Particle trap with coated fibre layer

p0001The invention relates to a particle trap for cleaning exhaust gases from mobile combustion engines with a high-temperature-resistant fiber layer.

p0002If the purification of exhaust gases, in particular diesel engines, is to be considered, hydrocarbons (HC) as well as carbon monoxide (CO) in the exhaust gas can be oxidized in a known manner by contacting them, for example, with components which optionally have a catalytically active surface. The reduction of nitrogen oxides (NO_x) Under oxygen-rich conditions is, however, more difficult. A three-way catalytic converter, as used, for example, in Otto engines, does not provide the desired effects for diesel engines alone. For this reason, for example, the method of Selective Catalytic Reduction (SCR) was developed.

p0003Furthermore, storage catalysts were tested for their use with regard to the reduction of nitric oxide. Apart from the customary noble metal components, the coating of a storage catalyst also contains barium carbonate or oxide. As a result, it is possible that, with oxygen excess, NO_x Can be stored. On the noble metal components, the nitric oxide (NO) from the exhaust gas is converted into nitrogen dioxide (NO₂). This is then stored on the catalyst to form barium nitrate. In this storage, a nitrate layer forms on the barium grain, which slows down the storage because NO₂ For further storage through this layer. Since the storage capacity is thus limited, the catalyst must be regenerated at regular intervals. This takes place, for example, by brief enrichment of the exhaust gas, ie by a short period with sub-stoichiometric conditions. In a reduced atmosphere the nitrate changes again (for example) carbonate and nitric oxide becomes free. This is immediately reduced to nitrogen. Since the regeneration runs faster than the storage, the regeneration periods can be substantially shorter than the storage periods.

p0004To reduce particle emissions, particle traps are known, which are constructed from a ceramic substrate. These have channels, so that the exhaust gas to be purified can flow into the particle trap. Adjacent ducts are closed on the exchange side so that the exhaust gas enters the duct on the inlet side, passes through a ceramic wall and escapes again through an adjacent duct on the outlet side. Such filters achieve an efficiency of approximately 95% over the entire width of the particle sizes occurring.

p0005In addition to chemical interactions with additives and special coatings, the safe regeneration of the filter in the exhaust system of an automobile is still a problem. The regeneration of the particle trap is necessary because the increasing accumulation of particle particles in the channel walls to be flowed leads to a steadily increasing pressure loss , Which has a negative effect on the engine performance. The regeneration essentially comprises the short-term heating of the particle trap or the particles accumulated therein, so that the soot particles are converted into gaseous constituents. This can also be achieved, for example, by using an upstream exothermic reaction (eg oxidation of fuel injected into the exhaust gas line in an oxidation catalytic converter ( "post-combustion")), the exhaust gas reaches the temperatures which are sufficient for the particles adhering to the particle trap Respectively. However, this high thermal stress on the particle trap has a negative effect on the service life.

p0006In order to avoid this discontinuous and thermally very wear-resistant regeneration, a continuous regeneration trap (CRT) system was developed. In such a system, the particles are heated at temperatures above 200 ° C. by means of oxidation with NO₂ Burned. The NO₂ Is often generated by an oxidation catalyst disposed upstream of the particle trap. However, the problem is that there is only an insufficient amount of nitric oxide (NO) in the exhaust gas, which leads to the desired nitrogen dioxide (NO₂) Can be converted. As a result, it can not yet be ensured that a continuous regeneration of the particle trap in the exhaust system takes place.

p0007It must also be taken into consideration that, in addition to non-convertible particles, oil or additional residues of additives are also deposited in a particle trap which can not be regenerated easily. For this reason, known filters must be replaced and / or washed at regular intervals.

p0008In addition to a minimum reaction temperature and a specific residence time, continuous regeneration of particles with NO₂ Sufficient nitrogen oxide can be provided. Tests on the dynamic emission of nitric oxide (NO) and particles have clearly demonstrated that the particles are emitted just when no or very little nitric oxide is present in the exhaust gas and vice versa. As a result, a filter with a real continuous regeneration must essentially function as a compensator or memory 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 be able to assume temperatures which are as high as possible immediately after the cold start. To provide the required nitrogen dioxide, an oxidation catalytic converter which reacts with carbon monoxide (CO) and hydrocarbons (HC) and in particular also nitrogen monoxide (NO) in nitrogen dioxide (NO₂). In a motorized arrangement of this system of oxidation catalytic converter and filter, the position in front of a turbocharger is particularly suitable, which is frequently used in diesel engines for increasing the charge pressure in the combustion chamber.

p0009Considering these fundamental considerations, the question arises as to how such a filter is constructed, which has a satisfactory filter efficiency in such a position and in the presence of extremely high thermal and dynamic loads. Particular consideration must be given to the spatial conditions, which require a new concept for filters. Whereas a large volume was placed in the forefront of the classical filters placed in the underbody of a motor vehicle in order to ensure a high residence time of the particles which had not yet been reacted in the filter and thus to ensure high efficiency, Room available.

p0010For this purpose, a new concept has been developed, which has become essentially known under the term "open filter system". These open filter systems are distinguished by the fact that a constructive, reversal closure of the filter channels can be dispensed with. In this case, it is provided that the channel walls are at least partly constructed of porous or highly porous material, and that the flow channels of the open filter have deflection or guide structures. These internals cause the flow or the particles contained therein to be directed towards the regions of porous or highly porous material. Surprisingly, it has been found that the particles adhere to and / or in the porous channel wall by interception and / or impaction. For the combination of this effect, the pressure differences in the flow profile of the flowing exhaust gas are important. Due to the deflection, local vacuum or overpressure conditions can also arise which lead to a filtration effect through the porous wall since the abovementioned pressure differences have to be compensated for.

p0011In contrast to the known closed screening or filter systems, the particle trap is open because there are no flow packing passages. This property can thus also be used for the characterization of such particle filters so that, for example, the parameter "flow-free" is suitable for the description. For example, a "flow-free" of 20% means that in a cross-sectional view approx. 20% of the area is transparent. For a particulate filter with a canal density of approximately 600 cpsi ( "cells per square inch") with a hydraulic diameter of 0.8 mm, this free flow would correspond to an area of ​​more than 0.1 mm². In other words, a particle trap can then be designated as open when it can be traversed completely by particles, and also by particles which are considerably larger than the particles actually to be filtered out (in particular the particles which are used for the diesel and / Or benzine fuel characteristic particle size range). As a result, such a filter can not become clogged even during agglomeration of particles during operation. A suitable method for measuring the openness of particle traps is, for example, the testing up to which diameter spherical particles can still trickle through such a filter. In the case of present applications, a particle trap is "open", in particular when balls of greater than or equal to 0.1 mm diameter can still trickle through, preferably balls with a diameter above 0.2 mm. Such "open" filter elements are, for example, taken from the documents<patcit id="pcit0001" dnum="DE20117873U1"><text>DE 201 17 873 U1</text></patcit>, <patcit id="pcit0002" dnum="DE20117659U1"><text>DE 201 17 659 U1</text></patcit>, <patcit id="pcit0003" dnum="WO0200326A"><text>WO 02/00326</text></patcit>, <patcit id="pcit0004" dnum="WO0192692A"><text>WO 01/92692</text></patcit>, <patcit id="pcit0005" dnum="WO0180978A"><text>WO 01/80978</text></patcit> , The content of which is hereby incorporated by reference into the entirety of the present description.

p0012With respect to the general design of honeycomb bodies with internal flow guiding surfaces, for example, the German utility model <patcit id="pcit0006" dnum="DE8908738U1"><text>DE 89 08 738 U1</text></patcit> Notes. This document describes honeycomb bodies, in particular catalyst support bodies for motor vehicles, of sheets arranged in layers, at least partially structured, which form the walls of a multiplicity of passages through which a fluid can flow. It is described therein that in most applications and in the usual dimensions of such honeycomb bodies, the flow in the channels is essentially laminar, ie very small channel cross sections are used. Under these conditions, relatively thick boundary layers build up on the channel walls, which reduce a contact of the core flow in the channels with the walls. In order to effect a swirling of the exhaust stream in the interior of the ducts and thus to ensure an intensive contact of the entire exhaust stream with a catalytically active surface of the ducts, conversions are proposed which form inflow surfaces inside the duct so that the exhaust gas diverges transversely to the main flow direction becomes.

p0013Out <patcit id="pcit0007" dnum="EP0798452A"><text>EP 0 798 452 A</text></patcit> A particle filter which is closed on the other side and has a filter layer is known. The filter layer comprises a filter material which can be covered on both sides by catalyst-bearing layers.

p0014<patcit id="pcit0008" dnum="WO0192692A"><text>WO 01/92692 A</text></patcit> Discloses the arrangement of an open particle trap in an exhaust system. The particle trap can be designed with a hydrolysis coating.

p0015Especially with regard to the realization of such an open particle trap, it is now the object of the present invention to improve the effectiveness with regard to the conversion of pollutants contained in the exhaust gas. In particular, it should be possible to provide exhaust systems, especially for automobiles with diesel engines of particularly small design. In addition, the production, assembly and maintenance of such exhaust gas systems is to be simplified considerably and thus be made more cost-effective.

p0016These objects are achieved by a particle trap for the purification of exhaust gases of an internal combustion engine with a high-temperature-resistant fiber layer with the features of patent claim 1. Further advantageous refinements are described in the dependent patent claims, wherein the features listed there can occur individually or in any desired, sensible combination with one another .

p0017According to the invention, a particle trap for cleaning exhaust gases from mobile combustion engines is proposed which has at least one partially structured metal film and at least one high-temperature-resistant fiber layer of the above-described design Are arranged. An "open" particle trap is formed, as described above. Accordingly, it is particularly advantageous to form an "open" filter element as described in the documents<patcit id="pcit0009" dnum="DE20117873U1"><text>DE 201 17 873 U1</text></patcit>, <patcit id="pcit0010" dnum="DE20117659U1"><text>DE 201 17 659 U1</text></patcit>, <patcit id="pcit0011" dnum="WO0200326A"><text>WO 02/00326</text></patcit>, <patcit id="pcit0012" dnum="WO0192692A"><text>WO 01/92692</text></patcit>, <patcit id="pcit0013" dnum="WO0180978A"><text>WO 01/80978</text></patcit> .

p0018The particle trap forms channels running essentially parallel to the axis, guide surfaces of the metal foil projecting into at least a part of the channels and causing a deflection of gases flowing through the channels towards the fiber layer. Such guide surfaces can be formed by projections, knobs, microwaves, blades or similar structures. It is also possible that these guide surfaces are formed by edges of holes in such metal foils. The guide surfaces themselves may also have holes.

p0019The high-temperature-resistant fiber layer of metal for the particle trap for the cleaning of exhaust gases of mobile combustion engines is characterized in that at least one coating is provided in at least one portion which is at least partially that of an oxidation catalyst and / or a three- Catalyst.

p0020The provision of such a catalytically active coating has a number of advantages, which are subsequently to be briefly outlined. For example, it can be achieved that the components originally provided in the exhaust system for the oxidation or reduction and / or storage of pollutants contained in the exhaust gas can be designed in a smaller volume or even can be dispensed with entirely. As a result, the exhaust system as such can be made significantly slimmer or smaller, which allows a simple construction, simple maintenance and a low-cost production of the exhaust system. Surprisingly, synergetic effects are also produced. Thus, for example, exhaust gas components are generated directly in the interior of a particle trap equipped with such a fiber layer, which components assist in the conversion or removal of the attached particles. These exhaust gas components are therefore directly produced and provided near the surface of the fiber layer, to which the particles adhere. Thus, for example, the regeneration temperature of the particle traps can also be significantly reduced, for example from over 900 ° C. to temperatures below 600 ° C.

p0021With regard to the arrangement of the at least one section of the fiber layer, it should be noted that this section can also extend over the entire surface of the fiber layer. However, it is also possible to provide a plurality of sections, which can be coated and / or partially also uncoated, it being possible, if desired, to choose different types of coating, sectional shapes different from one another, or section area contents. It is also possible for the at least one section to be located only on an outer surface or side of the high-temperature-resistant fiber layer.

p0022With regard to the properties of the coating of an oxidation catalyst, it should be noted that such catalysts serve to increase the rate of specific reaction without being consumed by itself. By means of suitable catalyst substances it can be achieved that the oxidation processes for CO (carbon monoxide) and HC (hydrocarbons) take place in the exhaust gas at lower temperatures. With the aid of such coatings, which generally contain catalyst substances of the platinum group, gaseous hydrocarbons and carbon monoxide can be oxidized at exhaust gas temperatures above 250 ° C. in the diesel-engine exhaust gas. A special feature of oxidation coatings of this type is that under certain circumstances an after-combustion of the hydrocarbons still accumulating on soot particles takes place, as a result of which the particle emission can be further reduced. Up until now, it had been spared to provide such a combination of oxidation-promoting coatings and filter elements in one unit, since it was feared that the catalytically active substances would be impaired by particles with increasing coverage. From this prejudice of the professional world, the invention has been deviated and a high-temperature-resistant fiber layer has been developed which enables the production of particularly effective particle traps.

p0023If the three pollutant components CO, HC and NO_x (Nitrogen oxides) are reduced by post-reaction, this can be achieved by coating the fiber layer with one of the 3-way catalyst. The active catalyst substance comprises platinum (Pt), palladium (Pd) or rhodium metal (Rh) in fine distribution on a large surface area. At a lambda value of 1, CO is converted to carbon dioxide (CO₂), CH to CO₂ And water (H₂O) and NO_x To nitrogen (N₂). The following coating is suitable for the oxidation catalyst:<ul><li>Pt / Pd = 2/1</li><li>0.93 - 1.2 grams Pt / liter_{Catalyst bearing volume}</li><li>0.46-0.6 grams Pd / liter_{Catalyst bearing volume}</li></ul>

p0024Regarding the multifunctional catalyst (reduction), it is proposed that the following relationships hold:<ul><li>Pt / Rh = 5/1</li><li>1.16-1.5 grams Pt / liter_{Catalyst bearing volume}</li><li>1.23 - 0.3 gram Rh / liter_{Catalyst bearing volume}</li></ul>

p0025Catalyst carrier volume is understood to mean the volume which comprises the material of the carrier (honeycomb structure, etc.) and the cavities, channels, etc. formed by the carrier.

p0026The coating of an SCR catalyst can, if appropriate, also be embodied in a multilayer or multi-stage manner. One possible urea SCR catalyst system consists of a plurality of successively arranged partial regions of the coating, which is applied to the fiber layer. The partial regions can be arranged in the flow direction of the exhaust gas as follows:<ul><li>A coating of an oxidation catalyst (optional),</li><li>The coating of a hydrolysis catalyst,</li><li>The coating of an SCR catalyst and</li><li>Optionally a downstream oxidation catalyst.</li></ul>

p0027The oxidation catalyst, which is optionally connected upstream, serves to increase the SCR activity at low exhaust gas temperatures (especially in the case of diesel passenger cars). By raising the NO₂(Optimum: 50% by volume) in the exhaust gas by means of partial oxidation of NO, the reaction rate of the SCR reaction can be significantly increased in a temperature range below about 573 K. In addition, the oxidation of carbon monoxide to carbon dioxide and the reaction of incompletely combusted hydrocarbons to carbon dioxide and water are carried out on the catalyst surface. Without the use of such a pre-stored area with an oxidation coating, the oxidation of the hydrocarbons would partly take place on the SCR catalyst and thus cause a reduction in the nitrogen oxide conversion.

p0028With the aid of the coating of a hydrolysis catalyst, the complete decomposition of an aqueous urea solution is possible even at low temperatures, for example by 470 K. Below about 470 K, the decomposition of the urea proves to be problematic because undesirable byproducts can be formed due to incomplete decomposition . The coating of the SCR catalyst serves for the selective reduction of the nitrogen oxides NO_x With ammonia to the unproblematic products of nitrogen and water.

p0029According to a further embodiment of the particle trap with the high-temperature-resistant fiber layer, the coating comprises washcoat. The coating of the relatively smooth surfaces of the fibers with washcoat results in an enlargement of the catalytically active surface. This rugged surface, on the other hand, ensures a sufficiently large amount of space for the fixing of a catalyst (for example, platinum, rhodium, etc.) and, on the other hand, serves to swirl the exhaust gas flowing therethrough with a particularly intensive contact with the catalyst.

p0030The application of the highly surface-area washcoat layer promoting the catalysis is known in such a way that the fiber layer (or later the entire particle trap of fiber layers and metal foils) is immersed in a liquid washcoat dispersion or sprayed with it. The excess washcoat dispersion is then removed, the washcoat is dried in the fiber layer and finally calcined at temperatures above 450 ° C. During calcination, the volatile constituents of the washcoat dispersion are expelled, so that a temperature-resistant and catalytically promoting layer with a high specific surface area is produced. If desired, this operation was repeated several times to achieve a desired layer thickness. The average layer thickness is preferably in a range from 0.001 to 0.02 mm, in particular from 0.005 to 0.012 mm.

p0031The washcoat usually consists of a mixture of an alumina and at least one promoter oxide such as rare earth oxides, zirconium oxide, nickel oxide, iron oxide, germanium oxide and barium oxide. During the application to the honeycomb body, the washcoat dispersion must have as good a flow property as possible in order to achieve a desired, uniform layer thickness over the entire channel length.

p0032To achieve such a flow property, known washcoat dispersions have a certain pH value, only a limited proportion of solids being allowed. However, experiments have shown that such a washcoat dispersion has a time-dependent viscosity. As a result, the washcoat dispersion gels very quickly and prevents the generation of a uniform layer thickness. This gelling can be delayed by keeping the washcoat dispersion in motion, ie, either the dispersion or the filter layer wetted therewith is agitated, in particular vibrated.

p0033According to yet another embodiment of the particle trap with the fiber layer, the fiber layer consists of a porous sintered material and / or fiber material (eg steel). In particular, high-temperature resistant and corrosion-resistant steels with relatively high proportions of chromium, nickel, aluminum and / or molybdenum are available here. In this case, it is particularly advantageous that the fiber layer has fibers with an average diameter which is less than 0.082 mm, in particular in a range of 0.01 to 0.05 mm. In order to prevent such a filter layer from generating a high static pressure in the exhaust stream, it is proposed that the fiber layer has a porosity which is at least 50%, in particular at least 75%, preferably at least 85% and preferably even at least 95%. In this context, it should be noted that such fiber layers can be produced relatively well with fibers of an average length of 0.4 mm to 0.05 mm, preferably smaller fiber lengths being to be selected with thicker fibers.

p0034Furthermore, it is proposed that the fiber layer has openings in a longitudinal section substantially parallel to the largest outer surface, which have an average extent of 0.01 mm to 0.5 mm, in particular 0.05 mm to 0.25 mm. In principle, it should be noted at this point that the fiber layer can have fibers in virtually any desired arrangement, in particular also to be understood as including entangling webs, woven fabrics or similar structures. Regular structures can also be present only regionally, whereas in the remaining areas a rather chaotic arrangement of the fibers is present.

p0035In order to ensure that sufficiently large cavities are provided for particles or their agglomerates, it is proposed here for the application in exhaust systems of diesel engines that a certain pore size is provided. To determine the pore size, a longitudinal section is used here through the material, which shows small cross-sections of the pores or cavities, which are called openings here. All these openings have an average extent in the above-mentioned range. Here, a mean value of all the maximum expansions of the openings which can be seen in the longitudinal section is meant. Since the dimension of the opening refers to the already coated fiber layer, a corresponding average fiber spacing can also be used, which is preferably selected to be less than 0.6 mm, in particular between 0.05 mm and 0.35 mm.

p0036Furthermore, it is proposed that the fiber layer has a thickness which is less than 3 mm, in particular less than 1.5 mm, preferably less than 0.5 mm and preferably less than 0.1 mm. The thicknesses mentioned here are selected especially with regard to the use of the fiber layer for particle traps for cleaning exhaust gases from mobile combustion engines.

p0037According to a further embodiment, the particle trap has a volume, and the coating quantity of the particle trap with respect to this volume is in the range from 20 to 300 g / l (grams per liter), preferably even between 50 and 120 g / l. By volume is meant in this context the volume which is composed of the metal foils, the fiber layers and the channels formed. Usually, such a volume is in the range from 0.01 to 1.51, preferably from 0.3 to 0.81.

p0038Furthermore, it is proposed that the at least one, at least partially structured metal foil has perforations which extend over at least one structural width, preferably even over 2, in particular 3, structural widths. This means that, for example, such a breakthrough connects several adjacent channels formed by the structure. In this way, a particularly effective mixing of the partial exhaust gas streams is ensured without an undesirably high static pressure being generated before the particle trap. It should also be noted that the openings extend essentially in the plane of the metal foil.

p0039The invention is now explained in more detail with reference to the figures. It should be pointed out that the figures show particularly preferred embodiments of the invention, but the invention is not limited thereto. Show it:<dl id="dl0001"><dt>FIG</dt><dd>Schematically and in an exploded view a detail of a particle trap according to the invention,</dd><dt>FIG</dt><dd>A further detail of an embodiment of the particle trap according to the invention,</dd><dt>FIG</dt><dd>Schematically an embodiment of an exhaust system of a mobile internal combustion engine,</dd><dt>FIG</dt><dd>Schematically and in perspective a further embodiment of the particle trap according to the invention,</dd><dt>FIG</dt><dd>Schematically a longitudinal section through an embodiment of the fiber layer, and FIG</dd><dt>FIG</dt><dd>10 a further longitudinal section of a fiber layer in the coated state.</dd></dl>

p0040<figref idrefs="f0001">FIG</figref> Shows schematically and in an exploded view a detail of a particle trap, such as is used, for example, for the exhaust gas treatment of mobile combustion engines. Two fiber layers 1, between which a metal foil 14 is arranged, are shown. The fiber layers 1 each have a section 3 in which a coating 4 is arranged. This coating 4 can be an oxidation catalyst, a three-way catalyst and / or an SCR catalyst. Preferably, the metal foils 14 (at least in some areas) also have a catalytically active and / or storage coating. Usually, the adjacent layers are adjacent to one another and are preferably connected to each other, in particular by soldering, in particular by brazing. For this purpose, it is necessary, for example, not to coat a partial region, in particular the edge of the fiber layer 1, in order here to ensure the possibility of forming joining-technical connections.

p0041The structuring of the metal foil 14 has the consequence that this "sandwich" of smooth layers (fiber layer 1) and corrugated layer (metal foil 14) for an exhaust gas can be flowed through in a flow direction 21. In this case, guide surfaces 18 are mounted in the channels 17, which lead to turbulence of the partial gas streams, so that these are guided in particular against the coated fiber layer 1. Here, the structure of the metal foil 14 is a corrugated structure with a predetermined structure width 36. Preferably, the guide surfaces 18 or underlying perforations 19 are designed to be larger than the structure width 36 so that a plurality of adjacent channels 17 can be connected to one another by means of the openings 19.

p0042<figref idrefs="f0002">FIG</figref> Shows an arrangement of metal foils 14 and a fiber ply 1 in detail. Once again, the metal foils 14 and the fiber layer 1 are alternately arranged, the structure of the metal foils 14 in conjunction with the fiber layer 1 forming channels 17, which can be flowed through for the exhaust gas in a flow direction 21. Conductive surfaces 18, which have been produced by punching, pressing or other means from the metal foil 14 themselves, extend into the channels 17. As a result, breakthroughs 19 are simultaneously created so that a partial edge flow can be "peeled off" from the gas flowing through the one channel 17 and can be guided to the fiber layer 1. In this way, the particles 22 are also entrained and guided to the fiber layer 1. There they remain, for example, on the outer surface 9, or adhere to cavities, pores or similar openings of the fiber layer 1. The fiber layer 1 shown 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 which is less than 3 mm.

p0043<figref idrefs="f0003">FIG</figref> Shows schematically the structure of an exhaust system of an automotive internal combustion engine. The exhaust gas generated in the internal combustion engine is fed via an exhaust gas line to the most diverse components for exhaust gas treatment before it is ultimately discharged into the environment. The exhaust system used in<figref idrefs="f0003">FIG</figref> , A reduction catalytic converter 26, a reducing agent supply 27, a mixer 28, a particle trap 2 according to the invention, as well as a main catalytic converter 29. In the embodiment shown in FIG.

p0044The starting catalytic converter 24 is distinguished by its particularly small volume (for example, less than 0.1 liter) and is heated to a very short time after a motor start to a catalytic conversion of pollutants contained in the exhaust gas due to its low heat capacity and its immediate proximity to the engine (Eg temperatures above 230 ° C after a few seconds). The function of the oxidation catalyst 26 before a particle trap 2 for regeneration has already been explained in detail above. The reducing agent supply 27 and the mixer 28 are used, for example, for the supply of solid or liquid urea, so that a reaction of pollutants with the SCR process is also possible. The mixer 28 can be designed as a guide surface, lattice, honeycomb body or in a similar manner. However, it is also possible to omit the mixer 28 in front of the particle trap 2 since the particle filter 2 itself also causes a swirling of the exhaust gas streams or a fine distribution of the introduced reducing agent. The downstream main catalytic converter 29 usually has a relatively large volume, in particular greater than 1.5 liters.

p0045<figref idrefs="f0003">FIG</figref> Shows the structure of a particle trap 2 in a perspective and schematic manner. The particle trap 2 for cleaning exhaust gases of mobile combustion engines comprises a structured metal foil 14 and a high-temperature-resistant fiber layer 1 which are arranged spirally about an axis 16 of the particle trap 2 (alternatively simple stack arrangements, Shaped loops or other turns of the metal foils and / or fiber layers). The metal foil 14 and the fiber layer 1 form channels 17, which extend substantially parallel to the axis 16 through the particle trap 2. The composite of metal foil 14 and fiber layer 1 is accommodated in a housing 15 and is advantageously also connected to it by a joining technique. In the illustrated embodiment of the particle trap 2, the housing 15 projects over the end faces 34 of the particle 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. It is particularly appropriate that the material thickness 30 or the coating 4 (not shown) or other parameters of the particle trap 2 are not constant over the total length 31 of the particle trap 2. That is, for example, the particle trap 2 has a lower thermal capacity, a higher porosity, a greater loading with respect to the catalytically active coating, an increased number / size of perforations 19, guide surfaces 18 or fibers in a first length section 32 than in a Second length section 33. In principle, the division of the particle trap 2 into more than two length sections is also possible.

p0046The particle trap 2 shown has a volume 20 which is characterized by the volume filled by the fiber layer 1 and the metal foil 14 inside the housing 15, the volume of the channels 17 also being covered. With regard to the coating 4, the particle trap according to the invention is provided with an amount which is in the range from 20 to 300 g / l. It is also possible that only the fiber layer 1 or only partial regions of the metal foil 14 with a catalytically active coating. For this purpose, it is also possible that this quantity is uniformly arranged over the entire length 31 on the outer surfaces 9 of the fiber layer 1 and / or of the covering films 14 4. It is also possible that different types or amounts of the coating 4 are provided in different lengths.

p0047<figref idrefs="f0004">FIG</figref> Shows schematically a longitudinal section 8 through the fiber layer 1. It can be seen that the fiber layer 1 is formed by a multiplicity of fibers 6, which are connected here in a partly ordered, partly chaotic manner. The fibers 6 preferably have a diameter 7 in the range of 0.012 and 0.035 mm. By arranging the fibers 6 in the longitudinal section 8, openings 10 are formed. These represent practically a cross-section of the cavities, which are formed in the interior of the fiber layer 1.

p0048<figref idrefs="f0004">FIG</figref> Also schematically shows a longitudinal section 8 of the fiber layer 1, the fibers 6 being now made with a coating 4. The coating 4 comprises washcoat 5, which due to its jagged surface provides sufficient possibility for the addition of the catalytically active substances 35. Despite the coating 4, the longitudinal section 8 still has openings 10 with an extension 11. This extent 11 of all openings 10 is on average between 0.05 and 0.4 mm. A porosity of approximately 87% is preferably to be maintained at the same time.

p0049The present invention is the result of a large number of complex technical tests to improve the effectiveness of particulate traps in exhaust systems of automotive internal combustion engines.

Reference list

p0050<dl id="dl0002"><dt>1</dt><dd>Fiber layer</dd><dt>2</dt><dd>Particle trap</dd><dt>3</dt><dd>section</dd><dt>4</dt><dd>coating</dd><dt>5</dt><dd>Washcoat</dd><dt>6</dt><dd>fiber</dd><dt>7</dt><dd>diameter</dd><dt>8th</dt><dd>longitudinal section</dd><dt>9</dt><dd>outer surface</dd><dt>10</dt><dd>opening</dd><dt>11</dt><dd>expansion</dd><dt>12</dt><dd>thickness</dd><dt>13</dt><dd>combustion engine</dd><dt>14</dt><dd>metal foil</dd><dt>15</dt><dd>housing</dd><dt>16</dt><dd>axis</dd><dt>17</dt><dd>channel</dd><dt>18</dt><dd>conductive surface</dd><dt>19</dt><dd>breakthrough</dd><dt>20</dt><dd>volume</dd><dt>21</dt><dd>flow direction</dd><dt>22</dt><dd>particles</dd><dt>23</dt><dd>exhaust pipe</dd><dt>24</dt><dd>starting catalyst</dd><dt>25</dt><dd>turbocharger</dd><dt>26</dt><dd>oxidation catalyst</dd><dt>27</dt><dd>Reduction agent supply</dd><dt>28</dt><dd>mixer </dd><dt>29</dt><dd>main catalyst</dd><dt>30</dt><dd>thickness</dd><dt>31</dt><dd>Total length</dd><dt>32</dt><dd>First length section</dd><dt>33</dt><dd>Second length section</dd><dt>34</dt><dd>end face</dd><dt>35</dt><dd>substance</dd><dt>36</dt><dd>structure</dd></dl>