Electrically heatable catalytic converter

Details Electrically heatable catalytic converter Electrically heatable catalytic converter

1998-05-29

2001-01-02

Tran, Hien (Department: 1764)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Waste gas purifier

C422S177000, C422S179000, C422S180000, C219S552000, C392S485000

Utility Patent

active

06168763

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an electrically heatable catalytic converter for the cleaning of exhaust gas from combustion processes.
BACKGROUND OF THE INVENTION
A generic catalytic converter is known from DE 42 43 904 A1. The known catalytic converter exhibits an external, closed shell into which a so-called monolith is embedded. The monolith of the catalytic converter which, in connection with this patent application, is also known as the carrier, is primarily a layered arrangement of smooth, flat metal foils or plates and corrugated metal foils or plates. The corrugated metal foils extend across the exhaust gas flow, with the corrugations being positioned in parallel to the exhaust gas flow and each forming channels for the exhaust gas flowing through. The carrier of the catalytic converter is coated with a wash coating in which platinum metals are embedded or onto which they are applied. Every third or fourth flat metal foil projects laterally at a right angle to the exhaust gas flow across the portion of the monolith that is interspersed with channels and exhibits, on each side of the monolith, an annular contact surface that has been printed using sealed layer technology. A resistance heating layer that has been printed using sealed layer technology and is electrically insulated against the carrier plate runs between the two contact surfaces of a smooth plate. Electrical contacting of the metal foils equipped with heating elements is achieved by means of electrically conductive rings, each of which is positioned between two opposing connection areas of the metal foils. The rings are arranged between the protruding ends of the metal foils in a stack with the same height as that of the monolith, and are pressed together with a continuous screw element, with the compression force ensuring a permanent contact between the rings and the connection areas. The rings, in turn, are connected to an electrical power supply by means of high-temperature resistant soldered connection wires.
The manufacture of the known electrically heatable catalytic converter is relatively complex.
There are other technical solutions for electrically heatable catalytic converters in which either the metal carrier foil of the monolith is traversed by current and is thus heated, or in which a separate electric heating element indirectly heats the carrier frame of the catalytic converter. Examples of these other technical solutions are found in DE-PS 563 757 or in WO89/10470. These technical solutions are more removed from the object of the invention than the aforementioned DE 42 43 904 A1.
The objective of the invention is to redesign a generic electrically heatable catalytic converter in such a way as to simplify its manufacture.
This objective is solved with an electrically heatable catalytic converter with the features of the present invention.
SUMMARY OF THE INVENTION
An electrically heatable catalytic converter for the cleaning of exhaust gas from combustion processes is provided. The catalytic converter includes a shell and a carrier inside the shell defining channels through which the exhaust gas being cleaned can flow. A layer on the carrier is catalytically active in relation to the exhaust gas. An electrically conductive resistance heating layer with electrical connection areas covers at least a portion of the surface of the carrier. An insulation layer is interposed between the carrier and the heating layer. One or more electrical connection elements contact the heating layer in the electrical connection areas and pass through the carrier and the insulation layer.
Because the connection elements run through the resistance heating layer, the insulation layer, and the carrier, the connection elements are fastened in interlocking fashion in a direction which parallels the layers and the carrier. Any remnants which act on the connection elements as a result of thermal expansion or acceleration forces can be directed or fed into the carrier in this manner. This removes stress from the sites where electrical contact is established.
It is advantageous if the carrier features openings, e.g., in the form of punched holes, in the vicinity of the connection areas. In this case, the connection elements can simply be inserted into the openings. If, in addition, a second insulation layer is to be provided on the side of the carrier facing away from the resistance heating layer, each connection element can be molded against the insulation layer on the side facing the resistance heating layer. In this case, the second insulation layer preferably exhibits approximately the same dimensions as the connection area, thus eliminating the need to apply unnecessary excess material. Nevertheless, it is advantageous if each opening is surrounded by a second layer of insulation, as this allows each connection element to be molded against the surface facing away from the resistance heating layer.
To ensure a simple and stable connection, the connection elements should, if possible, be form-fitted to match the openings, i.e., they should not just be form-fitting in parallel to the layers and to the carrier, but should also be secured in the openings in a form-fitting manner in the direction of insertion. The connection elements inside the openings should remain separated from the carrier, so that an electrical contact is not established between the connection elements and the carrier. A simple design is provided if the connection elements include a tubular projection. This tubular projection can be centered in the openings and, if its diameter is smaller than the inner diameter of the openings, provides adequate spacing from the carrier. In a particularly simple design, the connection elements are retained in the openings by means of plastic deformation and, particularly, by means of riveting. The connection elements can also be secured by welding them to the connection areas. This measure can be provided on its own or in addition to riveting. It may, in particular, involve thermal welding processes, such as resistance pressure welding, laser welding, or ultrasonic welding onto the resistance heating surface. The welding of connection elements to resistance heating layers is particularly reliable if a supplemental contact layer is applied.
Even though the manner of securing the connection elements in the carrier according to the invention is exceptionally stable, it is advantageous if the connection elements—at least those that are at right angles to the direction of exhaust gas flow—are designed as spring elastic elements. This reduces their sensitivity to vibration and thermal expansion.
A simple design is provided when a shared connection element is allocated to each pair of resistance heating layers in adjacent connection areas. The contacting of two resistance heating layers can be achieved with one continuous, tubular protrusion which runs through both carriers and both resistance heating layers and is riveted to one of the resistance heating layers. A space is advantageously maintained between the applicable carriers by means of a washer.


REFERENCES:
patent: 42 43 904 A1 (1994-06-01), None
patent: WO 89/10470 (1989-11-01), None
patent: 94/15079 (1994-07-01), None

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