This application claims the benefit of priority under 35 U.S.C. § 119 of German patent application 10 2015 111 689.8 filed Jul. 17, 2015, the entire contents of which are incorporated herein by reference.
The present invention relates to an electrically heatable catalytic converter as well as to a method for manufacturing same.
Catalytic converters for the treatment of a gas stream are generally known, especially in connection with exhaust gas treatment for internal combustion engines of motor vehicles. They may contain a number of components, especially three-way catalytic converters, hydrocarbon adsorbers and a porous structure, which may be embodied especially as a mesh, as a screen or as a honeycomb body. Such systems are known, for example, from EP 0 638 710 A2 and EP 0 485 179 A2.
A special problem of such catalytic converters is that they shall function already in the cold start phase. To ensure this, it is known, for example, from DE 10 2007 024 563 A1 that catalytic converters can be equipped with an electrically heatable honeycomb body, which is used to heat the exhaust gas.
Heated porous structures known from the state of the art operate according to the principle that the heating effect is achieved through a flow of current through at least some of the wires, plates or plate stacks, which together form the porous structure. Since a uniform heating effect is desirable, it is necessary to apply current to a plurality of wires, plates or plate stacks and to ensure, on the one hand, that the current paths thus formed have a resistance that is defined as a fixed resistance that is especially identical to the extent possible and, on the other hand, to ensure an electrical insulation between the wires, plates or plate stacks. In particular, an electrically insulated suspension of the wires, plates or plate stacks is necessary for this. All these insulations hinder the flow of exhaust gas. As a result, all this leads to a complicated and expensive manufacturing process, which also leads, moreover, to a heatable catalytic converter that is sensitive to vibrations and has a considerable risk of failure.
The object of the present invention is therefore to provide an electrically heatable catalytic converter that is cost-effective, can be manufactured in a simple manner and is robust and a method for manufacturing same.
This object is accomplished by an electrically heatable catalytic converter of the present invention and by a method for manufacturing same.
The electrically heatable catalytic converter according to the present invention for the treatment of a gas stream, especially of the exhaust gas stream of an internal combustion engine, has a tubular housing, an interior space enclosed by the tubular housing and a porous structure, which is arranged in the interior space of the tubular housing, can be heated by means of an electric heater and may be embodied especially as a mesh, as a screen or as a honeycomb body.
It is essential for the present invention that the electric heater is a mineral-insulated heater with a heat conductor, at least one front-side connection opening and with at least one outer metal jacket, wherein the mineral-insulated heater has at least one section that is passed through a housing wall, so that all front-side connection openings are arranged outside the interior space of the tubular housing and the outer metal jacket of the mineral-insulated heater is welded or soldered in this section to the tubular housing directly or via a mineral-insulated, vacuum-tight duct, and wherein the heat conductor is fully embedded, at least in the sections of the mineral-insulated heat conductor that are arranged in the interior space of the gas duct, in an insulation, which is preferably compacted. The material suitable for the insulation is especially a ceramic material.
It is ensured by the use of a mineral-insulated heater with an outer metal jacket with a front-side connection opening that is arranged outside the housing that the desired electrical insulation is ensured, while the outer metal jacket and its welding or soldering to the housing at the same time ensures a dimensionally stable and vibration-resistant arrangement of the electric heater.
Uniform heating of the porous structure and especially of a mesh, screen or honeycomb body can be achieved by at least one section of the mineral-insulated heater being rolled into the porous structure. This is achieved especially if the mineral-insulated heater is helical, for example, in the form of a coil spring with concentric windings with different radii.
A further improvement of the vibration stability can be achieved if the mineral-insulated heater is soldered, especially vacuum-soldered to the porous structure.
A special advantage of the use of a mineral-insulated heater with metal jacket is that the cross-sectional shape of the mineral-insulated heater can be modeled as desired. In particular, the gas stream in the sections of the catalytic converter, in which the mineral-insulated heater is arranged, can thus be influenced by adapting this shape and, further, homogenization of heating can be achieved by adapting the shape.
It proved to be especially advantageous if the mineral-insulated heater has a smaller cross section in the direction of flow of the gas than in the walls of the porous structure, especially in the direction the walls of the honeycombs of a honeycomb body and if the extension of the mineral-insulated heater—it should be noted that the extension is defined here as the geometric extension to avoid misinterpretation, although it would be unlikely—is at least four times and preferably at least 10 times greater than the extension in the direction facing the walls of the porous structure, especially walls of the honeycombs of a honeycomb body.
Also conceivable is an embodiment in which the heating element of the mineral-insulated heater is connected at one end to the tubular housing, so that the tubular housing acts as a return conductor. This reduces the effort needed for cabling.
It is especially advantageous if the tubular housing consists of an Inconel alloy material with a nickel content of at least 25% and preferably at least 50%.
Depending on the desired heat distribution, a plurality of mineral-insulated heaters may be arranged in the openings of the porous structure, especially in the openings of a honeycomb structure.
The method according to the present invention for manufacturing an electrically heatable catalytic converter has the following steps:
The great advantage of this method is that it can be carried out in a simple and cost-effective manner.
The method steps may be carried out in the manner described, but it is explicitly noted that it would also be possible to carry out especially the soldering of the rolled-up porous structure after one of the steps.
In particular, it is also possible that the mineral-insulated heater is provided with welded connection openings and the connection openings are uncovered only after the step of soldering, especially vacuum soldering.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
In the drawings:
Identical reference numbers are used for identical components of the same embodiment, which are shown in different figures.
As can be best seen in the cross-sectional view shown in
The mineral-insulated heater 103 shown in
Further, in the direction in which the gas flows, i.e., along the side of the metal jacket 108 marked by the letter b, the extension of the mineral-insulated heater 103 is more than four times the extension in the direction facing the walls having a porous structure 102, i.e., in the direction facing the walls of the honeycombs of the honeycomb body 102, which corresponds to the direction marked by the letter a.
As is seen in
The enlarged detail of a cross section according to
The embodiment of a heatable catalytic converter 200 shown in
Further, connector plugs 213, 214 are also provided for supplying the heat conductor 204 with current in
The embodiment of the heatable catalytic converter 400 shown in
Another difference is that the contact to the tubular housing 401 is formed here via a duct 421, which is placed on the metal jacket 401 and is filled with a mineral insulation 422.
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
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Number | Date | Country | |
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20170016370 A1 | Jan 2017 | US |