Title of Invention	A HONEYCOMB BODY FOR MOBILE EXHAUST GAS AFTERTREATMENT AND A METHOD OF PRODUCING IT
Abstract	A honeycomb body (1) comprising a housing (2) and a plurality of layers (3) with a curved profile (4) and a predetermined length (5), which each comprise at least one at least partially structured metal foil (6), so as to form a multiplicity of passages (7) with a passage cross section (8), in which the majority of the layers (3) are designed to have different lengths (5) than one another. The invention also proposes a process for producing a honeycomb body and a use of the honeycomb body.

Title of Invention

A HONEYCOMB BODY FOR MOBILE EXHAUST GAS AFTERTREATMENT AND A METHOD OF PRODUCING IT

Abstract

A honeycomb body (1) comprising a housing (2) and a plurality of layers (3) with a curved profile (4) and a predetermined length (5), which each comprise at least one at least partially structured metal foil (6), so as to form a multiplicity of passages (7) with a passage cross section (8), in which the majority of the layers (3) are designed to have different lengths (5) than one another. The invention also proposes a process for producing a honeycomb body and a use of the honeycomb body.

Full Text	Production of, in particular large, honeycomb bodies for mobile exhaust-gas aftertreatment The present invention relates to a honeycomb body comprising a housing and a plurality of layers with a curved profile and a predetermined length, wherein the layers each comprise at least one at least partially structured metal foil, so as to form a multiplicity of passages with a passage cross section. The invention also proposes a process for producing a honeycomb body and a particular use of the honeycomb body. Honeycomb bodies of this type are used in particular for exhaust- gas aftertreatment in the automotive industry. Metallic honeycomb bodies of this type are preferably constructed using metal foils and used as support bodies for a catalytically active, adsorbing, oxidizing, reducing and/or further coating in exhaust systems of mobile internal combustion engines. On account of the extreme thermal and dynamic stresses which are present in such applications, it is particularly important to ensure a permanent connection between the individual metal foils and also between the metal foils and the housing. The metal foils are usually connected to one another and to the housing by a joining technique, in particular by sintering, brazing and/or welding. For this purpose, it is necessary for sufficient contact locations between the adjacent metal foils and between the metal foils and the housing to be present at the desired connection locations such that these contact locations can serve as a basis for the connection. To ensure stable connection of the metal foils to the housing, EP 0 245 737 B1 reveals that by shortening the corrugated sheet-metal layers by a predetermined distance compared to the smooth sheet-metal layers, it is possible to ensure that the ends of the sheet-metal layers touch and nestle against the tubular casing. - 2 - This nestling action makes it easier to effect a secure connection to the tubular casing with various touching angles. WO 2005/033484 has disclosed a process for producing a metallic honeycomb body with a layer length difference, in which a plurality of smooth metal foils and at least partially structured metal foils are arranged in a housing, the smooth metal foils having a first length and the structured metal foils having a second length, and the difference between the first length and the second length being selected as a function of a prestress. In view of the fact that during the conventional production of honeycomb bodies of this type the structured metal foils are deformed if they are pressed into the housing under a considerable prestress, the production method proposed in WO 2005/033484 is supposed to nonetheless to ensure that the ends of the metal foils are in uniform contact. In particular in a configuration of honeycomb bodies in which the metal foils are not wound up helically or are only layered, however, zones of greater deformation and less successful formation of connections by joining techniques have occurred during production. This is attributable, for example, to the asymmetrical form of winding of the metal foils. However, in particular with a view to series production, there is a risk of unevenly configured honeycomb bodies which have regions with more or less strongly deformed passage cross sections. This, by way of example, also influences the flow properties of an exhaust gas flowing through a honeycomb body of this type, so that under certain circumstances it could be necessary to align the honeycomb body to the flow profile of the exhaust gas. Moreover, further difficulties have arisen in particular when producing large honeycomb bodies, for - 3 - example for stationary use or for trucks. In particular, the handling of large sets of metal foils and of the forces produced during winding have proven difficult to control in a reliable process. As the diameter increases, the effects of an asymmetry during winding and/or the forces which are required for winding also become considerably higher. If it is not possible to wind or twist the metal foils to form a body which substantially corresponds to the contour of the inner region of the housing, high forces have to be applied to force the body into the housing; under certain circumstances, on account of the housings having ever thinner walls, the housing itself may even be deformed, which can lead to problems with integration in an exhaust system. Working on this basis, it is an object of the present invention to reduce or resolve the problems which have been outlined in connection with the prior art. It is intended in particular to specify a honeycomb body which is distinguished by a particularly uniform configuration of the passage cross sections, with in particular defined connection points being realized between the individual metal foils or between the metal foils and the housing. Furthermore, it is intended to specify a process for producing a honeycomb body of this type, with which it is possible in particular to produce large honeycomb bodies with little force in a reliable process. It is preferentially also intended to specify how apparatuses for winding such large honeycomb bodies can be adapted in order to allow even series production of honeycomb bodies of a constant quality. Finally, it is also intended to specify uses for a honeycomb body of this type. These objects are achieved by the honeycomb body having the features of patent claim 1 and the process for producing a honeycomb body having the features of patent claim 6. Particularly preferred configurations - 4 - are given in the dependent patent claims. It should be noted that the features listed individually in the patent claims can be combined with one another in any technologically appropriate way so as to provide further configurations of the invention. The honeycomb body according to the invention comprises a housing and a plurality of layers with a curved profile and a predetermined length, which each comprise at least one at least partially structured metal foil, so as to form a multiplicity of passages with a passage cross section, in which the majority of the layers are designed with different lengths than one another. A "layer" is configured in such a way that it forms at least a series of passages. This can be achieved, for example, by stacking structured metal foils, one smooth and one structured metal foil, two smooth metal foils with one structured metal foil arranged between them. The structure of the metal foil, which is preferably formed over the entire length of a layer, is usually similar to a sine wave, but may also be of zig-zag and/or square-wave configuration. As a result of the metal foils bearing against one another and of the provision of the structure, passages are formed, which are generally delimited by at least two of the metal foils. As a result, a passage cross section of the passages is defined. The passage cross section in particular has a semicircle-like, bell-like, rectangular, omega-shaped or similar configuration. The configuration of the passage cross section is preferably identical over the entire length. The metal foil is preferably made from a high- temperature-resistant, corrosion-resistant material. In particular a steel material with high aluminum and chromium contents is suitable for this purpose. The metal foils are preferably designed with a thickness in the range of less than 0.15 mm, in particular in a - 5 - range from 0.02 mm to 0.12 mm. In principle, the metal foil can also be designed with openings, apertures or a microstructure (guide surfaces, studs, etc.) superimposed on the structure. It is now proposed that the majority of the layers be designed with different lengths than one another. This means first all that the honeycomb body is formed by at least two layers. It is preferable for the honeycomb body to include a plurality of layers numbering more than 5, 10 or even 20. The layers can be arranged in several groups and then intertwined, in which case all the layers of one group in each case follow a profile that is different from that of the further group(s). It is also possible for all the layers to be stacked on top of one another and thereby deformed to produce the honeycomb structure, so that substantially the same profile results for all the layers. In this case, it is possible to form different winding types or shapes of the profile of the layers, in particular a spiral shape, an S shape, a V shape or a W shape. The type of winding can be selected, for example, taking into account the configuration of the housing as well; in principle, any housing cross section can be used, in particular a round, oval, polygonal, triangular or similar housing cross section. A feature common to all these types of winding is that the layers are arranged with a curved profile, the layer preferably being completely curved, i.e. not having any flat sections. However, the curvature of the profile is irrelevant; by way of example, it is possible for different radii of curvature, concave and/or convex sections, turning locations, saddle locations or the like to be present. This curved profile and if appropriate also the cross- sectional shape of the housing now lead to different degrees of deformation of the layers, so that after the winding, intertwining and/or twisting they form an outer contour which, for the same length of layer, does - 6 - not correspond to the housing cross section. Therefore, the production process was hitherto configured in such a way that the layers had a length which was such that the entire housing cross section was reliably filled, with the projecting section of the layer being deformed during pressing into the housing. The invention for the first time deviates from this procedure, since it is proposed here that the layer length for each individual layer be selected in such a way that the ends of the layers, prior to insertion into the housing, form a contour which substantially corresponds to the housing cross section. In view of the fact that in this case a multiplicity of different housing cross sections can be considered, at least the majority of the layers are designed with layer lengths that are different from one another. It is particularly preferable for all the lengths of the layers arranged in the honeycomb body to be designed with a different length. A concept of this type has not hitherto been considered, since considerable difficulties were to be expected in the handling of the different layers and their positioning with respect to one another. However, it has now been discovered that in particular in the case of large honeycomb bodies which, for example, have a diameter of greater than 150 mm or even greater than 200 mm (as are used in particular in trucks as well as in stationary applications), the integration of the metal foils in a housing can be carried out in a reliable process and using relatively low forces, so that there is virtually no deformation to the structure comprising the metal foil, and therefore a very homogeneous honeycomb structure is formed. In addition to improved flow properties on the part of the exhaust gas passing through a honeycomb body of this type, this in particular also leads to a defined contact between the individual metal foils and between the metal foils and the housing, so that - 7 - connections by a joining technique can be formed in a reliable process and in a locally defined manner. This in turn leads to the thermal expansion properties of the metal foils with respect to one another and between metal foil and the housing, which are of importance in particular for large honeycomb bodies, being set deliberately and in a long-term manner. According to a further configuration of the honeycomb body, the passage cross section of at least 95% of the passages is identical. Very particularly preferably, at least 98% of all the passage cross sections are identical, and a special preference is given to a configuration in which all the passages which are completely delimited only by metal foils have the same passage cross section. This is made possible in particular on account of the different lengths of the layers, which are selected in such a way that the layer ends, without significant deformation, simply finish at the housing, in which case it is possible to dispense with the need for smooth end sections of the structured metal foils to ensure that they nestle against the housing, yet contact with the housing is nonetheless ensured. It should be noted by way of explanation at this point that the passage cross section can also be regarded as "identical" if standard manufacturing tolerances are present. Furthermore, it is proposed that the majority of the metal foils are designed with different lengths than one another. This is to be understood as meaning in particular that the metal foils within a layer can also be designed to be of different lengths from one another. In this case the length of the layer results from the mean value of the lengths of the metal foils in one layer. In view of the fact that the layers have a height in the range of less than 10 mm and in particular less than 5 mm, with this configuration of the honeycomb body adaptation is effected even with - 8 - such slight differing curvatures of the adjacent metal foils. For certain applications, it may be advantageous for the housing to have at least one curved housing section and for at least some of the layers to end at this at least one curved housing section. This is to be understood in particular as meaning that the layers butt against the curved housing section but predominantly do not nestle over a certain housing section (for example more than 10 mm or 6 mm) . The process of the ends of the layers nestling against the housing, which has been deployed hitherto, leads to increased consumption of material and greater deformation of the outer passages. As a result of the provision of different lengths of layers, it is possible for the layers to end directly at the housing even with this curved configuration. Furthermore, it is advantageous if the layers form touching points with the housing, distances to adjacent touching points being designed to be unequal for at least some of the touching points. The uneven configuration of the distances between adjacent touching points is substantially also influenced by the winding type or the shape of the profile of the layers. This type of configuration of the touching points in particular leads to a homogeneous radial prestress and a reduction in the passage deformations in the edge region. Finally, the invention also proposes a honeycomb body in which the metal foils form contact locations with one another and with the housing, which contact locations together determine an overall contact region, with a cohesive connection being formed for at most 50% of the overall contact region. Preference is given to configurations in which at most only 3 0% or even only - 9 - at most 10% of the overall contact region is formed with cohesive connections. In particular in the case of the configuration of rectilinear passages running substantially parallel to one another, a multiplicity of virtually linear contact locations between the individual metal foils or between the metal foil and the housing are formed. These contact locations are fundamentally available for forming connections by a joining technique between the abovementioned components, with the overall set of these contact locations being referred to here as the "overall contact region". If the contact locations are, for example, substantially linear in form, the overall contact region results as the sum of the linear contact locations, so that ultimately it would be possible to specify an overall length. In addition, it should also be noted that the contact locations between the individual metal foils represent by far the majority, with the proportion formed by contact locations between the metal foils and the housing being, for example, in a range of less than 10%, in particular approximately 5%. It is now proposed that at most 50% of this overall contact region is actually formed by a cohesive connection, while the remainder of the overall contact region is not used for this purpose, but rather the loose contact between the components allows sliding or different thermal expansion properties. The cohesive connection is preferably formed as a soldered connection generated by a brazing process. The arrangement of the cohesive connections with respect to the honeycomb body can be selected as desired taking into account the thermal stressing and the materials used for the honeycomb body. In particular, the cohesive connections can be provided independently of one another and in a locally defined manner in the radial, axial and any other desired direction of the - 10 - honeycomb body. By way of example, just an end-side attachment of all the contact locations over the first few millimeters (e.g. 6, 8 or 10 mm) is preferable over the entire cross section of the honeycomb body, for which purpose, preferably, a solder strip is placed between the individual layers and/or between the layers and the housing during production. In this way, depending on the size of the honeycomb body, it is even possible for less than 3 0% of the overall contact region actually to be formed by a cohesive connection. It is also possible for accurate application of solder to the desired contact locations to be carried out by means of printing methods (application in drop form, for example what is known as drop-on-demand, bubble- jet, continuous-jet processes). In which case in particular with processes of this type it is even possible for less than 10% of the overall contact region to be formed by a cohesive connection. A further aspect of the invention proposes a process for producing a honeycomb body, comprising at least the following steps: a) shaping a plurality of layers of a predetermined length, these layers in each case comprising at least one at least partially structured metal foil, so as to form a multiplicity of passages having a passage cross section, and the majority of the layers being designed with different lengths than one another; b) stacking at least some of the plurality of layers on top of one another so as to form at least one stack; c) deforming the at least one stack so as to produce a curved profile of the layers; d) arranging the at least one stack in a housing. The process is suitable in particular for producing a honeycomb body as described above in accordance with the invention. - 11 - With regard to step a) , it should be noted that the shaping of layers may encompass in particular the cutting of metal foils, the structuring of metal foils, the stacking of metal foils on top of one another, the aligning of metal foils with respect to one another, the temporary connection of metal foils (e.g. by a bonding agent or adhesive) and other operations. In particular, step a) forms at least one row of passages arranged next to one another, each passage preferentially being delimited partially by a structured metal foil and partially by a smooth metal foil. Then, in accordance with b) , at least some of the shaped layers are stacked on top of one another. The number of stacks can preferably always be selected in the range from 1 to 6. Next, in accordance with step c) , the stacks are deformed. This can, for example, also take place in a plurality of stages, so that, for example, first of all each stack is deformed, in particular bent or turned in, separately, then the stacks are positioned with respect to one another and jointly wound, intertwined, bent or deformed in a similar way. After step c) , the stacks or the layers contained therein are preferably formed with a curved profile over their entire length, in particular regions of different radii of curvature being present. Finally, in accordance with step d) , the stacks are arranged in a housing. Before and/or after the stack has been arranged in the housing, it is possible for additives to be applied in and/or on the honeycomb body, with the additives in particular comprising means for forming cohesive connections (such as in this case for example binders, bonding agents, bonding restrictors (e.g. wax, oil), solder, etc.). - 12 - Furthermore, it is proposed that step b) takes place in such a way that the plurality of layers of a stack are arranged offset with respect to one another. This means, for example, that adjacent layers may be designed not only with different lengths but may also be arranged offset with respect to one another, i.e. do not form one common terminating plane. The style and nature of the offset is in turn dependent on the configuration of the housing and the structures of the metal foils. Under certain circumstances, it may also be advantageous for even the metal foils within one layer to be arranged offset with respect to one another. It is also advantageous for the plurality of layers to be magnetically fixed at least during step a) or b). On account of the different lengths of the layers and/or of the offset realized between the individual layers, handling of the stacks or layers presents problems. It is now proposed that the layers or metal foils or stacks be held in defined positions with respect to one another by means of at least one magnet. This allows transporting and/or storage of the layers or stacks even without the use of a bonding agent, in which Case the handling units used for this purpose can be used for different layers and/or honeycomb bodies simultaneously. The layers can be fixed by magnetic grippers, magnetic underlays and the like. As has already been indicated, step c) can be carried out in at least two stages, in which case it is advantageous that at least one of the following actions is carried out: folding over the at least one stack; aligning a plurality of stacks with respect to one another; intertwining a plurality of stacks; deforming the at least one stack using a first tool as far as a first extent and deforming the at - 13 - least one stack further using at least one second tool. The implementation of the abovementioned actions is advantageous in particular in the case of honeycomb bodies which ultimately have a diameter of greater than 150 mm, in particular greater than 200 mm. In the two- stage configuration of the winding process, particularly gentle production can be realized with only slight deformation of the passages and/or using relatively low forces. This is to be explained below for a honeycomb body which has been wound helically and is formed (albeit not necessarily) with a plurality of layers of different lengths. For this case, the following procedure could be advantageous: shaping a layer which comprises at least one at least partially structured metal foil, so as to form a multiplicity of passages, fixing the layer in an end region using a gripping unit; rotating the gripping unit, so that the layer arranges itself around the gripping unit and forms a honeycomb body of increasing diameter; determining that the honeycomb body has reached a first extent; activating means comprising at least one second tool or guide means or drive means; further placing the stack against the existing circumferential surface of the honeycomb body until it has reached the desired diameter. In this context, reference is made in particular to the supplementary explanations given in connection with Fig. 11. The reaching of the first extent can be determined on the basis of the rotational angle of the gripping unit and/or directly at the honeycomb body. - 14 - According to a further advantageous configuration of the process, step c) is used to form a cylindrical honeycomb structure with a diameter, the honeycomb structure having a change in diameter of at most 5% before and after being arranged in the housing. It is preferable for the change in diameter to be in a range of less than 2% (corresponding for example to a diameter deviation of less than 3 mm). This illustrates the accuracy with which a honeycomb structure having a predetermined outer contour can be formed by the process according to the invention, so that this outer contour is very close to the housing cross section. Making the contour of the honeycomb structure so close to the housing cross section allows all the edge regions (in the case of housings which are not round) to be filled uniformly while at the same time avoiding deformation of passages in the edge region. Nevertheless, reliable contact between the ends of the layers and the housing, for example to form connections by a joining technique, is ensured. According to a further configuration of the process, a deformation of the honeycomb body over its circumference is carried out as step e) . This means in other words that after the stack has been arranged in the housing, a further, minor, plastic deformation of the honeycomb body is additionally carried out, known as "calibration". For this purpose, by way of example, radially inwardly directed pressure is exerted uniformly over the periphery of the housing, so that the housing is calibrated to a desired diameter or a predetermined roundness or other shape accuracy. At the same time, "relaxing" or "relieving" of the layers or metal foils in the interior can take place, so that once again reliable contact between the ends of the layers and the housing is ensured. Furthermore, it is proposed that, as step f) , regionally delimited cohesive connections are produced - 15 - at least between the metal foils or at least between a metal foil and the housing, the regions being designed differently in various planes of the honeycomb body. It is preferable to produce cohesive connections both between the individual metal foils and to the housing. The term "regionally delimited connections" is to be understood in particular as meaning that the honeycomb body has regions with cohesive connections and without cohesive connections to compensate for different thermal expansion properties. The regions may be large- area or large-volume parts of the honeycomb body, for example a star-shaped zone or a peripheral zone toward the housing, but it is equally possible for a region to be restricted to a certain number of passages, for example fewer than 10 passages arranged adjacent to one another. Regionally delimited cohesive connections may also be present in the direction of a passage, so that the metal foils forming the passage are not cohesively connected to one another over the entire length of the passage. Once again, it is preferable to use a configuration of the honeycomb body in which, for example, at most 10% of the overall contact region has a cohesive connection, in particular only at most 5%. The cohesive connections are formed differently in different planes. The planes may be considered both in the direction of the passages and transversely with respect thereto. In principle, there may also be planes in which no cohesive connections are arranged. Preference is given to a honeycomb body as described above in accordance with the invention or a honeycomb body which has been produced by the process described in accordance with the invention being used in combination with an exhaust system of an automobile. Very and particularly preferably, the invention proposes a use for exhaust systems of trucks, in which case the honeycomb body has a diameter of greater than 150 mm. - 16 - The invention and its technical background are explained in more detail below with reference to the figures. The figures also show particularly preferred exemplary embodiments of the invention, although without being restricted to these embodiments. Furthermore, it should be noted that the figures are schematic in form and accordingly are not generally suitable for representing size ratios. In the drawings: Fig. 1 shows an exemplary embodiment of the production of a layer for a honeycomb body; Fig. 2 shows the transporting of a layer; Fig. 3 shows a stack of a plurality of layers; Fig. 4 shows a honeycomb body with wound layers in a housing; Fig. 5 shows a diagram showing the layer lengths of a stack; Fig. 6 shows an illustration representing the touching points between the layers and the housing; Fig. 7 shows an illustration representing the technical problems involved in a known process for producing a honeycomb body; Fig. 8 shows a perspective view of a variant embodiment of the production process for a honeycomb body; Fig. 9 shows a detail of a honeycomb body; Fig. 10 shows an illustration representing regions with cohesive connections in a honeycomb body; - 17 - Fig. 11 shows an apparatus for the two-stage winding of a honeycomb body; and Fig. 12 shows an exhaust system with a honeycomb body. Figs. 1 to 4 illustrate a process for producing a honeycomb body; Fig. 1 shows the shaping of layers, Fig. 2 shows the transporting of the layer to a stack, which is then built up in accordance with Fig. 3, and finally Fig. 4 illustrates the arrangement of two stacks with a curved profile within a housing. The apparatus illustrated in Fig. 1 comprises a smooth- strip delivery mechanism 26, in which a smooth metal foil 6 is rolled up for example on a coiler. The smooth strip delivery mechanism 26 delivers a smooth metal foil 6 on the one hand to a corrugated strip installation 27, in which a structured metal foil 6 is produced from the smooth metal foil 6 (for example by corrugation rolling). Since to produce a layer 3 in the example illustrated one structured metal foil 6 and one smooth metal foil 6 are combined with one another, the smooth strip delivery mechanism 26 delivers the smooth metal foil 6 via a conveyor belt 28 which is designed with a magnet 29 to fix the smooth metal foil 6 in place. The two metal foils 6 are arranged on top of one another and together are fed to a cutting apparatus 47 which forms layers 3 of the desired length from the endless metal foils 6. As illustrated in Figs. 2 and 3, the layer 3 formed in this way, comprising a fully structured metal foil 6 and a fully smooth metal foil 6, is now arranged, by means of a gripper 3 0 which preferably likewise has means for magnetically fixing the layer 3 in place, so as to form a stack 15. A plurality of layers 3 (at least in some cases having different lengths 5 than one another) are now stacked individually on top of one another, with an offset 31 between the layers 3 - 18 - positioned adjacent to one another additionally being realized. In the variant embodiment illustrated, seven (7) layers 3 are combined to form a stack 15. Two of the stacks 15 are then first of all separately turned over, so that two ends of the layers 3 are positioned on one side. Then, the two stacks 15 are intertwined and introduced into the housing 2 illustrated in Fig. 4, so as to form the desired honeycomb body 1. In this way, the honeycomb body 1 comprises the housing 2 and the honeycomb structure 19 formed by the layers 3, the layers 3 being arranged with a curved profile 4 therein. The ends of the layers 3 butt directly against the housing 2 over the circumference 21, in particular including the curved housing section 9. The touching points 10 of the layers 3 in the region of the housing section 2 are preferably suitable for the production of connections by a joining technique between the layers 3 and the housing 2. To illustrate the honeycomb structure 19, Fig. 4 also partially illustrates the structure with passages 7. Fig. 5 shows an exemplary embodiment for the different lengths 5 of the layers 3 of a honeycomb body 1, which is configured with an S-shaped profile 4 of the layers 3, as in Fig. 4. The length 5 of the layers 3 is plotted on the ordinate, and the number of layers 3 of a stack 15 is plotted on the abscissa. It can be seen from the illustration that no layer 3 has two adjacent layers 3 of the same length 5 as itself, and in particular none of the adjacent layers 3 have the same length 5 as a specific layer 3. It can also be seen that more than 20 mm, 50 mm or even 100 mm can lie between the maximum length 5 and the minimum length 5 of a layer 3 within a stack 15. If the stack 15 illustrated in Fig. 5 is now wound in an S-shape, touching points 10 are formed at the housing 2, as illustrated in Fig. 6. It is noticeable here that the touching points 10 are not formed at a constant - 19 - distance 11 from one another, but rather at a varying distance 11 from one another. Fig. 7 illustrates, by way of example, a shaping error which has occurred in the known production method. In the left-hand illustration in Fig. 7, a stack 15 comprising a plurality of layers 3 is used, the layers 3 being designed of uniform length 5. After the winding operation, however, the result is a honeycomb structure 19 which has an oval contour. Should it be desired to introduce this honeycomb structure 19 into a cylindrical housing 2, particular forces have to act on the projecting deformation regions 32, with the passages formed there being deformed. This is avoided by the process according to the invention and the honeycomb body according to the invention. Fig. 8 illustrates a variant embodiment of a production line for layers 3 of a predetermined length 5 which each comprise at least one at least partially structured metal foil 6. In this case, a corrugated strip 34 is produced by means of a corrugated strip installation 27 and transported simultaneously with a smooth strip 33, which is being transported in the direction of advance 37 by means of a conveyor belt 28, to a cutting apparatus 47. The cutting apparatus 47 severs layers 3 from the corrugated strip 34 and smooth strip 33 simultaneously, and these layers are then connected in an intermediate tray 35. The cut layer 3 is transferred from the intermediate tray 35 to the stacking tray 36 by means of a gripper 30, which can move in different directions and can if appropriate also rotate; this transfer can be performed with the desired alignment with respect to the adjacent layer 3, for example with a specific offset. The stack 15 formed in this way can finally be transferred by the gripper 3 0 to a further processing station, the gripper 3 0 preferably being designed with means for magnetically fixing the layers 3 in place. - 20 - Fig. 9 shows a detail of a honeycomb body 1 which comprises a multiplicity of layers 3 arranged in a housing 2. The layers 3 are each formed by one smooth and one corrugated metal foil 6, so as to form passages 7 with a predetermined passage cross section 8. The passage cross section 8 of all the passages 7 which are formed entirely by metal foils 6 are substantially identical. It can also be seen from Fig. 9 that there are regions comprising connections 14. In the variant embodiment of the honeycomb body 1 illustrated, all the corrugated metal foils 6 are designed with a connection 14, which is a brazed connection, at the contact locations 12 with the housing 2. Although Fig. 9 does not show any connections 14 with regard to the contact locations 12 between the smooth metal foils 6 and the housing 2, these contact locations 12 may nevertheless at least in some cases be designed with a similar connection 14. Regionally delimited connections 14 are also provided in contact locations 12 between the metal foils 6 in the interior of the honeycomb structure 19. It can be seen that different layers 3 are designed with different numbers of connections 14, which may be based on regular intervals or may be variable. This regional formation of connections 14 by a joining technique enables the honeycomb body 1 to expand and contract relatively freely as a result of fluctuating thermal stresses, both in the direction of the profile of the passages and in the direction of the profile of the layers 3, both axially and radially with respect to the honeycomb body 1. Fig. 10 illustrates a somewhat greater regional extent of connections 14 formed by a joining technique. In the zone of an end side 48, the honeycomb body 1 illustrated has a first region 22 comprising connections 14, this region 22 being arranged - 21 - substantially in the vicinity of the housing 2 and widening radially inward in a sub-zone. This end-side region 22, however, does not extend over the entire depth of the honeycomb body 1 in the direction of the axis 49, but rather only over part of this depth. In addition, further regions 22 with connections 14 are formed in inner zones of the honeycomb body 1. In the illustration presented in Fig. 10, two planes 23 perpendicular to the axis 49 are indicated, the regions 22 being formed differently in the planes 23 of the honeycomb body 1 illustrated. Fig. 11 shows an apparatus for helical winding up at least one layer 3 to form a honeycomb body 1. The layer 3 is guided from a layer reservoir 41 to a mandrel 44, which fixes one end of the layer 3. The mandrel 44 is part of a first tool 16 which allows a rotation 43 of the mandrel 44 about its own axis. In a first stage of the winding process, the layer reservoir 41 is in a fixed position and the honeycomb body 1 is formed exclusively on the basis of the rotation 43 of the mandrel 44. When a predetermined extent 17, for example an extent 17 in the region of 50 mm, is reached, a second tool 18 is switched on in order to build up the honeycomb body 1 further until it reaches its ultimately desired diameter 20. Fig. 11 shows two (2) further second tools 18, which can be used individually in combination, on their own or to assist the first tool 16. The second tool 18 explained above comprises a ram 39 which is brought into engagement or contact with one of the end sides 48 of the honeycomb structure 19, for example by a lifting movement 40. This second tool 18 is preferably designed with a drive 38, so that the ram 39 can rotate synchronously with the mandrel 44. In this way, the forces required for rotation of the honeycomb structure are distributed between a plurality of drives 3 8 or over a larger area of the end side(s) 48 of the - 22 - honeycomb structure 19, so that even as the extent 17 becomes greater a uniform arrangement of the layer 3 around the honeycomb structure 19 which has already been formed is ensured. The ram 39 may also be provided as part of the base or in the circumferential region of the mandrel 44. Furthermore, it is also possible for the ram 39 to be designed with a plurality of recesses which, for example, engage in the passages 7 of the honeycomb structure 19 which has already been formed. Furthermore, it is also possible to use means with an equivalent action, such as further pins, magnetic plates, etc., for a large-volume force introduction space. Furthermore, it is also possible to use the layer reservoir 41 itself to form a second tool 18. In this case, the layer reservoir 41 can change its position relative to the honeycomb structure 19 formed, in particular can circulate around it, in which case the radius toward the mandrel 44 can be varied. It is in this way possible to describe a path 42 in which the layer reservoir 41 (similarly to a spiral) runs around the honeycomb structure 19 at an increasing distance and thus brings the layer 3 into contact. This second tool 18 may also be designed with a drive 38 in order to execute this path 42 and/or to realize rotation of the layer reservoir 41 itself. It is preferable for the first and second tools 16 and 18 to operate in a controlled way which is suitably adapted to one another. In addition, it is possible to provide means for determining the current extent 17, the positioning of the ram 39 and/or the production of relative movements of the second tools 18 with respect to the first tool 16. Fig. 12 illustrates the preferred use of a honeycomb body 1 described here. The figure illustrates an automobile 25 in the form of a truck with an internal - 23 - combustion engine which is designed as a diesel engine 45. The exhaust gases produced in the engine 45 are fed via an exhaust system 24, in the direction of flow 46, to a plurality of honeycomb bodies 1 of different functions before the purified exhaust gases are ultimately released to atmosphere. In automobiles 25 of this type, in particular honeycomb bodies 1 with a diameter of greater than 150 mm are used. The honeycomb bodies 1 described here and processes for producing them are especially suitable in particular for these honeycomb bodies 1. - 24 - List of designations 1 Honeycomb body 2 Housing 3 Layer 4 Profile 5 Length 6 Metal foil 7 Passage 8 Passage cross section 9 Housing section 10 Touching point 11 Distance 12 Contact location 13 Overall contact region 14 Connection 15 Stack 16 First tool 17 Extent 18 Second tool 19 Honeycomb structure 20 Diameter 21 Circumference 22 Region 23 Plane 24 Exhaust system 25 Automobile 26 Smooth strip delivery mechanism 27 Corrugated strip installation 28 Conveyor belt 29 Magnet 3 0 Gripper 31 Offset 32 Deformation region 33 Smooth strip 34 Corrugated strip 35 Intermediate tray 36 Stacking tray 37 Direction of advance - 25 - 3 8 Drive 3 9 Ram 40 Lifting movement 41 Layer reservoir 42 Path 43 Rotation 44 Mandrel 4 5 Engine 46 Direction of flow 4 7 Cutting apparatus 4 8 End side 49 Axis - 26 - Patent Claims 1. A honeycomb body (1) comprising a housing (2) and a plurality of layers (3) with a curved profile (4) and a predetermined length (5) , which each comprise at least one at least partially structured metal foil (6), so as to form a multiplicity of passages (7) with a passage cross section (8), in which the majority of the layers (3) are designed to have different lengths (5) than one another. 2. The honeycomb body (1) as claimed in claim 1, characterized in that the passage cross section (8) of at least 95% of the passages (7) is identical. 3. The honeycomb body (1) as claimed in claim 1 or 2, characterized in that the majority of the metal foils (6) are designed with different lengths (5) than one another. 4. The honeycomb body (1) as claimed in one of the preceding claims, characterized in that the layers (3) form touching points (10) with the housing (2), distances (11) to adjacent touching points (10) being designed to be unequal for at least some of the touching points (10). 5. The honeycomb body (1) as claimed in one of the preceding claims, characterized in that the metal foils (6) form contact locations (12) with one another and with the housing (2) , which contact locations (12) together determine an overall contact region (13), with a cohesive connection (14) being formed for at most 50% of the overall contact region (13). 6. A process for producing a honeycomb body (1), comprising at least the following steps: a) shaping a plurality of layers (3) of a predetermined length (5) , these layers in each - 27 - case comprising at least one at least partially structured metal foil (6) , so as to form a multiplicity of passages (7) having a passage cross section (8) , and the majority of the layers (3) being designed with different lengths (5) than one another; b) stacking at least some of the plurality of layers (3) on top of one another so as to form at least one stack (15); c) deforming the at least one stack (15) so as to produce a curved profile (4) of the layers (3) ; d) arranging the at least one stack (15) in a housing (2) . 7. The process as claimed in claim 6, in which step b) is carried out in such a way that the plurality of layers (3) of a stack (15) are arranged offset with respect to one another. 8. The process as claimed in claim 6 or 7, in which the plurality of layers (3) are magnetically fixed at least during step a) or b). 9. The process as claimed in one of claims 6 to 8, in which step c) is carried out in at least two stages. 10. The process as claimed in claim 9, in which at least one of the following actions is carried out: folding over the at least one stack (15); aligning a plurality of stacks (15) with respect to one another; intertwining a plurality of stacks (15); deforming the at least one stack (15) using a first tool (16) as far as a first extent (17) and deforming the at least one stack (15) further using at least one second tool (18). 11. The process as claimed in one of claims 6 to 10, in which step c) is used to form a cylindrical - 28 - honeycomb structure (19) with a diameter (20), the honeycomb structure (19) having a change in diameter (20) of at most 5% before and after being arranged in the housing (2) . 12. The process as claimed in one of claims 6 to 11, in which a deformation of the honeycomb body (1) over its circumference (21) is carried out as step e). 13. The process as claimed in one of claims 6 to 12, in which regionally delimited cohesive connections (14) are produced at least between the metal foils (6) or at least between a metal foil (6) and the housing (2), the regions (22) being designed differently in various planes (23) of the honeycomb body (1). 14. The use of the honeycomb body as claimed in claims 1 to 5 or of a honeycomb body (1) produced by the process as claimed in claims 6 to 13 in combination with an exhaust system (24) of an automobile (25). A honeycomb body (1) comprising a housing (2) and a plurality of layers (3) with a curved profile (4) and a predetermined length (5), which each comprise at least one at least partially structured metal foil (6), so as to form a multiplicity of passages (7) with a passage cross section (8), in which the majority of the layers (3) are designed to have different lengths (5) than one another. The invention also proposes a process for producing a honeycomb body and a use of the honeycomb body.

Full Text

Production of, in particular large, honeycomb bodies
for mobile exhaust-gas aftertreatment
The present invention relates to a honeycomb body
comprising a housing and a plurality of layers with a
curved profile and a predetermined length, wherein the
layers each comprise at least one at least partially
structured metal foil, so as to form a multiplicity of
passages with a passage cross section. The invention
also proposes a process for producing a honeycomb body
and a particular use of the honeycomb body. Honeycomb
bodies of this type are used in particular for exhaust-
gas aftertreatment in the automotive industry.
Metallic honeycomb bodies of this type are preferably
constructed using metal foils and used as support
bodies for a catalytically active, adsorbing,
oxidizing, reducing and/or further coating in exhaust
systems of mobile internal combustion engines. On
account of the extreme thermal and dynamic stresses
which are present in such applications, it is
particularly important to ensure a permanent connection
between the individual metal foils and also between the
metal foils and the housing. The metal foils are
usually connected to one another and to the housing by
a joining technique, in particular by sintering,
brazing and/or welding. For this purpose, it is
necessary for sufficient contact locations between the
adjacent metal foils and between the metal foils and
the housing to be present at the desired connection
locations such that these contact locations can serve
as a basis for the connection.
To ensure stable connection of the metal foils to the
housing, EP 0 245 737 B1 reveals that by shortening the
corrugated sheet-metal layers by a predetermined
distance compared to the smooth sheet-metal layers, it
is possible to ensure that the ends of the sheet-metal
layers touch and nestle against the tubular casing.

- 2 -
This nestling action makes it easier to effect a secure
connection to the tubular casing with various touching
angles.
WO 2005/033484 has disclosed a process for producing a
metallic honeycomb body with a layer length difference,
in which a plurality of smooth metal foils and at least
partially structured metal foils are arranged in a
housing, the smooth metal foils having a first length
and the structured metal foils having a second length,
and the difference between the first length and the
second length being selected as a function of a
prestress. In view of the fact that during the
conventional production of honeycomb bodies of this
type the structured metal foils are deformed if they
are pressed into the housing under a considerable
prestress, the production method proposed in
WO 2005/033484 is supposed to nonetheless to ensure
that the ends of the metal foils are in uniform
contact.
In particular in a configuration of honeycomb bodies in
which the metal foils are not wound up helically or are
only layered, however, zones of greater deformation and
less successful formation of connections by joining
techniques have occurred during production. This is
attributable, for example, to the asymmetrical form of
winding of the metal foils. However, in particular with
a view to series production, there is a risk of
unevenly configured honeycomb bodies which have regions
with more or less strongly deformed passage cross
sections. This, by way of example, also influences the
flow properties of an exhaust gas flowing through a
honeycomb body of this type, so that under certain
circumstances it could be necessary to align the
honeycomb body to the flow profile of the exhaust gas.
Moreover, further difficulties have arisen in
particular when producing large honeycomb bodies, for

- 3 -
example for stationary use or for trucks. In
particular, the handling of large sets of metal foils
and of the forces produced during winding have proven
difficult to control in a reliable process. As the
diameter increases, the effects of an asymmetry during
winding and/or the forces which are required for
winding also become considerably higher. If it is not
possible to wind or twist the metal foils to form a
body which substantially corresponds to the contour of
the inner region of the housing, high forces have to be
applied to force the body into the housing; under
certain circumstances, on account of the housings
having ever thinner walls, the housing itself may even
be deformed, which can lead to problems with
integration in an exhaust system.
Working on this basis, it is an object of the present
invention to reduce or resolve the problems which have
been outlined in connection with the prior art. It is
intended in particular to specify a honeycomb body
which is distinguished by a particularly uniform
configuration of the passage cross sections, with in
particular defined connection points being realized
between the individual metal foils or between the metal
foils and the housing. Furthermore, it is intended to
specify a process for producing a honeycomb body of
this type, with which it is possible in particular to
produce large honeycomb bodies with little force in a
reliable process. It is preferentially also intended to
specify how apparatuses for winding such large
honeycomb bodies can be adapted in order to allow even
series production of honeycomb bodies of a constant
quality. Finally, it is also intended to specify uses
for a honeycomb body of this type.
These objects are achieved by the honeycomb body having
the features of patent claim 1 and the process for
producing a honeycomb body having the features of
patent claim 6. Particularly preferred configurations

- 4 -
are given in the dependent patent claims. It should be
noted that the features listed individually in the
patent claims can be combined with one another in any
technologically appropriate way so as to provide
further configurations of the invention.
The honeycomb body according to the invention comprises
a housing and a plurality of layers with a curved
profile and a predetermined length, which each comprise
at least one at least partially structured metal foil,
so as to form a multiplicity of passages with a passage
cross section, in which the majority of the layers are
designed with different lengths than one another.
A "layer" is configured in such a way that it forms at
least a series of passages. This can be achieved, for
example, by stacking structured metal foils, one smooth
and one structured metal foil, two smooth metal foils
with one structured metal foil arranged between them.
The structure of the metal foil, which is preferably
formed over the entire length of a layer, is usually
similar to a sine wave, but may also be of zig-zag
and/or square-wave configuration. As a result of the
metal foils bearing against one another and of the
provision of the structure, passages are formed, which
are generally delimited by at least two of the metal
foils. As a result, a passage cross section of the
passages is defined. The passage cross section in
particular has a semicircle-like, bell-like,
rectangular, omega-shaped or similar configuration. The
configuration of the passage cross section is
preferably identical over the entire length.
The metal foil is preferably made from a high-
temperature-resistant, corrosion-resistant material. In
particular a steel material with high aluminum and
chromium contents is suitable for this purpose. The
metal foils are preferably designed with a thickness in
the range of less than 0.15 mm, in particular in a

- 5 -
range from 0.02 mm to 0.12 mm. In principle, the metal
foil can also be designed with openings, apertures or a
microstructure (guide surfaces, studs, etc.)
superimposed on the structure.
It is now proposed that the majority of the layers be
designed with different lengths than one another. This
means first all that the honeycomb body is formed by at
least two layers. It is preferable for the honeycomb
body to include a plurality of layers numbering more
than 5, 10 or even 20. The layers can be arranged in
several groups and then intertwined, in which case all
the layers of one group in each case follow a profile
that is different from that of the further group(s). It
is also possible for all the layers to be stacked on
top of one another and thereby deformed to produce the
honeycomb structure, so that substantially the same
profile results for all the layers. In this case, it is
possible to form different winding types or shapes of
the profile of the layers, in particular a spiral
shape, an S shape, a V shape or a W shape. The type of
winding can be selected, for example, taking into
account the configuration of the housing as well; in
principle, any housing cross section can be used, in
particular a round, oval, polygonal, triangular or
similar housing cross section. A feature common to all
these types of winding is that the layers are arranged
with a curved profile, the layer preferably being
completely curved, i.e. not having any flat sections.
However, the curvature of the profile is irrelevant; by
way of example, it is possible for different radii of
curvature, concave and/or convex sections, turning
locations, saddle locations or the like to be present.
This curved profile and if appropriate also the cross-
sectional shape of the housing now lead to different
degrees of deformation of the layers, so that after the
winding, intertwining and/or twisting they form an
outer contour which, for the same length of layer, does

- 6 -
not correspond to the housing cross section. Therefore,
the production process was hitherto configured in such
a way that the layers had a length which was such that
the entire housing cross section was reliably filled,
with the projecting section of the layer being deformed
during pressing into the housing.
The invention for the first time deviates from this
procedure, since it is proposed here that the layer
length for each individual layer be selected in such a
way that the ends of the layers, prior to insertion
into the housing, form a contour which substantially
corresponds to the housing cross section. In view of
the fact that in this case a multiplicity of different
housing cross sections can be considered, at least the
majority of the layers are designed with layer lengths
that are different from one another. It is particularly
preferable for all the lengths of the layers arranged
in the honeycomb body to be designed with a different
length. A concept of this type has not hitherto been
considered, since considerable difficulties were to be
expected in the handling of the different layers and
their positioning with respect to one another.
However, it has now been discovered that in particular
in the case of large honeycomb bodies which, for
example, have a diameter of greater than 150 mm or even
greater than 200 mm (as are used in particular in
trucks as well as in stationary applications), the
integration of the metal foils in a housing can be
carried out in a reliable process and using relatively
low forces, so that there is virtually no deformation
to the structure comprising the metal foil, and
therefore a very homogeneous honeycomb structure is
formed. In addition to improved flow properties on the
part of the exhaust gas passing through a honeycomb
body of this type, this in particular also leads to a
defined contact between the individual metal foils and
between the metal foils and the housing, so that

- 7 -
connections by a joining technique can be formed in a
reliable process and in a locally defined manner. This
in turn leads to the thermal expansion properties of
the metal foils with respect to one another and between
metal foil and the housing, which are of importance in
particular for large honeycomb bodies, being set
deliberately and in a long-term manner.
According to a further configuration of the honeycomb
body, the passage cross section of at least 95% of the
passages is identical. Very particularly preferably, at
least 98% of all the passage cross sections are
identical, and a special preference is given to a
configuration in which all the passages which are
completely delimited only by metal foils have the same
passage cross section. This is made possible in
particular on account of the different lengths of the
layers, which are selected in such a way that the layer
ends, without significant deformation, simply finish at
the housing, in which case it is possible to dispense
with the need for smooth end sections of the structured
metal foils to ensure that they nestle against the
housing, yet contact with the housing is nonetheless
ensured. It should be noted by way of explanation at
this point that the passage cross section can also be
regarded as "identical" if standard manufacturing
tolerances are present.
Furthermore, it is proposed that the majority of the
metal foils are designed with different lengths than
one another. This is to be understood as meaning in
particular that the metal foils within a layer can also
be designed to be of different lengths from one
another. In this case the length of the layer results
from the mean value of the lengths of the metal foils
in one layer. In view of the fact that the layers have
a height in the range of less than 10 mm and in
particular less than 5 mm, with this configuration of
the honeycomb body adaptation is effected even with

- 8 -
such slight differing curvatures of the adjacent metal
foils.
For certain applications, it may be advantageous for
the housing to have at least one curved housing section
and for at least some of the layers to end at this at
least one curved housing section. This is to be
understood in particular as meaning that the layers
butt against the curved housing section but
predominantly do not nestle over a certain housing
section (for example more than 10 mm or 6 mm) . The
process of the ends of the layers nestling against the
housing, which has been deployed hitherto, leads to
increased consumption of material and greater
deformation of the outer passages. As a result of the
provision of different lengths of layers, it is
possible for the layers to end directly at the housing
even with this curved configuration.
Furthermore, it is advantageous if the layers form
touching points with the housing, distances to adjacent
touching points being designed to be unequal for at
least some of the touching points. The uneven
configuration of the distances between adjacent
touching points is substantially also influenced by the
winding type or the shape of the profile of the layers.
This type of configuration of the touching points in
particular leads to a homogeneous radial prestress and
a reduction in the passage deformations in the edge
region.
Finally, the invention also proposes a honeycomb body
in which the metal foils form contact locations with
one another and with the housing, which contact
locations together determine an overall contact region,
with a cohesive connection being formed for at most 50%
of the overall contact region. Preference is given to
configurations in which at most only 3 0% or even only

- 9 -
at most 10% of the overall contact region is formed
with cohesive connections.
In particular in the case of the configuration of
rectilinear passages running substantially parallel to
one another, a multiplicity of virtually linear contact
locations between the individual metal foils or between
the metal foil and the housing are formed. These
contact locations are fundamentally available for
forming connections by a joining technique between the
abovementioned components, with the overall set of
these contact locations being referred to here as the
"overall contact region". If the contact locations are,
for example, substantially linear in form, the overall
contact region results as the sum of the linear contact
locations, so that ultimately it would be possible to
specify an overall length. In addition, it should also
be noted that the contact locations between the
individual metal foils represent by far the majority,
with the proportion formed by contact locations between
the metal foils and the housing being, for example, in
a range of less than 10%, in particular approximately
5%.
It is now proposed that at most 50% of this overall
contact region is actually formed by a cohesive
connection, while the remainder of the overall contact
region is not used for this purpose, but rather the
loose contact between the components allows sliding or
different thermal expansion properties. The cohesive
connection is preferably formed as a soldered
connection generated by a brazing process. The
arrangement of the cohesive connections with respect to
the honeycomb body can be selected as desired taking
into account the thermal stressing and the materials
used for the honeycomb body. In particular, the
cohesive connections can be provided independently of
one another and in a locally defined manner in the
radial, axial and any other desired direction of the

- 10 -
honeycomb body. By way of example, just an end-side
attachment of all the contact locations over the first
few millimeters (e.g. 6, 8 or 10 mm) is preferable over
the entire cross section of the honeycomb body, for
which purpose, preferably, a solder strip is placed
between the individual layers and/or between the layers
and the housing during production. In this way,
depending on the size of the honeycomb body, it is even
possible for less than 3 0% of the overall contact
region actually to be formed by a cohesive connection.
It is also possible for accurate application of solder
to the desired contact locations to be carried out by
means of printing methods (application in drop form,
for example what is known as drop-on-demand, bubble-
jet, continuous-jet processes). In which case in
particular with processes of this type it is even
possible for less than 10% of the overall contact
region to be formed by a cohesive connection.
A further aspect of the invention proposes a process
for producing a honeycomb body, comprising at least the
following steps:
a) shaping a plurality of layers of a predetermined
length, these layers in each case comprising at
least one at least partially structured metal
foil, so as to form a multiplicity of passages
having a passage cross section, and the majority
of the layers being designed with different
lengths than one another;
b) stacking at least some of the plurality of layers
on top of one another so as to form at least one
stack;
c) deforming the at least one stack so as to produce
a curved profile of the layers;
d) arranging the at least one stack in a housing.
The process is suitable in particular for producing a
honeycomb body as described above in accordance with
the invention.

- 11 -
With regard to step a) , it should be noted that the
shaping of layers may encompass in particular the
cutting of metal foils, the structuring of metal foils,
the stacking of metal foils on top of one another, the
aligning of metal foils with respect to one another,
the temporary connection of metal foils (e.g. by a
bonding agent or adhesive) and other operations. In
particular, step a) forms at least one row of passages
arranged next to one another, each passage
preferentially being delimited partially by a
structured metal foil and partially by a smooth metal
foil.
Then, in accordance with b) , at least some of the
shaped layers are stacked on top of one another. The
number of stacks can preferably always be selected in
the range from 1 to 6.
Next, in accordance with step c) , the stacks are
deformed. This can, for example, also take place in a
plurality of stages, so that, for example, first of all
each stack is deformed, in particular bent or turned
in, separately, then the stacks are positioned with
respect to one another and jointly wound, intertwined,
bent or deformed in a similar way. After step c) , the
stacks or the layers contained therein are preferably
formed with a curved profile over their entire length,
in particular regions of different radii of curvature
being present.
Finally, in accordance with step d) , the stacks are
arranged in a housing. Before and/or after the stack
has been arranged in the housing, it is possible for
additives to be applied in and/or on the honeycomb
body, with the additives in particular comprising means
for forming cohesive connections (such as in this case
for example binders, bonding agents, bonding
restrictors (e.g. wax, oil), solder, etc.).

- 12 -
Furthermore, it is proposed that step b) takes place in
such a way that the plurality of layers of a stack are
arranged offset with respect to one another. This
means, for example, that adjacent layers may be
designed not only with different lengths but may also
be arranged offset with respect to one another, i.e. do
not form one common terminating plane. The style and
nature of the offset is in turn dependent on the
configuration of the housing and the structures of the
metal foils. Under certain circumstances, it may also
be advantageous for even the metal foils within one
layer to be arranged offset with respect to one
another.
It is also advantageous for the plurality of layers to
be magnetically fixed at least during step a) or b). On
account of the different lengths of the layers and/or
of the offset realized between the individual layers,
handling of the stacks or layers presents problems. It
is now proposed that the layers or metal foils or
stacks be held in defined positions with respect to one
another by means of at least one magnet. This allows
transporting and/or storage of the layers or stacks
even without the use of a bonding agent, in which Case
the handling units used for this purpose can be used
for different layers and/or honeycomb bodies
simultaneously. The layers can be fixed by magnetic
grippers, magnetic underlays and the like.
As has already been indicated, step c) can be carried
out in at least two stages, in which case it is
advantageous that at least one of the following actions
is carried out:
folding over the at least one stack;
aligning a plurality of stacks with respect to one
another;
intertwining a plurality of stacks;
deforming the at least one stack using a first
tool as far as a first extent and deforming the at

- 13 -
least one stack further using at least one second
tool.
The implementation of the abovementioned actions is
advantageous in particular in the case of honeycomb
bodies which ultimately have a diameter of greater than
150 mm, in particular greater than 200 mm. In the two-
stage configuration of the winding process,
particularly gentle production can be realized with
only slight deformation of the passages and/or using
relatively low forces.
This is to be explained below for a honeycomb body
which has been wound helically and is formed (albeit
not necessarily) with a plurality of layers of
different lengths. For this case, the following
procedure could be advantageous:
shaping a layer which comprises at least one at
least partially structured metal foil, so as to
form a multiplicity of passages,
fixing the layer in an end region using a gripping
unit;
rotating the gripping unit, so that the layer
arranges itself around the gripping unit and forms
a honeycomb body of increasing diameter;
determining that the honeycomb body has reached a
first extent;
activating means comprising at least one second
tool or guide means or drive means;
further placing the stack against the existing
circumferential surface of the honeycomb body
until it has reached the desired diameter.
In this context, reference is made in particular to the
supplementary explanations given in connection with
Fig. 11. The reaching of the first extent can be
determined on the basis of the rotational angle of the
gripping unit and/or directly at the honeycomb body.

- 14 -
According to a further advantageous configuration of
the process, step c) is used to form a cylindrical
honeycomb structure with a diameter, the honeycomb
structure having a change in diameter of at most 5%
before and after being arranged in the housing. It is
preferable for the change in diameter to be in a range
of less than 2% (corresponding for example to a
diameter deviation of less than 3 mm). This illustrates
the accuracy with which a honeycomb structure having a
predetermined outer contour can be formed by the
process according to the invention, so that this outer
contour is very close to the housing cross section.
Making the contour of the honeycomb structure so close
to the housing cross section allows all the edge
regions (in the case of housings which are not round)
to be filled uniformly while at the same time avoiding
deformation of passages in the edge region.
Nevertheless, reliable contact between the ends of the
layers and the housing, for example to form connections
by a joining technique, is ensured.
According to a further configuration of the process, a
deformation of the honeycomb body over its
circumference is carried out as step e) . This means in
other words that after the stack has been arranged in
the housing, a further, minor, plastic deformation of
the honeycomb body is additionally carried out, known
as "calibration". For this purpose, by way of example,
radially inwardly directed pressure is exerted
uniformly over the periphery of the housing, so that
the housing is calibrated to a desired diameter or a
predetermined roundness or other shape accuracy. At the
same time, "relaxing" or "relieving" of the layers or
metal foils in the interior can take place, so that
once again reliable contact between the ends of the
layers and the housing is ensured.
Furthermore, it is proposed that, as step f) ,
regionally delimited cohesive connections are produced

- 15 -
at least between the metal foils or at least between a
metal foil and the housing, the regions being designed
differently in various planes of the honeycomb body. It
is preferable to produce cohesive connections both
between the individual metal foils and to the housing.
The term "regionally delimited connections" is to be
understood in particular as meaning that the honeycomb
body has regions with cohesive connections and without
cohesive connections to compensate for different
thermal expansion properties. The regions may be large-
area or large-volume parts of the honeycomb body, for
example a star-shaped zone or a peripheral zone toward
the housing, but it is equally possible for a region to
be restricted to a certain number of passages, for
example fewer than 10 passages arranged adjacent to one
another. Regionally delimited cohesive connections may
also be present in the direction of a passage, so that
the metal foils forming the passage are not cohesively
connected to one another over the entire length of the
passage. Once again, it is preferable to use a
configuration of the honeycomb body in which, for
example, at most 10% of the overall contact region has
a cohesive connection, in particular only at most 5%.
The cohesive connections are formed differently in
different planes. The planes may be considered both in
the direction of the passages and transversely with
respect thereto. In principle, there may also be planes
in which no cohesive connections are arranged.
Preference is given to a honeycomb body as described
above in accordance with the invention or a honeycomb
body which has been produced by the process described
in accordance with the invention being used in
combination with an exhaust system of an automobile.
Very and particularly preferably, the invention
proposes a use for exhaust systems of trucks, in which
case the honeycomb body has a diameter of greater than
150 mm.

- 16 -
The invention and its technical background are
explained in more detail below with reference to the
figures. The figures also show particularly preferred
exemplary embodiments of the invention, although
without being restricted to these embodiments.
Furthermore, it should be noted that the figures are
schematic in form and accordingly are not generally
suitable for representing size ratios. In the drawings:
Fig. 1 shows an exemplary embodiment of the production
of a layer for a honeycomb body;
Fig. 2 shows the transporting of a layer;
Fig. 3 shows a stack of a plurality of layers;
Fig. 4 shows a honeycomb body with wound layers in a
housing;
Fig. 5 shows a diagram showing the layer lengths of a
stack;
Fig. 6 shows an illustration representing the touching
points between the layers and the housing;
Fig. 7 shows an illustration representing the
technical problems involved in a known process
for producing a honeycomb body;
Fig. 8 shows a perspective view of a variant
embodiment of the production process for a
honeycomb body;
Fig. 9 shows a detail of a honeycomb body;
Fig. 10 shows an illustration representing regions with
cohesive connections in a honeycomb body;

- 17 -
Fig. 11 shows an apparatus for the two-stage winding of
a honeycomb body; and
Fig. 12 shows an exhaust system with a honeycomb body.
Figs. 1 to 4 illustrate a process for producing a
honeycomb body; Fig. 1 shows the shaping of layers,
Fig. 2 shows the transporting of the layer to a stack,
which is then built up in accordance with Fig. 3, and
finally Fig. 4 illustrates the arrangement of two
stacks with a curved profile within a housing.
The apparatus illustrated in Fig. 1 comprises a smooth-
strip delivery mechanism 26, in which a smooth metal
foil 6 is rolled up for example on a coiler. The smooth
strip delivery mechanism 26 delivers a smooth metal
foil 6 on the one hand to a corrugated strip
installation 27, in which a structured metal foil 6 is
produced from the smooth metal foil 6 (for example by
corrugation rolling). Since to produce a layer 3 in the
example illustrated one structured metal foil 6 and one
smooth metal foil 6 are combined with one another, the
smooth strip delivery mechanism 26 delivers the smooth
metal foil 6 via a conveyor belt 28 which is designed
with a magnet 29 to fix the smooth metal foil 6 in
place. The two metal foils 6 are arranged on top of one
another and together are fed to a cutting apparatus 47
which forms layers 3 of the desired length from the
endless metal foils 6.
As illustrated in Figs. 2 and 3, the layer 3 formed in
this way, comprising a fully structured metal foil 6
and a fully smooth metal foil 6, is now arranged, by
means of a gripper 3 0 which preferably likewise has
means for magnetically fixing the layer 3 in place, so
as to form a stack 15. A plurality of layers 3 (at
least in some cases having different lengths 5 than one
another) are now stacked individually on top of one
another, with an offset 31 between the layers 3

- 18 -
positioned adjacent to one another additionally being
realized. In the variant embodiment illustrated, seven
(7) layers 3 are combined to form a stack 15.
Two of the stacks 15 are then first of all separately
turned over, so that two ends of the layers 3 are
positioned on one side. Then, the two stacks 15 are
intertwined and introduced into the housing 2
illustrated in Fig. 4, so as to form the desired
honeycomb body 1. In this way, the honeycomb body 1
comprises the housing 2 and the honeycomb structure 19
formed by the layers 3, the layers 3 being arranged
with a curved profile 4 therein. The ends of the layers
3 butt directly against the housing 2 over the
circumference 21, in particular including the curved
housing section 9. The touching points 10 of the layers
3 in the region of the housing section 2 are preferably
suitable for the production of connections by a joining
technique between the layers 3 and the housing 2. To
illustrate the honeycomb structure 19, Fig. 4 also
partially illustrates the structure with passages 7.
Fig. 5 shows an exemplary embodiment for the different
lengths 5 of the layers 3 of a honeycomb body 1, which
is configured with an S-shaped profile 4 of the layers
3, as in Fig. 4. The length 5 of the layers 3 is
plotted on the ordinate, and the number of layers 3 of
a stack 15 is plotted on the abscissa. It can be seen
from the illustration that no layer 3 has two adjacent
layers 3 of the same length 5 as itself, and in
particular none of the adjacent layers 3 have the same
length 5 as a specific layer 3. It can also be seen
that more than 20 mm, 50 mm or even 100 mm can lie
between the maximum length 5 and the minimum length 5
of a layer 3 within a stack 15. If the stack 15
illustrated in Fig. 5 is now wound in an S-shape,
touching points 10 are formed at the housing 2, as
illustrated in Fig. 6. It is noticeable here that the
touching points 10 are not formed at a constant

- 19 -
distance 11 from one another, but rather at a varying
distance 11 from one another.
Fig. 7 illustrates, by way of example, a shaping error
which has occurred in the known production method. In
the left-hand illustration in Fig. 7, a stack 15
comprising a plurality of layers 3 is used, the layers
3 being designed of uniform length 5. After the winding
operation, however, the result is a honeycomb structure
19 which has an oval contour. Should it be desired to
introduce this honeycomb structure 19 into a
cylindrical housing 2, particular forces have to act on
the projecting deformation regions 32, with the
passages formed there being deformed. This is avoided
by the process according to the invention and the
honeycomb body according to the invention.
Fig. 8 illustrates a variant embodiment of a production
line for layers 3 of a predetermined length 5 which
each comprise at least one at least partially
structured metal foil 6. In this case, a corrugated
strip 34 is produced by means of a corrugated strip
installation 27 and transported simultaneously with a
smooth strip 33, which is being transported in the
direction of advance 37 by means of a conveyor belt 28,
to a cutting apparatus 47. The cutting apparatus 47
severs layers 3 from the corrugated strip 34 and smooth
strip 33 simultaneously, and these layers are then
connected in an intermediate tray 35. The cut layer 3
is transferred from the intermediate tray 35 to the
stacking tray 36 by means of a gripper 30, which can
move in different directions and can if appropriate
also rotate; this transfer can be performed with the
desired alignment with respect to the adjacent layer 3,
for example with a specific offset. The stack 15 formed
in this way can finally be transferred by the gripper
3 0 to a further processing station, the gripper 3 0
preferably being designed with means for magnetically
fixing the layers 3 in place.

- 20 -
Fig. 9 shows a detail of a honeycomb body 1 which
comprises a multiplicity of layers 3 arranged in a
housing 2. The layers 3 are each formed by one smooth
and one corrugated metal foil 6, so as to form passages
7 with a predetermined passage cross section 8. The
passage cross section 8 of all the passages 7 which are
formed entirely by metal foils 6 are substantially
identical.
It can also be seen from Fig. 9 that there are regions
comprising connections 14. In the variant embodiment of
the honeycomb body 1 illustrated, all the corrugated
metal foils 6 are designed with a connection 14, which
is a brazed connection, at the contact locations 12
with the housing 2. Although Fig. 9 does not show any
connections 14 with regard to the contact locations 12
between the smooth metal foils 6 and the housing 2,
these contact locations 12 may nevertheless at least in
some cases be designed with a similar connection 14.
Regionally delimited connections 14 are also provided
in contact locations 12 between the metal foils 6 in
the interior of the honeycomb structure 19. It can be
seen that different layers 3 are designed with
different numbers of connections 14, which may be based
on regular intervals or may be variable. This regional
formation of connections 14 by a joining technique
enables the honeycomb body 1 to expand and contract
relatively freely as a result of fluctuating thermal
stresses, both in the direction of the profile of the
passages and in the direction of the profile of the
layers 3, both axially and radially with respect to the
honeycomb body 1.
Fig. 10 illustrates a somewhat greater regional extent
of connections 14 formed by a joining technique. In the
zone of an end side 48, the honeycomb body 1
illustrated has a first region 22 comprising
connections 14, this region 22 being arranged

- 21 -
substantially in the vicinity of the housing 2 and
widening radially inward in a sub-zone. This end-side
region 22, however, does not extend over the entire
depth of the honeycomb body 1 in the direction of the
axis 49, but rather only over part of this depth. In
addition, further regions 22 with connections 14 are
formed in inner zones of the honeycomb body 1. In the
illustration presented in Fig. 10, two planes 23
perpendicular to the axis 49 are indicated, the regions
22 being formed differently in the planes 23 of the
honeycomb body 1 illustrated.
Fig. 11 shows an apparatus for helical winding up at
least one layer 3 to form a honeycomb body 1. The layer
3 is guided from a layer reservoir 41 to a mandrel 44,
which fixes one end of the layer 3. The mandrel 44 is
part of a first tool 16 which allows a rotation 43 of
the mandrel 44 about its own axis. In a first stage of
the winding process, the layer reservoir 41 is in a
fixed position and the honeycomb body 1 is formed
exclusively on the basis of the rotation 43 of the
mandrel 44. When a predetermined extent 17, for example
an extent 17 in the region of 50 mm, is reached, a
second tool 18 is switched on in order to build up the
honeycomb body 1 further until it reaches its
ultimately desired diameter 20.
Fig. 11 shows two (2) further second tools 18, which
can be used individually in combination, on their own
or to assist the first tool 16. The second tool 18
explained above comprises a ram 39 which is brought
into engagement or contact with one of the end sides 48
of the honeycomb structure 19, for example by a lifting
movement 40. This second tool 18 is preferably designed
with a drive 38, so that the ram 39 can rotate
synchronously with the mandrel 44. In this way, the
forces required for rotation of the honeycomb structure
are distributed between a plurality of drives 3 8 or
over a larger area of the end side(s) 48 of the

- 22 -
honeycomb structure 19, so that even as the extent 17
becomes greater a uniform arrangement of the layer 3
around the honeycomb structure 19 which has already
been formed is ensured. The ram 39 may also be provided
as part of the base or in the circumferential region of
the mandrel 44. Furthermore, it is also possible for
the ram 39 to be designed with a plurality of recesses
which, for example, engage in the passages 7 of the
honeycomb structure 19 which has already been formed.
Furthermore, it is also possible to use means with an
equivalent action, such as further pins, magnetic
plates, etc., for a large-volume force introduction
space.
Furthermore, it is also possible to use the layer
reservoir 41 itself to form a second tool 18. In this
case, the layer reservoir 41 can change its position
relative to the honeycomb structure 19 formed, in
particular can circulate around it, in which case the
radius toward the mandrel 44 can be varied. It is in
this way possible to describe a path 42 in which the
layer reservoir 41 (similarly to a spiral) runs around
the honeycomb structure 19 at an increasing distance
and thus brings the layer 3 into contact. This second
tool 18 may also be designed with a drive 38 in order
to execute this path 42 and/or to realize rotation of
the layer reservoir 41 itself.
It is preferable for the first and second tools 16 and
18 to operate in a controlled way which is suitably
adapted to one another. In addition, it is possible to
provide means for determining the current extent 17,
the positioning of the ram 39 and/or the production of
relative movements of the second tools 18 with respect
to the first tool 16.
Fig. 12 illustrates the preferred use of a honeycomb
body 1 described here. The figure illustrates an
automobile 25 in the form of a truck with an internal

- 23 -
combustion engine which is designed as a diesel engine
45. The exhaust gases produced in the engine 45 are fed
via an exhaust system 24, in the direction of flow 46,
to a plurality of honeycomb bodies 1 of different
functions before the purified exhaust gases are
ultimately released to atmosphere. In automobiles 25 of
this type, in particular honeycomb bodies 1 with a
diameter of greater than 150 mm are used. The honeycomb
bodies 1 described here and processes for producing
them are especially suitable in particular for these
honeycomb bodies 1.

- 24 -
List of designations
1 Honeycomb body
2 Housing
3 Layer
4 Profile
5 Length

6 Metal foil
7 Passage
8 Passage cross section
9 Housing section
10 Touching point
11 Distance
12 Contact location
13 Overall contact region
14 Connection
15 Stack
16 First tool
17 Extent
18 Second tool
19 Honeycomb structure
20 Diameter
21 Circumference
22 Region
23 Plane
24 Exhaust system
25 Automobile
26 Smooth strip delivery mechanism
27 Corrugated strip installation
28 Conveyor belt
29 Magnet
3 0 Gripper
31 Offset
32 Deformation region
33 Smooth strip
34 Corrugated strip
35 Intermediate tray
36 Stacking tray
37 Direction of advance

- 25 -
3 8 Drive
3 9 Ram
40 Lifting movement
41 Layer reservoir
42 Path
43 Rotation
44 Mandrel
4 5 Engine
46 Direction of flow
4 7 Cutting apparatus
4 8 End side
49 Axis

- 26 -
Patent Claims
1. A honeycomb body (1) comprising a housing (2) and
a plurality of layers (3) with a curved profile (4) and
a predetermined length (5) , which each comprise at
least one at least partially structured metal foil (6),
so as to form a multiplicity of passages (7) with a
passage cross section (8), in which the majority of the
layers (3) are designed to have different lengths (5)
than one another.
2. The honeycomb body (1) as claimed in claim 1,
characterized in that the passage cross section (8) of
at least 95% of the passages (7) is identical.
3. The honeycomb body (1) as claimed in claim 1 or 2,
characterized in that the majority of the metal foils
(6) are designed with different lengths (5) than one
another.
4. The honeycomb body (1) as claimed in one of the
preceding claims, characterized in that the layers (3)
form touching points (10) with the housing (2),
distances (11) to adjacent touching points (10) being
designed to be unequal for at least some of the
touching points (10).
5. The honeycomb body (1) as claimed in one of the
preceding claims, characterized in that the metal foils
(6) form contact locations (12) with one another and
with the housing (2) , which contact locations (12)
together determine an overall contact region (13), with
a cohesive connection (14) being formed for at most 50%
of the overall contact region (13).
6. A process for producing a honeycomb body (1),
comprising at least the following steps:
a) shaping a plurality of layers (3) of a
predetermined length (5) , these layers in each

- 27 -
case comprising at least one at least partially
structured metal foil (6) , so as to form a
multiplicity of passages (7) having a passage
cross section (8) , and the majority of the layers
(3) being designed with different lengths (5) than
one another;
b) stacking at least some of the plurality of layers
(3) on top of one another so as to form at least
one stack (15);
c) deforming the at least one stack (15) so as to
produce a curved profile (4) of the layers (3) ;
d) arranging the at least one stack (15) in a housing
(2) .

7. The process as claimed in claim 6, in which step
b) is carried out in such a way that the plurality of
layers (3) of a stack (15) are arranged offset with
respect to one another.
8. The process as claimed in claim 6 or 7, in which
the plurality of layers (3) are magnetically fixed at
least during step a) or b).
9. The process as claimed in one of claims 6 to 8, in
which step c) is carried out in at least two stages.
10. The process as claimed in claim 9, in which at
least one of the following actions is carried out:
folding over the at least one stack (15);
aligning a plurality of stacks (15) with respect
to one another;
intertwining a plurality of stacks (15);
deforming the at least one stack (15) using a
first tool (16) as far as a first extent (17) and
deforming the at least one stack (15) further
using at least one second tool (18).
11. The process as claimed in one of claims 6 to 10,
in which step c) is used to form a cylindrical

- 28 -
honeycomb structure (19) with a diameter (20), the
honeycomb structure (19) having a change in diameter
(20) of at most 5% before and after being arranged in
the housing (2) .
12. The process as claimed in one of claims 6 to 11,
in which a deformation of the honeycomb body (1) over
its circumference (21) is carried out as step e).
13. The process as claimed in one of claims 6 to 12,
in which regionally delimited cohesive connections (14)
are produced at least between the metal foils (6) or at
least between a metal foil (6) and the housing (2), the
regions (22) being designed differently in various
planes (23) of the honeycomb body (1).
14. The use of the honeycomb body as claimed in
claims 1 to 5 or of a honeycomb body (1) produced by
the process as claimed in claims 6 to 13 in combination
with an exhaust system (24) of an automobile (25).

A honeycomb body (1) comprising a housing (2) and a
plurality of layers (3) with a curved profile (4) and a
predetermined length (5), which each comprise at least
one at least partially structured metal foil (6), so as
to form a multiplicity of passages (7) with a passage
cross section (8), in which the majority of the layers
(3) are designed to have different lengths (5) than one
another. The invention also proposes a process for
producing a honeycomb body and a use of the honeycomb
body.

A HONEYCOMB BODY FOR MOBILE EXHAUST GAS AFTERTREATMENT AND A METHOD OF PRODUCING IT

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