal for a particulate trap for purifying
exhaust gases from mobile internal combustion engines is
distinguished by the fact that, at least in a section, there
is a coating which at least in part corresponds to that of an
oxidation catalyst and/or a three-way catalyst and/or an SCR
catalyst.
The provision of a catalytically active coating of this type
has numerous advantages, which will be briefly outlined below.
For example, it is possible to ensure that the components for
oxidation and/or reduction and/or storage of pollutants
contained in the exhaust gas which were originally provided in
the exhaust system can be constructed with a smaller volume or
can even be dispensed with altogether. This means that the
exhaust system per se can be of significantly more streamlined
or smaller design, so that a simple structure, simple
maintenance and inexpensive production of the exhaust system
become possible. Moreover, surprisingly, synergistic effects
are also achieved. For example, exhaust-gas constituents which
are helpful to the conversion or elimination of the
accumulated particulates are generated directly in the
interior of a particulate trap equipped with a fiber layer of
this type. These exhaust-gas constituents are therefore
produced and provided in the immediate vicinity of the surface
of the fiber layer to which the particulates adhere.
Therefore, by way of example, it is also possible to
considerably reduce the regeneration temperature of the
particulate trap, for example from over 900°C to temperatures
below 600°C.
With regard to the arrangement of the at least one section of
the fiber layer, it should be noted that this section may also
extend over the entire surface of the fiber layer. However, it
is also possible to provide a plurality of sections, which may
be coated and/or in some cases also uncoated, in which case if
appropriate it is also possible to select different types of
coating, different shapes of section or section areas. It is
also possible for the at least one section to be located only
on one outer surface or outer side of the high-temperature-
resistant fiber layer.
With regard to the properties of the coating of an oxidation
catalyst, it should be noted that catalysts of this type are
used to increase the rate of certain reactions without
themselves being consumed. Suitable catalyst substances allow
the oxidation reactions for CO (carbon monoxide) and HC
(hydrocarbons) in the exhaust gas to take place at lower
temperatures. Coatings of this type, which generally contain
catalyst substances belonging to the platinum group, allow
gaseous hydrocarbons and carbon monoxide to be oxidized at
exhaust-gas temperatures in the diesel engine exhaust gas of
only 250°C and above. One particular feature of oxidation
coatings of this type is that under certain circumstances the
hydrocarbons which still adhere to carbon particulates undergo
afterburning, with the result that the particulate emissions
can be reduced further. Hitherto, a combination of oxidation-
promoting coatings and filter elements of this type has not
been provided in a unit since it was feared that the
catalytically active substances would be adversely affected by
an increasing coverage with particulates. The present
invention ignored this commonly held prejudice in the
specialist field and developed a high-temperature-resistant
fiber layer which makes it possible to produce particularly
effective particulate traps.
If the levels of the three pollutant components CO, HC and NOX
(nitrogen oxide) are to be lowered by further reaction, this
can be achieved by coating the fiber layer with the coating of
a three-way catalyst. The active catalyst substance in this
case comprises platinum metal (Pt), palladium metal (Pd)
and/or rhodium metal (Rh) distributed finely over a large
surface area. At a lambda value of 1, CO is oxidized to form
carbon dioxide (CO2) , CH is oxidized to form CO2 and water
(H2O) , and NOx is reduced to form nitrogen (N2) . In this
context, the following coating is recommended for the
oxidation catalyst:
Pt/Pd = 2/1
0.93 - 1.2 gram Pt/litercatalyst support volume
0.46 - 0.6 gram Pt/litercatalyst support volume
With regard to the multifunctional catalyst (reduction) , it is
proposed for the following relationships to apply:
Pt/Rh = 5/1
1.16 - 1.5 gram Pt/litercatalyst support volume
1.23 - 0.3 gram Rh/litercatalyst support volume
The catalyst support body volume is to be understood as
meaning the volume of the material of the support (honeycomb
structure, etc.) and the cavities, passages, etc. formed by
the support.
The coating of an SCR catalyst may if appropriate also be of
multilayer and/or multistage form. One possible urean SCR
catalyst system comprises a plurality of partial regions of
the coating which are arranged in succession and are applied
to the fiber layer. The partial regions may in this case be
arranged as follows, as seen in the direction of the flow of
the exhaust gas:
a coating of an oxidation catalyst (optional),
the coating of a hydrolysis catalyst,
the coating of an SCR catalyst, and
if appropriate a downstream oxidation catalyst.
The oxidation catalyst which is optionally provided upstream
is used to increase the SCR activity at low exhaust-gas
temperatures (in particular in the case of a diesel
automobile) . By increasing the NO2 content (optimum: 50% by
vol.) in the exhaust gas by means of partial oxidation of NO,
it is possible to significantly increase the reaction rate of
the SCR reaction in a temperature range below approximately
573 K. In addition, carbon monoxide is oxidized to form carbon
dioxide and incompletely burnt hydrocarbons are reacted to
form carbon dioxide and water at the catalyst surface. If an
upstream region with an oxidation coating of this type were
not used, the oxidation of the hydrocarbons would take place
in part at the SCR catalyst and would therefore reduce the
nitrogen oxide conversion rate.
The coating of a hydrolysis catalyst allows an aqueous urea
solution to be completely broken down even at low
temperatures, for example around 470 K. Decomposition of the
urea has proven difficult below approx. 470 K, since
undesirable by-products may form on account of incomplete
decomposition. The coating of the SCR catalyst serves for the
selective reduction of the nitrogen oxides NOX with ammonia to
form the harmless products nitrogen and water.
According to a further configuration of the high-temperature-
resistant fiber layer, the coating comprises washcoat. Coating
the relatively smooth surfaces of the fibers with washcoat
causes the catalytically active surface area to be increased.
This fissured surface on the one hand ensures that sufficient
space is available for fixing a catalyst (e.g. platinum,
rhodium, etc.) and on the other hand serves to swirl up the
exhaust gas flowing through, effecting particularly intensive
contact with the catalyst.
The washcoat layer with a large surface area promoting
catalysis is applied in a known way by the fiber layer (or
subsequently the entire particulate trap comprising fiber
layers and metal foils) being immersed in a liquid washcoat
dispersion or sprayed with such a dispersion. Then, the excess
washcoat dispersion is removed, the washcoat in the fiber
layer is dried and finally the entire assembly is calcined at
temperatures of generally over 450°C. During calcining, the
volatile constituents of the washcoat dispersion are expelled,
so that a temperature-resistant, catalysis-promoting layer
with a high specific surface area is produced. If appropriate,
this operation is repeated a number of times in order to
achieve a desired layer thickness. The mean layer thickness is
preferably in a range from 0.001 to 0.02 mm, in particular
between 0.005 and 0.012 mm.
The washcoat usually consists of a mixture of an aluminum
oxide and at least one promoter oxide, such as for example
rare-earth oxides, zirconium oxide, nickel oxide, iron oxide,
germanium oxide and barium oxide. The washcoat dispersion must
have optimum flow properties during its application during its
application to the honeycomb body, in order to achieve a
desired uniform layer thickness over the entire passage
length.
To achieve flow properties of this nature, known washcoat
dispersions have a specified pH, and only a limited solids
content is permitted. However, tests have shown that a
washcoat dispersion of this nature has a time-dependent
viscosity. This means that the washcoat dispersion very
quickly forms a gel, preventing a uniform layer thickness frorr.
being generated. This gelation can be delayed by keeping the
washcoat dispersion in motion, i.e. moving, in particular
vibrating, the dispersion or the filter layer which it wets.
According to yet a further configuration of the fiber layer,
the latter consists of a porous sintered and/or fiber material
(e.g. steel). In this context, in particular high-temperature-
resistant, corrosion-resistant steels with relatively high
chromium, nickel, aluminum and/or molybdenum contents are
recommended. In this context, it is particularly advantageous
for the fiber layer to include fibers with a mean diameter of
less than 0.082 mm, in particular in a range from 0.01 to 0.05
mm. To prevent a filter layer of this type from generating a
high dynamic pressure in the exhaust-gas stream, it is
proposed for the fiber layer to have a porosity of at least
50%, in particular at least 75%, preferably at least 85% and
for preference even at least 95%. In this context, it should
be noted that fiber layers of this type can be produced
relatively successfully using fibers with a mean length of 0.4
mm to 0.05 mm, in which case it is preferable to select
shorter fiber lengths for thicker fibers.
Furthermore, it is proposed for the fiber layer, in a
longitudinal section substantially parallel to the largest
outer surface, to have openings which on average have a size
of 0.01 mm to 0.5 mm, in particular 0.05 mm to 0.25 mm. At
this point, it should be pointed out that the fiber layer may
fundamentally include fibers in virtually any desired
arrangement, and is to be understood as encompassing in
particular random layers, woven fabrics or other similar
structures. In this case, regular structures may also be
present only in regions, whereas a more chaotic arrangement of
the fibers is present in the remaining regions.
To ensure that sufficiently large cavities for particulates
and/or their agglomerates are provided, it is proposed here,
in particular for use in exhaust systems of diesel engines,
for a certain pore size to be provided. A longitudinal section
through the material which shows small cross sections of the
pores or cavities, referred to here as openings, is used to
determine the pore size. On average, all these openings have
an extent in the range mentioned above. What is meant in this
context is a mean of all the maximum extents of the openings
which can be seen in longitudinal section. Since the dimension
of the opening relates to the fiber layer which has already
been coated, it is also possible to use a corresponding mean
fiber spacing which is preferably to be selected as less than
0.6 mm, in particular between 0.05 mm and 0.35 mm.
Furthermore, it is proposed for the fiber layer to have a
thickness of less than 3 mm, in particular less than 1.5 mm,
preferably less than 0.5 mm and for preference less than 0.1
mm. The thicknesses mentioned here are selected in particular
with a view to the use of the fiber layer for particulate
traps for the purification of exhaust gases from mobile
internal combustion engines.
A further aspect of the invention proposes a particulate trap
for purifying exhaust gases from mobile internal combustion
engines which has at least one partially structured metal foil
and at least one high-temperature-resistant fiber layer of the
type described above, in which, preferably, a plurality of
structured metal foils and a plurality of fiber layers are
arranged alternately and in particular wound together in a
housing. This forms in particular an "open" particulate trap,
as described in the introduction. Accordingly, it is
especially advantageous to form an "open" filter element as
described in documents DE 201 17 873 U1, DE 201 17 659 U1, WO
02/00326, WO 01/92692, WO 01/80978.
Furthermore, it is proposed for the particulate trap to form
passages running substantially parallel to the axis, with
guide surfaces, preferably guide surfaces of the metal foil,
projecting into at least some of the passages and diverting
gas streams flowing through the passages toward the fiber
layer. Guide surfaces of this type may be formed by
projections, bosses, micro-undulations, vanes or similar
structures. It is also possible for these guide surfaces to be
formed by edges of holes in metal foils of this type. The
guide surfaces themselves may likewise have holes.
According to a further configuration, the particulate trap has
a volume, and the quantity of coating of the particulate trap
based on this volume is in the range from 20 to 300 g/1 (grams
per liter), preferably even between 50 and 120 g/1. In this
context, the term volume is to be understood as meaning the
volume which is composed of the metal foils, the fiber layers
and the passages formed. A volume of this type is usually in
the range from 0.01 1 to 1.5 1, preferably between 0.3 1 and
0.8 1.
Furthermore, it is proposed for the at least one, at least
partially structured metal foil to have apertures which extend
over at least one structure width, preferably even over 2, in
particular 3 structure widths. This means that, for example,
an aperture of this type connects a plurality of adjacent
passages formed by the structure to one another. This ensures
particularly effective mixing between the partial exhaust-gas
streams without an undesirably high dynamic pressure being
generated upstream of the particulate trap. In this context,
it should also be noted that the apertures extend
substantially in the plane of the metal foil.
The invention will now be explained in more detail with
reference to the figures. In this context, it should be noted
that the figures show particularly preferred exemplary
embodiments of the invention, but the invention is not
restricted to these embodiments. In the accompanying figures.
Fig. 1 shows a diagrammatic, exploded view of a detail of a
particulate trap according to the invention,
Fig. 2 shows a further detail of a configuration of the
particulate trap according to the invention,
Fig. 3 diagrammatically depicts a configuration of an exhaust
system of a mobile internal combustion engine,
Fig. 4 shows a diagrammatic and perspective illustration of a
further configuration of the particulate trap according to the
invention,
Fig. 5 diagrammatically depicts a longitudinal section through
a configuration of the fiber layer in accordance with the
invention, and
Fig. 6 shows a further longitudinal section through a fiber
layer in the coated state.
Fig. 1 shows a diagrammatic, exploded view of a detail of a
particulate trap as is used, for example, to treat the exhaust
gas from mobile internal combustion engines. The figure
illustrates two fiber layers 1 according to the invention,
between which a metal foil 14 is arranged. The fiber layers 1
each have a section 3 in which a coating 4 is arranged. This
coating 4 may be the coating of an oxidation catalyst, of a
three-way catalyst and/or of an SCR catalyst. It is preferable
for the metal foils 14 (at least in partial regions) to have a
catalytically active and/or storing coating. It is usual for
the adjacent layers to bear against one another, and they are
preferably connected to one another by a joining technique, in
particular by soldering. For this purpose it is necessary, for
example, for a partial region, in particular the edge of the
fiber layer 1, not to be coated, in order to ensure that the
possibility of forming connections by a joining technique is
preserved in this partial region.
The structuring of the metal foil 14 allows an exhaust gas to
flow through this "sandwich" of smooth layers (fiber layer 1)
and corrugated layer (metal foil 14) in a direction of flow
21. Guide surfaces 18 are arranged in the passages 17, causing
the partial gas stream to be swirled up, so that they are
guided in particular onto the coated fiber layer 1. The
structure of the metal foil 14 is in this case a corrugated
structure with a predetermined structure width 36. It is
preferable for the guide surfaces 18 and/or apertures 19 below
to be designed to be larger than the structure width 36, so
that a plurality of adjacent passages 17 can be connected to
one another through the apertures 19.
Fig. 2 shows an arrangement of metal foils 14 and a fiber
layer 1 in detail. Once again, the metal foils 14 and the
fiber layer 1 are arranged alternately, the structure of the
metal foils 14 in combination with the fiber layer 1 forming
passages 17 through which the exhaust gas can flow in a
direction of flow 21. Guide surfaces 18, which are produced
from the metal foil 14 itself by stamping, pressing or in some
other way, project into the passages 17. This simultaneously
creates apertures 19, so that a partial edge flow "peels off"
from the gas flowing through a passage 17 and can be diverted
toward the fiber layer 1. In this way, the particulates 22 are
also entrained and guided toward the fiber layer 1, where they
remain on the outer surface 9, for example sticking to it or
accumulating in cavities, pores or similar openings in the
fiber layer 1. The fiber layer 12 illustrated here has a
plurality of chaotically arranged fibers 6 which are provided
with a coating 4. Overall, the fiber layer 1 has a thickness
12 of less than 3 mm.
Fig. 3 diagrammatically depicts the structure of an exhaust
system of an automobile internal combustion engine 13. The
exhaust gas which is generated in the internal combustion
engine 13 is fed via an exhaust pipe 23 to the numerous
components for exhaust-gas treatment before ultimately being
released to the environment. The exhaust system illustrated in
Fig. 3 includes the following components in succession in the
direction of flow 21: a starting catalytic converter 24, a
turbo charger 25, an oxidation catalytic converter 26, a
reducing-agent feed 27, a mixer 28, a particulate trap 2
according to the invention and a main catalytic converter 29.
The starting catalytic converter 24 is distinguished by its
particularly small volume (for example less than 0.1 liter)
and, on account of its low heat capacity and its immediate
proximity to the engine, has been heated up sufficiently for
it to be possible to catalytically convert pollutants
contained in the exhaust gas just a short time after the
engine has started (e.g. to temperatures of over 230°C after a
few seconds). The function of the oxidation catalytic
converter 26 upstream of a particulate trap 2 for regeneration
has already been explained extensively above. The reducing-
agent feed 27 and the mixer 28 are used, for example, to
supply solid or liquid urea, so that it is also possible to
convert pollutants using the SCR method. The mixer 28 may be
designed as a guide surface, a grate, a honeycomb body or in
some similar form. However, it is also possible to omit the
mixer 28 upstream of the particulate trap 2, since the
particulate filter 2 itself is also responsible for swirling
up the exhaust-gas stream and/or finely distributing the
reducing agent which has been introduced. The downstream main
catalytic converter 29 usually has a relatively large volume,
in particular of greater than 1.5 liters.
Fig. 4 shows a perspective and diagrammatic view of the
structure of a particulate trap 2. The particulate trap 2 for
the purification of exhaust gases from mobile internal
combustion engines comprises a structured metal foil 14 and a
high-temperature-resistant fiber layer 1, which are arranged
helically around an axis 16 of the particulate trap 2 (simple
stacked arrangements, S-shaped loops or other wound
arrangements of the metal foils and/or fiber layers are also
possible as alternatives). The metal foil 14 and the fiber
layer 1 form passages 17 which extend through the particulate
trap 2 substantially parallel to the axis 16. The assembly
comprising metal foil 14 and fiber layer 1 is accommodated in
a housing 15 and is advantageously also connected to this
housing by a joining technique. In the embodiment of the
particulate trap 2 which is illustrated, the housing 15
projects beyond the end face 34 of the particulate trap 2 or
the metal foil 14 and the fiber layer 1. The material
thickness 30 of the corrugated metal foil 14 is preferably in
a range below 0.05 mm, preferably even below 0.02 mm. In this
context, it is recommended in particular for the material
thickness 30 or the coating 4 (not shown) or other parameters
of the particulate trap 2 not to be constant over the entire
length 31 of the particulate trap 2, which means, for example,
that in a first length section 32, the particulate trap 2 has
a lower heat capacity, a higher porosity, a higher loading
with regard to the catalytically active coating, a greater
number/size of apertures 19, guide surfaces 18 or fibers than
in a second length section 33. In principle, it is also
possible for the particulate trap 2 to be divided into more
than two length sections.
The particulate trap 2 illustrated has a volume 20 which is
characterized by the volume in the interior of the housing 20
which is filled by the fiber layer 1 and the metal foil 14,
also encompassing the volume of the passages 17. With regard
to the coating 4, the particulate trap according to the
invention is provided with a quantity in the range from 20 to
300 g/1. In this context, it is possible for this quantity to
be arranged over the entire length 31 uniformly on the outer
surfaces 9 of the fiber layer 1 and/or the metal foil 14, but
it is also possible for only the fiber layer 1 or only partial
regions of the metal foil 14 to be provided with a
catalytically active coating 4. It is also possible for
different types or quantities of the coating 4 to be provided
in different length sections.
Fig. 5 diagrammatically depicts the longitudinal section 8
through the fiber layer 1. In this context, it can be seen
that the fiber layer 1 is formed by a multiplicity of fibers
6, which are in this case connected to one another in
partially ordered and partially random fashion. The fibers 6
preferably have a diameter 7 in the range from 0.012 to 0.03 5
mm. Openings 10 are formed by the arrangement of the fibers 6
in the longitudinal section 8. These openings in practice
constitute a cross section through the cavities which are
formed in the interior of the fiber layer 1.
Fig. 6 likewise diagrammatically depicts a longitudinal
section 8 through the fiber layer 1, the fibers 6 now being
designed with a coating 4. The coating 4 comprises washcoat 5,
which on account of its fissured surface offers sufficient
options for the accumulation of the catalytically active
substances 35. Despite the coating 4, the longitudinal section
8 still has openings 10 with an extent 11. This extent 11 of
all the openings 10 on average is between 0.05 and 0.4 mm. At
the same time, it is preferable to maintain a porosity of
approx. 87%.
The present invention is the result of a large number of
technically complex attempts to improve the efficiency of
particulate traps in the exhaust systems of automobile
internal combustion engines.
WE CLAIM:
1. A high-temperature-resistant fiber layer (1) comprising metal
fibers for an open particulate trap (2) for purifying exhaust gases
from mobile internal combustion engines (13), wherein the fiber
layer (1), at least in a section (3) has a catalytically active coating
(4), in particular such as that of an oxidation catalyst and/or a
three-way catalyst and/or an SCR catalyst, characterized in that
the fiber layer (1) has a porosity of at least 50% and in a
longitudinal section (8) taken substantially parallel to the largest
outer surface (9), has openings (10) which on average have a size
(11) of 0.01 mm to 0.5 mm, in particular 0.05 mm to 0.25 mm.
2. The high-temperature-resistant fiber layer (1) as claimed in claim
1, wherein the coating (4) comprises washcoat (5).
3. The high-temperature-resistant fiber layer (1) as claimed in
claim 1 or 2, wherein the fiber layer (1) comprises a porous
sintered and/or fiber material.
4. The high-temperature-resistant fiber layer (1) as claimed in one of
the preceding claims, wherein the fiber layer (1) comprises fibers
(6) with a mean diameter (7) which is less than 0.082 mm, in
particular in a range from 0.01 to 0.05 mm.
5. The high-temperature-resistant-fiber layer (1) as claimed in one
of the preceding claims, wherein the fiber layer (1) has a porosity
of at least 75%, preferably at least 85% and for preference even at
least 95%.
6. The high-temperature-resistant fiber layer (1) as claimed in one of
the preceding claims, wherein the fiber layer (1) has a thickness
(12) of less than 3 mm, in particular less than 1.5 mm, preferably
less than 0.5 mm and for preference less than 0.1 mm.
7. A particulate trap (2) for purifying exhaust gases from mobile
least, one CM
partially structured metal foil (14) and at least one high-
temperature-resistant fiber layer (1) as claimed in one of claims 1
to 6, preferably with a plurality of structured metal foils (14) and
a plurality of fiber layers (1) arranged alternately, in particular
wound together, in a housing (15).
8. The particulate trap (2) as claimed in claim 7, wherein passages
(17) running substantially parallel to an axis (16) of the
particulate trap (2) are formed, with guide surfaces (18),
preferably guide surfaces (18) of the metal foils (14), projecting
into at least some of the passages (17) and diverting gas streams
flowing through the passages (17) toward the fiber layer (1).
9. The particulate trap (2) as claimed in claim 7 or 8, wherein the
particulate trap (2) has a volume (20), and the quantity of
coating with respect to this volume is in the range from 20 to 300
g/1 (grams per liter), preferably even between 50 and 120g/1.
10. The particulate trap (2) as claimed in one of claims 7 to 9,wherein
at least one, at least partially structured metal foil (14) has
apertures (19) which extend over at least one structure width
(36), preferably even over two or in particular even three
structure widths (36).
A high-temperature-resistant fiber layer (1) comprising metal
fibers for an open particulate trap (2) for purifying exhaust
gases from mobile internal combustion engines (13),
characterized in that the fiber layer (1), at least in a
section (3), has a catalytically active and/or adsorbent
coating (4), in particular such as that of an oxidation
catalyst and/or a three-way catalyst and/or an SCR catalyst.

Documents:

1301-KOLNP-2005-(03-11-2011)-OTHER PATENT DOCUMENTS.pdf

1301-KOLNP-2005-FORM 27.pdf

1301-KOLNP-2005-FORM-27.pdf

1301-kolnp-2005-granted-abstract.pdf

1301-kolnp-2005-granted-claims.pdf

1301-kolnp-2005-granted-correspondence.pdf

1301-kolnp-2005-granted-description (complete).pdf

1301-kolnp-2005-granted-drawings.pdf

1301-kolnp-2005-granted-examination report.pdf

1301-kolnp-2005-granted-form 1.pdf

1301-kolnp-2005-granted-form 18.pdf

1301-kolnp-2005-granted-form 2.pdf

1301-kolnp-2005-granted-form 3.pdf

1301-kolnp-2005-granted-form 5.pdf

1301-kolnp-2005-granted-gpa.pdf

1301-kolnp-2005-granted-reply to examination report.pdf

1301-kolnp-2005-granted-specification.pdf

1301-kolnp-2005-granted-translated copy of priority document.pdf

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Patent Number

222874

Indian Patent Application Number

1301/KOLNP/2005

PG Journal Number

35/2008

Publication Date

29-Aug-2008

Grant Date

27-Aug-2008

Date of Filing

05-Jul-2005

Name of Patentee

EMTTEC GESELLSCHAFT FUR EMISSIONSTECHNOLOGIE MBH

Applicant Address

HAUPSTRASSE 150, 53797 LOHMAR

Inventors:

#	Inventor's Name	Inventor's Address
1	BRUCK, ROLF	FROBELSTRASSE 12, 51429 BERGISCH GLADBACH

PCT International Classification Number

B01D 53/94

PCT International Application Number

PCT/EP2003/012455

PCT International Filing date

2003-11-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	102 57 113.9	2002-12-05	Germany