The present invention concerns a catalytic converter in a housing for an exhaust gas system of an internal combustion engine, in particular a small engine. The catalytic converter has at least one structured metal sheet which is provided with a catalytically active material and which is wound or twisted, and is formed with passages through which exhaust gas can flow, and which at least partially bears against the housing. The invention also concerns a silencer or muffler for an exhaust gas system of an internal combustion engine and a process for the production of a catalytic converter carrier body which is disposed in an exhaust gas system of an internal combustion engine, in particular a silencer or muffler for a small engine.
It is known for catalytic converters for exhaust gas systems of an internal combustion engine to be in the form of a honeycomb body. The honeycomb bodies are produced from sheet metal layers that are stacked or wound or twisted together. Other honeycomb bodies in turn contain sintered or extruded material. Those catalytic converters are intended to ensure that the convertible gases that still remain in the exhaust gas are further converted. A large number of ever increasingly strict exhaust gas requirements, in particular in relation to motor vehicles, results in that the catalytic converters must be of a configuration that they ensure almost complete conversion, even when the catalytic converter is in use over a prolonged period of time. The development in the catalytic converter art is in particular along the lines of maximizing the catalytically active surface area. Therefore in particular honeycomb bodies which have a large number of passages over their cross-section are used. Besides the possibility of increasing the surface area involved however the length and volume of the catalytic converter and therewith its cross-section are also increased. That however requires a large amount of space to be available for the catalytic converter in the exhaust gas system. In addition, with the catalytic converter being of an increasing size, the working processes for the production thereof become more expensive. In addition, in relation to large catalytic converters, particular attention must be paid to the durability thereof in relation to mechanical and thermal changes in operation, which necessitates a particular mounting configuration.
Set out hereinafter are various configurations of catalytic converters, to the features of which the present invention refers in respect of the configuration and form of the catalytic converter. Published, British Patent Application GB 2 231 283 A discloses a honeycomb body which has one layer. That layer is formed from a flat metal sheet and a structured metal sheet and is then shaped in a spiral to form a multi-layer catalytic converter. It has an internal cylindrical cross-section, the size of which is dependent on the outside diameter of the honeycomb body. The large number of mutually stabilizing layers which bear against each other is intended to ensure adequate stiffness for the honeycomb body constructed in that way. Published, Non-Prosecuted German Patent Application DE 37 15 040 A1 discloses another catalytic converter which contains a strip with non-cutting stampings therein. Those stampings are intended to increase the surface area involved. European Patent Application EP 0 473 081 A1 discloses mounting a catalytic converter in the bend of a motorcycle exhaust gas system. An apertured plate is used as the catalytic converter. The plate can be straight or also round. Published, Non-Prosecuted German Patent Application DE 24 36 559 Al in turn discloses a catalytic converter which is disposed directly in a bend of an internal combustion engine. The bend itself is in the form of a catalytic converter. Besides a catalytic coating on the inside wall of the bend, it is additionally possible to disposed catalytic shaped portions, in particular in screw form. Japanese Patent JP 61 65 940 discloses a catalytic converter which is made up of smooth and corrugated metal foils. Disposed upstream of that full catalytic converter is a further catalytic converter which is heatable. U.S. Pat. No. 4,195,063 in turn discloses a main catalytic converter with an additional, upstream-disposed catalytic converter. The catalytic converter contains primarily two catalytically coated mesh configurations that are each held between two mesh carriers. The catalytic converter can be disposed in the bend, but also in a conical configuration. Japanese Patent JP 61 096 120 discloses two tubes which are mounted in the proximity of an engine block in a curved configuration. The interior of the two tubes has holes. A catalytically active layer is disposed between those two tubes.
A particularly preferred area of use of a catalytic converter according to the invention is in relation to small engines. The term small engines is used hereinafter to denote engines with a cubic capacity of less than 250 cc. Such engines are used in particular in lawnmowers, motor-driven saws, transportable power generators, two-wheelers and similar uses. In the case of motor-driven saws, lawnmowers and other garden equipment the person operating the apparatus is often disposed over a prolonged period of time directly in the exhaust gas region of the small engine, and for that reason catalytic exhaust gas cleaning is particularly important there.
Attention is also directed to Published, Non-Prosecuted German Patent Application DE 38 29 668 A1 in which the catalytic converter, in a small engine, is used in a partitioning wall which extends approximately perpendicularly to the through-flow direction. European Patent EP 0 470 113 B1 also discloses a configuration of the catalytic converter, in which it is disposed with a spacing at all sides in an exhaust gas silencer or muffler for two-stroke engines. European Patent EP 0 049 489 B1 also discloses a process for the production of a carrier matrix for an exhaust gas catalytic converter. The features disclosed in those three documents can also be applied to this invention.
It is accordingly an object of the invention to provide a honeycomb body with a cross-sectional region which is bordered in the interior, in particular for small engines that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which can be produced in a small number of working steps, which is extremely compact, and which nonetheless makes available a sufficient catalytically active surface area so that limit values which are prescribed by statute in respect of the exhaust gas characteristics of an internal combustion engine are observed. A further object of the invention is to provide a housing for the catalytic converter, which does not nullify again the space gained by virtue of the compact catalytic converter. Another object of the invention is to provide a process for the production of a compact catalytic converter carrier body, which ensures continuous production thereof while avoiding a high level of production expenditure.
With the foregoing and other objects in view there is provided, in accordance with the invention, a catalytic converter assembly for an exhaust gas system of an internal combustion engine, including a small engine, the catalytic converter assembly including:
a housing having a cross-section with a cross-sectional area;
and
a catalytic converter having at most two layers formed of sheets and disposed in the housing, the catalytic converter containing:
an at least partially curved elongated body; and
at least one structured sheet having a structuring and a catalytically active material, the at least one structured sheet being wound on inclinedly around the at least partially curved elongated body and at least partially bears against the housing, the structuring of the at least one structured sheet in addition with one of the housing and a sheet of a layer of the at most two layers define closed passages there-between through which exhaust gases can flow and such that, as considered over the cross-section of the housing, a cross-sectional area bordered in by the closed passages constitutes at least half of a total of the cross-sectional area of the housing and defines a bordered-in cross-sectional area.
A catalytic converter in a housing for an exhaust gas system of an internal combustion engine, in particular a small engine, has at least one structured metal sheet provided with a catalytically active material. The sheet is twisted or wound, it forms passages through which an exhaust gas can flow, and it at least partially bears against the housing. The sheet is of such a structuring that, as considered over a cross-section of the housing, the cross-sectional area which is enclosed or bordered by closed passages constitutes at least half of the total cross-section of the housing, with the catalytic converter having at most two layers. Restricting the catalytic converter to a maximum of two layers makes it possible to achieve an extremely compact catalytic converter that requires a small amount of space. For that purpose it is desirable for the structuring of the sheet to be such, in terms of utilization of space, that, besides the passage effect of the catalytic converter, there is also sufficient catalytically active surface area available. The use of a maximum of two layers also facilitates heating of the catalytic converter to its useful or operating temperature as it involves less mass to be heated than other catalytic converters of an expensive and complicated construction. In addition the limitation to a maximum of two layers has proven to be advantageous in order to impart to the catalytic converter, besides flexibility, also a high level of stability and rigidity in respect of shape. The catalytic converter affords an at least satisfactory catalytic conversion effect for the exhaust gases, for the preferred uses in the small-engine sector. An improvement in catalytic conversion is achieved if the bordered cross-sectional area constitutes at least two-thirds of the total cross-section of the housing. If the sheet provided with catalytically active material is twisted or wound in such a way that the structuring comes to lie in mutually opposite relationship, that provides that the enclosed cross-sectional area defined by the passages is disposed in a region around the center point of the catalytic converter while the center point is disposed within a remaining area which is not completely provided with passages. That can be achieved for flattened cross-sectional regions of the catalytic converter, as well as round, oval or polygonal catalytic converters. Concentration of the bordered cross-sectional area around the center point makes it possible for the outside passage surfaces which face towards the center point also to be fully acted upon by exhaust gas. In addition the structuring of the maximum of two layers can then be particularly advantageously such that the flow resistance in relation to the passages formed is no greater than that of the cross-section which does not completely involve passages.
An embodiment of the catalytic converter provides that the mutually oppositely disposed structurings are intertwined or interlaced without touching each other. In that way a quasi-passage-like geometry is imparted to the area which remains free. The mutually oppositely disposed structuring makes it possible for the bordered cross-sectional area to make up at least three-quarters of the total cross-sectional area of the housing.
It is precisely in connection with small implements and apparatuses that under some circumstances have to be moved manually that it is important for them to be of small dimensions and low weight, from the point of view of construction thereof. The catalytic converter can contribute thereto by having a stabilizing reinforcement. The reinforcement ensures that the catalytic converter enjoys its rigidity in respect of shape without excessively limiting it in regard to its elasticity. The stabilizing reinforcement can also be so configured that it performs a load-bearing function for the small implement or apparatus. By virtue of that configuration the catalytic converter can be fully integrated into same. The housing and the catalytic converter are then in a position of also being incorporated in the detailing and interpretation of the torsional stiffness and structural engineering involved.
A catalytic converter which is particularly capable of resisting impacts, vibration and jarring is afforded by each passage-forming sheet of the catalytic converter bearing against a reinforcement. The resistance in this respect can be further increased by the passage-forming sheet which has a top side and an underside bearing respectively with the top side and the underside against the reinforcement. Another possibility of producing a catalytic converter having a high level of stability in respect of shape but also a high degree of elasticity involves constructing a layer thereof with an unstructured sheet and a structured sheet. It can be combined with the stabilizing reinforcement. A preferred embodiment of a catalytic converter has an unstructured sheet with a top side and an underside, wherein a respective structured sheet is disposed at each of the top side and the underside respectively. The structuring is in particular a corrugation configuration, a curvature configuration, a scalloping or a folding configuration of the sheet. It may also have microstructures as well as small incisions and openings. The catalytically active surface area can also be increased in that way. In regard to the structuring, nature and form of the layer, attention is directed in particular to European Patent EP 0 484 364 B1, International Patent Application WO 93/20339, European Patent EP 0 152 560 B1 and Published, Non-Prosecuted German Patent Application DE 29 611 143.
Making up the catalytic converter from three sheets which are joined together, wherein the outermost one is structured, affords the possibility of the catalytic converter being held in a housing solely by virtue of a clamping force of that outer sheet. Such a holding action is facilitated if at least a part of a layer of the catalytic converter is flexible. That is in particular a part of the layer, which is supported against the reinforcement, in particular a wall of the housing or the small apparatus or implement or the internal combustion engine.
In a further embodiment, to achieve a high level of stability for the catalytic converter, it has the configuration of a layer with a first metal sheet and a second metal sheet. In that configuration the first sheet is preferably thicker than the second sheet by a factor of between 1.5 and 5, in particular between 2 and 4. When using metal foils of between 20 xcexc and 100 xcexcm, it makes it possible to use the thinner foil that is particularly desirable in terms of a structuring, without having to abandon the idea of a self-stabilizing catalytic converter. It is therefore preferable for the first sheet to be unstructured and for the second sheet to be structured. A further embodiment of the catalytic converter provides the catalytic converter with a flattened cross-section. If the directions in which the forces which are applied from the outside will act on the catalytic converter are known, then with a flattened cross-section it is possible to provide a catalytic converter which enjoys particular stability in that direction. The catalytic converter can also be of such a configuration that it has preferred directions in respect of the effect of external forces, in which directions the catalytic converter reacts elastically and possibly also necessarily plastically. Destruction of the catalytic converter can be prevented by virtue of established regions of the catalytic converter that, in the event of an excessively heavy loading, involve plastic deformation in order to receive and adsorb the forces acting.
The catalytic converter can be disposed in an exhaust gas system that in internal combustion engines usually leads away therefrom. Equally however the catalytic converter can also be used in exhaust gas systems which are disposed in the casing of the internal combustion engine. For both situations it is desirable for the housing of the catalytic converter to be part of the exhaust gas system. That can ensure dissipation of heat of the catalytic converter as it heats up by flow transfer to the exterior. The housing can be a bend tube or a component of a silencer or muffler of the exhaust gas system. That ensures compact installation of the catalytic converter without an additional space being required for same.
In accordance with a further aspect of the invention, in order to make compact utilization of the space involved, a silencer or muffler for an exhaust gas system of an internal combustion engine, in particular a small engine, is used by the silencer or muffler having a device for receiving the above-described catalytic converter. That is for example a suitably configured and in particular adapted housing which facilitates disposing the catalytic converter therein and its fixing thereat. That can be achieved by a tubular casing as the housing as well as by virtue of a suitable spatial configuration in the casing of the internal combustion engine. Particularly in the case of small engines, the silencer/catalytic converter combination makes it possible to keep the exhaust gas systems thereof small.
It is preferable for a part of the silencer or muffler to have means for fixing the catalytic converter. That can be teeth, notches, transverse web portions, channels, grooves or similar structural formations. If teeth or the like are used they co-operate with at least the oppositely disposed sheet. Teeth engage into same and thereby hold the entire catalytic converter.
The service life of the catalytic converter also depends on the respective mode of operation of the internal combustion engine and the area of use thereof. If the engine is only ever repeatedly operated for a short period of time, and if the engine is subjected to large forces acting thereon from the exterior, all that reduces the service life of the catalytic converter.
It is therefore desirable for the catalytic converter to be interchangeably fitted in position. In the case of the silencer or muffler the catalytic converter can for example be disposed in a top housing and a bottom housing. One of the two housing halves preferably has a reinforcement by which a force, in particular a clamping force, can be exerted on the catalytic converter. The reinforcement can be a transverse web or bar portion in the silencer or muffler, as well as one of the sound-damping structures of the silencer or muffler. A further possible way of holding the catalytic converter in the silencer or muffler involves so squeezing at least a part of the catalytic converter in the silencer or muffler that the catalytic converter is immovable. A further embodiment of a silencer or muffler that is particularly suitable for small engines has at least two parts, a top housing and a bottom housing. A partitioning wall divides the silencer or muffler into a first region and a second region. The partitioning wall and/or the silencer or muffler has ways for holding the catalytic converter in each respective ones of the regions that are separated from each other. It is possible in that way for two catalytic converters to be disposed in one silencer or muffler. That is not necessarily the case. There may also be only a single one or also more than two catalytic converters.
In accordance with a further concept of the invention there is also provided a process for the production of a catalytic converter carrier body which is disposed in an exhaust gas system of an internal combustion engine, in particular a silencer or muffler of a small engine. The process includes:
a) a structured sheet is wound on inclinedly around an at least partially curved elongate body;
b) subsequently at least a part of the elongate body with the sheet wound thereon is cut into a plurality of portions; and
c) a respective portion becomes a catalytic converter carrier body.
That process is particularly suitable for a continuous production procedure, wherein the structured sheet can be unwound from an endless strip. The elongate body in turn can be a tube or also another suitably long available body. To provide for a particularly high degree of utilization of space in order to afford a large catalytically active surface area the body has a hollow interior in which a further structured sheet is disposed. The catalytically active surface is then afforded by the sheet and/or the body being coated with a catalytically active layer prior to the winding-on operation or by the portion which has been cut off being coated with a catalytically active layer after the cutting operation. Depending on the respective way in which the sheets are fixed together, that can be effected by soldering, welding, adhesive or similar methods but equally also by inherent stressing of one of the sheets, the moment when the catalytically active layer is most appropriately to be applied is a matter of choice.
To achieve a high degree of stability of the above-mentioned portion, it is provided that the body is a metal sheet that is thicker than the sheet that is to be wound on. Desirable values in respect of stability are achieved if the thicker sheet is about one to five times thicker than the sheet that is to be wound on. As described above a compact catalytic converter can be particularly inexpensively produced from the catalytic converter carrier body, in accordance with this method.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a honeycomb body with a cross-sectional region which is bordered in the interior, in particular for small engines, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.