WO2005021944A1

WO2005021944A1 - Catalyst body and exhaust system for a small engine and method for production of the catalyst body

Info

Publication number: WO2005021944A1
Application number: PCT/EP2004/009545
Authority: WO
Inventors: Matthias Mangold; Christian Mangold
Original assignee: Oberland Mangold Gmbh
Priority date: 2003-08-27
Filing date: 2004-08-26
Publication date: 2005-03-10
Also published as: DE10339468A1; US20070113540A1; DE10339468B4

Abstract

The invention relates to an annular catalyst body (1), with a radial throughflow, for assembly in a silencer housing (4) of a small engine, an exhaust system for a small engine and a method for production of the catalyst body (1). The catalyst body (1) is made from a perforated metal film (2). In a preferred embodiment, the holes (3) in the perforated metal film (2) are suitable for noise reduction such that the metal film can also adopt the function of a conventional baffle body. In a further preferred embodiment of the metal film (2) forming the catalyst body (1), webs (5) are arranged between the holes to reinforce the metal film, of a form to prevent a bulging of the metal film in the assembled state. In a yet further preferred embodiment, the ends (6, 7) of the metal film are connected with a detachable positive fit connection (8). Said catalyst body (1) is produced by bending the catalyst body (1) from a perforated metal film strip (2) with subsequent connection of the ends (6, 7) by means of a positive fit connection (8).

Description

CATALYST BODY AND EXHAUST SYSTEM FOR A SMALL ENGINE, AND METHOD FOR PRODUCING THE CATALYST BODY

The invention relates to a radially flowable ring-shaped catalyst body for installation in a muffler housing, an exhaust system for a small engine and a method for producing the catalyst body.

Small engines of this type are used, for example, in lawnmowers, chainsaws, hand-scythe machines, power generators and also in two-wheelers. Due to the increasing environmental awareness, the need has developed over time to continuously improve the exhaust gas cleaning and soundproofing of small engines. The ever stricter emission regulations require that the components are constantly adapted to the changing requirements.

In exhaust gas treatment, it is previously known in such devices to use radial or axial type catalyst bodies to reduce the pollutants contained in the exhaust gas. Radial or axial is understood to mean the main flow direction of the exhaust gas in which it flows through the catalyst body. For this purpose, it is also known to provide such catalyst bodies in the form of hollow cylinders. This shape results from production, flow technology or due to the intended type of fastening. In practice, annular catalyst bodies are used in particular. Up to now, such ring bodies mostly consist of pressed metal wire mesh or bent metal wire mesh. In practical use, however, it has been found that wire structures of this type have low mechanical stability, and in particular when used in a silencer housing, compressive and fluidic stresses and the elasticity of the wire structure can cause compression and bulging. With a pre-stressed catalyst body fixed in the silencer housing there are additional loads on the catalyst body. Due to the elastic and plastic deformations of individual wires or the entire ring body, the catalytically active coating and the washcoat are detached, which reduces the performance of the catalyst and thereby reduces the efficiency of the pollutant reduction. Individual wires can also be strung together, causing the coatings on the wires to crumble or break off. When using wire mesh, even when the wires are soldered, there are also kinks and bulges. In addition, closed ring structures made of wire require a high level of production effort. The transport of such prefabricated ring bodies also proves to be expensive, since a large space requirement is required due to the internal cavity.

As a further component in known exhaust systems of small devices, a silencer unit is installed in the muffler housing in addition to the catalyst body. The soundproofing unit usually consists of a so-called reflection body. The exhaust gas is introduced into the pipe and the openings in the pipe break the sound and thus reduce noise. With regard to the arrangement of the catalytic converter body and silencer unit, it is common to connect them in series, i.e. that the exhaust gas is first fed to the reflection body after entering the muffler housing and then flows axially or radially through the catalyst body. When using a radial catalyst, this is often arranged coaxially and at a distance around the reflection body. This requires a coordination of the geometric dimensions of the components to be arranged, a large number of means for fastening the components and a time-consuming assembly. In addition, the catalytic converter bodies or sound damping units cannot be used in every exhaust system type of a small engine as a replacement for used components.

The invention is therefore based on the object to provide a radially flowable, annular catalyst body, which is easy to manufacture, requires little space during transport and at the same time meets the requirements in terms of catalytic activity and sufficient stability, so that it during Use in an exhaust system also remains dimensionally stable. Furthermore, it is an object of the invention to provide an exhaust system which requires less installation work and also makes components more interchangeable. It is also an object of the invention to provide a method for producing the catalyst body which can be used to produce it more effectively in terms of time and cost. The object is achieved for a radially flowable, annular catalyst body in that it consists of a perforated metal foil. This creates a catalyst body with high mechanical stability, which is also simple and inexpensive to manufacture. Furthermore, the metal foil has a small volume in the flat state before assembly and can thus be transported in a space-saving manner. The stability of the metal foil also helps to ensure that the applied catalytic coatings last.

In a preferred embodiment, the perforations of the perforated metal foil are adapted to the sound reduction so that the metal foil also takes on the function of a conventional reflecting body. The metal foil, which is adapted to reduce noise as a replacement for a conventional soundproofing unit, has not only the catalytic effect but also good stability properties. Due to the fact that the perforations are adapted for sound reduction and pollutant reduction, the reflection body can be dispensed with, which saves one component of the exhaust system.

The term "metal foil" should be understood to mean any metallic layer that is designed so that the holes provided can be made and these can be formed into a ring. The term "metal foil" also includes metal sheets, and all of these materials can also be provided with a catalytic coating. A strip of certain dimensions is obtained from the metallic base material and shaped into a closed ring.

[0009] The term “perforation”, which also relates to the invention, denotes any type of opening in the metal foil. This can have a round, angular, circular, elliptical, slit-shaped and other linear or non-linear shapes and can be introduced into the metal foil in a known manner.

The thickness of the metal foil can be adapted according to the requirements with regard to pollutant treatment, noise reduction and the stresses resulting from the gas pressure and the fastening in the muffler housing.

With the metal foil according to the invention, a catalyst body is created, which is easy to manufacture, can also serve as a replacement for a conventional reflection body, and allows easy handling during assembly. Furthermore, the initially flat metal foil allows a different easy transportation with less space. After the final shaping into a closed ring, sufficient stability for use in a silencer housing is also achieved.

Another preferred embodiment is that webs for stiffening the metal foil are arranged between the perforations, which are adapted so that they prevent bulging of the metal foil in the installed state. These connecting webs or material bridges thus result from the interaction with the arrangement of the perforations and are in a mutual dependency relationship. The dimensions and the thicknesses of the webs are to be dimensioned such that they can withstand all loads, i.e. Resist permanently, both when the device is idle and in operation. Such webs ensure the dimensional stability of the catalyst body. In a further preferred embodiment, this is achieved in that the webs are aligned in accordance with the forces acting on the catalyst body. As a rule, compressive forces occur in the direction of the longitudinal axis of the annular catalytic converter body, in particular if it is fastened in the muffler housing with a preload, whereas tensile forces can occur perpendicularly thereto. The webs can also run obliquely over the circumference of the annular catalyst body. The grid-like bracing thus formed stabilizes the catalyst body and prevents crushing or barrel-shaped bulges. In a further expedient embodiment, the webs are aligned coaxially to the longitudinal axis and / or in the circumferential direction of the catalyst body. Optimal bracing is achieved in particular when the web directions are perpendicular to one another.

From the requirements described above with regard to the loads occurring and with regard to the exhaust gas treatment and assembly, there are certain requirements for the thickness of the metal foil. In a further preferred embodiment, the metal foil has a thickness of 0.05 mm to 2 mm and preferably of 0.3 mm to 1 mm. The thickness also depends on the desired inner hollow cross section of the ring or, in the case of a circular design, on the desired inner diameter. On the one hand, it should be chosen so that the metal foil is still sufficiently flexible to form the ring shape and, on the other hand, it also has sufficient dimensional stability. Furthermore, the metal foil should be heat-resistant and, for this purpose, can contain chromium and aluminum, for example.

To optimize the catalytic and / or sound-absorbing effect, the metal foil is expediently screw, star, trapezoidal or wave-shaped. Such shapes can be easily stamped into the initially flat metal foil using appropriate tools. The Turbulence caused at the leading edges increases the contacting of the exhaust gas with the catalytic layer and contributes to the refraction of the sound.

In order to simplify the assembly and reduction of the devices required for this purpose, it is provided in a further preferred embodiment that the ends of the metal foil are connected with a releasable form-fitting connection. It proves to be advantageous if the ends of the metal foil are hook-shaped and can be easily brought into engagement in a few simple steps. To form the hooks, the ends of the metal foil can be bent in opposite directions.

As a releasable positive connection, it is also expedient that one end of the metal foil has a recess and the other end of the metal foil has a counterpart for engaging in the recess. The counterpart, after it has been inserted into the recess and is in engagement with it, can have a greater extent than the recess, so that the connection cannot be released or opened by itself. In particular, when designing the ends of the metal foil with a recess or a counterpart, these can easily be integrated into the metal strip when punching out or cutting it out. The recess and the counterpart can have coordinated shapes of any linear or non-linear type, e.g. rectangular, oval or curved shapes. If required, the aforementioned positive-locking connections can also be secured by joining measures, for example by placing one or more spot welds in the corner regions of one end for permanent fixing to the other end of the metal foil.

Regarding the configuration of the perforations, these are formed in a further preferred embodiment by bending away the metal foil. At least part of the outline of the later perforation is predetermined, for example by punching or cutting on the initially flat metal foil, and then the material located at the location of the perforation to be produced is bent so that the bent part of the metal foil still connects to the metal foil or to the adjacent one Has jetty. The bending away can be done in different directions. The projections formed by the bending away, in conjunction with the openings, at least in the vicinity thereof, cause the exhaust gas to be deflected in the meantime from the radial to the horizontal direction. For the simultaneous formation of spacers, the bending takes place in one direction, for example outwards. Alternatively, the perforations can also be produced by completely removing the material which is still present at the intended location, for example by punching out becomes. With regard to the arrangement pattern of the perforations, a symmetrical pattern in the form of rows running parallel in the circumferential direction of the ring with or without an offset is selected in principle. An asymmetrical or irregular distribution of the perforations is also possible.

The object of the invention is achieved for an exhaust system in that the catalyst body consists of a perforated metal foil. This makes the catalyst body easier and cheaper to manufacture and easier to install in the exhaust system.

In a preferred embodiment, the catalyst body consists of a perforated metal foil, the perforations of the perforated metal foil being adapted for sound reduction in such a way that the metal foil also takes on the function of a conventional soundproofing unit. This reduces the number of components required for exhaust gas treatment in an exhaust system of a small engine. This leads to a reduction in the manufacturing costs and the assembly effort and to a better interchangeability of the components. For this purpose, reference is also made to what has been said with regard to the first-mentioned solution for forming the catalyst body according to the invention.

Preferably, the catalyst body is arranged coaxially to an inflow direction of the exhaust gas into the muffler housing around an inlet of the muffler housing. This creates suitable flow conditions within the muffler housing and in particular with regard to the radial flow against the metal foil from the inside, as a result of which good results are achieved with regard to sound absorption and pollutant reduction.

In a further preferred embodiment, the catalyst body is biased against the muffler housing. In order to fix the position of the catalyst body before and after the bracing, shaped impressions corresponding to the ends of the catalyst body are provided in the relevant parts of the muffler housing and / or additional parts such as retaining rings or retaining plates. The fasteners used to brace the housing parts, such as »screws, can at the same time serve to fasten the muffler housing to or near the single engine or to the device in question. By tightening the catalyst body between the housing parts or additional parts of the muffler housing, complex repair measures within the muffler housing can be dispensed with. The object of the invention is achieved for the production of the catalyst body according to the invention in that the catalyst body is bent into a ring from a perforated metal foil strip and then the ends of the strip are connected by means of a positive connection.

In a preferred manufacturing method, the perforated metal foil strip is previously cut from continuous goods, punched or broken at perforation points provided in advance. The production from continuous goods also enables a continuous coating process and in particular considerable cost savings. The foils or sheet metal strips can also be produced individually in sections.

The flat metallic base material in the initial state can also be provided with a catalytically active coating in advance. However, the coating can also be carried out after the metal foil strips have been obtained. The ends of the metal foil are hooked, for example, with a positive connection. To permanently fix the ends of the metal foil, these can also be pressed or spot welded.

The object is achieved for a catalyst body which can be flowed through perpendicular to its upper side and is intended for installation in a muffler housing of a small engine, in that the catalyst body has a metal foil provided with cuts. Cuts in a metal foil can be easily produced, such a metal foil being a product that is easy to stack for transport and has a small transport volume. A metal foil provided with cuts also allows it to be easily reshaped in the areas between the cuts. This allows channels to be formed through which gas to be catalytically treated is directed in a desired flow direction.

In a preferred embodiment of the invention, the metal foil is in the longitudinal direction of a screw, star, trapezoidal or wave-shaped. Such shapes can easily be stamped into an initially flat foil, the mechanical stability of the metal foil thus processed being increased. Furthermore, additional leading edges are formed, which lead to further turbulence and increase the probability that the exhaust gas comes into contact with the surface of the coated metal foil.

In the simplest embodiment, the metal foil is formed in one layer. The size of the surface of the metal foil is determined by the desired cleaning effect. If at one single-layer design, the requirements for exhaust gas cleaning are not met and there is still sufficient space in the muffler housing, according to a further embodiment of the invention the metal foil can be leporello-shaped. A fan-shaped metal foil can be easily produced, for example, by folding, the individual foil layers always being connected to one another and the width of each layer being variable depending on the available installation space. If, for example, the layer widths differ significantly from one another and a fan fold is difficult to produce, according to a further embodiment of the invention the catalyst body can have metal foils which are layered in layers. It is not necessary for the individual metal foils to be mechanically firmly connected to one another. However, conventional fixing methods such as soldering or welding increase the stability of the catalyst body, particularly in the case of many layers which are stacked on top of one another.

If the metal foil is planar in its longitudinal direction at its two ends, the ends can preferably be used for fixing the metal foil. A simple and inexpensive fixation is achieved if the metal foil is attached at its ends to the muffler housing by means of a non-positive connection. This can be done, for example, by clamping. One possibility is to clamp the ends of the metal foil between the joining surfaces of the housing. In this case, no further assembly elements are required. If other components, such as spacers, are provided in the interior of the muffler housing, the ends of the film can be clamped between the components and the housing. A non-positive clamping connection should be designed in such a way that additional assembly elements such as screws are not required. This simplifies the construction of the muffler housing and catalytic converter body and contributes to the cost-effective construction.

According to a preferred embodiment, the metal foil is designed such that the shape of the metal foil in a section formed between two cuts is oriented in a direction which is opposite to the shape of the metal foil adjacent to the section. In the case of a wave-shaped metal foil, for example, in a wave trough, the foil can be bent in a section between two cuts so that a wave crest is created. With unchanged film height and film width, it is possible to almost double the leading edges and turbulence, so that the cleaning effect of the catalyst body is increased.

If the catalytic converter body is arranged in the muffler housing with a front housing part and a rear housing part in a zone between two pins connecting the housing parts, the catalyst body can be guided laterally through the pins. Particularly in the case of a fan-shaped or layered catalyst body, this ensures that bulging or buckling under pressure in the longitudinal axis of the folded or layered catalyst body is avoided. This guidance by pins does not require any additional fastening means for the catalyst body, but does not exclude them if, for example, an oscillation node is to be created in the catalyst body.

Preferably, the pins are installed in the interior of the muffler housing. This makes it possible to build a completely closed housing, which has mounting elements and filters exclusively in the interior. If pins are provided on the edge of the housing, for example to screw the housing on from the outside, the metal foil would have to be led to the edge of the housing and clamped there by means of a non-positive connection. The metal foil would thus take up the entire inner width of the housing. This can be avoided by the embodiment according to the invention, so that the metal foil can only occupy a limited and defined part of the interior.

Is the catalyst body installed in the muffler housing so that it fills a distance which is formed in the interior of the muffler housing from the front housing part to the rear housing part, a maximum available flow path is provided with maximum cleaning effect. The sucked-in air can thus pass from the inlet of the housing through the layered catalyst body, for example, and can only emerge from the catalyst body immediately before the outlet of the muffler housing.

According to a further embodiment of the invention, an area which is formed outside the zone between two pins connecting the housing parts and inside the muffler housing is not filled by the catalyst body. A flow resistance of the muffler and thus the sound damping can thus be influenced. The muffler housing is thus not only intended to accommodate a metal foil that cleans the exhaust gas, which must fill a large part of the interior for a sufficient cleaning effect. In addition, the area which is not filled by the catalyst body provides a space which can be configured differently from the catalyst body and which can be optimally adapted for an even more effective sound refraction.

The invention further relates to an exhaust system for small engines with a silencer housing, the exhaust system having a catalyst body as described above. Because of the engagement Such a catalyst body allows for an overall simple and inexpensive manufacture of an exhaust system.

The invention further relates to a method for producing a catalyst body for installation in a muffler housing of a small engine, in which the catalyst body is folded like a leporello from a cut metal foil and is then connected to the ends of the metal foil by means of a non-positive connection with the muffler housing. This achieves an effective assembly of a catalyst body in terms of time and costs.

In the following, the invention will be further explained on the basis of several preferred exemplary embodiments with reference to the drawings. They show schematically:

Figure 1 is an exploded view of an exhaust system with a first embodiment of the metal foil as a radially flowable, annular catalyst body. and

2 shows a plan view of a second embodiment of the metal foil; and

3a shows a plan view of a third embodiment of the metal foil; and

3b shows a perspective view of a projection of the metal foil according to FIG. 3a; and

3c shows a cross section of a further projection of the metal foil according to the invention; and

3d shows a cross section of a further projection of the metal foil according to the invention; and

3e shows a cross section of a further projection of the metal foil according to the invention; and

3f shows a plan view of a plurality of cut line patterns in a metal foil according to the invention for forming the projections or perforations; and

4a shows a side view of the metal foil according to FIG. 3a; and

4b shows a side view of a fourth embodiment of the metal foil; and 4 c shows a side view of a fifth embodiment of the metal foil; and

4d shows a side view of a sixth embodiment of the metal foil; and

5a shows a cross section of a first positive connection of a metal foil; and

5b shows a cross section of a second positive connection of a metal foil; and

6 shows an exploded illustration of a further exhaust gas system with a metal foil according to the invention as a radially flowable, annular catalyst body; and

7 shows a perspective illustration of a metal foil provided with cuts before the shaping and after the shaping; and

8 shows a metal foil with a corrugated profile in the longitudinal direction; and

FIG. 9 shows a side view of a leporello-shaped folded metal foil with sections bent opposite to the wave shape of the metal foil; FIG. and

10 shows a catalyst body with an intermediate layer; and

11 shows a catalyst body with flat ends; and

12 shows a section of an endless belt of three metal foils placed one above the other; and

13 shows a cross section through a muffler housing with a single-layer metal foil in the interior of the muffler housing; and

14 shows a cross section through a muffler housing with a multilayer metal foil in the interior of the muffler housing.

1 shows an exploded view of a radially flowable, annular catalyst body 1 as part of an exhaust system 11 according to the invention. The catalyst body 1 consists of a metal foil 2 which has a large number of perforations 3 and webs 5, the measurement tall foil 2 and in particular their perforations 3 and webs 5 are adapted for sound reduction. The formation of the components of the metal foil 2 and their material properties, surface structure and dimensions are adapted in such a way that the metal foil 2 also takes on the function of a conventional reflection body.

To explain the configuration of the metal foil 2 per se, FIGS. 2 to 5 are used below. 2 shows the development of a metal foil 30 in a top view. The thickness of the metal foil is 230 μm. The rectangular holes 33 are arranged in three rows and in a symmetrical manner. Between the perforations 33 are longitudinal and transverse material bridges or webs 35. The webs 35 between the top and bottom row of perforations 33 and the respective longitudinal edge 38 and 39 are wider than the webs 35 between the perforations 33 designed to increase the stiffening in the transverse direction. This also provides sufficient stability with regard to the later fastening of the metal foil 30. Starting from the flat shape shown, the metal foil 30 is bent into an oval or elliptical ring. The ends 36 and 37 are then connected to one another, so that the catalyst body 1 is formed. For installation in a muffler housing 4, the annular metal foil 30 is then placed with its edges 38 and 39 on the rear walls 24 of the housing parts 18 and 19 or on additional parts and braced in the muffler housing (see also FIG. 1).

Figure 3a shows in a further embodiment, a metal foil 40. With regard to the thickness of the metal foil 40, the arrangement of the perforations 43 and webs 45, the same applies as in Fig. 2. The openings or perforations 43 are arcuate here and by bending away the metal foil 40 is formed upwards. The projections 44 formed in this way serve to enlarge the surface of the metal foil 40 in order to swirl the exhaust gas to reduce pollutants and also to break the sound. But they can also serve as spacers at the same time. To form the catalyst body 1, the metal foil 40 is in turn bent into a ring. The ends 46 and 47 are then connected to one another. 3b shows a perspective view of a section of the metal foil 40 with two arcuate perforations 43 and two tabs 48 arranged between them. The tabs 48 or projections 44 are bent away from the metal foil 40 in the same direction. In order to enable pushing away, the metal foil is at least cut or punched in advance at the predetermined locations. The tabs 48 or projections 44 can take any linear or non-linear shape. Figures 3c to 3f show further embodiments of the perforations or projections of the metal foil according to the invention. The embodiments in Figures 3c to 3e are shown in cross section. 3f shows a top view of six types of training of the cut lines or perforation points to be applied. These then allow the metal foil regions located between the cut lines to be pushed away, as a result of which, inter alia, the perforations and projections according to FIGS. 3c to 3e are produced.

3 c shows a roof-shaped or V-shaped design of a projection 91. The exhaust gas flowing in from below passes obliquely or vertically through the horizontal opening cross section below the projection 91 and bounces against the underside of the two legs 94 there the exhaust gas is deflected almost horizontally and flows upwards via triangular oblique or vertically oriented opening cross-sections above the metal foil level. FIG. 3d shows a projection 92, the leg 95 bent obliquely away from the metal foil plane being aligned horizontally at its free end. The exhaust gas flowing in from below is deflected even more horizontally. With a spiral winding of the metal foil, this projection 92 can simultaneously serve as a spacer. 3e shows a further projection 93, which is produced by bending the relevant metal foil region in opposite directions. The inclined legs 96 and 97 in turn cause an impact and a deflection of the exhaust gas. The transitions of all legs 94, 95, 96, 97 with one another or into the metal foil plane can be edge-like or rounded. The exhaust gas can also flow from above.

3f shows a top view of several cut line patterns 100 to 105 for forming the projections or perforations in a metal foil according to the invention. These cut line patterns are formed by the solid, cut or cut lines (hereinafter called cut lines). The dashed lines indicate the kinks that result when the metal foil areas are pushed away. To form the projections 91, 92, 93 from FIGS. 3c, 3d, 3e, the cut line patterns 100, 101, 102 are to be selected. The cut lines thus allow the metal foil regions delimited by the cut and crease lines to be pushed away, as a result of which the projections which protrude like legs from the rest of the metal foil are produced. The cut line pattern 104 is suitable for forming the projection 44 according to FIG. 3b. The patterns 103 and 105 represent additional alternatives. The possibilities for the formation of the projections shown in FIGS. 3b to 3f can be used in a uniform or mixed manner in each metal foil described in the context of this invention. FIG. 4a shows the metal foil 40 from FIG. 3a in a helical winding in a side view, the projections 44 also serving as spacers. The side views in FIGS. 4b to 4d show a corrugated metal foil 50, a star-shaped metal foil 60 and a trapezoidal metal foil 70. Their perforations 3 can be formed by punching, cutting, bending or pushing away. The exhaust gas does not necessarily have to flow radially through the respective perforations 3, but can also be deflected slightly in the vicinity thereof. If the perforation 3 is formed by bending away the metal foil 2 such that the passage surface of the opening or perforation 3 runs obliquely or vertically, the exhaust gas is briefly deflected in this area in order to be able to flow through the perforation 3. For example, the perforations 3 can run obliquely or vertically when the material pushed away assumes a roof shape. Such V-shaped or U-shaped roofs pressed out of the plane of the metal foil can be arranged in the mountains or valleys of the metal foils 40, 50, 60 or 70.

Figures 5a and 5b show two ways of forming a releasable positive connection 8 for attaching the two ends 6 and 7 of the metal foil 2. This accordingly applies equally to all other aforementioned metal foils. In Fig. 5a, the positive connection 8 is made possible by a hook-shaped design of the ends 6 and 7 of the metal foil 2. Thus, the metal foil 2 can be bent into a ring in a few simple steps before the exhaust system is assembled and then hooked. In FIG. 5 b, one end 6 of the metal foil 2 is provided with a recess 9 and the other end 7 with a counterpart 10 for engaging in the recess 9. The rectangular recess 9 is created by bending part of the metal foil 2 to form a tab 75. The other end 7 of the metal foil 2 is bent over to form a tab 76 as a counterpart 10, so that this end 7 is in engagement with the other end 6 after the counterpart 10 has been threaded into the recess 9. Thus, the positive connection 8 can be assembled or disassembled in a few simple steps. In principle, however, there is also the possibility of fixing the form-fit connection 8 by means of one or more spot welds for a permanent hold.

The composition of the exhaust system 11 according to the invention can also be seen from FIG. 1. The catalyst body 1 is formed by the metal foil 2. Instead of the metal foil 2, however, any other embodiment of the metal foils 30, 40, 50, 60 or 70 described in the context of this invention can also be used in the exhaust system 11. For reasons of simplification, only the embodiment with the metal foil 2 is explained. In addition to the metal foil 2, which also forms the sound absorption unit of a conventional exhaust system, the silencer housing 4 and two metal pins 16 consisting of the housing parts 18 and 19 can also be seen. The metal pins 16 are penetrated by screws or other fastening means for bracing the housing parts 18 and 19 with a metal foil 2 arranged between them. The screws are also used to attach the muffler housing 4 to or near a small motor (not shown). The housing part 18 has a plate-shaped central area 22 on its rear wall 24. An inlet 14 and two openings 23 are introduced therein for the passage of the screws. The other housing part 19 also has a plate-shaped central region 22 and two openings 23 on its rear wall 24. To discharge the exhaust gas from the muffler housing 4, an outlet 15 is arranged on a side wall of the housing part 19. To simplify handling during assembly, the outer diameter of the annularly bent metal foil 2 should be at most as large as the inner diameter of the circular central region 22, so that the metal foil 2 at least for temporarily fixing the position when assembling the exhaust system 11 into the plate-shaped central region which is recessed in relation to the surrounding rear wall 22 can be used. After inserting a screw or similar fastener along the axis 25 into the openings 23 of the one housing part 18, the metal pins 16 can be pushed over the screws in order to then insert the screw ends into the openings 23 of the other housing part 19 and this until it stops at the to push the peripheral edge 20 of the housing part 18. The peripheral edges 20 and 21 of the housing parts 18 and 19 are each formed as a web-like flange, so that a gas-tight seal of the housing parts 18 and 19 is achieved. Other sealing measures, such as rubber seals, can also be applied. The openings 23 and the connection of the inlet 14 to the engine are also gas-tight. The flanges 20 and 21 can also be shaped such that one housing part at least partially encompasses the other.

With regard to the geometric dimensions of the components to be assembled along the axis 25, the shell-like housing parts 18 and 19 have a certain depth, so that after inserting the metal foil 2 into the two plate-shaped central regions 22, the ends of the metal foil 2 directed along the axis 25 are in each case the rear wall 24 abut and the flanges 20 and 21 lie on top of each other. The screws running along the axis 25 penetrate the metal pins 16 and the two housing parts 18 and 19, and protrude beyond the silencer housing 4. In order to clamp the metal foil 2 and thus the catalyst body 1 in the muffler housing 4 or against the housing parts 18 and 19, the metal pins 16 therefore have a shorter length than the metal foil 2. The exhaust system 11 screwed together in this way and acted on with prestress can finally be attached to a small motor or in the vicinity of the protruding ends of the screws.

To reduce the pollutants and to reduce noise, the exhaust gas flows through the inlet 14 into the interior of the muffler housing 4 and enters an inner, cylindrical cavity 26, which is limited by the metal foil 2 and the rear walls 24 of the housing parts 18 and 19 , From there, the exhaust gas flows radially outward and hits the metal foil 2. Depending on the configuration of the perforations 3 and webs 5, contact is made with the catalytically active coating of the metal foil 2 and thus a reduction in the pollutants of the exhaust gas. The impact of the exhaust gas flow on the metal foil 2 also leads to a refraction of the sound waves and thus to a sound reduction. After the exhaust gas has flowed through the metal foil 2, it reaches the environment via the outlet 15.

FIG. 6 shows an exploded illustration of a further embodiment of an exhaust system with the catalyst body 1 according to the invention according to FIG. 1. Here, the same parts as from FIG. 1 are designated by the same reference numerals. In particular, the same components as from FIG. 1 are used for the metal foil 2 and the housing parts 18 and 19. However, all other metal foils 30, 40, 50, 60 or 70 described above can also be used. The formation of the components of the metal foil 2 and their material properties, surface structure and dimensions are adapted such that the metal foil 2 takes over the function of a catalyst. As additional components of this embodiment, two holding plates 82 and 83 and a reflection tube 80 are shown as additional parts. The reflection tube 80 is made of sheet metal and has a plurality of perforations 81 for sound reduction. The holding plates 82 and 83 each have an opening 84 in the center for attachment to the reflection tube 80, which corresponds to the outer contour of the cross-sectional shape of the reflection tube 80. The outer edges of the holding plates 82, 83 each have a circumferential indentation or groove (not shown), which serves to hold the metal foil 2.

6, the individual components are pushed into one another along the axes 25. First, the holding plate 82 is pushed onto the reflection tube 80 in such a way that it comes to lie at a certain distance from the end of the reflection tube 80 opposite the housing part 18. The annular metal foil 2 is then guided coaxially and at a distance from the reflection tube 80 via the reflection tube 80 and pressed into the indentation of the holding plate 82. The second holding plate 83 is then pushed over the reflection tube 80 until the still free edge of the metal foil 2 enters the indentation of the holding plate 83. In the Length dimensions of the metal foil 2 and the reflection tube 80 directed in the direction of the axis 25 can also be chosen such that at least one of the holding plates 82, 83 comes to rest on an end face of the reflection tube. If the holding plate 82 or 83 is fastened to an end face, the opening 84 can also be dispensed with. The holding plates 82, 83 can also both be arranged on the end faces of the reflection tube 80 or at a distance from the respective end of the reflection tube 80 and optionally additionally welded on. For the subsequent bracing of the outer housing parts 18 and 19, the same measures are taken as already explained for FIG. 1. The peripheral edges 20 and 21 of the housing parts 18 and 19 are again formed in the form of web-like flanges, so that a gas-tight seal of the housing parts 18 and 19 is achieved. Similar to FIG. 1, the rear walls 24 of the housing parts 18, 19 can also be provided with recessed central areas corresponding to the ends of the reflection tube. These recesses or indentations can be directed inwards or outwards.

To reduce pollutants and noise, the exhaust gas flows through the inlet 14 into the interior of the muffler housing 4 and enters the reflection tube 80. From there, the exhaust gas flows radially outward and hits the reflection tube 80. Depending on the design of the perforations 81 there is a certain reflection or refraction of the sound waves. The exhaust gas then flows through the perforations 81, flows further radially outward and strikes the metal foil 2. There is contact with the catalytically active coating of the metal foil 2 and thus a reduction in the exhaust gas pollutants. The impact of the exhaust gas flow on the metal foil 2 also leads to a refraction of the sound waves and thus also to a sound reduction. After the exhaust gas has flowed through the perforations 3 of the metal foil 2, it reaches the environment via the outlet 15.

FIG. 7 shows a metal foil 110 with cuts 111 which are introduced into the metal foil parallel to one another. A cut here does not represent a perforation from which material is removed. Ideally, only the material should be separated from one another at the designated places. In a subsequent manufacturing step, the metal foil can be deformed in a section 114, which is arranged between two cuts. If the metal foil 110 is pulled outwards in this section 114, an elevation 115 is created, through which a gas flowing on the top 119 of the metal foil can be deflected toward the bottom 120 of the metal foil, see arrows in FIG. 7. If the metal foil is undulating 8, the section 114 of the metal foil 110 can be oriented in a shape that is opposite to the shape of the metal foil adjacent to the section 114. At a given by the waveform Overall height of the metal foil 110 can be provided by providing elevations 115 in section 114 further leading edges and thus possibilities for swirling the gas.

If the metal foil is flowed perpendicularly to its top side 119, see FIG. 9, the gas can pass through from the top side 119 in the direction of the bottom side 120 due to the elevations 115, see arrows in FIG. 9. In the case of a corrugated metal foil, which is called a fanfold is folded and their wave crests meet each other, the gas passing through a first fan fold layer flows laterally towards a wave trough of the fan fold layer underneath. There it can meet a further elevation 115, under which it passes, so that a gas flowing in perpendicularly to the top of the first leporella layer is successively passed from one layer to the next layer and also laterally. The gas can also flow perpendicular to the drawing plane in FIG. 9 in the space between wave troughs and wave crests, see marking in FIG. 9 with a dot as a symbol for a flow out of the drawing plane or marking with a cross as a symbol for a flow into the drawing plane down into it. This variety of flow directions creates enough swirls to bring the gas into contact with the catalytically coated surface of the metal foil.

Vibrations in the housing and in the catalyst body can lead to a wave crest of one layer penetrating into a wave trough of an adjacent film layer and thus significantly reducing the flow cross section. A flat intermediate layer 121 can help to inhibit this process. In the case of a plurality of foil layers, it is therefore advantageous to provide flat intermediate layers 121 which prevent, for example, the wave-shaped metal foils from sliding into one another, cf. Fig. 10.

FIG. 11 shows a catalyst body which has two corrugated metal foils 110 and a gas-permeable, flat intermediate layer 121 arranged between them. The metal foils and the intermediate layer are each designed such that they are formed flat in the longitudinal direction at their two ends 112 and 113. These non-wavy or not uneven places are particularly suitable for a clamp connection, for example with the silencer housing. The flat ends 112, 113 can also be provided in an endless belt with individual film layers, see FIG. 12. It is advantageous to press the layered sheet metal layers flat against one another at predetermined intervals and to connect them at these points by means of spot welding. These flat pressed areas are particularly suitable for separating individual catalyst bodies from the endless belt. Corresponding parting planes 122 are shown schematically in FIG. 11. Such endless belts composed of individual film layers or having a plurality of layered film layers are preferably coated with catalyst material after the openings have been made and, if appropriate, after the individual films have been connected, before the division into the individual catalyst bodies is carried out.

[0057] The simplest embodiment of a catalyst body is a single-layer metal foil. In FIG. 13, a metal foil 110 is arranged in a silencer housing with a front housing part 18 and a rear housing part 19 directly at the gas inlet 14 in a zone 116 between two pins 16 connecting the housing parts. The pins are provided in the interior of the housing, the metal foil 110 at its flat ends 112, 113 being non-positively connected to the housing part 18 by means of the pins 16. No further assembly elements are therefore required for the metal foil. The gas flows onto the metal foil 110 perpendicular to the upper side 119. In order for the gas to pass through the metal foil, the metal foil must have openings such as perforations or elevations 115. After passing through the metal foil, the gas continues to flow through the scarf damper housing and exits at outlet 22.

If the metal foil is leporello-like or if several metal foils are stacked on top of one another, they can form a catalyst body which fills the interior of the muffler housing from the front housing part 18 to the rear housing part 19 along a distance 117, see FIG. 14. This achieves a maximum filter effect , In this embodiment, too, the catalyst body is non-positively connected to the housing by means of pins 16. The catalytic converter body does not fill out the area 118, which is defined outside the zone 116 but still within the interior space of the muffler housing, which is predetermined by the housing parts 18, 19. The area 118 can be completely free or provided with sound-absorbing elements, so that the muffler achieves a high sound-damping property in addition to the filter effect by the catalyst body.

With the metal foil according to the invention, a possibility is thus created to control the pollutant and noise reduction of a small motor, in particular through the formation of the perforations and elevations contained in the metal foil and their free cross section. The free cross section of the perforations can also be related to the opening cross section of the engine outlet. A suitable ratio of the cross section of the motor outlet to the free cross section of the perforations is e.g. one to two.

Claims

1. Radially flowable, annular catalyst body for installation in a silencer housing of a small engine, characterized in that it consists of a perforated metal foil (2, 30, 40, 50, 60, 70).

2. Catalyst body according to claim 1, characterized in that the perforations (3, 33, 43) of the perforated metal foil (2, 30, 40, 50, 60, 70) are adapted for sound reduction so that the metal foil (2, 30, 40, 50, 60, 70) also takes over the function of a conventional reflection body.

3. Catalyst body according to claim 1 or 2, characterized in that between the perforations (3, 33, 43) webs (5, 35, 45) for stiffening the metal foil (2, 30, 40, 50, 60, 70) are arranged which are adjusted so that they prevent bulging of the metal foil (2, 30, 40, 50, 60, 70) when installed.

4. A catalyst body according to claim 3, characterized in that the webs (5, 35, 45) are aligned in accordance with the forces acting on the catalyst body (1).

5. A catalyst body according to claim 3 or 4, characterized in that the webs (5, 35, 45) are aligned coaxially to the longitudinal axis and / or in the circumferential direction of the catalyst body (1).

6. Catalyst body according to one of the preceding claims, characterized in that the metal foil (2, 30, 40, 50, 60, 70) has a thickness of 0.05 mm to 2 mm.

7. A catalyst body according to claim 6, characterized in that the metal foil (2, 30, 40, 50, 60, 70) has a thickness of 0.3 mm to 1 mm.

8. Catalyst body according to one of the preceding claims, characterized in that the metal foil (2, 30, 40, 50, 60, 70) is screw, star, trapezoidal or wave-shaped.

9. Catalyst body according to one of the preceding claims, characterized in that the ends (6, 7) of the metal foil (2, 30, 40, 50, 60, 70) are connected to a releasable positive connection (8).

10. A catalyst body according to claim 9, characterized in that the ends (6, 7) of the metal foil (2, 30, 40, 50, 60, 70) are hook-shaped.

11. A catalyst body according to claim 9, characterized in that the one end (6) of the metal foil (2, 30, 40, 50, 60, 70) has a recess (9) and the other end (7) of the metal foil (2) Has counterpart (10) for engagement in the recess (9).

12. Catalyst body according to one of the preceding claims, characterized in that the perforations (3, 33, 43) are formed by bending away (48, 91, 92, 93) the metal foil (2, 30, 40, 50, 60, 70) ,

13. Exhaust system for small engines with a radially flowable, annular catalyst body, a silencing unit and a silencer housing, characterized in that the catalyst body (1) consists of a perforated metal foil (2, 30, 40, 50, 60, 70).

14. Exhaust system according to claim 13, characterized in that the perforations (3, 33, 43) of the perforated metal foil (2, 30, 40, 50, 60, 70) are so adapted for sound reduction that the metal foil (2, 30, 40, 50, 60, 70) also takes over the function of a conventional soundproofing unit.

15. Exhaust system according to claim 13 or 14, characterized in that the catalyst body (1) is arranged coaxially to an inflow direction (13) of the exhaust gas into the muffler housing (4) around an inlet (14) of the muffler housing (4).

16. Exhaust system according to one of claims 13 to 15, characterized in that the catalyst body (1) is biased against the silencer housing (4).

17. A method for producing a radially flowable ring-shaped catalyst body for installation in a silencer housing of a small engine, characterized in that the catalyst body (1) from a perforated metal foil strip (2, 30, 40, 50, 60, 70) is bent in a ring and then the ends (6, 7) of the strip are connected by means of a positive connection (8).

18. The method according to claim 17, characterized in that the perforated metal foil strips (2, 30, 40, 50, 60, 70) are cut beforehand from continuous goods, punched or broken at perforation points provided in advance.

19. Catalyst body which can be flowed through perpendicular to its upper side and is intended for installation in a silencer housing of a small engine, characterized in that the catalyst body (1) has a metal foil (110) provided with cuts (111).

20. Catalytic converter body according to claim 19, characterized in that the metal foil (110) in its longitudinal direction is screw, star, trapezoidal or wave-shaped.

21. A catalyst body according to claim 19 or 20, characterized in that the metal foil (110) is formed in one layer.

22. A catalyst body according to claim 19 or 20, characterized in that the metal foil (110) is leporello-shaped.

23. A catalyst body according to claim 19 or 20, characterized in that the metal foil (110) is layered in layers.

24. Catalyst body according to one of claims 19 to 23, characterized in that the metal foil (110) is at least partially planar at its edges.

25. Catalytic converter body according to one of claims 19 to 24, characterized in that the metal foil (110) can be mounted at its ends (112, 113) by a non-positive connection with the silencer housing.

26. Catalytic converter housing according to one of claims 19 to 25, characterized in that in a section (114) formed between two cuts (111) the shape of the metal foil is oriented in a direction which is adjacent to the section to the shape of the metal foil (110) (114) is opposite.

27. Catalyst body according to one of claims 19 to 26, characterized in that the catalyst body (1) in the muffler housing with a front housing part (18) and a rear housing part (19) in a zone (116) between two pins (16) connecting the housing parts ) is arranged.

28. Catalytic converter body according to one of claims 19 to 27, characterized in that the pins (16) are installed in the interior of the silencer housing.

29. Catalyst body according to one of claims 19 to 28, characterized in that the catalyst body is installed in the muffler housing so that it is a distance (117), which is formed in the interior of the muffler housing from the front housing part (18) to the rear housing part (19) , fills out.

30. Catalytic converter body according to one of claims 27 to 29, characterized in that an area (118) which is formed outside the zone (116) and within the muffler housing is not filled by the catalytic converter body (1).

31. Exhaust system for small engines with a silencer housing, characterized in that the exhaust system has a catalyst body (1) according to one of claims 17 to 27.

32. A method for producing a catalyst body for installation in a silencer housing of a small motor, characterized in that the catalyst body is folded like a leporello from a metal foil (110) provided with cuts (111) and then at the ends (112, 113) of the metal foil (110 ) is connected to the silencer housing by means of a non-positive connection.

33. A method for producing a catalyst body, characterized by the following steps: attaching gas passage openings to at least one metal foil (110) which is designed as an endless belt, coating the endless belt with catalyst material, and cutting the coated endless belt to a length corresponding to the catalyst body.

34. A method for producing a catalyst body according to claim 33, characterized in that a plurality of metal foils (110) provided with gas passage openings are layered one above the other as an endless belt, and the layered metal foils (110) are pressed flat together at predetermined intervals and connected to one another at the flat compressed regions before they are coated catalytically.

35. A method for producing a catalyst body according to claim 34, characterized in that the separation of the endless belt takes place in the flat-pressed areas.