Stock material or miscellaneous articles – All metal or with adjacent metals – Honeycomb – or with grain orientation or elongated elements...
Reexamination Certificate
2002-10-15
2004-01-06
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Honeycomb, or with grain orientation or elongated elements...
C422S180000, C502S527220, C228S118000, C228S181000, C029S890000
Reexamination Certificate
active
06673466
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a housing, in particular having a jacket tube, for a honeycomb body, a catalyst carrier body with a housing and a method for producing a catalyst carrier body with such a housing. Such catalyst carrier bodies with a housing are preferably used in exhaust systems of internal combustion engines, especially those of motor vehicles.
International Publication No. WO 99/37896 has described a method for the production of a honeycomb body surrounded by a jacket tube. The honeycomb body and the jacket tube have different thermal expansion behaviors due to differences in the properties of their materials and due to differences in temperature during operation. The aim is therefore to avoid a rigid connection between the honeycomb body and the jacket tube in at least one end region of the honeycomb body or at least in certain partial regions. For that reason, the jacketed honeycomb body described in International Publication No. WO 99/37896 is embodied with a sleeve, which is intended to ensure that direct brazed joints between the honeycomb body and the jacket tube are avoided in the at least one end region of the honeycomb body, despite manufacturing tolerances in the jacket tube and the honeycomb body. The use of a sleeve leads to a significant reduction in thermal stresses between the jacket tube and the honeycomb body but results in a higher outlay on production.
Measures that prevent a connection between metal surfaces during high-temperature processing (e.g. sintering or brazing) are also known. Those generally contain fine ceramic particles, a binder and a proportion of diluent and solvent. The binder, the diluent and the solvent are volatile even at relatively low temperatures. When producing catalyst carrier bodies, the connection between the jacket tube and the housing is preferably formed in a vacuum. The tendency of those agents to volatilize makes it significantly more difficult to maintain the vacuum and poses the risk that the system will be contaminated by volatile components.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a housing with a passivation layer, a catalyst carrier body with a housing and a method for producing a catalyst carrier body with such a housing, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which the housing allows selective connection by joining to compensate for differences in expansion behavior of a honeycomb body and a jacket tube and ensures permanent fixing of the honeycomb body, in an exhaust system, for example.
With the foregoing and other objects in view there is provided, in accordance with the invention, a housing for a honeycomb body, comprising a jacket tube with an inner wall surface, and a passivation layer in at least one section of the inner wall surface of the jacket tube for deliberately preventing connection to the honeycomb body by joining.
The passivation layer is thermally very stable and prevents any connection by joining of the metal surfaces that are in contact with one another. The section to which the passivation layer has been applied is situated at a location on the jacket tube at which relative motion between the honeycomb body and the jacket tube during subsequent operation of the catalyst carrier body is desired in order to prevent thermal stresses. This is preferably the end region in which the hot exhaust gas strikes the catalyst carrier body. Areas that are further inward can also be kept free of joints in this way.
Due to its insulating property, the passivation layer furthermore prevents conduction of heat from the honeycomb body to the jacket tube. This is particularly important, for example, if the light-off or activation temperature of a catalytic converter, at which effective cleaning of the exhaust gas takes place, is to be reached after as short as possible a time following the starting of a motor vehicle.
In accordance with another feature of the invention, the passivation layer is constructed as a surface oxide layer. Oxides, in particular metal oxides, have a high thermal stability, which prevents mutually-contacting metal surfaces from bonding together. It is likewise particularly advantageous that the oxides can be produced in a simple manner with components of the material of the jacket tube and that an additional material is not required for the production of the passivation layer. A metal oxide layer of this kind can also be produced, for example, simply by roughening the inner wall surface of the jacket tube in this section.
In accordance with a further feature of the invention, the passivation layer is embodied as an applied ceramic layer, in particular one involving aluminum oxide. Ceramic particles are distinguished by particularly strong forces of attraction to one another and very good thermodynamic stability. A ceramic layer composed of titanium oxide or magnesium oxide is likewise possible.
In accordance with an added feature of the invention, the passivation layer is constructed as an all-round strip. This ensures that brazed joints between the jacket tube and the honeycomb body are avoided in this section over the entire circumference of the jacket tube and enables differences in expansion behavior to be compensated for.
In accordance with an additional feature of the invention, the housing is oval or elliptical in shape, and the passivation layer is placed in a more-sharply-curved jacket-tube section. An oval shape of the housing is required, for example, if the installation of a catalyst carrier body together with the housing has to satisfy particular spatial constraints within an exhaust system. Experience has shown that it is advantageous to make the joints on the flat sides of such a structure and therefore to prevent joints on the rounded sides through the use of a passivation layer. This is, in particular, an additional measure to any passivation layer at one or both ends.
In accordance with yet another feature of the invention, the passivation layer has an axial length of 5 mm to 50 mm. This enables the housing to be adapted precisely to the respective application. If, for example, the housing is disposed relatively close to an internal combustion engine or the thermal expansion behavior of the honeycomb body and the jacket tube differ very greatly, the passivation layer is embodied with a longer axial length.
It is particularly advantageous if the passivation layer has a thickness of 0.03 mm to 0.12 mm. In particular, this enables manufacturing tolerances of the honeycomb body and the jacket tube to be compensated for in the assembled condition.
In accordance with yet a further feature of the invention, an adhesive layer is disposed between the jacket tube and the ceramic layer. This is advantageous particularly when the ceramic layer is exposed to high dynamic loading. The adhesive layer enables the ceramic layer to be bonded permanently to the metallic surface of the jacket tube.
In accordance with yet an added feature of the invention, there is provided a layer of brazing material placed on the passivation layer of the jacket tube before assembly with a honeycomb body. The passivation layer does admittedly prevent the formation of brazed joints between the honeycomb body and the jacket tube. However, if the honeycomb body is made up, for example, of a multiplicity of layers of sheet metal produced by winding and/or stacking, the brazing material disposed on the passivation layer can be used to ensure a brazed joint between adjacent ends of the layers of sheet metal. In this way, flapping of end regions of the layers of sheet metal is avoided and the service life of a honeycomb body of this kind is increased.
In accordance with yet an additional feature of the invention, there is provided an all-around layer of brazing material on the passivation layer. In particular, this has the effect of brazing all adjacent layers of sheet metal to one another.
With the objects of the invention
Brück Rolf
Faust Hans-Günter
Hodgson Jan
Kurth Ferdi
Schmitz Karl-Josef
EMITEC Gesellschaft fuer Emissionstechnologies mbH
Greenberg Laurence A.
Locher Ralph E.
Stemer Werner H.
Zimmerman John J.
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