Title of Invention	A FIBER LAYER SUITABLE FOR USE IN AN EXHAUST SYSTEM OF A MOBILE INTERNAL COMBUSTION ENGINE AND A METHOD FOR REMOVING THE PARTICULATES FROM THE GAS STREAM
Abstract	The invention proposes a method for removing particulates (21) from a gas stream (22) having a gas permeable filter layer (23) which has subregions (10) with a parameter of differing magnitudes in the direction of the layer thickness (5), this parameter relating at least to the porosity (7), the fiber diameter (8) of fibers (4) or the fiber type content of the filter layer (23) . In the method, the gas stream (22) is divided into partial gas streams (24) which are each passed through different subregions (10) of the filter layer (23) . The invention also describes fiber layers, particulate filters, exhaust systems and vehicles which are based on this method.

Title of Invention

A FIBER LAYER SUITABLE FOR USE IN AN EXHAUST SYSTEM OF A MOBILE INTERNAL COMBUSTION ENGINE AND A METHOD FOR REMOVING THE PARTICULATES FROM THE GAS STREAM

Abstract

The invention proposes a method for removing particulates (21) from a gas stream (22) having a gas permeable filter layer (23) which has subregions (10) with a parameter of differing magnitudes in the direction of the layer thickness (5), this parameter relating at least to the porosity (7), the fiber diameter (8) of fibers (4) or the fiber type content of the filter layer (23) . In the method, the gas stream (22) is divided into partial gas streams (24) which are each passed through different subregions (10) of the filter layer (23) . The invention also describes fiber layers, particulate filters, exhaust systems and vehicles which are based on this method.

Full Text	Method for removing particulates from exhaust gases, and corresponding fiber layer and particulate filter The present invention relates to a fiber layer which is suitable for use in an exhaust system of a mobile internal combustion engine. The invention also proposes a particulate filter for the same use. Moreover, the invention relates to a method for removing particulates from the exhaust gas from an internal combustion engine having a gas-permeable filter layer. To reduce the level of particulate emissions from exhaust gases from combustion processes, it is known to use particulate traps which are constructed from a ceramic substrate. These traps have passages, so that the exhaust gas which is to be purified can flow into the particulate trap. Adjacent passages are closed off on alternate sides, so that the exhaust gas enters the passage on the inlet side, is forced to pass through a ceramic wall and escapes again along an adjacent passage on the outlet side. Filters of this type achieve an efficiency of approx. 95% across the entire range of particulate sizes which occur. In addition to undesirable chemical interactions between the particulates and additives and special coatings, the reliable regeneration of a filter of this type in the exhaust system of an automobile still causes 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 causes the pressure loss across the filter or the back-pressure to rise continuously, which has adverse effects on the engine power. The regeneration generally comprises brief heating of the particulate trap or the particulates which have collected therein, so that the particulates are converted into gaseous constituents. This can be achieved, for example, by briefly raising the temperature of the exhaust gas to levels which are — 2 — sufficient to convert the particulates which have accumulated in the particulate trap, with the aid of an upstream exothermic reaction (e.g. oxidation of additional fuel injected into the exhaust pipe: "afterburning"). However, this high thermal loading of the particulate trap has adverse effects on the service life. Moreover, under certain circumstances it is necessary to monitor the extent of blockage of the particulate trap in order that a thermal regeneration of this nature should be initiated only at the required times. To avoid this discontinuous regeneration, which promotes thermal wear, a system for the continuous regeneration of filters or particulate traps has been developed (CRT: continuous regeneration trap). In a system of this type, the particulates are burnt at temperatures of well over 200°C by means of oxidation with NO2. The NO2 required for this purpose is often generated by an oxidation catalytic converter arranged upstream of the particulate trap. In this case, however, the problem arises specifically with a view to use in motor vehicles using 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. In this respect, it may under certain circumstances be necessary to add substances or additives which yield NO or NO2 (e.g. ammonia) so as to ultimately allow continuous regeneration of the particulate trap in the exhaust system. These fundamental considerations have given rise to a new filter concept, which has mainly become known under the name "open filter system" or "PM cat". These open filter systems are distinguished by the fact that there is no need for the filter passages to be designed such that they are closed off on alternate sides. In this context, it is provided that the passage walls are at - 3 - least in part composed of porous material and that the flow passages of the open filter have diverting and/or guiding structures. These internal fittings or microstructures in the passages cause the flow or the particulates contained therein to be diverted toward the regions made from porous material. In this context, it has surprisingly emerged that the particulates adhere to and/or in the porous passage wall as a result of interception and/or impacting. For this effect to occur, the pressure differences in the flow profile of the flow in the exhaust gas are of importance. The divergence or microstructures additionally make it possible to generate local subatmospheric or superatmospheric conditions, which lead to a filtration effect through the porous passage wall since the abovementioned pressure differences have to be compensated for. In this case, the particulate trap, unlike the known closed screen or filter systems, is "open", since there are no flow blind alleys and/or (at least almost) every passage has a cross section which, although it may vary, can ultimately still be flowed through freely. This property can also be used to characterize particulate filters of this type, which means that, for example, the parameter "freedom of flow" is suitable for descriptive purposes. A more extensive description of "open" filter elements of this type is to be found, for example, in documents DE 201 17 873, WO 02/00326, WO 01/92692, WO 01/80978, the content of disclosure of which is hereby incorporated in full in the subject matter of the present description and can also be used below for more detailed characterization of filter elements of this type in the context of the present invention. The provision of suitable materials for the porous passage sections has to be matched to a large number of factors, in particular material, resistance to - 4 - corrosion, thermal stability, manufacturing suitability, filter efficiency. By way of example, metallic fiber layers which have been configured with a protective sheath so as to comply with some of the factors required in the automotive industry have also been proposed. These are described, for example, in DE 101 53 283 or WO 03/038248. The known "open filter systems" or the filter layers used therein have already proven very successful. Important factors in this context are the low pressure loss and the possibility of arranging filter systems of this type relatively close to the internal combustion engine, where the particulate traps are usually exposed to an elevated temperature. Nevertheless, the intention now is to demonstrate a way of making the known particulate filters even more efficient in terms of their purifying action. Moreover, it is intended to provide a fiber layer or filter layer which can be produced at low cost even as part of series production and is suitable for use in metallic particulate traps, so as to be able to withstand the high thermal and dynamic loads in the exhaust system of an automobile for a prolonged period of time. These objects are achieved by a fiber layer and a particulate filter in accordance with the corresponding independent apparatus claims and a method for removing particulates in accordance with the independent method claim. Further advantageous configurations of the apparatuses and methods are described in the respective dependent claims. In this context, it should be noted that the features given individually in the patent claims can be combined with one another in any technologically expedient way and represent further advantageous configurations of the invention. The fiber layer according to the invention is suitable for use in an exhaust system of a mobile internal - 5 - combustion engine and comprises an assembly of fibers. It has a layer thickness which extends from one surface of the fiber layer toward an opposite surface. The fiber layer can in this context be characterized on the basis of at least one of the following parameters: porosity, fiber diameter, fiber type content. This fiber layer is now characterized in that at least one of the parameters listed has magnitudes which vary in the direction of the layer thickness, with an extreme of these magnitudes being at a distance from the surfaces of the fiber layer. In the present context, the term "fibers" is to be understood as meaning elongate elements, the fiber length of which is a multiple of the fiber diameter. The fibers have been combined with one another to form a sheet-like layer. The assembly may be of ordered or random nature. Examples of ordered assemblies include knitted fabrics, woven fabrics, meshes. An example of a random assembly is a tangled layer. The fibers may be directly cohesively bonded, but it is also possible for the fibers to be joined to one another by additional means. The fibers or fiber layers are made from a corrosion-resistant material which is able to withstand high temperatures, so that they are able to withstand the ambient conditions in an exhaust system for a prolonged period of time. Important variables for describing the fibers are fiber length, fiber diameter and fiber type content. It is preferable for the fiber length of fibers of this type to be in a range from 0.05 to 0.4 mm [millimeter]. The fiber diameter is usually in a range of less than 0.09 mm, preferably in a range from 0.015 to 0.05 mm. The arrangement of the fibers with respect to one another can be described, inter alia, by the porosity. In this context, the term porosity means the proportion of regions through which medium can flow freely within a cross section of the fiber layer. The porosity is usually in a range from 50% to 90%. The assembly of fibers generally forms - 6 - cavities, openings or pores, the maximum extent of which is in the range from 0.001 to 0.1 mm and can be selected on the basis of the particulates that are to be removed. A further parameter is what is known as the fiber type content, a term used to describe the proportion in which the fibers are present when different fiber types or configurations are used to form the fiber layer. For example, if the fiber layer includes a number of fibers (Fsmall) with a small fiber diameter, on the one hand, and a number of fibers (Flarge) with a larger fiber diameter, on the other hand, the fiber type content results from the ratio of Fsmall or Flarge to (Fsmall+ Flarge) . The fiber type content of one type of fibers preferably varies in the range of at least 10%, in particular 20%, over the layer thickness. In the case of the fiber layer proposed here, at least one of the characteristic parameters varies in the direction of the layer thickness, with an extreme in the interior of the fiber layer. In this context, the term "fiber layer" is actually only to be understood as meaning the combination of fibers; it does not include additional components of other forms of material (such as for example sheet-metal foils) for producing a filter layer. This does not mean that components of this type may not be present, but rather they are not taken into consideration in connection with the varying parameters. This has no effect on the configuration of the fiber layer with different types of fiber or fiber layers arranged adjacent to one another, which are intended to set the desired fiber layer parameter. This means in particular that the fiber layer is of different construction in edge layers than in central layers. The term "extreme" is to be understood as meaning a maximum value or a minimum value for the parameter under consideration. In this context, a variation in the magnitudes which is substantially symmetrical with - 7 - respect to the middle or center of the layer thickness is preferred. This has the advantage that the fiber layer has the same effect from both sides in terms of its filtering action and is therefore easier to produce, transport and process further in terms of manufacturing technology aspects. It is very particularly preferable for the respective extremes to be arranged substantially in a common cross-sectional plane of the fiber layer, i.e., for example, all to be at approximately the same distance from the surface of the fiber layer. The configuration of the fiber layer proposed here produces different flow resistances to a gas stream flowing through and/or particulates entrained therein at different depths of the fiber layer. The result of this is that the gas stream advances into different layers or depths of the fiber layer in accordance with the external flow forces and/or pressure differences. This fact can be exploited in order to achieve more effective purification of the gas streams, with an undesirable rise in the pressure loss being avoided at the same time. According to one advantageous refinement of the fiber layer, the latter comprises metallic fibers. In this context, it is preferable to use iron materials which contain a proportion of at least one of the following alloying elements: aluminum, chromium, nickel. The material itself can preferably be sintered, which means both that the fiber itself is made from sinterable material or produced by the sintering process and that the fibers have been joined to one another using the sintering process. Furthermore, it is proposed that the fiber layer have a plurality of subregions, in which at least one of the parameters is constant, in the direction of the layer thickness. In other words, this means that the fiber - 8 - layer is of stratified structure, with the parameter under consideration being substantially constant within one such stratum. A stratified fiber layer of this type may in principle also include a different fiber material, with the strata ultimately being joined to one another. However, it is preferable to form a fiber layer from one material, in which case the fibers themselves and/or their arrangement with respect to one another is configured in such a way that individual strata are formed. This has the advantage of ensuring more stable and durable cohesion of the layers, which is not necessarily the case with strata comprising different materials and/or strata which are joined to one another by additional joining materials. With a stratified structure of the fiber layer of this nature, it is particularly advantageous for there to be an odd number of subregions, with a centrally arranged subregion having the extreme magnitude of the parameter. It is preferable for a fiber layer of this type to have three (or if appropriate five) subregions, with the parameters in the edge layers being selected to be substantially identical and with a differing magnitude of the parameter being present in the centrally arranged subregion. The parameter may in this case have a magnitude which changes suddenly or continuously in the boundary region between the individual subregions. In principle, the layer thickness of a fiber layer or filter layer of this type is in a range of less than 3.0 mm, preferably in a range from 0.1 mm to 2.0 mm. Fiber layers with a layer thickness in the range from 0.3 mm to 0.5 mm have given good results for mobile use, with subregions with a thickness of approx. 0.1 mm being formed. The layer thickness may but does not have to be divided into subregions which form equal proportions of the overall thickness. - 9 - If the fiber layer is configured with a varying porosity, it is proposed in particular that the extreme represent a minimum value. In other words, this means that the porosity of the fiber layer is lowest in an inner, in particular, central region of the fiber layer, i.e. the highest flow resistance for a gas stream flowing through it is present there. This means that for complete flow through the fiber layer there must be a considerable pressure difference, whereas the flow of gases through the edge region can take place even at relatively low pressure differences. Moreover, it should be noted that experience has shown that these subregions of reduced porosity are the first to become blocked with solids or particles, which means that they may be partially blocked until the particulates have been converted into gaseous constituents and the fiber region has been regenerated. Nevertheless, the fiber layer usually still has some filtering action at these locations, since the exhaust gas or gas stream can still flow through the edge layers of the fiber layers and can therefore continue to be purified. If the fiber diameter is configured to be variable over the layer thickness of the fiber layer, it is preferably proposed that the extreme represent a minimum value. In other words, this means that fibers in an interior subregion of the fiber layer have a smaller fiber diameter than fibers in the edge layers. Tests have shown that the efficiency of the fibers in terms of their purifying action and/or their potential to accumulate particulates increases as the fiber diameter decreases. This therefore means that in this case there is a fiber layer which is particularly efficient in central regions, whereas edge regions are less efficient. By way of example, the fibers in the central region may, for example, be used with a fiber diameter of less than 50 n [micrometers] or even less than 25 urn, whereas, for example, fibers with a fiber - 10 - diameter in the range from 50 m to 100 m may be present in the edge region. Furthermore, by way of example it is also possible for the fiber type content to be configured so as to vary across the layer thickness of the fiber layer, in which case fibers (Fsmall) with a smaller fiber diameter and fibers (Flarge) with a larger fiber diameter are mixed or combined with one another. It is particularly preferable for the FSmall to have a fiber diameter in the range from 20-25 m [micrometers] , whereas the Flarge are designed with a fiber diameter in the range from 35- 4 5 m. The extreme of the fiber type content parameter is in this case preferably in the range from Fsmall = approx. 0.3-0.4 to Flarge = approx. 0.7-0.6. A fiber type content of this nature has given particularly advantageous results with regard to particulate separation if it is kept substantially constant across the layer thickness. However, further advantages can also be achieved if the fiber type content close to at least one edge region is in the range from Fsmall = 0.0-0.2 to Flarge = 1.0-0.8. According to a refinement of the fiber layer, at least some of the fibers have a fiber diameter which varies over their fiber length. In other words, this means that the fiber layer does not have to be produced with fibers of different configurations, but rather at least some of the fibers themselves are provided with a varying fiber diameter. This considerably simplifies the production of fiber layers of this type having varying parameters, in particular in series production. In this context, it is particularly advantageous for the magnitude of the fiber diameter to represent an extreme, in particular a minimum value, in a central portion of the fiber. In other words, this means that fibers which have two thick ends and a slender middle portion are provided. These fibers can then be combined - 11 - with one another in such a way that, for example, the portions of the fibers having the same fiber diameter are arranged adjacent to one another (in particular substantially in a cross-sectional plane parallel to the surface) , and in this way different strata are formed in the fiber layer. A further aspect of the invention proposes a particulate filter which is suitable for use in an exhaust system of a mobile internal combustion engine and comprises at least one fiber layer and at least one at least partially structured sheet. The at least one fiber layer and the at least one at least partially structured sheet together form passages of a honeycomb body, at least some of the passages having at least one honeycomb structure. In the particulate filter according to the invention, that at least one fiber layer has at least one parameter, selected from the group consisting of porosity and fiber diameter, which varies in the direction of a layer thickness. In this context, a particulate filter having a configuration of the fiber layer which has been described above in accordance with the invention is very particularly preferred. This particulate filter is preferably what is known as a "open filter system" as described in the introduction, in which context the content of disclosure of the abovementioned publications DE 201 17 873, WO 02/00326, WO 01/92692, WO 01/80978 can be used for additional explanation over and above the following description. All currently known methods, in particular continuous and discontinuous methods, can be used to regenerate the particulate filter according to the invention, but continuous regeneration using the "CRT" method is preferred. The configuration of the particulate filter with a honeycomb body is fundamentally known. In this case, a - 12 - multiplicity of passages arranged substantially parallel to one another are formed, connecting an inlet side of the honeycomb body to an outlet side of the honeycomb body. The exhaust gas which is to be purified flows in via the inlet end side and passes through the passages as partial exhaust-gas streams. The microstructures effect pressure differences in the interior of the honeycomb body, so that the partial exhaust-gas streams at least partially penetrate through the fiber layer and are purified in the process. Honeycomb bodies of this type are preferably designed with a cell density of at least 100 cpsi, preferably in the range from 150 cpsi to 400 cpsi (cpsi: cells per square inch; 1 cpsi corresponds to one passage per 6.4516 square centimeters). The passages are usually each delimited by a subregion of the structured sheet and a subregion of the fiber layer. The sheet is likewise made from a corrosion-resistant material which is able to withstand high temperatures, in particular a metallic material. It is designed with a sheet thickness (foil thickness) of less than 100 um [micrometers] and preferably has a recurring (macro-)structure, e.g. a corrugation. Both the sheet and the fiber layer may be at least partially provided with one or various coatings, if appropriate also including catalytically active material. To ensure a permanent joining of sheets and fiber layers, they are joined to one another, in particular by soldering or welding. In accordance with a refinement of this particulate filter, it is proposed that the at least one microstructure be arranged in such a way in a passage that a gas stream flowing through it be diverted toward the at least one fiber layer. For this purpose, the microstructure may be designed as a guide surface, elevation, projection, etc., in order to provide pressure differences and/or flow-facing edges and thereby to divert the gas stream, which usually flows - 13 - in laminar form inside the passage, toward the fiber layer. Together with the gas stream, the entrained particulates are also diverted toward the fiber layer, where they ultimately accumulate as they pass through or come into contact with the fiber layer. The residence time of the particulates in the interior of the passage, the fiber layer or the particulate filter is then maintained until at least a large proportion of them are converted into gaseous constituents. For this purpose, it is possible to carry out thermal conversion and also conversion or regeneration using nitrogen oxides. In particular, the particulate filter is configured in such a way that the microstructure and fiber layer form a gap with a gap width of less than 1.5 mm. It is advantageous for the gap width to be approximately 1.0 mm or in a range between 0.5 mm and 0.8 mm. In principle, it should be noted that a plurality of microstructures may be provided in the interior of a passage, in which case the gap does not have to be of identical design either within a passage or in adjacent passages. However, the provision of a gap ensures that an "open filter system" is produced. Consequently, at least part of the gas stream flowing through the passage is made to bypass the microstructure without completely penetrating through the fiber layer. The size and/or shape of the microstructure has a considerable influence on the flow diversion toward or through the fiber layer. In the configuration of the fiber layer with parameters which vary in the direction of the layer thickness which is proposed here, the result of this is that some of the exhaust gas or gas stream penetrates through the fiber layer and in this way enters an adjacent passage, while a further part of the exhaust gas or gas stream continues to flow along the passage, bypassing the microstructure. Configuring the fiber layer with an - 14 - edge layer which represents a lower flow resistance to the gas stream than centrally arranged layers allows this "bypass" partial gas stream to at least partially penetrate through the edge layer and thus likewise enables some of the particulates entrained therein to be deposited on the fibers. This increases the efficiency of the particulate filter with regard to the removal of particulates, in particular carbon particulates, from a gas stream, in particular an exhaust gas from an internal combustion engine. Moreover, the invention proposes an exhaust system for an internal combustion engine which comprises the particulate filter according to the invention. The term internal combustion engine is to be understood in particular as meaning engines which produce an exhaust gas containing solid particulates. A mobile engine which burns diesel fuel is of particular importance in this context. Furthermore, the invention also proposes a vehicle comprising a particulate filter of the type described above. Vehicles are mentioned as a preferred use in addition to other application areas (lawn mowers, chain saws, etc.) since statutory provisions require particularly efficient purification of the exhaust gases from vehicles. This applies in particular to passenger automobiles and trucks. A further aspect of the invention proposes a method for removing particulates from a gas stream using a gas- permeable filter layer, the filter layer having subregions with a parameter of differing magnitudes in the direction of the layer thickness. This parameter relates at least to the porosity or the fiber diameter of fibers in the filter layer. In the method, the gas stream is divided into partial gas streams which are each passed through different subregions of the filter layer. In other words, this means that although the - 15 - partial gas streams may equally well flow through one subregion or a few subregions of the filter layer together but are ultimately divided, with one of the partial gas streams flowing through other and/or further subregions of the filter layer. This is intended in particular to express the fact that separation into the respective partial gas streams takes place not in the direction of the surface of the filter layer, but rather in the direction of its layer thickness. This means in particular that a partial gas stream completely flows through the gas-permeable filter layer, whereas another part of the gas stream only penetrates into the gas-permeable filter layer but emerges again on the same side or surface without completely flowing through the filter layer. The partial gas streams differ in this context, for example, with regard to their direction of flow, their flow velocity, their temperature, the extent to which they are laden with particulates, etc. As has already been stated above, it is particularly advantageous for a partial gas stream to be passed only through at least one edge layer of the filter layer, whereas a further partial gas stream flows through all the subregions of the filter layer. In this context, it should also be noted that the term filter layer is to be understood as meaning both a fiber layer of the type according to the invention and also a filter layer composed of other materials or substances which likewise have magnitudes of the above mentioned parameters which vary in the direction of the layer thickness, with an extreme of these magnitudes being at a distance from the surfaces of the filter layer. According to a further configuration of the method, the partial gas stream which flows through only the edge layer is guided along a filter distance through the edge layer, this filter distance at least corresponding to the layer thickness of the filter layer. This means - 16 - that the partial gas stream which does not completely flow through the filter layer (bypass) is in contact with the filter material over at least the same distance of flow path. As has already been stated, the efficiency of the layers or subregions of the filter layer may differ, but by ensuring the filtering distance described here it is ensured that at least a proportionate filter action is achieved for this exhaust gas which is only passed through the filter material in the edge layers. It is preferable for the filter distance to be lengthened by the factor by which the adjacent strata differ in terms of their efficiency or another parameter. The filter distance can be effected by the targeted provision of pressure differences or forced flow profiles, for example by the specific configuration of microstructures in a flow passage which is delimited by a gas-permeable filter layer of this type. Finally, it is also proposed that the quantitative determination of the respective partial gas streams be effected by the filter layer itself. In other words, this means that the configuration of the filter layer itself has means responsible for dividing the overall gas stream into partial gas streams. These means may be realized by different configurations of the parameters of the fiber layer, i.e. may also be inherent. For example, the configuration of the filter layer with different flow resistances or porosities in the direction of the layer thickness constitutes one possible way of effecting a quantitative determination or division of this type. The method described here can be realized particularly successfully with one of the proposed fiber layers according to the invention and/or a proposed configuration of the particulate filter according to the invention. - 17 - The invention and the technical field of the invention are explained in more detail below on the basis of the figures. The figures also show particularly preferred embodiments of the particulate filter according to the invention and/or the fiber layer according to the invention, but the invention is not restricted to these embodiments. In the drawing: Fig. 1 diagrammatically depicts a filter layer which is suitable for the method according to the invention, Fig. 2 shows an embodiment of a fiber layer according to the invention; Fig. 3 diagrammatically depicts a further configuration of the fiber layer according to the invention; Fig. 4 shows a diagrammatic, detail view of a passage of an embodiment of the particulate filter; Fig. 5 shows a diagrammatic and perspective view of a vehicle having an exhaust system; and Fig. 6 diagrammatically depicts the structure of a particulate filter. Fig. 1 shows a diagrammatic and perspective view of a filter layer 23, which is usually provided in a predetermined layer length 29 and layer width 30. The filter layer 23 (and also the fiber layer 1) is delimited by two surfaces 6 which ultimately define a layer thickness 5 of the filter layer 23. In the direction of this layer thickness 5, the gas-permeable filter layer 23 has a plurality of subregions 10 (10.1, 10.2, 10.3) which differ on the basis of parameters which describe the filter layer 23. Parameters which are characteristic of the filter layer 23 include, for - 18 - example, the porosity 7 or the fiber diameter 8 of fibers 4 if the filter layer 23 is designed as a fiber layer 1. As can be seen from the detail view, a gas stream 22 which impinges on the filter layer 23 will partially penetrate into inner regions of the filter layer 23. After the entire gas stream 22 has penetrated through the first subregion 10.1, it reaches the second subregion 10.2. This subregion 10.2, which is arranged in the central region, has a porosity and/or fiber diameter which is impenetrable to part of the gas stream 22. Accordingly, this partial gas stream 24.1 is deflected at the transition to the second subregion 10.2 and flows back through the first subregion 10.1 before leaving the filter layer 23. Another partial gas stream 24.2 which, for example, has a higher flow velocity, a lower level of particulates, etc., however, also penetrates through the second subregion 10.2. Then, the partial gas stream 24.2 passes into the adjacent subregion 10.3, flows through the latter and emerges again on the opposite surface 6. Both the first partial gas stream 24.1 and the second partial gas stream 24.2 were in contact with at least a first subregion 10.1 of the filter layer 23. However, whereas the first partial gas stream 24.1 only flowed through a subregion 10.1, the partial gas stream 24.2 was passed through all the subregions 10.1, 10.2, 10.3. In this case, the quantitative determination of the partial gas streams 24 was effected by the filter layer 23 itself, since it presents different flow resistances in its subregions 10, leading to such a division of the gas stream 22. Fig. 2 diagrammatically depicts a detail of a fiber layer 1. Fibers 4 with a first fiber diameter 8 are provided in the vicinity of the surfaces 6 which delimit the fiber layer 1. Fibers 4 are also provided in a central region but have a different fiber diameter - 19 - 8. The differently shaped fibers 4 are permanently joined to one another and form a random assembly, with a porosity 7 being realized at the same time. In addition to this detail view of a fiber layer 1, the left-hand and right-hand sides of the figure diagrammatically depict profiles of magnitudes of the parameters porosity 7 and fiber diameter 8 over the layer thickness 5. The left-hand side of figure 2 illustrates the profile of the porosity 7. An extreme 9 where the porosity 7 is lowest is located in the central region, i.e. at a distance from the surfaces 6. The profile of the porosity 7 is substantially symmetrical with respect to a middle stratum of the fiber layer 1 and configured with continuous transitions. Similarly, the right-hand side of figure 2 illustrates the profile of the fiber diameter 8 over the layer thickness 5. On account of the fact that fibers 4 with a small fiber diameter 8 are provided in the central region and fibers 4 with a thicker fiber diameter 8 are provided in the edge layers, there is a sudden change in the fiber diameters 8, as illustrated on the right- hand side. An extreme 9 is once again formed in the central region. Fig. 3 once again diagrammatically depicts a fiber layer 1 with a particularly pronounced detail. This detail shows the fiber layer 1 with a coating 31 on both surfaces of the fiber layer 1; the coating may, of course, also extend into inner regions or even over all the free surfaces of the fibers 4. The fiber layer 1 is in this case configured as an ordered combination of fibers 4, the fibers 4 being designed with a fiber diameter 8 which varies over their fiber length 11. For this purpose, the fibers 4 have a central portion 12, in which the fiber diameter 8 reaches an extreme 9, as can also be seen diagrammatically on the right-hand - 20 - side from the profile illustrated. In the example shown here, the fiber diameters 8 are designed to be different in the vicinity of each surface 6, so that in this case the profile of the fiber diameters 8 is not symmetrical over the fiber length 9 or layer thickness 5. The identical, ordered orientation or alignment of the fibers 4 once again causes the formation of edge layers 25 which provide a configuration of the fiber layer 1 with parameters which vary in the direction of the layer thickness 5. With the configuration of the fibers 4 illustrated here it is also possible to provide further fibers 4 (for example of a different material or with a constant fiber diameter) in a subregion of the fiber layer 1, which further fibers are integrated in the fiber combination. Fig. 4 shows a diagrammatic view, in the form of partial cross sections, of the structure of a particulate filter 13 according to the invention which is suitable for use in an exhaust system of a mobile internal combustion engine. The particulate filter 13 comprises a fiber layer 1 with at least one parameter, selected from the group consisting of porosity and fiber diameter, which varies in the direction of a layer thickness 5 and at least one at least partially structured sheet 14, which together form a plurality of passages 15. In the embodiment illustrated, the sheet 14 has microstructures 17. A passage 15 of this type is illustrated in detail and in the form of a longitudinal section in the upper part of Fig. 4, indicated by "A". Beneath this, indicated by "B", a cross section through the passage 15 is diagrammatically depicted, the cross- sectional plane also being shown in illustration "A", indicating the direction of viewing. The mode of action is explained in more detail below. A gas stream 22 carrying particulates 21, in particular an exhaust gas stream, flows through the passage 15, where it impinges on the microstructure 17 which - 21 - projects into the passage 15. The result of this is that the gas stream 22 is diverted toward the fiber layer 1. The fiber layer 1 has edge layers 25 and a central layer in the interior. Whereas the entire gas stream 22 penetrates through the first edge layer 25, the middle layer, on account of its parameters (such as for example porosity and/or fiber diameter) , forms a flow resistance to a partial gas stream 24 which is such that said partial gas stream does not penetrate through this layer. Rather, this deflected partial gas stream 24 flows along a filter distance 26 through the edge region 25 before ultimately emerging back into the passage 15. Another part of the gas stream 22 penetrates through this middle layer and also the edge layer 25 which adjoins it and emerges again on the opposite surface. As the gas stream 22 flows through the fiber layer 1, the entrained particulates 21 collect on the fibers 4 of the fiber layer 1, so that ultimately the gas stream 22 is purified. The microstructures 17 are provided for the purpose of flow diversion and/or for producing pressure differences in adjacent passages 15. These microstructures 17 comprise projections which are worked into the material or structure of the sheet 14. It is possible to use pure deformation steps, but it is also possible for microstructures 17 of this type to be produced by stamping or other cutting processes, in which case openings 32 are generally introduced into the sheet 14. This also provides flow communication between adjacent passages 15, so that the exhaust gas which is to be purified can be mixed again and again. The microstructures 17, which are in this case formed as guiding surfaces, form a gap 18 together with the fiber layer 1, which gap has a predetermined gap width 19. The configuration of the microstructure 17 and the configuration of the fiber layer 1, and also the characteristics of the flow of the gas stream 22, now effect quantitative division into various partial gas - 22 - streams 24. Figure 5 shows a diagrammatic and perspective view of a vehicle 20 comprising an internal combustion engine 3 with an associated exhaust system 2. The exhaust gas which is generated in the internal combustion engine 3 flows through the exhaust system in a preferred direction of flow 33 and, after it has been purified, is released to the environment. The exhaust system 2 comprises an exhaust pipe 28 in which a plurality of different exhaust-gas treatment devices are provided in series. In the present case, the exhaust gas flows through the following components in succession: oxidation catalytic converter 27, particulate filter 13, catalytic converter 27. In principle, however, the particulate filter 13 can be integrated in any combination of known exhaust-gas treatment devices. Connecting an oxidation catalytic converter 27 and a particulate filter 13 in series as shown here in particular allows continuous regeneration of the particulate filter in accordance with the "CRT" principle described in the introduction. Fig. 6 diagrammatically depicts an end-side view of a particulate filter 13 which comprises a housing 34 and a honeycomb body 16 located therein. The honeycomb body 16 is formed with a plurality of stacks 35 of fiber layers 1 and sheets 14 which have been wound together. The alternately stacked fiber layers 1 and structured sheets 14 form passages 15 through which an exhaust gas can flow. Microstructures 17 (not shown), which cause the gas streams 22 to flow through the fiber layer 1, are provided in the interior of the passages. The invention described here allows particularly efficient removal of particulates from exhaust gases from mobile internal combustion engines. - 23 - List of reference numerals 1 Fiber layer 2 Exhaust system 3 Internal combustion engine 4 Fiber 5 Layer thickness 6 Surface 7 Porosity 8 Fiber diameter 9 Extreme 10 Subregion 11 Fiber length 12 Portion 13 Particulate filter 14 Sheet 15 Passage 16 Honeycomb body 17 Microstructure 18 Gap 19 Gap width 20 Vehicle 21 Particulates 22 Gas stream 23 Filter layer 24 Partial gas stream 25 Edge layer 26 Filter distance 27 Catalytic converter 28 Exhaust pipe 29 Layer length 30 Layer width 31 Coating 32 Opening 33 Direction of flow 34 Housing 35 Stack - 24 - Patent claims 1. A fiber layer (1) suitable for use in an exhaust system (2) of a mobile internal combustion engine (3), comprising an assembly of fibers (4) and having a layer thickness (5) which extends from one surface (6) of the fiber layer (1) toward an opposite surface (6), it being possible to characterize the fiber layer (1) on the basis of at least one of the following parameters: porosity (7), fiber diameter (8), fiber type content, characterized in that the at least one of the parameters listed has magnitudes which vary in the direction of the layer thickness (5), with an extreme (9) of these magnitudes being at a distance from the surfaces (6) of the fiber layer (1) • 2. The fiber layer (1) as claimed in claim 1, characterized in that the fiber layer (1) comprises metallic fibers (4). 3. The fiber layer (1) as claimed in claim 1 or 2, characterized in that the fiber layer (1) has a plurality of subregions (10), in which in each case at least one of the parameters is constant, in the direction of the layer thickness (5). 4. The fiber layer (1) as claimed in claim 3, characterized in that there is an odd number of subregions (10), with a centrally arranged subregion (10) having the extreme magnitude of the parameter. 5. The fiber layer (1) as claimed in one of the preceding claims, characterized in that the parameter is the porosity (7) and the extreme (9) represents a minimum value. - 25 - 6. The fiber layer (1) as claimed in one of the preceding claims, characterized in that the parameter is the fiber diameter (8) and the extreme (9) represents a minimum value. 7. The fiber layer (1) as claimed in one of the preceding claims, characterized in that at least some of the fibers (4) have a fiber diameter (8) which varies over their fiber length (11). 8. The fiber layer (1) as claimed in claim 7, characterized in that the magnitude of the fiber diameter (8) in a central section (12) represents an extreme. 9. A particulate filter (13) suitable for use in an exhaust system (2) of a mobile internal combustion engine (3) , comprising at least one fiber layer (1) and at least one partially structured sheet (14), which together form passages (15) of a honeycomb body (16) , at least some of the passages (15) having at least one microstructure (17), characterized in that the at least one fiber layer (1) has at least one parameter, selected from the group consisting of porosity (7) and fiber diameter (8), which varies in the direction of a layer thickness (5). 10. The particulate filter (13) as claimed in claim 9, characterized in that the at least one microstructure (17) is arranged in such a way in a passage (15) that a gas stream (22) flowing through the passage is diverted toward the at least one fiber layer (1). 11. The particulate filter (13) as claimed in claim 9 or 10, characterized in that the microstructure (17) and the fiber layer (1) form a gap (18) which has a gap width (19) of less than 1.5 millimeters. - 26 - 12. An exhaust system (2) of an internal combustion engine (3), comprising the particulate filter (13) as claimed in one of claims 9 to 11. 13. A vehicle (20) comprising the particulate filter (13) as claimed in one of claims 9 to 11. 14. A method for removing particulates (21) from a gas stream (22) using a gas-permeable filter layer (23) which has subregions (10) with a parameter of differing magnitudes in the direction of the layer thickness (5), this parameter relating at least to the porosity (7) or the fiber diameter (8) of fibers (4) of the filter layer (23), in which method the gas stream (22) is divided into partial gas streams (24) which are each passed through different subregions (10) of the filter layer (23) . 15. The method as claimed in claim 14, in which one partial gas stream (24) is passed only through at least one edge layer (25) of the filter layer (23), whereas a further partial gas stream (24) flows through all the subregions (10). 16. The method as claimed in claim 15, in which the partial gas stream (24) which comes into contact only with the edge layer (25) flows through a filter distance (26) which corresponds to at least the layer thickness (5) of the filter layer (23). 17. The method as claimed in claim 14 or 15, in which the quantitative determination of the respective partial gas streams (24) is effected by the filter layer (23) itself. The invention proposes a method for removing particulates (21) from a gas stream (22) having a gas permeable filter layer (23) which has subregions (10) with a parameter of differing magnitudes in the direction of the layer thickness (5), this parameter relating at least to the porosity (7), the fiber diameter (8) of fibers (4) or the fiber type content of the filter layer (23) . In the method, the gas stream (22) is divided into partial gas streams (24) which are each passed through different subregions (10) of the filter layer (23) . The invention also describes fiber layers, particulate filters, exhaust systems and vehicles which are based on this method.

Full Text

Method for removing particulates from exhaust gases,
and corresponding fiber layer and particulate filter
The present invention relates to a fiber layer which is
suitable for use in an exhaust system of a mobile
internal combustion engine. The invention also proposes
a particulate filter for the same use. Moreover, the
invention relates to a method for removing particulates
from the exhaust gas from an internal combustion engine
having a gas-permeable filter layer.
To reduce the level of particulate emissions from
exhaust gases from combustion processes, it is known to
use particulate traps which are constructed from a
ceramic substrate. These traps have passages, so that
the exhaust gas which is to be purified can flow into
the particulate trap. Adjacent passages are closed off
on alternate sides, so that the exhaust gas enters the
passage on the inlet side, is forced to pass through a
ceramic wall and escapes again along an adjacent
passage on the outlet side. Filters of this type
achieve an efficiency of approx. 95% across the entire
range of particulate sizes which occur.
In addition to undesirable chemical interactions
between the particulates and additives and special
coatings, the reliable regeneration of a filter of this
type in the exhaust system of an automobile still
causes 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 causes the pressure loss across
the filter or the back-pressure to rise continuously,
which has adverse effects on the engine power. The
regeneration generally comprises brief heating of the
particulate trap or the particulates which have
collected therein, so that the particulates are
converted into gaseous constituents. This can be
achieved, for example, by briefly raising the
temperature of the exhaust gas to levels which are

— 2 —
sufficient to convert the particulates which have
accumulated in the particulate trap, with the aid of an
upstream exothermic reaction (e.g. oxidation of
additional fuel injected into the exhaust pipe:
"afterburning"). However, this high thermal loading of
the particulate trap has adverse effects on the service
life. Moreover, under certain circumstances it is
necessary to monitor the extent of blockage of the
particulate trap in order that a thermal regeneration
of this nature should be initiated only at the required
times.
To avoid this discontinuous regeneration, which
promotes thermal wear, a system for the continuous
regeneration of filters or particulate traps has been
developed (CRT: continuous regeneration trap). In a
system of this type, the particulates are burnt at
temperatures of well over 200°C by means of oxidation
with NO2. The NO2 required for this purpose is often
generated by an oxidation catalytic converter arranged
upstream of the particulate trap. In this case,
however, the problem arises specifically with a view to
use in motor vehicles using 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. In this respect, it
may under certain circumstances be necessary to add
substances or additives which yield NO or NO2 (e.g.
ammonia) so as to ultimately allow continuous
regeneration of the particulate trap in the exhaust
system.
These fundamental considerations have given rise to a
new filter concept, which has mainly become known under
the name "open filter system" or "PM cat". These open
filter systems are distinguished by the fact that there
is no need for the filter passages to be designed such
that they are closed off on alternate sides. In this
context, it is provided that the passage walls are at

- 3 -
least in part composed of porous material and that the
flow passages of the open filter have diverting and/or
guiding structures. These internal fittings or
microstructures in the passages cause the flow or the
particulates contained therein to be diverted toward
the regions made from porous material. In this context,
it has surprisingly emerged that the particulates
adhere to and/or in the porous passage wall as a result
of interception and/or impacting. For this effect to
occur, the pressure differences in the flow profile of
the flow in the exhaust gas are of importance. The
divergence or microstructures additionally make it
possible to generate local subatmospheric or
superatmospheric conditions, which lead to a filtration
effect through the porous passage wall since the
abovementioned pressure differences have to be
compensated for.
In this case, the particulate trap, unlike the known
closed screen or filter systems, is "open", since there
are no flow blind alleys and/or (at least almost) every
passage has a cross section which, although it may
vary, can ultimately still be flowed through freely.
This property can also be used to characterize
particulate filters of this type, which means that, for
example, the parameter "freedom of flow" is suitable
for descriptive purposes. A more extensive description
of "open" filter elements of this type is to be found,
for example, in documents DE 201 17 873, WO 02/00326,
WO 01/92692, WO 01/80978, the content of disclosure of
which is hereby incorporated in full in the subject
matter of the present description and can also be used
below for more detailed characterization of filter
elements of this type in the context of the present
invention.
The provision of suitable materials for the porous
passage sections has to be matched to a large number of
factors, in particular material, resistance to

- 4 -
corrosion, thermal stability, manufacturing
suitability, filter efficiency. By way of example,
metallic fiber layers which have been configured with a
protective sheath so as to comply with some of the
factors required in the automotive industry have also
been proposed. These are described, for example, in
DE 101 53 283 or WO 03/038248.
The known "open filter systems" or the filter layers
used therein have already proven very successful.
Important factors in this context are the low pressure
loss and the possibility of arranging filter systems of
this type relatively close to the internal combustion
engine, where the particulate traps are usually exposed
to an elevated temperature. Nevertheless, the intention
now is to demonstrate a way of making the known
particulate filters even more efficient in terms of
their purifying action. Moreover, it is intended to
provide a fiber layer or filter layer which can be
produced at low cost even as part of series production
and is suitable for use in metallic particulate traps,
so as to be able to withstand the high thermal and
dynamic loads in the exhaust system of an automobile
for a prolonged period of time.
These objects are achieved by a fiber layer and a
particulate filter in accordance with the corresponding
independent apparatus claims and a method for removing
particulates in accordance with the independent method
claim. Further advantageous configurations of the
apparatuses and methods are described in the respective
dependent claims. In this context, it should be noted
that the features given individually in the patent
claims can be combined with one another in any
technologically expedient way and represent further
advantageous configurations of the invention.
The fiber layer according to the invention is suitable
for use in an exhaust system of a mobile internal

- 5 -
combustion engine and comprises an assembly of fibers.
It has a layer thickness which extends from one surface
of the fiber layer toward an opposite surface. The
fiber layer can in this context be characterized on the
basis of at least one of the following parameters:
porosity, fiber diameter, fiber type content. This
fiber layer is now characterized in that at least one
of the parameters listed has magnitudes which vary in
the direction of the layer thickness, with an extreme
of these magnitudes being at a distance from the
surfaces of the fiber layer.
In the present context, the term "fibers" is to be
understood as meaning elongate elements, the fiber
length of which is a multiple of the fiber diameter.
The fibers have been combined with one another to form
a sheet-like layer. The assembly may be of ordered or
random nature. Examples of ordered assemblies include
knitted fabrics, woven fabrics, meshes. An example of a
random assembly is a tangled layer. The fibers may be
directly cohesively bonded, but it is also possible for
the fibers to be joined to one another by additional
means. The fibers or fiber layers are made from a
corrosion-resistant material which is able to withstand
high temperatures, so that they are able to withstand
the ambient conditions in an exhaust system for a
prolonged period of time. Important variables for
describing the fibers are fiber length, fiber diameter
and fiber type content. It is preferable for the fiber
length of fibers of this type to be in a range from
0.05 to 0.4 mm [millimeter]. The fiber diameter is
usually in a range of less than 0.09 mm, preferably in
a range from 0.015 to 0.05 mm. The arrangement of the
fibers with respect to one another can be described,
inter alia, by the porosity. In this context, the term
porosity means the proportion of regions through which
medium can flow freely within a cross section of the
fiber layer. The porosity is usually in a range from
50% to 90%. The assembly of fibers generally forms

- 6 -
cavities, openings or pores, the maximum extent of
which is in the range from 0.001 to 0.1 mm and can be
selected on the basis of the particulates that are to
be removed. A further parameter is what is known as the
fiber type content, a term used to describe the
proportion in which the fibers are present when
different fiber types or configurations are used to
form the fiber layer. For example, if the fiber layer
includes a number of fibers (Fsmall) with a small fiber
diameter, on the one hand, and a number of fibers
(Flarge) with a larger fiber diameter, on the other hand,
the fiber type content results from the ratio of Fsmall
or Flarge to (Fsmall+ Flarge) . The fiber type content of
one type of fibers preferably varies in the range of at
least 10%, in particular 20%, over the layer thickness.
In the case of the fiber layer proposed here, at least
one of the characteristic parameters varies in the
direction of the layer thickness, with an extreme in
the interior of the fiber layer. In this context, the
term "fiber layer" is actually only to be understood as
meaning the combination of fibers; it does not include
additional components of other forms of material (such
as for example sheet-metal foils) for producing a
filter layer. This does not mean that components of
this type may not be present, but rather they are not
taken into consideration in connection with the varying
parameters. This has no effect on the configuration of
the fiber layer with different types of fiber or fiber
layers arranged adjacent to one another, which are
intended to set the desired fiber layer parameter. This
means in particular that the fiber layer is of
different construction in edge layers than in central
layers.
The term "extreme" is to be understood as meaning a
maximum value or a minimum value for the parameter
under consideration. In this context, a variation in
the magnitudes which is substantially symmetrical with

- 7 -
respect to the middle or center of the layer thickness
is preferred. This has the advantage that the fiber
layer has the same effect from both sides in terms of
its filtering action and is therefore easier to
produce, transport and process further in terms of
manufacturing technology aspects. It is very
particularly preferable for the respective extremes to
be arranged substantially in a common cross-sectional
plane of the fiber layer, i.e., for example, all to be
at approximately the same distance from the surface of
the fiber layer.
The configuration of the fiber layer proposed here
produces different flow resistances to a gas stream
flowing through and/or particulates entrained therein
at different depths of the fiber layer. The result of
this is that the gas stream advances into different
layers or depths of the fiber layer in accordance with
the external flow forces and/or pressure differences.
This fact can be exploited in order to achieve more
effective purification of the gas streams, with an
undesirable rise in the pressure loss being avoided at
the same time.
According to one advantageous refinement of the fiber
layer, the latter comprises metallic fibers. In this
context, it is preferable to use iron materials which
contain a proportion of at least one of the following
alloying elements: aluminum, chromium, nickel. The
material itself can preferably be sintered, which means
both that the fiber itself is made from sinterable
material or produced by the sintering process and that
the fibers have been joined to one another using the
sintering process.
Furthermore, it is proposed that the fiber layer have a
plurality of subregions, in which at least one of the
parameters is constant, in the direction of the layer
thickness. In other words, this means that the fiber

- 8 -
layer is of stratified structure, with the parameter
under consideration being substantially constant within
one such stratum. A stratified fiber layer of this type
may in principle also include a different fiber
material, with the strata ultimately being joined to
one another. However, it is preferable to form a fiber
layer from one material, in which case the fibers
themselves and/or their arrangement with respect to one
another is configured in such a way that individual
strata are formed. This has the advantage of ensuring
more stable and durable cohesion of the layers, which
is not necessarily the case with strata comprising
different materials and/or strata which are joined to
one another by additional joining materials.
With a stratified structure of the fiber layer of this
nature, it is particularly advantageous for there to be
an odd number of subregions, with a centrally arranged
subregion having the extreme magnitude of the
parameter. It is preferable for a fiber layer of this
type to have three (or if appropriate five) subregions,
with the parameters in the edge layers being selected
to be substantially identical and with a differing
magnitude of the parameter being present in the
centrally arranged subregion. The parameter may in this
case have a magnitude which changes suddenly or
continuously in the boundary region between the
individual subregions.
In principle, the layer thickness of a fiber layer or
filter layer of this type is in a range of less than
3.0 mm, preferably in a range from 0.1 mm to 2.0 mm.
Fiber layers with a layer thickness in the range from
0.3 mm to 0.5 mm have given good results for mobile
use, with subregions with a thickness of approx. 0.1 mm
being formed. The layer thickness may but does not have
to be divided into subregions which form equal
proportions of the overall thickness.

- 9 -
If the fiber layer is configured with a varying
porosity, it is proposed in particular that the extreme
represent a minimum value. In other words, this means
that the porosity of the fiber layer is lowest in an
inner, in particular, central region of the fiber
layer, i.e. the highest flow resistance for a gas
stream flowing through it is present there. This means
that for complete flow through the fiber layer there
must be a considerable pressure difference, whereas the
flow of gases through the edge region can take place
even at relatively low pressure differences. Moreover,
it should be noted that experience has shown that these
subregions of reduced porosity are the first to become
blocked with solids or particles, which means that they
may be partially blocked until the particulates have
been converted into gaseous constituents and the fiber
region has been regenerated. Nevertheless, the fiber
layer usually still has some filtering action at these
locations, since the exhaust gas or gas stream can
still flow through the edge layers of the fiber layers
and can therefore continue to be purified.
If the fiber diameter is configured to be variable over
the layer thickness of the fiber layer, it is
preferably proposed that the extreme represent a
minimum value. In other words, this means that fibers
in an interior subregion of the fiber layer have a
smaller fiber diameter than fibers in the edge layers.
Tests have shown that the efficiency of the fibers in
terms of their purifying action and/or their potential
to accumulate particulates increases as the fiber
diameter decreases. This therefore means that in this
case there is a fiber layer which is particularly
efficient in central regions, whereas edge regions are
less efficient. By way of example, the fibers in the
central region may, for example, be used with a fiber
diameter of less than 50 n [micrometers] or even less
than 25 urn, whereas, for example, fibers with a fiber

- 10 -
diameter in the range from 50 m to 100 m may be
present in the edge region.
Furthermore, by way of example it is also possible for
the fiber type content to be configured so as to vary
across the layer thickness of the fiber layer, in which
case fibers (Fsmall) with a smaller fiber diameter and
fibers (Flarge) with a larger fiber diameter are mixed or
combined with one another. It is particularly
preferable for the FSmall to have a fiber diameter in the
range from 20-25 m [micrometers] , whereas the Flarge are
designed with a fiber diameter in the range from 35-
4 5 m. The extreme of the fiber type content parameter
is in this case preferably in the range from
Fsmall = approx. 0.3-0.4 to Flarge = approx. 0.7-0.6. A
fiber type content of this nature has given
particularly advantageous results with regard to
particulate separation if it is kept substantially
constant across the layer thickness. However, further
advantages can also be achieved if the fiber type
content close to at least one edge region is in the
range from Fsmall = 0.0-0.2 to Flarge = 1.0-0.8.
According to a refinement of the fiber layer, at least
some of the fibers have a fiber diameter which varies
over their fiber length. In other words, this means
that the fiber layer does not have to be produced with
fibers of different configurations, but rather at least
some of the fibers themselves are provided with a
varying fiber diameter. This considerably simplifies
the production of fiber layers of this type having
varying parameters, in particular in series production.
In this context, it is particularly advantageous for
the magnitude of the fiber diameter to represent an
extreme, in particular a minimum value, in a central
portion of the fiber. In other words, this means that
fibers which have two thick ends and a slender middle
portion are provided. These fibers can then be combined

- 11 -
with one another in such a way that, for example, the
portions of the fibers having the same fiber diameter
are arranged adjacent to one another (in particular
substantially in a cross-sectional plane parallel to
the surface) , and in this way different strata are
formed in the fiber layer.
A further aspect of the invention proposes a
particulate filter which is suitable for use in an
exhaust system of a mobile internal combustion engine
and comprises at least one fiber layer and at least one
at least partially structured sheet. The at least one
fiber layer and the at least one at least partially
structured sheet together form passages of a honeycomb
body, at least some of the passages having at least one
honeycomb structure. In the particulate filter
according to the invention, that at least one fiber
layer has at least one parameter, selected from the
group consisting of porosity and fiber diameter, which
varies in the direction of a layer thickness. In this
context, a particulate filter having a configuration of
the fiber layer which has been described above in
accordance with the invention is very particularly
preferred.
This particulate filter is preferably what is known as
a "open filter system" as described in the
introduction, in which context the content of
disclosure of the abovementioned publications
DE 201 17 873, WO 02/00326, WO 01/92692, WO 01/80978
can be used for additional explanation over and above
the following description. All currently known methods,
in particular continuous and discontinuous methods, can
be used to regenerate the particulate filter according
to the invention, but continuous regeneration using the
"CRT" method is preferred.
The configuration of the particulate filter with a
honeycomb body is fundamentally known. In this case, a

- 12 -
multiplicity of passages arranged substantially
parallel to one another are formed, connecting an inlet
side of the honeycomb body to an outlet side of the
honeycomb body. The exhaust gas which is to be purified
flows in via the inlet end side and passes through the
passages as partial exhaust-gas streams. The
microstructures effect pressure differences in the
interior of the honeycomb body, so that the partial
exhaust-gas streams at least partially penetrate
through the fiber layer and are purified in the
process. Honeycomb bodies of this type are preferably
designed with a cell density of at least 100 cpsi,
preferably in the range from 150 cpsi to 400 cpsi
(cpsi: cells per square inch; 1 cpsi corresponds to one
passage per 6.4516 square centimeters). The passages
are usually each delimited by a subregion of the
structured sheet and a subregion of the fiber layer.
The sheet is likewise made from a corrosion-resistant
material which is able to withstand high temperatures,
in particular a metallic material. It is designed with
a sheet thickness (foil thickness) of less than 100 um
[micrometers] and preferably has a recurring
(macro-)structure, e.g. a corrugation. Both the sheet
and the fiber layer may be at least partially provided
with one or various coatings, if appropriate also
including catalytically active material. To ensure a
permanent joining of sheets and fiber layers, they are
joined to one another, in particular by soldering or
welding.
In accordance with a refinement of this particulate
filter, it is proposed that the at least one
microstructure be arranged in such a way in a passage
that a gas stream flowing through it be diverted toward
the at least one fiber layer. For this purpose, the
microstructure may be designed as a guide surface,
elevation, projection, etc., in order to provide
pressure differences and/or flow-facing edges and
thereby to divert the gas stream, which usually flows

- 13 -
in laminar form inside the passage, toward the fiber
layer. Together with the gas stream, the entrained
particulates are also diverted toward the fiber layer,
where they ultimately accumulate as they pass through
or come into contact with the fiber layer. The
residence time of the particulates in the interior of
the passage, the fiber layer or the particulate filter
is then maintained until at least a large proportion of
them are converted into gaseous constituents. For this
purpose, it is possible to carry out thermal conversion
and also conversion or regeneration using nitrogen
oxides.
In particular, the particulate filter is configured in
such a way that the microstructure and fiber layer form
a gap with a gap width of less than 1.5 mm. It is
advantageous for the gap width to be approximately
1.0 mm or in a range between 0.5 mm and 0.8 mm. In
principle, it should be noted that a plurality of
microstructures may be provided in the interior of a
passage, in which case the gap does not have to be of
identical design either within a passage or in adjacent
passages. However, the provision of a gap ensures that
an "open filter system" is produced. Consequently, at
least part of the gas stream flowing through the
passage is made to bypass the microstructure without
completely penetrating through the fiber layer. The
size and/or shape of the microstructure has a
considerable influence on the flow diversion toward or
through the fiber layer.
In the configuration of the fiber layer with parameters
which vary in the direction of the layer thickness
which is proposed here, the result of this is that some
of the exhaust gas or gas stream penetrates through the
fiber layer and in this way enters an adjacent passage,
while a further part of the exhaust gas or gas stream
continues to flow along the passage, bypassing the
microstructure. Configuring the fiber layer with an

- 14 -
edge layer which represents a lower flow resistance to
the gas stream than centrally arranged layers allows
this "bypass" partial gas stream to at least partially
penetrate through the edge layer and thus likewise
enables some of the particulates entrained therein to
be deposited on the fibers. This increases the
efficiency of the particulate filter with regard to the
removal of particulates, in particular carbon
particulates, from a gas stream, in particular an
exhaust gas from an internal combustion engine.
Moreover, the invention proposes an exhaust system for
an internal combustion engine which comprises the
particulate filter according to the invention. The term
internal combustion engine is to be understood in
particular as meaning engines which produce an exhaust
gas containing solid particulates. A mobile engine
which burns diesel fuel is of particular importance in
this context.
Furthermore, the invention also proposes a vehicle
comprising a particulate filter of the type described
above. Vehicles are mentioned as a preferred use in
addition to other application areas (lawn mowers, chain
saws, etc.) since statutory provisions require
particularly efficient purification of the exhaust
gases from vehicles. This applies in particular to
passenger automobiles and trucks.
A further aspect of the invention proposes a method for
removing particulates from a gas stream using a gas-
permeable filter layer, the filter layer having
subregions with a parameter of differing magnitudes in
the direction of the layer thickness. This parameter
relates at least to the porosity or the fiber diameter
of fibers in the filter layer. In the method, the gas
stream is divided into partial gas streams which are
each passed through different subregions of the filter
layer. In other words, this means that although the

- 15 -
partial gas streams may equally well flow through one
subregion or a few subregions of the filter layer
together but are ultimately divided, with one of the
partial gas streams flowing through other and/or
further subregions of the filter layer. This is
intended in particular to express the fact that
separation into the respective partial gas streams
takes place not in the direction of the surface of the
filter layer, but rather in the direction of its layer
thickness. This means in particular that a partial gas
stream completely flows through the gas-permeable
filter layer, whereas another part of the gas stream
only penetrates into the gas-permeable filter layer but
emerges again on the same side or surface without
completely flowing through the filter layer. The
partial gas streams differ in this context, for
example, with regard to their direction of flow, their
flow velocity, their temperature, the extent to which
they are laden with particulates, etc.
As has already been stated above, it is particularly
advantageous for a partial gas stream to be passed only
through at least one edge layer of the filter layer,
whereas a further partial gas stream flows through all
the subregions of the filter layer. In this context, it
should also be noted that the term filter layer is to
be understood as meaning both a fiber layer of the type
according to the invention and also a filter layer
composed of other materials or substances which
likewise have magnitudes of the above mentioned
parameters which vary in the direction of the layer
thickness, with an extreme of these magnitudes being at
a distance from the surfaces of the filter layer.
According to a further configuration of the method, the
partial gas stream which flows through only the edge
layer is guided along a filter distance through the
edge layer, this filter distance at least corresponding
to the layer thickness of the filter layer. This means

- 16 -
that the partial gas stream which does not completely
flow through the filter layer (bypass) is in contact
with the filter material over at least the same
distance of flow path. As has already been stated, the
efficiency of the layers or subregions of the filter
layer may differ, but by ensuring the filtering
distance described here it is ensured that at least a
proportionate filter action is achieved for this
exhaust gas which is only passed through the filter
material in the edge layers. It is preferable for the
filter distance to be lengthened by the factor by which
the adjacent strata differ in terms of their efficiency
or another parameter. The filter distance can be
effected by the targeted provision of pressure
differences or forced flow profiles, for example by the
specific configuration of microstructures in a flow
passage which is delimited by a gas-permeable filter
layer of this type.
Finally, it is also proposed that the quantitative
determination of the respective partial gas streams be
effected by the filter layer itself. In other words,
this means that the configuration of the filter layer
itself has means responsible for dividing the overall
gas stream into partial gas streams. These means may be
realized by different configurations of the parameters
of the fiber layer, i.e. may also be inherent. For
example, the configuration of the filter layer with
different flow resistances or porosities in the
direction of the layer thickness constitutes one
possible way of effecting a quantitative determination
or division of this type.
The method described here can be realized particularly
successfully with one of the proposed fiber layers
according to the invention and/or a proposed
configuration of the particulate filter according to
the invention.

- 17 -
The invention and the technical field of the invention
are explained in more detail below on the basis of the
figures. The figures also show particularly preferred
embodiments of the particulate filter according to the
invention and/or the fiber layer according to the
invention, but the invention is not restricted to these
embodiments. In the drawing:
Fig. 1 diagrammatically depicts a filter layer which
is suitable for the method according to the
invention,
Fig. 2 shows an embodiment of a fiber layer according
to the invention;
Fig. 3 diagrammatically depicts a further
configuration of the fiber layer according to
the invention;
Fig. 4 shows a diagrammatic, detail view of a passage
of an embodiment of the particulate filter;
Fig. 5 shows a diagrammatic and perspective view of a
vehicle having an exhaust system; and
Fig. 6 diagrammatically depicts the structure of a
particulate filter.
Fig. 1 shows a diagrammatic and perspective view of a
filter layer 23, which is usually provided in a
predetermined layer length 29 and layer width 30. The
filter layer 23 (and also the fiber layer 1) is
delimited by two surfaces 6 which ultimately define a
layer thickness 5 of the filter layer 23. In the
direction of this layer thickness 5, the gas-permeable
filter layer 23 has a plurality of subregions 10 (10.1,
10.2, 10.3) which differ on the basis of parameters
which describe the filter layer 23. Parameters which
are characteristic of the filter layer 23 include, for

- 18 -
example, the porosity 7 or the fiber diameter 8 of
fibers 4 if the filter layer 23 is designed as a fiber
layer 1.
As can be seen from the detail view, a gas stream 22
which impinges on the filter layer 23 will partially
penetrate into inner regions of the filter layer 23.
After the entire gas stream 22 has penetrated through
the first subregion 10.1, it reaches the second
subregion 10.2. This subregion 10.2, which is arranged
in the central region, has a porosity and/or fiber
diameter which is impenetrable to part of the gas
stream 22. Accordingly, this partial gas stream 24.1 is
deflected at the transition to the second subregion
10.2 and flows back through the first subregion 10.1
before leaving the filter layer 23. Another partial gas
stream 24.2 which, for example, has a higher flow
velocity, a lower level of particulates, etc., however,
also penetrates through the second subregion 10.2.
Then, the partial gas stream 24.2 passes into the
adjacent subregion 10.3, flows through the latter and
emerges again on the opposite surface 6. Both the first
partial gas stream 24.1 and the second partial gas
stream 24.2 were in contact with at least a first
subregion 10.1 of the filter layer 23. However, whereas
the first partial gas stream 24.1 only flowed through a
subregion 10.1, the partial gas stream 24.2 was passed
through all the subregions 10.1, 10.2, 10.3. In this
case, the quantitative determination of the partial gas
streams 24 was effected by the filter layer 23 itself,
since it presents different flow resistances in its
subregions 10, leading to such a division of the gas
stream 22.
Fig. 2 diagrammatically depicts a detail of a fiber
layer 1. Fibers 4 with a first fiber diameter 8 are
provided in the vicinity of the surfaces 6 which
delimit the fiber layer 1. Fibers 4 are also provided
in a central region but have a different fiber diameter

- 19 -
8. The differently shaped fibers 4 are permanently
joined to one another and form a random assembly, with
a porosity 7 being realized at the same time. In
addition to this detail view of a fiber layer 1, the
left-hand and right-hand sides of the figure
diagrammatically depict profiles of magnitudes of the
parameters porosity 7 and fiber diameter 8 over the
layer thickness 5.
The left-hand side of figure 2 illustrates the profile
of the porosity 7. An extreme 9 where the porosity 7 is
lowest is located in the central region, i.e. at a
distance from the surfaces 6. The profile of the
porosity 7 is substantially symmetrical with respect to
a middle stratum of the fiber layer 1 and configured
with continuous transitions.
Similarly, the right-hand side of figure 2 illustrates
the profile of the fiber diameter 8 over the layer
thickness 5. On account of the fact that fibers 4 with
a small fiber diameter 8 are provided in the central
region and fibers 4 with a thicker fiber diameter 8 are
provided in the edge layers, there is a sudden change
in the fiber diameters 8, as illustrated on the right-
hand side. An extreme 9 is once again formed in the
central region.
Fig. 3 once again diagrammatically depicts a fiber
layer 1 with a particularly pronounced detail. This
detail shows the fiber layer 1 with a coating 31 on
both surfaces of the fiber layer 1; the coating may, of
course, also extend into inner regions or even over all
the free surfaces of the fibers 4. The fiber layer 1 is
in this case configured as an ordered combination of
fibers 4, the fibers 4 being designed with a fiber
diameter 8 which varies over their fiber length 11. For
this purpose, the fibers 4 have a central portion 12,
in which the fiber diameter 8 reaches an extreme 9, as
can also be seen diagrammatically on the right-hand

- 20 -
side from the profile illustrated. In the example shown
here, the fiber diameters 8 are designed to be
different in the vicinity of each surface 6, so that in
this case the profile of the fiber diameters 8 is not
symmetrical over the fiber length 9 or layer thickness
5. The identical, ordered orientation or alignment of
the fibers 4 once again causes the formation of edge
layers 25 which provide a configuration of the fiber
layer 1 with parameters which vary in the direction of
the layer thickness 5. With the configuration of the
fibers 4 illustrated here it is also possible to
provide further fibers 4 (for example of a different
material or with a constant fiber diameter) in a
subregion of the fiber layer 1, which further fibers
are integrated in the fiber combination.
Fig. 4 shows a diagrammatic view, in the form of
partial cross sections, of the structure of a
particulate filter 13 according to the invention which
is suitable for use in an exhaust system of a mobile
internal combustion engine. The particulate filter 13
comprises a fiber layer 1 with at least one parameter,
selected from the group consisting of porosity and
fiber diameter, which varies in the direction of a
layer thickness 5 and at least one at least partially
structured sheet 14, which together form a plurality of
passages 15. In the embodiment illustrated, the sheet
14 has microstructures 17. A passage 15 of this type is
illustrated in detail and in the form of a longitudinal
section in the upper part of Fig. 4, indicated by "A".
Beneath this, indicated by "B", a cross section through
the passage 15 is diagrammatically depicted, the cross-
sectional plane also being shown in illustration "A",
indicating the direction of viewing.
The mode of action is explained in more detail below. A
gas stream 22 carrying particulates 21, in particular
an exhaust gas stream, flows through the passage 15,
where it impinges on the microstructure 17 which

- 21 -
projects into the passage 15. The result of this is
that the gas stream 22 is diverted toward the fiber
layer 1. The fiber layer 1 has edge layers 25 and a
central layer in the interior. Whereas the entire gas
stream 22 penetrates through the first edge layer 25,
the middle layer, on account of its parameters (such as
for example porosity and/or fiber diameter) , forms a
flow resistance to a partial gas stream 24 which is
such that said partial gas stream does not penetrate
through this layer. Rather, this deflected partial gas
stream 24 flows along a filter distance 26 through the
edge region 25 before ultimately emerging back into the
passage 15. Another part of the gas stream 22
penetrates through this middle layer and also the edge
layer 25 which adjoins it and emerges again on the
opposite surface. As the gas stream 22 flows through
the fiber layer 1, the entrained particulates 21
collect on the fibers 4 of the fiber layer 1, so that
ultimately the gas stream 22 is purified.
The microstructures 17 are provided for the purpose of
flow diversion and/or for producing pressure
differences in adjacent passages 15. These
microstructures 17 comprise projections which are
worked into the material or structure of the sheet 14.
It is possible to use pure deformation steps, but it is
also possible for microstructures 17 of this type to be
produced by stamping or other cutting processes, in
which case openings 32 are generally introduced into
the sheet 14. This also provides flow communication
between adjacent passages 15, so that the exhaust gas
which is to be purified can be mixed again and again.
The microstructures 17, which are in this case formed
as guiding surfaces, form a gap 18 together with the
fiber layer 1, which gap has a predetermined gap width
19. The configuration of the microstructure 17 and the
configuration of the fiber layer 1, and also the
characteristics of the flow of the gas stream 22, now
effect quantitative division into various partial gas

- 22 -
streams 24.
Figure 5 shows a diagrammatic and perspective view of a
vehicle 20 comprising an internal combustion engine 3
with an associated exhaust system 2. The exhaust gas
which is generated in the internal combustion engine 3
flows through the exhaust system in a preferred
direction of flow 33 and, after it has been purified,
is released to the environment. The exhaust system 2
comprises an exhaust pipe 28 in which a plurality of
different exhaust-gas treatment devices are provided in
series. In the present case, the exhaust gas flows
through the following components in succession:
oxidation catalytic converter 27, particulate filter
13, catalytic converter 27. In principle, however, the
particulate filter 13 can be integrated in any
combination of known exhaust-gas treatment devices.
Connecting an oxidation catalytic converter 27 and a
particulate filter 13 in series as shown here in
particular allows continuous regeneration of the
particulate filter in accordance with the "CRT"
principle described in the introduction.
Fig. 6 diagrammatically depicts an end-side view of a
particulate filter 13 which comprises a housing 34 and
a honeycomb body 16 located therein. The honeycomb body
16 is formed with a plurality of stacks 35 of fiber
layers 1 and sheets 14 which have been wound together.
The alternately stacked fiber layers 1 and structured
sheets 14 form passages 15 through which an exhaust gas
can flow. Microstructures 17 (not shown), which cause
the gas streams 22 to flow through the fiber layer 1,
are provided in the interior of the passages.
The invention described here allows particularly
efficient removal of particulates from exhaust gases
from mobile internal combustion engines.

- 23 -
List of reference numerals

1 Fiber layer
2 Exhaust system
3 Internal combustion engine
4 Fiber
5 Layer thickness
6 Surface
7 Porosity
8 Fiber diameter
9 Extreme
10 Subregion
11 Fiber length
12 Portion
13 Particulate filter
14 Sheet
15 Passage
16 Honeycomb body
17 Microstructure
18 Gap
19 Gap width
20 Vehicle
21 Particulates
22 Gas stream
23 Filter layer
24 Partial gas stream
25 Edge layer
26 Filter distance
27 Catalytic converter
28 Exhaust pipe
29 Layer length
30 Layer width
31 Coating
32 Opening
33 Direction of flow
34 Housing
35 Stack

- 24 -
Patent claims
1. A fiber layer (1) suitable for use in an exhaust
system (2) of a mobile internal combustion engine
(3), comprising an assembly of fibers (4) and
having a layer thickness (5) which extends from
one surface (6) of the fiber layer (1) toward an
opposite surface (6), it being possible to
characterize the fiber layer (1) on the basis of
at least one of the following parameters: porosity
(7), fiber diameter (8), fiber type content,
characterized in that the at least one of the
parameters listed has magnitudes which vary in the
direction of the layer thickness (5), with an
extreme (9) of these magnitudes being at a
distance from the surfaces (6) of the fiber layer
(1) •
2. The fiber layer (1) as claimed in claim 1,
characterized in that the fiber layer (1)
comprises metallic fibers (4).
3. The fiber layer (1) as claimed in claim 1 or 2,
characterized in that the fiber layer (1) has a
plurality of subregions (10), in which in each
case at least one of the parameters is constant,
in the direction of the layer thickness (5).
4. The fiber layer (1) as claimed in claim 3,
characterized in that there is an odd number of
subregions (10), with a centrally arranged
subregion (10) having the extreme magnitude of the
parameter.
5. The fiber layer (1) as claimed in one of the
preceding claims, characterized in that the
parameter is the porosity (7) and the extreme (9)
represents a minimum value.

- 25 -
6. The fiber layer (1) as claimed in one of the
preceding claims, characterized in that the
parameter is the fiber diameter (8) and the
extreme (9) represents a minimum value.
7. The fiber layer (1) as claimed in one of the
preceding claims, characterized in that at least
some of the fibers (4) have a fiber diameter (8)
which varies over their fiber length (11).
8. The fiber layer (1) as claimed in claim 7,
characterized in that the magnitude of the fiber
diameter (8) in a central section (12) represents
an extreme.
9. A particulate filter (13) suitable for use in an
exhaust system (2) of a mobile internal combustion
engine (3) , comprising at least one fiber layer
(1) and at least one partially structured sheet
(14), which together form passages (15) of a
honeycomb body (16) , at least some of the passages
(15) having at least one microstructure (17),
characterized in that the at least one fiber layer
(1) has at least one parameter, selected from the
group consisting of porosity (7) and fiber
diameter (8), which varies in the direction of a
layer thickness (5).
10. The particulate filter (13) as claimed in claim 9,
characterized in that the at least one
microstructure (17) is arranged in such a way in a
passage (15) that a gas stream (22) flowing
through the passage is diverted toward the at
least one fiber layer (1).
11. The particulate filter (13) as claimed in claim 9
or 10, characterized in that the microstructure
(17) and the fiber layer (1) form a gap (18) which
has a gap width (19) of less than 1.5 millimeters.

- 26 -
12. An exhaust system (2) of an internal combustion
engine (3), comprising the particulate filter (13)
as claimed in one of claims 9 to 11.
13. A vehicle (20) comprising the particulate filter
(13) as claimed in one of claims 9 to 11.
14. A method for removing particulates (21) from a gas
stream (22) using a gas-permeable filter layer
(23) which has subregions (10) with a parameter of
differing magnitudes in the direction of the layer
thickness (5), this parameter relating at least to
the porosity (7) or the fiber diameter (8) of
fibers (4) of the filter layer (23), in which
method the gas stream (22) is divided into partial
gas streams (24) which are each passed through
different subregions (10) of the filter layer
(23) .
15. The method as claimed in claim 14, in which one
partial gas stream (24) is passed only through at
least one edge layer (25) of the filter layer
(23), whereas a further partial gas stream (24)
flows through all the subregions (10).
16. The method as claimed in claim 15, in which the
partial gas stream (24) which comes into contact
only with the edge layer (25) flows through a
filter distance (26) which corresponds to at least
the layer thickness (5) of the filter layer (23).
17. The method as claimed in claim 14 or 15, in which
the quantitative determination of the respective
partial gas streams (24) is effected by the filter
layer (23) itself.

The invention proposes a method for removing
particulates (21) from a gas stream (22) having a gas permeable filter layer (23) which has subregions (10)
with a parameter of differing magnitudes in the
direction of the layer thickness (5), this parameter
relating at least to the porosity (7), the fiber
diameter (8) of fibers (4) or the fiber type content of
the filter layer (23) . In the method, the gas stream
(22) is divided into partial gas streams (24) which are
each passed through different subregions (10) of the
filter layer (23) . The invention also describes fiber
layers, particulate filters, exhaust systems and
vehicles which are based on this method.

Documents:

02426-kolnp-2007-abstract.pdf

02426-kolnp-2007-claims.pdf

02426-kolnp-2007-correspondence others 1.1.pdf

02426-kolnp-2007-correspondence others.pdf

02426-kolnp-2007-description complete.pdf

02426-kolnp-2007-drawings.pdf

02426-kolnp-2007-form 1.pdf

02426-kolnp-2007-form 18.pdf

02426-kolnp-2007-form 2.pdf

02426-kolnp-2007-form 3.pdf

02426-kolnp-2007-form 5.pdf

02426-kolnp-2007-gpa.pdf

02426-kolnp-2007-international publication.pdf

02426-kolnp-2007-other pct form.pdf

02426-kolnp-2007-pct request form.pdf

02426-kolnp-2007-priority document.pdf

2426-KOLNP-2007-(02-05-2012)-CORRESPONDENCE.pdf

2426-KOLNP-2007-(31-10-2011)-ABSTRACT.pdf

2426-KOLNP-2007-(31-10-2011)-AMANDED CLAIMS.pdf

2426-KOLNP-2007-(31-10-2011)-CORRESPONDENCE.pdf

2426-KOLNP-2007-(31-10-2011)-DESCRIPTION (COMPLETE).pdf

2426-KOLNP-2007-(31-10-2011)-DRAWINGS.pdf

2426-KOLNP-2007-(31-10-2011)-FORM 1.pdf

2426-KOLNP-2007-(31-10-2011)-FORM 2.pdf

2426-KOLNP-2007-(31-10-2011)-FORM 3.pdf

2426-KOLNP-2007-(31-10-2011)-OTHERS.pdf

2426-KOLNP-2007-ABSTRACT 1.1.pdf

2426-KOLNP-2007-AMANDED CLAIMS.pdf

2426-KOLNP-2007-CORRESPONDENCE OTHERS 1.2.pdf

2426-KOLNP-2007-CORRESPONDENCE OTHERS 1.3.pdf

2426-KOLNP-2007-CORRESPONDENCE.pdf

2426-KOLNP-2007-DESCRIPTION (COMPLETE) 1.1.pdf

2426-KOLNP-2007-DRAWINGS 1.1.pdf

2426-KOLNP-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

2426-KOLNP-2007-FORM 1-1.1.pdf

2426-KOLNP-2007-FORM 2-1.1.pdf

2426-KOLNP-2007-FORM 26.pdf

2426-KOLNP-2007-FORM 3-1.1.pdf

2426-KOLNP-2007-OTHERS 1.1.pdf

2426-KOLNP-2007-OTHERS 1.2.pdf

2426-KOLNP-2007-PETITION UNDER RULE 137.pdf

2426-KOLNP-2007-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

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Patent Number

252233

Indian Patent Application Number

2426/KOLNP/2007

PG Journal Number

18/2012

Publication Date

04-May-2012

Grant Date

02-May-2012

Date of Filing

02-Jul-2007

Name of Patentee

EMITEC GESELLSCHAFT FUR EMISSIONSTECHNOLOGIE MBH

Applicant Address

HAUPTSTRASSE 128, 53797 LOHMAR

Inventors:

#	Inventor's Name	Inventor's Address
1	HIRTH, PETER	BIRKENWEG 57, 53127 BONN
2	HARIG, THOMAS	RATHAUSSTRASSE 14 43819 NEUNKIRCHEN- SEELSCHEID
3	BRUCK, ROLF	FROBELSTRASSE 12, 51429 BERGISCH GLADBACH

PCT International Classification Number

F01N 3/022

PCT International Application Number

PCT/EP2006/000717

PCT International Filing date

2006-01-06

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	102005000890.9	2005-01-07	Germany