Catalytic converter body with reduced wall thickness on an inflow side and process for producing a catalytic converter body

A catalytic converter body includes at least one honeycomb body, in particular with a catalytically active coating, having a multiplicity of axial passages through which a fluid can flow. The passages have passage walls ending in a common plane perpendicular to a flow direction. The passage walls each have average wall thicknesses and starting sections with reduced wall thicknesses, at least in the vicinity of the end surface. A process for producing a catalytic converter body includes forming at least one honeycomb body with a catalytically active coating and a multiplicity of axial passages through which a fluid can flow. The passages have walls delimited in a common plane perpendicular to a flow direction. Each of the walls has an average wall thickness and starting sections with reduced wall thicknesses at least in the vicinity of an end surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a sectional plan view of a catalytic converter body according to a preferred embodiment of the invention. The catalytic converter body includes a honeycomb body 1 having sheet-metal layers which are intertwined in involute form. In this case, the catalytic converter body includes alternating layers of substantially smooth metal sheets and corrugated metal sheets, a coating 2 (shown in FIGS. 3A, 3B , 3 C, 4 A and 4 B) of the honeycomb body 1 , which contains a catalytically active material, and preferably a housing that surrounds the honeycomb body 1 . In the honeycomb body 1 , the intertwined metal sheets form respective passage walls 4 of a multiplicity of axial passages 3 through which a fluid can flow. FIG. 2 shows a sectional side view of the catalytic converter body of FIG. 1 . The intertwined metal sheets which form the honeycomb body 1 are disposed in a housing that is shown in section with hatching. The catalytic converter body 1 is constructed as a honeycomb body and includes a multiplicity of axial passages 3 through which a fluid can flow and the respective passage walls 4 of which each have substantially average wall thicknesses over their axial extent. According to the invention, in the region or vicinity of an end surface of the catalytic converter body, the respective passage walls 4 have starting sections 6 with reduced wall thicknesses. In each case, the starting sections 6 start from the end surface 5 and have an extent in the axial direction which is indicated by a dashed line in FIG. 2 . FIG. 3A shows an enlarged side view of the area of the end surface 5 of the catalytic converter body with the corresponding starting sections 6 of the respective passage walls 4 according to a first preferred embodiment of the invention. The axial passages 3 through which a fluid can flow are in each case formed between the individual passage walls 4 . The passage walls 4 substantially have an average wall thickness over their axial longitudinal extent. This wall thickness results from the actual honeycomb body 1 and the coating 2 , which is present in each case in FIG. 3 on both sides of the actual honeycomb body 1 . This coating preferably is formed of a substantially porous wash coat of A 1 2 O 3 , in which the catalytically active material is, for example, Pt and/or Rh. In this first preferred embodiment, the starting sections 6 according to the invention are formed by the passage walls 4 not having any coating 2 on these sections. In the case of the catalytic converter body shown in FIG. 3 A, this applies to both sides of the honeycomb body 1 . However, it is also conceivable for only one side in each case to remain uncoated in the region of the starting sections 6 or for only some of the respective starting sections 6 to remain uncoated. The size relationships, in particular the ratios of the mean wall thicknesses of the respective passage walls 4 to the widths of the respective passages 3 , are not to scale in FIG. 3A or the other figures. FIG. 3B shows a plan view of a section taken along a line IIIB-IIIB in FIG. 3A . The figure shows a section of the passage walls 4 in the region of the honeycomb body in which the passage walls 4 are each provided with the coating 2 on both sides of the honeycomb body 1 and each have an average wall thickness. By contrast, FIG. 3C shows a plan view of a section taken along a line IIIC-IIIC through the catalytic converter body shown in FIG. 3A . The section IIIC-IIIC runs in the region of the respective starting sections 6 of the respective passage walls 4 . In contradistinction to the section shown in FIG. 3 B, it can be seen from the section shown in FIG. 3C that the wall thickness in the region of the starting sections 6 is significantly less than the average wall thickness as illustrated in FIG. 3B . In the first preferred embodiment shown in accordance with FIGS. 3A, 3B and 3 C, the reduced wall thickness of the passage walls 4 in the region of the end surface 5 is achieved by the fact that the starting sections 6 of the passage walls 4 do not have any coating 2 . This can be seen in particular in the section IIIC-IIIC of FIG. 3C . FIG. 4A shows an enlarged side view of the area of an end surface 5 of the catalytic converter body according to the invention with a second preferred embodiment of the starting sections 6 according to the invention, which have reduced wall thicknesses as compared to the average wall thicknesses of the passage walls 4 . In this case too, the catalyst carrier body 1 is substantially constructed as a honeycomb body with a coating 2 which contains a catalytically active material and with a multiplicity of axial passages 3 through which a fluid can flow. With regard to the composition of the coating, the same statements as those which have already been made in connection with FIG. 3A apply. In this second embodiment of the starting sections 6 , the passage walls 4 are constructed to taper substantially to a point toward the end surface 5 in the region or vicinity of the starting sections. FIG. 4A shows a decreasing thickness of the coating 2 of the honeycomb body 1 looking upward from the lower part of the starting sections 6 . In each case partial sections of the honeycomb body 1 taper to a point in the upper part above the coating that tapers to a point, as a result of the reduction in thickness. Naturally, it may also be possible, in this second embodiment, for the starting sections 6 , in a similar manner to that shown in FIG. 3 A, to remain substantially free of the coating 2 and for only the respective sections of the honeycomb body 1 to taper to a point. FIG. 4B shows a plan view in section taken along a line IVB-IVB in FIG. 4A . The figure shows the reduced wall thickness of the respective passage walls 4 in the region of the respective starting sections 6 , with reduced thicknesses of the coating 2 on both sides in each case. The result, therefore, in addition to the reduced wall thicknesses of the passage walls 4 , in a similar manner to the first exemplary embodiment shown in FIGS. 3A, 3B and 3 C (and as can be seen in particular from FIG. 3C ), is also a widening of the axial passages 3 in the region of the respective starting sections 6 . The widening also counteracts blocking of these passages 3 by soot deposits and therefore constitutes a further advantage of the catalytic converter body according to the invention.